Abstract:
Refrigerated transport equipment is increasing rapidly with the development of the cold chain in China. High energy consumption of refrigerated trucks can often occur correspondingly in recent years. In most cases, the envelope material of the transport equipment can be improved to reduce energy consumption. Alternatively, the heat transfer mechanism can be widely expected to significantly promote the energy efficiency of refrigerated equipment in a short term. Particularly, the heat load of cold chain transportation can originate mainly from the air-convection heat exchange and the solar radiation heat. In this study, the radiative cooling coating was developed and applied to the external surface of the cold chain incubator. The paint material was also characterized by the white homogeneous liquid with a relatively high resistance to impact, adhesion, acid, alkali, and artificial aging. A series of tests were then carried out to evaluate the performance of radiative cooling coatings on the thermal insulation of the cold chain incubator. The test results show that the solar radiation heat gain of the incubator decreased significantly using radiation cooling coating. Specifically, the average temperature of the outside surface of the insulation box decreased by 0.7-6.9 ℃ with an average decrease rate of 10.0% than before. The maximum decrease rate of the peak temperature was 17.3 ℃, decreasing over 28.5%. The average temperature of the inner surface also decreased by 3.6-5.5 ℃. The peak temperature of the inside surface decreased by 15.0% and the average temperature of the inside surface decreased by 11.2%. The average temperature of the central air inside the box decreased by 10.0%. At the same time, the uniform distribution of the temperature field inside the insulated box greatly contributed to the cooling performance of the final quality of the food. The temperature range decreased by 30.2%-30.7% using the radiative cooling coating, where the variance of the temperature field decreased by 26.3%-29.9%, indicating the uniform temperature field of the internal box. Energy consumption analysis showed that the cold chain incubator with the radiation cooling coatings was reduced the annual heat leakage by 44.3 kW·h, and the carbon emissions by 17.3-51.8 kg., compared with the original. Specifically, there was a total reduced heat leakage of 212.3 kW·h from the incubator coated with the radiation cooling paint, when the thickness of the box envelope increased from 40 to 100 mm. The total heat leakage rate decreased gradually with the increase of coating thickness. Additionally, the color of the coating was an important indicator of the optical properties of the paint. An excellent insulation property was achieved in the insulated boxes with the white radiant cooling paint, where the total annual heat leakage decreased by 22.4%, compared with the dark coffee-colored paints with high solar absorption ratios. The finding can provide new ideas for the energy-saving application of cold chain transportation equipment, particularly for agricultural facilities with the heat insulation requirements, such as grain, cold storage, and oil tanks.