Nano-encapsulated Phase Change Material Slurry Research Articles

Improving the thermal performance of nano-encapsulated phase change material slurry by changing fins configurations in a rectangular cavity

The transition to renewable energy is heavily reliant on batteries and energy storage devices, making them a crucial technology of the modern era. The sensitivity of batteries to temperature has been a constant challenge in the development of this technology. Thermal management, creating uniform temperature and proper heat transfer by cooling is very critical in these systems. The popularity of nePCMs is increasing in energy storage and cooling systems due to their remarkable latent heat during phase change. This is because nano-encapsulated phase change materials are being widely used. They are considered to be one of the most promising particles in this application. This research is a case study free convection of nano-encapsulated Phase Change Materials (nePCM) slurry with a volume fraction of 5% and a polyurethane shell and n-nonadecane core in a rectangular chamber was homogeneously simulated and investigated. The temperature of the left wall remains consistent and there are three fins present to enhance the transfer of heat. The governing equations are transformed into dimensionless form and solved numerically using OpenFOAM software. Various parameters such as fin geometry, chamber angle, Rayleigh number, and melting point temperature are altered to assess their impact on velocity profile components, temperature distribution, Cr contours, Nusselt number, and fin efficiency. Based on the results, Y-shape and T-shape fin geometries can increase the efficiency of water-nePCM fluid by about 10% for Ra = 100 and about 26 % for Ra = 104 compared to I-shape fin. Also, increasing the Rayleigh number from Ra = 100 to Ra = 104 improves the average Nusselt number for water-nePCM nanofluids by about 100 % in each of the fin geometries.

Experimental study on spray heat transfer enhancement by micro-structured surface with nanoencapsulated phase change material slurry (NPCMS)

Spray cooling is receiving increased attention due to the highly efficient and uniform heat transfer. However, previous investigations seldomly focused on its enhancement with the combination of phase change materials (PCMs) and micro-finned surface. Herein, in this article, we enhance the spray cooling with NPCMS and micro fins to improve the heat capacity of coolant, heat transfer area and nucleate sites of contact boiling. Results show that two peaks of heat transfer coefficient are observed in sequence as heatflux increases, separately derived from latent heat absorption of melting of core PCM and nucleate boiling of carrying fluid. Compared to the smooth surface, the convective heat transfer coefficients under three cubic fin heights (0.2 mm, 0.3 mm and 0.4 mm) are improved maximally by 22.3 %, 17.6 % and 11.8 % in phase change of NPCMS, while the maximum improvements of 45.8 %, 39.8 % and 39.8 % are obtained in the nucleate boiling. The staggered arrangement of cylinder fins can induce stronger capillary force, which is responsible for the best enhancement of nucleate boiling. Also, the shortest survival time of droplet on the staggered cylinder fins are observed, confirming that capillary force is the reason of increasing heatflux and lifting Leidenfrost point of boiling.

Thermoregulating gypsums by using nanoencapsulated phase change material slurry

Thermoregulating composites were produced by using a thermoregulating slurry (NPCS) containing nanoencapsulated phase change material (NPCM) from poly(styrene-co-divinylbenzene) as shell and the commercial paraffin Rubitherm®RT27 as core material. These composites were synthesized by using the constitutive water of the slurry as setting water and changing the NPCM/Hemihydrate (NPCM/Hem) mass ratio within 0.0–0.41. It was found that nanoparticles were uniformly dispersed into the gypsum, and the gypsum crystal morphology was tuned by the addition of the slurry. Attending to the thermal properties, these materials can work either as insulating or thermal energy storage materials, decreasing the thermal conductivity up to ~ 50%, whereas the thermal energy storage (TES) capacity is enlarged in a ~ 140%, respect to the pure gypsum, when the maximum NPCM/Hem mass ratio was used. This composite had a latent heat of 30.2 J g−1 and a heat capacity of equivalent 3.5 J g−1 K−1. Composites from a NPCM/Hem mass ratio up to 0.15 satisfied European mechanical standard EN 13,279–1 for gypsum binders and gypsum plasters and all of them, presented a bulk density higher than 0.60 g cm−3. The addition of a 41% in mass of nanocapsules allowed to save 13.5 kWh m−3 and, reducing the CO2 emissions up to 3.4 kg of CO2 per operating cycle. The use of this new material would lead to significant energy and economic savings, as well as a considerable reduction in the emission of polluting gases into the atmosphere.

Thermo-hydraulic and entropy generation investigation of nano-encapsulated phase change material (NEPCM) slurry in hybrid wavy microchannel

PurposeThis study aims to capture the heat transfer and entropy generation characteristics of temperature-dependent nano-encapsulated phase change material (NEPCM) slurry in a hybrid wavy microchannel. In addition, the effect of substrate material combined with NEPCM slurry on conjugate heat transfer condition is captured for different microchannel heat sinks.Design/methodology/approachA novel “hybrid wavy microchannel” is proposed to enhance the overall heat transfer and reduce the pressure drop by combining wavy and raccoon geometry. NEPCM–water slurry is implied in the hybrid wavy, conventional wavy and raccoon microchannel. A user-defined function (UDF) is used to observe the effect of phase-change of paraffin material in thermophysical properties of NEPCM–water nanofluid. All three (hybrid, wavy, raccoon) microchannels are engraved on a rectangular substrate of 1.8 mm width (ωs) and 30 mm length (L), respectively. For hybrid, wavy and raccoon microchannel, waviness (γ) of 0.067 is selected for the investigation.FindingsThe result shows that NEPCM particle presence reduces the fluid domain temperature. The thermal performance of proposed Heat sink 2 is found better than the Heat sink 1. The effect of the geometrical modification, wall thermal conductivity, different volumetric concentrations of nanoparticles (ϕ ∼ 1 – 5%) and Reynolds number (Re ∼ 100 – 500) on thermodynamic irreversibility is also observed. Additionally, the effect of thermal and frictional entropy generation is reduced with a combination of NEPCM slurry and higher conductive material for all heat sinks.Practical implicationsA combination of NEPCM slurry with laminar flow microchannel cooling system emerged as a better alternative over other cooling techniques for higher power density devices such as microprocessors, electronic radar systems, aerospace applications, semiconductors, power electronics in modern electronic vehicles, high power lasers, etc.Originality/valueThe phase-change process of the NEPCM slurry is tracked under conjugate heat transfer in a hybrid wavy microchannel. Furthermore, the phase-change process of NEPCM slurry is captured with different heat sink materials (SS316, silicon and copper) under conjugate heat transfer situation for different heat sinks and concentrations (ϕ ∼ 1–5) of NEPCM.

Jet Impingement Cooling Enhanced with Nano-Encapsulated PCM

In the present study, the laminar flow and heat transfer of water jet impingement enhanced with nano-encapsulated phase change material (NEPCM) slurry on a hot plate is analytically investigated for the first time. A similarity solution approach is applied to momentum and energy equations in order to determine the flow velocity and heat transfer fields. The effect of different physical parameters such as jet velocity, Reynolds number, jet inlet temperature, and the NEPCM concentration on the cooling performance of the impinging jet are investigated. The volume fraction of NEPCM particles plays an essential role in the flow and heat transfer fields. The results show that NEPCM slurry can significantly enhance the cooling performance of the system as it improves the latent heat storage capacity of the liquid jet. However, the maximum cooling performance of the system is achieved under an optimum NEPCM concentration (15%). A further increase in NEPCM volume fraction has an unfavorable effect due to increasing the viscosity and reducing the conductivity simultaneously. The effect of adding nano-metal particles on the heat transfer performance is also investigated and compared with NEPCM slurry. NEPCM slurry shows a better result in its maximum performance. Compared with the water jet, adding nano and NEPCM particles would overall enhance the system’s thermal performance by 16% and 7%, respectively.

Numerical study and experimental verification on spray cooling with nanoencapsulated phase-change material slurry (NPCMS)

Spray cooling is an efficient cooling method with high heatflux removal capability. In this study, we propose a spray cooling regime with nanoencapsulated phase-change material slurry (NPCMS), aiming to improve the coolant's heat capacity. We develop a three-dimensional model of spray cooling of NPCMS based on DPM and Lagrangian Wall Film (LWF) models. Also, the equivalent heat capacity method is integrated in LWF model to characterize the solid-liquid phase change of NPCMS. In addition, the experiment of spray cooling of NPCMS is conducted to verify our model. The influences of initial temperature of NPCMS and dynamic properties on flow and heat transfer of NPCMS are discussed. The results show that NPCMS greatly improves the heat transfer coefficient within the phase-change temperature range, especially the coefficient at the stagnation point of heated surface, but reduces the uniformity of heat transfer. The optimal heat transfer performance occurs when the initial temperature of NPCMS is 301 K, 0.9 K lower than the peak temperature of phase change. The heat transfer coefficient at the center of wall is almost twice of that of the water due to latent heat absorption. Lower surface tension and viscosity are beneficial to improving spray cooling performance.

Optimization of the thermal performance of nano-encapsulated phase change material slurry in double pipe heat exchanger: Design of experiments using response surface methodology (RSM)

The immersion of nano-encapsulated phase change material (NPCM) in a carrier fluid to form NPCM slurry can ensure of the latent heat absorption and effective heat transfer. Here, the convective heat transfer of the NPCM slurry stream in a double-pipe heat exchanger were studied experimentally. PCM nanocapsules have been prepared via a mini-emulsion polymerization process. The nanocapsules consisting of n-dodecanol as the core, and polymethyl methacrylate (PMMA) as the shell were modified by graphene oxide (GO) nanosheets as an additional protective layer. Morphology as well as thermal and structural features of nanocapsules were examined and analyzed. The least particle size corresponded with a latent heat of 148.5 J/g. The enhancement mechanism of the convective heat transfer of NPCM slurry was studied via the response surface method. The heat transfer features were evaluated based on experiments designed statistically to determine the optimal values of inlet temperature (Tin), NPCM concentration (ϕ), and Reynolds number (Re). The optimization was performed aiming at the maximum enhancement of thermal efficiency (η). The validity of the developed regression models was assessed using the ANOVA technique. It is found that in the turbulent tubular flow of NPCM slurry, the inlet temperature and the mass fraction of nanocapsules have the most significant effects on the heat transfer performance. The optimum values of ϕ, Tin and Rein were found to be 14%, 83 °C and 5046, respectively, resulted in the maximum η of 4.5.

Parametric evaluation of a hydrofoil-shaped sidewall rib-employed microchannel heat sink with and without nano-encapsulated phase change material slurry as coolant

The application of hydrofoil-shaped sidewall ribs (SWRs) in microchannel heat sinks (MCHSs) with nano-encapsulated phase change material (NEPCM) particle slurry as coolant has recently been proven as an improvised solution for enhancing heat transfer, with a reasonable penalty in pressure drop. However, the further mitigation of high-power densities of modern micro/nanoscale devices is limited owing to manufacturing complications and design constraints. By using the geometrical and thermophysical parameters of hydrofoil-shaped SWRs and NEPCM slurry, the present study numerically evaluates the thermal and hydrodynamic performance of an MCHS device. The preliminary results reveal the superior performance of NEPCM slurry with hydrofoil-shaped SWRs compared with that of water without ribs in an MCHS owing to the improved latent heat storage capability of the former fluid as well as the enhanced heat transfer area of the rib structure. Increase in the width and height of hydrofoil-shaped SWRs and particle diameter, latent heat of fusion and mass concentration of the NEPCM slurry at a constant Reynolds number (Re) and inlet temperature enhances heat transfer. However, increase in the pitch of the hydrofoil-shaped SWRs and melting temperature range of the NEPCM slurry degrades heat transfer. The inlet temperature of the NEPCM slurry, with a slightly lower value than the melting point of the NEPCM particles, yields superior performance. The maximum ratios of the Nusselt number, that is, Nuavg,SWR/Nuavg,ref and Nuavg,NEPCM/Nuavg,ref, are 1.88 and 2.68, respectively. A particle loading of more than 10% at a high Re of 1000 is not reasonable from the thermodynamic efficiency perspective. The findings are expected to serve as a benchmark for the selection of the geometric, thermophysical and operational parameters of future MCHS devices with hydrofoil-shaped SWRs and NEPCM slurry as coolant.

A review on the applications of micro-/nano-encapsulated phase change material slurry in heat transfer and thermal storage systems

In modern heat transfer systems, thermal storage not only causes the balance between demand and supply, but also improves the heat transfer efficiency in these systems. In the present study, a comprehensive review of the applications of micro- or nano-encapsulated phase change slurries (MPCMs/NPCMs), as well as their effects on thermal storage and heat transfer enhancement, has been conducted. MPCMs/NPCMs have a myriad of applications and various usages such as pipe and channel flows, photovoltaic/thermal, solar heaters, air conditioning systems, storage tanks and heat pipes that have been categorized and studied. It was found that there are many advantageous adding MPCM/NPCM to the base fluid. The most important effect is that the addition of PCMs to the base fluid can intensify the capacity of energy absorption in the base fluid. These materials can absorb a high proportion of received energy by changing their phase and prevent temperature increment of the base fluid. Thereupon, the specific heat of the fluid in the presence of the micro-/nano-capsules increases. Moreover, in most studies reviewed, heat transfer coefficient and Nusselt number increase by the addition of micro-/nano-capsules to the base fluid. Also, the addition of MPCM/NPCM to the base fluid could make this material pumpable, although increment in the concentration of micro-/nano-capsules raises the viscosity of the working fluid and thereupon the pumping power. On the other hand, for a same heat load, the pumping power decreases due to the lower required flow rate in comparison with pure working fluid. The most important factor that must be considered in the application of MPCMs/NPCMs is the complete phase change of the material. Given the favorable thermal and fluid characteristics of MPCMs/NPCMs, the utilization of these materials could be a promising method to transfer heat and store it with high efficiency and low pumping power.

Nano-encapsulated phase change material slurry (Nano-PCMS) saturated in metal foam: A new stable and efficient strategy for passive thermal management

Nano-encapsulated phase change material slurry (nano-PCMS) has the merits of high latent heat and high surface area, and overcomes the defects of supercooling and volume expansion that exist in most organic/inorganic PCMs. Subjected to the low thermal conductivity, the thermal management systems using nano-PCMS are highly dependent on slurry's convection coefficient, which cannot be guaranteed in the condition where the natural convection is constrained. Here, this article proposed a novel thermally stable and efficient hybrid PCM that infiltrating nano-PCMS into metal foam for passive thermal management. The experimental results indicated that the addition of metal foam could reduce the heated surface temperature by maximum 38% in regardless of heated angle, while this contribution was 24% achieved by natural convection of pristine nano-PCMS. The flow convection of nano-PCMS was completely suppressed in the foam cells due to the high viscosity of slurry and flow resistance of foam matrix. Higher porosity composite obtained lower heat transfer efficiency and more pronounced thermal non-equilibrium effect attributed to its lower effective thermal conductivity and less interfacial area. This newly-proposed foam/nano-PCMS composite not only provides high heat transfer efficiency, but reduces the dependency on the convection coefficient of nano-PCMS.

Heat Transfer Characteristics of a Volumetric Absorption Solar Collector using Nano-Encapsulated Phase Change Slurry

ABSTRACTThe conventional solar collectors which absorb solar energy through surface of the receiver have much energy waste during energy conversion process due to heat loss from the pipe surface. Volumetric absorption solar collectors (VASC) can overcome this problem through directly absorbing solar energy by nanofliud with excellent optical absorption property. Nano-encapsulated phase change material (NPCM) is a kind of novel composite PCMs widely adopted in thermal energy storage system. The NPCM slurry (NPCS) has great potential to be used in VASC since it can be used as both the heat transfer fluid and energy storage medium. In the present study, a numerical model based on the Eulerian-Eulerian approach is built to investigate the heat transfer characteristics of NPCS in a parallel plate channel for volumetric absorption of solar energy. Influences of different parameters such as the extinction coefficient, flow velocity, radiative intensity on the performance of collector are studied through the numerical simulation. The results indicate that the NPCS shows better performance in the VASC compared with the conventional nanofluids without phase change. The information provided is helpful in the further study of solar energy volumetric absorption.

Numerical study on free-surface jet impingement cooling with nanoencapsulated phase-change material slurry and nanofluid

The free-surface jet impingement technique operating with two-phase advanced coolants has recently drawn much favorable attention in cooling applications. However, numerical understanding of free-surface jets along with improved realization of pros and cons associated with these advanced coolants remains a challenge. In this work, the flow and thermal performances of free-surface jet impinging on a heated copper plate are numerically investigated using water, nanoencapsulated phase-change material (NEPCM) slurry, and nanofluid as coolants. Three-dimensional continuity, momentum, and energy equations are discretized with a commercial finite volume code in accordance with a standard k-ε turbulence model. The volume of fluid multiphase technique is adopted in this study to model the free surface between the liquid jet and surrounding ambient air. A single-phase fluid approach is employed using existing models from other references to determine the effective thermophysical properties of NEPCM slurry and nanofluid. The predicted Nu and pressure drop calculations agreed well with the experimental data from references. Physical understanding of the effects of fluid jet inlet temperature, nozzle-to-target distance, and nanoparticle concentration is reported. The addition of both NEPCM and Al2O3 particles to water helps in improving the Nusselt number and decreases the stagnation point temperature with certain pressure drop penalty. The NEPCM slurry enhances the cooling performance of the system by improving its latent heat storage capability, whereas nanofluids improve the cooling performance by enhancing the effective thermal conductivity. The thermal performance can be further improved with increased particle concentration. The NEPCM slurry demonstrates performance superior to nanofluid working at the same particle loading. Overall, the proposed model can provide valuable guidelines for the use of advanced coolants in a free-surface jet impingement cooling system.

Thermophysical properties of n-tetradecane@polystyrene-silica composite nanoencapsulated phase change material slurry for cold energy storage

Based on the synthesis of n-tetradecane@polystyrene-silica (Tet@PS-SiO2) composite nanoencapsulated phase change material (NEPCM), a novel composite NEPCM slurry for cold energy storage was prepared by dispersing NEPCM into base fluid. The thermal performances of the Tet@PS-SiO2 NEPCM were measured by differential scanning calorimetry (DSC) and thermogravimetric analyzer (TG). The thermophysical properties of the NEPCM slurry including morphology, particle size, specific heat capacity, thermal conductivity, viscosity and mechanical stability were investigated systematically. The results showed that the Tet@PS-SiO2 NEPCM had a melting latent heat of 83.38kJkg−1 and excellent thermal stability. Transmission electron microscope (TEM) images displayed that the synthesized nanocapsules had regular spherical core-shell structure, and particle size analysis of NEPCM dispersed in slurry showed the mean particle size of Tet@PS-SiO2 NEPCM was 151.3nm. Moreover, the Tet@PS-SiO2 slurry had a high specific heat capacity and obtained an enhancement 8.4% in thermal conductivity by the grafting of SiO2 on the PS shell. In addition, the slurry showed an acceptable viscosity and excellent mechanical stability. Those results indicate the Tet@PS-SiO2 slurry can be considered as an up-and coming latent heat fluid for cold energy storage.

Three-dimensional numerical study of laminar confined slot jet impingement cooling using slurry of nano-encapsulated phase change material

This Article presents a three dimensional numerical model investigating thermal performance and hydrodynamics features of the confined slot jet impingement using slurry of Nano Encapsulated Phase Change Material (NEPCM) as a coolant. The slurry is composed of water as a base fluid and n-octadecane NEPCM particles with mean diameter of 100nm suspended in it. A single phase fluid approach is employed to model the NEPCM slurry.The thermo physical properties of the NEPCM slurry are computed using modern approaches being proposed recently and governing equations are solved with a commercial Finite Volume based code. The effects of jet Reynolds number varying from 100 to 600 and particle volume fraction ranging from 0% to 28% are considered. The computed results are validated by comparing Nusselt number values at stagnation point with the previously published results with water as working fluid. It was found that adding NEPCM to the base fluid results with considerable amount of heat transfer enhancement.The highest values of heat transfer coefficients are observed at H/W=4 and Cm=0.28. However, due to the higher viscosity of slurry compared with the base fluid, the slurry can produce drastic increase in pressure drop of the system that increases with NEPCM particle loading and jet Reynolds number.

Confined jet array impingement cooling with spent flow distraction using NEPCM slurry

The confined jet array impingement cooling with spent flow distraction using nano-encapsulated phase change material (NEPCM) slurry (or nanofluids) is investigated numerically using a homogeneous model, based on effective thermophysical properties of the slurry. The NEPCM slurry consists of the carrier fluid of polyalphaolefin (PAO) and the NEPCM particles with Polystyrene shell and paraffin core. The jet impingement cooling of a slot jet array with jet width of 100μm, confinement height of 300μm, and jet-to-jet distance of 400μm is investigated numerically under conditions of different jet velocities, inlet temperatures, particle volumetric concentrations, as well as heat fluxes. Unlike MEPCM (micro-encapsulated phase change material) where micro-convection effect plays an important role in heat transfer enhancement, it is found that this effect has little impact on heat transfer of NEPCM because of much smaller particles of NEPCM. There exists an optimal volumetric concentration to achieve the best heat transfer performance for a given jet velocity, and this optimal volumetric concentration at first increases and then becomes saturated with increasing jet velocity in the range of the present study. An optimal inlet temperature, close to (but lower than) the peak of melting curve of PCM, is determined for the maximum heat transfer enhancement; it is found that the higher the jet velocity (when heat flux is fixed) or the lower the heat flux (when jet velocity is fixed), the closer the optimal inlet temperature to the peak of melting curve. The local heat transfer under the exit slot is the lowest because of the formation of a stagnant zone by the head-to-head collision of the two adjacent wall jets, and adding of NEPCM does not change the basic characteristics of local heat transfer, but a little bit extends the low heat transfer region.

Effects of pin tip-clearance on the performance of an enhanced microchannel heat sink with oblique fins and phase change material slurry

The performance of an enhanced microchannel heat sink with sectional oblique fins and with a coolant that contains Nano-Encapsulated Phase Change Material (NEPCM) particles is investigated using a 3D conjugated heat transfer model. Three volume fractions from ξ=0 (pure water) to 0.3 are studied to investigate the effects of presence of NEPCM particles. Then the effects of introducing tip-clearance to the heat sink on thermal and hydrodynamic performance is examined at low Reynolds numbers (less than 215). Four values of tip-clearance to channel width ratio (t/Wc) are investigated ranging from a no gap (t/Wc=0) to t/Wc=0.74. On the bottom wall of the heat sink a range of uniform and fixed temperatures of 299.15K to 340.15K are applied. The cooling and hydrodynamic performance of the heat sink is studied using Nusselt and Euler numbers, respectively. It was observed that using of NEPCM slurry in contrast with pure water, enhanced the cooling performance of the heat sink but increased the Euler number. Furthermore, it was seen that the introduction of tip-clearance to the heat sink, if the clearance ratio is chosen properly, has the potential to enhance the cooling performance and reducing the Euler number simultaneously.

Heat Transfer Enhancement of Backward-Facing Step Flow by Using Nano-Encapsulated Phase Change Material Slurry

Laminar forced convection of nano-encapsulated phase change material (NEPCM) slurry over a 2D horizontal backward-facing step is numerically investigated using a finite volume method based on a collocated grid. The slurry consists of water as base fluid and n-octadecane NEPCM particles with an average diameter of 100 nm. Uniform heat flux boundary condition is imposed to the downstream wall while the step and upstream walls are subjected to adiabatic boundary condition. The effects of Reynolds number ranging from 20 to 80, volume fractions of nanoparticles ranging from 0% to 30%, as well as heat flux ranging from 500 to 2,500 W/m2 are studied. In order to understand the physics of flow and heat transfer of slurry over the backward-facing step, the streamlines and isotherms of the flow were studied. An enhancement in heat transfer coefficient up to 67% using slurry as working fluid compared with pure water can be observed. However, because of the higher viscosity of mixture compared with pure water, the slurry can cause a higher pressure drop in the system. Furthermore, as wall heat flux and Reynolds number increase, the heat transfer coefficient of the bottom wall increases until a critical heat flux is reached and heat transfer performance becomes independent of heat flux.

Flow and Heat Transfer of Nanoencapsulated Phase Change Material Slurry Past a Unconfined Square Cylinder

Numerical solution is carried out to analyze the effect of nanoencapsulated phase change material (NEPCM) slurry on forced convection heat transfer of steady laminar flow past an isothermal square cylinder. The base fluid is water while the NEPCM particles material is n-octadecane with an average diameter of 100 nm. A parametric study was performed for different volume fraction of nanoparticles ranging from 0% to 30%, two melting temperature ranges, i.e., 10 K and 20 K, and different inlet Reynolds numbers ranging from 15 to 45. The governing equations of flow and energy are solved simultaneously using a finite volume method (FVM) on collocated grid arrangement. It was found that for both NEPCM slurry and pure water, local and average heat transfer coefficients increases with increasing Reynolds number. The results of heat transfer characteristics of slurry flow over the square cylinder showed remarkable enhancement relative to that of the base fluid. The enhancement intensifies for higher particle volume concentrations and higher Reynolds numbers. However, utilizing the slurry can cause higher shear stress on the wall due to higher viscosity of mixture compared to the pure water. The melting temperature range of NEPCM particles has slight effect on heat transfer, although with increasing volume fraction and Reynolds number, lower melting range leads to higher heat transfer coefficient.

Three dimensional numerical study of heat-transfer enhancement by nano-encapsulated phase change material slurry in microtube heat sinks with tangential impingement

This paper presents a three-dimensional model describing thermal and hydrodynamic characteristics of a Microtube heat sink with tangential impingement with nanoencapsulated phase change materials (NEPCM) slurry as coolant. In this study, octadecane for NEPCM and polyalphaolefin (PAO) is used as a base fluid. The continuity, momentum, and energy equations are solved using a finite volume method. The model is validated by comparing results with available data in the literature. The effects of dominant parameters including mass concentration and melting range of NEPCM as well as Reynolds number on temperature uniformity, thermal resistance, Nusselt number, pressure drop and generated entropies in the system are investigated. Results indicated that adding NEPCM to base fluid leads to considerable heat transfer enhancement. However, using NEPCM slurry as coolant has also induced drastic effects on the pressure drop that increases with mass concentration and Reynolds number. It was found that that an increase in nanoparticles mass concentration, inlet Reynolds number and melting range of NEPCM, results in a higher Nusselt number, better temperature uniformity and lower thermal resistance. Furthermore, the effects of different parameters on slurry entropy production are demonstrated. It is found that generated total entropy decreases with increasing mass concentration and Reynolds number.

Encapsulated Phase Change Material Slurry Flow in Manifold Microchannels

The heat transfer performance of water-based microencapsulated phase change material slurry (particle size 5 μm) flow inside manifold microchannels of hydraulic diameter 170 μm was experimentally and numerically investigated. Slurry performance was poorer compared with pure fluid due to the large size of particles used and lower thermal conductivity of slurry compared with water. A parametric study was performed with nanoencapsulated phase change material slurry flow (particle size of 100 nm) in microchannels of hydraulic diameters 170 and 47 μm. Two different base fluids were considered and the heat transfer enhancement of slurry with various particle mass concentrations compared with its base fluid was presented. For developing flows, the performance of phase change material slurry depends on various parameters such as base-fluid thermal conductivity, channel dimensions, amount of phase change material melted, and particle mass concentration. In the case of manifold microchannel heat sinks, where the microchannel flowpath is much shorter compared with traditional microchannels, using higher-thermal-conductivity phase change material, narrower channels, smaller particles, and optimum parameters will aid in obtaining better thermal performance of phase change material slurry compared with pure fluid.