03-02: Flow Measurement and All That Jazz

Flow measurement is the single most critical parameter in cooling tower testing, yet in most instances, only one measurement is taken over the course of the test and all to often that is at a less than ideal location. In this study, a controlled environment has been created in which to compare the flow measurements obtained with different instruments under several conditions including ideal, significantly less than ideal, and the unwritten rule of 10D upstream and 5D downstream. The three specific "significantly less than ideal" conditions include a single elbow, a double ell in two distinct planes, and a butterfly valve, fully open and partially closed. The instruments will include a Simplex Pitot tube, a Simplex tube with a modified Fechheimer tip, and Annubar, and insertable turbine meter, an insertable mag meter, two transit time ultra-sonic meters, and possibly others. Each meter at each location will be checked at three flow rates, 3 fps, 7 fps, and 11 fps and compared to a Magmeter with calibration traceable to NIST, permanently installed in the same loop at an "ideal" location. In the paper, the measurements obtained by each type meter at each position and at each flow rate will be tabulated, compared, and conclusions discussed, particularly as they may pertain to cooling tower testing.