Evaporation is one of the most used phenomena in industrial process. It wasevident from the literature review that the problem of film evaporation outsideborizontal grooved tube still needs more investigation. Therefore the present work is concerned with the study of water film evaporation heat transfer outside a horizontal grooved tube. The problem is tackled theoreticall y and experimentally. The theoretical work introduces a simple model for calculating heat transfer coefficient outside a horizontal grooved tube. For this purpose, ahelically U-grooved tube is proposed to investigate the effect of the mainparameters such as mass flow rate per unit length, temperature difference andvaCULDT1 pressure on the average heat transfer coefficient . It is considered thatthe cross-section of the groove in the tube is composed of top, bottom portionsand two vertical sides.Also, the heat transfer coefficient is assumed to have the same value on thetop and bottom portions. To find general form of heat transfer on the twovertical sides of the groove, an inclined surface is considered as function of ioclination angle [Le. if e = 0 means a vertical side]. A theoretical formula for local and average heat transfer coefficients is obtained. A computer program is constructed in order to calculate local and average heat transfercoefficients. Experimental work was carried out a constructed test loop to verify the theoretical model developed in this work. The experimental loop consists of