The Effect of Water Quality Characteristics on Cavitation Noise
This study investigated the effects of seawater on cavitation noise using a water jet test, a two-dimensional wing test, and a three-dimensional wing test. A model propeller cavitation test was conducted in a cavitation tunnel using seawater, in order to determine the effects of propeller cavitation more precisely. In the cavitation tests, measured propeller performance for both cavitation noise inception and desinence, as well as the cavitation noise spectrum (see, for example, figure 7). On the basis of the results of the present propeller cavitation test and tests that were carried out previously, we discuss how to control the water quality in the cavitation tunnel to reproduce the cavitation phenomena, especially cavitation noise, in seawater (see, for example, figure 9).
Propagation of non-linear transient pressures through fresh and sea water
The propagation of pressures generated by wave or jet impact into water filled cracks and fissures can create internal bursting pressures and resulting damages in structures such as blockwork breakwaters or coastal rock cliffs. Experimental investigations of pressure pulse propagation showed that the pressure pulses travelled as elastic waves in a water–air mixture inside of the cracks. Most previous experimental investigations were conducted at small scale, with near linear air compressibility. In reality, pressures will be well above atmospheric pressure so that non-linear effects can be expected. A series of drop tests was conducted to investigate the characteristics of pressure pulse propagation in the non-linear range of air compressibility in fresh and sea water. It was found that with pressure magnitudes exceeding approximately 100 kPa, the pulses become distinctly non-linear, with steep and short peaks and long, shallow troughs. The speed of propagation in fresh water ranged from 300 to 400 m/s, indicating air contents of 0.11 to 0.07% air. In sea water, the speed of propagation reached 290 m/s, indicating a slightly larger resident air content of 0.12%. Cavitation occurred and was accompanied in fresh water by short pressure bursts, which could not be observed in sea water.
Laminar heat or mass transfer in rectangular channels and in cylindrical tubes for fully developed flow: comparison of solutions obtained for various boundary conditions
Abstract A comparison is made of results obtained with various boundary conditions at the wall of the channels. By comparing blood Sherwood numbers for finite wall resistance with those for constant concentration boundary condition only a small variation is found for various points along the blood channel.