Research On Airflow Organization Of Constant Temperature Fruit And Vegetable Cold Storage With Partial Top Row Pipe

Natural convection air cooler is particularly important for reducing system energy consumption and reducing weight loss of fruits and vegetables.Indirect refrigeration system is an important way to reduce refrigerant charge.The small heat exchange temperature difference is a key factor to maintain the air humidity in the cold storage and reduce the energy consumption of defrosting.In order to solve the influence of condensation and frosting of traditional top row pipes on the goods in the cold storage,it is necessary to study the indirect cooling refrigeration system with local top row pipes and small heat exchange temperature differences.Pre-cooling the harvested fruits and vegetables in the pre-cooling room can quickly take away the heat from the field.After cooling to a certain temperature,place the goods in a cold storage room for refrigeration.It provides a reference mode for precise temperature control of cold storage and stable operation of refrigeration system.It provides protection for the preservation of fruits and vegetables.Based on the industry's pain points of the original cold storage,and the many advantages of natural convection air coolers and indirect refrigeration systems,this article focuses on the application of local top row pipes in the indirect cooling refrigeration system of constant temperature fruit and vegetable storage.First of all,FLUENT is used for simulation analysis.In this paper.the influence of the position of the top row pipe,goods and liquid supply temperature of the top row pipe on the air distribution in the cold room is studied.The main conclusions of the numerical simulation part of this paper are as follows:(1)A three-dimensional laminar steady-state cold storage model with natural convection and radiation heat transfer in the top row of tubes is established.It is verified that the refrigeration system scheme using partial top row pipes is feasible.It provides theoretical guidance and reference basis for the actual production of the original cold storage.(2)Determination of the location of the top row of pipes.An empty cold storage model with top row pipes at three different positions was established.The first position is that the pipes are arranged in two vertical rows on both sides of the cold room.The second position is that the pipes are arranged horizontally in the middle of the cold room.Position three is the staggered arrangement of rows of pipes.Under the same boundary conditions,when the top row pipes are arranged in the form of position one,the temperature of the cargo area when the warehouse is empty is within-1.9°C?-1.33°C,the temperature range is 0.57°C,and the temperature inhomogeneity coefficient is 0.107.The average air velocity is0.0648m/s.When the top row pipes are arranged in the form of position two,the temperature range is 0.59°C,the temperature inhomogeneity coefficient is 0.124,and the average air velocity is 0.0512m/s.When the top row pipes are arranged in the form of position three,the temperature range is 0.68°C,the temperature inhomogeneity coefficient is 0.116,and the average air velocity is 0.0465m/s.When the top row pipes are arranged in the form of position one,the temperature homogeneity in the cold room is better,and the air circulation in the cold storage is better.The evaporator layout is reasonable.Therefore,the top row pipe was installed according to the first position.In addition,this experiment added slide rails to the top row of pipes.The pipes can slide left or right,and the movable distance of each group of pipes is 1.5m.(3)When the cold storage is full,as the height increases,the average temperature of the Z section of the cargo area first rises and then drops.When Z=0.9m,the temperature field is the most uniform.In the height of 0.1m?2.0m,the average temperature of the cargo area is-1.4?,the temperature range is 1.25?,the temperature inhomogeneity coefficient is 0.21,and the air velocity is 0?0.03m/s.Because the upper cargo is close to the pipe,the temperature inhomogeneity coefficient of the space Z=1.5m and above increases significantly.In the height of 0.1m?1.5m,the air temperature is within-1.75??-0.97?,the temperature range is 0.78?,and the temperature inhomogeneity coefficient is 0.13.(4)The relationship between the liquid supply temperature of the top row pipe and the temperature in the reservoir was linearly fitted.When there is no goods in the cold storage,the formula is Y=0.993X+1.66.When the cold storage is full of goods,the formula is Y=0.985X+1.755.Among them,X is the liquid supply temperature,and Y is the average temperature in the cold storage.(5)There should be a distance of about 0.3m between the cargo and the enclosure structure to reduce the adverse effect of the heat of the enclosure structure on the airflow organization.When placing the goods,we need to avoid the space directly below the pipes as much as possible to avoid chilling and freezing damage to the fruit and vegetable products due to low temperature.For a 2.7m high cold storage,the height of the goods can be placed at 1.2m?1.5m,that is,leave a space of about 0.8m?1.1m from the bottom of the pipe.Place a dunnage board under the goods,which is conducive to heat insulation and heat dissipation.A certain space between cargo and cargo can enhance air circulation.In summary,this article can draw conclusions.The refrigeration system scheme using partial top row pipes proposed in this paper is feasible.The system has good results.Secondly,based on the refrigeration principle,this paper determines the scheme and process of the indirect cooling refrigeration system with local top row pipes.According to the temperature difference between the inlet and outlet of the top discharge pipe,the system adjusts the pump liquid supply to ensure the load balance under the small heat exchange temperature difference,thereby reducing or avoiding condensation and frosting of the evaporator.The three-way proportional regulating valve adjusts the ratio of liquid supply and return by measuring the temperature of the refrigerant at the outlet of the pump to control the liquid supply temperature of the evaporator.The local top row pipe can be divided into regions for cooling and defrosting.Under the premise of ensuring the constant temperature and humidity in the cold storage,the influence of condensation and frosting of the natural convection air cooler on the goods stored in the cold storage is solved.