Testing an Axial Flow Fan Designed for Air-Cooled Steam Condenser Application

B2 - HVAC and Condenser Fans

Air-cooled heat exchangers (ACHEs) and steam condensers (ACSCs) offer a substantial benefit to the process and power generation industries, primarily by virtue of their sustainable use of cooling water. This technology is therefore particularly attractive to regions where cooling water is expensive or its availability is limited. An ACHE or ACSC consists of a rectangular array of axial flow fans that supply cooling air to a bank of heat exchangers. Based on their location within the array, for instance around the perimeter, the fans may be subjected to distorted inlet conditions. The distorted inlet conditions may be exacerbated by the presence of atmospheric winds.
A set of 1.5 m diameter axial flow fans, referred to as the B1- and B2-fans, were designed to address specific areas of concern associated with axial flow fans in an ACSC. These are the distorted inlet conditions that occur upstream of the fans and the occurrence of reverse flow at the fan hub (Venter, 1990). The B1- and B2-fans were designed for a specific design point while attempting to improve the efficiency of the fan. The format of the fans was constrained for practical reasons to be an 8-bladed rotor without stationary blade rows. This publication details the experimental evaluation of the B1- and B2-fans in comparison to an existing fan design. The design procedure followed in the development of the B1- and B2-fans is addressed in a separate publication.
Individual tests for the B1- and B2-fans were performed on a BS848 Type A fan test facility. The tests were performed for an operating domain that straddles the design point specified previously. The experimental results were compared to results obtained for a comparative industrial fan, referred to as the V-fan. The results showed that the B1- and B2-fans exhibit a higher fan static efficiency at the design point, when compared to the V-fan.
Numerical simulations performed with the B-fan showed that it may exhibit a high volumetric effectiveness when used in a multiple fan installation (Bredell et al., 2005). 630 mm diameter models of the B2-fan and V-fan (referred to as the B-fan and N-fan) were therefore manufactured and tested in the perimeter fan position in a multiple fan test facility (Conradie, 2010). The facility consisted of three fans, in parallel, extracting air from a common inlet chamber. One of the three fans resembled a perimeter fan, while the format of the two inner fans was left unchanged. The floor height of the inlet chamber was adjusted to vary the level of inlet distortion experienced by the perimeter fan.
The multiple fan results showed that the B-fan and N-fan exhibit a similar volumetric effectiveness at large floor heights. At the lowest floor height the volumetric effectiveness of the N-fan is however considerably lower than that of the B-fan. When considering the fan shaft power consumption in relation to the volumetric effectiveness of the B- and N-fans, the benefit of the higher efficiency of the B-fan is apparent.
1. Venter, S.J., The Effectiveness of Axial Flow Fans in A-Frame Plenums, Ph.D. Thesis, Department of Mechanical Engineering, University of Stellenbosch, South Africa, 1990.
2. Bredell, J.R., Kröger, D.G., Thiart G.D., Numerical Investigation of fan performance in a forced draft air-cooled steam condenser, Applied Thermal Engineering, 26, 2005.
3. Conradie, P.J.F., Edge fan performance in air cooled condensers, M.Sc.Eng. Thesis, Department of Mechanical and Mechatronic Engineering, University of Stellenbosch, South Africa, 2010.