Microencapsulated Phase Change Material Suspensions Research Articles

Micro-encapsulated phase change material suspensions for heat and mass transfer: A thermo-physical characterization

Despite the growing popularity of phase change materials (PCM) and suspensions of micro-encapsulated phase change materials (mPCM) in both industrial and scientific applications, their properties characterization remains partial and mainly limited to thermal properties. The characterization of such suspension is a crucial aspect for comprehending their behavior and optimizing their performance. This paper is dedicated to a wide characterization of two suspensions containing micro-encapsulated phase change material. In pursuit of a thorough understanding, we also extend our characterization efforts to the bulk PCM encapsulated within the particles.Our primary focus is on determining the materials thermal properties such as latent heat and specific heat capacity using differential scanning calorimetry. Different cooling and heating rates have been employed in our measurements. Regarding our experiments, the bulk phase change material is predominantly identified as octadecane. Results obtained from calorimetry are then compared between the bulk PCM and the mPCM suspensions. By comparing the magnitudes of latent heat obtained for suspensions with the bulk material, we can accurately determine the mass fraction of PCM within each suspension. Noteworthy, during the solidification process an additional latent heat peak is observed only for the encapsulated PCM.The density of the materials is also measured. The phase change of PCM included in the capsules can be observed in densimetry: within the studied temperature range (283.15–306.15 K), the most significant density variations occur during intervals associated with phase change transitions. In ranges where the PCM, included in the capsules, is in a single-phase state (solid/liquid), we provide linear laws that account for density variations with temperature.Finally, our characterization work focuses on the rheological properties of the materials. While the bulk PCM in liquid phase exhibits a Newtonian viscosity, mPCM suspensions present a non-Newtonian viscosity. Both shear-thinning and shear-thickening behaviors are observed depending on the suspension particle volume fraction ϕ of mPCM. This paper concludes with a full comparison of our characterization results with models and correlations proposed in the literature.

Heat transfer enhancement in a loop thermosyphon with microencapsulated phase change material suspension

The microencapsulated phase change material suspension (MPCMS) is a novel functional thermal fluid. The application of MPCMS to loop thermosyphon is an innovative attempt, which can effectively improve the heat transfer efficiency of loop thermosyphon. In this paper, a three-phase loop thermosyphon using water-based MPCMS as the medium is developed. A comprehensive experimental investigation was conducted to study the heat transfer performance by varying the filling ratio (50 %, 60 %, and 70 %), heat flux (25 − 125 W/cm2), and mass concentration (0 %, 0.1 wt%, and 1 wt%). The findings of this study indicate that the loop thermosyphon incorporating MPCMS exhibits improved heat transfer performance compared to a two-phase loop thermosyphon utilizing pure water. The addition of MPCMS has been observed to reduce the wall temperature by up to 6.6 °C and decrease the loop thermal resistance by 13.5 %. Furthermore, the loop thermosyphon with MPCMS demonstrates superior start-up characteristics and thermal homogeneity when compared to water-based systems.

Optical, electrical, and thermal performance of low-concentrating photovoltaic/thermal system using microencapsulated phase change material suspension as a coolant

Concentrated photovoltaic/thermal (C-PV/T) systems exhibit superior output compared to common PV/T collectors. To address potential issues caused by excessive concentration of conventional parabolic concentrators and enhance the electro-thermal co-generation capability, this work proposes a low-concentrating PV/T (LC-PV/T) system that integrates two improved concentrator designs and a coolant of microencapsulated phase change material suspension (MPCMS). A numerical model is established to investigate the effects of working conditions and meteorological conditions on the optical, electrical and thermal performances. The results indicate that the improved concentrator designs effectively prevent over-concentration of sunlight while maintaining a comparable concentration ratio (CR). The electrical output increases with an increase in mass fraction, inlet mass flow rate and solar irradiance, but decreases with an increase in ambient temperature and inlet temperature. Conversely, thermal output increases with an increase in all of these parameters except for the inlet temperature. This system can achieve 17 % electrical efficiency and 72 % thermal efficiency due to the high-efficiency solar cells, optimized concentrator design, and unique MPCMS coolant. The system can produce a maximum electrical power of 4.76 kW/m2 and a maximum thermal power of 19.53 kW/m2. Throughout the day, total electrical and thermal energies are approximately 4.1 kWh and 58.8 MJ.

Experimental study on a loop thermosyphon with microencapsulated phase change material suspension

Microencapsulated phase change material suspension (MPCMS) represents an innovative category of functional thermal fluids. This novel working fluid not only preserves the substantial energy density and high latent heat of phase change materials (PCM), but also mitigates the issues related to PCM, including susceptibility to aggregation and low thermal conductivity. This article selects phase change microcapsules with a phase change temperature of 70 °C, and uses pure water as the base liquid to prepare MPCMS as the working fluid for the loop thermosyphon. A series of heat transfer experiments are conducted, and the results are compared with those of pure water experiments. A 135mm*650mm copper loop thermosyphon, is designed and constructed to investigate the effect of various input power on the heat transfer performance. The results show that the addition of MPCMS can reduce the wall temperature by up to 2.9°C and the loop thermal resistance by 6.3%. Compared with water, the loop thermosyphon with MPCMS has better start-up characteristics. The performance of the MPCMS is affected by various parameters, which are interconnected. Particles in close proximity to the wall display erratic movement, fluctuating across different temperature zones, thereby undergoing a continuous cycle of melting and solidification. This study establishes a basis for further investigation into the practical implementation of MPCMS in industries.

Numerical investigation on rheological and thermal performances of microencapsulated phase change material suspension (MPCMS) in microchannel

Rheological and thermal performances of microencapsulated phase change material suspension (MPCMS) in microchannel are investigated with different mass fractions, Reynolds numbers and particle size distributions. The deviations of the two-phase model and the single-phase model from experiments are also examined and compared. The solid-liquid phase change process of MPCMS is described by the effective heat capacity method. The results show that as the mass fraction Cm increases up to 30%, the MPCMS flow starts to transform from the Newtonian fluid to pseudoplastic behavior (shear rate 0–110 s−1), and the resultant performance evaluation factor (PEF) increases from 1 to 1.27. As the Reynolds number is raised from 96 to 960 (Cm = 15%), the viscosity remains nearly constant (shear rate 100–1000 s−1) flowing as a Newtonian fluid, and the PEF decreases from 1.24 to 1.14. With the particle size increasing (dp = 0.1–10 μm), non-Newtonian characteristics of the suspension become more obvious (shear rate 9300–15,000 s−1), and the PEFs are all 1.15. The average deviation of the single-phase model is 12.3% compared with the experimental data, while it is only 3.65% for the two-phase model. The results provide a reference for the optimization of MPCMS application in microchannel from a rheological perspective.

CFD-VOF-DPM numerical simulation of enhanced boiling heat transfer characteristics of microencapsulated phase change material slurry

Two-dimensional (2D) computational fluid dynamics (CFD) simulations of water-based microencapsulated phase change material suspension (MPCMS) on the flow boiling in a gas–liquid–solid flow system was performed with volume of fluid (VOF) method and discrete particle model (DPM). The Lagrangian particles were linked to the Eulerian phases through the interchange terms such as the drag force in the respective momentum equations. Influences of particle properties including mass fraction and core phase transition temperature, fluid properties including liquid surface tension force and viscosity, detachment time and rise velocity of gas bubbles and particle entrainment in the gas–liquid–solid flow under ambient conditions were numerically investigated. The effects of particles on bubble nucleation, growth and rupture during boiling were studied by visualization. The results show that MPCM can enhance the boiling heat transfer ability of the base liquid. The maximum heat transfer enhancement rate of MPCMS (28 °C) is 4.8%, the maximum heat transfer enhancement rate of MPCMS (90 °C) is 5.1%, the maximum heat transfer enhancement rate of MPCMS (110 °C) can reach 6.7%. MPCM can promote the formation of new bubbles and the rupture of large bubbles, reduce the departure diameter of bubbles, and enhance the boiling heat transfer capacity of the base liquid. The MPCM with core phase change temperature higher than the boiling temperature of base fluid has the best enhancement effect. Through the combination of numerical simulation methods such as VOF and DPM, the complex phase transition heat transfer process of gas-liquid-solid particle coupling of latent thermal functional thermal fluid can be accurately simulated. The work lays a foundation for further explorations on the gas–liquid–solid flows and possible industry applications.

Entropy generation analysis on thermo-hydraulic characteristics of microencapsulated phase change slurry in wavy microchannel with porous fins

• Combined design enables smaller temperature gradient and more uniform temperature. • Larger h m and lower ΔP can be concurrently gained in wavy MCHS with porous fins. • Thermal entropy is three orders of magnitude larger than the frictional entropy. • Thermal entropy increases with heat flux but the frictional entropy is opposite. • Lower irreversible losses can be achieved at the cost of higher power consumption. Recent advancement in micro/nano-scale electronic systems, the need for efficient heat dissipation has become more rigorous, and traditional thermal management solutions are facing enormous challenges. In this study, a novel combined design of wavy microchannel heat sink (MCHS) with porous fins and microencapsulated phase change material (MPCM) suspension is developed and numerically studied to achieve a balance between flow and heat transfer behaviors. The equivalent heat capacity method is adopted to deal with the phase change process of microcapsule particles in steady and laminar states, and the Brinkman–Darcy–Forchheimer model based on the volume-averaged method is employed to characterize the fluid flow in porous fins. A three-dimensional solid-fluid conjugate model is established based on the finite-volume method to investigate the effects of different coolant types (water and MPCM suspension), geometric parameters (wavy amplitude, wavelength, and channel width ratio), and working conditions (inlet flow velocity, heat flux, and slurry concentration) on the thermo-hydraulic properties and entropy generation of wavy MCHS. The results reveal that the combination of porous fins and MPCM suspension presents smaller temperature gradient and more uniform temperature distribution than conventional design. Larger heat transfer coefficient and lower pressure drop can be simultaneously obtained in wavy MCHS with porous fins than in solid fin configuration. The thermal entropy generation is three orders of magnitude larger than the frictional entropy generation, and the Bejan number is close to 1 for different microchannel configurations. Thermal entropy generation increases with increasing heat flux but the frictional entropy generation decreases. Lower irreversible losses can be achieved at the expense of greater pumping power consumption caused by increasing inlet velocity and suspension concentration. The superior effect of wavy MCHS with porous fins using MPCM suspension as coolant has been observed in all cases.

A Microencapsulated Phase-Change Material Suspension-Based Integrated Thermal Management System for Extended Range Electric Vehicle

Abstract In order to improve the temperature maintenance capacity for the battery of the extended-range electric vehicle (EREV) in a low-temperature environment, a microencapsulated phase-change material suspension (MPCMS)-based integrated thermal management system (ITMS) is proposed. The working modes of the proposed ITMS are divided based on series-parallel connections of the battery thermal management system (BTMS), motor thermal management system, motor thermal management system, and auxiliary power unit (APU) thermal management system; the structural parameters of the proposed ITMS are determined by robust design, and the system performance difference between the proposed ITMS and the traditional BTMS is verified through the comparative simulation in −20 °C environment. The results show that the proposed ITMS can significantly delay the decline of battery temperature in the charge-depleting (CD) stage and can reduce the time of the positive temperature coefficient (PTC) heater being on by 27.26%, and the total time being on by 54.82%. During the charge-sustaining (CS) stage, when the PTC heater is off, the average battery temperature will increase by 15.33 °C compared with the traditional BTMS. Based on the proposed ITMS, the temperature maintenance capability for the battery can be significantly improved, and the energy consumption of the PTC heater and vehicle can be reduced by 48.12–100% and 13.44–33.58%, respectively.

Thermal performance of double-layer porous-microchannel with phase change slurry

Combining porous media paved on sidewall and microencapsulated phase change material (MPCM) suspension as coolant is presented in double-layered microchannel heat sink (MCHS), in which more surface area of porous copper matrix with high thermal conductivity as well as greater temperature difference between the heating wall and working fluid during phase transition of MPCM will enhance heat transfer. The Forchheimer-Brinkman-Darcy model together with energy equation in local thermal equilibrium are employed to deal with fluid flow and heat transfer in porous ribs, and the equivalent heat capacity method is used to describe the phase change process of microcapsules under laminar flow. The influences of coolants, heat sink designs (including the thickness, height, porosity and pore size of porous medium as well as channel number) and working conditions (involving inlet velocity, heat flux and suspension concentration) on thermal and hydraulic characteristics are numerically investigated. The performance evaluation factor (PEF) is introduced to evaluate the comprehensive thermal–hydraulic performance of double-layered MCHS, and the effective performance evaluation factor (PEFeff) is used to compare the overall performance of porous-wall MCHS between conventional arrangements, different channel aspect ratio and channel height ratio configurations. The thickness and height of porous media paved on sidewall should be adjusted reasonably, especially for the arrangement of non-equal porous media, to obtain better overall performance. Different from the variable porosity configuration, the double-layered MCHS cannot rely on losing part of flow performance to obtain better thermal performance in smaller pore size mode, so a larger pore size can be selected to obtain better thermal–hydraulic performance according to actual working conditions. The PEF at larger flow velocity decreases due to higher pressure drop exceeding the benefit of more convection on heat transfer enhancement, in which case the phase change effect in porous-wall mode with MPCM suspension as coolant is suppressed and higher viscosity amplifies the effect of frictional resistance, resulting in a greater drop ratio of PEF than water. The greater PEF in porous-wall MCHS with suspension concentration increasing from 3% to 20% arises than that in non-porous mode, due to the larger surface area of copper matrix with high thermal conductivity and more MPCM particles available for phase transition. The larger aspect ratio configuration can achieve greater PEFeff rise and better overall performance by optimizing fluid velocity in the current mode due to greater thermal resistance drop and less pressure drop rise at lower flow rates, but the variable height ratio structure makes the comprehensive performance of porous-wall MCHS inferior to conventional arrangement due to larger pressure drop rise outweighing the benefits of heat transfer enhancement at the same total volume flux.

Experimental performance of a LED thermal management system with suspended microencapsulated phase change material

• Experimental study of thermal management with suspended microencapsulated PCM. • Using suspended PCM microcapsules instead of water improved thermal management. • Optimal MPCMS concentration was analyzed by a dimensionless thermophysical factor. • Variations of cooling performance were attributed to phase change of MPCM. Effective thermal management is crucial for electronic devices, while microencapsulated phase change material (MPCM) has great potential in the field of electronic heat dissipation. However, no existing study has conducted experimental research on the influence of MPCM suspension (MPCMS) on the thermal management performance of electronic devices. In the present study, improvement in the thermal management of LED by using MPCMS as coolant was experimentally demonstrated. The morphology, phase-change and thermophysical properties of the MPCM were observed. Experimental results indicate that the TEC-MHS system that uses MPCMS as coolant exhibited enhanced cooling capacity compared with the system that uses water. A dimensionless thermophysical factor was defined to study the effect of variation in thermophysical properties on cooling performance. Interestingly, the highest thermophysical factor and the best cooling performance were achieved at the same MPCMS concentration. The variation of cooling performance with the ambient temperature and flow rate of MPCMS were found to be attributed to the phase change of MPCM. The experimental results indicate that increased MPCMS concentration does not always lead to improvement of the cooling performance, while the thermophysical and phase change properties of MPCM play critical roles.

Properties and performance of hybrid suspensions of MPCM/nanoparticles for LED thermal management

Mono suspensions of either nanoparticles or microencapsulated phase change material (MPCM) capsules (microcapsules) have shown superior thermophysical properties and heat transfer performance for thermal management. In this study, hybrid suspensions of nanoparticles and MPCM particles were prepared to integrate the advantages of both materials. The properties of hybrid MPCM/nanoparticle suspensions were investigated in terms of dispersion stability and thermal conductivity, and the cooling performance of the hybrid suspensions on thermal management of light-emitting diodes (LED) were studied. The experimental results show that the addition of graphene oxide, titanium dioxide (TiO2), and aluminum oxide (Al2O3) nanoparticles effectively improved the dispersion stability of the MPCM suspension (MPCMS). The thermal conductivity of the MPCMS was enhanced by the TiO2 and Al2O3 nanoparticles. The hybrid MPCM/Al2O3 suspensions, which exhibited remarkable improvement in both dispersion stability and thermal conductivity, were applied to an LED thermal management system. The results show that the cooling performance of the hybrid suspensions was enhanced compared with that of the mono suspensions of MPCM or nanoparticles. The optimal concentration of the hybrid suspension was obtained. The effects of inlet temperature of the hybrid suspensions on the cooling performance were studied.

Thermohydraulic performance analysis of graded porous media microchannel with microencapsulated phase change material suspension

The phase change process in microcapsules is described using equivalent heat capacity method, and the Forchheimer-Brinkman-Darcy equation based on the volume-averaging method is employed to account for the fluid flow in porous ribs. The feasibility in the novel design is validated by analyzing the effects of porosity (ε) arrangement, pore size (dp) arrangement as well as geometric parameters of porous-wall microchannel heat sink (MCHS) on the thermal and hydraulic characteristics under different inlet velocity, heating flux and mass fraction of microencapsulated phase change material (MPCM) suspension. The thermal resistance of the porosity gradient in porous media is less than that of linear variation, which is due to the more uneven velocity distribution in porous and fluid regions. The lower thermal resistance and more uniform temperature distribution occur in the graded porous media microchannel with higher height ratio, as well as the smaller and larger porosity in porous media respectively near the bottom and top walls. The size of microchannel limits the size of dp, making the thermo-hydraulic characteristics of gradient-dp mode worse than that of gradient-ε under the same conditions, and the thermal resistance decreases as well as pressure drop increases with the augment thickness of porous media, so it is necessary to select the appropriate structural parameters and coolants according to the specific working conditions to obtain better comprehensive performance. The performance evaluation factor (PEF) is introduced to evaluate the overall thermohydraulic performance of MCHS under different heat sink designs, and the stepwise increasing porosity mode with porosity varying along the y direction has larger velocity difference between the upper and lower layers and more reasonable MPCM particle distribution under the larger mass fraction of suspension, so as to obtain the larger rise ratio of PEF, up to 61%.

Numerical investigation of heat transfer in the double-layered minichannel with microencapsulated phase change suspension

A three-dimensional heat transfer model of a double-layered minichannel heat sink (MCHS) with microencapsulated phase change material (MPCM) slurry as working fluid was established. The equivalent heat capacity method was used to deal with the phase transition process of microcapsules under turbulent conditions. The flow and heat transfer of MPCM slurries in the minichannel with constant heat flux at the bottom were investigated. In comparison with the single-layered MCHS and the water as working fluid, lower thermal resistance and more pressure drop occur double-layered minichannel with MPCM suspensions of different concentrations, thus, a comprehensive performance factor is defined to evaluated the overall behavior of minichannel, that is related to the thermal resistance and pressure drop. In the presented mode with MPCM suspensions, more than 13.8% higher performance factor occurs than that of water, and more effects on heat transfer happens in the lower channel. The optimized structures of double-layered minichannel are related to the operating conditions.

Study the hydro and thermal performance of microchannel heat exchanger with hybrid suspension of nanoparticles and MEPCM particles

This paper aims to study the flow and heat transfer of hybrid suspension in counter flow micro channel heat exchanger (CFMCHE). In order to enhance the thermal properties of micro encapsulated phase change material (MEPCM) suspension. The hybrid suspension studied in this paper consists of nanoparticles and MEPCM particles, these particles are suspended in water as abase fluid, two types of hybrid suspension are used (Cu + MEPCM suspension) and (Al2O3+ MEPCM suspension) by n-octadecane as a PCM for both of them. The hydrodynamic and thermal characteristics of thes suspensions flow in micro channels of CFMCHE is numerically investigated. From obtained results, using of hybrid suspensions as a cooling fluid lead to modify thermal performance of a CFMCHE by increase its effectiveness but it also lead to high increasing in pressure drop. The results showed considerable enhancement in cooling effectiveness of (Al2O3 + MEPCM suspension) above of the pure PCM suspension, Nanofluids, and water. While (Cu + MEPCM suspension) showed enhancement above of the pure PCM suspension and water, but was not best effectiveness than Nanofluids. Extra increase in pressure drop in both types of hybrid suspension above are leads to reduce the overall performance compared with pure PCM suspension. Therefore its use depends on the application at which this heat exchanger is employed

Hybrid Microencapsulated Phase-Change Material and Carbon Nanotube Suspensions toward Solar Energy Conversion and Storage

In this study, a new type of functional hybrid suspension for solar energy conversion and thermal energy storage was prepared by adding carbon nanotube (CNT) and microencapsulated phase-change material (MEPCM) into deionized water. MEPCM with octadecane as the core material and titania (TiO2) as the shell material was synthesized by the sol–gel method. The MEPCMs were spherical particles with diameters of 2–4 μm, and the thickness of the shell was about 100 nm. The MEPCM achieved better thermal stability and thermal conductivity than the pure octadecane due to the TiO2 shell. The melting and solidification latent heats of the MEPCM were about 154.24 and 154.26 J/g, respectively. The encapsulation efficiency of octadecane was calculated to be 65.84%. Most of all, the novel hybrid CNT and MEPCM suspensions exhibited remarkable dispersion stability owing to the stable reticular structure composed of CNT in the suspension. Compared with pure water, the thermal conductivity, specific heat of the MEPCM/CNT suspension improved by 34.48 and 43.57%, respectively and the photo-thermal conversion efficiency reached a high value of 86.0%. This work provided a new type of hybrid functional suspension towards direct absorption solar collector for solar energy conversion and storage.

Performance investigation of a battery thermal management system with microencapsulated phase change material suspension

In electric vehicles, the performance of the battery thermal management system (BTMS) is closely related to the life and safety of the power batteries. Microencapsulated phase change material suspension (MEPCMS) has good thermal management property, and has been used in many fields of industry. In order to investigate the feasibility of applying MEPCMS to the BTMS, a BTMS model using liquid cold plates is established. It is found that compared with natural heat dissipation condition, using water or MEPCMS as the coolant can significantly reduce the maximum temperatures of the tabs and on the battery body at the end of 5C discharge, but increase the maximum temperature difference on the battery body. The effects of the flow rate of the MEPCMS, the volume fraction of the microencapsulated phase change material (MEPCM), the latent heat and the melting temperature range of the phase change material (PCM) on the thermal management performance are investigated. All these above design parameters can significantly affect the temperature distribution of the battery. Based on the analysis results, an improved design using MEPCMS as the coolant is obtained, and its performance is better than that using water.

Microencapsulated phase change material suspensions for cool thermal energy storage

In this study, dimethyl adipate, an organic ester, as the phase change material (core) was microencapsulated into melamine-formaldehyde (shell) in different shell-to-core ratios using in-situ polymerization technique. The microencapsulated phase change material suspensions (MPCMS) were prepared through the dispersion of microcapsules in appropriate proportions into the carrier fluid. The surface morphology of the prepared microcapsules were observed to be almost spherical. The microcapsules with low crystallinity offered greater resistance towards crack, which was attributed to the flexible structure of the shell. Surface structure studies has confirmed the chemical stability between the core and shell. In addition, the microcapsules exhibited good latent heat enthalpy of around 53 kJ/kg and 70 kJ/kg and they were thermally stable up to 160 °C. Furthermore, the viscosity of MPCMS was found to be very low, which enabled them to exhibit Newtonian flow behaviour. Thus, the test results have signified the MPCMS to be considered as a viable candidate for cool thermal energy storage application.

Effect of micro encapsulated phase change material on the anti-dry-out ability of pulsating heat pipes

Anti-dry-out ability is one of the key performance indexes of the Pulsating Heat Pipe (PHP). In order to improve the anti-dry-out ability, the Micro Encapsulated Phase Change Material (MEPCM) suspension is added to the closed PHP. The Computational Fluid Dynamics (CFD) technique is used to establish the numerical model and analyze the anti-dry-out ability of the PHPs with water and with MEPCM suspension as the working fluids respectively. By changing the phase change temperature range of the MEPCM suspension, the effect of the MEPCM suspension with different phase change temperatures on the anti-dry-out ability, start-up performance and heat transfer performance of the PHP is further studied. The results show that the MEPCM suspension within a certain phase change temperature range can effectively improve the anti-dry-out ability of the PHP. The appropriate phase change temperature range should be selected around the evaporation section temperature when the PHP transforms from the circulating flow state to the dry-out state. After the MEPCM suspension is used as the working fluid, the start-up time and thermal resistance of the PHP are also increased, but the changes are not significant.

Numerical investigation on the performance of microencapsulated phase change material suspension applied to liquid cold plates

A three-dimensional thermo-hydrodynamic coupling model is established to study the performance of microencapsulated phase change material suspension (MEPCMS) applied to liquid cold plates. The cooling effect of three liquid cold plates with different flow channels is compared. And the liquid cold plate with the 3-elbow flow channel is chose to analyze the performance when using MEPCMS as coolant. The results show that compared with pure water, the MEPCMS not only can lower the maximum temperature of the liquid cold plate, improve the temperature uniformity, but also lessoning the load of the cooling system.

Efficacy of divergent minichannels on cooling performance of heat sinks with water-based MEPCM suspensions

This work aims to investigate the influence of diverging minichannels on the contribution of microencapsulated phase change material (MEPCM) suspensions in heat sinks. The cross-section divergence angle is varied from 0° (parallel) to 1.38° and 2.06° and the behaviors of wall temperature distribution and thermal resistance are evaluated at different flow rates and heat fluxes. Furthermore, in order to clarify the effectiveness of the MEPCM suspensions, the measurements of the coefficient of performance (COP) and the figure of merit (FOM) are conducted and compared in the parallel and divergent MCHSs. It was found that increasing MEPCM particle concentration up to 10% can effectively suppress the wall temperature distributions by up to 20%, thereby reducing the difference between the bulk fluid and wall temperatures leading to the reduction of thermal resistance and the improvement of heat transfer. Diverging cross-section of channels increased the suppression of wall temperature profile by up to 33%. It also led to the enhancement of COP values (more than 2 times), especially at high Reynolds numbers (Re = 1375). It was due to the significant reduction in the required pumping power in the divergent MCHSs in comparison with that in the parallel one. However, the measurements of FOM revealed that the increase of pumping power outweighs the enhancement of heat transfer by adding MEPCMs in most of the experiments (0.7 ≤ FOM ≤ 1.1), especially at lower Reynolds numbers (Re = 238). Therefore, diverging minichannels is only effective to improve the contribution of MEPCM suspensions in heat sinks in a certain range of parameter combinations.