Plenum chamber flow losses in forced draught air-cooled heat exchangers

The primary objective of this experimental investigation is to determine the influence that different fan and heat exchanger characteristics as well as the plenum chamber geometry have on the flow losses in the plenum chamber of a forced draught air-cooled heat exchanger (ACHE). The effect of air flow maldistribution on the heat exchanger thermal performance is also investigated. A series of model tests are conducted employing different fans and heat exchangers. It is found that there is a critical minimum distance between the outlet of the fan and the heat exchanger. The heat exchanger loss coefficient and its inlet geometry have a relatively strong influence on plenum losses as well as on the air velocity distribution at the outlet of the heat exchanger. Other variables, including the position of the fan in the fan casing, fan-to-heat exchanger area ratio and fan characteristics, have a lesser effect on plenum performance. A plenum chamber recovery coefficient is defined and expressed in terms of measured parameters. This coefficient can be employed in the design of practical ACHEs. It is further found that air flow maldistribution only has a small influence on the heat exchanger thermal performance. (C) 1998 Elsevier Science Ltd. All rights reserved.