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Enhanced Heat Transfer Experimental and Simulation Research of Nanocomposite Phase Change Materials

Author: WuShuYing
Tutor: ZhuDongSheng
School: South China University of Technology
Course: Chemical Engineering
Keywords: Nano- composite heat storage material Heat transfer enhancement Phase change thermal storage Thermal conductivity Latent heat Numerical Simulation
CLC: TB383.1
Type: PhD thesis
Year: 2010
Downloads: 730
Quote: 2
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Abstract

The heat storage technology is an important way to improve energy efficiency and protect the environment, mainly used in solar thermal storage, power \Its heat storage density, the temperature change is small, easy to control, etc., is increasingly becoming the rational use of energy, improve energy efficiency, reduce environmental pollution, the preferred method of phase change thermal storage. The phase change material (Phase change materials, PCMs) phase change energy storage technology research foundation. Currently, the vast majority of inorganic PCMs corrosive and cold and phase separation in the phase transition process, its application is limited; the organic PCMs corrosive, in the process of phase change little cold and phase separation and chemically stable, cheap, and therefore, in the field of waste heat recovery and utilization of solar energy, building energy efficiency, application of organic PCMs widespread. However, organic PCMs shortcomings of low thermal conductivity, resulting in poor performance of the system heat transfer applications of energy storage systems, heat storage capacity utilization is low, reducing the system's energy efficiency. Therefore, the phase change energy storage technology is an important basic research work is the development of energy storage materials. In this paper, the organic phase change problem of low thermal conductivity material, the use of nanotechnology to its modified preparation of nanocomposite one for domestic hot water industry in the low-temperature phase change thermal storage material. The material not only has the existing organic phase change thermal storage material has the advantage, and to overcome the shortcomings of its low thermal conductivity. The phase change material of the reservoir, the rate of heat obtained in the heat storage process, greatly improves. Papers around the nano-composite phase change thermal storage material preparation, latent heat, specific heat, thermal conductivity, and phase change heat transfer characteristics, the following research: nano-composite phase change thermal storage materials preparation. Through visualization settlement analysis and temperature - time curve test method, both stable suspension in liquid paraffin phase change heat transfer rate of nanoparticles can improve. Investigated so that the object of this study on the basis of determined Cu-paraffin liquid Cu-paraffin is a stable suspension of the optimum dispersant type and concentration, and Hitenol BC-10 as a dispersing agent, and nano Cu particle mass ratio was 2.6:1 , the liquid stability of Cu-paraffin. Colloidal stable dispersion theory to explain the mechanism of liquid Cu-paraffin suspension stabilizer system. Finally, using scanning electron microscopy and infrared spectroscopy to analyze its microstructure. Cu-paraffin phase change latent heat and specific heat. Using a differential scanning calorimeter measurement of the phase of the thermal storage material of nano-composite latent heat, the phase transition temperature and specific heat. Investigated the concentration of nanoparticles and the heating and cooling cycles of latent heat and phase transition temperature; nanoparticle concentration and temperature on the Cu-paraffin specific heat. Nano-composite heat storage material phase change latent heat is slightly lower than that of pure paraffin, and with increasing the concentration of nanoparticles gradually decreases, and the phase transition temperature changes. The biggest changes in the latent heat value of 3.2% after 100 cycles, the phase transition, the phase transition temperature of the biggest changes in value of 1.9%, and found no obvious energy storage performance decay, the composite material has good storage characteristics. The specific heat of the Cu-paraffin decreases with increasing nanoparticle content, and increased slightly with increasing temperature. Latent heat and specific heat decreases reasons explained nano-composite heat storage material. Cu-paraffin thermal conductivity studies. Cu-paraffin system transient hot test solid and liquid thermal conductivity, to study nanoparticle mass fraction, temperature and thermal cycles on the Cu-paraffin thermal conductivity. Nanometer Cu content of 1.2 wt% particles, the thermal conductivity of the liquid is higher than that of pure paraffin 14.3%, a 10% increase in solid-state. After 100 cycles, the coefficient values ??of the thermal conductivity of the material is still stable. The theoretical model of the two-phase mixture of traditional computing thermal conductivity has not truly reflect the energy of the nano-composite heat storage material transfer process, this article attempts to theory from the preliminary study on the micro nano lattice vibrations, the interfacial thermal resistance, Brownian motion and nanoparticles effectively reunion enhanced conduction mechanism of the composite heat-accumulating material. 4, Cu-paraffin phase change heat transfer experimental study. Using temperature - time curve method for different concentrations of nano-composite heat storage material storage, exotherm, the distribution of real-time observation of the temperature field of the infrared camera of its melting and solidification process, design a storage system for the Cu-paraffin energy heat pump water heater bench. Temperature - time curve method research results show that the nano Cu particles in paraffin phase change material storage, heat release rate has been significantly improved, and increased with the increase of the mass fraction of nano-Cu. The nano Cu mass fraction of 1%, the phase change material melting and solidification rate increased by 30% and 28.2%, respectively. The temperature distribution results show that the addition of nanoparticles to improve the thermal conductive coefficient of the phase change material, and the diffusion rate is increased with the concentration of particles and accelerate; Cu-paraffin present in the melting and solidification process of two distinct phase mushy zone. The results of the energy storage heat pump water heater to the Cu-paraffin as a heat storage material of the heat pump water heater, energy storage heat pump water heater system has good stability during operation. 5, Cu-paraffin phase change heat transfer numerical simulation. Fluent software simulation of phase change material melting and solidification process of phase change heat transfer. Analog of the melting process, taking into consideration the liquid natural convection, the volume expansion of the melting process, and the sinking of the solid phase in the liquid phase, the close contact melting. Simulation results show, the addition of nanoparticles to improve the paraffin melting and solidification rate, the Cu-paraffin melting process mainly by natural convection, solidification process to heat conduction of the main mode of heat transfer. Due to the solid state density of the phase change material is greater than the liquid, the the solid PCMs sinking cause occurs in the melting process in the \rate. Nucleation, thermal conductivity analysis of nanoparticles to improve the rate of heat output and thermal diffusivity three aspects of the phase change material melting and solidification rate. The present paper through a method of adding Cu nanoparticles in the organic phase change material paraffin effectively improve the thermal performance of the paraffin and the accumulator, the exothermic phase change heat transfer rate. The study not only for the development of new composite phase change thermal storage materials to provide a new way to provide the necessary experimental evidence and theoretical support, but also for the development of energy storage heat pump water heater.

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