Research On Characteristics Of Heat Transfer And Pressure Drop Of Evaporators Under High Gravity

The aircraft environmental control system plays an increasingly important role on protecting the normal applications of high-power and highly integrated avionics. There are many investigations focused on the developments of new environmental control systems. Air cooling systems as a traditional method cannot meet the cooling demands of the high-power avionics, and vapor cycle cooling systems with liquid cooling become an alternative.In the vapor cycle cooling system, the coolant works as circulating fluid to prevent freezing. The most common coolants in liquid cooling systems are aqueous solution of propylene glycol, ethylene glycol, methanol and ethanol. Mathematical modeling of thermodynamic properties of coolants is an important in designing vapor cycle cooling systems. In this paper, the research focuses on several thermodynamic parameters including thermal conductivity, specific heat capacity, dynamic viscosity and density and two coolants of methanol and propylene glycol. The thermal property data of the two coolants are collected. Using the regression analysis method, some new correlations with higher accuracy are put forward.In vapor cycle cooling systems, the evaporator is one of principal components. The heat transfer capability of evaporator directly leads to the quality of the system. In this paper, based on the summary of two-phase flow study at home and abroad, the characteristics of heat transfer and pressure drop in evaporators are compared and analyzed separately in earth gravity and high gravity. Then the mathematical models are built and the numerical simulations are carried by FORTRAN program developed in the properly chosen algorithms. The heat transfer and resistance of the evaporators under high gravity are calculated. The results show that the gravity has remarkable effects on heat transfer. Friction resistance and gravity pressure drop are monotonic increasing functions of gravity. Then analysis and sizing of evaporators are carried, 225 fin combinations were compared, and the optimum evaporator structures base on weight, size, and thermal performances are find out.