Study On The CFD-based Micro-environment Dynamic Simulation For The Compartment Of Cold-chain Transport Vehicles

During the food cold-chain logistics, there are some directly affect factors to thetemperature level and its homogeneity in refrigerated compartment and the cargo area,such as airflow patterns, the goods of stack methods, and cooling fan speed. Too high ortoo low temperature will harm the quality of the products. Too high temperature willresult in the phenomenon of food hazards such as increasing the respiration,accelerating the of microorganism breeding, etc. and too low temperature will inducethe immediate cold injury for food. Therefore, the uniform distribution of temperaturethroughout the cargo has become the key to preserve the quality, shelf life of perishablefood and the overall economic benefit in the cold chain. However, it is required toreduce unnecessary energy consumption and overall transportation costs when keepingthe low temperature environment for the transportation of the refrigerated food, which isnot only the current supplier’s pursuing goals, but an important role on energyconservation and emission reduction.Computational fluid dynamics is to analyze the coupled transport phenomena of theflow processes from the qualitative and quantitative aspects by solving partialdifferential equation sets. The numerical simulation technology in computational fluiddynamics has been widely used in agricultural cold-chain logistics for the past few years,due to its mature, accuracy and reliability has been improved more and more. Thistechnology has also essential significances to improve the temperature uniformity of thelow-temperature environment, determine the stuff stack methods, control the coolingtime reasonably, and increase the economic benefits of overall cold-chain logistics. Thestudy content of this article is divided into the following three parts:（1） Taking the short-distance transportation refrigerated truck and potatoes in theexperiment cargo as the study objects, this paper establishes a computational modelusing the unsteady Shear Stress Transport (SST)-model of Computational Fluid Dynamics (CFD) and fluid modeling software-FLUENT. Under specific boundaryconditions with alternating the wind speed in the outlet and the cargo stack mode, themodel took the wind speed at the air-conditioning outlet, air temperature, cars wall andcargo area temperature of the refrigerated truck as the initial boundary conditions, andwas used to simulate the temperature field distribution on different boundary conditionsand stack methods in the refrigerated truck. The model could determine the best outletwind speed and stack way of cargo through comparative analysis. The results showedthat when the wind speed was5m/s and stack methods was void in the middle and twosides, the temperature field distribution in the refrigerated truck was the best uniform.The tests showed that the simulated values were in a sound agreement with themeasured ones and the mean absolute error of the temperature was not higher than1℃.（2） According to the power of refrigeration units and temperature range of bestrefrigerating for goods, the cooling process was simulated under two kinds of fancooling temperatures (0and3℃) and cargo areas under the blanks on both two sidesand middle stack methods.. The optimal time interval was defined to open and close acooling fan in the process of transportation. The results indicated that when therefrigeration temperature was3℃and cooling plus closing time of cooling fan wereboth10minutes, the energy cost of3.6×105J was reduced compared with theenvironment of refrigeration temperature was0℃, cooling time was15min and theclosing fan lasted20minutes.（3） To make full use of the simulation data, get the point temperature and rapidlyunderstand the temperature distribution in refrigerated trucks, the development ofmonitoring system for carriage micro-environment becomes inevitable. A carriagemicro-environment monitoring system was developed based on CFD, using SQL server2000to manage and store data, and Microsoft Visual Studio2005+R2009a MATLABto develop, compile and debug in Windows environment. The simulation results wereintuitively shown to the user, allowing the user conveniently and quickly to query,analysis, and validation results. This system analyzed and verified the result of thesimulation by the diagram and recorded the errors during the process of operation toimprove the system stability.The paper takes the refrigerated truck for the short-distance transportation as the object,stimulates the temperature distribution and variation in the compartment, determinesstack methods and the fan speeds which are helpful to reduce the temperature differences. Combined with the refrigerated truck refrigeration units power and the bestrefrigeration temperature range for goods, this paper also provides the optimalcombination mode of cooling fan temperature and cooling time to reduce transportationcosts and realize energy conservation with emission reduction. The numericalpredictions showed the reasonable agreement with experimental data. Combined withsimulation data, the development of a micro-environmental simulation system, make thequery and analysis for refrigerated truck temperature more intuitively and efficiently.Finally, this paper looked into the future trends of CFD application in agriculturalcold-chain logistics. The study revealed the temperature distribution in the refrigeratedtruck under different boundary conditions and cooling time. These provided reliablytheoretical support and reference to reduce temperature difference, energy waste plusthe transportation cost, and realize automatic and intelligent control temperature inrefrigerated transports.