Employing phase-change materials (PCM) is considered a very efficient and cost-effective option for addressing the mismatch between the energy supply and the demand. The high storage density, little temperature degradation, and ease of material processing register the PCM as a key candidate for the thermal energy storage system. However, the sluggish response rates during their melting and solidification processes limit their applications and consequently require the inclusion of heat transfer enhancers. This research aims to investigate the potential enhancement of circular fins on intensifying the PCM thermal response in a vertical triple-tube casing. Fin arrays of non-uniform dimensions and distinct distribution patterns were designed and investigated to determine the impact of modifying the fin geometric characteristics and distribution patterns in various spatial zones of the heat exchanger. Parametric analysis on the various fin structures under consideration was carried out to determine the most optimal fin structure from the perspective of the transient melting evolution and heat storage rates while maintaining the same design limitations of fin material and volume usage. The results revealed that changing the fin dimensions with the heat-flow direction results in a faster charging rate, a higher storage rate, and a more uniform temperature distribution when compared to a uniform fin size. The time required to fully charge the storage system (fully melting of the PCM) was found to be reduced by up to 10.4%, and the heat storage rate can be improved by up to 9.3% compared to the reference case of uniform fin sizes within the same fin volume limitations.

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Improved Melting of Latent Heat Storage Using Fin Arrays with Non-Uniform Dimensions and Distinct Patterns

Performance investigation of a vertically configured LHTES via the combination of nano-enhanced PCM and fins: experimental and numerical approaches

Emergence of asymmetric straight and branched fins in horizontally oriented latent heat thermal energy storage units

In the process of industrial waste heat recovery, phase change heat storage technology has become one of the industry's most popular heat recovery technologies due to its high heat storage density and almost constant temperature absorption/release process. In practical applications, heat recovery and utilization speed are particularly critical. Developing fins with reasonable structure or optimizing the original fins can speed up the process of heat storage and utilization to a certain extent. To improve the heat transfer enhancement design efficiency of fins and expand their application and reference range, this paper summarizes the current development process of new fins in the industry and the optimization results of the size, shape, and arrangement of fins by related researchers. It aims at these research results and how to design the shape, size, quantity, and arrangement of heat exchange fins from four proposed ideas and methods. The strengthening mechanism of heat transfer effect enhancement is analyzed. The research results show that the multi-branch structure is the research direction of the new fin design in the future; the non-uniform fin array has better heat transfer performance than the uniform fin array; the targeted arrangement of fins can maximize the heat transfer effect; there is an optimal number of fins in the heat accumulator; the parameters such as the size and number of fins and the size parameters of the heat accumulator are not independent of each other, but influence and restrict each other. The design process needs to be considered comprehensively; the topology optimization method, multi-objective response surface method, Taguchi method, orthogonal test method, etc., are commonly used in optimizing the shape and size of fins, which are simple and efficient. • Fine, multi-branched structure for deeper thermal penetration • Topology optimization, RSM, Taguchi, and orthogonal methods are commonly used in fin design. • Non-uniform fin arrays have better unilateral heat transfer than uniform arrays. • Optimal design of fins for the dominant heat transfer mechanism in different zones • Optimum heat transfer level in relation to optimum number of fins, thickness etc. 

Heat transfer enhancement technology for fins in phase change energy storage

This study aims to evaluate the melting characteristics of a phase change material (PCM) in a latent heat storage system equipped with hemispherical and quarter-spherical fins. A vertical triple-pipe heat exchanger is used as the PCM-based heat storage unit to improve the melting performance compared with a double-pipe system. Furthermore, the fins are arranged in inline and staggered configurations to improve heat transfer performance. For the quarter-spherical fins, both upward and downward directions are examined. The results of the system equipped with novel fins are compared with those without fins. Moreover, a fin is added to the heat exchanger’s base to compensate for the natural convection effect at the bottom of the heat exchanger. Considering similar fin volumes, the results show that the system equipped with four hemispherical fins on the side walls and an added fin on the bottom wall has the best performance compared with the other cases with hemispherical fins. The staggered arrangement of the fins results in a higher heat transfer rate. The downward quarter-spherical fins with a staggered configuration show the highest performance among all the studied cases. Compared with the case without fins, the heat storage rate improves by almost 78% (from 35.6 to 63.5 W), reducing the melting time by 45%.

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Improving the melting performance in a triple-pipe latent heat storage system using hemispherical and quarter-spherical fins with a staggered arrangement

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.

Naif Khalaf Alshammari

Papers

Melting Enhancement in a Triple-Tube Latent Heat Storage System with Sloped Fins.