Abstarct: Removal of dissolved salts and toxic chemicals in water, especially at a few parts per million levels is one of the most difficult problems. There are several methods used for water purification. The choice of the method depends mainly on the level of feed water salinity, source of energy and type of contaminants present. Evaporators are the heart of the desalination process and there are different types that are used in the desalination industry, mainly the type of falling film. Falling film evaporators are divided into two categories, horizontal and vertical, which are used in both models in the desalination industry. In this study, the effect of effective parameters on the evaporative heat transfer coefficient on a vertical tube bundle in a falling film evaporator has been investigated. The purpose of this study is to provide a model for designing and manufacturing falling film evaporators with vertical tubes that in addition to the desalination industry in various other industries such as chemical industry, food industry, and process engineering are useful.Therefore, in this study, the parameters affecting the evaporation heat transfer coefficient such as Reynolds number from 1900 to 4400, heat flux from 6 to 18 KW/m2, and saturation temperature from 65 to 75 ° C on a vertical tube bundle in a falling film evaporator is covered. The results showed that in the turbulent flow regime with increasing Reynolds number in constant heat flux, the evaporative heat transfer coefficient increases due to the formation of turbulence eddies. Also, as the heat flux increases, the evaporative heat transfer coefficient increases at a constant Reynolds number. For example, in a heat flux of 6 KW/m2, by increasing the Reynolds number from 2256 to 2806, the average heat transfer coefficient increases by %24.38, and in the same heat flux, by increasing the Reynolds number from 2806 to 3692, the average heat transfer coefficient increases by %31.57 .The results of this experiment are compared with previous experimental studies and despite the lower prediction of heat transfer coefficient in this experiment, using the results of this research as well as further studies in this field can be a model for designing and building a small scale multi-effect desalination plant.