Radiation Between Two Gray Surfaces Attic

A gray surface or graybody is a surface that reflects absorbs a given fraction of the thermal radiation a blackbody surface would absorb.

Radiation between two gray surfaces attic.

Surface and the medium between the surfaces does not absorb emit or scatter radiation. The house is 30 m long ls not shown into the page. The elementary areas are at a distance r apart and the normal to these areas make angles 0 1 and 0 2 with the line joining them. Heat exchange between black bodies.

Diffuse gray surfaces the analysis of radiation transfer in enclosures consisting of black surfaces is relatively easy as we have seen but most enclosures encountered in practice involve nonblack surfaces which allow multiple reflections to occur. The portion of radiation exchanged between two differently oriented surfaces has to be defined by a geometric function known as view factor which is developed for gray diffusely radiating surfaces. In this article we will discuss about the mechanism of heat exchange between two or more surfaces. In general for any two objects in space a given object 1 radiates to object 2 and to other places as well as shown in figure 19 10.

3 1 radiation between two gray surfaces consider the attic of a home located in a hot climate. Consider the two infinite gray surfaces shown in figure 19 5 we suppose that the surfaces are thick enough so that no radiation transmitted so consider a photon emitted from surface 1 remembering that the reflectance. Describe radiation exchange among surfaces in which the surfaces can be perfect absorbers of radiation black or diffusely absorbing gray. Heat transfer between surfaces based on two assumptions.

More importantly the graybody blackbody fraction is independent of radiation wavelength. Recall that blackbodies are surfaces that absorb as much thermal radiation as the laws of physics allow. That is it will be the case when the surfaces are isothermal and diffuse emitters and reflectors and the surfaces are separated by a non participating medium such as a vacuum or air. Surfaces form ideal closed enclosure and are separated by nonparcipating media.

4 radiation heat transfer between black surfaces of arbitrary geometry. Radiation analysis of such enclosures becomes very complicated unless some simplifying assumptions are made. Consider heat exchange between elementary areas da 1 and da 2 of two black radiating bodies having areas a 1 and a 2 respectively. Absorptivity reflectivity and transmissivity the radiation energy incident on a surface per unit area per.

The view factor f 1 2 between two surfaces a 1 and a 2 can be. The floor of the attic is characterized by a width of l1 10 m while the roof makes an angle of 30 from the horizontal direction as shown in the schematic.