In this Section, heat transfer (without phase change) between a statically stable foam flowing in cross flow over a single tube, a vertical row of tubes and a bank of tubes is considered. In Section 224A we discuss the relationship between heat flux and temperature difference and Section 224B discusses row-to-row variations in heat transfer coefficient. Foam heat transfer can only be applied over a limited range of conditions and this is discussed in Section 224C. Finally, Section 224D, Section 224E and Section 224F present information and correlations for average heat transfer coefficients for single tubes, a vertical row of tubes and for tube banks respectively.

A. Relationship between heat flux and temperature difference

An experimental investigation has been performed in order to investigate the relationship between heat flux and temperature gradient for a foam (Gylys et al., 1989). The experiments were carried out for a single horizontal tube and the results are presented in the form of heat transfer coefficient as a function of temperature difference and heat flux in Figure 1 and Figure 2 respectively. It is seen (Figure 1) that the temperature difference \(\overline{\varDelta T}\) does not have an influence on the heat transfer coefficient in the range 4 < \(\overline{\varDelta T}\) < 35; ᾱ = 310 W/m² K for the case investigated. The average temperature difference was calculated as follows:

\[\label{eq1} \overline{\varDelta T}=\overline{T}_{w}-\overline{T}_{f}, \tag{1}\]

where T̅_w is the tube external surface mean temperature (K), T̅ _f is the mean temperature of the foam flow just before the tube (K). The average heat transfer coefficient ᾱ (W/m² K) was calculated as follows: