Macroscopic energy balance

Abstract

This chapter is closely related to Chap. 4, as we analyze the macroscopic aspect of heat transport by performing energy balances over macroscopic slab or shells perpendicular to the direction of the heat flow. First, in the introductory Sect. 11.1, the Bernoulli equation is re-derived, stressing all its heat-related features, instead of the terms related to momentum transport, as we did in Chap. 3. In fact, we see that the heat exchanged equals the enthalpy variation and is the product between a temperature difference (i.e., the driving force) and a coefficient of heat transfer. This latter, as shown in Sect. 11.2, can be determined using experimental or analytical expressions, which are then applied in Sects. 11.3 and 11.4 to design shell&tube and finned heat exchangers, respectively.