Banks of plain and finned tubes are one of the most important arrangements for heat transfer. In what follows, Section A deals with plain tubes and Section B introduces general features of finned tubes. Sections C and D then deal with prediction methods for high fin and low fin tubes respectively.

A. Banks of plain tubes

(a) Introduction

In the field of power generation, in the chemical industries, and in other technologies, heat exchangers involving tubes in crossflow are widely employed. A bundle of circular tubes is one of the most common heat transfer surfaces, particularly in shell – and tube heat exchangers.

Detailed studies have established the relation between the heat transfer and the arrangement of tubes within the bundle (staggered or in-line), and have also established the effect of relative transverse (a = s₁ /d), longitudinal (b = s₂ /d) and diagonal (b₁ = s' /d) pitches (as defined in Figure 1). The fluid approaches the bundle at an angle ψ to the axis of the tube, the "yaw angle". The most common case is where the fluid approaches in a direction normal to the tube axes (ψ = 90°), but often tubes operate at different yaw angles ψ to the flow, and this affects the heat transfer behaviour. Inside a bundle, the flow converges in the intertube spaces and forms a highly turbulent flow over the inner tubes. The recirculation region in the rear of an inner tube is smaller than that for a single tube. The situation is governed by the relative pitches and the bundle geometry. The more compact a bundle is, the larger is the deviation in heat transfer from the single-tube situation. The average heat transfer coefficient depends on the number of longitudinal rows because changes in the turbulence level in inner rows and because of the inlet-outlet effects.