Computational fluid dynamics analysis of cooling tower inlets

Reuter H.C.R.; Kroger D.G.

Computational fluid dynamics analysis of cooling tower inlets

Date

2011

Authors

Reuter H.C.R.

Kroger D.G.

Abstract

Cooling tower inlet losses are the flow losses or viscous dissipation of mechanical energy affected directly by the cooling tower inlet design, which according to the counterflow natural draft wet-cooling tower performance analysis example given in Kröger (Kröger, 2004, Air-Cooled Heat Exchangers and Cooling Towers: Thermal-Flow Performance Evaluation, Pennwell Corp., Tulsa, OK), can be more than 20% of the total cooling tower flow losses. Flow separation at the lower edge of the shell results in a vena contracta with a distorted inlet velocity distribution that causes a reduction in effective fill or heat exchanger flow area. In this paper, a two-dimensional (axi-symmetric) computational fluid dynamic (CFD) model is developed using the commercial CFD code ANSYS FLUENT, to simulate the flow patterns, loss coefficients and effective flow diameter of circular natural draft cooling tower inlets under windless conditions. The CFD results are compared with axial velocity profile data, tower inlet loss coefficients and effective diameters determined experimentally by Terblanche (Terblanche, 1993, "Inlaatverliese by Koeltorings," M. Sc. Eng. thesis, Stellenbosch University, Stellenbosch, South Africa) on a cylindrical scale sector model as well as applicable empirical relations found in Krger, determined using the same experimental apparatus as Terblanche. The validated CFD model is used to investigate the effects of Reynolds number, shell-wall thickness, shell wall inclination angle, fill loss coefficient, fill type, inlet diameter to inlet height ratio and inlet geometry on the flow patterns, inlet loss coefficient and effective diameter of full-scale cooling towers. Ultimately, simple correlations are proposed for determining the cooling tower inlet loss coefficient and inlet effective flow diameter ratio of full-scale cooling towers excluding the effect of rain zones and the structural supports around the cooling tower entrance. © 2011 American Society of Mechanical Engineers.

Keywords

CFD, cooling tower, effective diameter, inlet flow, loss coefficient, Air-cooled heat exchanger, Axial velocity, Axisymmetric, CFD codes, CFD models, Computational fluid dynamics analysis, Counterflow, Diameter ratio, effective diameter, Empirical relations, Experimental apparatus, Flow area, Flow loss, Height ratio, Inclination angles, Inlet design, Inlet geometry, Inlet loss coefficients, loss coefficient, Loss coefficients, Mechanical energies, Natural draft, Natural draft cooling towers, Performance analysis, Performance evaluation, Rain zone, Shell wall, South Africa, Structural support, Vena contracta, Viscous dissipation, Wet cooling tower, Cascades (fluid mechanics), Computational fluid dynamics, Cooling, Cooling towers, Flow patterns, Heat exchangers, Intake systems, Reynolds number, Towers, Walls (structural partitions), Inlet flow

Citation

Journal of Fluids Engineering, Transactions of the ASME
133
8
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