Research On Microencapsulated Phase Change Slurry Heat Transfer Characteristic

With the development of Combined Heat and Power system in China, the capacity of cogeneration unit is increasing. And the wind power in China develops fast as well. The conflict of wind and heat in winter north China is serious. In order to solve this problem, increasing the cogeneration capacity for power peaking is an effective way. In the dissertaiton the reaearch object includes:the characterics of (MPCS) microencapsulated phase change slurry, the numerical simulation of MPCS and the power peaking capacity of cogeneration unit with MPCS thermal storage system.First, based on physical model, the MPCS physical properitis is investigated comparing with conventional single-phase fluid. The properitis include, density, thermal conductivity, specific heat and the viscosity. At the same time, the influencing factors of MPCS heat transfer enhancement is also analyzed from the energy equation. There are two important influencing factor, first is latent heat leading to an effective increase in the specific heat of the fluid, and another is micro-convection effect between microcapsule particles and carrier fluid.Next is the numerical simulation of MPCS. The simulation includes two parts: one is the microencapsuale internal melting simulation, another is MPCS flow in circular tube simulation. For the internal mellting simulation the enthalpy model is into use. Ignoring the internal natural convection, only energy equation should be solved. The melting process in different dismeters is analyzed in detail. It is found that internal melting rate is progressively smaller,90 percent of latent heat can be absorbed in 63% melting time. Also the influence of particle size and the microcapsules melts driving temperature difference in melting time is investgated as well. The study found that the melting time of particles in micron is vevy short. The melting time for dp=10um,40um is 28.4ms,2.3ms which indicates microcapsules with a carrier fluid between the smaller resistance. It proved that equivalent specific heat model assumptions is reasonable.For the MPCS flow in circular tube simulation, the equivalent specific heat model is built. The laminar flow in low Re and turbulence flow in high Re is investigated respectively. Laminar flow simulation analysis aimed at 0-30% concentration, and microcapsules at 0.025m/s-0.1m/s flow conditions within the tube flow characteristics and the microcapsules melts area. Turbulent process analysis focused on the pipe and the heat transfer fluid temperature process under two boundary conditions.The last study is MPCS thermal storage system for fluid cogeneration units peaking capacity enhancement. The research uses mathematical models of extraction cogeneration electric characteristics. And a design of MPCS investigated above is set up to do the analysis. For a 300MW cogeneration unit at rated 280MW thermal load conditions, the use of micro-encapsulated phase change thermal storage system enables fluid peaking capacity increased from 52.20MW 92.88MW which improves to 81.4%. Description thermal storage system has positive significance for cogeneration units peaking capacity increase.