Study On The Effect Of Head-on Wind Speed And Spray Density On The Performance Of Evaporative Condenser

Evaporative condenser is a kind of equipment with high heat exchange efficiency,which has the advantages of air-cooled and water-cooled and combines heat and mass transfer processes.What’s more,it has great advantages in reducing the condensation temperature of refrigeration system,reducing the air flow of fan with unit cooling capacity,reducing the head of cooling water pump,improving the energy consumption and COP of unit condensation.The most important is that it has the advantages of low operating cost,good heat transfer effect,less water consumption,environmental protection and no pollution to the environment and it has been used in many large power plants,chemical sites,refrigeration systems and air conditioning systems.However,most of the evaporative condenser devices used in the market is designed under the maximum operating conditions,so in the actual application process,it will cause the use of"big car to small car",and the energy consumption loss is too serious.In order to study the optimum operating conditions of evaporative condenser,the heat and mass exchanges of refrigerant,cooling water and air outside the heat exchange coil inside the evaporative condenser are analyzed in detail.The results show that the main factors affecting the heat transfer of the evaporative condenser are in-pipe heat resistance R₁,on-pipe wall heat resistance R_2,on-pipe wall water film heat resistance R₃ and between air-water film interface heat resistance R₄.Among them,on-pipe wall water film heat resistance R₃ and between air-water film interface heat resistance R₄play a decisive role in the heat exchange process of the whole device,and the ratio of air volume to water volume is the main operating parameters affecting thermal resistance R₃and R₄.Therefore,through two different operating conditions of constant water variable air volume and constant air variable water volume,summarizing the relationship between condensation pressure,refrigeration capacity and energy efficiency ratio,and head-on wind speed,spray density.The evaporative condenser was numerically simulated by Fuent software,and its three-dimensional physical model was established after reasonable simplification of the experimental platform.What’s more,the boundary conditions were set up for the air inlet,air outlet,cooling water inlet and outlet,the wall of heat exchange coil and the surroundings of the model,and Mixture model was selected for calculation and analysis.The simulation results show that the size of the head-on wind speed has a great influence on the heat transfer efficiency of evaporative condenser.When the spray water velocity is constant,the temperature between heat exchanger coils and the temperature at the air outlet will gradually increase with the increase of the wind speed.The spray water velocity also has a certain influence on the heat transfer efficiency of evaporative condenser.When the head-on wind speed is 3 m/s,the upper part of the heat exchanger coil tube bundle will be increased.The temperature increases with the increase of cooling water velocity.Through the operation of constant water volume variable air volume,it is found that the head-on wind speed has great influence on condensation pressure,refrigeration capacity and energy consumption ratio.Under spray density(0.031 kg/（m·s）,0.039 kg/（m·s）and0.057 kg/（m·s）,the condensation pressure decreases sharply first and then decreases gently with the increase of the head-on wind speed,the refrigeration capacity increases sharply with the increase of the head-on wind speed and then increases gently,and the energy efficiency ratio increases first and then decreases with the increase of the head-on wind speed.The head-on wind speed is at the inflection point of 3.15 m/s,the slope of the curve is zero,and the corresponding air volume per unit heat transfer area is 288.01 m³/（h·m²）.At the inflection point of the head-on wind speed,the condensation pressure of the device is minimal,the refrigeration capacity is maximal,the energy efficiency ratio is maximal,and the operation state of the device is optimum.Therefore,the best head-on wind speed of the device under different spray densities is 3.15 m/s.It is found that the spray density has a great influence on the condensation pressure,refrigeration capacity and energy consumption ratio,especially on the condensation pressure of the device.The spray density is 0.057 kg/（m·s）at inflection point when the wind speed is 2.94 m/s,3.28 m/s and 3.46 m/s,and the air volume corresponds to 6056.4m³/h,6756.8 m³/h and 7127.6 m³/h.Before the inflection point value of 0.057 kg/（m·s）,the cooling capacity of evaporative condenser is dominant,and increases with the increase of the wind speed.When the cooling capacity reaches the extreme value,the spray density is at the inflection point value of 0.057 kg/（m·s）,the spray density continues to increase,the benefit of the refrigeration capacity remains unchanged,the power of the pump keeps increasing,which leads to the increase of power consumption and the performance of the whole system is reduced.The efficiency ratio decreases.When the spray density inflection point is 0.057 kg/（m·s）,the comprehensive operation effect of the device is the best.