Overall heat transfer coefficients and log mean temperature difference

3 Overall heat transfer coefficients and log mean temperature difference 

Consider heat being transferred through several slabs, each of area A in good thermal contact with each other (Fig. 4). The heat transfer coefficients for the slabs are /ij, h, . . . h and the corresponding tempera- 

The reciprocals of the heat transfer coefficients are known as the resistances and eqn. (78) shows that the resistances are additive. 

When the areas for heat transfer are not the same, it can be shown that 

Any additional resistance due to the formation of a layer of dirt or scale is usually allowed for by the addition of a fouling factor, R, and the expression for h then takes the form 

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Calculate the overall heat transfer coefficient and log mean temperature difference. (9) Calculate the heat transfer area required and compare it with the area available. (10) Vary Nj- or D. Repeat steps 1 to 9 until A/A = 1. (11) Cost evaluation since most steps are described in the previous case (reactant on the tube side), one case is presented briefly below (refer to case 10 in Table CS1.3). 

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