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Heat Transfer in Combustors

DOI 10.1615/hedhme.a.015516

3.11 FURNACES AND COMBUSTION CHAMBERS
3.11.5 Heat Transfer in Combustors

This section will highlight some of the important aspects of heat transfer in industrial combustion, while the next section will discuss modeling of industrial combustors.

Hottel (1961) developed a relatively simple equation to calculate the heat transfer in a combustor. The model assumes the gas in the combustion space is isothermal and is referred to as a one-gas-zone furnace model. The wall and load temperatures are both assumed to be constant and the furnace walls are assumed to be radiatively adiabatic. A sketch of the combustion system is shown in Figure 35. The heat transfer to the load can be calculated as follows:

\[\label{eq5} q_1=\dfrac{\sigma\left(T_{\rm g}^4-T_1^4\right)}{\big[(1-\varepsilon_1)/A_1\varepsilon_{\rm g}\big]+(K_{\rm s}/4K_{\rm a}V)+\Big|1\big/\left\langle A_1\varepsilon_{\rm g}+\left\{1/\big[1/A_1F_{\rm 1w}(1-\varepsilon_{\rm g})\big]+(1/A_{\rm w}\varepsilon_{\rm g})\right\}\right\rangle\Big|}+h_1A_1\left(T_{\rm g}-T_1\right) \tag{5}\]

where σ is the Stefan-Boltzmann constant; Tg and T1 are the absolute temperatures of the gas and load, respectively; ε1 and εg are the emissivities of the load and the gas, respectively; A1 and Aw are the surface areas of the load and the wall, respectively; Ks and Ka are the scattering and absorption coefficients for the gas, respectively; V is the volume of the gas; F1w is the view factor to the wall from the load; and h1 is the convection coefficient to the load. The equation is only valid when multiple scatter is negligible (KsL << 1). An enthalpy balance on the gas can be written as follows:

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