EFFECT OF VOLUTE AND ROTOR WIDTHS ON SQUIRREL CAGE FAN VELOCITY PROFILES

The volute of a squirrel cage fan controls the flow .field through the rotor and therefore the complete fan. Performance tests on fans with four rotors of the same diameter but with different widths. Inside two different volutes showed that larger volute widths flatten the fan characteristics curve and allow a larger maximum volumetric flow into the fan. When the volute width is fixed, the performance curves closely overlap and the rotor width only changes the maximum flow rate. The velocity profiles after the rotor were measured using laser Doppler anemometry for four different fans. They show that in each of the four volute/rotor combinations, the flow out of the rotor is not uniform at different peripheral angles. This pattern changes with volute width and at different operating conditions. At angular positions closer to fan exit where the cross section is larger and the volute resistance is smaller, more flow exits the rotor. This flow has a shorter path inside the volute before it reaches the fan exit and therefore a higher efficiency ensues.