Investigation On Cooling And Dehumidification Performance Of A Novel Convective-radiant Evaporator Based On Room Air Conditioner

The indoor evaporator of traditional room air conditioner depends on forced convection to exchange heat with indoor environment.Due to the high velocity of air supply,it is easy to cause local draught sensation and reduce thermal comfort of occupants.Moreover,the fan noise interferes with occupants and indoor fan needs to consume power.To avoid the defects of traditional room air conditioners,a novel convective-radiant evaporator based on room air conditioner is proposed in this paper.Through the combination of numerical simulation and experiment,the performance of the convective-radiant evaporator is investigated and its structural parameters is optimized.The main work of this paper is as follows:(i)A novel convective-radiant evaporator based on room air conditioner is proposed,which adopts R410A as circulating medium.The convective-radiant evaporator depends on natural convection and radiation heat transfer to provide cooling and eliminate moist load,without indoor fan.It can avoid draught sensation and fan noise,which has good thermal comfort.Besides,it also can avoid energy consumption caused by indoor fan.A steady-state numerical model is established to describe the heat and mass transfer process of the convective-radiant evaporator and validated with the experimental data.Results show that the maximum deviations between the simulated mean surface temperature and total heat exchange capacity of this evaporator and the experimental data are 9.8%and 7.7%.(ii)Based on the numerical model,the effects of several parameters on the total heat exchange capacity and dehumidification capacity of the convective-radiant evaporator are studied.The order of sensitivity of the total heat exchange capacity obtained by grey correlation analysis is as follows:evaporating temperature,refrigerant mass flow rate,indoor air temperature and relative humidity,and mean radiant temperature of internal surface.The order of sensitivity of the dehumidification capacity is as follows:refrigerant mass flow rate,evaporating temperature,indoor air temperature and relative humidity,and mean radiant temperature of internal surface.In addition,the characteristic equation between the total heat exchange capacity of the convective-radiant evaporator and refrigerant mass flow rate,air excess enthalpy and excess temperature of internal surface is proposed,which provides basis for its selection and matching with outdoor unit.(iii)A multi-objective heuristic optimization method of the convective-radiant evaporator is proposed.Under the conditions of indoor air temperature of 26.0 ~oC,relative humidity of 60.0%,condensing temperature of 40.0 ~oC and evaporating temperature between 8.0 ~oC and 12.0 ~oC,the evaporator with heat exchange capacity of2500 W matched with room air conditioner is optimized.The appearance area and initial cost of the convective-radiant evaporator are taken as objective function.Results show that the optimal structure of this evaporator is the fin height of 36.5～38.6 mm,the copper pipe diameter of 6.0～6.5 mm and the copper pipe spacing of 42.8～44.6mm.The corresponding optimal exterior area is 1.09～1.32 m~2,and the initial cost is668.4～876.4 CNY.The test piece of this work is the copper pipe diameter of 6.35 mm.(iv)According to different indoor air temperature,relative humidity and angle scale,the mean surface temperature of the convective-radiant evaporator is determined.Then the evaporating temperature corresponding to the mean surface temperature of the evaporator is obtained based on the established numerical model.Thus,the relationship between the evaporating temperature and indoor air temperature,relative humidity and angle scale is fitted,which provides guidance for the regulation of evaporating temperature of the convective-radiant evaporator.