MODEL OF HEAT AND MASS TRANSFER THROUGH THIN PARTIALLY PERMEABLE WALLS

Abstract

The model under consideration addresses the transfer of heat and mass (air) through thin walls, described as partially permeable, which are composed of numerous impermeable metal sheets joined together by seams that are not entirely airtight and are permeable to mass. Such walls are found in large industrial facilities in the form of roofs and shells, covering areas of tens of thousands of square meters with metal sheets and tens of kilometers of seams between them. Therefore, modeling the transfer of heat and mass through these thin walls, which are subject to pressure differentials, poses a significant challenge not fully addressed by current CFD models. While modeling the part of heat transfer across the general surface area of thin walls is relatively straightforward, accurately modeling the transfer of mass and heat fraction through the numerous seams between sheets is problematic with CFD technology.

This work proposes a method for calculating mass flowrates and the heat fraction through the seams between sheets, distributing it across the entire surface area of the wall according to the signs and values of local pressure differentials between the calculation cells on both sides of the wall. It is noted that while a porous wall model could be used for such purposes, it does not account for the conjugate and radiative heat exchanges between both surfaces of such a wall with airflows and other walls. Unlike this approach, the proposed model incorporates conjugate and radiative heat exchanges and can also accommodate a wall of zero thickness, significantly reducing the number of cells in the main model required for CFD simulation. This submodel has been verified on number of simplified cases and currently applied to simulate air and moisture exchange through the inner and outer shells of the New Safe Confinement of the Chernobyl Nuclear Power Plant.