A study of heat transfer, pressure drop and residence time distribution for two-phase, two component flow in a plate and frame heat exchanger

This thesis presents a literature review and the results of the present
investigation for the upward flow of mixtures of air and water, water or air
only in the channel of two Alfa-Laval plate heat exchangers.
The flow patterns and their areas in the channel were identified photographically
and visually. For both single-phase and two-phase flow, the embossed
section of the channel was occupied by the slow and fast zones of flow. The
ratio of the areas of these zones varied from nearly one to negligibly small
as the flow rate of the phase(s) was increased gradually. These data were
correlated empirically with the flow variables of the phase(s). High speed
photography was used to analyse mixing in the channel as well as each cell
formed by the herringbone patterns of the plates.
The data on the flow patterns were used to develop a mathematical model of
mixing in the channel to predict the exit concentration profiles of the
phase(s). The residence time distribution of the phase(s) predicted by the
present model compared very well with the experimental data for both singlephase
and two-phase flow of the phases. However, the fit between the
experimental and predicted exit concentrations was exceptionally good at
high flow rates of the phase(s). The fractional volume of air occupied in
the mixture of two-phase flow derived from the mean residence time of twophase
flow were correlated empirically with dimensionless groups. The mixing
parameters of the gamma distribution model were also correlated with the
single-phase and two-phase flow dimensionless groups.
The mean heat transfer film coefficients of water (hsL) and mixtures of air
and water (htp) for the clean plates were correlated empirically. A Nusselt
type equation was used to correlate the mean heat transfer film coefficients
for water. The ratio (htp/hsL) was also correlated empirically against
single-phase and two-phase dimensionless groups by two correlations which
suggest the presence of two widely different flow patterns and mixing
characteristics in the channel. Within the range of the variables investigated
the values of htp increased by 53 to 340 percent over those for hsL.
The pressure drop data for both metal and perspex plate heat exchangers were
analysed with the Fanning friction factor (fr) v. Reynolds Number of water
or air type of relationships. For air and water two different curves were
obtained for the fr: Re relationships. For the analysis of the two-phase
pressure data, an empirical approach incorporating the use of the dimensionless
groups viz. the ratio of the liquid to gas superficial Reynolds Numbers
and the Lockhart & Martinelli parameter (XLM) was found to correlate the twophase
friction factor data extremely well. Finally, the pressure drop data
were correlated equally well by a Lockhart & Martinelli (12) plot similar to
that presented for the tubes.

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