The published literature on forced convection vaporization of mixtures is much more limited than that for pool boiling of mixtures. However, there is growing interest in the subject and useful reviews are given by Collier and Thome (1994), Fujita and Tsutsui (1997), Carey (1992) and Kandlbinder (1997). One of the earliest published studies is that of McAdams et al. (1942), who in 1940 carried out experiments using a four-pass horizontal-tube evaporator heated by steam. Each pass had three separate steam jackets to allow the local heat flux to be measured. The fluid was a benzene-oil mixture. Bulk fluid temperatures were found to increase throughout the saturated boiling length as the liquid became richer in oil. Thus, some of the heat transferred to the liquid was retained in the form of sensible heat to maintain the fluid at saturation conditions and was not available for evaporation. Average boiling heat transfer coefficients were calculated for each pass where boiling occurred in all three jackets. At a given vapor mass quality, the coefficient decreased as the oil content of the feed increased.

A number of workers [Bonnet and Gerster (1951); Shellene et al. (1968)] have studied the performance of complete reboilers. but such studies cannot provide information on the local conditions in the evaporating stream.

A. Saturated nucleate boiling

Saturated nucleate boiling will be influenced by the addition of a second component in the same qualitative manner as nucleate pool boiling (Section 197). Thus, where the heat transfer is dominated by nucleate boiling, reductions in the heat transfer coefficient may occur, as in the case of pool boiling, and can be estimated using the methodologies described in Section 197. Results in this category include those of Müller-Steinhagen and Jamialahmadi (1996), Fujita and Tsutsui (1996), Celata et al. (1996) and Steiner (1996). Typical results of this kind are shown in Figure 1.

Figure 1 Variation of heat transfer coefficient with composition in forced convective boiling of R134a/R123 mixtures (Fujita and Tsutsui, 1996)