Session: 11-01: Micro/Miniature Two-Phase Devices/ Systems

Paper Number: 130635

130635 - Performance Optimization on a Shell-and-Tube Latent Heat Storage Device by Enhanced Close-Contact Melting Mechanism and Nano-Enhanced Phase Change Material 

Abstract: 

Latent heat thermal energy storage (LHTES) is an important technology to overcome the time/space difference and instability between the supply and demand ends of thermal energy. There exists an inherent problem during heat charging process, i.e., the increasing thermal resistance as a result of the phase interface moving away from the heat source, which greatly restricts the practical application of the LHTES technology. Close-contact melting (CCM), featuring heat conduction through a micro-liquid film, can solve the problem of increasing thermal resistance caused by the phase interface evolution in convection-driven melting process, because the solid phase change material (PCM) and the heat source can always maintain a "close contact" state. Although CCM can be realized in shell-and-tube LHTES devices by using fins, such as annular fins, to form a specific angle with the heat flow direction and gravity, the solid PCMs in the early stage of melting are often unable to form CCM due to the adherence of the solid PCM to the lateral walls and the surface tension of the liquid PCM.

To break through this bottleneck, this paper proposes a passively enhanced approach based on pulse-heating on the lateral wall, which realizes rapid triggering of CCM. The pulse-heating film can deliver an instantaneous thermal power of 640W, enabling the formation of a liquid film between the solid PCM and the lateral wall of the device in a short period. The area between adjacent annular fins in the TES device was selected for visualization experiments to analyze the occurrence process of CCM. A shell-and-tube phase change TES system was constructed for further analyzing the enhancement effects of enhanced CCM on the heat charging process. Furthermore, leveraging the efficient heat conduction characteristics inherent to CCM, high thermal conductivity nano-enhanced PCMs (NePCMs) were utilized to increase the charging power density. Graphene nanoplatelets (GNPs) were subsequently dispersed in the matrix PCMs to produce NePCM samples with mass fractions of 0.0 wt.%, 1.0 wt.%, and 3.0 wt.%. It is shown that thermal conductivity of the composites increased by more than a factor of 2 at the loadings of 3.0 wt.%. Although the viscosity of NePCM also grows due to the addition of GNPs, pulse-heating still could realize rapid triggering of CCM. In the shell-and-tube phase change TES system, the volume expansion method was employed to further analyze the synergistic effects of enhanced CCM and nano-additives loading on the heat charging process. The melting time and power density of TES devices under different working conditions were also analyzed quantitatively. This research provides guidance for practical applications of high-efficiency TES devices in the fields of LHTES and high-power-density thermal management.

Presenting Author: Zirui Li Zhejiang University

Presenting Author Biography: Zi-Rui Li is currently pursuing his Ph.D. in the School of Energy Engineering, Zhejiang University. His research interests mainly focus on heat transfer during close-contact melting process and its application for high-power-density thermal energy storage.

Authors:

Zirui Li Zhejiang University
Wenze Yang Zhejiang University
Liwu Fan Zhejiang University