Grease particle deposition measurements in a kitchen exhaust duct for the development of low cost grease sensors.

Abstract

Grease deposition in kitchen exhaust ducts is an imminent fire hazard. There exists the need to quantize and measure the amount of grease deposition in a commercial kitchen exhaust duct in a cheap and efficient manner. Results from a real cooking emission study (ASHRAE 1375-RP) were used to model grease deposition onto a cylinder. Simulated cooking experiments were performed using a 200:1 ratio of non volatiles: uranine using a Polydisperse Aerosol Generator (PAG). The use of a cylinder in cross flow with a strain gage arrangement and a LED-photo resistor arrangement on two opposite walls of a 0:254 m by 0:203 m (10 inches by 8 inches) duct at two exhaust velocities namely 2:54 m/s (500 ft/min) and 7:62 m/s (1500 ft/min) were investigated. The size distributions obtained by the simulated cooking experiments were similar to that obtained in the ASHRAE 1375-RP study. The modeling results were within a factor of 1:5 of the simulated cooking results. This is reasonable considering the complexities of actual grease deposits. The photo resistor was very sensitive to minute changes of grease deposition layers. It would be beneficial to inspect the output signal of the photo resistor for greater thickness of grease deposits. The strain gage technique did not prove successful to measure grease deposition inside a duct due to the constant vibrations. Deposition results obtained flurometrically showed that deposition flux on to a cylinder placed in cross flow and all four walls of the duct increases with increasing exhaust velocity. Deposition flux on the windows for the LED and the photo resistor were in close proximity to the deposition flux on the two side walls. Correlations were developed for particle deposition on all four walls of the duct. Flow Reynolds number has a major impact on particle deposition in large exhaust ducts. A different approach is required in representing deposition results in terms of non dimensional parameters.