Estimations of Radiative Heat Transfers in Enclosures

Abstract

In large closed spaces of buildings, the heat radiation dominates over the other two transfer mechanisms, i.e. over conduction and convection. This fact may be easily illustrated on the basis of the Stefan-Boltzmann law, Fourier’s law and convective correlations of Nusselt’s number. For this reason, when the computations of heat losses of buildings are performed, the radiative heat transfers running between inner sources of heat and inner surfaces of walls should not be overlooked. This conference contribution is devoted to such problems. In the preceding two conference contributions called “Radiative Heat Transfer in Buildings” and “Radiosity Model and Compensation Theorem”, a general model for radiative heat transfer in inner spaces of buildings has been developed and completed by the compensation theorem. This theorem mirrors the basic property of closed building envelopes stating that the total radiative heat flow in a closed envelope is zero. The present conference contribution thematically continues the preceding two contributions and applies their theoretical results to the case of radiative heat flows established within a living room consisting of 6 different grey interior surfaces. The surfaces mutually differ in temperatures and emissivities. Such an arrangement represents a real room without too much simplification. The corresponding matrix of view factors has 36 elements determined on the basis of formulae and graphs published in the technical literature. The system of 6 equations determines the 6 values of radiosities belonging to 6 interior surfaces. The radiosities represent auxiliary values that facilitate finding the heat fluxes and heat flows associated with each inner surface of the room. The sum of all the obtained positive and negative values of the heat flows has resulted in zero value which documents validity of the compensation theorem also in this complicated enclosure consisting of 6 thermodynamically different surfaces.