Session: 10-02 Fan Applications

Paper Number: 120962

120962 - Axial Flow Fan Performance in a Forced Draught Air-Cooled Heat Exchanger for a sCO2 Brayton Cycle 

An axial flow cooling fan has been designed for use in a concentrated solar power plant. The plant is based on a supercritical CO₂ (sCO₂) Brayton cycle, and uses a forced draught air-cooled heat exchanger for cooling. The fan performance has been investigated using both computational fluid dynamics (CFD) simulations and scaled fan tests.

This paper details the development of a CFD model to simulate the fan coupled to the heat exchanger that it was designed for. The aim of this work is to provide a point of departure for the development of similar models in the future, and for the design of effective air-cooled heat exchangers for sCO₂ power cycles.

The CFD simulations make use of a simplified model of the finned-tube bundle. The heat transferred to the cooling air is neglected and a Porous Media Model is used to model the pressure drop and flow straightening effects. Pressure inlet and -outlet boundary conditions are used instead of specifying a fixed cooling air flow rate. The flow rate is therefore solved based on the interaction between the fan and finned-tube bundle.

The cooling air flow rate predicted by the CFD model is found to be 0.5% higher than the expected flow rate, and 3.6% lower than the design flow rate. This agreement demonstrates that the assumptions used in the fan design procedure are reasonable. The results further show that the height of the plenum chamber has a significant effect on the predicted flow, with shorter plenums resulting in higher flow rates and fan efficiencies, and longer plenums resulting in more uniform cooling air distributions through the bundle.

Finally, recommendations are made for future work, including estimating the heat transferred and modelling the sCO₂-side fluid behavior, which allows the effects of non-uniform flow on air-cooled heat exchanger performance to be evaluated.

Presenting Author: Francois D. Boshoff Stellenbosch University

Presenting Author Biography: I am a PhD candidate and part-time laboratory engineer at Stellenbosch University, with research focusing on the design and testing of an axial flow fan.

Authors:

Francois D. Boshoff Stellenbosch University
Sybrand J. Van Der Spuy Stellenbosch University
Johannes P. Pretorius Stellenbosch University