Heat transfer system

Abstract

A heat transfer device, such as a heat exchanger, has a size and flow rate such that the Reynolds number of the flow is in the range of 1 to 1000. The device uses a working fluid in a resilient turbulent flow state. This enhances heat transfer to or from the working fluid. In some embodiments, the fluid is an emulsion having a dispersed phase that varies between liquid and solid such that its latent heat of fusion contributes to the heat carried by the working fluid.

Description

Cross-reference to related applications

[0001] This disclosure claims priority to GB application number GB 2314042.9, filed on September 14, 2023, which is incorporated herein by reference in its entirety. Technical Field

[0002] This disclosure relates to heat exchangers and working fluids for devices that manage thermal energy by storing heat, absorbing heat, or transferring thermal energy from one location to another. Background Technology

[0003] Various forms of equipment use working fluids to absorb heat and transfer it to another location. One example is a heat exchange loop. Another example is a solar water heating system, where solar energy heats the working fluid, which in turn heats domestic hot water. Working fluids can also be used to receive and store heat energy when it is available, and release it at a later time. Systems also exist where heat is extracted from the working fluid, and the cooled fluid is used to absorb heat at a later time. Such working fluids are typically water or aqueous solutions, or can be some other single-phase liquid. Summary of the Invention

[0004] This summary is provided to introduce concepts that will be further elaborated and described in the detailed description below. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid to limiting the scope of the claimed subject matter.

[0005] One aspect of this disclosure is a method for removing heat into or out of a flowing fluid, the method comprising pumping the fluid through a heat transfer device comprising: a chamber through which the fluid flows, wherein a chamber wall in contact with the flowing fluid is an interface through which heat is transferred to or from the flowing fluid, wherein the chamber contains a spaced array of barriers that force the streamlines of the flowing fluid to repeatedly change direction to flow through the gaps between the barriers; the viscosity of the fluid, the flow velocity of the fluid within the chamber, and the width of the gaps between the barriers determine the Reynolds number (Re) of the flow, which ranges from 1 to 1000, and may be from 1 to 100, 1 to 250, or 1 to 500; the fluid contains a solute that enables the fluid to exhibit elastic turbulence; and the flow velocity of the fluid through the chamber causes the flowing fluid to be in an elastic turbulent state.

[0006] A system for moving thermal energy may include a heat transfer device comprising: a chamber through which a fluid flows, wherein the chamber walls are interfaces through which thermal energy is transferred to or from the flowing fluid; a fluid; and a pump for pumping the fluid through the chamber, wherein the chamber contains a spaced array of barriers that force the streamlines of the flowing fluid to repeatedly change direction to flow through the gaps between the barriers; the fluid contains a solute that enables the fluid to exhibit elastic turbulence; and the system is configured such that the viscosity of the fluid, the flow velocity of the fluid within the chamber, and the width of the gaps between the barriers determine the Reynolds number (Re) of the flow, which ranges from 1 to 1000, and may be from 1 to 500, 1 to 250, or 1 to 100.

[0007] In some implementations, the heat transfer device is part of a heat exchange system that includes a second heat transfer device at different locations, a pump, and a piping system connecting the pump and the heat exchange device to form a closed loop containing fluid.

[0008] The obstruction can be multiple columns extending across the chamber from the interface to the other wall of the chamber. The columns can be arranged such that flow through the gaps between columns in a row is forced to change direction by columns in adjacent rows.

[0009] In another aspect, this disclosure provides a working fluid for a heat exchange system, wherein the working fluid is a multiphase system having a continuous phase and at least one suspended dispersed phase, the suspended dispersed phase changing between solid and liquid at a temperature where the continuous phase is a liquid, and wherein the continuous phase is a solution containing a solute that enables the continuous phase and thus the entire working fluid composition to exhibit elastic turbulence. Attached Figure Description

[0010] In the following detailed description, the subject matter disclosure is further described with reference to the several accompanying drawings, which are labeled with non-limiting examples of the subject matter disclosure, wherein the same reference numerals denote similar parts throughout the several views of the drawings, and wherein: Figure 1 This is a schematic diagram of a heat transfer system with two devices for heat transfer, both of which are shown in cross-section. Figure 2 As shown Figure 1 Part of the column array used in heat transfer devices; Figure 3 It is a heat transfer device along Figure 1 The cross section intercepted by line AA; Figure 4 yes Figure 3 A magnified view of a portion of the image; Figure 5 Is with Figure 4 A similar view shows columns with different cross-sections; Figure 6 This is a graph showing the experimental results of the onset of elastic turbulence; Figure 7 It is used to determine Figures 1 to 3 A schematic diagram of the equipment showing the system's operating parameters; Figures 8 to 10 Experimental results obtained using an implementation of this device are shown; Figure 11 , Figure 12 and Figure 13 Experimental results relating to elastic turbulence in phase change emulsions are presented; Figure 14 This is a perspective view of the air deflector; Figure 15 This is a diagram of an apparatus used for observing elastic turbulence by means of birefringence; and Figure 16 The grayscale image shows the use of Figure 15 The image was obtained by the device. Detailed Implementation

[0011] The details shown herein are merely illustrative and for the purpose of a illustrative discussion of embodiments of the subject matter disclosure, presented in the manner that is considered most useful and readily understood in terms of the principles and concepts of the subject matter disclosure. In this regard, no attempt is made to show structural details in more detail than is necessary for a basic understanding of the subject matter disclosure, and the description, taken in conjunction with the accompanying drawings, will be readily apparent to those skilled in the art as to how various forms of the subject matter disclosure may be manifested in practice. Furthermore, the same reference numerals and names in the various drawings denote the same elements.

[0012] This detailed description relates to embodiments of this disclosure and the possibilities that may be used. It should be understood that the features or possibilities described in combination may be used individually, if doing so is feasible. Furthermore, the features or possibilities described in any embodiment may be used in any other embodiment, provided that doing so is possible.

[0013] This disclosure uses the phenomenon of elastic turbulence. It is well known, of course, that Newtonian fluids (such as water) can experience laminar or turbulent flow. This turbulence can be called inertial turbulence. The conditions for laminar and turbulent flow are usually expressed by the Reynolds number, which is the ratio of inertial forces to viscous forces within the fluid. The Reynolds number is dimensionless because it is a ratio. Inertial turbulence exists at Reynolds numbers above approximately 2000. At Reynolds numbers below approximately 1500, Newtonian fluids are in a laminar state.

[0014] Elastic turbulence is a distinct physical phenomenon discovered in the late 20th century. It is observed that at low Reynolds numbers and low flow velocities, Newtonian fluids will flow in a laminar state. Elastic turbulence is sometimes referred to using the older and more general term "elastic instability."

[0015] Numerous documents have mentioned the potential use of elastic turbulence in microfluidics, where the size of the flow path and the flow velocity are very small, resulting in a device volume of less than 10 ml and a very small Reynolds number, well below one. In contrast, this disclosure uses elastic turbulence in apparatuses where the size of the apparatus and the flow velocity are large enough that the Reynolds number is one or greater but less than one thousand. When the Reynolds number is in this range, the flow of Newtonian fluids (such as pure water) is laminar. As previously mentioned, the heat exchange apparatus according to this disclosure has a chamber through which a fluid exhibits elastic turbulence as it flows. The fluid volume within this chamber can be at least 50 ml (possibly in experimental apparatuses) and can be more, such as at least one liter or at least fifty liters in larger-scale apparatuses.

[0016] The formula that can be used to determine the Reynolds number of a flow passing through a chamber containing obstructions, forcing the flow streamlines to bend, is: Where ρ is the density of the fluid, in kilograms per cubic meter. U is the flow velocity, measured in meters per second. L is the width of the gap between obstacles in the chamber. η is the viscosity of the fluid, measured in Pascals per second.

[0017] If the flow velocity is measured as volume per unit time, then the above formula becomes Where Q is the flow velocity in cubic meters per second, and A is the cross-sectional area of ​​the fluid flowing through it, transverse to the overall flow direction.

[0018] Elastic turbulence occurs in solutions containing solutes with flexible structures. Materials capable of undergoing elastic deformation and causing the solution to exhibit elastic turbulence are polymers containing long, flexible linear chains. The number of monomer units in the polymer can be at least 5000, and can be significantly more, such as at least 25,000. Monomer units can exist in linear chains of at least 1000 monomer units, each linked to each other by a single covalent bond, allowing one monomer unit to rotate relative to its neighbor. Individual linear chains can be longer, and the polymer can contain at least 5000 or even at least 10,000 linear chains of monomer units. The average molecular weight of the polymer can be 10. 6Daltons or higher. The concentration of this long-chain / high molecular weight polymer contained in the solution used to generate elastic turbulence can be less than 5% by weight, for example, in the range of 0.05% or 0.1% to 1% or 2% by weight.

[0019] The long-chain polymers that enable elastic turbulence can be polymers of a single monomer or copolymers of more than one monomer, such as linear block copolymers. The polymer may contain side chains of long chains connected to monomer units linked together by a single covalent bond. The polymer may contain chain branches, for example at branch points where three or more chains are linked together, with each chain containing at least 1000 monomer units, and possibly at least 2000 or 5000 monomer units.

[0020] The flexibility of polymer chains allows polymer molecules to become entangled. This flexibility can be described using mathematical models. The free-linked chain model is commonly used, and the flexibility of a particular polymer can be represented by the parameters of an equivalent free-linked chain (which is itself a mathematical model). This method is described in Chapter 2 of Rubinstein and Colby, “Polymer Physics”, 2003, Oxford University Press. The equivalent free-linked chain has the same mean-square end-to-end distance and the same maximum end-to-end distance as the actual polymer, but is considered to consist of so-called Kuhn monomers that can rotate freely relative to each other. These model monomers have a certain length (called the Kuhn length) and a certain molar mass.

[0021] Polymers capable of elastic turbulence may contain at least one flexible polymer chain whose length and composition are represented by at least 1,000 Kuhn monomers, with a Kuhn length not exceeding 100 angstroms (10 nm) and possibly not exceeding 50 angstroms. If the polymer is a single unbranched chain, its length and composition may be represented by at least 5,000 Kuhn monomers with a Kuhn length not exceeding 100 angstroms, and possibly more, such as at least 20,000 such Kuhn monomers.

[0022] Elastic turbulence has been observed in solution with several different long-chain polymers. One such polymer is polyacrylamide, which can be hydrolyzed or partially hydrolyzed. Groisman and Steinberg presented experimental evidence of elastic turbulence in high molecular weight polyacrylamide solutions in "Elastic Turbulence in a polymer solution flow" Nature, Vol. 45, p. 53 (2000). Other examples of long-chain polymers that have been reported to generate elastic turbulence include polyisobutylene with a molecular weight of 4 to 6 megadaltons dissolved in organic solvents (Dris and Shaqfeh, J. Non-Newtonian Fluid Mech. Vol. 80, pp. 1–58 (1998)), polystyrene with a molecular weight of 18 megadaltons dissolved in organic solvents (Magda and Larson, J. Non-Newtonian Fluid Mech. Vol. 30, pp. 1–19 (1988)), and polyethylene oxide with a molecular weight of 4 megadaltons dissolved in aqueous solution (Davoodi et al., J. Fluid Mech. Vol. 857, pp. 823–850 (2018)). Rubinstein and Colby, p. 53, give Kuhn lengths of 18 Å and 11 Å for polystyrene and polyethylene oxide, respectively. The Kuhn length of polyacrylamide is reported to be 15 to 25 angstroms (Fetters, Lohse and Colby, Chain Dimensions and Entanglement Spacings. In Physical Properties of Polymers Handbook; Mark, JE, ed.; Springer: New York, 2007; pp. 447-454).

[0023] When using long-chain linear polymers to induce elastic turbulence, it is desirable to include biocides to protect the polymer from biodegradation.

[0024] Long-chain partially hydrolyzed polyacrylamide linear polymers with molecular weights exceeding 1 megadaltons are available from SNF Floerger, headquartered in Andrézieux, France.

[0025] Elastic turbulence has also been observed in solutions containing surfactants that form worm-like micelles in solution. A large body of scientific literature addresses surfactants that form worm-like micelles, their properties, and applications. One review is Yang, “Viscoelastic wormlike micelles and their applications,” Current Opinion in Colloid & Interface Science, Vol. 7, pp. 276–281 (2002). Discussions of properties include Raghavan and Kaler, “Highly Viscoelastic Wormlike Micellar Solutions Formed by Cationic Surfactants with Long Unsaturated Tails,” Langmuir, Vol. 17, pp. 300–306 (2001), and Beaumont et al., “Turbulent flows in highly elastic wormlike micelles,” Soft Matter, Vol. 9, p. 735 (2013). Favolin et al. cited an example of using hexadecyltrimethyl bromide as a surfactant in Physical Review Letters, Vol. 104, pp. 178303 (2010).

[0026] When a solution contains substances capable of inducing elastic turbulence, elastic turbulence occurs if the solution flows at a sufficient velocity (which can be low) and the flow path causes the streamlines of the flow to bend. Therefore, one known possibility for a flow path inducing elastic turbulence is a serpentine channel. Another possibility is described below with reference to the accompanying figures. Steinberg provides a detailed discussion of elastic turbulence in the Annual Review of Fluid Mechanics, Vol. 53, pp. 27-58 (2021).

[0027] As mentioned below, the ability of a fluid composition to exhibit elastic turbulence can be demonstrated using laboratory equipment. Experimentally, the flow rate through the heat exchanger sufficient to cause the selected fluid composition to exhibit elastic turbulence can be determined, as shown below.

[0028] In this disclosure, elastic turbulence mixes the working fluid as it flows across a solid interface, through which heat is transferred to or from the working fluid. Due to the elastic turbulence, the heat transfer rate is increased because heat transfer to and from the interface is not limited to conduction through the working fluid.

[0029] As an example embodiment of this disclosure, the accompanying drawings illustrate a heat transfer system for transferring thermal energy from a heat source to a volume of water. Figure 1 The device 10 on the left is exposed to the sun so that it can be heated. Figure 1 The device 12 on the right is immersed in water. The two devices 10 and 12 are connected by a pipe 14 for circulating a working fluid, which is pumped around the loop by a pump 16. The pipe section carrying the hot working fluid is surrounded by insulation 24. Devices 10 and 12, together with pipe 14 and pump 16, form a heat exchange loop for transferring solar thermal energy received at surface 20 to the water surrounding device 12.

[0030] The device 10 has a cubic housing defining a chamber through which the working fluid is pumped. The housing surface 20, exposed to solar heat, forms the interface between the working fluid inside the housing and the heat source. This surface is made of a thermally conductive material, such as copper or aluminum. The opposing surface 22 has a heat-insulating element 24 abutting it to reduce heat loss.

[0031] The interior of the housing of device 10 is an array of rods 30 formed by rods that extend across the interior chamber from the housing surface 20 to the opposite surface 24. Figure 2 The arrangement of such columns 30 is shown in a perspective view taken from one side, in which there is no enclosed housing 20. Figure 3 yes Figure 1 The cross-section taken along line AA also shows the arrangement of column 30. For example... Figure 3 and Figure 4 As shown in the enlarged view, column 30 has a square cross-section, where flat surfaces 32 intersect at corner edges 33 and 34. The width of flat surface 32 is... Figure 4 The distance between the faces 32 of adjacent pillars is denoted as "a", and the distance between them is denoted as "b". The width of the gap between the edges 34 of two faces is given by the Pythagorean theorem as √2b. 2 .like Figure 3 As shown, the edges of the array are completed by pillars 31 with triangular cross-sections. Each pillar 30 is positioned such that the diagonal of the square cross-section spanning the corner edges 33 is aligned with the overall flow direction, i.e., the diagonal is parallel to the imaginary line from inlet 26 to outlet 28. The flat surface 32 of each pillar is inclined relative to this overall flow direction. Figure 4 As shown in the magnified view, the working fluid flows through the gap between the opposing edges 34 of adjacent columns 30, but is then forced to deflect by another column. Therefore, the array of columns 30 obstructs the straight flow of the working fluid, resulting in… Figure 4 The dashed lines in the middle represent the flowing streamlines that bend repeatedly.

[0032] The heat exchange device 12, submerged in water to be heated, has a cubic housing 40, which is the interface through which thermal energy leaves the working fluid. Fins 42 protruding from the housing 40 facilitate the conduction of heat from the housing 40 to the surrounding water.

[0033] The interior of device 12 is similar to that of device 10. Housing 40 defines a chamber through which the working fluid flows. As described with respect to device 10, rods extending from one side to the other across the internal chamber provide an array of columns 30 that impede flow.

[0034] Figure 5 Another possible cross-section of column 30 is shown. Surface 54 has a convex curvature and intersects with concave surface 55 at edge 56. Fluid flows through the gap between edges 56, as shown by dashed lines, and is forced to change direction as it does so by the arrangement of the columns.

[0035] The working fluid circulating through heat exchangers 10 and 12 may be an aqueous solution of a long-chain, partially hydrolyzed linear polyacrylamide polymer with a molecular weight greater than 1 megadalton and possibly greater than 3, 5, or 10 megadaltons. Its concentration may not exceed 5% by weight and may not exceed 1% by weight. Such polymers are available from SNF Floerger, headquartered in Andrézieux, France. The working fluid also contains a low concentration of biocide to prevent biodegradation of the polymer.

[0036] The circulating pump 16 propels the working fluid at a certain flow rate, such that the flow entering the device at inlet 26 of device 10 is laminar, and the flow entering device 12 is also laminar. This flow rate causes the working fluid to be in a state of elastic turbulence as it flows through the column arrays within devices 10 and 12. In device 10, this has the effect of transferring heat energy from the housing surface 20 to the working fluid much faster than the effect of conduction under laminar flow conditions without elastic turbulence. Similarly, in device 12, elastic turbulence increases the rate of heat transfer from the working fluid to the housing 40 of device 12, and heat energy is transferred from the housing to the water surrounding device 12.

[0037] The ability of solutions to exhibit elastic turbulence can be demonstrated experimentally. In a cone-plate rheometer cell, the onset of elastic instability manifests as a significant increase in viscosity at a specific shear rate with the application of increasing shear force, which is associated with a sudden increase in noise in the measured torque signal. This has been described by DO Olagunju, “Instabilities and bifurcations of von Karman similarity solutions in swirling viscoelasticflow”, Z angew Math Phys, 46 (1995) 224-238, and also by E. Tran, A. Clarke, “The relaxation time of entangled HPAM solutions in flow”, Journal of Non-Newtonian Fluid Mechanics, 311 (2023) 104954.

[0038] Figure 6 This is a graph showing the viscosity versus increasing shear rate for two aqueous solutions containing 0.456 wt% sodium chloride, a small percentage of linear polyacrylamide with a molecular weight greater than 10 megadaltons, and a few drops of a biocide composed of isopropanol and thiourea. In one of these aqueous solutions, the polyacrylamide is 0.24 wt% Flopaam 3630 from SNF Floerger, with an average molecular weight of 18 to 20 megadaltons. In the other aqueous solution, the polyacrylamide is 0.2 wt% Flopaam 6040, also from SNF Floerger, with an average molecular weight between 25 and 30 megadaltons. For both solutions, the onset of elastic turbulence with increasing shear rate can be seen as the curve plotted at approximately 150 s. -1 The change in slope at that point. (For) Figures 1 to 4 The heat transfer device shown will have a lower shear rate at which elastic turbulence begins. (See below for reference.) Figure 14 and Figure 15 Describe further experimental work demonstrating elastic turbulence in polymer solutions and viscoelastic surfactant solutions.

[0039] The minimum flow velocity required to induce elastic turbulence in a heat exchanger and the rate of heat transfer to or from the circulating working fluid can both be determined experimentally. Equipment used for this purpose... Figure 7As shown in the diagram. In this device, a heat exchange unit 10 (or a preliminary model of such a device) is connected to a pump 60, which pumps liquid from a tank 62 maintained at a constant temperature. Pressure sensors 64, 65 and temperature sensors 66, 67 are mounted at the inlet and outlet of the device 10. Temperature sensors 66, 67 may be thermocouples. The outlet 28 of the device 10 is connected to a graduated container 68 for measuring the volume of liquid pumped through the device 10 within selected time intervals, thereby determining the flow rate.

[0040] When liquid from tank 62 is pumped through device 10, a pressure drop will exist between inlet pressure sensor 64 and outlet pressure sensor 65. When the flow velocity through device 10 is very low, the flow will be laminar, without any elastic turbulence. The minimum flow velocity that induces elastic turbulence in device 10 can be found by gradually increasing the pump speed to increase the flow velocity and plotting the pressure drop versus flow velocity, or by plotting the pump speed versus flow velocity indicating the pressure drop. This plot will show the change in slope as the flow velocity reaches the point where elastic turbulence begins.

[0041] This is achieved through the following use of, for example Figure 7 The experimental operation of the equipment shown is described below. The experimental results are... Figure 8 and Figure 9 As shown in the diagram. Initial calibration determined the relationship between pump speed and flow rate. Tank 62 is filled with water. The pump is used to propel the water through device 10 at a gradually increasing flow rate. Pump speed and flow rate measured downstream of device 10 are recorded and... Figure 8 The triangle is shown in the diagram. The calibration procedure was then repeated in jar 62 with an aqueous solution containing 0.1% by weight of Flopaam 3630 polyacrylamide. This is also shown in the diagram. Figure 8 The nonlinear graph shown in the image (circular dots) is as follows.

[0042] Figure 9 The measured pressure drop is shown as plotted against the flow velocity. For water, the curve is approximately linear (as expected, since water is a Newtonian fluid), but for the polyacrylamide solution, the slope of the curve changes very sharply at point 70, indicating that the flow velocity at that point is the minimum required to induce elastic turbulence with the polyacrylamide solution and device 10.

[0043] Given the flow velocity in elastic turbulence, the Reynolds number is calculated as follows: The flat surface 32 of the column has a width "a" of 4 mm and a height of 7 mm. The spacing "b" between adjacent column surfaces 32 is 2 mm, therefore the gap between adjacent edges 34 is √8 = 2.83 mm. A row of columns transverse to the overall flow direction contains 12 columns, with 11 gaps between edges 34 and d, therefore the cross-section available for flow is: 11 x 7 x 2.83mm2 = 11 x 7.10 -3 x 2.83.10 -3 m 2 .

[0044] The flow rate was measured at 75 ml / s. -1 = 7.5 x 10 -5 m 3 s -1 .

[0045] The density of the fluid is 1000 kg / m³. 3 The dynamic viscosity is 0.008 Pa·s.

[0046] Substitute these numbers into the formula above: Its Re = 12.17.

[0047] Figure 7 The device is also used to observe the rate of heat transfer through surface 20 and into device 10. For this purpose, a resistor 72, serving as a heating element, is fitted to surface 20. The outlet 28 of device 10 is connected to tank 62 along a flow path partially indicated by 71, such that the flow is in a closed loop. A cooler is used to maintain tank 62 at a constant temperature.

[0048] Measurements were taken using a Flopaam 3630 polyacrylamide solution in the flow loop and water in the loop. Measurements were taken at various pump speeds. At each pump speed, the electrical power of resistor 72 was gradually increased, and the temperature difference between thermocouples 66 and 67 was recorded. For each pump speed, this temperature difference was plotted against the electrical power supplied to resistor 72. These plots are all linear, and the slope of the line is the rate at which the fluid flowing through device 10 is heated. It was observed that the heating rate increases significantly when the flow velocity is sufficient to induce elastic turbulence. In the absence of elastic turbulence, heat transfer into the flowing fluid is purely conductive. When elastic turbulence is present, heat transfer involves the movement of the heated fluid away from surface 20 and into the bulk of the flowing fluid caused by elastic turbulence. In short, when elastic turbulence is present, heat transfer is both convective and conductive.

[0049] The calculations that quantitatively demonstrate this use the Nusselt number, a dimensionless number indicating the ratio of convective to conductive heat transfer. The formula for the average Nusselt number related to heat transfer between a fluid and a flat solid surface is: in It is mass flow rate. and These are thermal conductivity and specific heat capacity, respectively. and These are the geometric parameters (surface area and width) of the flow channel. and These are the outlet temperature and the inlet temperature, respectively. The logarithmic mean temperature difference is defined as: in This is the wall temperature, in this case, the temperature of plate 20 heated by resistor 70. For each pump speed, the ratio of the average Nusselt number of the polyacrylamide solution in the flow loop to the average Nusselt number of the water in the flow loop is given by the following formula: Calculate this ratio for each pump speed, and the calculated ratio is in Figure 10 As shown in the figure, it can be seen that at pump speeds below 62 rpm, in the absence of elastic turbulence, the ratio is close to one, but above 62 rpm, the ratio gradually increases with pump speed, thus confirming that elastic turbulence significantly improves the rate of heat transfer to the fluid in the flow loop.

[0050] In some embodiments of this disclosure, the working fluid is an emulsion or suspension, wherein the dispersed phase is capable of melting and freezing at temperatures where the continuous phase is a liquid. Emulsions and suspensions are widely used in a wide variety of commercial products across various industries. An emulsion is a liquid-in-liquid system in which small droplets of one liquid (dispersed phase) are distributed within another liquid (continuous phase). The two liquids can be (and typically are) immiscible. Agglomeration can be prevented by surfactants in the composition or possibly by solid particles (smaller than emulsion droplets) at the interface between the dispersed and continuous phases. Emulsions stabilized with solid particles are sometimes referred to as Pickering emulsions. Suspensions have small solid particles suspended within a continuous liquid phase.

[0051] If the melting and freezing of the dispersed phase of an emulsion occurs within a temperature range where the continuous phase is liquid, the dispersed phase can freeze and remain as a suspension of solid particles within the continuous phase. Because the continuous phase remains liquid, this suspension remains mobile, flowable, and pumpable. Such a two-phase liquid is called a phase change material emulsion (PCME). If a PCME is used as a working fluid for heat exchange or storage, and its temperature causes the dispersed phase to melt or freeze, the fluid's heat-carrying capacity includes the latent heat of fusion of the dispersed phase (or, if two or more dispersed phases exist and change between solid and liquid), because this latent heat is supplied to cause melting and release upon freezing.

[0052] As an explanation, if a specific heat capacity is used... c p 水If a unit mass of water is heated from temperature T1 to temperature T2, then the enthalpy change is: If the proportion is φ If a unit mass of an emulsion of an oil is heated within the same temperature range, and the melting point of the oil is between T1 and T2, then the enthalpy change is: Where L 油 This is the latent heat of fusion of the oil, and for simplicity, it is assumed that the specific heat of the oil is the same for its frozen and liquid forms. In the case where the PCME contains 30 vol% hexadecane as the dispersed phase in water as the continuous phase, and with a temperature increase of 15° across the melting temperature of hexadecane, the enthalpy change of the PCME calculated using the published specific heat and latent heat values ​​is 1.97 times that of water alone.

[0053] Using PCME as the working fluid and using a working fluid exhibiting elastic turbulence can work synergistically. Using PCME reduces the volume and / or flow rate of the working fluid required to carry heat without directly altering the rate at which heat enters or leaves the working fluid. In fact, using PCME can even reduce the rate at which heat is transferred from or to the working fluid, as PCME may have a lower overall thermal conductivity than its continuous phase. Using elastic turbulence improves heat transfer at the interface through which heat is carried into or out of the working fluid. This allows for a reduction in the required size of the interface or a decrease in the required flow rate at the interface, thereby reducing the required pumping power. Therefore, using PCME as the working fluid and employing elastic turbulence at the point of heat transfer to or from the working fluid can reduce the size and / or power requirements of equipment that relies on flowing working fluids for heat transfer.

[0054] The continuous phase used for PCME can be an aqueous solution. However, it can be a non-aqueous liquid, such as an organic solvent or a low-viscosity polydimethylsiloxane, commonly known as a low-viscosity silicone oil.

[0055] One or more dispersed phases of the PCME should not agglomerate through interaction with polymers capable of generating elastic turbulence. Therefore, the dispersed phase can be an organic compound without heteroatoms, such as alkanes, or an organic compound in which the only heteroatom is an oxygen atom in an ester or ether group. The dispersed phase can also be a fluorocarbon.

[0056] Many factors can destabilize emulsions. Specifically, so-called "emulsification" is a problem encountered when the dispersed and continuous phases have different densities. It refers to the migration of emulsion droplets to the top of the emulsion, leading to eventual phase separation. Emulsions are also prone to coalescence, where droplets merge to form larger droplets unless kinetically prevented using surfactants. Polymers capable of generating elastic turbulence can also stabilize emulsions and prevent stratification. Another possibility is the incorporation of a second polymer, which itself does not induce elastic turbulence but slightly increases viscosity, thereby stabilizing PCMEs to prevent emulsion stratification. More specifically, the second polymer can be weakly associated, causing the formation of a weak gel or critical gel (i.e., imparting solid-like properties to the fluid) under static conditions. Once flow begins, the weak structure is disrupted, and the emulsion becomes readily flowable.

[0057] The amount of the second polymer included for stabilizing the emulsion may be less than 5% by weight and may be in the range of 0.05% or 0.1% by weight to 1% or 2% by weight.

[0058] The following experimental work illustrates PCME exhibiting elastic turbulence. The continuous phase is an oil-in-water emulsion containing the following materials:

[0059] The polyacrylamide is Flopaam 3630, as mentioned above, with a molecular weight of 18-20 megadaltons. The dispersed phase is hexadecane.

[0060] The preparation of emulsions begins with the preparation of the following three compositions: 1. Xanthan Gum Saline Solution. Add 0.5 g xanthan gum powder to 99.5 g of 4.55 g / L NaCl saline solution. Mix the xanthan gum using a Silverson L5 laboratory mixer equipped with a universal disintegrating tip at 5000 rpm for 5–10 minutes. Heat the mixture to 80 °C using a hot plate and magnetic stirrer, then cool.

[0061] 2. A saline solution of partially hydrolyzed polyacrylamide (HPAM). Add 0.12 g Flopaam 3630S to 99.88 g of 4.55 g / L NaCl brine. Stir the mixture overnight with a magnetic stirrer at 200 rpm.

[0062] 3. Hexadecane emulsion. 46.38 g of hexadecane was added to 153.62 g of 2% sodium dodecyl sulfate (SDS) solution in 4.55 g / L brine, while simultaneously shearing at 6000 rpm in a Silverson L5 mixer equipped with a high-shear sieve. Droplet size distribution was measured in a Malvern Instruments Mastersizer 3000. The de of the emulsion droplets...50 The parameter was measured to be 4.56 µm.

[0063] Xanthan gum solution and HPAM solution were combined in a 1:1 weight ratio. The combined solution exhibited elastic turbulence, which was detected as rheological flow instability observed using a cone-plate rheometer as mentioned above. Figure 11 This is a graph showing the viscosity versus shear rate of this example HPAM / xanthan gum mixture. This measurement, performed in a rheometer cell, can be completed in approximately 150 seconds. -1 We observed the onset of elastic turbulence as the shear rate increased.

[0064] PCME was then prepared by mixing the combined solution with a hexadecane emulsion. When tested using the cone-plate rheometer described above, PCMEs containing 0.6 vol%, 1.5 vol%, and 3 vol% initial hexadecane emulsions were observed to be emulsified stably and exhibited elastic turbulence, respectively. At approximately 150 s... -1 Here we see again the onset of elastic turbulence as the shear rate increases.

[0065] The sample portion of this PCME formulation was examined using differential scanning calorimetry. Results were obtained through... Figure 12 As shown. Measurements were started at 30°C and the temperature was decreased at 1°C / min. Freezing of the hexadecane droplets occurred at approximately 11°C. The sample was cooled to -10°C and then heated (for this composition, at this cooling rate, the continuous phase did not freeze). The hexadecane was then melted at 18°C.

[0066] For example, such as Figures 1 to 3 The heat exchange loop in the device is used to heat the incoming water at a temperature of 5°C. The working fluid is as described above, wherein hexadecane is the dispersed phase in an aqueous continuous phase containing polyacrylamide and xanthan gum. The heat exchange device 10, exposed to sunlight, raises the temperature of the working fluid to at least 25°C, such that the dispersed phase is an emulsified droplet as it exits device 10 through outlet 28 and as it enters device 12. In heat exchange device 12, the working fluid is cooled to 10°C, causing the hexadecane dispersed phase to freeze into suspended solid particles. The working fluid is then pumped back into device 10, where solar heat provides latent heat to melt the frozen hexadecane droplets and raise the fluid temperature to 25°C. Therefore, the heat transferred from heat exchange device 10 to device 12 and released from device 12 into the surrounding water comes both from the temperature drop of the working fluid and from the latent heat of fusion released when the dispersed phase solidifies. Simultaneously, elastic turbulence increases the rate at which heat is carried into and out of the working fluid. Therefore, the heat exchange device can be smaller than originally required, and the energy used in pumping the working fluid can be less than the energy required to pump the working fluid at a flow rate that generates inertial turbulence.

[0067] Further evidence of elastic turbulence, when induced by viscoelastic surfactants and when induced by high molecular weight polymers, is found in... Figure 15 The device illustrated in the diagram uses, for example Figure 14 The guide vane 100 shown is constructed using this method. The guide vane 100 has a regularly spaced array of columns 102 with a square cross-section integral with the base 103. The two edges of the array are formed by columns 104 with triangular cross-sections. This column array is similar to... Figure 2 The array 30 shown, but with a smaller number of columns, is illustrated. The baffle 100 is made of a transparent polymer and is located within the surrounding chamber 108, as shown... Figure 15 The cross-section is shown in the figure. Chamber 108 is formed by two transparent polymer blocks 110, 112 held together by bolts (not shown). A baffle 100 is located in the cavity between the two blocks. A liquid inlet 113 and a liquid outlet 114 are present, leading to the cavity. When liquid is pumped through chamber 108, it flows through the gap between the columns 102. If the liquid contains substances capable of exhibiting elastic turbulence and the flow velocity is sufficient, these factors force the flow direction to repeatedly change (as mentioned above) as the liquid flows through the gap between the columns (which causes elastic turbulence to occur). Figure 4 (As shown).

[0068] Figure 15 The apparatus shown can be used to observe the occurrence of elastic turbulence using birefringence. This apparatus has some similarities to the apparatus described by Moss GR and Rothstein JP in “Flow of wormlike micelle solutions through a periodic array of cylinders” Journal of Non-Newtonian Liquid Mechanics, Vol. 165, pp. 1-13, 2010.

[0069] The light beams from the red LED 125R and the green LED 125G are guided toward the camera 126 along paths shown by solid and dashed lines, respectively. A chamber 108, including a deflector 100, is positioned between linear polarizing filters 128R and 129R, whose polarization directions are set at right angles (i.e., intersecting), and between linear polarizing filters 128G and 129G, whose polarization directions are also set at right angles to each other. Therefore, no light can reach the camera 126 unless birefringence in chamber 108 alters the polarization angle of the light passing through the chamber. Filters 128R and 128G are set at right angles to each other, such that the polarization planes of the red and green light entering the chamber are at right angles to each other. The red and green beams are combined using a dichroic mirror 130 that allows the red beam to pass through and reflects the green beam, then separated after they pass through chamber 104, and subsequently recombined before they reach the camera 126.

[0070] The other components of the device are a reflector 138, a lens 132, red and green bandpass filters 134G and 134R, and a dichroic mirror 136, which are rotated 90° relative to the path of the red beam to counteract the polarization rotation caused by Fresnel refraction. The green beam does not require such a dichroic mirror because its polarization does not cause polarization rotation.

[0071] The worm-like micelles formed by the viscoelastic surfactant are birefringent. Therefore, when these molecules are aligned by the liquid flow within chamber 108 and irradiated with polarized red and green light, they alter the plane of polarization of the light, allowing some light to pass through filters 129R and 129G to reach the camera, although this would not occur if the micelle alignment coincided with the plane of polarization of the light. Providing two beams with different planes of polarization upon entering chamber 104 solves this problem: any micelle aligned with red polarized light will not align with green polarized light, and vice versa. Therefore, the device is sensitive to polarization alignment in any direction.

[0072] As the liquid containing worm-like micelles flows through the chamber, these micelles are aligned by stretching the flow as the liquid flows around the column 102 of the guide plate 100, and the birefringence from the aligned micelles can be perceived as red or green in the pictures or videos recorded by the camera 126.

[0073] The first experiment was conducted using a solution similar to that mentioned by Moss and Rothstein in the aforementioned paper. This solution contained 100 mM (approximately 4 wt%) of the viscoelastic cationic surfactant hexadecylpyridine chloride and 50 mM (approximately 0.8 wt%) sodium salicylate, dissolved in a 100 mM (approximately 0.6 wt%) distilled aqueous solution of NaCl.

[0074] The viscoelastic solution is pumped through chamber 108 at a low flow rate of 5 ml per minute. Camera 126 records video at 20 frames per second for 5 seconds, recording a consistent flow pattern around column 102 of guide vane 100. Four images from this video recording, spaced at half-second intervals, are displayed in grayscale. Figure 16 The top row shows the flow rate, and it can be seen that the variation from one image to the next is negligible. The original color images show red lines extending along the flow direction from the downstream corner of each column. In one image, a white outline is drawn around one of these, as shown in 140. These red lines maintain the same intensity and position throughout the video recording. The flow rate was then increased to 25 ml / min, and the video was recorded again for 5 seconds. The video recording at a flow rate of 25 ml / min is very different from the video recording at a flow rate of 5 ml / min. It exhibits continuous movement. The color patches showing the stretching flow aligned with the micelles constantly move from one position to another, and the intensity also varies. Four images from the video with a flow rate of 25 ml / min are reproduced as grayscale images. Figure 15 The bottom row shows numerous variations from one image to the next. For example, arrow 141 points to a red patch that appears in one image but is absent in the previous one, and gradually diminishes in the following two images. At position 142, a red area is present, which is absent in the previous image and again gradually diminishes in the next two images. The second image in the row also shows a strong green area 143, which is absent in the first image and largely disappears in the third image. Thus, it can be seen that the flow at 5 ml / min is laminar, but at 25 ml / min, the flow becomes turbulent.

[0075] Similar experiments were conducted using a solution containing partially hydrolyzed polyacrylamide (HPAM) with an average molecular weight of 18 MDa, which allowed for the observation of elastic turbulence, and also containing xanthan gum as an additional thickener. A similar experiment was also conducted using a comparative solution containing only xanthan gum (which is too rigid to induce elastic turbulence, as mentioned above). These polymers did not form micelles, but did induce birefringence upon alignment. Again, no elastic turbulence was observed at a flow rate of 5 ml / min, but it was observed at faster flow rates. The table below presents the flow rates and observations, and also repeats the comments from the experiments using viscoelastic surfactants described above.

[0076] These comments clearly show that solutions containing HPAM and xanthan gum exhibit elastic turbulence at 15 ml·s and above, but solutions containing xanthan gum but not HPAM do not exhibit elastic turbulence even at 30 ml·min.

[0077] The various embodiments of this disclosure described above are intended to aid in understanding this disclosure and not to limit the scope of this disclosure as defined by the following claims in any way. It should be understood that any feature or possibility described in combination may be used individually, if doing so is feasible. Furthermore, features or possibilities mentioned in the appended claims or described in any embodiment may be used in any other embodiment, as long as doing so is feasible, and particularly where two or more of the appended claims are dependent on the same preceding claim, the reader should understand that this disclosure includes any two or more or all of those dependent claims with each other and with any possible combination of those dependent claims and the preceding claim.

Claims

1. A method for removing heat into or out of a flowing fluid, comprising: The fluid is pumped through a heat transfer device, wherein the heat transfer device comprises: A chamber for fluid flow, wherein the chamber wall in contact with the flowing fluid is an interface through which heat is transferred to or from the flowing fluid, wherein the chamber contains a spaced array of barriers that force the streamlines of the flowing fluid to repeatedly change direction to flow through the gaps between the barriers. The fluid contains a solute that enables the fluid to exhibit elastic turbulence; The flow velocity of the fluid in the chamber causes the fluid to be in an elastic turbulent state, and The viscosity of the fluid, the flow rate of the fluid within the chamber, and the width of the gap between the obstacles determine the Reynolds number (Re) of the flow, which ranges from 1 to 1000.

2. The method of claim 1, wherein the heat transfer device is part of a heat exchange system, the heat exchange system comprising: A second heat transfer device, a pump, and a piping system connecting the pump and the heat exchange device in different locations to form a closed loop containing the fluid.

3. The method of claim 1, wherein the solute enabling the fluid to exhibit elastic turbulence is a polymer containing at least 5,000 monomer units in one or more linear polymer chains, each linear polymer chain containing at least 1,000 monomer units, the monomer units being connected to each other by a single covalent bond such that a monomer unit is capable of rotation relative to an adjacent monomer unit.

4. The method of claim 1, wherein the solute enabling the fluid to exhibit elastic turbulence has a molecular weight greater than 10. 6 Dalton's polymer.

5. The method of claim 4, wherein the polymer comprises a linear chain of at least 5,000 monomer units.

6. The method of claim 5, wherein the polymer is polyacrylamide or a polyacrylamide derivative.

7. The method of claim 1, wherein the solute enabling the fluid to exhibit elastic turbulence is a worm-like micelle surfactant system comprising one or more aggregated molecular species.

8. The method of claim 1, wherein the chamber has a volume of at least 50 ml.

9. The method of claim 1, wherein the fluid is an aqueous solution containing no more than 5% by weight of the solute that enables the fluid to exhibit elastic turbulence.

10. The method of claim 1, wherein the fluid is an emulsion having a continuous phase and a suspended dispersed phase, the continuous phase being a solution of the solute that enables the fluid to exhibit elastic turbulence, and the suspended dispersed phase varying between solid and liquid states at a temperature where the continuous phase is liquid.

11. The method of claim 10, wherein the suspended dispersion is melted at a temperature above -80°C and below 150°C.

12. The method of claim 10, wherein the continuous phase is an aqueous solution of the solute that enables the fluid to exhibit elastic turbulence.

13. The method of claim 10, wherein the suspended dispersion comprises one or more aliphatic organic compounds containing alkyl groups having at least 12 carbon atoms.

14. The method of claim 13, wherein the suspended dispersion comprises one or more saturated alkanes having at least 14 carbon atoms.

15. The method of claim 1, further comprising: An obstacle extends across the chamber from the interface to the chamber wall spaced apart from the interface.

16. A system for moving thermal energy, comprising: A heat transfer device comprising: a chamber through which a fluid flows, wherein the chamber wall is an interface through which heat is transferred to or from the flowing fluid; a fluid; and a pump for pumping the fluid through the chamber, wherein: The chamber contains a spaced array of barriers that force the streamlines of the flowing fluid to repeatedly change direction to flow through the gaps between the barriers; The fluid contains a solute that enables it to exhibit elastic turbulence; and The system is configured such that the viscosity of the fluid, the flow rate of the fluid within the chamber, and the width of the gap between the obstacles determine the Reynolds number (Re) of the flow, which ranges from 1 to 1000.

17. The system of claim 16, wherein the heat transfer device is part of a heat exchange system comprising: A second heat transfer device, a pump, and a piping system connecting the pump and the heat exchange device in different locations to form a closed loop containing the fluid.

18. The system of claim 16, wherein the solute enabling the fluid to exhibit elastic turbulence is a polymer containing at least 5,000 monomer units in one or more linear polymer chains, each linear polymer chain containing at least 1,000 monomer units, the monomer units being connected to each other by a single covalent bond such that a monomer unit is capable of rotation relative to an adjacent monomer unit.

19. The system of claim 16, wherein the fluid is an aqueous solution containing no more than 5% by weight of the solute that enables the fluid to exhibit elastic turbulence.

20. The system of claim 16, wherein the fluid is an emulsion having a continuous phase and a suspended dispersed phase, the continuous phase being a solution of the solute that enables the fluid to exhibit elastic turbulence, and the suspended dispersed phase varying between solid and liquid states at a temperature where the continuous phase is liquid.

Images