| Drying is a complex,high energy-consuming process in which the drying method has a great impact on drying.Heat pump drying technology is particularly suitable for dry processing of agricultural products,can be good energy conservation,but also has a good product quality after drying.The use of CO2 as a refrigerant has the characteristics of environment-friendly,the use of CO2 heat pump drying equipment has a wide range of adjustable temperature range,CO2 as the current replacement of Freon and other environmentally harmful refrigerant excellent working fluid is the main research point.Contents of this paper are as follows:.(1)The general structure of the heat pump dryer,heat pump drying device to analyze the principle,mainly for closed heat pump drying device to determine the closed heat pump drying device pollution-free,high heat utilization advantages.The CO2 transcritical cycle analysis of the heat pump drying unit,the pressure analysis of the high and low pressure zone in the system,the thermodynamic analysis of the drying medium,and the analysis of the refrigeration cycle and the performance evaluation index of the heat pump system in the system.(2)Analyze the specific performance parameters of the components of the heat pump drying unit and put forward the optimization suggestions.The safety of the equipment in the experiment analysis,and in order to make better use of the performance of the compressor,better improve the efficiency of the use of energy,equipment used in the high and low pressure area to optimize the distinction between the analysis.In order to better record the data during operation,many sensors have been added to optimize the position of the sensor's detection points,making it easier to understand the changes in the parameters during the drying process.(3)The carrots were selected as dry materials,and the drying temperature was different from that of dried carrots.The mechanical properties,VC content and VA content were the best of the heat pump drying process conditions.The average water loss rate is 0.35%/min,the drying rate is the slowest at 50?,the average water loss rate is 0.17%/min,the drying rate is the highest at 70?.The shear stress was measured by the texture analyzer,indicating that there was a significant difference between the drying groups with different displacement values at the maximum hardness,which indicated that the carrot slices were different in different drying groups.The maximum rehydration ratio was 6.33,the minimum rehydration ratio was 4.83,the average rehydration ratio was 5.8357,and the maximum rehydration ratio was dry temperature 65 ?.The results showed that the VC loss rate was the highest,the value was 94.30%,the lowest VC loss rate was 64.45%,and the maximum loss rate was 96.95%,70? dry VA loss rate is the lowest,the value of 82.93%.(4)In order to reduce the cost of equipment development,this paper puts forward the optimization suggestions for the high-pressure solenoid valve on the oil return device,and completes the test according to the design,the conclusion is as follows:In the heat pump system does not return oil,the system runs 10 hours after a total of 85.29g oil does not return to the compressor.When using the needle valve to return oil,when the opening is 1 turn,20.52g oil is not returned;when the opening is 3 laps,the heat pump system is overheated after running 4.5h,and 28.27g oil is not returned.Not conducive to high temperature and high pressure of the CO2 heat pump system return oil.The use of capillary back to the oil,the length of 250mm,300mm back to the oil effect is poor,corresponding to 18.15g,22.30g oil is not returned,use a length of 200mm capillaries to return to the oil could meet the requirements,the system's best return length of the capillary between 200?250mm. |
PDF Full Text Request