Air heater


This text offers a rigorous, step-by-step methodology for calculating core dimensions of a compact heat exchanger. Considering the analytical complexity of implemented calculations, the most intricate basic flow arrangement situation in a single-pass configuration would be a crossflow in which fluids do not mix orthogonal to the respective flow

directions. Such a flow arrangement is selected to be considered in this calculation. The set of known input data is provided in the problem formulation. Subsequently, calculations are executed using an explicit step-by-step routine. The procedure follows a somewhat modified thermal design (sizing) procedure derived from the routine advocated in Shah and Sekulic (2003). The modification is related to the fact that iterative steps are listed and executed for both intermediate and overall refinements of all assumed and/or estimated entities. The overall pressure drop constraints are ultimately satisfied without further optimization of the design. The main purpose of the calculation sequence is to illustrate the procedure, usually hidden behind a user-friendly, but content-non-revealing, platform of any existing commercial software package. Such a black-box approach executed by a computer, although very convenient for handling by a not necessarily sophisticated user, is utterly nontransparent for a deeper insight. Consequently, this example calculation is not intended to discuss a particular design; rather, it illustratesthe procedure. Therefore, the numerical values calculated do not have importance for any particular design.

this drawing compact air heater 2 phase air to air

Problem Formulation

A task at hand is to design (“to size”) a heat exchanger, specifically, to determine principal heat-exchanger core dimensions (width, length, and height of the core having specified heat-transfer surfaces) (see Fig. 29.1). The heat exchanger has to cool a hot-air gas stream, available at an elevated temperature, with a cold-air stream, available at a significantly lower temperature