Current trends indicate that two-thirds of the world's population will be living in water-stressed countries by 2025. In order to eradicate or to provide sufficient water requirement for human kind desalination plays a pivotal role.
Sea water desalination using multi-effect distillation (MED) principle has been increasingly pre-dominant during the last two decades due to higher thermal efficiency, low initial cost and maintenance expenses. Large capacity multi-effect distillation plants have been installed and presently about 9% of the water production in the world is by MED technology. In MED system, the thin film evaporation of seawater takes place at the outer surface of the bundle of tubes, normally arranged in horizontal. Heat of condensation inside the tube is transferred to the falling water film outside the tube. Heat transfer on the outside is more or less unpredictable due to the uncertainty nature of film, film thickness, film dry out, etc. and film heat transfer coefficient is considerably less compared to the inside condensing heat transfer coefficient. Hence, in order to study deep into flow and thermal behaviour, we developed a novel interferometric method to calculate film interface temperature and a shadowgraph approach to estimate film thickness simultaneously. A Mach-Zehnder interferometer with infinite fringe setting was used to capture the thermal fluctuations around the horizontal tube falling film evaporator. Interferometric method implemented in this work also serves as an image visualization technique and does the purpose of qualitative as well as quantitative analysis. An in house designed experimental setup was fabricated for producing a thin and uniform falling film with a fully wetted flow over the horizontal copper tube. A heater cum controller setup was incorporated into it for accurate temperature control. This method holds the advantage of scanning falling film thickness over circumferential angle for the range 5°  θ  175°, which is an improvement to state of the art. Furthermore, CFD analysis was also carried out for the entire process by means of VOF scheme and was found to be in good agreement with the experimental results, which proves this technique to be a good one. A standard error of mean analysis was performed on every data set, which validates the reproducibility and the dynamic measurement capability of the technique used.