The Design And Experimental Research Of Data Acquisation System For The Heat Pump Dryer

In our country, fruit and vegetable resources are rich. At present, companying the rapid development of their dryness technology, the integrated economic benefit is becoming more and more prominent. But fruit and vegetable, often containing lots of water and rich vitamin, are sensitive to heat and need long time to be dried, so the quality of them after drying courses cannot be guaranteed. The traditional drying method, in which fruit and vegetable is dried by constant hot wind, cannot meet the requirement to produce high quality fruit and vegetable products anymore because of the high temperature and huge energy consumption. In another method, which is called the cooling drying method, high quality products can be produced but the equipments are expensive and the productive cost is very high. So we developed this heat pump drying method hi purpose of improving products quality and reducing energy consumption.At present, some plants are using heat pump dryers to dry material such as wood, food and other agricultural products, but in these plants online parameters such as temperature, humidity and material weight are detected manually, thus large quantity of human power and material resource are wasted. At the same time, precision of auto-control and effect of real-time surveillance cannot be achieved. So at present, the research of the parameter auto-detection and auto-control of the heat pump dryer is of great importance.In this paper, the general drying process and the working principles of heat pump dryer are discussed, and the design of a set of heat pump drying equipment is described. This equipment mainly includes six parts: evaporator, condenser, compressor, expanding valve, assistant heater, and drying chamber. Its electric control part is the SIMENSE PLC; at the wind-in entrance, wind-out entrance and in the drying chamber one wind speed sensor and five temperature and humidity sensors are installed; in the drying chamber a drying nacelle for material is designed on which a weight sensor is installed to detect the real-time weight of the material.During the food drying process, the temperature, humidity and wind speed of the drying medium (air) can affect the quality of the drying material, so the variance of these parameters must be detected and controlled. The author designed a computer dataacquisition system according to this requirement. The software system, which is compiled by the Visual C++6.0 and which is mainly faced by the managers and workers, can acquire the values of temperature, humidity, wind speed and the weight of the material in a real-time mode. The acquired data can be browsed in two ways: data list mode and image section mode. In the research work, several drying experiments on apple under different temperatures have been done. According to the data from the test, the software can draw out the drying curve and drying speed curve, and can analyze the relationship between the moisture content and the time, the relationship between the drying speed and the time, and the effect of the temperature in the drying process.The data acquisition system discussed in the paper can complete the real-time data acquisition of the heat pump dryer accurately and timely, and can show the drying features during drying process; and the data acquired can provide a basis for the auto-control system of the heat pump dryer.