Temperature Distribution In Phase Change Material Research Articles

Heat transfer performance of copper foam/paraffin composite phase change material under different centrifugal forces-A visual experimental study

Copper foam is used to enhance the heat transfer of phase change material (PCM) due to its high thermal conductivity. However, its porous structure can restrict the convection of PCM. The natural convection of PCM embedded in copper foam under external force remains unclear. A visual experimental system was established to investigate the effect of copper foam on the heat transfer process of PCM under external force. The phase interface, temperature distribution, and heat storage rate of composite PCM (CPCM) were conducted under centrifugal forces from -5 g to 5 g. Results indicate that there is a significant difference in the melting rate and temperature distribution of PCM under different forces. Under forward force, the convection of PCM is inhibited, and the isotherm is parallel to the end-state isobars line, increasing the total melting time of CPCM and creating a large temperature gradient near the heat source. Conversely, under the backward force, the melting rate of CPCM is increased due to the enhanced natural convection of liquid PCM. The development of isotherms is influenced by buoyancy, which results in a more uniform temperature distribution of CPCM. However, the enhancement effect of the backward force is limited when it exceeds -3 g. In general, CPCM exhibits more apparent improvement in heat transfer performance under the backward force. This article provides references for the optimization design of thermal management systems.

EFFECT OF METAL FOAM FILLING POSITION AND POROSITY ON HEAT TRANSFER OF PCM: A VISUALIZED EXPERIMENTAL STUDY

The application of phase change material (PCM) in energy storage systems is limited by its low thermal conductivity. One of the effective methods to improve the thermal conductivity of PCM is to embed foam metal within it. To investigate the effects of foam metal infill position and porosity on the melting process and temperature distribution of PCM, a visualized experimental system study is built. Paraffin is employed as the PCM with a melting point of 62°C, while 85%, 90%, and 95% porosity copper foams are chosen in the experiment. The evolution of the liquid-solid phase interface and the temperature distribution in the PCM are recorded. Singlelayer filling schemes show that placing copper foam closer to the bottom accelerates melting, while double-layer schemes further optimize the melting time and temperature distribution. Additionally, decreasing the porosity of copper foam enhances heat transfer, shortening melting times. The study introduces a melting efficiency index, demonstrating that optimizing filling schemes and porosities improves the overall melting performance. When the copper foam with 90% and 85% porosity is arranged in the middle and bottom layers, respectively, the complete melting time is shortened by 38.2% and the maximum and average temperature differences are reduced by 30.0% and 45.2%, respectively, compared with pure paraffin. The findings contribute valuable insights into designing efficient PCM systems for thermal energy storage applications, emphasizing the importance of copper foam arrangement and porosity optimization.

Simulation and optimization of square fin concentric tube heat storage exchanger

The square fin was used to improve the heat transfer rate of the concentric tube phase change heat exchanger. The effects of fin spacing, fin arrangement, and fin length on the melting process of phase change material (PCM) were studied. The influence and mechanism of non-uniform fin arrangement were discussed in detail. The liquid phase distribution and temperature distribution of PCM with time were analyzed. The results indicated that the heat exchanger with square fins can significantly improve the heat storage rate and shortened the complete melting time of PCM. Compared with heat exchangers without fins, the melting time of PCM in a 40 mm equidistant fin heat exchanger was shortened by 15.85%, and that in a 70 mm, non-uniformly spaced fin heat exchanger was shortened by 36.79%. Due to the different distances between the square fins and the outer boundary of the concentric tube, the temperature distribution near the square fin showed anisotropy, which enhanced the melting rate of PCM. The sensitivity order was fin arrangement > fin length > fin spacing. The research results can provide a reference for the design of phase change heat exchangers.

Comparative study of performance enhancement of latent thermal energy storage system with copper porous fin

Phase change material (PCM)-based thermal energy storage (TES) has attained significant attraction towards energy savings and ensures a continuous energy supply. However, the lower thermal conductivity of PCM impedes the efficient transfer in the storage systems, thereby causing longer charging time. Therefore, this paper introduces a novel heat transfer augmentation technique by incorporating copper porous fins in the shell-tube latent heat thermal energy storage. Further, to demonstrate the contribution of porous fins in heat transfer improvement, full-foam, solid-fin and without-fin TES systems are also evaluated and compared. A two-dimensional axisymmetric numerical model is developed and validated with in-house experimental results. It is found that conduction strongly affects the solidification process, exhibiting a greater response rate than the melting process of heat transfer enhancement techniques. Full-foam has higher melting and solidification rates, followed by solid-fin, porous-fin and without-fin. Compared to the without-fin configuration, the temperature response rates of the full-foam, solid-fin and porous-fin are improved by 169.9 %, 44.8 % and 41.88 %, respectively, during the melting process. Moreover, it is revealed that the porosity of foam has a marginally higher impact on the liquid fraction than the pore density. Further, the inclusion of porous-fin and full-foam leads to more uniform temperature distribution in PCM during melting and solidification compared to solid fin and without-fin. Therefore, the porous-fin and full-foam may be utilised for electronic cooling and battery thermal management, which requires uniform cooling at faster rates.

Study on improving the storage efficiency of ocean thermal energy storage (OTES) unit by using fins

It is a central challenge for energy self-supplied underwater vehicles converting the huge ocean thermal energy to electrical energy effectively. However, the energy storage efficiency of ocean thermal energy storage (OTES) unit limits the conversion efficiency. Fins are proposed for OTES unit to improve energy storage efficiency in this paper. Firstly, this paper develops a non-stationary model of solidification heat transfer for OTES unit and uses FLUENT to accomplish its numerical analysis. Then, the influence of radial fin and fractal fin on the solidification behavior of phase change material (PCM) are compared. Finally, several fractal fins with different fractal levels, bifurcation angles and ambient temperature are analyzed for the evolution of the liquid phase rate and temperature distribution of PCM. The results show that fractal fins can reduce the solidification time of PCM by 34.46% compared with radial fins. Furthermore, the solidification rate of PCM can be improved by increasing the number of fractal levels and choosing a proper bifurcation angle. However, the solidification behavior of PCM changes slightly when the fractal level increases to 3. The bifurcation angle of 90° is appropriate for practical applications. Furthermore, keeping the temperature difference above 10K can achieve faster solidification.

Experimental study on thermal performance of a mobilized thermal energy storage system: A case study of hydrated salt latent heat storage

A mobilized thermal energy storage (M-TES) system was proposed to utilize the renewable energy or recover the industrial waste heat in this paper. The M-TES system with 215 kg sodium acetate trihydrate as phase change material (PCM) filled into a tube-in-tank heat exchanger was designed and experimental tests were conducted to evaluate its thermal performance. The charging-discharging behavior of M-TES system was observed and temperature evolutions of PCM and heat transfer fluid (HTF) were monitored. The charging process of the M-TES system could be accomplished in 1200 s; while for energy discharging process, it took a little longer (1400 s) due to the prevention of natural convection. It also revealed that the non-uniform temperature distribution of PCM would result in asynchrony of melting/solidification. The PCM in the middle part of the tubes would melt at first, whereas the temperature of the PCM close to the end of the tubes increased much slower. The temperature difference was much more significant during the discharging process. Super cooling could be found easily for the PCM in the ends of tubes. The released heat in the discharging process was applied to heat the cooling water to mimic the domestic consumption of hot water to investigate the thermal performance of energy discharging. With perfect performance of our indirect contact heat exchanger, the thermal efficiency was estimated of 79.4%. Our tests would provide an experimental basis for the application of the low-temperature mobilized LHTES system.

Experimental and modeling study on thermal performance of hydrated salt latent heat thermal energy storage system

Phase change material (PCM) holds tremendous promise in the fields of renewable energy utilization and waste heat recovery. In this context, a series of experiments of low-temperature hydrated salt latent heat thermal energy storage (LHTES) system have been conducted to investigate its thermal performance and charging-discharging behavior. Sodium acetate trihydrate mixed with nucleating agent and thickening agent was applied as the PCM and filled into the experimental tube. The temperature evolution of PCM was observed and thermal properties were measured. Numerical model was established to monitor the phase transition process and predict the temperature distribution of PCM filled tube, to make a comparison with the experimental results. It revealed that heat conduction played predominate role in heat transfer when the PCM temperature was below the fusion value, whereas the natural convection was the controlling mode when liquid PCM appeared during the phase transition process. The tube diameter and flow rate were studied to present their effects on the performance of heat storage/release. Compared to smooth tubes, the stainless steel fins and aluminum fins with various thickness added to inside of the tube to enhance the heat transfer. It was found that the heat transfer between thermal fluid and PCM relied greatly in the geometry of the storage tube and fins attribution. The optimized fins geometry can effectively reduce the charging time and discharging time by 27% and 24%, respectively. Our conclusions drawn from this research can provide a theoretical basis for the application of the low-temperature hydrated salt LHTES system.

Application of Paraffin Based Nanocomposite in Heat Pipe Module for Electronic Equipment Cooling

The paper reports the thermal performance of heat pipe module with paraffin and paraffin based nanocomposites as energy storage material (ESM) for electronic cooling. The adiabatic section of heat pipe is covered by the phase change material (PCM) stored in a container made of acrylic material. Here, paraffin is used as phase change material (PCM). PCM can absorb and release thermal energy depending upon the fluctuations in the heating load. Tests are conducted to obtain the temperature distributions in PCM during charge/discharge processes. Present study utilizes two different ESM (paraffin and nanocomposite) and different working fluid for heat pipe (water and nanofluid) in the cooling module. The addition of CNTs in paraffin stores higher amount energy compared pure paraffin material for same operating conditions. The cooling module with nanofluid charged heat pipe and paraffin as ESM found to save higher fan power consumption compared to the cooling module that utilizes only a heat pipe

Investigation of PCM-assisted heat pipe for electronic cooling

Today, higher-power computer chips are available, but they generate too much heat that irreparably damages inside components. In this paper, a horizontal phase change material (PCM)-assisted heat pipe system for electronic cooling was introduced asa potential solution to this problem. A computational fluid dynamic model was developed and validated to assist the investigation. A surface temperature profile along the heat pipe was used to validate the CFD model. The liquid fraction and temperature distribution of PCM were reported during the charging process at different input powers. It was found that the PCM-assisted heat pipe provided up to 86.7% of the required cooling load in the working power range of 50–80W. Contribution of PCM was calculated to be 11.7% of the provided cooling load and preventing heat dissipation.

Experimental Investigation of a Spiral Tube Embedded Latent Thermal Energy Storage Tank Using Paraffin as PCM

Latent thermal energy storage (LTES) is widely used in excess energy reservation. The performance of a LTES unit is critical for its application. In this study, the spiral tube embedded LTES tank is investigated experimentally, with a composite of paraffin as the phase change material (PCM). Temperature distribution of PCM in the tank was obtained, for both charging and discharging processes. The results showed that during the charging process, the temperature of upper part of PCM increases faster than that in the lower part, which is considered as the effect of natural convection of PCM that dominates the charging process. Inlet water temperature has a greater influence rather than flow rate on heat transfer performance since the increase of temperature difference between HTF and PCM reduces all thermal resistance in the heat transfer, however it could not be increased infinitely to enhance heat transfer performance.

The quasi-enthalpy based lattice Boltzmann model for solid-liquid phase change

The phase change material (PCM) receives more and more attention for the large amount of latent heat and little temperature variation during phase change. In this paper, a new phase change lattice Boltzmann (LB) model, which is based on the quasi-enthalpy (QE) method, has been developed. The update of temperature is divided into two step, the “prediction” and “consumption (for melting)” or “release (for solidification)”. The problems of one-region phase change, two-region phase change, phase change under constant heat flux and phase change by convection are solved by the present model. All the results are compared with that of analytical solution, integral approximate solution and numerical method. No significant differences can be obtained for all the simulations, which demonstrates that the QE based LB model is able to capture the location of solid-liquid interface and reveal the temperature distribution of PCM accurately.

Thermal Performance of Nanofluid Charged Heat Pipe With Phase Change Material for Electronics Cooling

The paper reports the thermal performance of a nanofluid (MCNT/water) charged heat pipe with phase change material (PCM) as energy storage material (ESM) for electronic cooling. The adiabatic section of heat pipe is covered by the PCM stored in a container made of acrylic material. Here, paraffin is used as PCM. PCM can absorb and release thermal energy depending upon the fluctuations in the heating load. Tests are conducted to obtain the temperature distributions in PCM during charge/discharge processes. Present study utilizes two different ESM (water and paraffin), different fan speeds and heating powers in the PCM cooling module. The cooling module with heat pipe and paraffin as ESM found to save higher fan power consumption compared to the cooling module that utilities only a heat pipe.

Numerical study on coupling phase change heat transfer performance of solar dish collector

In solar dish collector system, the heat transfer process is a typical coupling heat transfer problem, where the heat conduction, radiation heat transfer, convection heat transfer and phase change heat transfer are coexisting. In the present paper, a coupling model for Monte Carlo Ray Trace Method (MCRTM) and Finite Volume Method (FVM) was established to study the coupling heat transfer problem. Firstly, based on MCRTM, the non-uniform 3D heat flux distributions on the solar dish receiver inner surface were obtained. Then the non-uniform heat flux distribution is used as the boundary condition to simulate the phase change and convection heat transfer process inside the heat transfer tube. The effects of the non-uniform heat flux distribution on temperature field in phase change material (PCM) were examined. The results show that the non-uniform heat flux on the tube surface will result in seriously non-uniform temperature distribution in PCM. Then the optimization analyses for the temperature distribution were performed according to the convection heat transfer process and heat conduction process respectively. The results show that in the studied conditions, when heat transfer fluid (HTF) velocity increases from 10m/s to 25m/s, the maximum temperature difference in PCM will decrease from 781.2K to 497.8K, which reduces about 36.3%. However, it will cause the heat storage capacity and HTF outlet temperature decrease. When the thermal conductivity increases from 3.8Wm−1K−1 to 19.0Wm−1K−1, the maximum temperature difference will decrease from 781.2K to 409.5K, which reduces about 47.6%. And it will not result in HTF outlet temperature and heat storage capacity decreasing. So, enhancing the PCM thermal conductivity is an efficient method to achieve more uniform temperature distribution in PCM.

Simulation of energy storage system with phase change material (PCM)

Thermal energy storage plays an important role in a wide variety of industrial, commercial and residential applications. Phase change material (PCM) is used in these systems in order to store heat. Latent heat storage in a PCM is very attractive, because of its high-energy storage density and isothermal behavior during the phase change process. Increasing of building energy storage capacity can be achieved with decreasing the indoor air temperature variations so that the indoor temperature goes near comforting temperature for a long time that results in more comfort for human. In this paper, a mathematical model was developed based on an enthalpy formulation and the effect of PCM thickness on temperature distribution in PCM and melting fraction was investigated. Results show that melting time change linearly with the amount of PCM and lower thicknesses are suitable for a better PCM performance.