SYSTEMS FOR DEGASSING WATER USED IN ULTRASONIC MEASUREMENTS

Four approaches are compared to determine the suitability of degassing systems for use in ultrasonic measurements. Included are descriptions of both systems currently being developed and some used in previous work. The degassing systems discussed are (1) direct exposure of a water surface to a vacuum, (2) reduced pressurization of water by circulation through a pipe, (3) heating of water, and (4) exposure of water to a vacuum through a gas permeable membrane. Of these, a system based on a gas permeable membrane is convenient and desirable if strong degassing is required and/or loss of liquid vapor is a problem. Other less expensive techniques can be used for less degassing, particularly if continuous degassing is not required. This information is not intended as a definitive survey of all possible techniques but rather a rationale for choosing some appropriate degassing systems for use in ultrasound calibration, bioeffects, and shock wave formation studies, and other ultrasonic measurements where gas content of the liquid medium is important.