Numerical studies on a fin-foam composite structure towards improving melting phase change

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

Effect of Twisted Fins on the Melting performance of PCM in a Latent Heat Thermal Energy Storage System in Vertical and Horizontal Orientations: Energy and Exergy Analysis

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

Latent thermal energy storage (LTES) heat exchangers can provide energy storage in a broad range of energy systems. Implementing LTES heat exchangers requires an assessment of their performance in a given system. The performance of a LTES heat exchanger is described by its performance indicators which are classified as technical, economical, and life-cycle indicators. The current paper focusses on the technical performance indicator and specifically on predictive methods which aid the assessment of the performance of a LTES heat exchanger in a system. To structure the analysis, a thermodynamic framework is provided which allows to clearly define LTES heat exchangers and classify the technical performance indicators. In a second step, the literature is reviewed for reported technical performance indicators with a specific focus on predictive methods for these indicators. The averaged effectiveness-number of transfer units (ε-NTU) and phase change time method are identified as important predictive models, analyzed, and compared based on their theoretical derivation. The relation between the averaged effectiveness and phase change time is investigated both theoretically and based on data available in literature which results in recommendations for standardizing the characterization of LTES heat exchangers. By standardizing characterization of LTES heat exchangers, researcher can assess their performance in different energy systems without additional experiments or CFD calculations. 

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Standardised methods for the determination of key performance indicators for thermal energy storage heat exchangers

This work evaluates the influence of combining twisted fins in a triple-tube heat exchanger utilised for latent heat thermal energy storage (LHTES) in three-dimensional numerical simulation and comparing the outcome with the cases of the straight fins and no fins. The phase change material (PCM) is in the annulus between the inner and the outer tube, these tubes include a cold fluid that flows in the counter current path, to solidify the PCM and release the heat storage energy. The performance of the unit was assessed based on the liquid fraction and temperature profiles as well as solidification and the energy storage rate. This study aims to find suitable and efficient fins number and the optimum values of the Re and the inlet temperature of the heat transfer fluid. The outcomes stated the benefits of using twisted fins related to those cases of straight fins and the no-fins. The impact of multi-twisted fins was also considered to detect their influences on the solidification process. The outcomes reveal that the operation of four twisted fins decreased the solidification time by 12.7% and 22.9% compared with four straight fins and the no-fins cases, respectively. Four twisted fins improved the discharging rate by 12.4% and 22.8% compared with the cases of four straight fins and no-fins, respectively. Besides, by reducing the fins’ number from six to four and two, the solidification time reduces by 11.9% and 25.6%, respectively. The current work shows the impacts of innovative designs of fins in the LHTES to produce novel inventions for commercialisation, besides saving the power grid.

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Wang Zixiong

Papers

Solidification Enhancement in a Triple-Tube Latent Heat Energy Storage System Using Twisted Fins