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Journal ArticleDOI

Experimental investigation of phase change in a multitube heat exchanger

TL;DR: In this paper, the melting and solidification processes in a multitube heat exchanger were investigated and the thermal characteristics of the units involving melting front, heat transfer rate and Nusselt number were also analyzed.
Abstract: The present paper investigates melting and solidification processes in a multitube heat exchanger. The shell side is filled with paraffin (RT35) while water flows through the tube passes as the heat transfer fluid (HTF). The arrangements of one, two, three and four inner tubes cases are studied for HTF inlet temperatures of 70 °C, 75 °C and 80 °C. The thermal characteristics of the units involving melting front, heat transfer rate and Nusselt number are also analyzed. Results indicate that increasing the number of inner tubes results in a faster pace of melting and solidification. The effect is so pronounced that, when the HTF inlet temperature is 80 °C, application of 4-tube heat exchanger reduces the duration required for complete melting and solidification up to 43 and 50 percent, respectively as compared to the corresponding single-HTF-tube case. The results also show that by increasing the number of tubes, the surface-averaged Nusselt number decreases. This can be attributed to the inhibition of upper pipes against PCM melt movement. Also a correlation is proposed to calculate Nusselt number of tubes. Comparing the temperatures recorded by the thermocouples in rotational direction, it is indicated that the variation of the inner tube arrangement affects solidification process more than melting.
Citations
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Journal ArticleDOI
TL;DR: In this article, experimental and numerical investigations are performed for heat transfer enhancement in a horizontal Latent Thermal Energy Storage System using multiple heat transfer tubes and modified shell designs, where Stearic acid is used as phase change material and it is placed in the annulus of steel shell and copper tubes carrying water as the heat transfer fluid.
Abstract: In this paper, experimental and numerical investigations are performed for heat transfer enhancement in a horizontal Latent Thermal Energy Storage System using multiple heat transfer tubes and modified shell designs. Stearic acid is used as phase change material and it is placed in the annulus of steel shell and copper tubes carrying water as the heat transfer fluid (HTF). A single Y-fin HTF tube, used as Base Case, is split up into 2 – 5 tubes with different arrangements while ensuring constant mass of the PCM. The vertical double tube and triple tube V-configuration improve the average heat transfer rates by 33.6% and 23.7%, respectively, as compared to the Base Case. The corresponding complete melting times is also reduced by 27.7% and 21.7%. Additionally, elliptic and triangular shell design modifications are proposed for double and triple tube arrangements, respectively. Both configurations increase the average heat transfer rate by 85% which results in reduction of the complete PCM melting time by 50% with respect to Base Case of Y-fins single tube arrangement. In comparison to the Base Case, an increase in HTF temperature of 5.6% improves the average Nusselt number by more than 37% for both the cases. Additionally, the correlations for melting Fourier number and average Nusselt number are also developed.

66 citations

Journal ArticleDOI
TL;DR: In this article, the authors investigated the relationship between the charge water flowrate and the charging completion time and the total energy use and evaluated quantitatively using case studies, according to which optimal water flow rate was identified.
Abstract: Nowadays air-source heat pumps are widely used to collect heat from ambient air, which can reduce operating cost and protect environment when compared with fossil-based heating systems. To increase the flexibility of heat collection and supply, air-source heat pump should be used together with a thermal storage tank. In this heating system, air-source heat pump needs to charge the storage tank regularly based on a predefined time schedule. When a PCM storage tank is used, the charging completion time and the total energy use are nonlinearly relative to the charging water flow rate. This study, therefore, systematically investigates the relationships between the charge water flowrate and the charging completion time and the total energy use. These relationships are analyzed qualitatively and then evaluated quantitatively using case studies, according to which optimal water flow rate is identified.

51 citations

Journal ArticleDOI
TL;DR: In this article, an experimental investigation is carried out on a Latent Heat Thermal Energy Storage system (LHTES). All the experimental data are optimized using thermodynamic principles in which exergy analysis is conducted to examine the system performance at different time constants.

46 citations

Journal ArticleDOI
TL;DR: In this paper, the effect of the number and arrangement of tubes on the melting performance of a phase change material (PCM) in a multi-tube shell-and-tube latent heat thermal energy storage (LHTES) system was numerically investigated.
Abstract: This study numerically investigates the effect of the number and arrangement of tubes on the melting performance of a phase change material (PCM) in a multi-tube shell-and-tube latent heat thermal energy storage (LHTES) system. An enthalpy-porosity model was used to simulate the phase change process. Eight arrangements of tubes were examined. The melting characteristics, energy density, distributions of the liquid fraction and temperature, heat transfer rate, and melting time were analyzed. The melting performance and energy density were influenced by both the number and arrangement of tubes. An increase in the number of tubes enhanced the melting rate in the initial stage and the energy density. The tube arrangement affected the required melting time. Two vertically arranged tubes resulted in the lowest melting time, and eight tubes resulted in the highest energy density. A correlation is proposed to estimate the total melting time with respect to the number and arrangement of tubes in LHTES.

35 citations

Journal ArticleDOI
TL;DR: In this paper, three inner tubes of heat transfer fluid were employed with four different arrangements: inline-central array (normal case, Case A), downward and upward triangle arrays (Case B and C), and an arc array at the shell bottom (Case D).
Abstract: Thermal energy storage plays an essential role in energy systems to reduce the mismatch between the energy supply and demand. Phase change materials are widely used in different technologies but suffer from low heat transfer performance. This numerical study aims to investigate the enhancement in the melting thermal characteristics of lauric acid as a phase change material by using Ansys-Fluent. Three inner tubes of heat transfer fluid were employed with four different arrangements: inline-central array (normal case, Case A), downward and upward triangle arrays (Case B and C) and an arc array at the shell bottom (Case D). Results revealed that the arc array and downward triangle configurations reduced the melting time by about 76% and 72%, respectively. However, the upward triangle tube arrangements increased the melting time by about 10% compared with the normal case.

24 citations

References
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Book
01 Jan 1980
TL;DR: In this article, the authors present an active and passive building heating system for solar thermal power systems, where the active system is designed by f--chart and the passive one by Utilizability Methods.
Abstract: FUNDAMENTALS. Solar Radiation. Available Solar Radiation. Selected Heat Transfer Topics. Radiation Characteristics of Opaque Materials. Radiation Transmission Through Glazing: Absorbed Radiation. Flat--Plate Collectors. Concentrating Collectors. Energy Storage. Solar Process Loads. System Thermal Calculations. Solar Process Economics. APPLICATIONS. Solar Water Heating----Active and Passive. Building Heating----Active. Building Heating: Passive and Hybrid Methods. Cooling. Industrial Process Heat. Solar Thermal Power Systems. Solar Ponds: Evaporative Processes. THERMAL DESIGN METHODS. Simulations in Solar Process Design. Design of Active Systems by f--Chart. Design of Active Systems by Utilizability Methods. Design of Passive and Hybrid Heating Systems. Design of Photovoltaic Systems. Appendices. Author Index. Subject Index.

9,391 citations

Journal ArticleDOI
TL;DR: In this article, the authors present an active and passive building heating system for solar thermal power systems, where the active system is designed by f--chart and the passive one by Utilizability Methods.
Abstract: FUNDAMENTALS. Solar Radiation. Available Solar Radiation. Selected Heat Transfer Topics. Radiation Characteristics of Opaque Materials. Radiation Transmission Through Glazing: Absorbed Radiation. Flat--Plate Collectors. Concentrating Collectors. Energy Storage. Solar Process Loads. System Thermal Calculations. Solar Process Economics. APPLICATIONS. Solar Water Heating----Active and Passive. Building Heating----Active. Building Heating: Passive and Hybrid Methods. Cooling. Industrial Process Heat. Solar Thermal Power Systems. Solar Ponds: Evaporative Processes. THERMAL DESIGN METHODS. Simulations in Solar Process Design. Design of Active Systems by f--Chart. Design of Active Systems by Utilizability Methods. Design of Passive and Hybrid Heating Systems. Design of Photovoltaic Systems. Appendices. Author Index. Subject Index.

7,831 citations

Journal ArticleDOI
TL;DR: The use of a latent heat storage system using phase change materials (PCMs) is an effective way of storing thermal energy and has the advantages of high energy storage density and the isothermal nature of the storage process.
Abstract: The use of a latent heat storage system using phase change materials (PCMs) is an effective way of storing thermal energy and has the advantages of high-energy storage density and the isothermal nature of the storage process. PCMs have been widely used in latent heat thermal-storage systems for heat pumps, solar engineering, and spacecraft thermal control applications. The uses of PCMs for heating and cooling applications for buildings have been investigated within the past decade. There are large numbers of PCMs that melt and solidify at a wide range of temperatures, making them attractive in a number of applications. This paper also summarizes the investigation and analysis of the available thermal energy storage systems incorporating PCMs for use in different applications.

4,482 citations

Journal ArticleDOI
TL;DR: In this article, the state of the art of phase change materials for thermal energy storage applications is reviewed and an insight into recent efforts to develop new phase change material with enhanced performance and safety.

1,399 citations