A small scale multi-effect distillation (MED) unit for rural micro enterprises: Part-III Heat transfer aspects

Overall Heat Transfer Co-efficient (OHTC) is the governing factor for heat transfer and depends on surface area utilized for heat transfer and temperature difference. The aspects of fabrication, design and operation along with design optimization of various components of the small scale multiple effect distillation (MED) unit have been discussed in part I and part II of the paper. As highlighted therein, the MED system can be operated as n effects + condenser (n + C), where 1 ≤ n ≤ 9. Extensive experiments have been carried out respectively using 9 + C, 6 + C and 3 + C systems. The present part III is devoted to understanding the physics of the OHTC, based on parametric studies on the input conditions for all the above three systems. The most important input parameters for operation of the MED system are the input steam pressure, and the number of effects used. The most important output parameter is the total distillate produced per hour.

Research Highlights
► Analysis of vertical tube evaporators (VTE) for efficacy of heat transfer.
► Steam in tube side and feed water film in shell side using outside fluted tubes.
► Use of stainless steel mesh inserts in the tube side, to break condensate film so that condensing film can be prolonged.
► Very high potential for overall heat transfer rates, with Overall Heat Transfer Coefficient (OHTC) up to 20,000 W/m2 °C.