The Design of a Large Diameter Axial Flow Fan for Air-Cooled Heat Exchanger Applications

Abstract

An axial flow fan design methodology is developed to design large diameter, low pressure rise, rotor-only fans for large air-cooled heat exchangers. The procedure aims to design highly efficient axial flow fans that perform well when subjected to off design conditions commonly encountered in air-cooled heat exchangers. The procedure makes use of several optimisation steps in order to achieve this. These steps include optimising the hub-tip ratio, vortex distribution, blading and aerofoil camber distributions in order to attain maximum total-to-static efficiency at the design point. In order to validate the design procedure a 24 ft, 8 bladed axial flow fan is designed to the specifications required for an air-cooled heat exchanger for a concentrated solar power (CSP) plant. The designed fan is numerically evaluated using both a modified version of the actuator disk model and a three dimensional periodic fan blade model. The results of these CFD simulations are used to evaluate the design procedure by comparing the fan performance characteristic data to the design specification and values calculated by the design code. The flow field directly down stream of the fan is also analysed in order to evaluate how closely the numerically predicted flow field matches the designed flow field, as well as determine whether the assumptions made in the design procedure are reasonable. The fan is found to meet the required pressure rise, however the fan total-to-static efficiency is found to be lower than estimated during the design process. The actuator disk model is found to under estimate the power consumption of the fan, however the actuator disk model does provide a reasonable estimate of the exit flow conditions as well as the total-to-static pressure characteristic of the fan.

Numerical Investigation of Pressure Recovery for an Induced Draught Fan Arrangement

“…Fixed velocity and turbulence profiles at the fan outlet were used to specify the inlet boundary conditions. Circumferentially averaged outlet profiles for the M-fan at flow rates ranging from 260 to 380 m 3 /s were obtained from Wilkinson [41]. He measured these profiles from the hub to the tip of a periodic three-dimensional CFD model, approximately 0.1 m downstream of the fan blade trailing edge at the hub.…”

“…He measured these profiles from the hub to the tip of a periodic three-dimensional CFD model, approximately 0.1 m downstream of the fan blade trailing edge at the hub. Since Wilkinson [41] used the realisable k-ε turbulence model, the turbulence dissipation rate had to be converted to turbulence frequency using = /( * ), where * = 0.09 [42].…”

“…The fan under consideration in this study is the M-fan of Wilkinson et al [5]. They evaluated the fan numerically using a three-dimensional periodic fan model with a zero tip clearance.…”

Numerical investigation of CSP air cooled condenser fan

“…The air serves as the cooling fluid to condensate steam, flowing across a tube bundle (not shown). In this configuration a squared grid is present upstream the tubes and acts as pavement for operators (4). The fan design and operative parameters are summarized in Table 1.…”

“…This dissertation focuses on the certification of fan performance, that follows ISO 5801 [3]. Given the size of the actual ACC fan, it is not possible to test it in its full-size, but scaling of the device is required to fit it to smaller facilities, like the Stellenbosh laboratory that was used in this case, where the maximum diameter is fixed at 1.5 m. This of course poses some problems when scaling performance (previous works [4] showed that the scaled performance fits quite well the full size pressure ratio, whilst underestimating efficiency). Another issue in this case is the derating of performance from ISO to real-life installation layout, that is a key issue like in most fan installations.…”