Thermal and hydraulic analysis for air flow across flat tubes air cooled condensers

Abstract EN

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 cross 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 theoretically 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 (CFD) 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 best 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 (KΔp) 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, the enhancement factor of heat transfer rate per unit of mass flow rate of refrigerant (K Q / m• ) is about 1.2 and 2.2 for case-1 and case-2 respectively.