The Research Of Flow And Heat Transfer In Micro-Scale Intermittent Recuperator

In recent years, the Micro Internal Combustion Engine with the great advantages of high energy density is becoming the main trend in the area of portable power. Micro Internal Combustion Swing Engine(MICSE) proposed by the University of Michigan is one of them. Based on it, Energy Institute of Chinese Academy of Sciences and so on proposed one with three arms. All of them have a low thermal efficiency which is a common drawback. So how to improve the thermal efficiency has become a popular research topic in the field. Therefore this paper analyzes the main ways causing the energy loss. After the feasibility discuss about the heat exchanger used for MICSE, the method that using micro recuperator to recycle the heat in exhaust and heating cold gas before working strokes is put forward to improving the thermal efficiency of the engine. At the same time, in order to enable the normal operation of the engine with the installation of the recuperator, a new thermal cycle called mixing cycle for multi cylinder micro swing engine with recuperator is invented.There are two main characteristics in the recuperaotr mentioned above, one is small scale channel and another is intermittent flow and heat transfer.For the first characteristict, this paper, using two-dimensional parallel plate channel with channel height of 0.5mm~1.0mm and plate thickness of 0.1mm~0.5mm, finds that the differences between the inlet enthalpy of hot and cold gas, the thermal conductivity of solid materials and area-volume ratio are the main factors affecting the heat transfer boundary condition.In the micro tube which using wall constant heat flux boundary condition instead of hot gas, the result shows that the relations between f and Re is same with that of commom scale, except the smaller the diameter is, the smaller is the f at low Reynolds number. Besides, the effect of axial heat conduction on the heat transfer effect can not be ignored and the geometric size will affect the axial heat conduction.In light of these conclusions, this paper designs and improves the geometric size of double-pipe heat exchanger, the result shows that the different geometric parameters and the thermal conductivity coefficient of solid material have different degree of effects on the axial heat conduction.For the second characteristic, the numerical simulation study about the intermittent flow and heat transfer in double-pipe heat exchanger is done in this paper. There are two main characteristics that differing from that of common scale: the axial thermal conductivity of the solid wall and the periodic fluctuation of the wall temperature with time. Therefore, the two non dimensional parameters, such as thermal resistance ratio of heat transfer between gas and solid and the axis guide of solid, called *R and the heat capacity ratio of gas and solid wall, called *C, are proposed in this paper. Meanwhile, the factors affecting the above two parameters are also mentioned.Finally, based on the above study of intermittent flow and the heat transfer under small scale, the shell and tube recuperator used in micro swing engine is preliminarily designed. Then, it was used as a research object in numerical calculation which is under simplification and real working conditions. At last, this paper also design experiment to verify the efficiency of the recuperator mentioned above. As for heat dissipated and conduction in the wall is very terrible, more measures need to be raised.