Molten Phase Change Material Research Articles

Improving Wastewater Heat Recovery Using Phase Change Material Heat Exchangers: A Numerical Study of Thermal Performance

ABSTRACTIndustrial processes often generate substantial amounts of wastewater with significant thermal energy content, which is typically discarded as waste. A promising approach to increase energy efficiency and advance sustainable resource management is waste water heat recovery. Utilizing a phase change material (PCM) to extract waste heat from wastewater and transfer it to cold water is an innovative method that separates the demand and supply of heat, while also integrating storage and transmission within a single heat exchanger (HE). A 3D numerical model of PCM‐based HE is developed and simulated. The thermal behavior of PCM and preheating of cold water are investigated in this study. In order to increase the thermal conductivity of the PCM, fins are strategically positioned. Around 71.13% of melting time is reduced by adding fins. Further, the 10° orientation of the fins is also numerically observed and it is found that it helps to improve natural circulation of molten PCM. Thus, melting time is reduced by 34% compared to the vertical fin. A 3.5°C–4.5°C temperature rise in cold water is obtained with the inclined fin, which is 14.28% higher than the vertical fin model.

Magnetically- regulated close contact melting for high-power-density latent heat energy storage

Rapid melting of solid-liquid phase change materials (PCMs) is critical to the high-power-density latent heat energy storage and efficient thermal management. The pressure-enhanced close contact melting is seen as a promising method because of the suppressed heat transfer resistance between the heating surface and the melt front during thermal charging, but it remains a key challenge how to tactfully apply external pressure for a practical device. Herein, we present a magnetically-regulated close contact melting strategy for rapid melting of PCMs from the perspective of the practical application. In this method, a PCM and a permanent magnet are contained inside a highly thermally conductive vessel, and the magnet regulated by another one can push the solid PCM toward the heating surface. Consequently, the superheated molten PCM can be instantly removed from the heating surface due to the magnetic force so as to achieve the suppressed thermal resistance. The temperature-control performance of paraffin wax is evaluated under various applied external forces and heat loads. Experimental results indicate that the heating surface temperature can be controlled near the melting temperature of PCM even under a relatively high heating flux. With applying the external pressure of 900 Pa, the average heat transfer resistance is reduced to lower than 4.5 × 10−4 K·m2·W−1. Finally, a closed thermal management device is fabricated and measured by using a graphite vessel to encapsulate the magnet and the PCMs such as paraffin and low-melting-point alloy. This device demonstrates good recyclability for repeated thermal charging/discharging. Our work provides a new method to develop the practical thermal management device based on pressure-enhanced close contact melting.

High-Efficiency Thermal-Shock Resistance Enabled by Radiative Cooling and Latent Heat Storage.

Radiative cooling technology is well known for its subambient temperature cooling performance under sunlight radiation. However, the intrinsic maximum cooling power of radiative cooling limits the performance when the objects meet the thermal shock. Here, a dual-function strategy composed of radiative cooling and latent heat storage simultaneously enabling the efficient subambient cooling and high-efficiency thermal-shock resistance performance is proposed. The electrospinning and absorption-pressing methods are used to assemble the dual-function cooler. The high sunlight reflectivity and high mid-infrared emissivity of radiative film allow excellent subambient temperature of 5.1°C. When subjected the thermal shock, the dual-function cooler demonstrates a pinning effect of huge temperature drop of 39°C and stable low-temperature level by isothermal heat absorption compared with the traditional radiative cooler. The molten phase change materials provide the heat-time transfer effect by converting thermal-shock heat to the delayed preservation. This strategy paves a powerful way to protect the objects from thermal accumulation and high-temperature damage, expanding the applications of radiative cooling and latent heat storage technologies.

CFD simulation of a solar collector integrated with PCM thermal storage

AbstractThermal energy storage is indeed a valuable solution for addressing the time lag or mismatch between energy supply and demand. The study aims to computationally model the melting and solidification processes of phase change material (PCM) using ANSYS Fluent that utilizes the finite volume technique. The simulations provide insights into the shapes of the liquid fraction, corresponding times, and temperature distribution of the PCM particles under the given conditions. The study considers factors such as solar radiation, thermal conductivity, density, latent heat, and the melting temperature of the PCM. The study finds that paraffin wax melts more quickly under a higher average maximum solar irradiance of 985 W/m2, while a lower solar radiation of 300 W/m2 has the opposite effect. Enhanced heat transfer resulting from conduction within the molten PCM, especially at a thermal conductivity of k = 0.25 W/m·K, accelerates the melting process. The thermal conductivity of the PCM affects the overall performance of the thermal energy storage system. The study highlights the potential application of thermal storage for drying purposes. Through the controlled release of stored heat energy, thermal storage enables the provision of heat in the absence of sunlight.

Numerical thermal performance assessment of phase change process in a PCM/foam-fins enclosure under various thermal conditions

ABSTRACT The low ability of phase change material (PCM) to transfer thermal energy has created a serious challenge for the development of latent heat storage (LHTES) units. Embedding foam with high thermal conductivity material like copper has attracted significant attention. Besides, high porosity, lightweight, and easy usage are other important benefits of copper. However, its higher cost and decreasing effective volume of PCM led to the creation of amendments in the foam design. Employment of the foam in the form of fin or foam fin has emerged as an alternative method to benefit from the advantages of porous material and overcome its defects. In this study, various LHTES units with different numbers of foam fins have been simulated numerically and compared with pure PCM and fully foam PCM enclosures. Two practical boundary conditions including constant temperature and constant heat flux were examined for the designed systems. The obtained results demonstrated that foam fins have a remarkable effect on the thermal performance enhancement of LHTES under constant temperature boundary condition. For LHTES with six foam fins, 42% and 30% reductions in melting time were achieved for both types of boundary conditions including constant temperature and heat flux, respectively. At the beginning of charging process, a significant enhancement of input heat rate was proved for LHTES with 6 foam fins and fully foam up to 112% and 155%, respectively. In addition, the foam fins method provided some free volume of PCM to permit the falling out of natural convection of molten PCM.

Experimental comparative study on thermal performance of latent heat storage tanks with pin, perforated, and rectangular fins at different orientations

The low thermal conductivity of phase change materials (PCMs) has limited their widespread use in practical applications. In the present study, different fin structures, namely, rectangular, perforated, and pin were examined to analyze the thermal performance of the melting process in rectangular latent heat storage tanks. Experiments were performed at both horizontal and vertical orientations to evaluate the effectiveness of different fin configurations. Visual observation of the phase change evolution at different time intervals was enabled through a transparent plexiglass shell. Instantaneous heat transfer rate and energy storage were measured using thermocouple readings and melting photographs. The results show that the maximum heat transfer coefficient between the heated wall and PCM is obtained by the pin-finned tank followed by perforated and rectangular-finned tanks. This thermal behavior is justified by the intensification of the upward convection flows through the voids provided by pin fins or perforated fins. Although the rectangular fin structure has the lowest convective heat transfer coefficient, its heat transfer rate is slightly higher than the other structures due to its larger heat transfer area. At a wall temperature of 70℃, the convective heat transfer coefficient and heat transfer rate obtained by the pin fin configuration are respectively 25% higher and 4% less than those of the rectangular fin. It reveals that the pin fin structure provides the most effective heat transfer area compared to its counterparts which have a significantly larger fin volume. In addition, it was found that regardless of the fin configuration, the melting rate in the horizontal tank was significantly higher than in the vertical tank due to the formation of more vortical flow structures within the molten PCM. The melting time in the unfinned horizontal tank was less than those of the vertical finned tanks implying that the tank orientation should be well-chosen to minimize the melting time along with adding fins of various configurations.

Applying artificial intelligence for spiral blade pitch distance optimization installed on the tubes containing nanofluid embedded in PCM-filled solar panel: A two-phase simulation model

The use of phase change materials (PCMs) to store energy in solar systems can be very useful to augment their efficiency. This paper presents a numerical study on the effect of using PCM in a thermal solar panel system. Four tubes containing alumina/water nanofluids (NFs) flow are used in this system, and NFs flow is analyzed. A spiral blade is employed on the tubes. By changing the pitch distance (d-P) of the spiral blade, the variations of the molten PCM (MPCM) and the temperature of different components of the solar system are determined transiently for 25 min. The numerical study is carried out using the FEM. The results demonstrate that the outlet temperature (T-O) is enhanced from 293 K at time 0 s to a temperature of more than 327 K at 1500s. The value of the heat transfer coefficient (HTC) reaches a value of more than 44 W/m2K up to 25 min. The value of the HTC is lower most of the time for a d-P of 20 mm than other distances. Changing the d-P from 20 to 30 mm can vary the T-O by 0.5 degrees. The minimum of MPCM corresponds to a d-P of 20 mm.

Artificial intelligent modeling and optimization of pin-fin configuration on the thermal performance of two tubes inside phase change material for cooling of a solar panel using Ag-water nanofluid

This paper performs a two phase numerical analysis on a solar thermal panel of dimensions 80 × 100 cm in the presence of Ag-water nanofluid flow. The nanofluid flows in two individual tubes beneath the panel, and there are some circular pin fins on the tubes. Tubes and pin fins under the panel are surrounded with a phase change material (PCM), paraffin wax. By increasing the length of pin fins from 1 to 7 cm, the volume fraction (VOF) of molten PCM, outlet nanofluid temperature (T-NF), and heat transfer coefficient (HTC) are examined from the transient state up to reaching the steady state. Utilizing a FEM based on a weak form, namely Galerkin, to find a numerical solution for mathematical modeling. Results of this study indicated that increasing the length of pin fins from 3 to 7 cm maximally increases the outlet nanofluid flow up to 2.11 °C. In the transient conditions, increasing the length of pin fins decreases the VOF of molten PCM. When the problem is evaluated in the transient conditions, increasing the length of pin fins decreases the mean temperature of the panel (T-PL), but in the steady-state conditions, the T-PL is the same for different lengths of pin fins. The lowest value of the HTC occurs for pin fins of length 3 cm, and in most cases, the average HTC is maximum for pin fins of length 1 cm.

Natural Convection in the Melting of Phase Change Materials in a Cylindrical Thermal Energy Storage System: Effects of Flow Arrangements of Heat Transfer Fluid and Associated Thermal Boundary Conditions

Abstract Latent thermal energy storage systems (LTESS) have received widespread attention due to their high energy density to store a significant amount of thermal energy in the form of latent heat into phase change materials (PCM) at a nearly constant melting temperature. The thermal efficiency of LTESS is usually limited by poor heat conduction in PCM but enhanced by the natural convection of molten PCM. The natural convection increases the uniformity of temperature by mixing in a PCM enclosure and therefore increases the heat transfer rates and accelerates the melting. While there is negligible natural convection, periodic reciprocation of heat transfer fluid (HTF) through the PCM enclosure has been demonstrated to increase the heat transfer rates to PCM by increasing the melt interface area and reducing temperature gradients across PCM compared to fixed-directional flow arrangements. The current study examines the effects of HTF flow direction on the strength and duration of natural convection in PCM in a vertical cylindrical shell-and-tube container. Gallium is used as the PCM because of its low melting temperature and high thermal conductivity, and water is used as the HTF. A 2-D axisymmetric numerical model developed in ANSYS Fluent was used for the study of the cylindrical LTESS. The aspect ratio of the cylindrical container is nearly 1, which allows the generation of natural convection currents of strong magnitude in molten PCM in the vertical orientation. The irregular melting front in the PCM is caused by both natural convection in molten PCM and thermal boundary conditions for different HTF flow arrangements. The temperature and melting front profiles of PCM with the reciprocating flow arrangement are compared to unidirectional flows in upward and downward directions. The influence of HTF operating parameters such as temperature, velocity, and reciprocation period on PCM melting is studied. Scale analysis is also applied to characterize the different melting regimes of PCM under different flow arrangements.

Enhancing thermal performance of latent heat storage unit for solar cooling: A hybrid approach with C-shaped fins and nano-additives

The performance of solar cooling systems is significantly affected by the intermittent nature of solar energy. To address this problem, thermal energy storage systems such as sensible and latent heat storage systems can be a viable option. Among these, the latent heat storage systems are promising due to their high energy storage density and nearly isothermal charging/discharging characteristics. However, the low thermal conductivity of the phase change material used within the storage unit hinders heat transfer, leading to longer charging and discharging periods. To overcome this problem, a hybrid approach that uses fins and nano additives is proposed in this study. A novel C-shaped fin design is introduced that effectively utilises the natural convection current in the molten phase change material. A comprehensive geometrical and material optimisation study is performed to determine the optimal shape, position, and material of the fins. The study also investigates the effect of the inclusion of graphene nanoplatelets (GnP) on the latent heat storage units. An experimental study is conducted to characterise the composite phase change material, and empirical correlations for viscosity and thermal conductivity are developed. The performance of an optimally designed LHS stacked with nano PCM composite of varying mass fractions is also evaluated. The study reveals that the C-shaped fins can reduce melting time by up to 59% compared to conventional fin designs, while PCM dispersed with 1% GnP reduces melting time by 27% when compared to the base PCM. Finally, a two-bed solar vapour adsorption cooling system with a 500 W capacity is considered to conduct a case study for demonstrating the performance of the proposed LHS. The result shows that the solar adsorption system integrated with the proposed heat storage unit can operate up to 3.3 h longer than it currently does. Thus the study presents a promising solution to overcome the obstacles limiting the widespread utilisation of solar cooling systems.

Multi-objective optimization of multiple droplet impacts on a molten PCM using NSGA-II optimizer and artificial neural network

Embracing an interaction between the phase change material (PCM) and the droplets of a heat transfer fluid, the direct contact (DC) method suggests a cutting-edge solution for expediting the phase change rates of PCMs in thermal energy storage (TES) units. In the direct contact TES configuration, when impacting the molten PCM pool, droplets evaporate, provoking the formation of a solidified PCM area (A). Then, they reduce the created solid temperature, leading to a minimum temperature value (Tmin). As a novelty, this research intends to maximize A and minimize Tmin since augmenting A expedites the discharge rate, and by lowering Tmin, the generated solid is preserved longer, resulting in a higher storage efficacy. To take the influences of interaction between droplets into account, the simultaneous impingement of two ethanol droplets on a molten paraffin wax is surveyed. Impact parameters (Weber number, impact spacing, and the pool temperature) govern the objective functions (A and Tmin). Initially, through high-speed and IR thermal imaging, the experimental values of objective functions are achieved for a wide range of impact parameters. Afterward, exploiting an artificial neural network (ANN), two models are fitted to A and Tmin, respectively. Subsequently, the models are provided for the NSGA-II algorithm to implement multi-objective optimization (MOO). Eventually, utilizing two different final decision-making (FDM) approaches (LINMAP and TOPSIS), optimized impact parameters are attained from the Pareto front. Regarding the results, the optimum amount of Weber number, impact spacing, and pool temperature accomplished by LINMAP and TOPSIS procedures are 309.44, 2.84 mm, 66.89 °C, and 294.98, 2.78 mm, 66.89 °C, respectively. This is the first investigation delving into the optimization of multiple droplet impacts for TES applications.

A two-phase analysis of the use of water-aluminum nanofluid in a solar still with a layer of phase change materials

This study employed the finite element method to simulate a solar still three-dimensionally. Aluminum nanoparticles were used in the still's tank, at the bottom of which was a layer of the N-auxin Phase Change Material (PCM). The variables of the problem included the degree of solar radiation for 12 different hours a day, the 10–45˚ angle of the front glass plate of the still, and the ambient temperature ranging from 293˚K to 330˚K. The effects of these variables on the air temperature, glass, PCM, and PCM volume fraction were examined. A two-phase method was used to analyze the nanofluid in the tank. The results showed that solar radiation generally had the highest effect on the maximum PCM temperature, maximum air temperature, and PCM volume fraction. However, the drop in the ambient temperature had the maximum impact on the maximum glass temperature. The PCM inside the solar still made the maximum air temperature slightly higher in the evenings than in the mornings. As a result, the maximum glass temperature could reach 330˚K at the ambient temperature of 330˚K and maximum solar radiation. In the last hours of the study, a decline in the angle of the solar still's front plate reduced the volume fraction of the molten PCM. Besides, at the 10˚ angle of the still's front plate, a drop in the outside temperature led the PCM to freeze faster.

Effect of filling height of metal foam on improving energy storage for a thermal storage tank

Heat storage eliminates the imbalance of supply and demand for renewable energies. Metal foam holds phase change materials (PCMs) inside the porous network through both enhancing conduction and enlarging heat transfer area. To synergically utilize the buoyancy convection in the molten PCM as well as the heat conduction penetration by the porous matrix, a partially filling configuration on the metal foam was proposed to enhance the energy efficiency for the storage tank. Numerical models were established and verified by comparing with experimental results. Metal foams with five different porosities were filled in the tank, under nine filling ratios ranging from 60% to 100% in an interval of 5%. By evaluating the melting characteristics of the different cases, the influences of both the filling ratio and porosity upon the melting performance were analyzed. Results demonstrated that there existed an optimal filling ratio to maximally reduce the complete melting time, and this ratio decreased with an increase in porosity. The full melting time under a high porosity of 0.98 was the least affected by different filling ratios. However, excessively reducing the filling ratio significantly retarded the melting process regardless of the filling porosities. Upon saving 5% mass for the metal foam, a reduction of 15.7% in complete melting time was achieved. The partially filling design provided a competitive solution to thermal applications by improving the energy storage efficiency and reducing the material consumption.

Impact of the number of tubes containing nanofluid flow on the melting and freezing of phase change materials in the thermal management of plate lithium-ion batteries

Phase change material (PCM) and nanofluids (NFs) flow are used in three-dimensional simulations for the thermal management (TMGT) of a plate battery. On each side of the battery, there are two enclosures in which the PCM is housed. Within the PCM, there is a tube that allows alumina/water NFs to flow. The two-phase model is used to simulate the NFs flow, the number of tubes inside the PCM is varied from 1 to 4, and the NFs velocity (VNF) is changed from 10 to 30 mm/s. Also, the distance of the tubes from the battery center changes to determine the volume fraction of molten PCM (VFMPC) and the maximum temperature of the battery (T-BT). For the simulations, the finite element technique (FEM) is used. The findings show that the lowest maximum T-BT and VFMPC are caused by a 5-mm distance between the tubes, whereas the greatest maximum temperature (T-MX) and VFMPC are caused by an 8-mm gap. The use of more tubes in PCM causes the VFMPC to be decreased. Besides, the maximum T-BT is reduced with time. Enhancing the VNF causes the maximum T-BT to decrease. The maximum T-BT is decreased by 45.37% in 1200 s by adjusting the VNF from 10 to 30 mm/s.

Effect of tube location on the temperature of plate lithium-ion battery applicable in the aerospace industry in the presence of two-phase nanofluid flow inside a channel placed in phase change material

This article presents three-dimensional simulations of the cooling system of a plate lithium-ion battery (BTY) using the finite element method (FEM). Since weight is of particular importance in the aerospace industry, this type of batteries can be used. The cooling system consists of two enclosures containing phase change material (PCM) on both sides of the BTY cell and alumina/water nanofluid flows in a tube in the middle of the PCM. This simulation is performed using the two-phase model. By changing the nanofluid velocity (VNF) from 10 to 30 mm/s and changing the location of the tube in the PCM enclosure, the temperature contours of the BTY, PCM, and tube, as well as the contours of PCM melting and volume fraction (VFN) of molten PCM are provided. According to the findings, increasing the VNF from 10 to 30 mm/s decreases the average temperature of the BTY (TBT) by 14.8% and the VFN of molten PCM by 18.9% in 1200 s. Also, when the tube distance is 8 mm, the TBT is minimal and the amount of solid PCM is maximal. When the tube distance is 11 mm, the TBT is maximal and the VFN of solid PCM is minimal.

Simultaneous double droplet impact on a molten phase change material pool: An experimental investigation

Although momentous in numerous authentic applications, multiple droplet impacts on the liquid pool are overlooked in most studies. Hence, the impingement of simultaneous double ethanol droplets on the molten phase change material (PCM) pool, instigating the evaporation of droplets and the solidification of PCM, is comprehensively scrutinized for the first time. Experiments were carried out through high-speed imaging for various Weber numbers ranging from 179 to 464, pool temperatures from 70 to 95 °C, and several horizontal impact spacing. By altering impact parameters, five distinct regimes were observed in the case of double droplets. Based on observations, regime maps were also established for conducted experiments. Furthermore, the influences of the impact parameters on the central uprising sheet, formed between two impinging droplets, crater width, crater depth, jet height, and solidified PCM area, created after the impact was investigated. Additionally, the time evolution of crater width and depth was compared with the existing theoretical predictions. It was ascertained that boosting either the Weber number or the impact spacing intensifies the droplets' spreading areas, leading to a larger solidified PCM area, whereas temperature inversely affects this parameter. Moreover, increasing the impact spacing diminishes the central uprising sheet height and retards its formation, while raising the Weber number monotonously strengthens the central uprising sheet. The research, whose results have an immediate application in novel energy storage devices containing droplet–PCM interaction, fills the gap between droplet impact and energy storage.

Numerical assessment of the multi-phase nanofluid flow inside a microchannel during the melting and solidification of PCM in the thermal management of a heatsink

This article presents a numerical simulation of a heatsink with a large number of square pin-fins using the finite element method. A nanofluid passes helical microchannel that is placed inside the heatsink. The two-phase mixture method is employed to simulate the nanofluid flow. The space between the pin-fins and the microchannel in the heatsink is filled with phase change material (PCM). The values ​​of the heatsink temperature (T-HK), including the maximum and average temperature, the temperature of the nanofluid (T-NF) exiting the heatsink, the molten PCM fraction, and the heat transfer coefficient (HTC) are estimated by changing the Reynolds number (Re) ranging from 100 to 500 and the volume fraction of nanoparticles (φ) varying from 0 to 3% up to 500 s. The results demonstrate that an increment in the Re reduces the T-NF exiting the heatsink significantly; however, enhancing the amount of φ decreases it slightly. In 500 s and 250 s, an enhancement in the Re from 100 to 500 intensifies the maximum T-HK by 17.28 and 9.92 °C, respectively. At Re = 100, 200, and 300, the PCM melting process starts in approximately 150, 200, and 250 s, respectively.

Investigation into the use of phase change materials in thermal management of a solar panel in the vicinity of tubes with slotted rectangular fins

In this paper, a thermal solar panel is simulated numerically. An enclosure of CaCl2·6H2O phase change material (PCM) is placed at the bottom of the panel in the presence of graphene nanoparticles. A tube is placed in the middle of the enclosure in which alumina-water nanofluid flows at the Reynolds numbers of 200 to 800. A number of fins are installed on the tube. The effect of using three different types of fins in a period of 0 to 5 h and Reynolds number on the panel temperature, PCM volume percentage, output nanofluid temperature, bottom panel thermal resistance, and panel temperature uniformity is examined. The finite element method is employed to solve governing equations. The results demonstrate that the best temperature uniformity on the solar panel occurs at Reynolds number of 800. The Reynolds number of 800 also has the lowest maximum temperature, average panel temperature, and thermal resistance. Using the Reynolds number of 800 instead of 200 reduces the PCM volume percentage from 93.14% to 23.40% and reduces the nanofluid output temperature by 4.3 °C. Using fins case 3 creates the minimum temperature on the panel and minimum amount of thermal resistance. The fins case 3 and case 2 produce the minimum and maximum amounts of molten PCM.

Melting dynamics analysis of a multi-tube latent heat thermal energy storage system: Numerical study

This numerical study investigates the melting dynamics of paraffin wax as a phase change material (PCM) in a multi-tube latent heat thermal energy storage system (MT-LHTESS). The performance of an arrangement with four tubes is compared with a concentric single tube arrangement keeping the same cross-section area of heat transfer fluid tubes and the same PCM quantity. Four longitudinal fins of two types are also incorporated to further improve the melting. Thirteen cases with different arrangements of tubes and fins are compared in this study. The study attempts to select a suitable arrangement of the tubes. A two-dimensional enthalpy-porosity model in ANSYS-Fluent is used to solve the governing equations. The melting results are depicted as the contours of liquid fraction, temperature, and flow streamlines. The transient performance is assessed based on progress plots of liquid fraction and average domain velocity. It is observed that splitting into multiple tubes and using fins enhance the melting performance. The generation and coalescence of small vortices in the molten PCM accelerate the melting performance. The staggered array, larger eccentricity, and (+ type) finned tubes outperform their counterparts. The lowest melting time is observed in Case 2(+), having four staggered tubes, at 30 mm eccentricity, and with (+ type) fins. This case takes 75 min for complete melting, and 1411.1 kJ/m heat at a rate of 322 W/m is stored. The melting time gets reduced by 53.3–71.1% using four tubes and by 65.78–83.33% using finned four tubes as compared to the single tube case.

Experimental Study on the Melting Behavior of a Phase Change Material under Random Vibration

ABSTRACT An experimental investigation of the effect of random vibration on the melting behavior of a phase change material (PCM) and the thermal performance of a PCM-based heat sink is presented. While random vibration from 2 to 16 g rms for the frequency range from 15 to 2000 Hz was applied to a rectangular enclosure, which contains paraffin wax and the heat sink, a constant heat flux was imposed on the heat sink to melt the PCM. The experimental results showed that the random vibration has no effect on the melting behavior early in the melting process during which conduction is the primary mode of heat transfer. However, the random vibration significantly affected the melting behavior later in the process during which natural convection is the primary mode of heat transfer. The random vibration augmented heat transfer in the molten PCM and increased the Nusselt number, 1.56 times greater under the vibration of 16 g rms than without vibration. The augmented heat transfer accelerated PCM melting and delayed the rise in temperature of the heat sink. The time for the temperature of the heat sink to rise to a threshold increased as the intensity of random vibration increased, 5.9 times longer under the vibration of 16 g rms than without vibration.