Heat Transfer Characteristics and Temperature Distribution of Falling Film over Horizontal Hot Tube Arrays

Falling film heat exchanger is widely used in the industry, because of its high heat transfer coefficient, low liquid quantity and lower fouling factor. The heat exchanger considered here is a falling film one. It consists of a unique feeding tube, supply liquid such as pure water over seven parallel horizontal tubes which are heated internally. Convection heat transfer takes place outside the tubes surface and it is experimentally investigated. The falling film over the test tubes may be in the form of a droplet, jet or sheet. A combination of these forms is also possible. The tested tubes are made of copper and have 28.5 mm outer diameter and 300 mm length, each. They are arranged in series so that heated water enters each tube with the same flow rate, from bottom to top. The temperatures at the entrance and exit of the hot water flow and the falling film liquid are recorded. Also, the average surface temperature at one test tube is measured using five impeded thermocouples. An infrared camera is used to show the temperature distribution on the test tubes surfaces. The flow rates of each liquid path are controlled and monitored. The effects of different falling film forms and hot water flow rate, on the heat transfer coefficient are studied. Initial results show that changing the falling film forms and internal flow rate has a significant effect on the heat transfer coefficient. They also show that jet mode falling film has the best heat transfer coefficient.