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An experimental study has been carried out on a continuously operated pilot fractional distillation column equipped with an external heat pump. The distillation column was a 15 cm internal diameter glass unit containing eleven single bubble cap plates. A methanol‐water mixture was fed to the column. After operating the heat pumps with R114 as the working fluid, further experiments have been conducted with R11 as the working fluid. Plots of pressure against enthalpy, condensation pressure and latent heat of vaporization against condensation temperature and theoretical Rankine coefficient of performance against gross temperature lift and condensation temperature are presented for both R114 and R11. R11 has correspondingly higher theoretical Rankine coefficients of performance than R114. The experiments show that the actual coefficients are also higher for R11 than for R114. A maximum actual coefficient of performance of 5.3 was obtained using R11 as the working fluid with a gross temperature lift of 38.4°C. The experimental data for R11 were found to be reproducible during operation over a number of weeks. This showed that the relative thermal instability of R11 compared to R114 had not apparently affected the performance of the system.

More than one hundred and fifty references for heat pump assisted distillation systems have been listed and classified under the following categories: heat pump assisted distillation (1) with an external working fluid, (2) using one of the distillation components as the working fluid, (3) overall assessments and (4) experimental data.

Various correlations available in literature for predicting two‐phase heat transfer coefficient in annular flow regime are reviewed. Accurate prediction of these coefficients effect not merely the efficient and economic design of equipment but also its safety in operation. Instabilities can result in boiling crises, disturb the control systems and cause mechanical damage. It is observed that applicability of these correlations for a multi‐tubular heat exchanger has not been investigated. Experimental studies on a heat pump assisted distillation unit have been conducted. Results show that the actual values of heat transfer coefficients are consistently higher than those predicted by Shah, Pierre and Guerrier's correlations.