Engineering Conversion

Table 1 provides data for engineering conversion applicable to the use of an evaporation in food processing.

Estimating Residence Time

It is difficult to estimate the residence time in film evaporators, especially rising film units. Correlations, however, are available to estimate the volume of the channel occupied by liquid. Table 2 describes a number of applicable equations. Equation 1 is recommended for vacuum systems.

For falling film evaporators, the film thickness without vapor shearing can be calculated by equation 2.

Since the film is thin, this can be converted to liquid volume fraction in a tubular evaporator by equation 3.

For a falling film plate evaporator, equation 4 is used. As liquid travels down the plate and evaporation starts, vapors will accelerate the liquid. To account for this action, the rising film correlation is used when the film thickness

Table 1. Engineering Conversions

To convert from to

Multiply by


Heat capacity


Pounds/gallon Pounds/ft3

Molecular weight 1.0

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