Correlations of flow maldistribution parameters in an air cooled heat exchanger

Abstract

SUMMARYThe present paper provides correlations of flow maldistribution parameters in air-cooled heat exchangers. The flow field in the inlet header was obtained through the numerical solution of the governing partial differential equations including the conservation equations of mass and momentum in addition to the equations of the turbulence model. The results were obtained for different number of nozzles of 2-4, different inlet flow velocities of 1-2.5 m/s and different nozzle geometries in addition to incorporation of a second header. The results are presented in terms of mass flow rate distributions in the tubes of the heat exchanger and their standard deviations. The results indicate that the inlet flow velocity has insignificant influence on maldistribution while the nozzle geometry shape has a slight effect. Also, the results indicate that reducing the nozzle diameter results in an increase in the flow maldistribution. A 25% increase is obtained in the standard deviation as a result of decreasing the diameter by 25%. Increasing the number of nozzles has a significant influence on the maldistribution. A reduction of 62.5% in the standard deviation of the mass flow rate inside the tubes is achieved by increasing the number of nozzles from 2 to 4. The results indicate that incorporating a second header results in a significant reduction in the flow maldistribution. A 50% decrease in the standard deviation is achieved as a result of incorporation of a second header of seven holes. It is also found that the hole-diameter distribution at the exit of the second header has a slight influence on the flow maldistribution. Correlations of the flow maldistribution in terms of the investigated parameters are presented.

Experimental Investigation of the Flow Maldistribution Inside an Air-Cooled Heat Exchanger

“…At high flow rates of excess of around 5.7 kg/s, the case of two nozzles provide reduced maldistribution than the case of single nozzle. This supports the numerical results of Habib et al [12,14] which show similar conclusions for flow rate of around 12 kg/s. Table 1 (second row of data) summarizes the results of the nozzle number effect on the standard deviations (STD) in the mass flow rates inside the tubes of the header.…”

“…9b. The present experimental results do not match the conclusions of Habib et al [12,14] where the effect of nozzle diameter provide contradicting results. The differences may be attributed to differences in the heat exchanger geometry, number and location of nozzles and tube geometrical distribution.…”

“…The differences may be attributed to differences in the heat exchanger geometry, number and location of nozzles and tube geometrical distribution. As well, the flow rates considered in the present study are much lower than the cases of Habib et al [12,14].…”

“…It should be noted that the present study is of the experimental type. The previous studies by Habib et al [12,14] are based on numerical investigations.…”

“…A better approach of the analysis of the heat transfer data for plate heat exchangers was suggested by Rao et al [11]. Habib et al [12], based on numerical studies, provided correlations of flow maldistribution parameters in air-cooled heat exchangers and indicated that the inlet flow Reynolds number and nozzle geometry do not greatly influence flow maldistribution. In addition, the results indicated that reducing the nozzle diameter results in an increase in the flow maldistribution.…”