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Thermal and Hydraulic Analysis for Air Flow Across Flat Tubes Air Cooled Condensers.

Corresponding Author

Awad, M.

Subject Area

Mechanical Power Engineering

Article Type

Original Study

Abstract

Thermal and hydraulic analysis is performed theoretically for air flow across flat tubes which used in air cooled condensers. Simultaneous forced convection of air outside condenser tubes and condensation of refrigerant inside it takes place. Many cros section configurations of flat tubes has been studied and compared with circular tube, for both equal perimeter (case-1) and for equal cross sectional area (case-2). The effect of tube spacing to height of flat tube (s/a) and the ratio between breadth to height of flat tube section (m-b/a) on the tube performance (rate of heat transfer and pressure drop for air side) is investigated theoreticaly to get the best effect cross section shape for each one of the proposed two cases. This study is based on equilateral triangle staggering configuration for both of circular and flat tube arrangements. A computational fluid dynamic software (CFD0 commercial package (FLUENT 6.0) is applied to flat tubes to study and evaluate the proposed two cases and compared with circular tube. The obtained theoretical results showed that the bet effect tube spacing (s/a) equal to 2 for case-1, and case -2 to achieve high performance for flat tubes. Also the best effect cross section has m = 4 for case-1 and m-8 for case-2. This leads to enhancement of outside air heat transfer rate by factor (KQ) of about 1.5 and 2.1 against increase in pressure drop factor (K∆p < /sub>) of about 1.7 and 3.3 for case-1 and case-2 respectively. Also, for the same volume of heat exchangers the enhancement factor of outside air heat transfer rate (KQ) is about 3.15 and 3.35 for case-1 and case -2.respectively at the best values of s/a and m for the studied two cases. In the same time, for condensation of refrigerant inside tubes for the same mass flow rate of refrigerant (KQ/m.) is about 1.2 and 2.2 for case-1 and case-1 and case-2 respectively.

Keywords

Air cooled condenser; Flat tubes; enhancing heat transfer

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