INDUSTRIAL HYGIENE
SAMPLING STRATEGIES
AIR FLOW MEASUREMENT
AIR FLOW MEASUREMENT Purpose This experiment allows the student to have a good understanding of the equipment used in air sampling. Students will use 6 types of meters and gauges for the measurement of air flow. Air flow and volume measurements are essential for determining the concentration of airborne contaminants. Part I 1) Calibration of a rotameter with a wet-test meter. The calibration train instruments must be set as shown below. WET-TEST METER-->ROTAMETER-->VALVE-->PUMP - Maintain rotameter readings @ 10, 30, 50, 70, 90, 110, 130, & 140 - At each rotameter reading measure the time for 1 revolution on the wet-test meter. - Repeat each calibration point three times. - Calculate Q (l/min.) for each rotameter reading and plot results. - Keep and save the results and plot for later use. 2) Calibration of air flow through an impinger. The calibration train instruments must be set as shown below. WET-TEST METER-->IMPINGER-->MAGNAHELIC GAUGE--> -->VALVE-->PUMP - At impinger pressure drops of 8, 10, 12, 14, and 16" H2O, measure the time for 1 revolution on the wet-test meter. - Repeat each calibration point three times. - Calculate Q (l/min.) for each pressure drop and plot results. - Keep and save the results and plot for later use. 3) Calibrating a magnahelic gauge with a soap-bubble meter. The calibration train instruments must be set as shown below. SOAP-BUBBLE METER-->FILTER HOLDER-->MAGNAHELIC GAUGE--> -->(VIRTUAL) ORIFICE METER-->VALVE-->PUMP - At pressure drops of 5, 10, 15, and 20" H2O, measure the time that it takes the soap bubble to rise from 500 ml to 1000 ml. - Repeat each calibration point three times. - Calculate Q (l/min.) for each pressure drop and plot results. - Keep and save the results and plot for later use. Note: Plot all results on arithmetic and logarithmic graph paper with the flow as the ordinate. Part II 1) What is the probable error due to time measurement in these calibrations? 2) Over what range does the orifice follow the relationship of volumetric flow being proportional to pressure drop? 3) At what pressure ratio does the flow through the orifice become critical? Part III After the orifice meter was calibrated the soap-bubble meter was removed and a 0.3 mm filter weighing 0.00002 mg was placed in the filter holder. At a pressure drop of 18" H2O you sampled for two hours and immediately after you were done with sampling you weighed the filter; your balance indicated that the weight of the filter was 2.00345 mg. Determine the concentration of the collected material in air in mg/m3, and in ppm given that the molecular weight of this material is 35 g/mole and that sampling took place at 20 °C and 29.92" Hg.