Effect of radiation and convection heat transfer on cooling performance of radiative panel

Highlights

Cover test is made to study radiation and convection heat transfer of radiative panel.

The radiation cooling capacity occupies 64%–90% of the net cooling capacity.

The cloud affects the radiation cooling capacity greatly.

With temperature difference rise, the radiation cooling capacity increase.

With tilt angel increase, the radiation cooling capacity decreases.

Abstract

The radiative panel is an equipment combining the solar heating and nocturnal radiant cooling technology. This study conducted the thermal performance of radiative panels for both radiation and convection cooling. Using the cover test by the mirror polished aluminum plate, the net cooling capacity of radiative panel was tested. The net cooling capacity of the radiative panel and contribution degree of the radiation heat transfer and convection heat transfer to the net cooling capacity was computed using the simulation model, and the influences of the cloud, ambient temperature and inclination angle on the radiation cooling were discussed. From the experimental results, the net cooling capacity was 45–70 W/m2 when the radiative panel wasn’t covered, and the net cooling capacity was 10–30 W/m2 when the mirror polished aluminum plate existed on a clear night in February in Tianjin. From the simulation results, the net cooling capacity of the radiative panel was about 50–70 W/m2, and the radiation cooling was about 45 W/m2, being responsible for 64%–90% of the net cooling capacity. The temperature differences between radiative panel and environment were the main influencing factors for the radiation cooling capacity. With an increase of the temperature difference, the radiation cooling capacity increased, and when the variation 5 °C of the temperature difference, the radiation cooling capacity will increase about 10–20 W/m2. When it was partly cloudy, the radiation cooling capacity was about 50 W/m2 and the fall rate of the radiation cooling capacity was less than 24%. With an increase of the cloud, the radiation cooling will decrease significantly. When it was overcast, the radiative panel even absorbed heat around 45 W/m2 from the environment. When the tilt angle of radiative panel was less than 30°, the fall rate of the radiation cooling capacity was less than 11.3%. When the tilt angle was greater than 30°, the radiation cooling decreased significantly. In the case of being placed vertically, the radiation cooling capacity reduced by 84.8%.

Keywords

  • Radiative panel;
  • Radiation heat transfer;
  • Convection heat transfer;
  • Cloud;
  • Temperature difference;
  • Tilt angle

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