Theoretical And Experimental Research On The Vacuum Cooling Of High Temperature Food

In recent years，a cooling technology，vacuum cooling，has been greatly used forfood cooling. Vacuum cooling is a method of removing the heat by water evaporationunder the low pressure，so as to achieve rapid cooling. This article researchedtheoretical and experimental on the vacuum cooling of high-temperature food usedVCH-50M Vacuum Pre-cooling Machine of Cooked FoodThe specific contents and conclusions of this article are described as followed:1The simulation of the vacuum environment:Considered the influence factors that the air leakage of vacuum chamber,amathematical model is developed for the heat and mass transfer of air duringvacuuming the vacuum chamber. ANSYS is used for simulation of the unsteady model.The simulation results fit experimental data well， for instance, the maximumdifference between simulated and tested pressure with the relative error of9.2%whenthe pressure ranges from100000Pa to1000Pa. The results show that the model isable to be used predict the variations of vacuum pressure. It provides the theoreticalsupport for food vacuum cooling process. The changes of pressure field are analyzed.The pressure gradually decreases from inside to outside with bleeding point as thecenter. The pressure changed very small in the vacuum chamber，meaning pressurefield distribute uniformity.2. The Simulation of food vacuum coolingFirstly，a mathematical model is developed for porous food during vacuumcooling. Through ANSYS based simulation of porous food vacuum cooling process iscompleted. After that，compared the simulate values with experimental data，the resultsare in good agreement，and the errors between simulated values and experimental dataare analyzed. Some basic rules of heat transfer during vacuuming are mentioned aswell. In the vacuuming process，The temperature gradually decreases from inside tooutside，and temperature gradient in this direction is the largest. Finally，the loss ofquality and the distribution of temperature during the cooling process was analyzed.3. Experiment of food’s vacuum coolingWith steamed buns to do experiments，during natural cooling，cold wind coolingand vacuum cooling. Respectively used2m/s and4m/s wind speed in the process ofcold wind cooling. After the end of the experiment，quality loss、texture、color andmicroorganism are tested.The conclusion as followed：(1)Vacuum cooling is900s，consumption is0.59kw/w;cold wind cooling is1500s，consumption is0.083kw/h;natural cooling is2100 s in three cooling ways，center temperature is higher than the surface temperature invacuum cooling.(2)When reduced to the same temperature，4m/s wind speed less than900s than2m/s in cold wind cooling.(3)The loss of quality existed in three coolingways，and vacuum cooling quality loss is the largest.(4)In terms of hardness、viscosityand chewiness，vacuum cooling value is larger than cold wind cooling，cold windcooling value is larger than natural cooling.(5)Vacuum cooling color brightness valueis the lowest of76.35.(6)Vacuum cooling has the least number of microbial and thelongest keeping days.