applied sciences Article Shell-and-Tube Latent Heat Thermal Energy Storage Design Methodology with Material Selection, Storage Performance Evaluation, and Cost Minimization Lizhong Yang 1,2 , Haoxin Xu 3, Fabrizio Cola 3, Bakytzhan Akhmetov 1 , Antoni Gil 1 , Luisa F. Cabeza 2 and Alessandro Romagnoli 3,* 1 SJ-NTU Corporate Lab, Nanyang Technological University, Singapore 637335, Singapore; [email protected] (L.Y.); [email protected] (B.A.); [email protected] (A.G.) 2 GREiA Research Group, Universitat de Lleida, Pere de Cabrera s/n, 25001 Lleida, Spain; [email protected] 3 School of Mechanical and Aerospace Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore; [email protected] (H.X.); [email protected] (F.C.) * Correspondence: [email protected] Abstract: Shell-and-tube latent heat thermal energy storage units employ phase change materials to store and release heat at a nearly constant temperature, deliver high effectiveness of heat transfer, as well as high charging/discharging power. Even though many studies have investigated the material formulation, heat transfer through simulation, and experimental studies, there is limited research dedicated to the storage unit design methodology. This study proposes a comprehensive methodol- ogy that includes the material assessment with multi-attribute decision-making and multi-objective Citation: Yang, L.; Xu, H.; Cola, F.; decision-making tools, epsilon-NTU method, and cost minimization using Genetic Algorithm. The Akhmetov, B.; Gil, A.; Cabeza, L.F.; methodology is validated by a series of experimental results, and implemented in the optimization Romagnoli, A. Shell-and-Tube Latent of a storage unit for solar absorption chiller application. A unit cost of as low as USD 8396 per Heat Thermal Energy Storage Design unit is reported with a power of 1.42 kW. The methodology proves to be an efficient, reliable, and Methodology with Material Selection, systematic tool to fulfill the preliminary design of shell-and-tube LHTES before the computational Storage Performance Evaluation, and fluid dynamics or detailed experimental studies are engaged. Cost Minimization. Appl. Sci. 2021, 11, 4180. https://doi.org/10.3390/ Keywords: shell-and-tube; phase change material (PCM); latent heat; multi-attribute decision- app11094180 making; multi-objective decision-making; design; material selection; epsilon-NTU; optimization; genetic algorithm Academic Editor: Miguel R. Oliveira Panão Received: 25 March 2021 Accepted: 27 April 2021 1. Introduction Published: 4 May 2021 The demand for improving energy efficiency to battle with the shortage of energy supply, volatile oil prices, and climate change is increasing [1]. Some energy production Publisher’s Note: MDPI stays neutral processes, such as renewable energy generation and waste heat recovery, face the issues with regard to jurisdictional claims in of mismatch between demand and supply. Thermal energy storage (TES) provides a published maps and institutional affil- promising solution to bridge this mismatch by storing and releasing heat or cold at given iations. conditions, thus upgrading the system efficiency [2,3]. Common TES technologies include sensible heat thermal energy storage (SHTES), la- tent heat thermal energy storage (LHTES), and thermochemical storage (TCS) [4,5]. Among them, LHTES demonstrates unique advantages over the others by providing a large storage Copyright: © 2021 by the authors. density while being chemically stable [5,6]. LHTES uses phase change materials (PCMs) Licensee MDPI, Basel, Switzerland. to absorb and release the latent heat during phase transition at a nearly constant tem- This article is an open access article perature, making it a good fit for the temperature management services [7,8]. Previous distributed under the terms and studies have reported design integration of LHTES in an extensive range of applications, conditions of the Creative Commons including concentrating solar power plants (CSP) [9], solar-absorption chilling systems [10], Attribution (CC BY) license (https:// buildings [11,12], waste thermal energy recovery [13], and thermal management of elec- creativecommons.org/licenses/by/ tronics [14]. 4.0/). Appl. Sci. 2021, 11, 4180. https://doi.org/10.3390/app11094180 https://www.mdpi.com/journal/applsci Appl. Sci. 2021, 11, x FOR PEER REVIEW 2 of 18 Appl. Sci. 2021, 11, 4180 2 of 16 systems [10], buildings [11,12], waste thermal energy recovery [13], and thermal manage‐ ment of electronics [14]. Among various LHTES configurations, the shell‐and‐tube type is widely studied [15]. AmongDue to variousits advantages, LHTES configurations,such as simple thedesign, shell-and-tube low cost, typelow pressure is widely drop studied [16,17], [15]. Duelarge to heat its transfer advantages, area, such high asdischarging simple design, power, low and cost, high low effectiveness pressure drop [5], the [16 ,shell17], large‐and‐ heattube transfertype of LHTES area, high is the discharging most employed power, configuration and high effectiveness [18]. [5], the shell-and-tube typeThe of LHTES design is of the a most shell employed‐and‐tube configurationLHTES unit encompasses [18]. a wide range of topics. ManyThe past design studies of ahave shell-and-tube been dedicated LHTES to heat unit transfer encompasses enhancement a wide range by inclusions of topics. of Many ma‐ pastterial studies additives have or been metal dedicated objects into to heatthe PCMs transfer [19,20]. enhancement Others focused by inclusions on the ofrefinement material additivesof storage or configuration metal objects to into achieve the PCMs satisfactory [19,20 ].melting Others and focused solidification on the refinement performance of storage[21,22]. configurationHowever, very to few achieve studies satisfactory have been melting found and to answer solidification the question performance of what [21 spe,22].‐ However,cific steps veryto follow few studiesin searching have beenfor both found the to best answer storage the material question and of what the corresponding specific steps toschematic follow in design searching of a shell for both‐and the‐tube best LHTES storage unit. material and the corresponding schematic designRegin of a et shell-and-tube al. [23] proposed LHTES a flowchart unit. that describes different design stages of LHTES, fromRegin material et al. research [23] proposed to commercial a flowchart product. that describesHowever, different since this design flowchart stages involves of LHTES, the fromfull life material span of research the design to commercial process, it product.does not specify However, the since detailed this design flowchart method, involves for theexample, full life how span to obtain of the designmaterial process, and geometrical it does not properties. specify the No detailed optimization design was method, men‐ fortioned example, in the howflowchart. to obtain Tehrani material et al. and [24] geometricaldescribed the properties. design process No optimization of the shell‐and was‐ mentioned in the flowchart. Tehrani et al. [24] described the design process of the shell- tube LHTES system for CSP tower plants, as illustrated in Figure 1. The design process and-tube LHTES system for CSP tower plants, as illustrated in Figure1. The design process covers PCM selection, storage volume estimation, selection of geometric parameters, and covers PCM selection, storage volume estimation, selection of geometric parameters, and optimizing storage volume with the given design alternatives. It pioneers the design optimizing storage volume with the given design alternatives. It pioneers the design methodology of the shell‐and‐tube LHTES system even though a few limitations still exist. methodology of the shell-and-tube LHTES system even though a few limitations still exist. The PCMs selection, according to this study, adopts the melting temperature and the The PCMs selection, according to this study, adopts the melting temperature and the availability of detailed properties of the materials to filter the database. This practice is availability of detailed properties of the materials to filter the database. This practice is commonly seen in most studies and engineering cases. For example, in the methodology commonly seen in most studies and engineering cases. For example, in the methodology developed by Liu et al. [18] to design a cascade PCM storage unit, three PCMs were se‐ developed by Liu et al. [18] to design a cascade PCM storage unit, three PCMs were selected lected based on the temperature restrictions and material properties. However, when based on the temperature restrictions and material properties. However, when dealing with dealing with a broad spectrum of materials with detailed property data available, re‐ a broad spectrum of materials with detailed property data available, researchers should spendsearchers a significant should spend amount a significant of effort choosing amount of the effort best choosing alternatives. the best alternatives. FigureFigure 1.1. The design process ofof thethe PCM-HEXPCM‐HEX unitunit forfor solarsolar towertower powerpower plantsplants [[24].24]. Another limitation found in this designdesign processprocess andand otherother commonlycommonly usedused designdesign processes isis thethe employmentemployment ofof numericalnumerical simulations,simulations, whichwhich isis complicatedcomplicated byby thethe highhigh demand forfor computational computational resources, resources, especially especially for for optimizing