The significance of research on refrigerated trucks
With the rapid growth of our country's economy and the continuous improvement of people's living standards, the exchange and circulation of goods between different regions are becoming more and more frequent, and the number and variety are also constantly increasing and expanding, especially some perishable foods. If these foods are stored and transported under normal conditions, they are easily affected by external conditions and their quality is damaged. Common perishable goods in transportation include fruits and vegetables, meat and meat products, seafood, milk, and certain dairy products with strong seasonal and regional characteristics. The transportation of these types of food places high requirements on transportation equipment, requiring them to have refrigeration and insulation effects. Therefore, research on the refrigeration methods of refrigerated trucks will further deepen our understanding of the detailed applications in the refrigeration industry, and also have certain reference value for the development and improvement of refrigerated trucks.
Analysis of 2 Refrigeration Methods
(1) Water ice and salt ice refrigeration. Under atmospheric pressure, the melting point of ice is 0 ℃. The principle of heat absorption in voucher melting is that the heat absorption of ice during melting is about 334.8 kJ/kg, and adding salts to water ice can reduce its melting point. Within certain limitations, the more salt factors in water ice, the lower the melting point. When the temperature in the refrigerator rises, ice absorbs heat and melts into water; Salt dissolves in water and then absorbs the heat of ablation.
After packaging the goods that need to be preserved and frozen, place them in a container set by a
Refrigerated Truck, and place water ice or salt ice around the goods. During transportation, the water ice or salt ice melts and absorbs the heat in the goods to achieve the purpose of preservation and freezing. The investment in water ice refrigeration equipment is low, and the operating efficiency is low. However, the heat absorption capacity of the common water (salt) ice unit is relatively small, and the cooling inside the carriage is limited. In addition, the melting of salt ice can pollute the environment and food, corrode carriages, and make goods damp. Therefore, water (salt) ice refrigeration mainly relies on the refrigerated transportation of aquatic products such as fish.
(2) Dry ice cooling. The principles of dry ice refrigeration and water ice refrigeration are similar in comparison, except that the water ice melts and absorbs heat during refrigeration, while the sublimation and absorption of heat during dry ice refrigeration achieve similar effects. Dry ice is solid CO2, with a freezing point of 215.55K (-58.61 ℃). At scale atmospheric pressure, it sublimates to carbon dioxide gas at -78.9 ℃, with an absorbed gasification latent heat of 137 kcal per kilogram. The specific heat of CO2 gas is 0.2 kcal/kg, ranging from -78.9 ℃ to 0 ℃. Dry ice can absorb heat of 153 kcal per kilogram, which is about twice that of water ice. The specific gravity of dry ice is heavier than that of water ice, and its cooling capacity per unit volume is about three times that of water ice. At an atmospheric pressure, the sublimation temperature of dry ice (solid CO2) is low (-78.9 ℃), and the sublimation heat absorption is large (573.5 kJ/kg). Therefore, using it as a cold source for the carriage can not only achieve a lower temperature (usually lower than -20 ℃), but also obtain a larger refrigeration capacity. Therefore, this refrigeration method is suitable for the transportation of frozen food.
The dry ice refrigeration device is simple, has low investment and operating costs, is convenient to use, and the goods will not be affected by moisture. Due to its low sublimation temperature and high heat absorption capacity, dry ice can maintain a lower temperature inside the carriage. The CO2 gas generated during dry ice gasification can suppress Wei
