Heat exchanger component configured for mitigation of scaling and method of mitigating scaling during a heat transfer process

Abstract

A heat exchanger component configured for mitigation of scaling has a surface including a wettability pattern thereon. The wettability pattern comprises hydrophobic regions and hydrophilic regions. A method of mitigating scaling during a heat transfer process includes providing a heat exchanger component having a surface including a wettability pattern thereon, where the wettability pattern comprises hydrophobic regions and hydrophilic regions. The heat exchanger component is introduced into a heat transfer process, where the surface of the heat exchanger component is exposed to flow of a process fluid. During the exposure to flow of the process fluid, scale deposits form with a nonuniform thickness distribution and / or a nonuniform adhesion force over the wettability pattern on the surface. The flow of the process fluid introduces a shear force that periodically or intermittently removes the scale deposits, thereby enabling self-cleaning of the surface.

Description

RELATED APPLICATION

[0001] The present patent document claims the benefit of priority under 35 U.S.C. 119(e) to U.S. Provisional Patent Application No. 63 / 669,005, which was filed on Jul. 9, 2024, and is hereby incorporated by reference in its entirety.STATEMENT OF FEDERALLY FUNDED RESEARCH OR DEVELOPMENT

[0002] This invention was made with government support under contract number DEEE0008392 awarded by the United States Department of Energy. The government has certain rights in the invention.TECHNICAL FIELD

[0003] The present disclosure relates heat transfer technology and more particularly to a patterned coating and method for reducing scaling on heat exchanger tubes.BACKGROUND

[0004] Heat exchanger fouling (or scaling) is a severe issue that can affect most industries in the modern world, especially in processes that involve heating or cooling in an aqueous environment, such as desalination, food processing industries, chemical plants, and many others. The undesired fouling deposits may form a thick layer on the heat transfer surfaces, causing heat transfer performance deterioration along with corrosion, substantial pressure loss, increased flow friction, and flow maldistribution. To battle the fouling issue, fluid pre-treatment, significant safety margins in the design, and routine heat exchanger cleaning may be utilized, resulting in increased expenditure and downtime. Concerning factors include the financial loss and environmental risks associated with utilizing chemical fouling inhibitors (e.g., polyphosphate, chlorine, hypochlorite, and coagulants) and cleaning agents (e.g. surfactants, solvents, acids, and alkaline solutions).

[0005] Typical scaling control may include removing the scale-forming ions by precipitation or nanofiltration or creating an unfavorable environment for scale formation in operation with acid and chemical additives. Pre-precipitation, nanofiltration, and acid additives can remove many scale-forming ions but not all. Chemical additives (antiscalants) are comparatively low cost, low dose rate, and especially their effectiveness in scaling prevention during operation. However, the efficacy of antiscalants highly depends on system conditions (ion concentration, temperature, pH, pressure), their types (functionality, molar mass, polydispersity, structure) usage (concentration, application technique). Additionally, several available physical methods (e.g., pressurized air backwash, flow reversal, and sponge ball cleaning) are selectively adaptable to some processes. The effectiveness of many scale control methods is limited by the skill of the operators and the environment of the heat exchanger surfaces. In addition, the added expenses of scale control methods and the harmful impact of chemical additives on the environment encourage development of low-cost and environment-friendly ways of controlling scale formation.SUMMARY

[0006] A heat exchanger component configured for mitigation of scaling has a surface including a wettability pattern thereon. The wettability pattern comprises hydrophobic regions and hydrophilic regions.

[0007] A method of mitigating scaling during a heat transfer process includes providing a heat exchanger component having a surface including a wettability pattern thereon, where the wettability pattern comprises hydrophobic regions and hydrophilic regions. The heat exchanger component is introduced into a heat transfer process, where the surface of the heat exchanger component is exposed to flow of a process fluid. During the exposure to flow of the process fluid, scale deposits form with a nonuniform thickness distribution and / or a nonuniform adhesion force over the wettability pattern on the surface. The flow of the process fluid introduces a shear force that periodically or intermittently removes the scale deposits, thereby enabling self-cleaning of the surface.

[0008] A method of applying a wettability pattern to a heat exchanger component includes: cleaning a surface of a heat exchanger component; covering a portion of the surface of the heat exchanger component with surface protection, wherein the surface protection is removable from the surface of the heat exchanger component without altering the surface; after covering the portion of the surface with surface protection, applying a hydrophobic coating to the surface; and, after applying the hydrophobic coating, removing the surface protection from the portion of the surface, thereby exposing a hydrophilic region and producing a wettability pattern on the surface.BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The embodiments may be better understood with reference to the following drawing(s) and description. The components in the figures are not necessarily to scale. Moreover, in the figures, like-referenced numerals designate corresponding parts throughout the different views.

[0010] FIG. 1 illustrates an embodiment of a heat exchanger component having a surface including a wettability pattern thereon.

[0011] FIG. 2A provides a cross-sectional view (top) and a top view (bottom) of the heat exchanger component of FIG. 1 with an inset showing details of the wettability pattern.

[0012] FIGS. 2B and 2C show bottom and side views, respectively, of the heat exchanger component of FIG. 1.

[0013] FIG. 3 is a flow chart showing exemplary steps in a method of mitigating scaling during a heat transfer process.

[0014] FIG. 4 is a flow chart showing exemplary steps in a method of applying a wettability pattern to a heat exchanger component.

[0015] FIG. 5 is a schematic showing a horizontal tube falling film flow experiment setup.

[0016] FIGS. 6A and 6B show a comparison of net scale mass between baseline and wettability patterned tubes and a repeatability test with radially polished tubes, respectively.

[0017] FIG. 7 shows variation of scale layer thickness step at the wettability boundaries with time including a measurement of scale layer height difference.

[0018] FIGS. 8A and 8B show scanning electron microscope (SEM) images of deposited scale layer (scale deposit) on a wettability patterned tube at 152 h, where thicker-compact scale layers in hydrophilic bands and lower scaling in hydrophobic band lead to scale layer height difference at wettability boundary (FIG. 8A) and cracks are observed at the wettability boundaries (FIG. 8B).

[0019] FIGS. 9A-9H show SEM images of scale layer wash-off regions on wettability patterned tubes, including (FIGS. 9A-9D) scale layer wash off from hydrophilic bands, (FIGS. 9E and 9F) scale layer wash off from scale-covered hydrophobic bands and neighboring hydrophilic bands, and (FIGS. 9G and 9H) a closer look at cleaned hydrophilic bands.

[0020] FIGS. 10A and 10B show a heat transfer comparison between baseline and wettability patterned tubes, respectively.

[0021] FIG. 11 provides a schematic of flashing (intermittent wetting and drying cycle) in hydrophobic regions.DETAILED DESCRIPTION

[0022] An effective and environmentally friendly scale mitigation strategy for heat exchanger components is described in this disclosure. The strategy involves application of a wettability pattern to a heat transfer surface of a heat exchanger component. By manipulating the scale layer distribution over the surface using differences in surface wettability, stronger flow shear and weaker scaling adhesion may be achieved, enabling self-cleaning of the heat exchanger component while in use.

[0023] Scaling is the deposition of unwanted inorganic components, such as salts and minerals, as scale on heat exchanger surfaces. Scale deposits usually build up as a fouling layer with time. The complex phenomenon of scaling involves crystallization and transport processes concurrently, such as solute diffusion between surface and bulk solution, dissolution of ions, and ion surface integration with scale growth. Heat exchanger surface characteristics and flow regime can govern heat and momentum diffusivity among fluid layers; a thermal gradient is formed by heat exchanging from wall to adjacent fluid layers. Due to stagnant fluid film near the wall, the temperature may rise, and inversely soluble ions may surpass their solubility limits within the near-wall stagnant region, resulting in scale formation on the heat exchanger surface. Furthermore, solution compositions and operating parameters such as salt content, ion diffusion rate, operating temperature, flow velocity, pH of the water environment, duration, and / or CO2 release rate may impact scale formation and development.

[0024] A demonstration of the effectiveness of the scale mitigation strategy set forth in this disclosure is described below in the experimental examples. To summarize, the experiments utilize a horizontal-tube falling-film evaporator to mimic a multiple-effect distillation process. A millimetric wettability pattern including alternating hydrophilic and hydrophobic regions is created by coating metal tubes. The results show scale layers may be thicker in hydrophilic regions and thinner in hydrophobic regions and / or may have approximately uniform thickness in both regions but exhibit cracks near wettability boundaries. The scale layers on patterned tubes are observed to wash-off with fluid flow, demonstrating the self-cleaning process. In contrast to persistent deterioration in overall heat transfer coefficient (HTC) for baseline tubes (77% of initial HTC after 192 hours), the HTC of patterned tubes initially increases due to surface wetting effects, then stays roughly constant (15% higher than that of baseline after 192 hours) along with lower scale mass accumulation.

[0025] FIG. 1 shows an example of a heat exchanger component 100 configured for mitigation of scaling. The heat exchanger component 100 has a surface 120 including a wettability pattern 150 comprising hydrophobic regions 130 and hydrophilic regions 140. The surface 120 is understood to be a heat transfer surface of the heat exchanger component 100. In this example, the surface 120 including the wettability pattern 150 is a curved surface and the heat exchanger component 100 has the form of a tube, but in other embodiments the patterned surface 120 may or may not be curved and the heat exchanger component 100 may have a different shape. For example, the heat exchanger component 100 may be a plate or other object and the surface 120 may be a planar surface. The hydrophobic regions 130 of the wettability pattern 150 may comprise a contiguous section of the heat transfer surface 120 or unconnected sections of the surface 120. Similarly, the hydrophilic regions 140 of the wettability pattern 150 may comprise a contiguous section of the heat transfer surface 120 or unconnected sections of the surface 120.

[0026] The hydrophobic regions 130 may comprise coated regions of the surface 120 that include a hydrophobic coating and the hydrophilic regions 140 may comprise uncoated regions of the surface 120. More specifically, the uncoated regions may be devoid of a coating and may be intrinsically hydrophilic due to the characteristics of the surface. The hydrophilic regions 140 may exhibit a water contact angle less than 90 degrees, such as from 40 degrees to 89 degrees. Due to the presence of the hydrophobic coating, the hydrophobic regions 130 may exhibit a water contact angle greater than 90 degrees. In some examples, the water contact angle may be greater than 120 degrees, such as from 121 to 150 degrees, or greater than 150 degrees (for superhydrophobicity). A higher hydrophobicity may reduce the possibility of crystallization nucleation, thereby retarding scale formation. Additionally, a more hydrophobic surface may lead to a weaker adhesive force and thus easier removal of any scale deposits that form. The hydrophobic coating may comprise a hydrophobic polymer, silica, metal oxide, carbon nanotubes, edible wax or any other low surface energy material that is inherently hydrophobic or may be modified to be hydrophobic. Suitable polymers may include, for example, a polyolefin such as polyethylene (PE) or polypropylene (PP), polytetrafluoroethylene (PTFE), polydimethylsiloxane (PDMS), polyvinylidene fluoride (PVDF). A suitable commercially available product for forming the hydrophobic coating is Glaco Mirror Coat Zero produced by Soft99 Corporation of Osaka, Japan. This product yields a hydrophobic coating comprising microscopic silica particles. Other than by a direct coating process, the hydrophobic surface might also be created by modification of the surface morphology, such as surface roughening, or creating micro-nano structures on materials that are inherently water repellent.

[0027] The wettability pattern 150 may include an alternating pattern of the hydrophobic regions and the hydrophilic regions. Table 1 shows examples of different wettability patterns 150 that may be employed for the heat transfer surface 120, including a half coating pattern, strip coating patterns, a ring coating patterns, grid coating patterns, or some combination of these patterns, such as the hybrid coating pattern, which is discussed further below. The exemplary wettability patterns 150 are depicted along a longitudinal face of a tube where, in Table 1, the unshaded areas represent hydrophobic regions 130 and the shaded areas represent hydrophilic regions 140. The third column of the table provides for each exemplary wettability pattern the areal coverage (%) of the hydrophobic (coated) regions relative to the entire heat transfer surface, e.g., the tube face. In these examples, the areal coating coverage or “coating ratio” of the hydrophobic region is in a range from 19-50%. More broadly speaking, the areal coverage of the hydrophobic region may be in a range from 10% to 50% of the heat transfer surface. As can be seen by comparing the strip, ring, grid and hybrid coating examples, the dimensions of and / or spacing between the hydrophobic and / or hydrophilic regions 130, 140 may be altered with or without changing the areal coverage.

[0028] The wettability pattern 150 is designed to balance surface wetting (for improved heat transfer) with shear washing (for removal of accumulated scale deposits) during use of the heat exchanger component 100. Due to differences in wettability across the surface 120, a scale layer can selectively build up on certain locations of the surface 120 (preferentially on the hydrophilic regions 140); accordingly, the distribution of the scale layer may follow the wettability pattern 150. The scale layer across the heat transfer surface 102 may thus exhibit a thickness gradient (instead of a uniform thickness) that reflects the wettability pattern. When the thickness gradient of the scale layer reaches a certain value during a heat transfer process, that is, when the thickness or height difference between the hydrophilic and hydrophobic regions 140,130 is sufficiently large, the scale layer may be fractured and removed due to shear stress of the flow. Additionally, the adhesion / bonding force between the scale layer and heat transfer surface may vary over the wettability pattern 150; more specifically, due to the low surface energy of the hydrophobic coating, a weaker adhesion force can be expected for the hydrophobic regions. This weaker adhesion at the hydrophobic regions 130, together with the enhanced flow shear triggered by the uneven scale layer distribution, is believed to contribute to the self-cleaning mechanism for heat exchanger components 100 having a wettability pattern 150. Due to this self-cleaning effect, there is a larger / more frequent fluctuation of net mass deposition on patterned tubes than on baseline tubes, as discussed in the experimental examples below.

[0029] For balancing surface wetting and shear washing, it is preferred that the wettability pattern 150 has millimeter-scale dimensions. For example, a width or other lateral dimension of each of the hydrophobic and the hydrophilic regions 130,140 may be in a range from about 0.5 mm to about 25 mm, or more specifically from 0.5 mm to 15 mm, or from 1 mm to 10 mm. If the width of the wettability pattern is too large, such as meter-scale (e.g., including widths of 1 meter or larger) instead of millimeter-scale for the same coating coverage, the flow flashing range due to the hydrophilic uncoated region may not be able to cover the entire hydrophobic coated region, and the scale layer built up on the hydrophilic uncoated region may be packed tightly over a relatively large distance; thus, even if there is a sufficient thickness / height difference at the hydrophilic-hydrophobic boundary, the shear force may not be sufficient to remove the scale layer. On the other hand, if the pattern width is at the microscale (less than 100 microns) or even nanoscale (less than 1 micron), it may not be possible to generate a sufficient thickness / height difference at the hydrophilic-hydrophobic boundary for the scale to be removed by shear flow. The relative widths of the hydrophobic and hydrophilic regions may be selected such that, in regions of the wettability pattern 150 that include an alternating pattern of hydrophilic and hydrophobic regions 140,130, the hydrophilic regions 140 are wider than the hydrophobic regions 130. This may be advantageous because a higher heat transfer is associated with a wider wetting area of the surface. For example, a ratio of the width of the hydrophilic regions 140 to the width of the hydrophobic regions 130 may be in a range from about 2:1 to about 5:1, such as 3:1. The precise milliscale width of each of the hydrophobic and hydrophilic regions 130,140 may depend on the flow rate of the process fluid, the particular hydrophobic coating material (which may affect adhesion and wettability), and other variables that can influence the flow conditions, such as tube diameter, salt species, process fluid temperature and related thermal properties.

[0030] Referring again to the heat exchanger component 100 of FIG. 1 and the exemplary wettability patterns shown in Table 1, it can be seen that the embodiment shown in FIG. 1 includes a hybrid coating pattern. More specifically, the wettability pattern 150 comprises hydrophobic regions 130 including first circumferentially-extending rings 132 and hydrophilic regions 140 including second circumferentially-extending rings 142 alternating with the first circumferentially-extending rings 132. In addition to the second circumferentially-extending rings 142, the hydrophilic regions 140 may include a longitudinally-extending strip 144 along a top surface of the tube designed to promote a uniform distribution of an impinging process fluid over the top surface. For example, during a heat transfer process in a horizontal tube falling film evaporator, a process fluid impinging on the hydrophilic strip 144 may be distributed along the length of the tube and may flow under the force of gravity around the tube over the hydrophilic and hydrophobic regions (circumferentially-extending strips 142,132) while exchanging heat with a fluid flowing through the tube. The process fluid may preferentially wet the hydrophilic regions 140.

[0031] FIGS. 2A-2C show multiple views of the heat exchanger component 100 of FIG. 1. More specifically, FIG. 2A provides a cross-sectional view (top) and a top view (bottom) with an inset showing details of the wettability pattern 150. FIGS. 2B and 2C show bottom and side views, respectively, of the heat exchanger component 100. Referring to the cross-sectional view of FIG. 2A, the top of the tube (liquid impinging region) may be designated as 0° (360°), the bottom of the tube (liquid departure region) as 180°, and the region in between as 90° (front) and 270° (back) respectively. The longitudinally-extending strip 144 shown in FIG. 1 has a width spanning a circumferential angle ⊖ in a range from −45 degrees to 45 degrees. The exemplary “hybid coating” wettability patterns shown in Table 1 include longitudinally-extending strips 144 spanning circumferential angles ⊖ of + / −14 degrees and + / −43 degrees. The self-cleaning capability and heat transfer performance of a heat exchanger component 100, specifically a stainless steel tube, including the wettability pattern 150 shown in FIG. 1 and FIGS. 2A-2C is explored in the experimental demonstration section below.

[0032] A method of mitigating scaling during a heat transfer process is now described in reference to the flow chart of FIG. 3. The method includes providing 310 a heat exchanger component 100 having a surface 102 including a wettability pattern 150 thereon, where the wettability pattern 150 comprises hydrophobic regions 130 and hydrophilic regions 140. The wettability pattern 150 and the hydrophobic and hydrophilic regions 130,140 may have any of the characteristics or features described above or elsewhere in this disclosure.

[0033] The heat exchanger component 100 is introduced 320 into a heat transfer process, where the surface of the heat exchanger component 100 is exposed to a flow of a process fluid. The heat transfer process may play a role in thermal desalination or food processing, for example, where the process fluid may be seawater or another aqueous solution containing salts to be removed. The heat transfer process may entail evaporation of the process fluid, e.g., in a horizontal tube falling film evaporator, as known in the art.

[0034] During the exposure of the surface of the heat exchanger component 100 to flow of the process fluid, scale deposits form 330 with a nonuniform thickness distribution and / or a nonuniform adhesion force over the wettability pattern 150. Cracks may form in the scale deposits at boundaries between the hydrophobic and hydrophilic regions 130,140. The nonuniform thickness distribution of the scale deposits may be described as a thickness gradient across the surface 102 that is influenced or determined by the wettability pattern 150. The thickness gradient may include continuous and / or step changes in the thickness of the scale deposits between the hydrophobic and the hydrophilic regions 130,140 that make the scale deposits susceptible to removal by shear flow. Typically, the hydrophilic regions include scale deposits of a larger thickness than those on the hydrophobic regions. Additionally, the adhesion or bonding force between the scale deposits and the surface 102 may vary over the wettability pattern 150. More specifically, a weaker adhesion force may be obtained between the scale deposits and the hydrophobic regions than between the scale deposits and the hydrophilic regions due to the low surface energy of the hydrophobic coating. The flow of the process fluid introduces 340 a shear force that periodically or intermittently removes the scale deposits due to the nonuniform thickness distribution, differences in adhesion force, and / or cracks at the hydrophobic-hydrophilic boundaries, thereby enabling self-cleaning of the surface. The process fluid may have a Reynolds number greater than 200 and preferably at least 350 to provide the requisite shear force for removal of the scale deposits.

[0035] Also described in this disclosure is a method of applying a wettability pattern to a heat exchanger component. The method is summarized first in reference to the flow chart of FIG. 4, and then described in more detail below. Referring to the flow chart, the method includes: optionally cleaning 410 a surface of a heat exchanger component; covering 420 a portion of the surface of the heat exchanger component with surface protection, wherein the surface protection is removable from the surface of the heat exchanger component without altering the surface of the heat exchanger component; applying 430 a hydrophobic coating to an uncovered portion of the surface of the heat exchanger component; and removing 440 the surface protection, thereby exposing a hydrophilic region of the surface of the heat exchanger component and producing a wettability pattern on the surface.

[0036] As discussed above, the heat exchanger component 100 to which the wettability pattern 150 is applied may be, in some examples, a metal or alloy tube, such as a stainless steel tube. The optional cleaning 410 may include removing particles from the surface 120 such that the surface protection (e.g., an adhesive and / or coating) can adhere to the surface 120. The surface 120 of the heat exchanger component 100 may be cleaned with an ultrasonic cleaner, ethanol rinse, distilled water rinse, or a combination thereof. In some implementations of the method, the heat transfer surface 120 may be polished (e.g., with sandpaper) prior to cleaning 410 in order to smoothen the surface 120.

[0037] A portion of the surface 120 is covered 420 with surface protection to ensure that the hydrophobic coating, which is applied in the next step, adheres only to desired regions of the surface 120 and a desired wettability pattern of hydrophobic and hydrophilic regions 130,140 may be formed. The surface protection may comprise an adhesive or coating that is removable from the surface 120 and which functions as a mask when the hydrophobic coating is applied 430. For example, a polyamide film tape may be employed as the surface protection and applied to a portion (“the covered portion”) of the surface of the heat exchanger component 100 (e.g., stainless steel tube). In some embodiments, the covered portion may comprise a contiguous section of the surface 120. In other embodiments, the covered portion may comprise unconnected sections of the surface 120.

[0038] After application 420 of the surface protection to the surface, a hydrophobic coating is applied 430 to the surface. Stated differently, an uncovered portion of the surface 120 may be treated with a hydrophobic coating. Treatment with a hydrophobic coating comprises a process to adhere a hydrophobic coating to the surface 120, more particularly, to the uncovered portion of the surface 120. For example, Soft99, a commercially available hydrophobic coating product, may be deposited onto the surface of the stainless steel tube, e.g., by spraying. Due to the masking function of the surface protection, the hydrophobic coating is effectively limited to the uncovered portion of the surface 120; any of the hydrophobic coating that adheres to the covered portion of the surface 120 may be removed along with the surface protection in the next step. In some embodiments, the treatment or application of the hydrophobic coating may include spraying, curing, priming, and / or other steps that are beneficial to adhere the hydrophobic coating to the uncovered portion of the surface 120.

[0039] After application of the hydrophobic coating, the surface protection is removed 440 from the covered portion of the heat transfer surface 120. Removal 440 exposes the hydrophilic region 140 of the surface 120, and a wettability pattern 150 comprising the hydrophobic region 130 and hydrophilic region 140 is thus formed. The dimensions and orientation of the wettability pattern 150 may be determined by the dimensions and orientation of the surface protection applied in step 420.Experimental Examples

[0040] In this investigation, the scaling process on a stainless-steel tube with a calcium carbonate solution during a falling-film flow is evaluated. An exemplary millimeter-scale wettability pattern including hydrophobic and hydrophilic regions is designed to align with the horizontal tube falling film flow regime to ensure proper wetting, thereby mitigating dry-out, and promoting the antifouling and heat transfer performance. With the designed wettability pattern, the scale layer can selectively build up on certain locations of the surface; in this way, the distribution of the scale layer follows a millimeter-scale grid with a thickness gradient instead of a uniform deposition. When the thickness gradient in the grid reaches a certain value, the scale layer breaks due to shear stress of the flow, inducing a self-cleaning mechanism. The scaling layer thickness distribution through wettability-gradient methods developed in this work represents a novel “green,” inline scale mitigation strategy, with potential as a resilient alternative to current scale control methods.Methods and Data Reduction

[0041] Heat and mass transfer of falling film flow over a horizontal tube with different surface treatments has been studied through experimental investigation. The scaling mass deposition has been measured over a certain period, and the scale layer thickness has been monitored using SEM and laser confocal microscope. The tube surface wetting and drying, scaling layer building up, and peeling off have been partially recorded through a high-speed camera.Experimental Apparatus and Procedure

[0042] Prior to the start of the experiment, the temperature of the calcium carbonate (CaCO3) test solution in the solution tank was raised to match and maintain at the solution inlet temperature. This was achieved by utilizing a heating and cooling coil located inside the test solution tank, which was driven by the water bath 2 and a chiller, respectively. Meanwhile, in-tube heating water was circulated inside the sample tube by the water bath 1 loop, as shown in the schematic diagram in FIG. 5. Once the water and solution within the tube have both reached the setting temperatures, the solution loop is connected to the test tube. This allows the system to attain the thermal equilibrium conditions within a very short time and the effect of this initial short developing time on the scale deposition is considered negligible. The test solution is delivered by a magnetic-driven pump (Pump1) from the solution tank to the distributor at the controlled temperature and concentration, where the distributor uniformly spreads the test solution over a blind tube (non-heated). The solution then impinges on the top of the sample tube, flowing around and exchanging heat with the in-tube fluid. After draining from the sample tube, the solution is collected and pumped by a centrifugal pump (Pump2) back into the solution tank. The blind tube helps the fluid further distribute before reaching the sample tube and remains at a center-to-center distance of 50 mm from the test tube. Both inlet and outlet temperatures of the test solution and heating water were measured by thermocouples. The volumetric flow rate of the test solution was measured using a panel-mount rotameter. A freshwater circulation loop was connected from the freshwater tank to the test loop (except the solution tank) to clean the experiment setup as needed.

[0043] Test solution preparation. Calcium chloride dihydrate 99-105% ACS grade (CaCl2·2H2O) and sodium hydrogen carbonate 99.7-100.3% ACS grade (NaHCO3) were mixed in 55 gallons of water to create the calcium carbonate (CaCO3) test solution (Note that seawater is not selected to avoid corrosion of the facilities, although it is more practical). The mass of CaCl2·2H2O and NaHCO3 was precisely controlled during the solution preparation, and by adding the necessary mass with concentration monitoring during the whole test period, the CaCO3 concentration maintained a constant of 0.0015 M. The chemical reaction in this procedure is:

[0044] Sample preparation and characterization. A cylindrical stainless-steel tube (120×25.4×1 mm in length×diameter×thickness) was selected as the baseline, polished with 1500 grit size sandpaper. The baseline tube was cleaned thoroughly with an ultrasonic cleaner, washed with ethanol, acetone, and distilled water, and blow-dried with compressed gas to ensure no contamination. The wettability pattern is designed to incorporate the horizontal tube falling film flow character—an impinging region on the top, flow along the radial direction, and stagnation region at the bottom. Accordingly, the wettability pattern is as follows: no wettability gradient (baseline / hydrophilic surface) at the impinged region for better longitudinal distribution, band shape wettability gradient along the tube length direction for the rest of the tube area, as shown in FIG. 2A. The top impinging region has a specific circumferential angle (−45°≤θ≤45°), and the alternating strips / bands are 3 mm in width (noncoated, hydrophilic) with 1 mm distance (coated, hydrophobic) from each other. The cleaned baseline tube was masked with 3 mm wide polyimide tape following the designed wettability pattern, and then it was spray-coated with a commercial hydrophobic coating (Soft99-Glaco mirror coat zero; supplier: Soft99 corporation). After 24 hours of drying at room temperature, the masking tape was unwrapped, and the baseline tube was imprinted with the wettability pattern.

[0045] Different parameters of the sample tubes are listed in Table 2 (below). The surface wettability is characterized by the contact angle, using a sessile drop of 3 μL deionized water, as listed that the contact angle of the baseline (uncoated) surface is around 87°, while it is around 138° on the coated area. Although the surface roughness of the baseline surfaces before the coating is similar for all samples (around 0.46˜0.53 μm), the roughness was created with different polishing directions. The baseline tube BSL, WP-r1, and WP-r2 were polished only along the radial direction of the tube, while the WP-b was polished along both radial and longitudinal directions. The average coating thickness was 0.1±0.04 μm, measured by the Keyence VK-X1000 3D Laser Scanning Confocal Microscope.TABLE 2Sample propertiesHydrophilic / SurfacePreparationSampleHydrophobicPolishingroughness,Initial contactmethoddenotationbandwidth (mm)directionSa (μm)angle θi (°)BaselineBSLN / ARadial0.53 ± 0.0289 ± 7°WettabilityWP-r13 / 1(BSL, WP-r1,(Baseline)patterned tubeWP-r2WP-r2)& 138 ± 3°WP-bRadial and0.46 ± 0.03(Coated)longitudinal(WP-b)Experimental Conditions and Parameters

[0046] Experiments were conducted with baseline and wettability patterned tubes for 192 hours to understand the wettability pattern's impact on anti-fouling performance and heat transfer. The experiments were interrupted every eight hours for the scale deposition measurement and test solution / facility maintenance (test solution checking, facilities cleaning etc.). The salt concentration was maintained as a constant by adding necessary amount of CaCl2·2H2O, NaHCO3 and water in the solution tank after each experiment interval (8 hours), which is monitored through the initial salinity and pH using a refractometer (Brix RF20) and a pH meter (Apera instrument pH20 pH tester), respectively. The test conditions were maintained constant throughout the experiment period, as described in Table 3. The inlet temperature of both the test solution and in-tube heating water was around 50° C. and 68° C., respectively. The flow rate of the falling film was at a film ReF of 380 (ReF defined at Eq. (4)), which puts the flow at the jet-droplet mode.TABLE 3Experimental conditionsFilm ReynoldsFlow rateIn-tubeTotalSamplesnumber (ReF)(L / s)Solutionheating watertime (hrs)BSL380SolutionInlet TempInlet Temp192WP-r10.025 ± 0.002(Ts, in) = 50 ± 1° C.(Tt, in) =WP-r2& In-tubeMolarity = 0.0015M68 ± 2° C.WP-b0.11 ± 0.002pH = 7.8 ± 0.1Salinity = 5 pptData Reduction

[0047] At the end of each testing interval (8 hours of scaling process), the solution flow was first stopped, followed by the in-tube heating water flow. The scaled tube then stayed stationary without in-tube / out-tube fluid flow for a short time before being disassembled from the apparatus. After that, the test tubes were placed in an airtight chamber with desiccant and allowed to dry completely for 24 hours before being weighed. The scale mass deposition on the sample tubes was measured from the difference between the before and after experiment weights using an analytical balance scale (Torbal AGN Series: resolution 0.0001 g). The experiment-stopping procedure conducted in the weight-measuring process may result in the presence of water-soluble salt in the measured scale mass. According to energy-dispersive spectroscopic investigations on the elemental composition of the scaled regions, the composition is made up of different elements, including Na, Cl C, O, and Ca. While Na takes only ˜4% of the overall scale composition, the representation of the scaling in this study is considered mainly the scaling of CaCO3.

[0048] From the inlet solution temperature (Ts,in), in-tube water inlet (Tw,in), and outlet temperature (Tw,out), the overall heat transfer coefficient, U (W / m2K) was calculated using Eq. 1.U=Q.As(Tw-Ts,in)(1)Q˙=M˙⁢Cp(Tw,in-Tw,out)(2)Tw=(Tw,in+Tw,out)2(3)

[0049] Here, {dot over (Q)} (W) is the heat transfer rate between in-tube heating water and the test solution, as described in Eq. 2. Tw (K) is the tube surface temperature beneath the scale layer as Eq. 3, which is assumed as the average of the tube inlet (Tw,in) and outlet temperature (Tw,out). Additionally, As (m2) is the surface area of the tubes, {dot over (M)} (kg / s) is the mass flow rate of heating water and Cp (J / kgK) is the specific heat of heating water at temperature Tw (K).

[0050] To describe the falling film flow, film Reynolds number (ReF) was calculated using the following equation as Eq. 4.ReF=2⁢Γη(4)Γ=m´L(5)

[0051] Where Γ is the wetting rate calculated as Eq. 5 using the solution mass flow rate ({dot over (m)}) on both sides of the tube per unit tube length (L), and η is the dynamic viscosity of test solution (assumed as water) at temperature Ts,in (K).

[0052] The uncertainty of thermocouples is ±0.2° C. and uncertainty in calculated values is estimated based on Eq. 6.UY=∑i(∂Y / ∂Xi)2⁢ UXi2(6)

[0053] Where UX<sub2>i < / sub2>is the uncertainty of the measured property and UY is the uncertainty of the calculated value. The absolute uncertainties are presented in scale mass deposition calculated from five measurements repetition, wettability and roughness from measurement of five different spots, and coating thickness from measuring ten different spots. The heat transfer coefficient errors are calculated from the standard deviation of calculated values over the averaging period.

[0054] The sample tube surface was examined at different stages of experiments using Field-Emission Environmental Scanning Electron Microscope with Energy-Dispersive Spectroscopy (FEI Quanta FEG 450 ESEM). The surface roughness, scale layer height, and coating thickness were measured by Keyence VK-X1000 3D Laser Scanning Confocal Microscope. Videos of sample tubes in operation were captured with a high-speed camera (Phantom VEO 410L) at 500 fps. Change in tube surface wettability during the experiment is quantified with a specific parameter called flashing frequency, fF (Hz), which is counted based on the average flashing period over an observing time of 25 seconds.Results and Analysis

[0055] Results of the crystallization fouling on the wettability patterned tube during horizontal tube falling film flow have been presented, including the mass deposition and heat transfer performance. Through the results, the mechanism of how the wettability pattern triggers the surface self-cleaning and improves heat transfer performance has also been explored.Effects on Scale Mass Deposition

[0056] The net scale mass deposition on different tested tubes, measured as the mass difference between the scaled and clean tube, is plotted against the experiment time in FIG. 6A, which is at constant inlet temperature and flow rate for both the test solution and in-tube heating water, as described in Table 3. The comparison of baseline (BSL) and two wettability patterned tubes is shown in FIG. 6A, of which the WP-r and WP-b are tubes with the same wettability pattern but different polishing methods, as described earlier. The mass deposition of WP-r is an average of two repeated tests (WP-r1 and WP-r2), as shown in FIG. 6B. Note that due to time constraint, only one repeatability test has been conducted, the consistency between WP-r1 and WP-r2 tube test within long testing period shows a reasonable repeatability.

[0057] It can be found that the variation of net mass deposition over time has a generally similar trend for the patterned tube and the baseline, which can be characterized as periodically increasing and decreasing. The mass accumulation on the baseline tube initially increases for roughly 56 hours, and then it gradually decreases for roughly another 56 hours, after that, it increases till the end of the testing time. Similarly, the net mass deposition on the patterned tubes goes through an initial quick increase (8 hours for WP-r and roughly 24 hours for WP-b), and a sharp decrease period (for about 48 hours for both WP-r and WP-b); after that, it goes through another increasing-decreasing cycle, which is clearly demonstrated on both WP-r1 and WP-r2 for the last 70 hours, shown in FIG. 6B. The net mass deposition is dictated by the competing mechanism of deposition and removal—a higher rate of deposition than removal leads to a net fouling buildup, while a higher rate of removal than deposition can cause a drop in net fouling in a certain period. The deposition is mainly driven by a higher salt ions concentration at the liquid solution-tube wall interface, which results from the local temperature gradient within the solution, while the removal is mainly driven by the shear stress from the falling film flow. As the scale layer builds up, the surface roughness or (and) wettability-induced heterogeneity in the local scale thickness distribution is enhanced; meanwhile, the local temperature at the interface decreases due to the increasing thermal resistance imposed by the scaling layer. As a combined effect, the removal dominates, and the net mass deposition slowly decreases after the initial increasing time period. As the scale layer is continuously polished by the flow shear, to a point that a less heterogeneous distribution is exhibited, meanwhile the interfacial temperature keeps increasing as the removal proceeds, finally another deposit process starts to dominate, and an increasing net mass can be observed. The cycle repeats until it reaches a balance of deposition and removal.

[0058] Although net mass deposition follows a similar general trend, the increasing-decreasing cycling period, the amplitude of each cycle is very different between the baseline and patterned tubes. The cycling period for the baseline tube is roughly 112 hours (to be noted that net scale mass continuously increases from 112 hours to the end of the experiment, so the exact time required to achieve the next peak in the current study is unclear). The cycling period for the patterned tubes is somewhat hard to quantify; roughly, it accomplishes the first peak / valley cycle for around 72 hours for all patterned tubes and the last cycle for about 70 hours for both WP-r tubes in FIG. 6B, while it is hard to make a precise estimation for the WP-b tube. There are more significant and frequent fluctuations for the patterned tubes than the baseline tube (here, the changes between the neighboring measurements are defined as fluctuation). The maximum fluctuation between the immediate two measurements is 43%, 56%, and 72% for the baseline, WP-b, and WP-r tubes, respectively (the initial clean tube condition is excluded), while the changes of direction (from increasing to decreasing, or vice versa) occurs every 1.5 / 1.9 / 2.3 measurements on average for WP-b / WP-r1 / WP-r2 tube respectively, which is much higher for the baseline tube of 4.1 measurements. The measuring period can play an important role in the presented quantity of net mass deposition, 8 hours / measurement is adopted in the current experiment. While in the repeat tests of WP-r1 and WP-r2 in FIG. 6B, both the overall variation and the fluctuation show comparable similarity, although the maximum deviation between these two quantities can be as high as 49 g / m2 at the very early scaling period. Note that the scaling mass fluctuations on the patterned tube are not simply from the sample-tube handling process, including assembling and disassembling, storing, weighing, SEM observing etc., the process was conducted following a strict standard. The mass of tube with scale layers has almost no changes after 12 hours of drying time, which is confirmed by frequent rechecking of the mass after different periods (24 hours, 3 days, 1 week). There was no trace of falling off / losing scale layers during the sample handling process. Sample mass was also monitored before and after any investigation under SEM and microscope, ensuring no changes.

[0059] Multiple factors may contribute to the above observation: 1) the added heterogeneity in the surface due to the wettability bands, especially edge imperfections, and irregularities on the transition from hydrophilic to hydrophobic region, acts as preferential heterogeneous nucleation sites of crystallization. Similarly, when comparing different polishing methods for the patterned tubes WP-r and WP-b, the surface polished from both directions (WP-b) has more nucleation sites for crystallization. This triggers a faster accumulation of scale in a much more unevenly distributed manner; as a result, the local temperature and shear stress from flow accelerate the deposition and removal cycles. 2) the modified wetting behavior on the patterned tubes can promote the uneven distribution of scale layer (discussed in detail in the following section), especially at the earlier stage (roughly within 24 hours), some surface area stays dry or partially dry, which leads to a higher local temperature and a thicker local scale layer. As a result, the flow shear-induced washing / self-cleaning mechanism can kick in. 3) the adhesion / bonding force between the scale layer and tube wall varies along different wettability area, due to the low surface energy of the hydrophobic coating, a weaker adhesion force is expected on the hydrophobic band area. Weaker adhesion at hydrophobic band, together with the enhanced flow shear triggered by the uneven scale layer distribution, forms the self-washing mechanism for the patterned tubes, for which an active washing / shedding of the scaling layer was observed. This self-cleaning process is attributed to a larger / more frequent fluctuation of net mass deposition on the patterned tubes than that on the baseline tube.

[0060] Accumulated scale mass with the wettability patterned tube “WP-b” was measured higher than that with the baseline tube (BSL), while average scaling on radially polished tubes (WP-r) shows comparatively lower scaling, which could be due to the difference in the nucleation sites. However, after 192 hours, the scale mass deposition amount for both wettability patterned tubes (WP-r and WP-b) was lower than the baseline tube (BSL) due to the self-cleaning mechanism.Effects on Scale Layer Distribution

[0061] The scale layer distribution on both baseline tube and patterned tubes, in which the top of tubes (liquid impinging region) is designated as 0° (360°), and the bottom of tubes (liquid departure region) is as 180°, and the region in between is 90° (front) and 270° (back) respectively, also indicated in FIG. 7. The scale layer distribution is a transient property and dynamically linked to the scale growth and removal. The scale layer uniformly covers most areas of the baseline tube (the initial shiny appearance is lost completely), reflected by a uniform gray color, except for the region of liquid departure, around 180°, where a thicker scale layer can be observed reflected by the light gray area. It is very different for the patterned tubes, where the scale layer distribution follows the wettability pattern. At the region around 0° (360°), where it is an uncoated hydrophilic tube surface, a very uniform scale layer is formed, especially for WP-r2 and WP-r1. The scale layer distributes very nonuniformly around the 180° region, where a clean tube surface can be observed along the wettability band. At areas near 90° and 270°, although there are alternating light gray / gray regions (thicker / thinner scale layers), very few clean spots can be observed. The liquid film's tangential velocity increases and then decreases as the film flows around the tube, while the temperature continuously increases. Near the departure region where the two streams from both sides of the tube mix, the liquid film reaches a higher temperature and lower velocity, which exhibits a perfect condition for a higher deposition and lower shear removal around this region. The scale layer distribution at any moment is the combined effect of the deposition, flow shear, and adhesion. The baseline surface promotes a homogeneous scale layer coverage in general-uniform deposition and uniform adhesion between the scale layer and the tube surface. As a result, a higher scale layer thickness around the 180° region on the baseline tube is observed. The low surface energy on the hydrophobic band manipulates both the wettability and the adhesion of the scale to the surface. This can cause the following effects: 1) a lower scaling on the hydrophobic band caused by the lower solution contact duration due to the local non-wetting behavior; 2) an enhanced flow shear due to the wettability induced heterogeneity in scale layer distribution; 3) an enhanced removal due to the surface energy induced heterogeneity in scale layer adhesion.

[0062] The scale layer distribution at the wettability gradient region presents two different patterns, as demonstrated in FIGS. 8A and 8B under SEM, both of which are observed around 152 hours. One scaling pattern, shown in FIG. 8A, is characterized by a thicker-compact scale layer on the hydrophilic band and a much thinner scale layer on the hydrophobic bands, which leaves a significant heterogeneity in the scale layer distribution. The thickness difference is almost like a step at the wettability boundary. The other pattern, in FIG. 8B, is characterized by a relatively uniform scale layer with a crack across the wettability boundary. Those cracks verify the discontinuity of scale layers between hydrophilic and hydrophobic bands.

[0063] When the balance between the flow shear and the adhesion is broken, an intense scale wash-off / removal is expected. The two different scale layer distribution patterns discussed above result in different removals. The wash-off on hydrophilic bands, shown in FIGS. 9A-9D, is initiated by the scale layer step at the wettability boundary, corresponding to distribution pattern one (discussed above). A big piece of scale layer covering the hydrophobic region is shed off from the boundary step and carried away by the fluid, leaving a clean surface (shown in FIGS. 9G and 9H) with a trace of initially deposited crystals). Based on the observation in FIG. 7, spots with an approximate scale height difference range of 90-130 μm showed a tendency to wash off with the examined flow rate. Another type of wash-off corresponds to distribution pattern two, shown in FIGS. 9E and 9F, for which the scale layer is peeled off from the hydrophobic region along the cracks between the wettability boundaries. Due to tube curvature and momentum of the impinging fluid, the flow around the tubes exhibits a chaotic and unsteady feature, and the scale layer step height would not be the only reason for the wash-off; a favorable flow shear force was required to overcome the adhesion between the scale layers and the tube surface. A weaker local adhesion might trigger the wash-off at a relatively small height difference or even no height difference region. Both distribution steps enhanced flow shear, and the low surface energy triggered weaker adhesion, contributing to the intense scale wash-off. As a result, this intense wash-off phenomenon on the wettability patterned tube is attributed to the frequent scale mass fluctuation compared with the baseline tube.Effects on Heat Transfer Coefficient

[0064] The overall heat transfer coefficients (HTC) of the baseline (BSL) and wettability patterned tubes (WP-r1, WP-r2, and WP-b) are plotted against time in FIGS. 10A and 10B, respectively. Calculated overall HTC averaged and plotted with the standard deviation as error bars for every 8 hours. Based on initial 8 hours of experiment, the overall HTC with baseline tube (BSL) was the highest (3712 W / m2K), while the wettability patterned tubes performed poorly (2859 W / m2K, 3029 W / m2K, and 2744 W / m2K for sample tube “WP-r1”, “WP-r2”, and “WP-b”, respectively). However, the overall HTC with baseline tube (BSL) gradually falls to a minimum (2865 W / m2K) in 192 hours of experimentation. In contrast, the overall HTC with the wettability patterned tubes keeps increasing and reaches a plateau of comparatively higher HTC within 24-48 hours, maintained until the end of the total experiment period. The final overall HTC (184-192 hours) is measured as 3337 W / m2K, 3109 W / m2K, and 3310 W / m2K for sample tube “WP-r1”, “WP-r2”, and “WP-b”, respectively. Interestingly, the overall HTC for wettability patterned tubes remains a constant trend with nearly no degradation yet improves around 15% in the final overall HTC compared to the concurrent baseline tube, while the baseline tube overall HTC gradually deteriorates to 77% of its initial performance in 192 hours.

[0065] The baseline tube has superior wetting compared with that of the wettability patterned tubes at the initial stage. Having the cleaned-unscaled surface and favorable wetting conditions, the baseline tube (BSL) shows a superior heat transfer performance initially (0-24 hours). However, due to the crystallization fouling process, the whole baseline tube (BSL) continuously accumulates uniform scale layers, which thicken and become compact over time. The added thermal resistance causes the deterioration of heat transfer performance with time, such that a continuous decline in overall HTC is observed.

[0066] On the other hand, the initial wetting with wettability patterned tubes can be inferior. The fluid may shed off from the impinging region without flowing along and across the tube, and in some cases there may be no proper wetting on the surfaces at the same flow rate as that of the baseline tube (BSL). That is, it is difficult to establish a full thin film flow on wettability patterned tubes due to the hydrophobic bands. This initial improper wetting is surely attributed to a lower heat transfer than that on the fully wetted baseline surface. However, after 24 hours of testing, the scale deposition improves the surface wettability on the patterned tubes. It is observed that the impinging fluid fully wets the tube top area and flows down through part of the surfaces, mainly remains in the uncoated hydrophilic region at early time. The improvement in the heat transfer on the patterned tubes is largely caused by the changes in surface wetting at the early stage. Although the hydrophilic bands are usually constantly wetted after the early stage, an alternation of intermittent wetting and drying on the hydrophobic bands is observed, which is defined here as flashing, and a schematic representation of the ideal flashing scenario along with associated photographs is shown in FIG. 11. The momentum of falling film gained from the upper flow pushes the fluid downward from the tube top region through hydrophilic bands. However, due to a lower surface energy on the hydrophobic band, the liquid film flows and partially wets the surface for a very short time, as shown in FIG. 11(i). After that, it bounces backward instantly, causing drying on hydrophobic bands, as shown in FIG. 11(ii, iii). Immediately, the regained momentum from the mainstream flow and gravity pushes the film flow past the hydrophobic band again, rewetting the surface as in FIG. 11(iv), and the cycle of intermittent wetting and drying repeats. The flashing frequency, fF (Hz), is defined as the number of times the intermittent wetting and drying cycle happened per second in a specific hydrophobic band, noting the whole cycle of wetting and drying was considered as one flash. The flashing frequency is quantified using the captured slow-motion videos to understand the wetting behaviors of sample tubes. Initially, the high hydrophobicity of hydrophobic bands makes them hard to wet, and flash occurs very quickly; the frequency is as high as 20 Hz, while with increasing wettability as scaling builds up, the flashing process slows down and the flashing frequencies decrease to only about 5 Hz. So, the higher hydrophobicity on those hydrophobic bands reflects as higher flashing frequencies and vice versa. This improvement in wetting, along with a comparatively clean surface in hydrophobic bands, might provide substantial enhancement in the overall HTC after 24-48 hours of the experiment. Additionally, continuous inline wash-off may maintain lower thermal resistance of scaling and stabilize the overall HTC throughout the whole experiment period.

[0067] To summarize, a unique method of inline scale mitigation with self-cleaning surface is described on the falling film flow around horizontal tubes, commonly employed in multi-effect distillation processes, and validated in this experimental work. Sample tube surfaces (stainless steel) with a novel wettability pattern design are examined for crystallization fouling (calcium carbonate), heat transfer performance, and self-cleaning behavior. In addition to providing appropriate wetting of tube surfaces during operation, the wettability pattern promotes heterogeneous scale layer distribution and non-uniform adhesion, which in turn initiates flow shear-based self-cleaning. Falling film flowing on the wettability gradient surfaces and scale layer washing off are captured by photographs and videos, and the scale layer distribution is examined by SEM. The findings are summarized as follows:

[0068] The wettability patterned tubes show antifouling performance compared with the baseline tube with lower scale mass deposition for a 192-hour period; especially, multiple spots of scale layer wash-off can be observed. The scale mass amount fluctuates more frequently with the wettability patterned tube than with the baseline, an indication of periodic wash-off.

[0069] Scale layer distribution on patterned tubes follows either thickness-step or cracks along the wettability boundary due to the difference in the surface energy on different bands. This can trigger an intense wash-off of the scale layers for the higher flow shear and the weaker adhesion.

[0070] While baseline tube overall HTC gradually declines to 77% of its clean tube heat transfer performance in 192 hours, the overall HTC for wettability patterned tubes maintains a constant trend of overall HTC with almost no degradation and improved by 15% at the final hour compared to concurrent baseline tube performance. Though initial (0-24 hours) inadequate wetting makes the overall HTC with wettability patterned tubes lower, later improvement in wetting along with less scale makes them superior in heat transfer performance.

[0071] To clarify the use of and to hereby provide notice to the public, the phrases “at least one of , , . . . and <N>” or “at least one of , , . . . <N>, or combinations thereof” or “, , . . . and / or <N>” are defined by the Applicant in the broadest sense, superseding any other implied definitions hereinbefore or hereinafter unless expressly asserted by the Applicant to the contrary, to mean one or more elements selected from the group comprising A, B, . . . and N. In other words, the phrases mean any combination of one or more of the elements A, B, . . . or N including any one element alone or the one element in combination with one or more of the other elements which may also include, in combination, additional elements not listed. Unless otherwise indicated or the context suggests otherwise, as used herein, “a” or “an” means “at least one” or “one or more.”

[0072] While various embodiments have been described, it will be apparent to those of ordinary skill in the art that many more embodiments and implementations are possible. Accordingly, the embodiments described herein are examples, not the only possible embodiments and implementations.

Claims

1. A heat exchanger component configured for mitigation of scaling, the heat exchanger component comprising:a surface including a wettability pattern thereon, the wettability pattern comprising hydrophobic regions and hydrophilic regions.

2. The heat exchanger component of claim 1, wherein the hydrophobic regions comprise coated regions of the surface, the coated regions including a hydrophobic coating, andwherein the hydrophilic regions comprise uncoated regions of the surface.

3. The heat exchanger component of claim 1, wherein the hydrophobic coating comprises a polymer, silica, metal oxide, carbon nanotubes, and / or wax.

4. The heat exchanger component of claim 1, wherein the surface comprises a curved surface.

5. The heat exchanger component of claim 1, wherein the heat exchanger component comprises a tube.

6. The heat exchanger component of claim 1, wherein the wettability pattern comprises an alternating pattern of the hydrophobic regions and the hydrophilic regions.

7. The heat exchanger component of claim 1, wherein areal coverage of the hydrophobic regions over the surface is in a range from 10-50%.

8. The heat exchanger component of claim 1, wherein the wettability pattern includes an alternating pattern of the hydrophobic and the hydrophilic regions, and wherein, within the alternating pattern, the hydrophilic regions are wider than the hydrophobic regions.

9. The heat exchanger component ofclaim 1, wherein a ratio of the width of the hydrophilic regions to the width of the hydrophobic regions is in a range from about 2:1 to about 5:1.

10. The heat exchanger component of claim 1, wherein a width of each of the hydrophobic and the hydrophilic regions is in a range from about 0.5 mm to about 25 mm.

11. The heat exchanger component of claim 1, wherein the wettability pattern comprises a strip coating pattern, a ring coating pattern, a grid coating pattern, and / or a hybrid coating pattern.

12. The heat exchanger component of claim 1 being a tube, andwherein the hydrophobic regions have a form of first strips extending in a longitudinal direction and wherein the hydrophilic regions have a form of second strips extending in the longitudinal direction and alternating with the first strips.

13. The heat exchanger component of claim 1 being a tube, andwherein the hydrophobic regions have a form of first rings extending in a circumferential direction and wherein the hydrophilic regions have a form of second rings extending in the circumferential direction and alternating with the first rings.

14. The heat exchanger component of claim 13, wherein the hydrophilic regions further comprise a longitudinal band extending from a first end to a second end of the tube and intersecting with the first and second rings.

15. The heat exchanger component of claim 14, wherein the longitudinal band has a circumferential angle ⊖ in a range from −45 degrees to +45 degrees.

16. A method of mitigating scaling during a heat transfer process, the method comprising:providing a heat exchanger component having a surface including a wettability pattern thereon, the wettability pattern comprising hydrophobic regions and hydrophilic regions;introducing the heat exchanger component into a heat transfer process, the surface of the heat exchanger component being exposed to flow of a process fluid;wherein, during the exposure to flow of the process fluid, scale deposits form with a nonuniform thickness distribution and / or a nonuniform adhesion force over the wettability pattern on the surface, andwherein the flow of the process fluid introduces a shear force that periodically or intermittently removes the scale deposits, thereby enabling self-cleaning of the surface.

17. The method of claim 16, wherein the heat transfer process is part of thermal desalination or food processing.

18. The method of claim 16, wherein the process fluid has a Reynolds number of at least 350.

19. The method of claim 16, wherein the heat transfer process includes evaporation of the process fluid in a horizontal tube falling film evaporator.

20. A method of applying a wettability pattern to a heat exchanger component, comprising:cleaning a surface of a heat exchanger component;covering a portion of the surface of the heat exchanger component with surface protection, wherein the surface protection is removable from the surface of the heat exchanger component without altering the surface;after covering the portion of the surface with surface protection, applying a hydrophobic coating to the surface; andafter applying the hydrophobic coating, removing the surface protection from the portion of the surface, thereby exposing a hydrophilic region and producing a wettability pattern on the surface.

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