News

Jo Jan 21, 2025

The most widely used materials for covering greenhouses these days are plastic films of various types. However, plastic films are partly transparent to long wave thermal radiation. This is why all the methods recently proposed take into consideration the influence of the divisional transparence of those materials relative to long wave radiation on the whole radiation heat exchange.

In these methods, the radiation heat exchange in the radiation system including partly transparent bodies like glass or films has been calculated in different ways, but detailed quantitative analysis of the radiative structure when radiation goes through the partly transparent bodies has not been conducted. Furthermore, since different studies developed formulas with individual radiation properties, the amount of determinant became large, and therefore, calculation methods by computer was the only solution to the calculation of the heat quantity of resultant radiation and transmitting radiation, which took a long time for its calculation. Meanwhile, the study on determining the radiation heat quantity by multiple reflections, ray tracing and radiant light methods became more complicated than the effective radiation method. Introducing computers to technical calculations made it possible to calculate the heat quantities in greenhouses by the repeated radiation method, but programming also required much labor. In a word, they are complicated and less intuitive than the effective radiation method.

Kim Chol Gon, a researcher at the Faculty of Heat Engineering, has derived a generalized formula for calculating radiation heat exchange by the effective radiation method when both grey bodies randomly placed in the space are non-transparent and partly transparent.

Then, he has proved that the analysis result of the calculated characteristic of the daily temperature variation in a single-covering plastic filmed solar greenhouse by the derived formula is just the same as the one by the repeated reflection method.