Studies On Vacuum Pre-cooling Processes Of Fruits And Vegetables And Characteristics Of Water Catcher

The study and application of the vacuum precooling technology are in the firsttime step, and there are no accurate calculating methods and testing standards aboutthe design and manufacture of vacuum precoolling installing. The precooling processof vegetable and fruit by vacuum precooling are operated based on experienceswithout an existing arts and crafts. So there is a need to study the key technologiesand processes in the vacuum precooling unit and to provide the theoretical basis forthe design and application of vacuum precooling unit. The dissertation presents somecontents about the vacuum precooling as follows: 1. Studies on the evaporation cooling principles of fruit and vegetable There are different optimal storing conditions for different vegetables and fruits.And the vegetable and fruit precooled by vacuum must be fit with the storingcondition. A low temperature will result in the frozen scald, and a high temperaturewill not meet the precooling objective. A low humidity will result in a high weightloss of vegetable and fruit, and a high humidity will result in decay. For the irregularshape of vegetable and fruit, the shapes were simplified as plate, cylinder and sphere,and based on these simplifications, the universal mathematical model of evaporationcooling of different shapes were derived in different precooling conditions. Based onthis, the laws of precooling rate and weight loss of different vegetable with differenttemperature were obtained under different vacuum degree. 2. Studies on the performance characteristics of water catcher The water catcher is the most important part in the vacuum precooling unit. Thewater vapor condensates on the catcher surface when it passes the catcher powered bythe vacuum pump. If not, the performance of the vacuum pump will be deducedaffecting the performance of the total system. And the catcher is also known as theevaporator in the refrigeration system whose performance is also affected by thecatcher. At here, the performances of the catcher with different temperatures werestudied under different areas of catcher and different humidity. 3. Energy analysis of vacuum precooling unit There are two sets of power unit in the vacuum precooling unit including therefrigeration system and vacuum pump system. There is no a mature theory to guidethe design of the unit in most manufactories at present. Most of the vacuumprecooling units have a large volume and power based on the experience or the IIprinciple of large resulting in the energy waste. In this paper, the energy consuming ofthe unit was analyzed and the evaluating indexes were proposed including thetemperature reducing per time unit, the consumed energy per time unit and theprecooling time used by different vegetable and fruit, which can be seen as thetheoretical basis of the optimum design and operating process of vacuum precooling. 4. Experimental setup and experiment Some representative vegetables and fruits were selected to be studied byexperiments under different precooling conditions and were compared with thetheoretical results, and the optimum precooling process conditions were defined. Atthe same time, the real performance of the water catcher were tested and comparedwith the theoreticalresults showing that the theoreticalmodel is right.