C INVESTIGATION OF HEAT TRANSFER COEFFICIENT AUGMENTATION IN DIVERGENT RECTANGULAR DUCT FOR TWO PHASES FLOW (AIR-WATER)

Abstract

In this project, the flow distribution for air and water, and the enhancement of the heat
transfer coefficient are experimentally studied. Experimental studies have been performed to
test the influence of discharge, pitch, the height of ribs at a constant heat flux on the
temperature and pressure distributions. Along the channel of the test and the heat transfer
coefficient, the water volume flow rate was about (5-12 L/min), the air volume flow rate was
about (5.83-16.66 L/min), and heat were (80, 100,120, watt). An experimental rig was
constructed within the test whole system. On the other hands, the channel has a divergent
section with an angle =15o with vertical axis. The study included changing in the ribs height
by using three values (12, 15, 18 mm) and changing the ribs pitch into three values (5, 8, 10
mm).The results indicated an increasing in the local heat transfer coefficient as a result of
increasing the discharge. While there was an inverse influence for the temperature distribution
along the test channel which drops when the discharge rise. The results also confirm that the
increasing in the pitch distance leads to reduce the heat transfer coefficient. Increasing the
ribs height increases the coefficient of heat transfer. However, the experiment heat transfer
coefficient improves about (15.6 %) when the water volume flow rate increased from (5 to 12
L/min), and about (18.7%) when the air volume flow rate increased from (5.83 to 16.66
L/min). The best heat transfer coefficient was about (35.6 %) which can be achieved when
the pitch decreased from (10 to 5mm). The increasing of the height from (12 to 18) mm
improves the heat transfer coefficient about (11.2 %). The best rib dimension was 18 mm
height, and 5 mm pitch, which give a maximum heat transfer coefficient (1212.02 W/m2. oC).