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Open accessJournal ArticleDOI: 10.3390/SU13052685

Effect of Twisted Fin Array in a Triple-Tube Latent Heat Storage System during the Charging Mode

02 Mar 2021-Sustainability (Multidisciplinary Digital Publishing Institute)-Vol. 13, Iss: 5, pp 2685
Abstract: This study aims to assess the effect of adding twisted fins in a triple-tube heat exchanger used for latent heat storage compared with using straight fins and no fins. In the proposed heat exchanger, phase change material (PCM) is placed between the middle annulus while hot water is passed in the inner tube and outer annulus in a counter-current direction, as a superior method to melt the PCM and store the thermal energy. The behavior of the system was assessed regarding the liquid fraction and temperature distributions as well as charging time and energy storage rate. The results indicate the advantages of adding twisted fins compared with those of using straight fins. The effect of several twisted fins was also studied to discover its effectiveness on the melting rate. The results demonstrate that deployment of four twisted fins reduced the melting time by 18% compared with using the same number of straight fins, and 25% compared with the no-fins case considering a similar PCM mass. Moreover, the melting time for the case of using four straight fins was 8.3% lower than that compared with the no-fins case. By raising the fins’ number from two to four and six, the heat storage rate rose 14.2% and 25.4%, respectively. This study presents the effects of novel configurations of fins in PCM-based thermal energy storage to deliver innovative products toward commercialization, which can be manufactured with additive manufacturing.

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Topics: Fin (66%), Phase-change material (53%), Heat transfer (52%) ... show more
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6 results found


Open accessJournal ArticleDOI: 10.3390/NANO11102647
09 Oct 2021-Nanomaterials
Abstract: Inherent fluctuations in the availability of energy from renewables, particularly solar, remain a substantial impediment to their widespread deployment worldwide. Employing phase-change materials (PCMs) as media, saving energy for later consumption, offers a promising solution for overcoming the problem. However, the heat conductivities of most PCMs are limited, which severely limits the energy storage potential of these materials. This study suggests employing circular fins with staggered distribution to achieve improved thermal response rates of PCM in a vertical triple-tube heat exchanger involving two opposite flow streams of the heat-transfer fluid (HTF). Since heat diffusion is not the same at various portions of the PCM unit, different fin configurations, fin dimensions and HTF flow boundary conditions were explored using computational studies of melting in the PCM triple-tube system. Staggered configuration of fin distribution resulted in significant increases in the rates of PCM melting. The results indicate that the melting rate and heat charging rate could be increased by 37.2 and 59.1%, respectively, in the case of staggered distribution. Furthermore, the use of lengthy fins with smaller thickness in the vertical direction of the storage unit resulted in a better positive role of natural convection; thus, faster melting rates were achieved. With fin dimensions of 0.666 mm × 15 mm, the melting rate was found to be increased by 23.6%, when compared to the base case of 2 mm × 5 mm. Finally, it was confirmed that the values of the Reynolds number and inlet temperatures of the HTF had a significant impact on melting time savings when circular fins of staggered distribution were included.

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Topics: Fin (58%), Phase-change material (57%), Heat transfer enhancement (56%) ... show more

1 Citations


Zhihao Sun1, Kang Luo1, Jian Wu1Institutions (1)
Abstract: This work extends our recent study (Sun et al., 2021 [ 1 ]) on the n-octadecane's melting with electric field inside a cavity. The combined heat-transfer enhancement technique involving a passive fin and active electric field is used to experimentally investigate the n-octadecane's melting inside a vertically heated cavity. The effects of magnitude and direction of applied voltage on phase-change heat transfer are studied with and without the fin. Results are provided for the real-time evolution of the melting front, the liquid fraction, as well as the velocity fields and the current-voltage curve. It is found that the adding of fin structure can solely reduce 40.0% total melting time in a 40.0 mm × 40.0 mm × 40.0 mm cavity. For the cavity without fin, a +20.0KV applied voltage from the left wall or right wall of cavity can separately increase 40.0% or decrease 33.3% melting time, respectively. But for a cavity with fin, a left or right side applied +20.0KV voltage will induce a 3.7% decrease or a 48.1% increase of melting time. It is also found that Coulomb force plays a dominant role on melting after the initial stage, and free space charges are mainly produced by the conduction mechanism.

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Topics: Fin (extended surface) (55%), Electric field (53%)

1 Citations


Open accessJournal ArticleDOI: 10.3390/NANO11113153
22 Nov 2021-Nanomaterials
Abstract: Due to the potential cost saving and minimal temperature stratification, the energy storage based on phase-change materials (PCMs) can be a reliable approach for decoupling energy demand from immediate supply availability. However, due to their high heat resistance, these materials necessitate the introduction of enhancing additives, such as expanded surfaces and fins, to enable their deployment in more widespread thermal and energy storage applications. This study reports on how circular fins with staggered distribution and variable orientations can be employed for addressing the low thermal response rates in a PCM (Paraffin RT-35) triple-tube heat exchanger consisting of two heat-transfer fluids flow in opposites directions through the inner and the outer tubes. Various configurations, dimensions, and orientations of the circular fins at different flow conditions of the heat-transfer fluid were numerically examined and optimized using an experimentally validated computational fluid-dynamic model. The results show that the melting rate, compared with the base case of finless, can be improved by 88% and the heat charging rate by 34%, when the fin orientation is downward–upward along the left side and the right side of the PCM shell. The results also show that there is a benefit if longer fins with smaller thicknesses are adopted in the vertical direction of the storage unit. This benefit helps natural convection to play a greater role, resulting in higher melting rates. Changing the fins’ dimensions from (thickness × length) 2 × 7.071 mm2 to 0.55 × 25.76 mm2 decreases the melting time by 22% and increases the heat charging rate by 9.6%. This study has also confirmed the importance of selecting the suitable values of Reynolds numbers and the inlet temperatures of the heat-transfer fluid for optimizing the melting enhancement potential of circular fins with downward–upward fin orientations.

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Topics: Fin (64%), Heat transfer enhancement (57%), Phase-change material (56%) ... show more

Abstract: In this paper, a twisted double-pipe heat exchanger containing phase change material is designed and analyzed as an energy storage unit in solar collectors. Since solar heat exchangers cannot store energy, a study of such devices is essential. The governing equations solving and numerical simulation were performed by Ansys 19 software in a 3D model based on enthalpy–porosity method and PRESTO! scheme. The effects of several parameters like pipe's position, twisting, and cross-section on the PCM melting in the storage unit have been investigated, which was unprecedented. The outcomes illustrate that vertical heat exchangers are less efficient and have 15.3% more melting time than horizontal ones. And, 3-lobed cross-sections comparing to circle cross-sections enhance the PCM melting by 6%. Moreover, a double-pipe helical coil or twisted pipe heat exchanger with a 3-lobed cross-section decreases the melting time. The reduction for the helical coil is 10%, while it is 14.6% for twisted pipe heat exchangers. Finally, we examined the twisted inner pipe with 2, 3, 4, and 5-lobed cross-sections. The achievements demonstrated that the 3-lobed twisted cross-section has the highest heat transfer surface and the melting time for 3-lobed is 1.5%, 5%, and 6% less than 2-lobed, 4-lobed, and 5-lobed.

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Topics: Phase-change material (59%), Heat transfer (59%), Thermal energy storage (58%) ... show more

Open accessJournal ArticleDOI: 10.3390/EN14227489
09 Nov 2021-Energies
Abstract: The solidification process in a multi-tube latent heat energy system is affected by the natural convection and the arrangement of heat exchanger tubes, which changes the buoyancy effect as well. In the current work, the effect of the arrangement of the tubes in a multi-tube heat exchanger was examined during the solidification process with the focus on the natural convection effects inside the phase change material (PCM). The behavior of the system was numerically analyzed using liquid fraction and energy released, as well as temperature, velocity and streamline profiles for different studied cases. The arrangement of the tubes, considering seven pipes in the symmetrical condition, are assumed at different positions in the system, including uniform distribution of the tubes as well as non-uniform distribution, i.e., tubes concentrated at the bottom, middle and the top of the PCM shell. The model was first validated compared with previous experimental work from the literature. The results show that the heat rate removal from the PCM after 16 h was 52.89 W (max) and 14.85 W (min) for the cases of uniform tube distribution and tubes concentrated at the bottom, respectively, for the proposed dimensions of the heat exchanger. The heat rate removal of the system with uniform tube distribution increases when the distance between the tubes and top of the shell reduces, and increased equal to 68.75 W due to natural convection effect. The heat release rate also reduces by increasing the temperature the tubes. The heat removal rate increases by 7.5%, and 23.7% when the temperature increases from 10 °C to 15 °C and 20 °C, respectively. This paper reveals that specific consideration to the arrangement of the tubes should be made to enhance the heat recovery process attending natural convection effects in phase change heat storage systems.

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Topics: Natural convection (62%), Heat capacity rate (60%), Phase-change material (59%) ... show more

References
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39 results found


Journal ArticleDOI: 10.1016/S0196-8904(98)00025-9
S.M. Hasnain1Institutions (1)
Abstract: This paper reviews the development of available thermal energy storage (TES) technologies and their individual pros and cons for space and water heating applications. Traditionally, available heat has been stored in the form of sensible heat (typically by raising the temperature of water, rocks, etc.) for later use. In most of the low temperature applications, water is being used as a storage medium. Latent heat storage on the other hand, is a young and developing technology which has found considerable interest in recent times due to its operational advantages of smaller temperature swing, smaller size and lower weight per unit of storage capacity. It has been demonstrated that, for the development of a latent heat thermal energy storage system, the choice of the phase change material (PCM) plays an important role in addition to heat transfer mechanisms in the PCM. Attempts have also been made to utilize technical grade phase change materials as storage media and embedded heat exchange tubes/heat pipes with extended surfaces in order to enhance the heat transfer rate to/from the PCM.

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Topics: Phase-change material (66%), Thermal energy storage (65%), Waste heat (63%) ... show more

1,024 Citations


Journal ArticleDOI: 10.1016/J.RSER.2010.08.007
Li-Wu Fan1, Jay M. Khodadadi1Institutions (1)
Abstract: A review of experimental/computational studies to enhance the thermal conductivity of phase change materials (PCM) that were conducted over many decades is presented. Thermal management of electronics for aeronautics and space exploration appears to be the original intended application, with later extension to storage of thermal energy for solar thermal applications. The present review will focus on studies that concern with positioning of fixed, stationary high conductivity inserts/structures. Copper, aluminum, nickel, stainless steel and carbon fiber in various forms (fins, honeycomb, wool, brush, etc.) were generally utilized as the materials of the thermal conductivity promoters. The reviewed research studies covered a variety of PCM, operating conditions, heat exchange and thermal energy storage arrangements. The energy storage vessels included isolated thermal storage units (rectangular boxes, cylindrical and annular tubes and spheres) and containers that transferred heat to a moving fluid medium passing through it. A few studies have focused on the marked role of flow regimes that are formed due to the presence of thermally unstable fluid layers that in turn give rise to greater convective mixing and thus expedited melting of PCM. In general, it can be stated that due to utilization of fixed high conductivity inserts/structures, the conducting pathways linking the hot and cold ends must be minimized.

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Topics: Thermal break (63%), Thermal bridge (62%), Heat transfer (61%) ... show more

865 Citations


Journal ArticleDOI: 10.1016/J.ENCONMAN.2013.05.003
Abstract: Thermal energy storage is critical for eliminating the discrepancy between energy supply and demand as well as for improving the efficiency of solar energy systems. This study numerically investigates the melting process in a triplex-tube heat exchanger with phase-change material (PCM) RT82. A two-dimensional numerical model is developed using the Fluent 6.3.26 software program. Three heating methods were used to melt the PCM from the inside tube, outside tube, and both tubes. Internal, external, and internal–external fin enhancement techniques were studied to improve the heat transfer between the PCM and heat transfer fluid. Enhancement techniques were compared with the inside tube heating, outside tube heating, both tube heating as well as the finned and internally finned tube. The effects of fin length on the enhancement techniques were investigated. Using a triplex-tube heat exchanger with internal–external fins, predicted results indicated that melting time is reduced to 43.3% in the triplex tube without fins. Experiments were conducted to validate the proposed model. Simulated results correspond with the experimental results.

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243 Citations


Journal ArticleDOI: 10.1016/J.APPLTHERMALENG.2013.01.011
Abstract: The importance of latent heat thermal energy storage is significant in contrast to sensible energy storage because of the large storage energy densities per unit mass/volume at nearly constant thermal energy. In this paper, heat transfer enhancement technique by using internal and external fins for PCM melting in a triplex tube heat exchanger (TTHX) was investigated numerically. A two-dimensional numerical model is developed using the Fluent 6.3.26 software program, and pure conduction and natural convection are considered in the simulation. The number of fins, fin length, fin thickness, Stefan number, TTHX material, and the phase change material (PCM) unit geometry in the TTHX are found to influence the time for complete melting of the PCM. Experiments were conducted to validate the proposed model. Simulated results agree with the experimental results. The computational results show that case G (8-cell PCM unit geometry) achieved a shorter time in completing the melting of the PCM, the total melting time is decreased to 34.7%.

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Topics: Heat transfer (64%), Annular fin (63%), Phase-change material (63%) ... show more

235 Citations


Babak Kamkari1, Hossein Shokouhmand1Institutions (1)
Abstract: This paper presents an experimental investigation of phase change material (PCM) melting in a transparent rectangular enclosure with and without horizontal partial fins. The enclosure was heated isothermally from one side while the other walls were thermally insulated. Experiments were performed with wall temperatures of 55, 60 and 70 °C ( 3.6 × 10 8 ⩽ Ra ⩽ 8.3 × 10 8 ) for finned and unfinned enclosures. Visualization of the melting process and the temperature field were performed directly. Both qualitative and quantitative information about the melting phenomena were obtained using digital photographs of the instantaneous melt front evolutions and temperature recordings at the vertical mid-plane of the enclosure. Temperature histories revealed that the thermally stratified region became smaller as the number of fins increased. Experimental data were used to calculate melt fractions, heat transfer rates and Nusselt numbers during the melting process. Furthermore, two correlation equations were developed using the dimensionless parameters to predict the Nusselt number and melt fraction. Also, in order to evaluate the improved thermal performance of the enclosure in the presence of partial fins, two other parameters were defined, melting enhancement ratio and overall fin effectiveness. Experimental results indicated that increasing the number of fins decreased the melting time and increased the total heat transfer rate while the surface-averaged Nusselt number reduced. Melting enhancement ratio and overall fin effectiveness increased with increasing the number of fins and decreased with raising the wall temperature. Melting enhancement ratios decreased with time after reaching some maximum values indicating that partial fins are more beneficial during the initial time of the melting.

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Topics: Fin (60%), Nusselt number (56%), Heat transfer (51%) ... show more

177 Citations


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