Performance comparison of a group of thermal conductivity enhancement methodology in phase change material for thermal storage application

Abstract

a b s t r a c tPhase change materials (PCM) are able to store thermal energy when becoming liquids and to release it when freezing. Recently the use of PCM materials for thermal energy storage (TES) at high temperature for Concentrated Solar Power (CSP) technology has been widely studied. One of the main investigated problems is the improvement of their low thermal conductivity. This paper looks at the current state of research in the particular field of thermal conductivity enhancement (TCE) mechanisms of PCM to be used as TES. This work considers a numerical approach to evaluate the performance of a group of TCE solutions composed by particular configurations of two of the principal TCE systems found on the literature: finned pipes and conductive foams. The cases are compared against a single PCM case, used as reference. Three different grades of graphite foams have been studied, presenting a charge time 100 times lower than the reference case for the same capacity. For fins two materials are analyzed: carbon steel and aluminum. The charge times of fin cases are from 3 to 15 times faster, depending on the amount and type of material employed. The internal mechanisms are analyzed to understand the results and locate possible improvement.

Polyurethane Foams: Past, Present, and Future

“…According to their phase change states, PCMs can be classified as liquid–gas PCMs, solid–solid PCMs, and solid–liquid PCMs. Liquid–gas PCMs have the highest energy density, but their high volume variation is a major drawback [ 223 , 224 ]. For that reason, the materials that are used for thermal energy storage are typically salt hydrates or paraffins.…”

Thermal Energy Processes in Direct Steam Generation Solar Systems: Boiling, Condensation and Energy Storage – A Review

“…Compared to the use of metal fins, such as aluminium and steel, protruding into the PCM volume, the use of expanded graphite foams can dramatically reduce charging and discharging times. Graphite foams do, however exhibit lower energy densities (Abujas et al, 2016). Another important implication is the choice of material paring where the resistance of the encapsulation material against corrosion by the phase change material is important as has been highlighted by Riuz-Cabanas et al (Ruiz-Cabañas et al, 2017).…”

“…The phase-change temperature should be matched as closely as possible to the saturation temperature of the steam at the desired pressure. For Rankine type cycles this temperature should be approximately between 310 • C and 350 • C (Abujas et al, 2016) which makes some metal alloys such as Mg-Zn (Weinstein et al, 2015), inorganic salts such as NaNO 3 and KNO 3 , and salt mixtures suitable choices. Challenges associated with PCMs are, however, the relatively higher material cost, low thermal conductivities of non-metal PCMs, density changes, property stability during long term cycles, subcooling, phase segregation and corrosion (Vasu et al, 2017).…”

“…To overcome this, several enhancement techniques have been investigated. These include extended surfaces using fins (Guo and Zhang, 2008;Sciacovelli et al, 2015), micro encapsulations and the use of composite PCM mixtures such as the inclusion of nano-particles or using expanded foams to create form-stable composites (Zhao et al, 2010;Khalifa et al, 2015;Abujas et al, 2016;Zhang et al, 2016f). The use of form-stable composites is a good option because it results in significantly higher effective thermal conductivities and produces stable thermo-physical properties under thermal cycling.…”

Optimisation and optimal geometry design for thermal energy storages in high temperature concentrating solar power

“…Singh et al [7] developed a graphite foam/phase change material (PCM) composite that could be used in a latent heat‐based TES system that will be compatible with a supercritical steam power cycle. Abujas et al [8] considered a numerical approach to evaluate the performance of a group of TCE solutions composed of particular configurations of two of the principal TCE systems found on the literature: finned pipes and conductive foams. Fernandez and Gomez‐Vidal [9] investigated the thermo‐physical properties characterisation of lithium nitrate containing salts.…”