The Research On Flow Capacity Of Capillary Pumped In The AMTEC

Alkali Metal Thermal to Electric Converter, AMTEC for short, is a novel conversionsystem which could convert thermo into electric directly. AMTEC has the advantage of highreliability, high power density, low consumption, low noise and no moving parts. So it willhave a bright future. As the key component of AMTEC, the capillary pump will absorb andtransfer heat, adjust the evaporation of the working fluid, and offer the cycle power for theentire system. The performance of the capillary pump reflects the operating conditions of theAMTEC. The paper will give a numerical simulation about the capillary pump from differentangles, which may have a good help to the design of a high performance capillary pump.Based on the Darcy’s law, a axisymmetric2D mathematical model coupled withdynamics and thermodynamics was set up.With the changes of the parameter, a numericalsimulation about the flow characteristics of the capillary pump which has the single-stage,two and multi-level is given. The Phase Field Method is used on tracking liquid-vaporinterface and the source terms are added in the Continuity Equation, Momentum Equation andEnergy Equation to simulate the processes of phase change and the capillary forces. Thetemperature, the density, velocity and the pressure field will also be given from themathematical model. It could also track to the liquid-vapor interface more precisely.The simulation results show that the change of pore size in the single-stage capillarypump has effect on the pressure, the larger of pore size, the smaller of pressure drop. As theporosity increases, the temperature of the working fluid is increased, but the density, velocity,pressure drop decrease. While with the changes in the pore size and porosity of the porousmedium, the flow field at the porous medium interface of the two and multi-stage capillarypump is more complex. When the thermal conductivity of the capillary material increases, thefluid temperature rises, the pressure drop falls, but the trend of changes in the velocity field inthe three types of capillary pumped has large differences. The evaporation rate of the workingfluid increases in parabolic shape with the temperature of the higher side and the outputpower density increase. Compared with the four materials, it is showed that the criticalaperture of stainless steel is most desirable. The performance of the through-flow of the alkalimetal potassium is better than lithium and sodium, and the multi-level capillary pumped alsoshows its strong advantages.