Change Material Heat Exchanger Research Articles

Two-Dimensional Inverse Method to Estimate the Heat Flux Function in a Phase Change Material Heat-Exchanger

A two-dimensional inverse method is presented for estimating the boundary heat flux imposed on phase change materials in the melting/solidification process. The inverse problem is handled by the conjugate gradient method with the adjoint problem for function estimation. The method is verified using unsynthetic data, and the effect of the number of sensors, sensor placement, and measurement errors on the accuracy is investigated. In all cases, it is found that the method remains stable and accurate with a root mean square relative error less than 10%. Also, the number of sensors depends on the desired accuracy, computing time, and frequency of spatial changes in heat flux. Using field measurement is the best option for high accuracy and time-efficient estimation of spatial changes in the heat flux function. The accuracy of the estimated heat flux strongly depends on the sensor distance from the boundary. Therefore, it is desirable to place the sensor as close to the boundary as possible. With the addition of measurement errors, the presented method remains stable even with high measurement errors. This shows that this method can be used for real conditions.

Numerical investigation of heat transfer in wire and tube-based phase change material heat exchanger

The utilization of latent heat storage units with their high energy density and isothermal heat transfer behavior can enhance the performance of thermal energy systems. This study aims to investigate the effect of fin placement on the melting time of a wire and tube-based Phase Change Material (PCM) heat exchanger using numerical simulations. The study introduces a new complex geometry for the heat exchanger, and numerical analysis of heat transfer was conducted in Ansys Fluent software using an established solidification and melting model. The numerical results were validated against experimental data, and it was found that the position of the tubes and fins had a significant impact on heat transfer within the PCM. The model was able to predict temperature data with a maximum discrepancy of 3%.

A numerical study on control mechanism of heat transfer in a double pipe PCM heat exchanger by changing eccentricity

The thermal analysis of a double pipe phase change material heat exchanger is studied numerically. The study is done for three cases as; a) Case A: a melting process when inner pipe is maintained at a constant temperature higher than melting point, b) Case B: a solidification process when the inner pipe temperature is constant but less than melting temperature, and c) Case C: for a cyclic thermal storage when the inner pipe surface temperature periodically changes between temperatures of Cases A and B. The aim of this study is to find the optimum position of the inner pipe for each studied cases and to investigate the differences in heat transfer mechanism of the above cases for various Rayleigh numbers. The obtained results show that for Case A, the best position of the inner pipe depends on Rayleigh number, but the bottom region provides the shortest melting time for Ra>105. For the Cases B and C, the center must be preferred for all Reynolds numbers since the conduction heat transfer controls the process. In spite of many reported studies in literature, it is better to study on the enhancement of heat transfer for solidification rather than melting process.

Experimental Investigation of Energy and Exergy Assessment of Vapor Compression Refrigeration Unit Enhanced via Encapsulated Phase Change Material

Energy and exergy performance of simple vapor compression refrigeration unit is investigated experimentally with and without coupling heat exchanger of phase change material before the condenser. The hot outside air is cooled before entering the condenser throughout the day by flowing over the cooled phase change material structure that previously solidified during nighttime. Phase change material SP24 is employed because its melting/freezing range is suitable for most selected countries' climates. An experimental set‐up of an air‐phase change material heat exchanger coupled with the unit is constructed to examine its performance, including pressure–enthalpy curve, coefficient of performance, exergy performance, and power consumption including inflow air temperatures and flow rates impacts. Results affirm that the coefficient of performance, cooling capacity, power usage, and exergy destruction are improved by using phase change material. Compared to the unmodified unit, the maximum percentage of saved power and exergy destruction enhancement for the modified refrigeration unit with phase change material is about 8.8% and 10%, respectively. The maximum coefficient of performance and exergy efficiency rise is about 15.1% and 14.2%, respectively. Increasing the temperature differential across the phase change material heat exchanger, either by increasing inlet temperature or decreasing airflow, enhances the refrigeration unit power saving.

Numerical analysis of melting time and melt fraction for bottom charged tube in tube phase change material heat exchanger

Numerical analysis of melting time and melt fraction for bottom charged tube in tube phase change material heat exchanger

Enhancement of thermal energy storage in a phase change material heat exchanger having elliptical and circular tubes with & without fins

The objective of this study is to examine the thermal performance of a heat exchanger having multiple elliptical tubes and a phase change material (PCM) filled in the cylindrical shell of a heat exchanger. To improve the heat transmission from elliptical tubes to PCM, two and four fins are incorporated on the circumference of the elliptical tubes. The use of elliptical tubes with fins in the enhancement of heat transfer is an innovative approach in thermal performance studies of heat storage systems. The geometry of heat exchangers having elliptical tubes without fin, with two fins, and four fins are compared with the geometry of heat exchanger with circular tubes having no fin, two fins, and four fins respectively. The current investigation is carried out with the use of a 2D CFD model using a physical enthalpy-porosity technique to explore the phase transition of the solid PCM. The effect of integrating a number of fins on heat transfer has also been explored, and outcomes of elliptical and circular tube geometries in terms of PCM mean temperature and liquid percentage at two different temperatures of 50 °C and 60 °C have been compared. Results show, that PCM melting time is being reduced to 550 s in PCM heat exchanger geometry having elliptical tubes with four fins compared to 585 s for the same heat exchanger with two fins and 665 s for heat exchanger without fin at 50 °C resulting 12 % & 17 % reduction in melting time by applying two and four fins respectively. Whereas PCM melting time is 515 s in PCM heat exchanger geometry having circular tubes with four fins compared to 560 s for heat exchanger with two fins and 655 s for heat exchanger without fin resulting 14.5 % and 21 % reduction in melting time by applying two and four fins respectively. It has been concluded that adding fins on the circumference of elliptical and circular tubes enhances the heat transmission and reduces melting time as well as more heat can be transferred by circular tube geometry compared to elliptical tube heat exchanger geometries. The findings of the investigations are validated with the available simulation data and show good agreement, suggesting a 3.8 percent deviation.

Performance estimation of dehydriding process in metal hydride hydrogen storage tank with coiled-tube heat exchanger

Various thermal management methods are widely adopted in the metal hydride (MH) system to release the thermal effect and obtain acceptable hydrogen storage performance. In this work, an axisymmetric numerical model for a simple MH system without a heat exchanger (HE) has been established and validated to study the system performance during dehydriding. Then the coiled-tube heat exchanger (CTHE) and the phase change material heat exchanger (PCMHE) are used in the hydrogen storage system to improve heat transfer and release negative thermal effect, respectively. The performance of the MH-CTHE system and the MH-PCMHE has been estimated in the dehydriding process. CTHE shows more obvious impact than that of PCMHE. Effects of three common operation parameters on the hydrogen storage capacity of the MH-CTHE system have been investigated. The research results show that the influences of the heating water temperature and the outlet pressure on the system performance are more prominent than that of the heat transfer coefficient. In addition, the relationship between the average dehydriding rate of the MH-CTHE system and the two main operation parameters has been fitted as a simple equation, which can be used to predict and control the dehydriding rate based on given operation conditions.

Experimental and model validation of a phase change material heat exchanger integrated into a real building

Latent heat thermal energy storages (LHTES) are a promising technology with a wide range of applications in the framework of energy efficiency improvement. Phase change materials provide a big storage capacity, but their thermal conductivities are always extremely low. The use of finned tube heat exchangers is nowadays the best solution to enhance PCMs thermal performances. This allows significant charging and discharging rates. The major challenge concerns the balance between thermal performances and high material costs. A proper design of the heat transfer surfaces is essential to limit the system overall cost. Two different heat exchangers solutions, with radial and longitudinal fins are here examined. The design of the LHTES is performed by deploying a simplified FEM numerical model specifically developed for the application. A validation procedure based on laboratory tests with a small LHTES prototype was also carried out. The obtained results confirmed the reliability of the numerical model and justify its adoption as a tool for the design phase. The FEM model allows to effectively simulate the system thermal behaviour and assess the impact of the different HEX geometrical parameters on thermal performances. Based on this information it was possible to perform the optimization of the heat transfer surfaces and to derive the best heat exchanger layout in terms of material usage. The results showed that the solution with longitudinal fins is the most efficient, with 215 kg of steel less required for the realization of the finned heat exchanger.

Experimental investigation on thermosyphon aid phase change material heat exchanger for electronic cooling applications

In this work, cooling of electronic modules is experimentally investigated using a thermosyphon aid phase change material (PCM) heat exchanger with different thermic fluids such as n-hexane, benzene and DI water respectively. The experiments are conducted simultaneously by evaluating the thermal performance of thermic fluids and heat power stored by PCM for various heat inputs ranging from 70 to 110 W. At high heat input conditions, the value of low thermal resistance, maximum convective heat transfer coefficient (CHTC) and percentage of heat extraction of n-hexane are 0.350 K/W, 185.53 W/m2K and 99.2% respectively. Low enthalpy of vapourization and a high degree of superheat is the criteria for the obtained results. Also, temperature variation in PCM during melting is analysed by the influence of vapourized thermic fluids for different heat inputs. The maximum heat power stored by PCM is found as 7.78 W for vapourized n-hexane at 110 W due to high mass flow rate and less time for reaching steady-state temperature (SST) of PCM. The solidification of PCM is noted using cold water at regular time intervals during power-off conditions and observed that n-hexane influenced molten PCM takes 25 min for complete solidification.

Research on defrosting of refrigerator using phase change material heat exchanger

Research on defrosting of refrigerator using phase change material heat exchanger

Multiobjective optimization of an air-phase change material heat exchanger for free cooling in a single-family house

Free cooling systems based on phase change materials (PCM) are a possible alternative to air conditioning systems for summer comfort in buildings. However, the performance of such cooling systems is closely related to the climatic conditions and building configurations to be cooled. The objective of this work is to present an application of multiobjective optimization of an air cooling system using PCM at the preliminary stage of the design process. A dynamic thermal model simulating the thermal behaviour of an air-PCM heat exchanger is therefore presented and then coupled to the EnergyPlusⓇ software for the dynamic thermal simulation of the system. Finally, a first application of the optimization is presented to define a set of optimal configurations of the systems maintaining summer comfort in the house NAPEVOMO, minimizing both the initial cost of PCM and energy use of the fan.

Effect of airflow channel arrangement on the discharge of a composite metal foam‐phase change material heat exchanger

Effect of airflow channel arrangement on the discharge of a composite metal foam‐phase change material heat exchanger

Performance analysis of a cascade PCM heat exchanger and two-phase closed thermosiphon: A case study of geothermal district heating system

In this paper, a geothermal energy extraction system has been designed based on a two-phase closed thermosiphon, cascade phase change material heat exchanger, and an organic Rankin cycle. The proposed system is thermodynamically analyzed for supplying power and heat to a selected hotel in Sarein city in Iran. In the first step, the optimum diameter of the two-phase closed thermosiphon, according to the average yearly energy consumption rate (3100kW), is obtained. A two-level cascade heat exchanger with a storage medium of phase change materials is used to supply the building's energy consumptions. For the summertime, only the first level of the heat exchanger is operating to drive the ORC unit with two turbines for power generation. The second turbine output power is transmitted to the upper grid. On the other hand, in the wintertime, since the heating demands dominated, besides the first level of the heat exchanger, the second level of the heat exchanger is operated to supply the heating demand. Based on the thermodynamic analysis, employing phase change materials in the heat exchanger is an effective method for reducing overall exergy destruction, and consequently, increasing system efficiency. The energy and exergy efficiency is more favorable in terms of the application of PCM in the heat exchanger.

Simulation and Analysis of Fuel Tank Heat Exchanger Based on Phase Change Material

A replaceable heat exchanger plate fuel tank is designed for the heat dissipation problem of the fuel tank. The oil temperature curve of the fuel tank without the heat exchanger plate and the heat exchanger plate is simulated and analyzed. It is proved that the phase change material heat exchanger plate can reduce the equilibrium temperature of the fuel tank. The latent heat and phase transition temperature of the phase change material were changed, and the influence of the properties of the phase change material on the oil temperature change of the fuel tank was simulated.

Circuitry arrangement optimization for multi-tube phase change material heat exchanger using genetic algorithm coupled with numerical simulation

This study focused on circuitry arrangement optimization for a multi-tube phase change material heat exchanger. The optimization approach was developed based on a genetic algorithm approach coupled with numerical simulation and was aimed at maximizing the equivalent hot water output during the discharging process. Validated two-dimensional and three-dimensional simulations were used to support the genetic algorithm optimization process and to accurately investigate the thermal performance of the optimal circuitry arrangement. The results showed that adding more connections near the outlet side of the phase change material heat exchanger could lengthen the flow path in the high temperature zone, which was beneficial for a high mass flow rate condition of 1.68 kg min−1 with a 5% increment. Under medium and low mass flow rates of 1.2 kg min−1 and 0.5 kg min−1, a 3% increment and a 6% decrement, respectively, were observed. It was found that different mass flow rates require their own optimal circuitry arrangements, and the arranged rules were not necessarily the same. Therefore, circuitry arrangement optimization should be performed according to the operating flow rate or designed range to maximize the optimization effect. The proposed optimization approach could serve as an effective way to improve the energy efficiency of multi-tube latent thermal energy storage systems.

Defrosting performances of a multi-split air source heat pump with phase change thermal storage

Recently, multi-split air source heat pumps (ASHPs) have been used increasingly for space heating in cold winter. When it operates in frosting environment, periodic defrosting is necessary to maintain a high system performance. However, researches on its defrosting were few due to its high capital and complicated controls. To solve its fundamental problem of insufficient heat available during defrosting, a novel reverse-cycle defrosting (NRCD) method based on the phase change thermal storage has been developed. In this paper, comparative experiments using both standard reverse-cycle defrosting (SRCD) method and NRCD method were carried out on a multi-split ASHP unit with a phase change material heat exchanger (PCM-HE) acting as energy accumulator during heating operation and heat source during defrosting operation. Experimental results suggested that when using the NRCD method, the system performances, such as suction pressure and temperature, defrosting and heat-resumption durations, COP during defrosting operation can be effectively improved.

Investigating and Modeling of Simultaneous Charging and Discharging of a PCM Heat Exchanger

The performance of the simultaneous discharging and charging of a horizontal shell and tube heat exchanger filled with phase change material in the shell side was investigated. The temperature field was obtained and values of the solid-liquid interface were calculated. Finite difference modeling scheme was developed for validating the obtained result. The effects of the simultaneous operation time wise temperature profile shows more advantages for the phase change material heat exchanger performance. The obtained operation cycle charging time of the phase change material still indicates less heat transfer resistance along with reduced heat loss potentials. Moreover, less margin of difference from 0.1 - 0.2°C/min for rate of temperature increase means the Stable-Transient-Period is independent of the varied heat fluxes. Obtained average mean absolute error values indicate a good agreement between the experimental and modeling result.

05/00819 The main constructional characteristics of contemporary urban residential buildings in Greece

Recently, multi-split air source heat pumps (ASHPs) have been used increasingly for space heating in cold winter. When it operates in frosting environment, periodic defrosting is necessary to maintain a high system performance. However, researches on its defrosting were few due to its high capital and complicated controls. To solve its fundamental problem of insufficient heat available during defrosting, a novel reverse-cycle defrosting (NRCD) method based on the phase change thermal storage has been developed. In this paper, comparative experiments using both standard reverse-cycle defrosting (SRCD) method and NRCD method were carried out on a multi-split ASHP unit with a phase change material heat exchanger (PCM-HE) acting as energy accumulator during heating operation and heat source during defrosting operation. Experimental results suggested that when using the NRCD method, the system performances, such as suction pressure and temperature, defrosting and heat-resumption durations, COP during defrosting operation can be effectively improved.