Studies On The Heat-pump Combined Drying For Vegetables

Heat-pump drier is a closed cycle dehumidifier. Exhaust waste heat is well recycled and the major heat loss is the loss of heat exchange through the equipment to the environment.It can greatly reduce energy consumption of the drying. It's of great significance for the enterprises to improve product competitiveness, energy conservation and emission reduction, and to protect the environment. As the traditional air drying's exhaust air is a medium with a the high temperature and humidity, it take a lot of waste heat away, making the current domestic production of dehydrated fruits and vegetables high energy consumption. Although the vacuum freeze-drying is a high-quality fruit and vegetable dehydration, but drying costs and initial investment is still high. The price of your freeze-dried products, the market can not be completely open. In this paper, author chooses cabbage and scallion as raw materials. Research is done in heat pump combined drying. Energy consumption is reduced while the sample get the best quality.Through equipment design with overall structure and the calculation of main component selection, the overall size of equipment, material, parameters and layout of major parts in heat-pump system and drying system is determined for the manufacturer to further design and manufacture. In certain experimental conditions, use cotton material for the experiment, the biggest dehydration amounted to 1.2kg water per hour. At the same time it also shows that the volume of desiccant is not only determined by the vapor rate of water in drying target, but also the overall performance of desiccant of heat pump system.On the basis of single-factor test of cabbage heat pump drying, the type of joint drying is determined as that first heat pump drying, later hot air drying(HPD+AD). Use heat pump drying temperature, moisture conversion point, later hot air drying temperature as factors, SMER and chlorophyll content as composite indicator Y for the final evaluation of response surface optimization analysis. Finally get the optimum parameters with heat pump drying temperature(xl=57.2℃), moisture changing point (x2=26.4%) and hot air drying temperature(x3=54.5℃). Under optimal conditions, Comparison is done to sample quality and energy consumption between HPD, HPD+AD, AD, in addition to chlorophyll content, the cabbage quality dried by HPD+AD is better than that by hot air drying, but also lowered the consumption of traditional air drying to 40.67 percent.Finally, choose scallion for the study. By the comparison between different combined drying methods, the joint drying form with first vacuum freeze-drying, later heat pump drying (FD+HPD) is determined. Select FD heater's temperature, moisture conversion, heat pump drying temperature, which effect composite index, as three main effect factors. By RSM optimization, get the best drying process parameters with vacuum freeze-drying temperature (xl=61.1℃), humidity changing point (x2=36.5%) and heat pump drying temperature (x3=57.4℃). Under optimal conditions, comparison of sample quality and energy-consuming is done between FD, FD+HPD, HPD. The results show that in addition to the acid content, the appearance of sample with joint drying is closer to vacuum freeze-drying's, and combined drying also decrease energy-consumption of the dry part by 55.08 percent. But the index of nutrition and rehydration rate are still gaps to the freeze-dried sample. A further in-depth study is also needed.