Phase Change Material Slurry Research Articles

Multi-scale modeling and investigation of thermo-fluidic performance of microencapsulated phase-change material slurry

Using the microencapsulated phase change material (MPCM) slurry is an effective measure to improve the balance between the supply and demand of energy with renewable and clean energy sources. However, most previous studies have neglected the nonlinear release of phase-change latent energy of the microcapsules and used an empirical modification of the heat transfer coefficient between the two phases to ensure that the simulation results were consistent with experimental data. In order to avoid the empirical modification of the heat transfer coefficient, a new multiscale model was developed by combining the heterogeneous multiscale method (HMM) framework and the correlative multi-scale methodology, whose numerical results are in good agreement with the experimental results in terms of the flow and heat transfer. By introducing the MPCM nonlinear phase change behavior into the thermal performance of the MPCM slurry, this multiscale model can be used to better understand the mechanism of the enhanced heat transfer of MPCM for the slurry. By the new model, the heat transfer performance of the MPCM slurry under various capsule sizes and concentrations is discussed by analyzing the slurry temperature distribution, liquid volume fraction of the PCM, and heat transfer coefficients. The results show that a smaller capsule size has the advantage of improving the heat transfer coefficient when the size is above 100 μm. Furthermore, the average heat transfer coefficient first increases and then decreases as the concentration increases, and the value reaches a maximum of 106.84 W/(m2∙K) when the concentration is 20 vol%.

Investigation of Counterflow Microchannel Heat Exchanger with Hybrid Nanoparticles and PCM Suspension as a Coolant

The effect of the hybrid suspension on the intrinsic characteristics of microencapsulated phase change material (MEPCM) slurry used as a coolant in counterflow microchannel heat exchanger (CFMCHE) with different velocities is investigated numerically. The working fluid used in this paper is a hybrid suspension consisting of nanoparticles and MEPCM particles, in which the particles are suspended in pure water as a base fluid. Two types of hybrid suspension are used (Al2O3 + MEPCM and Cu + MEPCM), and the hydrodynamic and thermal characteristics of these suspensions flowing in a CFMCHE are numerically investigated. The results indicated that using hybrid suspension with high flow velocities improves the performance of the microchannel heat exchanger while resulting in a noticeable increase in pressure drop. Thereupon, it causes a decrease in the performance index. Moreover, it was found that the increment of the nanoparticles’ concentration can rise the low thermal conductivity of the MEPCM slurry, but it also leads to a noticeable increase in pressure drop. Furthermore, it was found that as the thermal conductivity of Cu is higher than that for Al2O3, the enhancement in heat transfer is higher in case of adding Cu particles compared with Al2O3 particles. Therefore, the effectiveness of these materials depends strongly on the application at which CFMCHE is employed.

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.

Experimental study on micro-encapsulated phase change material slurry flowing in straight and wavy microchannels

Abstract Micro-encapsulated phase change material slurry (MPCS) is a novel heat transfer fluid with a good promise due to its latent heat of phase change material during melting/solidification. In this context, an experiment system was set up to study the flow and heat transfer performances of MPCS in straight and wavy microchannels. The results showed that the pressure drop increased with more micro-encapsulated phase change material (MEPCM) adding to the fluid. The pressure drop of the MEPCM slurry flowing in the wavy microchannel was much larger than that in the straight microchannel, especially with more particles loading in the fluid and slurry flowing at large Re. Compared to water, MPCS displayed superior heat transfer performance during phase change region due to latent heat absorbed during MEPCM melting. Moreover, compared to MPCS flowing in the straight microchannel, with perfect performance, the heat transfer of MPCS in the wavy channel would be enhanced as 1.29 times, and 1.7 times than that of pure water.

Dispersion stability and thermophysical properties of microencapsulated phase change material slurry for liquid desiccant dehumidification

The dispersion stability and the thermophysical properties of the microencapsulated phase change material slurry (MPCMS) for liquid desiccant dehumidification were investigated experimentally. The results show that, the dispersion stability of the MPCMS can be improved greatly by adding surfactant. The maximum absorbency of MPCMS with polyoxyethylene sorbitan monooleate (Tween80) is 4.1 times that of MPCMS with cetyltrimethyl ammonium bromide (CTAB). The monolayer adsorption model is suitable for predicting the optimal mass content of surfactant with the maximum relative error of 13.3%. The thermal conductivity of MPCMS is lower than that of the base fluid and decreases with the increasing MicroPCMs concentration, when the mass fraction of MicroPCMs increases from 0% to 2.0% at the temperature of 20 °C and 40 °C, the thermal conductivity decreases by 25% and 14.8%, respectively. When the mass concentration of MicroPCMs is lower than 1.0%, the thermal conductivity of MPCMS keeps increase with the temperature rise. While the mass concentration of MicroPCMs ranges from 1.0% to 2.0%, the thermal conductivity of MPCMS increases firstly and then declines gradually. Moreover, an improved interfacial layer based thermal conductivity calculation correlation was proposed, in which the influence of temperature and concentration of MPCMS were considered, the maximum deviation and mean deviation between the calculated value and the experimental one are 5.62% and 1.85%, respectively. In the range of phase transformation temperature, the specific heat capacity of the slurry can be significantly improved by the MicroPCMs, the maximum specific heat capacity of the MPCMS reaches 2.3 times that of the pure lithium chloride aqueous solution. In addition, the effect of the mass concentration of MicroPCMs on the specific heat capacity is much greater than that of the temperature and the mass concentration of LiCl. The findings provide experimental foundation and guidance for the practical application of MPCMS in liquid desiccant dehumidification.

Research on falling film dehumidification performance of microencapsulated phase change materials slurry

In the process of liquid desiccant dehumidification, the temperature-rise of the desiccant solution caused by moisture absorption will seriously affect the dehumidification capacity and performance. It is expected that the temperature rise of solution can be restrained by adding microencapsulated phase change materials (MicroPCMs) into the liquid desiccant solution. In this paper, based on computational fluid dynamics (CFD) method, two-dimensional models of flat plate and corrugated plate falling film dehumidification of the microencapsulated phase change material slurry (MPCMS) were developed and validated. The dynamic boundary method was used to determine the interfacial mass transfer coefficient. The influences of several factors on the dehumidification performance, including the concentration of MicroPCMs, the inlet temperature of the MPCMS and the falling film plate configuration, were investigated. The results show that, adding MicroPCMs into the liquid desiccant solution is beneficial to the dehumidification performance improvement. The inlet temperature of MPCMS is a very critical variable. When the inlet temperature of the slurry is in the phase transformation temperature range of MicroPCMs, with the adding of the microcapsule, the temperature rise in dehumidification process can be restrained, and the moisture removal performance can be improved significantly. When the MPCMS inlet temperature is at the phase transformation onset point, and the concentration of MicroPCMs is 5%, the water condensation rate is 14.2% higher than that of the base solution. Moreover, it’s not that the more microcapsules added, the larger mass transfer coefficient is. There is an optimum concentration of MicroPCMs to achieve the maximum interfacial mass transfer coefficient. The corrugated plate configuration is more conducive to the dehumidification enhancement by the MPCMS.

Preparation and thermal properties of encapsulated 1-Decanol for low- temperature heat transfer fluid application

The high heat-carrying capacity of encapsulated phase change material slurries (EPCMS) is instrumental in improving the performance of heat transfer fluid system (HFS). In the present study, we analysed 1-Decanol, a low-cost organic PCM, encapsulated in a urea-formaldehyde shell (UFS) for potential usage in low-temperature heat transfer fluid application (LTHFA). Discrete and uniformly shaped EPCM capsules have been prepared with an encapsulation efficiency of 59.56 % at an optimised core content of 10 g. Further, the thermal response of EPCM was enhanced by preparing EPCM modified (EPCMM) with 2, 6, and 10 wt% GnP or CuO nanoparticles (NP). SEM analysis revealed the rough and smooth surface morphologies of EPCMM with GnP and CuO, respectively. Particles size analysis showed that the prepared capsules are in the submicron size, and FTIR results revealed that 1-Decanol, UFS, and NP are chemically compatible with each other. DSC, FTIR, and TGA results proved that 1-Decanol had been encapsulated inside UFS. Based on the acquired results, EPCMM with 6 wt% GnP and 10 wt% CuO exhibited the most suitable thermal characteristics with an encapsulation efficiency of 56.14 % and 54.52 %, respectively, and thermal conductivity enhancement of 2.19 and 1.98 times that of EPCM, respectively. Experimental results concede that the prepared capsules have suitable thermal and heat transfer characteristics, proving its applicability in LTHFA.

Microencapsulated phase change materials as slurries for thermal energy storage: A review

Abstract Phase change materials (PCM) have the potential to store and release large amounts of thermal energy by undergoing phase transitions from solid to liquid. The microencapsulation technique improves chemical stability and enhances the thermal properties of PCMs, thereby implement these materials for a wide range for applications. The dispersion of these materials into a base fluid (carrier fluid) results in a microencapsulated phase change material slurry. The slurry being in a state of flow can store and release energy with minimal temperature rise. This paper reviews the methods available for slurry preparation and discusses the techniques of characterization. In further, the applications of these slurries in the fields of thermal energy storage are also presented.

Gallium-indium nanoparticles as phase change material additives for tunable thermal fluids.

One of the most critical limitations for high-power electronics today is thermal management and routing thermal energy efficiently away from thermally sensitive components. A potential solution to this problem is the integration of cooling channels in close proximity to thermally sensitive materials for increased heat removal efficiency. These channels typically use single phase fluids (liquid), dual phase fluids (vapor-liquid), or suspended organic/polymer phase change material particles in a fluid (PCM slurry). Expanding upon the latter, this work demonstrates the use of inorganic Ga-In alloy nanoparticles (NPs) suspended in a traditional thermal transport fluid to simultaneously (1) increase the overall thermal diffusivity of the fluid and (2) serve as a cyclable solid-liquid PCM slurry which provides a thermal sink that is definable over a wide range of relevant temperatures for power electronics. Herein, the relationship between particle size, composition, and volume fraction are explored as they relate to the PCM slurry optimum working temperature, total energy absorption, and rheological properties. A mere 0.10 volume fraction of Ga-In NPs is reported to increase the overall thermal conductivity by nearly 50% and can be optimized to melt at temperatures as low as -46 °C. Based on thermal measurements, it was observed that these nanoparticle systems lack the preference to form αGa and have a large thermal hysteresis due to exhibiting extreme undercooling, with crystallization temperatures near -130 °C, enabling opportunities within extreme environments such as space applications or low temperature imaging systems.

Determining the Heat of Fusion and Specific Heat of Microencapsulated Phase Change Material Slurry by Thermal Delay Method

This paper details an experimental study that was performed to investigate the specific heat of microencapsulated phase change material (mPCM) slurry and its heat of fusion at the PCM phase change transition temperature. Six samples (mPCM slurry concentrate with the water solution of propylene glycol used as a main base liquid) were prepared. As the concentrate contains 43.0% mPCM, the actual mass fraction amounts to 8.6, 12.9, 17.2, 21.5, 25.8, and 30.1 wt%, respectively. The thermal delay method was used. Samples were cooled from 50 °C to 10 °C. A higher concentration of microcapsules caused a proportional increase in the specific heat of slurry at the main peak melting temperature. The maximum value of the specific heat changed from 9.2 to 33.7 kJ/kg for 8.6 wt%, and 30.1 wt%, respectively. The specific heat of the mPCM slurry is a constant quantity and depends on the concentration of the microcapsules. The specific heat of the slurry (PCM inside microcapsules in a liquid form) decreased from 4.0 to 3.8 kJ/(kgK) for 8.6 wt%, and 30.1 wt% of mPCM, respectively. The specific heat of the slurry (PCM inside microcapsules in a liquid form) was higher than when the PCM in the microcapsules is in the form of a solid and increased from 4.5 to 5.2 kJ/(kgK) for 8.6 wt% and 30.1 wt% of mPCM, respectively.

Numerical investigation on laminar forced convection of MEPCM-water slurry flow through a micro-channel using Eulerian-Eulerian two-phase model

A numerical study of water-based microencapsulated phase change material (MEPCM) slurry flow through a wide rectangular microchannel is performed using an in–house FORTRAN based solver. Eulerian-Eulerian two-phase approach, which is more accurate than the commonly used single-phase approach, is used in this study for modeling MEPCM-water slurry flow. Compact finite difference scheme with sixth-order accuracy is used for discretizing convective terms in the governing equations of liquid and solid phases. An extensive parametric study is performed using two phase change materials, namely n-octadecane and n-eicosane. Results show that significant enhancement of heat transfer is observed for the MEPCM-water slurry compared to pure water when particles undergo melting. It is also observed that the heat transfer enhancement increases with an increase in particle concentration. A drop of 2.6 K in mean temperature is observed for the slurry compared to water when 20% volume concentration of MEPCM-water slurry is used. For a 5% volume concentration of n-octadecane MEPCM-water slurry at a wall heat flux of 100kW/m2, there exists an optimum Reynolds number around 200, at which the heat transfer performance of the slurry is maximum. Results show that a significant change of the local Nusselt number with a decrease in particle size from 13.2 μm to 0.5 μm. Present results show that using a combination of different phase change materials with varied melting temperatures can help maintain the melting of particles throughout the channel, leading to enhancement of heat transfer performance. The present results are validated with numerical and experimental results available in the literature.

Barriers facing Micro-encapsulated Phase Change Materials Slurry (MPCMS) in Photovoltaic Thermal (PV/T) application

Photovoltaic generation is a temperature-dependent technology, with each 1 °C temperature rise of the PV module, the efficiency drops by 0.2–0.5 % depending on the material of the PV cells. MPCM slurry is employed in the study to work as a cooling medium that circulates through a serpentine pipe to absorb heat from the back of a (0.8m x1.6m) 1.28 m2 PV module for cooling purpose. The paper presents the experimental rig, the procedure of using MPCM slurry in PV/T and the limitations to its application. The experiments run under specific laboratory conditions with three concentrations of MPCM (5%, 10%, and 15%) in the slurry to test the effect of the major parameters such as radiation, Reynolds number and the concentration of the MPCM in the slurry on the performance of the system. The results showed that the system achieves 83% overall efficiency and 5.9 coefficient of performance (COP) when it operates with 10 % MPCM concentration slurry. Despite the good experimental outputs, the system is facing some problems that impede its application mostly due to the complexity of the cooling medium (MPCMS).

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.

Numerical simulation of convective heat transfer of microencapsulated phase change material slurrys in a circular tube

For the Microencapsulated Phase Change Materials slurry(MPCMs)having a large latent heat during the phase change period and having a higher heat convection coefficient than the single-phase fluid, it has become a new thermal fluid of widespread investigation. In this paper, the model of equivalent specific heat is presented to numerical simulate the laminar convective heat transfer performances of MPCMs in a tube under the condition of constant heat flux. The heat transfer of MPCMs in a tube is investigated under various concentrations of MPCMs and heat flux and the correlation of the convective heat transfer with MPCMs in a tube is obtained.

Inhibition of exothermic runaway of batch reactors for the homogeneous esterification using nano-encapsulated phase change materials

Reaction inhibition is a promising option as an emergency measure to mitigate hazards caused by exothermic runaway reactions. The applications of phase change materials (PCMs) as inhibitors of runaway reactions have been influenced by thermal energy storage technologies. In this work, nano-PCMs powders with silica shells were fabricated using the sol–gel method at alkaline conditions. The prepared nano-PCMs had perfect core–shell microstructures and spherical morphologies, with an average encapsulated PCM particle diameter of 717.34 nm. In addition, the nano-PCMs exhibited high latent heats of fusion (129.1 J g−1), which could inhibit the uncontrolled self-heating caused by runaway reactions through conversion of the heats of reaction to the latent heats of PCMs. The homogeneous esterification of propionic anhydride with n-butanol catalyzed by sulfuric acid was chosen as target reaction with risk of exothermic runaway. Inhibition experiments was conducted in a batch reactor coupled with an in situ FTIR spectrometer. The heat transfer performance of reactant flow was studied to analyze the mechanism of thermal runaway inhibition with nano-PCMs. The results revealed that thermal runaway can be halted by applying nano-PCMs and that the reaction can proceed to completion steadily. The effect of Re on heat transfer performance was enlarged with addition of nano-PCMs. The enhancement in the heat transfer coefficient for PCM slurry was proved. Furthermore, the effectiveness of the thermal runaway inhibition can be significantly influenced by the warning temperature, stirring rate, and mass of added nano-PCMs. The applications of nano-PCMs for runaway reaction inhibition holds great potential for use in industrial processes.

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.

Experimental study on characteristics of a nano-enhanced phase change material slurry for low temperature solar energy collection

Phase change material (PCM) slurry with nanoparticles added has been proved to improve the performance of solar thermal storage. While, it is found that previous studies have not systematically dealt with the thermo-physical properties of PCM slurry (PCS) based on the type and mass fraction of nanoparticles and its stability and viscosity. Therefore, the purpose of this research is to experimentally evaluate the effects of nanoparticles and dispersants on the thermal-physical properties of PCS and determine the role and the associated optimal mass fraction ratio of dispersants in promoting the stability of suspension. The 30% mass fraction alkyl hydrocarbon PCS was employed for our study. Three types of nanoparticles (i.e., Cu, Al2O3 and TiO2) were selected for the study on performance improvement of PCS. Static and dynamic stability were measured by the static precipitation method and thermal cycle method. Thermo-physical properties including viscosity, thermal conductivity and latent heat were measured by a digital display rotary viscometer, a thermal conductivity measuring instrument and a differential scanning calorimeter, respectively. The experimental results revealed that the nanoparticles can improve the thermal properties of PCS, while the dispersants can improve the stability of the nano-enhanced PCS. The PCS with 0.1% TiO2 added had the best latent heat property and minimum viscosity. The 30% mass fraction PCS with 0.1% TiO2 and 0.1% SDBS added was the ideal choice for the application on low temperature solar energy collection.

Experimental and numerical investigation of microencapsulated phase change material slurry heat transfer inside a tube with butterfly tube inserts

In this research, the effect of microencapsulated phase change material (MEPCM) addition to water and producing MEPCM slurry (MPCS) for heat transfer augmentation was investigated, experimentally and numerically. Copper tube with and without butterfly tube inserts (BTI) was used as a test section in a laboratory apparatus and was heated at a constant heat flux. Experiments were performed to determine heat transfer coefficient of MPCS at the Reynolds number of 1500 and 2600 and containing up to 15 wt% MEPCM. The effect of tube inserts type was also investigated numerically. The results showed that for the plain tube, the addition of MEPCM to the base fluid improves heat transfer rate by up to 40.3% and 38.9% for non-laminar and laminar flow regimes, respectively. Moreover, when the BTI was used, it was observed that the heat transfer rate increased by up to 234% for pure water and by up to 180% for the 10 wt% MEPCM slurry under laminar flow regime. This is due to the turbulence induced in the flow and the disturbance to the thermal boundary layer. Moreover, tube inserts cannot have a significant effect on the heat transfer under non-laminar flow regimes. The inserts only increase the pressure drop in these conditions. However, performance evaluation criteria (PEC) analysis indicated that 5% MEPCM slurry provides the highest ratio of heat transfer enhancement to pressure drop increment. Furthermore, in the simulation section, the results clearly indicated that the inserts shape have no significant effect on the heat transfer coefficient.

Exergy and energy analysis of wavy tubes photovoltaic-thermal systems using microencapsulated PCM nano-slurry coolant fluid

To develop a more efficient water-cooled photovoltaic-thermal system, energy and exergy analysis of a photovoltaic-thermal system with wavy tubes are investigated numerically using different coolant fluids. A comparison between the straight tube and wavy tubes is conducted for various wavelengths and wave amplitudes. The geometrical parameters of the wavy tubes as well as the velocity of the coolant fluid are examined. Besides, the consequences of coolant fluid including water, Ag/water nanofluid, microencapsulated phase change material slurry, and also a new type of cooling fluid called microencapsulated phase change material nano-slurry are studied. The results show that the electrical, thermal, and exergy efficiencies of the photovoltaic-thermal module enhance by using the wavy tubes compared with the corresponding straight tubes. By declining wavelength in a constant wavelength/amplitude, the heat absorbed by the heat transfer fluid raises. For the best configuration, the primary and exergy efficiencies of the module increase by 6.06% and 4.25%, respectively, for the wavy tubes system compared with those for the straight unit. Furthermore, in both configurations, by increasing the inlet velocity, the overall performance of the photovoltaic-thermal module increases due to a higher heat transfer rate. The results also reveal that among different types of cooling fluids, the microencapsulated phase change material nano-slurry has higher performance in terms of both energy and exergy efficiencies due to having higher thermal conductivity and heat capacity. By employing the wavy tube and the novel proposed coolant fluid, the primary and exergy efficiencies increase in comparison with a typical photovoltaic-thermal module.