Microencapsulated Phase Change Material Slurry Research Articles

Experimental Investigation of the Viscosity and Density of Microencapsulated Phase Change Material Slurries for Enhanced Heat Capacity and Transfer

Working fluids that incorporate solid microencapsulated phase change materials (MPCMs) can benefit from properties such as density and viscosity, which are crucial for improving heat capacity and transfer. However, limited data are available on these parameters for specific slurry and mass ratios. In this study, we present a comparative analysis of the experimental results on the viscosity of three different MPCM aqueous dispersions, namely MPCM 31-S50, MPCM 25-S50, and Micronal 5428X. Varying MPCM mass ratios of distilled water were used to obtain different mass concentrations of the phase change material (PCM), and the resulting slurries were analysed at temperatures ranging from 15 to 40 °C. Our findings showed that all slurries exhibited non-Newtonian characteristics at low shear rates, with viscosity stabilising at higher shear rates, resulting in the characteristics of a Newtonian fluid. The viscosity results were highly dependent on the type of MPCM base dispersion, particularly at high mass ratios, with the slurries having viscosities higher than those of water. Furthermore, we conducted density experiments as a function of temperature, using a flow test setup and a Coriolis flowmeter (Endress+Hauser, Reinach, Switzerland) to determine the density of two MPCMs, namely MPCM 25-S50 and Micronal 5428X. The test samples were prepared at mass concentrations of 10%, 15%, and 20% of the phase change material. We found significant differences in density and viscosity for different MPCM slurries as a result of both the PCM concentration and the material studied. Our results also revealed an apparent PCM phase change process, in which the slurry density significantly decreased in the temperature range of the phase transition from solid to liquid.

Field synergy analysis on thermal-hydraulic behavior of phase change slurry in porous microchannel heat sink with graded porosity configuration

In this study, a novel design of porous microchannel heat sink (MCHS) with graded porosity configuration is proposed in the hope of attaining lower flow and thermal resistances than constant porosity (CP) configuration. The efficacy of new scheme is validated by utilizing a three-dimensional solid-fluid conjugate model based on the finite volume method, which considers the flow and heat transfer of microencapsulated phase change material slurry (MPCMS) inside the porous fins. It is reported that the thermal performance of porous MCHS with constant and graded porosity configurations is significantly better than that of non-porous MCHS. The feasibility of new design is verified by comparing the hydrothermal behavior of multiple graded porosity MCHSs and CP configuration for different fin designs (involving the number of graded equidistant fins N, graded length ratio R, and fin-to-pitch width ratio β) and operating conditions (including Reynolds number Re, mass fraction cm, and inlet velocity uin). The comprehensive performance improvement mechanism of MPCMS in graded porosity microchannels is discussed through the analysis of flow and thermal details, field synergy angle (θ) and field synergy number (Fc), and the overall performance of new design is evaluated by performance evaluation factor (PEF). Results indicate that the six types of porous MCHS with stepwise varying porosity exhibit lower thermal resistance than CP mode, and better thermal behavior and larger PEF can be obtained at N = 2 and β = 0.7. Smaller and larger R should be chosen for stepwise increasing porosity (SIP) and stepwise decreasing porosity (SDP) modes, respectively, to achieve higher heat transfer enhancement while avoiding greater friction losses. The Fc value of porous MCHS with various porosity configurations is about two orders of magnitude less than 1 and shows a monotonically reducing trend with Re, and the synergistic effect deteriorates at high Re. Compared to the CP mode, a low-θ “drift” toward the low porosity region of porous fin occurs within the graded porosity MCHS, which decreases and increases in the downstream and upstream directions of the “drift”, respectively. Among the novel MCHS designs, the z-directional SIP mode acquires the best overall performance due to the excellent synergy between the velocity and temperature fields, and its PEF consistently exceeds 1.13 and reaches up to 1.33. Generally speaking, the fin porosity of graded porosity MCHS near the channel cavity, channel top, and channel inlet should be greater for superior comprehensive performance.

Heat transfer enhancement of electrospray cooling with microencapsulated phase change material slurry (MPCMS): A comprehensive numerical model and experimental study

Electrospray cooling (ESC) technology is increasingly emphasized due to its efficient heat removal capacity, minor coolant consumption and accurate thermal control. Previous articles had focused on either experimental exploration on ESC performance or numerical methods on solitary electrospray such as Volume of Fluid [1], Boundary Element Method [2] and Lagrangian model [3]. However, there is no comprehensive model characterizing the whole ESC process. Moreover, there was barely investigation on ESC enhancement using phase change materials (PCM). Herein, this study has bridged this gap by developing a new comprehensive model to explore the ESC enhancement with microencapsulated phase change material slurry (MPCMS), and conducted experiment to verify it. The influences of applied voltage, mass concentration and inlet temperature of MPCMS on the ESC were discussed. Results revealed that MPCMS offered superior cooling performance during melting process due to latent heat absorption compared to deionized water. Nevertheless, as wall temperatures increased, the deposition, higher viscosity and lower thermal conductivity of MPCMS would compromise cooling efficiency. Moreover, higher applied voltage enhanced cooling performance by increasing droplet velocity, and reducing the possibility of droplet rebound. When the inlet temperature approached the peak melting temperature, the convective heat transfer coefficient reached its maximum.

Numerical Investigation on Heat Transfer Characteristics of Microencapsulated Phase Change Material Slurry in a Rectangular Minichannel

Numerical Investigation on Heat Transfer Characteristics of Microencapsulated Phase Change Material Slurry in a Rectangular Minichannel

Heat transfer and thermal stress of a parabolic trough solar collector with secondary reflector using microencapsulated phase change material slurries

The traditional parabolic trough solar collectors (PTSC) often face the problems of high thermal stress and the deformation of the tubular receiver. In this paper, a secondary reflector (SR) is put into the traditional PTSC, and the microencapsulated phase change material (MEPCM) slurries with 7 vol%, 12 vol%, and 15 vol% are used as the operating fluids. By associating the Monte Carlo ray-tracing (MCRT), finite volume (FVM), and finite element (FEM) methods, the optical-thermal–mechanical coupling problem of the absorber tube is settled, the flow and heat transmission of MEPCM slurries in the collector tube are numerically investigated by applying the Eulerian-Eulerian multiphase flow model. The results show that the solar flux and wall temperature of the absorber tube with the SR are more uniform along the circumferential direction. The use of SR enhances the local heat transfer of the MEPCM slurries at the phase change section in the absorber tube, while when the phase changes finish, the local heat transfers of the slurries in the PTSC with SR have no difference with the traditional PTSC. Compared with the water, the MEPCM slurries obviously enhance the heat transfer of the absorber tube due to the phase change and the interactive motion of the microencapsulated particle, and the higher the slurry concentration, the larger the mean Nusselt number, the smaller the thermal stress. The addition of SR significantly decreases the thermal stress of the absorber tube, the maximal equivalent stress is reduced by 81.8%

Flow and heat transfer characteristics of microencapsulated phase change material slurry in bonded triangular tubes for thermal energy storage systems

Three nanoscale metal oxides composed of nano TiO2, nano Al2O3, and nano MgO were added to the phase change microcapsule slurry for optimising the heat transfer behaviour. The thermal and rheological properties of the resulting microencapsulated phase change materials (MPCMs) and microencapsulated phase change material slurries (MPCSs) were characterized to determine the effects of added metal oxides in optimising the performance of MPCSs. The impacts of factors like metal oxides, concentrations, and flow rates on the heat transfer behaviour of MPCSs were investigated by forced convective heat transfer experiment with various working conditions. Compared to 6 wt% MPCSs, the heat transfer coefficients (hx) of 6 wt% slurries containing 1 wt% TiO2, 1 wt% Al2O3, and 1 wt% MgO increased by 4.0 %, 2.5 %, and 7.13 %, respectively. Nano-MgO showed the most significant heat transfer enhancement effect on MPCSs. Moreover, the heat transfer performance gradually enhanced as a function of the concentration for nano MgO. Overall, the addition of metal oxides enhanced heat transfer by increasing the thermal conductivity of the slurry, as well as improved the micro-convection effect. The proposed MPCSs are promising for applications in solar photovoltaic/thermal (PV/T) systems, chip cooling, thermal management, buildings, and automotive cooling.

Uniform cooling for concentrator photovoltaic cell by micro-encapsulated phase change material slurry in double-layered minichannels

The concentrator photovoltaic (CPV) systems often suffer high heat flux, leading to cell temperatures rising, which will affect its performance and reduce the service life. Double-layered minichannel heat sink (DL-MCHS) is an efficient cooling technology, which could effectively lower down the top temperature of CPV cell. Micro-encapsulated phase change material slurry (MPCS) is a novel type of latent heat functional fluid and has a good application prospect in the field of cooling. Therefore, MPCS flowing in the DL-MCHS, as the thermal management device was investigated for the cooling of CPV cell. Three configurations of minichannels, including staggered arrangement, parallel arrangement and dual unequal arrangement were compared and optimized. On the basis of optimization, the flow and heat transfer performance of MPCS with different concentrations in double-layered straight and wavy minichannels had been numerically studied. The results indicated that the lowest top temperature of dual unequal DL-MCHS obtained by counter arrangement could be reduced by 0.56 °C compared with the parallel arrangement at Re = 152. Both the ΔP and h were significantly influenced by concentrations. When Re reached 262, ΔP of 5 wt% MPCS in wave minichannel with 5 mm wavelength was 44 % larger than that of pure water in straight minichannel, which would consume more pumping power. However, the heat dissipation performance was improved significantly and Nusselt number in double-layered wavy minchannels also increased with the wavelength decreasing. Therefore, Performance Evaluation Criteria (PEC) was proposed to evaluate the overall performance, which was also greatly influenced by particle concentration and channel wavelength. After optimization, the highest PEC of MPCS in the wavy minichannel was achieved to 1.60. Because of the wavy minichannel with concave-convex structure, the obstacle of total thermal resistance became smaller for the wavelength decreasing. These findings of MPCS in minichannel can provide a good theoretical basis and engineering application in the cooling technology of CPV.

Performance analysis of groove-cut tube based double-pipe heat exchanger using microencapsulated phase change material slurry

It is commonly accepted practice to improve a thermal-fluid device by adopting surface enhancement techniques for better heat transfer. On the other hand, Microencapsulated phase change material (MPCM) slurry has been used as a heat transfer fluid (HTF) due to its improved heat capacity and heat transfer performance. The current paper attempted to study the combined effect of the two enhancement methods in a double-pipe heat exchanger. The results were first validated with experimental work taking into account the hydraulic and heat transfer characteristics of the MPCM slurry flow. Groove-cut geometrical models of MGGC, RGC, CGC, and TGC were proposed to modify heat transfer tube geometry. The effect of the number of helical turns (3, 4, 5, and 6-turns) and various Reynolds numbers were also considered for the investigation. The result showed that the proposed groove-cut models demonstrate enhanced flow mixing for MPCM slurry but with a higher friction factor, which increases with increasing helical turns. The impact was also manifested by improving the heat transfer by facilitating a uniform melting of MPCM particles, and the RGC model shows higher performance. The overall thermohydraulic performance assessment showed that the groove-cut tube models outperformed the corresponding plain tube. The highest performance factor value of 1.24 was observed for the RGC model, while the TGC model shows only 1.14 for the 6-turns. Similarly, the Q/Wp ratio indicates that the groove cut models transport more heat than the pumping power requirement for MPCM slurry.

Performance and life cycle assessment of pillow plate heat exchanger utilizing microencapsulated phase change material slurry

The pillow plate heat exchanger is a promising and relatively new heat exchanger design that enhances heat transfer by augmenting flow turbulence. This study focuses on further enhancing the heat exchanger’s performance by utilizing Microencapsulated Phase Change Material (MPCM) slurry which increases the heat capacity of the working fluid. So, the heat transfer characteristics, flow performance, and life cycle assessment of the pillow plate heat exchanger when employing MPCM slurry with varying particle concentrations are evaluated. The investigation takes into account the intricate phenomenon of conjugate heat transfer between channels, enabling a comprehensive analysis of the system's behaviour. To avoid modelling errors, a lab-scale heat exchanger is simulated instead of using periodic boundary conditions to capture the effects of both developing and fully developed regions. The results showed that temperature distribution in the heat exchanger is highly affected by developing regions in both inner and outer channels. Meanwhile, by adding MPCM, a better cooling performance with a lower temperature variation in cold temperatures is provided at the cost of a higher pressure drop. However, 6.2% enhancement in the heat transfer rate is achieved by using a 15% MPCM concentration which is a considerable amount in thermal management systems in industries requiring efficient heat dissipation, such as electronics cooling. The Life Cycle Assessment indicated that although there is a slight increment in emissions as the concentration of MPCM increases, the overall impact is minimal on the environment.

Evaluation of the integrated performance for floor heating using micro-encapsulated phase change material slurry

The micro-encapsulated phase change material (MPCM) slurry has the advantage of high heat transfer performance and heat capacity. Using MPCM slurry in the radiant floor heating (RFH) system could improve the indoor environment, but the overall performance was highly affected by heat transfer and pressure drop. In this paper, the flow and heat transfer model of MPCM slurry was developed and verified. The performance of serpentine and counterflow spiral structures was compared. Afterward, the optimized MPCM slurry material was selected as the heat transfer medium in RFH systems. Meanwhile, the flow and thermal performance of water and MCPM slurry were compared. Finally, the effects of different volume fractions and inlet velocities on integrated performance were investigated. The results indicated that the comprehensive performance of the serpentine system was better than the counterflow spiral. When the volume fraction was 15%, the comprehensive evaluation coefficients of three MPCM slurry heat systems are 17.9%, 22.9% and 13.8% higher than water respectively. MPCMS2 (n-dodecane) was suitable to use as the heat transferring medium in RFH system. Furthermore, as the volume fractions were 10%, 20% and 30%, the optimized velocities were 0.5 m s−1, 0.9 m s−1 and 1.1 m s−1, respectively.

Study on the regeneration process and overall performance of a microencapsulated phase change material slurry dehumidification system

Building on previous findings that showed the efficacy of microencapsulated phase change materials (MicroPCM) in augmenting liquid desiccant dehumidification performance, this study endeavors to further explore the extent of the impact of MicroPCM in the regeneration and the entire dehumidification system. The results of the regeneration experiment on the microencapsulated phase change material slurry (MPCMS) reveal that the addition of MicroPCM impedes regeneration. Specifically, as the concentration of MicroPCM increases, both the regeneration rate and the MPCMS concentration after regeneration decrease, while the regeneration effectiveness exhibits an initial decline followed by an increase. An empirical correlation was proposed to predict the regeneration rate of MPCMS for their future application. The results showed that the addition of MicroPCM led to a decrease in the regeneration rate by as much as 48.1%, when compared to a pure LiCl solution. However, a simulation analysis of the entire system revealed that within a certain concentration range of MicroPCM addition, the coefficient of performance (COP) of the system could still be increased by up to 4.28%. This finding suggests that if a more suitable non-heating regeneration method were used, the addition of MicroPCM could further enhance the overall performance of the liquid desiccant dehumidification system.

Experimental study of phase change microcapsule-based liquid cooling for battery thermal management

Thermal management of power battery is important to ensure the safety of electric vehicle. Coupling phase change materials (PCMs) with liquid cooling technology is an efficient temperature uniformity strategy. In this paper, a self-made microencapsulated PCM (MPCM) was used to prepare MPCM slurry (MPCMS), and three base liquids (water, ethanol, and silicone oil) were evaluated, which confirmed that the silicone oil could maintain slurry without sedimentation for 7 days, providing the best stability. Also, graphene (GE) was introduced to increase the heat transfer rate of slurry. Then the prepared slurries were applied to the prismatic lithium-ion battery module to verify their thermal management performance. The results indicated that the prepared slurries' latent heat, thermal conductivity, and specific heat capacity were all rose with the increase of MPCM concentration. In addition, the slurries' viscosity changed little when the concentration was below 40 wt%. Compared with the blank module, GE-MPCMS-Si could reduce the battery module temperature and the temperature variance by 14.49 °C and 3.8 °C2, respectively. Besides, the influence of flow rate was further investigated, which showed 6 mL/s is the most economical and efficient flow rate option.

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.

Photovoltaic-thermal system combined with wavy tubes, twisted tape inserts and a novel coolant fluid: energy and exergy analysis

To create a highly efficient photovoltaic-thermal (PV-T) system and maximise the energy and exergy efficiency, this study aims to propose an innovative configuration of a PV-T system comprising wavy tubes with twisted-tape inserts. Following the validation of a numerical model, a parametric study has been conducted to assess the geometrical effects of twisted tape and wavy tubes, as well as the coolant fluid type and velocity, on the overall performance of a PV-T system, located in Shiraz, Iran. It is found that employing twisted tape improves the energy and exergy efficiency by approx. 6.3%. The best configuration yields 12.4% and 16.8% increase in energy and exergy efficiency compared to conventional PV systems. This is achieved at 15% volumetric concentration of microencapsulated phase change material slurry. The monthly variation of global horizontal irradiance in Shiraz highly affected the energy and exergy efficiency of PV-T, with July and October exhibiting the most efficient months, corresponding to 90% and 11.3%, respectively.

Numerical investigation of double-walled direct absorption evacuated tube solar collector using microencapsulated PCM and nanofluid

In the present study, the thermal performance of direct absorption solar evacuated tube collectors utilizing CuO nanofluid, CuO/Al2O3 binary nanofluid, and CuO nanofluid combined with microencapsulated phase change material (MPCM) is investigated. The impact of base fluid types (water and ethylene glycol (EG)), nanofluid volume fraction, and flow velocity, are analyzed by the numerical simulation of the collector. Also, two models (single-phase and mixture) are used for simulating the MPCM slurry. Due to the insignificant difference between the results of the single-phase and two-phase models, the single-phase model is recommended to reduce computational time. It is found that the most significant differences in outlet temperature occur using 0.06 % Al2O3+ 0.002 % CuO/water nanofluid and 0.06 % Al2O3+ 0.002 % CuO/EG nanofluid which are equal to 28.34 K, and 36.64 K, respectively. The collector efficiency using binary nanofluids is higher than using CuO nanofluids in both water- and EG-based nanofluids. Results indicate that combining MPCM and CuO nanofluid increases the collector efficiency by 4.53 % and lowers the heat loss by 5.84 %. The simultaneous application of MPCM and CuO nanofluid has the highest efficiency among all working fluids.

Comparative study on the thermal performance of microencapsulated phase change material slurry in tortuous geometry microchannel heat sink

The microencapsulated phase change material slurry (MPCMS) exhibits improved performance in microchannels as a result of its increased latent heat and thermal conductivity. This study investigates the thermo-hydraulic performance of paraffin encapsulated with titanium and a silica shell in straight, wavy, and zigzag rectangular microchannel configurations. The length of the heat sink is 30 mm and its hydraulic diameter is 0.4 mm. A uniform heat flux is supplied at various mass flow rates of 200–400 ml/min with a Reynolds number corresponding to 400–800 at 10, 20, and 30 W/cm2 respectively. Using prepared MPCMS, the performance of selected microchannels is evaluated. The experimental result demonstrates that the MPCMS improves the heat transfer rate of all configurations relative to deionized water (DI). At conditions of medium heat flux (i.e., 20 W/cm2) and high flow rate (i.e., Re = 780), the low titanium (Ti) encapsulated slurry-based straight microchannel has a higher Nusselt number (i.e., 6.5%) than the DI. This enhancement is further improved by 21.9% and 27% in wavy and zigzag microchannels, respectively. Under the same conditions, the zigzag microchannel with low Ti concentration MPCM (i.e., 1%) demonstrates 77% and 234.7% higher performance than the wavy and straight channels, respectively.

Effectiveness of MPCMS on Straight, Dimple-cavity & Rib-groove microchannel heat sinks – a comparative study

ABSTRACT The novelty of microencapsulated phase change material slurry (MPCMS) in the microchannel is a proven technique for enhancing the heat transfer due to its combination of high latent heat transfer and surface area. In this experimental investigation, the paraffin is encapsulated with silica and titanium shells, and its thermal performance is compared with three different configurations like straight, dimple-cavity, and rib-groove microchannel heat sinks. The operating parameters are mass flow rate of 200–400 ml/min with Reynolds number (Re) 400–1350, heat flux of 10, 20, and 30 W/cm2, and 1% and 2% of mass fraction (concentration of the MPCM in DI) with constant inlet sub-cooling 25°C. From the results, at Re. 780 and heat flux of 20 W/cm2, the Nusselt number (Nu) shows an improved performance of 6.5% with Ti-1 in the straight channel configuration, when compared to plain DI. Further, Nu enhancement is up to 11.5% in the dimple-cavity and 26.9% in the rib-groove microchannel heat sinks under the same conditions. To clarify the effectiveness of MPCMS in three configurations, the measurement of COP is conducted. The results reveal that the heat transfer outweighs the required pumping power in all three configurations. Overall, the Rib-groove microchannel shows enhanced heat transfer of 131.6% than straight channel heat sinks and 47.85% higher than the dimple-cavity channel using Ti-1.

Experimental evaluation of latent heat use of a microencapsulated phase change material slurry in spraying

A spraying system was constructed with a microencapsulated phase change material (MPCM) slurry as the working medium to weaken the adverse effects of the slurry's high viscosity and low thermal conductivity on heat transfer in a wall tube heat exchanger. The temperature distributions of pure water and MPCM slurry were first obtained through infrared thermal imaging in spraying. Furthermore, the latent heat use of MPCM slurry was investigated through a new method based on the temperature properties of the phase change fluid, in which the working and phase change temperature ranges are matched. The heat-mass transfer characteristics are compared and discussed with those of the base fluid, and the latent heat use of 10wt% MPCM slurry containing the core material n-docosane (C22H46). The experimental results indicate that the phase change enables the MPCM slurry droplets to maintain a higher temperature than a fluid with no phase change or base fluid. Different application modes (static and spraying) have correspondingly different phase change temperature ranges owing to supercooling, and the degree of matching between the working and phase change temperature ranges has a critical impact on the latent heat use of the MPCM slurry. Finally, comparing the heat transfer coefficients and Lewis numbers between the base liquid and MPCM slurry reveals that the phase change not only enhances the heat transfer but also slightly reduces water evaporation compared with pure water spraying.

Experimental study of the surface vapor pressure of a microencapsulated phase change material slurry liquid desiccant within the entire temperature range of a dehumidification system

The surface vapor pressure is a critical physical property of a liquid desiccant, which has a direct influence on the mass transfer driving force in the dehumidification and regeneration process. In this study, a measurement system for the surface vapor pressure of the microencapsulated phase change materials slurry (MPCMS) was built using a static method. The surface vapor pressure of the MPCMS at 293.2 K–353.2 K was measured, which covered the entire range of dehumidification and regeneration. Experimental results showed that the surface vapor pressure of the MPCMS decreased compared with that of the pure LiCl solution. The surface vapor pressure drop ratio of the MPCMS increased with increasing MicroPCM and LiCl mass concentrations. The phase transition of the MicroPCMs intensified the drop in the MPCMS surface vapor pressure. When the MicroPCM and LiCl mass concentrations were 2 % and 40 %, respectively, and at the phase transition temperature of 303.2 K, the vapor pressure drop ratio reached a maximum of 17 %. A correlation for the MPCMS surface vapor pressure calculation was proposed, and the deviation between the calculated and measured values was less than 10 %. The results of this study provide basic data for the future development of the MPCMS liquid desiccant system.

Experimental and Photothermal Performance Evaluation of Multi-Wall Carbon-Nanotube-Enhanced Microencapsulation Phase Change Slurry for Efficient Photothermal Conversion and Storage

Melamine formaldehyde was used as the shell material and n-eicosane as the core material with the method of in situ polymerization to synthesize microencapsulated phase change materials (MPCMs). To enhance the thermophysical characteristics and photothermal conversion performance of the MPCM slurry, multi-wall carbon nanotubes were added, and the microscopic morphology and thermophysical parameters of the MWCNT-MPCM slurry were analyzed. The thermal conductivity, viscosity, and photothermal conversion properties of the slurry were examined. The results indicated that the synthesized MPCMs were nucleated and unbroken, with a spherical form and a latent heat of phase transition of up to 135.92 kJ/kg. The MPCM was stable when dispersed in water, and its thermal conductivity rose with the temperature but slightly decreased during the phase transition period. The viscosity rose with the addition of the MPCM, with a jump at 20% MPCM content. The addition of MWCNTs had a minor effect on the material’s thermophysical properties. The thermal conductivity increased from 0.55 W/m·°C to 0.6 W/m·°C when MWCNTs were added to the material. The viscosity of a 20% MPCM slurry exceeded 3000 mPa·s when 0.5% MWCNTs were introduced. Under 1 sun of sunlight, the mixture’s peak temperature could reach 60 °C at 0.5% MWCNT concentration. The MWCNT-MPCM slurry is capable of producing efficient solar photothermal conversion without sacrificing other thermophysical properties, and it has several applications in solar energy consumption and thermal engineering.