Numerical study on thermal energy storage performance of phase change material under non-steady-state inlet boundary

Due to the solar radiation intensity variation over time, the outlet temperature or mass flow rate of heat transfer fluid (HTF) presents non-steady-state characteristics for solar collector. So, in the phase change thermal energy storage (PCTES) unit which is connected to solar collector, the phase change process occurs under the non-steady-state inlet boundary condition. In present paper, regarding the non-steady-state boundary, based on enthalpy method, a two dimensional physical and mathematical model for a shell-and-tube PCTES unit was established and the simulation code was self-developed. The effects of the non-steady-state inlet condition of HTF on the thermal performance of the PCTES unit were numerically analyzed. The results show that when the average HTF inlet temperature in an hour is fixed at a constant value, the melting time (time required for PCM completely melting) decreases with the increase of initial inlet temperature. When the initial inlet temperature increases from 30°C to 90°C, the melting time will decrease from 42.75min to 20.58min. However, the total TES capacity in an hour reduces from 338.9kJ/kg to 211.5kJ/kg. When the average inlet mass flow rate in an hour is fixed at a constant value, with the initial HTF inlet mass flow rate increasing, the melting time of PCM decreases. The initial inlet mass flow rate increasing from 2.0×10−4kg/s to 8.0×10−4kg/s will lead to the melting time decreasing from 37.42min to 23.75min and the TES capacity of PCM increasing from 265.8kJ/kg to 273.8kJ/kg. Under all the studied cases, the heat flux on the tube surface increases at first, until it reaches a maximum then it decreases over time. And the larger the initial inlet temperature or mass flow rate, the earlier the maximum value appearance and the larger the maximum value.

[1]  Ya-Ling He,et al.  A MCRT and FVM coupled simulation method for energy conversion process in parabolic trough solar collector , 2011 .

[2]  Bernard Franković,et al.  Analysis of the influence of operating conditions and geometric parameters on heat transfer in water-paraffin shell-and-tube latent thermal energy storage unit , 2006 .

[3]  Luisa F. Cabeza,et al.  Review on thermal energy storage with phase change: materials, heat transfer analysis and applications , 2003 .

[4]  D. Buddhi,et al.  Numerical heat transfer studies of the fatty acids for different heat exchanger materials on the performance of a latent heat storage system , 2005 .

[5]  Frank P. Incropera,et al.  Fundamentals of Heat and Mass Transfer , 1981 .

[6]  L. Cabeza,et al.  Experimental evaluation of commercial heat exchangers for use as PCM thermal storage systems , 2009 .

[7]  G. Fang,et al.  Thermal performance simulations of a packed bed cool thermal energy storage system using n-tetradecane as phase change material , 2010 .

[8]  Hamid El Qarnia,et al.  Numerical analysis of a coupled solar collector latent heat storage unit using various phase change materials for heating the water , 2009 .

[9]  Hassan E.S. Fath,et al.  Heat exchanger performance for latent heat thermal energy storage system , 1991 .

[10]  Wujun Zhang,et al.  Numerical simulation and parametric study on new type of high temperature latent heat thermal energy storage system , 2008 .

[11]  Kamil Kaygusuz,et al.  Thermal energy storage performance of paraffin in a novel tube-in-shell system , 2008 .

[12]  Long Jian-you,et al.  Numerical and experimental investigation for heat transfer in triplex concentric tube with phase change material for thermal energy storage , 2008 .

[13]  K. Kaygusuz,et al.  Experimental study on melting/solidification characteristics of a paraffin as PCM , 2007 .

[14]  Jinyue Yan,et al.  Enhanced thermal conductivity and thermal performance of form-stable composite phase change materials by using β-Aluminum nitride , 2009 .

[15]  John Currie,et al.  Integrated collector storage solar water heater: Temperature stratification , 2009 .

[16]  Francis Agyenim,et al.  A review of materials, heat transfer and phase change problem formulation for latent heat thermal energy storage systems (LHTESS) , 2010 .

[17]  Pichai Namprakai,et al.  A new version of a solar water heating system coupled with a solar water pump , 2009 .

[18]  S. Garimella,et al.  Molten-salt thermal energy storage in thermoclines under different environmental boundary conditions , 2010 .

[19]  Ya-Ling He,et al.  Numerical study on coupled fluid flow and heat transfer process in parabolic trough solar collector tube , 2010 .

[20]  M. Lacroix.  Numerical simulation of a shell-and-tube latent heat thermal energy storage unit , 1993 .

[21]  Juan Xiao,et al.  Three-dimensional numerical study of heat transfer characteristics in the receiver tube of parabolic trough solar collector , 2010 .

[22]  Wei Xiao,et al.  Analytical optimization of interior PCM for energy storage in a lightweight passive solar room , 2009 .

[23]  Ming Fang,et al.  Effects of different multiple PCMs on the performance of a latent thermal energy storage system , 2007 .

[24]  F. Kuznik,et al.  Experimental assessment of a phase change material for wall building use , 2009 .

[25]  A. Sharma,et al.  Review on thermal energy storage with phase change materials and applications , 2009 .

[26]  Anica Trp,et al.  An experimental and numerical investigation of heat transfer during technical grade paraffin melting and solidification in a shell-and-tube latent thermal energy storage unit , 2005 .

[27]  Hamid Ait Adine,et al.  Numerical analysis of the thermal behaviour of a shell-and-tube heat storage unit using phase change materials , 2009 .

[28]  John W. Kelton,et al.  Testing of Thermocline Filler Materials and Molten-Salt Heat Transfer Fluids for Thermal Energy Storage Systems in Parabolic Trough Power Plants , 2004 .