Air Friction, Condensate, Heat Exchanger
Experimental tests on the air friction of several plate fin-tube heat exchangers were conducted under dry-surface and wet-surface conditions. The impacts of face velocity and condensate rate on the air friction were investigated through the tests. Under dry-surface conditions, the standard face velocity changed from 100 to 2,000 FPM. Under wet-surface conditions, the standard face velocity changed from 300 to 500 FPM. The inlet relative humidity changed from 30% to 90%. Under dry-surface conditions, air-friction is a function of face velocity. Tube size, tube pattern, fin density, number of rows, fin thickness and surface geometry also have an impact on the air friction. Under wet-surface conditions, the additional impact from condensate rate on air friction was found through the experimental tests. At 300 FPM face velocity, the air friction increased as the condensate flow rate increased. When the condensate rate reached a certain level, further increasing of condensate rate did not cause higher air friction. At 480 FPM face velocity, the air friction continuously increased as the condensate rate increased. Condensate carryover was found in such high face velocity conditions and is considered to be the reason.