Design, Fabrication and Optimization of a Water-vapor Condenser

Abstract

A thermal desalination system that relies on solar energy for water evaporation is currently under development at the Institute of Nuclear Science and Technology (INST), University of Nairobi. The system uses the electrospray technique to break up the water into small droplets. This creates a large surface area for evaporation. Such a system is comprised of evaporation and condensation processes. This study reports on the Design, Fabrication and Optimization of a Water-vapor Condenser from the evaporation process. To study the condensation process, an evaporation chamber was constructed and the physical and flow properties of the moist air [relative humidity, temperature, mass flow rate, velocity] were used as the input parameters for the condensation process. The condenser was then modeled using the iterative process provided in Kern method (1950). Using the results from the model, an experimental condenser was fabricated and measurements were carried out to investigate its performance. From experiments, the condenser efficiency was 41% for a relative humidity of 70% and condenser inlet water temperature of 20 oC; and 54% for a relative humidity of 70% and condenser inlet water temperature of 5 oC. It was observed that higher relative humidity favors condensation and a relative humidity lower than 40% produces very little condensation. The results from the experiment and the simulation showed on average a 15% deviation; thereby the simulation results could be relied upon to give an indication of the performance of the condenser. The highest simulated efficiency the system achieved was 78% which is comparable to the existing condensers that have efficiency range of 80 -85%. The average rise in temperature ΔT of the cooling water was 2oC. It was also observed that the larger the temperature difference (ΔT) between the warm and cold fluid streams of the condenser the higher the rate of condensation.