A new model of phase change process for thermal energy storage

Abstract

Summary Thermal energy can be converted into mechanical energy through the melting process of a phase change material (PCM). A PCM mixed with an insoluble liquid has higher energy converting efficiency during the whole melting process, where the massive microvacuum formed during the freezing process is filled by the insoluble liquid, which increases utilization of the volume change. The traditional theoretical model of the phase change process is unable to sufficiently describe the mixed PCM; therefore, a new model aimed at analyzing the characteristics of the volumetric change rate, as well as the freezing and melting times of the mixed PCM, is theoretically constructed. In this paper, the effective heat capacity method is used, and the effects of porosity are considered when the PCM is in the solid state. Comparisons of this model with the traditional model are carried out using both simulations and experiments for different pressures and geometric structures. Our results indicate that the introduced model has better accuracy when describing the phase change process of the pure PCM mixed with an insoluble liquid.

Ocean thermal energy utilization process in underwater vehicles: Modelling, temperature boundary analysis, and sea trail

“…Based on the thermal engine model in Section 3.1, PCM region realizes heat transfer through heat conduction. The innermost layer of PCM coupled with center rubber tube is adiabatic boundary, as shown in Equation (15), and the outermost layer of PCM coupled with metal shell is conduction boundary (Equation 16).…”

“…Qingchao Xia et al developed a new model aimed at analyzing the characteristics of the volumetric change rate, as well as the freezing and melting times of the mixed PCM, is theoretically constructed. He also carried out a platform experiment to verify the accuracy of his proposed model …”

“…He also carried out a platform experiment to verify the accuracy of his proposed model. 15 In addition, some scholars have studied the working pattern of ocean thermal vehicles. By coupling phase change model of thermal engine with the hydraulic system, Carneiro developed a quasi-static model of a thermal-driven volumetric pump for energy harvesting.…”

Maximum efficiency point tracking for an ocean thermal energy harvesting system

“…In ocean fields, Chao Yi et al creatively designed an energy producing device using ocean thermal energy, and this scheme is used by underwater profiler and glider. In these underwater vehicles, PCMs that are filled in enclosed containers are used as the working fluid of the thermal engine to absorb and release heat through the wall of the container, and then adjust the buoyancy of the underwater vehicles . Compared with other ocean carriers, these vehicles have a longer lifetime because no electric power consumption is needed for buoyancy control .…”

“…In these underwater vehicles, PCMs that are filled in enclosed containers are used as the working fluid of the thermal engine to absorb and release heat through the wall of the container, and then adjust the buoyancy of the underwater vehicles. 2,[18][19][20][21] Compared with other ocean carriers, these vehicles have a longer lifetime because no electric power consumption is needed for buoyancy control. 22 However, simply reducing the power consumption for a vehicle that carries many sensors for a long-term ocean observation is not sufficient.…”