A method for determining nanofluid stability

Abstract

The invention relates to a method for determining the stability of nanofluids. In this method, nanofluid stability is assessed quickly and easily by measuring changes in the color of the nanofluid, caused by nanoparticle sedimentation, using a color spectrophotometer. This approach enables the stability of nanofluids containing any type of nanoparticle to be evaluated and reduces costs by shortening the test duration.

Description

[0001] A METHOD FOR DETERMINING NANOFLUID STABILITY

[0002] Technical Field of the Invention

[0003] The invention relates to a method for determining the stability of nanofluids. In the method subject to the invention, nanofluid stability is determined quickly and easily by measuring the change occurring in the color of nanofluids due to the sedimentation of nanoparticles using a color spectrophotometer instrument (Colorimeter).

[0004] This method enables the stability of nanofluids containing any type of nanoparticle to be evaluated and reduces costs by shortening the test duration.

[0005] State of the Art

[0006] Nanofluids are advanced thermally conductive fluids obtained by dispersing nanoscopic particles (1-100 nm in diameter) into base fluids (such as water, oil, ethylene glycol, etc.). These nanoparticles can be metal oxides, metals, carbides, nanotubes, graphene, and other nanomaterials. Thanks to their improved thermal and physical properties, nanofluids offer higher heat conduction performance compared to traditional fluids [1],

[0007] Nanofluids possess several essential properties compared to base fluids. The most prominent feature is increased thermal conductivity. The addition of nano-sized particles accelerates heat transfer, providing more efficient heat management. Additionally, the viscosity and density of nanofluids can change, which may affect their flow and pumpability characteristics. Stability, i.e., the ability of nanoparticles to remain homogeneously distributed within the fluid, is of critical importance for long-term performance.

[0008] Nanofluids have a wide range of applications. They are used in heat exchangers, electronic cooling systems, solar energy systems, engine coolants in the automotive industry, and biomedical devices. They have the potential to increase energy efficiency thanks to their high thermal conductivity. They are evaluated as high-performance cooling solutions, especially in the fields of microelectronics and nanotechnology.

[0009] Among the most commonly used nanofluids, water-based alumina (AI2O3) nanofluids, copper (Cu) nanofluids, and titanium dioxide (TiCh) nanofluids are particularly prominent. Alumina (AI2O3) nanofluids are used in microelectronic cooling systems and solar energy applications due to their high thermal conductivity and chemical stability. Copper (Cu) nanofluids are effective in applications requiring high performance, such as heat exchangers and engine cooling systems, thanks to the high thermal conductivity of metals. Titanium dioxide (TiCE) nanofluids are widely used in photocatalytic applications and solar energy systems due to their high refractive index and chemical stability. Carbon-based nanofluids, especially those containing carbon nanotubes (CNT) and graphene oxide, offer high thermal conductivity and mechanical durability. While carbon nanotubes improve heat transfer properties, graphene oxide nanofluids are used in electronic cooling and energy storage systems. These nanofluids make significant contributions to energy efficiency and environmental sustainability.

[0010] Nanofluid stability refers to the ability of nanoparticles to remain homogeneously and stably distributed within the base fluid. A stable nanofluid must be able to maintain its performance over an extended period without exhibiting sedimentation or agglomeration (clustering). The behavior of nanoparticles in the liquid directly affects several thermophysical properties of the nanofluid, including viscosity, density, and thermal conductivity. Factors affecting nanofluid stability include nanoparticle concentration, particle size and shape, surface modifications, pH level, ionic strength, and temperature. Surface modifications can help nanoparticles adapt better to the base fluid and disperse. Additionally, the chemical structure of the base fluid and the presence of additives can also affect stability.

[0011] The stability of nanofluids is provided by mechanical-ultrasonic mixing, the use of surfactant substances, or adjusting the pH value of the base liquid. However, over time, the stability of nanofluids deteriorates due to the sedimentation of particles in the liquid. It is necessary to determine the stability of nanofluids after they are prepared and at specific intervals.

[0012] The sedimentation method, zeta potential measurement method, UV-Vis spectroscopy method, dynamic light scattering spectrometry method (DLS), and scanning / transmission electron microscope measurement methods (SEM, TEM) are used to determine the stability of nanofluids [2],

[0013] The sedimentation method is a simple yet long-lasting method for determining nanofluid stability. In this approach, the prepared nanofluid is placed into a graduated tube, and stability is assessed by measuring the volume or amount of particulate matter that settles over time. In the zeta potential measurement method, stability is determined by quantifying the electrical repulsion potential between nanoparticles suspended in the nanofluid. In the UV-Vis spectroscopy method, a UV-Vis light beam is directed through the nanofluid, and stability is evaluated by measuring the amount of light that passes through it. In the DLS method, stability is determined by analyzing the intensity and change of the light scattered from the nanoparticles in the nanofluid after the light is directed onto it. In the TEM / SEM method, nanofluid stability is assessed by examining images of particles that have settled within the nanofluid.

[0014] Although the sedimentation test is simple and applicable, it has several disadvantages, including its lengthy duration, limited applicability to certain nanofluid types, and relatively low accuracy. Furthermore, it is insufficient in determining the stability of very light or darkcolored nanofluids. The zeta potential measurement method is particularly suitable for nanofluids containing metallic nanoparticles; however, it is not applicable to all nanofluid types and is relatively expensive. Similarly, although the DLS method offers high sensitivity and detailed information, it requires complex sample preparation and expensive devices. UV- Vis spectroscopy and dynamic light scattering spectrometry methods may also be inadequate for assessing the stability of nanofluids containing low concentrations of nanoparticles. TEM / SEM methods are used to determine the stability of nanofluids, but careful preparation of dried samples is essential. These methods are costly, and analyzing non-metallic nanoparticles can pose challenges; they are also not suitable for every nanofluid.

[0015] Due to the limitations and inadequacies of the current technique's solutions, and because the methods used are complex, time-consuming, have low sensitivity, and high cost, and are not suitable for all nanofluids, a development in the field of nanofluid stability determination methods has been necessitated.

[0016] Brief Description and Objectives of the Invention

[0017] The invention relates to a method of determining nanofluid stability by measuring, using a color spectrophotometer, the change in the nanofluid's color at a time t=tn(t: time, n: hour) relative to the reference fluid over time, and evaluating stability based on the resulting color difference.

[0018] One objective of the invention is to develop a method for determining nanofluid stability that is both fast and easy to apply. For this reason, the method described above employs a color spectrophotometer as the analysis instrument, which is practical and provides measurements within approximately one second. Moreover, the method does not require complex or timeconsuming additional procedures, such as drying the sample or coating it with metal. Additionally, the invention includes a high-sensitivity method for determining the stability of nanofluids. Unlike methods that rely on human senses, such as sedimentation, the invention enables stability to be evaluated by easily measuring color differences at levels that are imperceptible to the human eye.

[0019] Another objective of the invention is to develop a method for determining nanofluid stability that can be applied to all types of nanofluids. Since the method is based on detecting color differences, it is not affected by the type, size, or concentration of nanoparticles within the nanofluid. Even when the nanofluid contains the lowest level (1 ppm) of nanoparticles, a change in the color of the nanofluid still occurs. This color change can be easily detected using a color spectrophotometer with a photometric resolution of 0.01%. An overall color difference greater than 0.1 indicates a clearly distinguishable change. Therefore, the method subject to the invention can be reliably used to determine the stability of all nanofluids.

[0020] Another objective of the invention is to develop a low-cost method for determining nanofluid stability. In the method subject to the invention, the lack of need for standard samples and the use of low-cost devices reduce the overall cost of the method.

[0021] Description of Figures

[0022] Figure 1. Flowchart of the nanofluid stability determination method

[0023] Figure 2. Change of overall color difference relative to the nanofluid at different times in the case where the nanofluid at the initial moment of preparation is selected as the reference fluid

[0024] Figure 3. Change of overall color difference relative to the nanofluid at different times in the case where the base fluid is selected as the reference fluid

[0025] Detailed Description of the Invention

[0026] The invention relates to a method for determining nanofluid stability by measuring the change in color of nanofluids over time using a color spectrophotometer.

[0027] Colors and color differences are expressed numerically with a color spectrophotometer device. In the three-dimensional L*a*b* color scale developed by the International Commission on Illumination (CIE: Commission Internationale de 1'eclairage), basic colors are expressed with negative and positive numerical values. The L* value ranges from 0 to 100 (L*=0 is black and L*=100 is white), indicating the lightness / darkness of the color. Positive a* values indicate red color, while negative a* values indicate green color. Similarly, positive b* values indicate yellow color, and negative b* values indicate blue color.

[0028] In this method, the L*a*b* color values of the reference (base) fluid (a fluid containing no nanoparticles) or of the nanofluid at the initial moment of preparation are first measured using a color measurement device. Then, after the nanofluid has been left to stand for a period of time, its L*a*b* values are measured again, and the overall color difference AE is calculated relative either to the reference fluid or the color values at the initial moment of preparation of the nanofluid (Equation 1). (Equation 1)

[0029] Here, AL* represents the lightness / darkness difference between the base fluid containing no nanoparticles or the sample at the initial moment the nanofluid was prepared, and the nanofluid after it has been left to stand for a period of time; Aa* and Ab* represent the color differences between the base fluid or initial sample and the nanofluid kept for a while. These color differences are calculated using Equations 2, 3, and 4 below.

[0030] AL* = L*1- L*° (Equation 2)

[0031] Aa* = a*1— a*0(Equation 3)

[0032] Ab* = b*1— b*° (Equation 4)

[0033] In these equations, superscript 1 indicates the nanofluid kept for a while (t=tn), and superscript 0 indicates the reference fluid sample (base fluid or the initial state of the nanofluid).

[0034] As a result of the sedimentation of nanoparticles suspended in the nanofluid at the initial moment, the color of the nanofluid changes over time, and the rate of change in the color of the nanofluid is proportional to the sedimentation rate of its nanoparticles. In this way, the change in the nanofluid's color is measured at specific time intervals with a color measurement device, allowing for the accurate determination of the nanofluid's stability.

[0035] A method for determining nanofluid stability, characterized by comprising the process steps: a. Measuring the color values of the reference fluid on the L*a*b* color scale using a color spectrophotometer; b. Measuring the color values of the nanofluid on the L*a*b* color scale at times t=ti, t=t2, t=tnusing a color spectrophotometer; c. Calculating the differences (AE) between the color values obtained in process step (b) and the color value obtained in process step (a) using the following equations: a*: axis value corresponding to the red (positive) - green (negative) color range in the color coordinate, b*: axis value corresponding to the yellow (positive) - blue (negative) color range in the color coordinate,

[0036] AE: overall color difference,

[0037] AL*: difference between the axis values corresponding to the black (L*=0) - white (L*=100) range between two colors,

[0038] Aa*: difference between the axis values corresponding to the red (positive) - green (negative) color range between two colors,

[0039] Ab*: difference between the axis values corresponding to the yellow (positive) - blue (negative) color range between two colors,

[0040] Superscript 1 : nanofluid after waiting until time t=tn,

[0041] Superscript 0: reference fluid sample, d. Determining the nanofluid as stable when the AE value is greater than 40 when the base fluid is selected as t=too, and when the AE value is smaller than 5 when the base fluid is selected as t=to.

[0042] In one application of the invention, the method comprises the process steps: a. Measuring the color values of the prepared nanofluid at the initial moment (t=to) on the L*a*b* color scale using a color spectrophotometer; b. Measuring the color values of the nanofluid on the L*a*b* color scale at times t=ti, t=t>, t=tn using a color spectrophotometer; c. Calculating the differences (AE) between the color values obtained in process step (b) and the color value obtained in process step (a) using the following equations: a*: axis value corresponding to the red (positive) - green (negative) color range in the color coordinate, b*: axis value corresponding to the yellow (positive) - blue (negative) color range in the color coordinate,

[0043] AE: overall color difference,

[0044] AL*: difference between the axis values corresponding to the black (L*=0) - white (L*=100) range between two colors,

[0045] Aa*: difference between the axis values corresponding to the red (positive) - green (negative) color range between two colors,

[0046] Ab*: difference between the axis values corresponding to the yellow (positive) - blue (negative) color range between two colors,

[0047] Superscript 1 : nanofluid after waiting until time t=tn,

[0048] Superscript 0: reference fluid sample, d. determining the nanofluid as stable when the AE value is smaller than 5.

[0049] As nanoparticles sediment within the nanofluid over time, a change occurs in the nanofluid’s color. This color change increases over time, resulting in an increasing overall color difference relative to the nanofluid at moment to. The smaller the overall color differences between the nanofluid at the initial moment (t=to) and the nanofluid at time t=tn, the more stable the nanofluid. This indicates that the nanoparticles within the nanofluid remain suspended or settle at a slow rate. In another application of the invention, the method comprises the process steps of: a. Measuring the color values of the base fluid containing no nanoparticles (t=too) on the L*a*b* color scale using a color spectrophotometer; b. Measuring the color values of the nanofluid at times t=ti, t=t2, t=tnusing a color spectrophotometer; c. Calculating the differences (AE) between the color values obtained in process step (b) and the color value obtained in process step (a) using the following equations: a*: axis value corresponding to the red (positive) - green (negative) color range in the color coordinate, b*: axis value corresponding to the yellow (positive) - blue (negative) color range in the color coordinate,

[0050] AE: overall color difference,

[0051] AL*: difference between the axis values corresponding to the black (L*=0) - white (L*=100) range between two colors,

[0052] Aa*: difference between the axis values corresponding to the red (positive) - green (negative) color range between two colors,

[0053] Ab*: difference between the axis values corresponding to the yellow (positive) - blue (negative) color range between two colors,

[0054] Superscript 1 : nanofluid after waiting until time t=tn,

[0055] Superscript 0: reference fluid sample (without nanoparticle), d. determining the nanofluid as stable when the AE value is greater than 40.

[0056] When the color value of the nanofluid measured at different times (t=tn) is compared with the color value of the base fluid containing no nanoparticles (t=too), a higher overall color difference between the two fluids indicates greater nanofluid stability. This suggests that the nanoparticles within the nanofluid remain suspended or settle at a slow rate.

[0057] As nanoparticles sediment within the nanofluid over time, the nanofluid’s color gradually shifts towards that of the base fluid, resulting in a decrease in the overall color difference between the two fluids.

[0058] If the base fluid containing no nanoparticles (t=t / ) is used as the reference in determining nanofluid stability, a nanofluid with a AE value greater than 40 is considered stable. Conversely, if the initial state of the nanofluid at preparation (t=to) is used as the reference, a nanofluid with a AE value smaller than 5 is considered stable. By plotting the overall color differences between two samples on a graph, changes in nanofluid stability over time becomes clearly visible (Figures 2 and 3).

[0059] References

[0060] 1. Ali, A.R.I., Salam, B. A review on nanofluid: preparation, stability, thermophysical properties, heat transfer characteristics and application. SNAppl. Sci. 2, 1636 (2020). 2. Setia, H., Gupta, R., & Wanchoo, R. K. (2013). Stability of nanofluids. Materials

[0061] Science Forum, 757, 139-149.

Claims

CLAIMS1. A method for determining nanofluid stability, characterized by comprising the following process steps: a. Measuring the color values of the reference base fluid on the L*a*b* color scale using a color spectrophotometer; b. Measuring the color values of the nanofluid on the L*a*b* color scale at times t=ti, t=t2, t=tnusing a color spectrophotometer; c. Calculating the differences (AE) between the color values obtained in process step (b) and the color value obtained in process step (a) using the following equations:AL* = L*1- L*°Aa* = a*1- a*0Ab* = b*1— b*°Where;L*: axis value corresponding to the black (L*=0) - white (L*=100) range in the color coordinate, a*: axis value corresponding to the red (positive) - green (negative) color range in the color coordinate, b*: axis value corresponding to the yellow (positive) - blue (negative) color range in the color coordinate,AE: overall color difference,AL*: difference between the axis values corresponding to the black (L*=0) - white (L*=100) range between two colors,Aa*: difference between the axis values corresponding to the red (positive) - green (negative) color range between two colors,Ab*: difference between the axis values corresponding to the yellow (positive) - blue (negative) color range between two colors,Superscript 1 : nanofluid after waiting until time t=tn,Superscript 0: reference fluid sample, d. Determining the nanofluid as stable when the AE value is greater than 40 when the base fluidis selected as t=t , and when the AE value is smaller than 5 when the base fluid is selected as t=to.

2. A method for determining nanofluid stability according to Claim 1, characterized by comprising the following process steps: a. Measuring the color values of the nanofluid on the L*a*b* color scale using a color spectrophotometer when the reference fluid is selected as the initial state of the prepared nanofluid (t=to); b. Measuring the color value of the nanofluid on the L*a*b* color scale at times t=ti, t=t2, t=tnusing a color spectrophotometer; c. Calculating the differences (AE) between the color values obtained in process step (b) and the color value obtained in process step (a) using the following equations:AL* = L*1- L*°Aa* = a*1- a*0Ab* = b*1— b*°Where;L*: axis value corresponding to the black (L*=0) - white (L*=100) range in the color coordinate, a*: axis value corresponding to the red (positive) - green (negative) color range in the color coordinate, b*: axis value corresponding to the yellow (positive) - blue (negative) color range in the color coordinate,AE: overall color difference,AL*: difference between the axis values corresponding to the black (L*=0) - white (L*=100) range between two colors,Aa*: difference between the axis values corresponding to the red (positive) - green (negative) color range between two colors,Ab*: difference between the axis values corresponding to the yellow (positive) - blue (negative) color range between two colors,Superscript 1 : nanofluid after waiting until time t=tn,Superscript 0: reference fluid sample, d. Determining nanofluids with a AE value smaller than 5 as stable.

3. A method for determining nanofluid stability according to Claim 1, characterized by comprising the following process steps: a. Measuring the color values of the base fluid on the L*a*b* color scale using a color spectrophotometer when the reference fluid is selected as the base fluid containing no nanoparticles (t=too); b. Measuring the color values of the nanofluid at times t=ti, t=t2, t=tnusing a color spectrophotometer; c. Calculating the differences (AE) between the color values obtained in process step (b) and the color value obtained in process step (a) using the following equations:AL* = L*1- L*°Aa* = a*1- a*0Ab* = b*1— b*°Where;L*: axis value corresponding to the black (L*=0) - white (L*=100) range in the color coordinate, a*: axis value corresponding to the red (positive) - green (negative) color range in the color coordinate, b*: axis value corresponding to the yellow (positive) - blue (negative) color range in the color coordinate,AE: overall color difference,AL*: difference between the axis values corresponding to the black (L*=0) - white (L*=100) range between two colors,Aa*: difference between the axis values corresponding to the red (positive) - green (negative) color range between two colors,Ab*: difference between the axis values corresponding to the yellow (positive) - blue (negative) color range between two colors,Superscript 1 : nanofluid after waiting until time t=tn,Superscript 0: reference fluid sample, d. Determining the nanofluid as stable when the AE value is greater than 40.

4. A method for determining nanofluid stability according to Claim 1, characterized by the reference fluid being the base fluid containing no nanoparticles (t=t / ).

5. A method for determining nanofluid stability according to Claim 1, characterized by the reference fluid being the initial state of the prepared nanofluid (t=to).

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