Radiative heat exchange

In the case of a given surface temperature, the amount of energy released is determined by the parameters for the convective and radiative heat exchange. As far as convection is concerned, these are the temperatures ol the heat source surface and room air, respectively, and the heat transfer coefficient. The radiative heat exchange is determined by the view factors and the temperatures of the surrounding surfaces. 

A fictive sky temperature, dependent on ambient temperature, emissivity, and cloudiness, is introduced to account for the long-wave radiative heat exchange between the building envelope and the sky. 

The room models implemented in the codes can be distinguished further by how detailed the models of the energy exchange processes are. Simple models use a combined convective-radiative heat exchange. More complex models use separate paths for these effects. Mixed forms also exist. The different models can also be distinguished by how the problem is solved. The energy balance for the zone is calculated in each time step of the simulation. 

Radiative heat exchange The heat exchange by radiation between the clothing surface, including uncovered skin, and the environment, in W m -. 

Radiative heat exchange, globe The heat exchange by radiation that takes place... 

Since the other modes of heat transfer discussed depend upon the difference in temperature, Tx - T2, it would be convenient to express radiative heat exchange in terms of Tx - T2 rather than in terms of the difference in fourth powers of temperature. For this purpose, we express the difference in fourth powers of temperature as... 

During the flight of droplets in the spray, the forced convective and radiative heat exchanges with the atomization gas lead to a rapid heat extraction from the droplets. A droplet undergoing cooling and phase change may experience three states (a) fully liquid, (b) semisolid, and (c) fully solid. If the Biot number of a droplet in all three states is smaller than 0.1, the lumped parameter model 1561 can be used for the calculation of droplet temperature. Otherwise, the distributed parameter model 1541 should be used. 

The first assumption made is that each element of a tube exchanges heat only with the two elements located in front of it respectively on the previous and on the subsequent tubes (Figure 6.12). The equation used to calculate the radiative heat exchange (qij) between two facing elements is the following one ... 

Fig. 6.12 Simulation of radiative heat exchange between tubes.

The paper by Haynes and Wepfer (2001) highlights the importance of heat exchange in SOFCs. To achieve an accurate temperature field, they propose a model that takes into account conduction, convection and radiation. The authors show how important the radiative heat exchange is. In particular, on heat transfer from the inner surface of the cell, radiation plays a much more important role than convection, which contributes for about 10%. 

Fig. 10.3 Radiative heat exchange dqi-j between two domains dAi and dAj with different temperatures at the interconnector.

Wen, J.X., Huang, L.Y., and Roberts, J. The effect of microscopic and global radiative heat exchange on the field predictions of compartment fires. Fire Safety Journal, 2001. 36(3), 205-223. 

Eckert, E. R. G., and E. M. Sparrow Radiative Heat Exchange between Surfaces with Specular Reflection, Int. J. Heat Mass Transfer, vol. 3, pp. 43-54, 1961. 

Kondratyev, K. Y. Radiative Heat Exchange in the Atmosphere, Pergamon Press, New York, 1965. 

Conductive heat transfer in all solid components, radiative heat exchange between all diffusive surfaces in the unidirectional solidification furnace, and the Navier-Stokes equations for the melt flow in the crucible are coupled. 

In many applications heat transfer by convection must be considered in addition to radiative heat transfer. This is, for example, the case where a radiator releases heat to a room which is at a lower temperature. Radiative heat exchange takes place between the radiator and the walls of the room, whilst at the same time heat is transferred to the air by convection. These two kinds of heat transfer are parallel to each other and so the heat flow by convection and that by radiation are added together in order to find the total heat exchanged. The heat flux then becomes... 

Open-weave liner (Murphy/Jahn Architects, 2006 Holst, 2006). The low-emissivity coating has the effect of blocking the radiative heat exchange between the external membrane surface and internal surfaces whilst reflecting the coolness of the chilled floor (Holst and Schuler, 2003). Without this... 

The technology described in this part of the chapter addresses the radiative heat exchange between the building envelope to the outside and to the inside. Every material with a temperature above absolute zero (0 kelvin) emits energy by radiation towards a surface with a lower temperature. The... 

Radiative heat exchange between opaque solid surfaces through a nonparticipating fluid can be accounted for under the assumption of gray-diffusive surface radiation. Computation of the configuration factors (view factors) with account for the shadowing effect is described in detail in [41]. The total radiative flux incoming to the elementary surface element i(i = 1, N, where Ne is the total number of elementary surfaces on the boundary) is... 

Kakimoto and Liu [10] developed a partly 3D global model that takes into account feasible 3D global modeling with moderate requirements of computer memory and computation time. AH convective and conductive heat transfers, radiative heat exchanges between diffuse surfaces and the Navier-Stokes equations for the melt are all coupled and solved simultaneously by a finite-volume method in a 3D configuration. 

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