Study On Electric Heater Defrosting Of The Gravity Feeding Evaporator

The gravity feeding recirculation refrigeration system is based on the thermal siphon principle,rely on the height difference between the gas-liquid separator and the evaporator to realize super times feeding liquid for the evaporator,the refrigerant supply is far greater than the amount of evaporation,thus ensuring inner surface of the evaporating pipe is fully wetting,improving the flow rate of the refrigerant,forcing the convective heat transfer of refrigerant side,improving the heat exchange efficiency of the evaporator.When the evaporator surface is covered with frost,increase the thermal resistance of the tube wall,impede air circulation,change the fan working point,and deteriorate the effect of heat transfer,thus affecting the overall performance of the refrigerating unit.Therefore,studying defrosting of the evaporator is of great significance for the whole refrigeration system operation.Due to the gravity feeding evaporator is super times feeding liquid,when the refrigerating unit shut down,the evaporator is filled with liquid refrigerant,if using internal heating defrosting evaporator,liquid storage tank and the corresponding pipeline is needed to add,moreover the control system will be very complicated.Based on the simple and practical principle,the external electric heating defrosting is used for the gravity feed evaporator.In order to better study the energy consumption of each part and the energy distribution in the defrosting process of the evaporator with and without refrigerant,the defrosting mathematical models of the evaporator are established.A test bench of the gravity feeding refrigeration system is established to study the defrosting effect of the evaporator with and without refrigerant,analysing and comparing the defrosting rate of two kinds of defrosting ways,the temperature fluctuation range of the cold storage in the defrosting process,and when restoring the refrigeration the cooling rate of the cold storage and the change of the evaporator pressure,to find a suitable for gravity feed evaporator defrosting method.The defrosting model of gravity feed evaporator is established for theoretical calculation,through analysing the energy consumption of each part and the energy distribution of the defrosting process,it can be found that,the defrosting time for evaporator without refrigerant is shorter than that of evaporator with refrigerant,the total energy consumption is smaller,the proportion of the energy used for defrosting is bigger.From the energy consumption point of view,the defrosting mode of evaporator without refrigerant will obtain a better effect.Experimental studies have shown that,delaying to open the fan when restoring therefrigeration could effectively reduce the temperature rise.The two defrosting modes each have advantages,for the evaporator without refrigerant,the defrosting time is shorter,but the range of temperature rise is slightly larger,the whole experiment process takes longer.Under the same condition,for the evaporator without refrigerant,the frost quantity is more than that of evaporator with refrigerant,but the defrosting time is shorter;when defrosting in the same way,the lower temperature of the working condition,the more amount of frost,and the longer defrosting time.