Heat Transfer Fluid Inlet Temperature Research Articles

Experimental Investigation on Prototype Latent Heat Thermal Battery Charging and Discharging Function Integrated with Solar Collector

This paper reports the performance investigation of a newly developed Latent Heat Thermal Battery (LHTB) integrated with a solar collector as the main source of heat. The LHTB is a new solution in the field of thermal storage and developed based on the battery concept in terms of recharge ability, portability and usability as a standalone device. It is fabricated based on the thermal battery storage concept and consists of a plate-fin and tube heat exchanger located inside the battery casing and paraffin wax which is used as a latent heat storage material. Solar thermal energy is absorbed by solar collector and transferred to the LHTB using water as Heat Transfer Fluid (HTF). Charging experiments have been conducted with a HTF at three different temperatures of 68°C, 88°C and 108°C and three different flow rates of 30, 60 and 120 l/h. It is followed by discharging experiments on fully charged LHTB at three different temperatures of 68°C, 88°C and 108°C using HTF at three different flow rates of 30, 60 and 120 l/h. It is found that both higher HTF inlet temperature and flow rate have a positive impact on stored thermal energy. However, charging efficiency was decreased by increasing the HTF flow rate. The highest charging efficiency of 29% was achieved using HTF of 108°C at a flow rate of 30 l/h. Most of paraffin melted in this case, while part of the paraffin remained solid in other experiments. On the other hand, the results from discharging experiments revealed that both recovered thermal energy and recovery efficiency increased by either increasing the LHTB temperature or HTF flow rate. Highest recovered thermal energy of 5,825 KJ at 35% recovery efficiency achieved at LHTB of 108°C using 120 l/h of HTF.

Experimental investigation of shellac wax as potential bio-phase change material for medium temperature solar thermal energy storage applications

Thermal performance of shellac wax as a novel bio-phase change material (BPCM) and Therminol®-55 as heat transfer fluid (HTF) in a vertical shell and tube latent heat thermal energy storage (LHTES) unit is analyzed experimentally. Operational parameters considered, namely HTF flow rate and inlet temperature in the range of 2–5 LPM and 100–120 °C, respectively. The comprehensive study of contours and plots reveals the impact of natural convection and the progress of the melting and solidification front in the charging and discharging process. As the HTF flow rate increases, the charging rate improves considerably, and a maximum reduction in melting time is obtained as 43.6% for 4 LPM. The maximum reduction in melting time and storage efficiency are 42.2% and 73.4%, respectively, at 120 °C and 4 LPM. However, the discharging process's increased flow rate has no significant effect on solidification and discharge efficiency, which attributes the dominant mode of heat transfer is conduction during the solidification. Shellac wax storage efficiency is comparable to existing paraffin wax, stearic acid and palmitic acid-based LHTES unit. In this regard, shellac wax can be a potential Bio-PCM for medium temperature range (60–80 °C) solar thermal applications such as domestic water heating and food drying.

Effects of geometric and operating parameters on thermal performance of conical cavity receivers using supercritical CO2 as heat transfer fluid

In this paper, a comprehensive optical-thermal numerical model of the conical cavity receiver using supercritical CO2 (S–CO2) as the heat transfer fluid (HTF) is established by combining ray tracing with computational fluid dynamics method, which is verified with published data in the literature. Based on the model, the effects of critical geometric parameters (tube inner diameter, aspect ratio and cone angle ratio) and operating parameters (solar direct normal irradiance (DNI), HTF inlet mass flow rate and inlet temperature) on the thermal performance of the receiver are discussed thoroughly. The results indicate that a decrease in the tube inner diameter is beneficial to improve the optical-thermal performance of the receiver. When the aspect ratio and cone angle ratio are 1.5 and 0.25, respectively, the optical-thermal conversion efficiencies reach their optima, which are 75.13% and 75.30%, respectively. Moreover, for the S–CO2 receiver with optimal geometric parameters, the HTF outlet temperature increases linearly with increasing DNI and inlet temperature. Increasing mass flow rate can improve the optical-thermal conversion efficiency, but once the flow rate exceeds 0.04 kg/s, it has little effect on the efficiency improvement. These results can provide a reference for the design and operation of the S–CO2 conical cavity receiver.

Thermal performance evaluation of a latent heat thermal energy storage unit with an embedded multi-tube finned copper heat exchanger

ABSTRACT The experimental thermal characterization during charging and discharging of a prototype compact latent heat thermal energy storage system (LHTESS) with an embedded horizontally oriented finned multi-tube copper heat exchanger is presented. The thermal store was filled with a commercial-grade, CrodaTherm™ 60, phase change material (PCM) with a nominal melting temperature of 60°C. The proposed heat exchanger (HX) configuration mitigates the effect of low PCM thermal conductivity and increases the rates of heat transfer to and from the store during the charging and discharging processes compared to multi-tube copper HX without fins. The experimental testing regime assessed the impact of heat transfer fluid (HTF) volume flow rate and inlet temperature on I) transient PCM temperature distribution, II) the total charging/discharging time and III) instantaneous/average power during the charging and discharging processes. The experimental results showed that the HTF volume flow rate and inlet temperature play a significant role in the thermal performance of the LHTESS during the charging/discharging process. During the charging process, the influence of increasing HTF inlet temperature is greater than that due to increasing HTF volume flow rate. Moreover, it is shown that during the first 30 minutes of the discharging process, the average power output was 4.3, 5.1 and 5.3 kW for HTF volume flow rate of 2.5 and 7.2 and 10.5 l/min, respectively.

Experimental Investigation on Evacuated Tube Solar Collector Using Biofluid as Heat Transfer Fluid

Bio-oil extracted from waste of different plant kernel was used as heat transfer fluid in evacuated tube solar collector. Thermal performance of the biofluids to the enhancement of the evacuated tube solar collector under varying weather conditions and experimental analysis was carried-out. Thermal analysis on the storage water tank temperature, outlet and inlet heat transfer fluid temperature, and heat gains by was studied. In addition, the biofluids thermophysical properties and degradation analysis was conducted and compared with conventional base-fluids. From the results the biofluids caused enhancement of heat gain in the collector receiver by 9.5%, 6.4% and 3.2% for moringa oleifera kernel oil (MOKO), date kernel oil (DKO) and palm kernel oil (PKO), respectively. The storage water tank temperature at night fall was 53, 49, 51 and 47oC, for the MOKO, DKO, PKO and water HTFs, respectively. The biofluids were thermal stable and with no degradation. The biofluids demonstrated potentials as heat transfer fluids in thermal applications but there are needs for more investigations on their enhancement with organically synthesized nano particles to preserve there no corrosive and toxicity nature, and experimental performance on heat exchangers after several heating cycles.

Numerical investigation on latent heat storage enhancement using a gradient-concentration nanoparticles phase change material

Latent heat storage (LHS) using phase change materials (PCMs) is a promising option for storing thermal energy. However, PCMs melting rate is low and non-uniform due to their low conductivity and local natural convection respectively, which limits the thermal energy storage efficiency. The combined full-fins and nanoparticles in gradient-concentration is proposed in this study to overcome this shortcoming. A vertical shell-tube LHS system is taken as the study objective. Two-dimensional transient numerical model considering natural convection was developed to analyze the performances of the storage system. The effects of half-fins, full-fins, and combination of both on the melting process were firstly studied. Results show that the design of full-fins inhibits the negative effect of natural convection at the last melting stage, which reduces the melting time by 5.4 and 4.1% compared to the case of half-fins at fins volume fraction (φf) of 0.5 and 1.0 vol%, respectively. Then, the finned case of φf = 1.0 vol% dispersed with 1.0 wt% multiple-walled carbon nanotubes (MWCNTs) was investigated and the effects of heat transfer fluid (HTF) inlet temperature and flow rate were explored. Results show that a 65.6% improvement on melting uniformity is obtained for combined full-fins and MWCNTs in the negative gradient-concentration compared to the combined half-fins and MWCNTs in uniform concentration. Besides, the complete melting time is reduced by 11.4%. The enhancement potential of combined full-fins and nanoparticles in the negative gradient-concentration first increases and then decreases with the increase of HTF inlet temperature, and it decreases with the increase of HTF flow rate.

Numerical and experimental investigation on a latent heat thermal storage device featuring flat micro heat pipe arrays with offset strip fins

In this paper, a latent heat thermal storage device is designed and manufactured. The device uses flat micro heat pipe arrays as the core heat transfer element, multichannel flat pipes as the heat transfer fluid channel to provide and remove heat, and offset strip fins to strengthen the heat exchange of the phase change material side. The performance of the device under different operating conditions was explored, and a 3D computational fluid dynamic model of the device is established. The model is simplified by using the method of equivalent thermal conductivity and equivalent specific heat capacity. The performance of a latent heat storage unit under small temperature difference is also studied. Results show that the inlet temperature of fluid has a great influence on the performance of the device. During charging process, when the fluid temperature changes from 63 °C to 73 °C, the charging power increases from 921.1 W to 1302.1 W (41.3%). During discharging process, when the fluid temperature decreases from 18 °C to 8 °C, the discharging power increases from 831.1 W to 1210.5 W (48.9%). Regarding the flow rate, when the fluid flow rate increases from 2 L/min to 3 L/min (50%), the average charging power increases from 1,069.2 W to 1,199.3 W (12.2%), and the average discharging power increases from 895.1 W to 1,068.3 W (19.3%). Simulation results show that the phase change material in the thermal storage unit can melt completely when the temperature difference is 4 °C, but the melting time is longer when the heat transfer temperature difference is less than 6 °C. Heat transfer temperature difference refers to the variance between the heat transfer fluid inlet temperature and the phase change material phase transition temperature. The main thermal resistance is concentrated in the part where multichannel flat pipes transfer heat to the flat micro heat pipe arrays and the phase change material side.

Numerical simulations and experimental verification of the thermal performance of phase change materials in a tube-bundle latent heat thermal energy storage system

• Thermal performance of tube-bundle LHTS studied numerically and experimentally. • Charging and discharging are studied using lauric acid and water as PCM and HTF. • Three HTF initial temperatures and flow rates are examined. • PCM charging and discharging results were superior in comparison with double pipe LHTS. • Charging and discharging time was shortened by 85.3% and 82.5% respectively. Theoretical simulation and experimental validation of a new design tube-bundle latent-heat thermal storage (LHTS) working under solar-thermal application conditions was performed. A laboratory-scale experimental test rig was designed and tested for charging and discharging processes by using lauric acid and water as a phase-change material (PCM) and heat-transfer fluid (HTF), respectively. Six equal size tubes with 2 cm diameter and 45 cm length were clamped together with a central diameter tube for carrying the HTF. The temperature of the PCM during charging and discharging in the tubes in the bundle was measured radially. A 3D numerical model using ANSYS FLUENT was developed to simulate the time-dependent liquid fraction, temperature, and stored power of the PCM. The simulation was conducted after the successful validation with the experimental results at different HTF inlet temperatures (70 °C, 75 °C, and 80 °C) and (10 °C, 15 °C, and 20 °C) for charging and discharging processes, respectively, as well as with different Reynolds numbers (750, 1250, and 1750) for both processes. Although the design of the proposed LHTS was very simple, the results revealed that it has a superior thermal performance and fast charging and discharging period when compared to a double-pipe LHTS. Accordingly, the time was shortened by about 85.3% and 82.5% for charging and discharging processes, respectively.

Experimental thermal study of a new PCM-concrete thermal storage block (PCM-CTSB)

Phase change material concrete as a new building envelope has been widely used in passive building energy conservation, but less research has been done for it as a heat storage block in an active low-temperature thermal storage system. To enhance the heat storage capacity of PCM-concrete, overcome the PCM leakage problem and reduce the cost of heat storage, clastic light shale ceramsite (CLSC) was used to absorb paraffin to prepare PCM-CLSC aggregate and PCM-concrete thermal storage blocks with different PCM weight percentage (0, 2 wt%, 4 wt% and 6 wt%). The absorption, compatibility, thermal and mechanical properties of PCM-CLSC aggregate and PCM-concrete thermal storage blocks have been tested. To improve the charging and discharge rate, the active thermal storage and release system has been designed. Besides, the study presents the effects of PCM weight percentage and the characteristics of heat transfer fluid (HTF) on the performance of an active thermal storage system. The experimental results show that PCM-CLSC aggregate has good absorption and compatibility. The thermal conductivity and compressive strength of PCM-concrete thermal storage blocks decreased with the increase of PCM weight percentage, and the average specific heat capacity increased by 12.54% (2 wt% PCM), 31.60 (4 wt% PCM) and 41.23% (6 wt% PCM), respectively. Also, by increasing the PCM weight percentage, HTF flow rate and inlet temperature, it is possible to improve the heat storage and release capacity while effectively increasing the heat transfer rate and reducing the thermal resistance.

Thermal performance analysis of compact thermal energy storage unit-An experimental study

In this study, an experimental setup is developed to assess the thermal performance of a compact Latent Heat Thermal Energy Storage System (LHTESS) prototype during the charging/discharging stages. The LHTESS consists of a shell and horizontally oriented multi-tube heat exchanger and a commercially available paraffin wax RT44HC, which has a phase change temperature between 41°C and 43 °C as the energy storage medium. The testing campaign evaluated the influence of several operating conditions including the heat transfer fluid (HTF) volume flow rate and inlet temperature on the LHTESS power input and output, melting and solidification time and the energy stored and released. From the experimental results, it was observed that increasing the HTF inlet temperature has a significant effect on charging time compared to changing the HTF volume flow rate. When the LHTESS was charged using a fixed HTF inlet temperature of 60 °C, the charging process period took 296.3 min, 233.5 min, 204.8 min and 197.8 min when the HTF volume flow rate is 3.0, 4.5, 6.0 and 7.5 L/min. However, when the LHTESS was charged at HTF volume flow rate of 4.5 L/min, the results show that the charging completion time for HTF inlet temperatures of 55°C, 60 °C and 65°C are 316.6, 233.5 and 209.67 min, respectively. The results from the experimental analysis showed that the discharge time was significantly longer than the charging time due to an ever-growing layer of solid PCM around the external surface of heat exchanger throughout the discharging process which reduces the heat transfer coefficient between the PCM and HTF. This did not change substantially with the changing HTF volume flow rate.

Experimental analysis of Thermal Efficiency of functionalized Graphene (COOH) reinforced PCM for thermal energy storage system

In this work, the emphasis is on the thermal conductivity of paraffin wax and nano material which is functionalized graphene (COOH). Firstly COOH graphene is combined in various concentrations with paraffin wax to achieve higher thermal conductivity and then it is analysed for thermal conductivity having flow rate of heat transfer fluid(HTF) as 50ml at 8 second. When COOH functionalized graphene is used in this experiment, the thermal conductivity of paraffin wax increases. This study included experiments on varying concentrations of functionalized graphene (COOH) and inlet HTF temperatures for thermal properties, density, specific heat and nanofluid properties. The graphene is combined by stirring it with the paraffin wax. Graphene concentrations are 0.25 volume%, 0.5 volume% and 0.75 volume% for the flow rate of 50 ml in 8 second. Thermal conductivity increases with increase in the concentration of graphene. In the winter season, where environmental losses are higher than the summer season and the air temperature is 18°C, while it is above 29°C in the summer season, it also reduces PCM charging time around 30 to 50 percent with the use of functionalized graphene. In all concentrations, HTF temperature varies from 80°C to 90°C, with observed input energy, environmental losses, charging time, charging rate and performance. All values are noted after a 10 minute interval, till the cylinder is fully charged.

Thermal energy storage performance of PCM/graphite matrix composite in a tube-in-shell geometry

Melting heat transfer performance and measuring energy storage efficiency via total melting time of PCM/graphite matrix in a tube-in-shell for solar thermal energy storage and recovering waste heat applications is studied experimentally. The phase change material (PCM)-organic/paraffin (P56-58), is impregnated into the graphite matrix, with the bulk density of 50 g/L. The effect of inlet temperature (Tinlet = 75 °C and 85 °C) of heat transfer fluid (HTF) on total melting time is obtained. The time-history of temperature measurements, thermal camera imaging, and liquid fraction are obtained to reveal the thermal performance of PCM/graphite matrix in a tube-in-shell latent heat thermal energy storage (LHTES) system in detail. The results show that the PCM/graphite matrix has a remarkable effect on the phase change heat transfer and total melting time. The thermal performance of the PCM/graphite matrix is presented comparatively with the conventional tube-in-shell storage unit. Effective thermal conductivity which enhances the heat transfer rate is shown to increase 35 times compared to that of pure paraffin. The total melting time decreases by about 92% compared to the conventional tube-in-shell unit. Uniform melting behaviour is observed based on highly conductive abundant thermal paths for PCM/graphite matrix. Heat transfer takes place by dominant conduction for the PCM/graphite matrix. Leakage issue is prevented using graphite matrix encapsulation. Total melting time is decreased by about 31% with the increase in HTF inlet temperature for the PCM/graphite matrix.

The effect of the inlet temperature of the heat transfer fluid in a rectangular latent heat energy storage

Solar energy is available during the day only. The excess heat energy collected during sunshine hours can be stored in the thermal energy storage and it can be reused during off sunshine hours. Latent heat energy storage systems by using phase change materials (PCMs) can be used effectively for storing thermal energy. It has high-energy storage density and the constant temperature storage process. In this paper, the performance of the latent heat storage system and phase change characteristics of PCM inside a rectangular latent heat energy storage unit will be presented. In this study, purified water is used heat transfer fluid (HTF) which is passed through the copper tubes inside the test unit and commercial-grade paraffin wax is used as PCM and indirect contact heat transfer method is used to heat exchange from the HTF to PCM. It was found that the PCM at the upper layer of the test section first melted during the melting process. Moreover, the effects of inlet temperature of HTF on the charging process was investigated. It can be concluded that increasing the inlet temperature of HTF effectively decreases the total charging time of the melting process. The amounts of heat storage for the inlet temperature of HTF 70 °C and 80 °C are 7400 kJ and 6555 kJ respectively during the melting process.

Design and investigation of single tank phase change thermal storage domestic hot water system

Thermal energy storage (TES) is extensively applied in production and daily life. As a basic work, we designed a single tank phase change TES domestic hot water system using night valley power. Based on the single tank TES experimental platform, a 2D numerical model of the system was established. To optimize the performance of a single tank TES system, the effect of heat transfer fluid (HTF) inlet velocity and temperature on the heat release of the storage tank was analyzed based on simulation. The enhanced heat transfer effect of the radial cascade system and axial cascade system was also compared. The results showed that 0.8 m/s is the optimal HTF inlet velocity in the calculation range. The rule of the heat release about the HTF inlet temperature just meets the different hot water requirements in winter and summer. The heat release capacity of the radial cascade system and axial cascade system is higher than that of the conventional single-stage system, and the proportion of latent heat release in radial cascade is larger. This study will provide theoretical guidance for the optimal design of the single tank TES domestic hot water system in the future.

Compound charging and discharging enhancement in multi-PCM system using non-uniform fin distribution

In the present study, a numerical model of a vertical shell and tube latent heat storage system validated with the experimental data is presented. The developed model comprises of three blocks of phase change materials (PCMs) having melting point temperatures (Tm) 360 °C, 335.8 °C and 305.4 °C, respectively. A non-uniform distribution of fins in three PCM blocks is initially employed to study the performance of the single PCM system (Tm=335.8 °C). The effect of inlet heat transfer fluid temperature on the charging and discharging performances of the single PCM and multiple PCM (m-PCM) systems is analysed by varying a Stefan number (Steref) parameter, calculated based on the single PCM system. The charging and discharging times for the m-PCM system are either similar or lesser than the single PCM system for Steref≥1, however, there is an improvement of 21–25% in the specific power charged and discharged by the m-PCM system for all the Sterefvalues (0.5, 1, 1.5 and 2) considered. By employing a compound enhancement technique which is a combination of non-uniform fin-distribution and PCM blocks length ratio optimization for the m-PCM system, 30% and 9% reduction in the charging and discharging time, respectively, over the single PCM system is achieved.

Exploration of a plate heat exchanger utilising a phase change material: an experimental and computational study

In this article, the heat transfer mechanism of a phase change material (PCM) chamber during charging and discharging processes was studied both numerically and experimentally. A flat plate thermal storage system with dimensions of 500 × 100 × 12 mm, and a PCM thickness of 12 mm was thus investigated. The thermal storage material selected was commercial paraffin wax with a melting temperature of about 60 °C. A diffusion-advection numerical model was used to study heat transfer in this system, as it was observed that the experimental results were in good agreement with this model. In this way, natural convection was found to be the dominant phenomenon in the model. The effects of heat transfer fluid (HTF) temperature and volume flow rate on the melting and solidification time were also assessed, producing the finding that, by elevating the inlet HTF temperature from Th = 343 K to 348 K and then 353 K, the charging time can be reduced by up to 35%.

A technical, financial and CO2 emission analysis of the implementation of metal foam in a thermal battery for cold chain transport

Latent thermal energy storage (LTES) can be a valuable component in a wide range of energy systems. The low thermal conductivity of most phase change materials (PCMs) has resulted in the development of several PCM enhancement methods. However, most of the comparisons of enhancement techniques implemented in LTES heat exchangers are based on a single operating point which limits the findings to the tested heat transfer fluid inlet temperature and mass flow rate. Furthermore, an analysis of the financial impact of an enhancement method is not available. In this article, the validity of implementing metal foam as a thermal conductivity enhancer is assessed in a cold chain application. A modular LTES design is constructed with and without metal foam. The charging time of both thermal batteries is experimentally correlated as a function of the heat transfer fluid inlet temperature and mass flow rate. The metal foam reduces the charging time of the battery between 24 % and 40 % depending on the heat transfer fluid inlet condition. Discounted savings for the implementation of metal foam of up to 10 times the investment cost are possible but depend on the number of cycles per year and the rate of return.

Experimental investigation on thermal behavior of paraffin in a vertical shell and spiral fin tube latent heat thermal energy storage unit

Aided by the phase change material (PCM) with high thermal storage density, latent heat thermal energy storage (LHTES) technology may provide a solution to the energy supply-demand dilemma, e.g. LHTES in solar energy utilization and waste heat recovery. This paper presents an experimental investigation on the thermal performance of a LHTES unit equipped with vertical multitube shell and spiral-finned tube. Using paraffin as PCM and water as heat transfer fluid (HTF), the thermal charging and discharging characteristics of the LHTES unit can be evaluated. The thermophysical properties of latent heat and phase change temperature of PCM were characterized by the differential scanning calorimeter (DSC). Tests were conducted under different inlet temperatures and flow rates of HTF, during which the temperature variation of PCM, heat stored/released, mean charging/discharging power, total charging/discharging time and instantaneous effectiveness were acquired. Experimental results indicate that the natural convection of melted paraffin impacts substantially on the phase-change rate of paraffin. Once melt completes, the natural convection intensity surges temporarily. Moreover, the increase of inlet HTF temperature and flow rate during charging can dramatically improve the heat transfer between HTF and PCM, which in turn shortens the total charging time. The HTF flow rate was found to play little role on the heat transfer during discharging since the thermal resistance of the solidified PCM increases considerably.

Performance analysis of a waste heat recovery solar chimney for nocturnal use

Solar chimney is one of the best ways to produce artificial wind to drive wind turbines. But the main problem associated with is that it’s dependence on solar energy and hence can’t be used during night times. The objective of the present work is to modify the existing model; so that it can be used for the generation of power even in nocturnal and cloudy conditions. There are many ways to recover waste heat from different industries, but solar chimney can give one of the leading possible ways to recover it. Waste heat can be used to heat the base or absorber of the solar chimney’s collector; or it can be used to heat the air flowing inside the chimney. Ansys 2019 R1 has been used for the Computational Fluid Dynamics (CFD) validation and analysis of the solar chimney with heat recovery heat exchanger. A heat exchanger (HE) plate of aluminium alloy has been used with syltherm-800 as heat transfer fluid (HTF), and exchanging heat with the air inside the chimney near its base. Effect of different parameters like HTF inlet temperature, mass flow rate of HTF, ambient temperature of air, and diameter of heat exchanger plate on the performance of solar collector of chimney has been analysed. Also, the maximum conversion efficiency of about 5% is achieved, which is more in comparison to solar chimney operating at normal day conditions. Limitation of the present work is related to the storage of heat during day time or there should be continuous supply of waste heat during chimney operations. In this paper, authors have proposed a CFD method for the modification and improvement of solar chimney in Manzanares (Spain) with a waste heat recovery heat exchanger for nocturnal use.

Effect of Inlet and Geometrical Parameters on the Melting of PCM Capsules of Elliptical Cross Section.

This paper focuses on the melting of phase change material capsulated in the elliptical cross-section horizontal cylinder under convective boundary conditions. Different parameters are discussed, namely, the HTF inlet temperature and velocity and the axes ratio of the capsule cross-section. The effect of HTF inlet temperature, inlet velocity, and the capsule axes ratio was studied using the CFD software FLUENT 6.3.26. A comparison between the numerical and experimental results was made for the system. The experimental results matched well with the heat transfer model. It is shown that the inlet temperature of the heat transfer fluid (HTF) has a great effect on the process of paraffin wax melting. The increase of HTF inlet temperature increases the Phase change material( PCM) liquid fraction at constant charging time and decreases at the same time the total time of the capsulated paraffin wax melting. The geometry of the capsule cross-section represented by its axes ratio has a sensible effect on the process of paraffin wax melting. Increasing the axes ratio of the capsule, i.e. elongated the capsule in the perpendicular direction of flow increasing the PCM liquid fraction at constant charging time and decreases the total time of the capsulated paraffin wax melting. The increase of HTF inlet velocity has a weak effect on the process of paraffin wax melting in the inlet velocity range 0.003-0.012 m/s.