0 Foreword
At present, China's food freezing and refrigerating industry is mainly distributed in livestock product processing and manufacturing, aquatic product processing and manufacturing, fruit and vegetable processing, frozen food manufacturing, frozen beverage manufacturing, and the circulation of these various products. According to incomplete statistics, by the end of 2003, the total cold storage capacity of China's food freezing and refrigerating industry will exceed 7 million tons/time; in China, approximately 20,000 enterprises are involved in food freezing and refrigeration; the direct employees in food freezing and refrigeration industry are approximately There are 800,000 people; the output of frozen food in China is currently estimated to be close to 4.5 million tons per year; the output of frozen drinks will exceed 1.5 million tons this year. The food refrigerated transportation technology is a specialized and scientific food refrigerated transportation system that transports food, especially perishable foods, from one place to another by scientific means and special transportation tools under a special transportation condition and is quickly and intactly transported to another place. It is of great significance to develop and utilize food resources, improve food production, transportation, and sales, increase the economic benefits of the food industry, and improve and improve people's health and living standards.
It is easy to see that refrigerated transport is an important link to ensure the integrity of the cold chain. It includes land transport (refrigerated transport vehicles, refrigerated trains, pipeline transport, etc.), maritime transport (refrigerated ships, etc.) and air transport. In the field of food circulation, in order to ensure food quality and reduce food waste, the use of refrigerated transport is an essential key link.
The key to refrigerated transport is the transport temperature. This article focuses on the division of the status of the internal temperature field of the refrigerated truck in the loading of cargo. It measures the temperature values ​​of the internal measuring points and uses these data to evaluate whether the structure of the refrigerated carriage is reasonable and whether the cargo is loaded properly. , To provide effective assistance in improving the design of cargo loading methods and systems in order to achieve energy conservation.
1 experimental conditions
In this experiment, indoor experiments were used to simulate the actual transport of refrigerated trucks. The experimental refrigerated transport box is located in an air-conditioned laboratory, and the outdoor temperature and humidity of the refrigerated transport vehicle are simulated using air-conditioning. The temperature outside the box is controlled at 38±1°C and the humidity is controlled at 65%±5%. The air is sent back and forth.
In this experiment, the distribution of the internal temperature field of the refrigerated transport carriage under the conditions of cargo loading was measured under six operating conditions. The loading height of the cargo was 2.0m and 1.2m, respectively, and the inlet air inlet temperature of the six operating conditions was The inlet speeds are:
· Working condition 1: The inlet air inlet temperature is -18°C and the inlet air speed is 5m/s.
· Working condition 2: The inlet air inlet temperature is -15°C, and the inlet air speed is 5m/s.
· Condition 3: The inlet air inlet temperature is -12°C and the inlet air speed is 5m/s.
Working condition 4: The inlet air inlet temperature is -9°C, and the inlet air speed is 5m/s.
Working condition 5: The inlet air inlet temperature is -6°C, and the inlet air speed is 5m/s.
Operating condition 6: The inlet air inlet temperature is 0°C and the inlet air speed is 5m/s.
2 Refrigerated truck box temperature measuring point layout plan
The experiment is mainly to measure the temperature value of the temperature field under load conditions, so as to evaluate the rationality of cargo loading and cold box structure, so the arrangement of measuring points needs to be representative. In this experimental device, the temperature inside the refrigerated transport box is measured. The measuring point layout is as shown in the figure:
Figure 1-1 Distribution of Temperature Measurement Points
There are a total of twelve temperature measurement points in this experiment. If the center of the AB section is the origin O(0,0,0), the coordinates of the twelve measurement points are 1 (2620, 1040, 1045), and 2 (2620,- 1040,1045),3(2620,-1040,-1045),4(2620,1040,-1045),5(0,1040,0),6(0,200,1040),7(0,-1040 ,0),8(0,200,-1040),9(-2620,1040,1045),10(-2620,-1040,1045),11(-2620,-1040,1045),12(-2620 , 1040,-1045), as shown, (unit: mm).
3 experimental data and processing
Under stable conditions, resistance temperature sensors were used to measure the measuring points inside the refrigerated transport box under the condition that the cargo loading height was 1.2m and 2.0m, and a total of 12 sets of data were obtained. In order to more intuitively and effectively analyze the differences in temperature at various points under different inlet conditions and inlet air temperatures, the temperature profiles of the above six conditions under the conditions of loading cargo heights of 1.2 m and 2.0 m were plotted. 1-2 and Figure 1-3) and the temperature profiles of 1.2m and 2.0m cargo heights loaded under the above six conditions (see Figure 1-4 to Figure 1-9).
4 Data Analysis and Conclusions
4.1 Analysis and Conclusion of Temperature Curves for Working Conditions at Different Loading Levels
From the above chart, we can see that in the stable supply condition (the experimental air speed is 5m/s), the temperature field inside the box is relatively stable at both ends, the temperature difference is not large, and the middle temperature is slightly higher than the temperature at both ends, especially The lower the supply air temperature is, the more obvious this difference is. For example, if the cargo loading height is 1.2m, under the condition 1 (supply air temperature is -18°C), the middle temperature is about 2°C higher than the two ends. Under condition 6 (air supply temperature is 0°C), the temperature difference is less than 1°C. The same is true when the cargo loading height is 2.0m. This means that when transporting frozen foods, special attention should be paid to stacking, especially when the goods are not fully loaded, the goods should be placed as far as possible in the lower temperature of the box, ie both ends.
4.2 Analysis and Conclusion of Temperature Curves for the Same Working Conditions at Different Loading Levels
It can also be seen from the above chart that under the same air supply speed, the loading height is different, and the distribution of the temperature field in the carriage is also inconsistent. The higher the loading height is, the higher the temperature in the upper middle of the box is. According to condition 1 and condition 6, when the condition is 1, the loading height is 2.0m higher than the loading height of 1.2m, the upper middle temperature is about 1.0°C higher; in working condition 6, the loading height is 2.0. m is about 1-2°C higher than the upper middle temperature of 1.2m. This shows that the stacking height of the cargo has a greater influence on the refrigerated transport temperature, and the higher the height, the higher the temperature in the middle and upper part of the tank. Therefore, if the transported frozen food has a high transport temperature requirement, the loading height is not too high.
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