Research On Vertical Tube Indirect Evaporative Cooler And Its Performance Strengthening

In recent years,with the rapid development of Chinese economy,the utilization rate of energy is greatly increased,which causes the problems of energy shortage and environmental pollution.The country has proposed a"dual-carbon"policy to promote green technology,adjust the energy structure,and realize the new concept of low-carbon and high-quality development,Currently,building energy consumption is an important component of total energy consumption.Evaporative cooling technology is currently one of the energy-saving and environmentally friendly methods for HVAC.The evaporative cooling system is simple and only relies on circulating water and fans.Therefore,the research on evaporative cooling technology is of great significance.It generally has two forms:direct and indirect evaporative cooling.Direct evaporation is not suitable for occasions with high humidity requirements,and indirect evaporative cooling has a wider range of applications than direct evaporative cooling.At present,The horizontal tube indirect evaporative cooling air conditioning system is becoming increasingly mature in technology and application scope.The heat exchange tube contains primary air,and in areas with high dust concentration and severe sandstorms,there are defects such as blockage,difficulty in cleaning,low efficiency,large floor area and inconvenient reinforcement inside the heat exchange tube.This article proposes a vertical structure based on the above shortcomings of the horizontal tube indirect evaporative cooler.The heat exchanger has secondary air and water inside the tube,and the self-flushing of the water flow can effectively solve problems such as blockage and difficulty in cleaning.The primary air outside the tube is more convenient for strengthening heat exchange,thereby reducing the equipment’s footprint and conducting performance analysis.This article first elaborates on various types of evaporative coolers.Currently,there is little research on vertical tube indirect evaporative cooling air conditioning in the research status of evaporative coolers at home and abroad.In terms of numerical models,Most of them use simple heat and mass transfer models such as single tube,one-dimensional,and two-dimensional,which cannot truly simulate the heat and mass transfer process of secondary air and water,resulting in a significant difference between the temperature drop of the primary air in the simulation results and the actual situation;In terms of water distribution inside heat exchange tubes:Most studies have adopted new structural materials,added clean water membranes,or direct water distribution inside the tubes,which may lead to problems such as large water flow,thick water membranes,or low heat and mass exchange efficiency of heat exchangers.In this paper,the structure of vertical tube type indirect evaporative cooler with internal groove is proposed,which can improve the uneven distribution of water film thickness.A three-dimensional full-size physical model is established for it,and the structural parameters and operating conditions are changed to conduct numerical simulation research.Finally,a vertical tube type indirect evaporative cooler with good performance is obtained.Then,on this basis,straight fins are added to enhance the performance of heat transfer.The numerical calculation method in this paper adopts FVM and SIMPLE algorithm,and introduces VOF and k-εUsing the Pressure Based Solver and the component transport model,the following conclusions were obtained through numerical simulation research:(1)For the vertical tube indirect evaporative cooler with added inner grooves,the operating conditions are selected:temperature is 28℃～40℃,humidity is 45%RH～70%RH;The primary air speed is 1m/s～5m/s,and the secondary air speed is 7m/s～17m/s;Structural parameters:The primary air side length is 0.7m～1.2m,the secondary air side length is 0.8m～1.3m,the pipe diameter is 15mm～40mm,and the relative pipe spacing is 1.2～3.2 for numerical simulation.The results show that when the inlet temperature of the primary and secondary air is 29℃,the inlet humidity of the secondary air is 45%,and the primary and secondary wind speeds are 2.5m/s and 13m/s,respectively;When the side length of the secondary air is 0.9m and 1m,the pipe diameter is 25mm,and the relative pipe spacing is 2,the structural parameters are the optimal operating conditions and structural parameters for the heat exchanger.At this time,the outlet temperature of the primary air is 24.05℃,the cooling efficiency is 55.6%,and the cooling capacity is 174.95W/m~2.(2)For the vertical tube indirect evaporative cooler with added flat fins for enhanced heat transfer,numerical simulation research was conducted under the structural parameters of primary air speed of 1m/s～5m/s,fin spacing of 6mm,7mm,8mm,and fin thickness of 2mm,2.5mm,and 3mm.When the primary air speed is less than 2m/s,the heat transfer performance deteriorates as the fin spacing increases;When the wind speed is greater than 2m/s,the heat transfer performance increases with the increase of fin spacing.The thickness of the finned tube has a relatively low impact on the performance of the vertical tube indirect evaporative cooler.(3)A comparative analysis was conducted on the performance of vertical tube indirect evaporative coolers with added inner groove structure and light tube structure,and it was found that the cooling efficiency of the former was about 13%better than that of the latter;The performance of adding a flat fin with an inner groove structure outside the tube is about10%better than adding an inner groove structure inside the tube.