mahony

Sorry for the delay in getting back and thanks for all the help its fantastic help! I apologise I am not a scientist but an Engineer thats why I am asking you guys, The temperature is controlled at 20 degrees Celcius. The pressure applied as rightly pointed out is -80 to -100kPa which is about 20 to 1kPa absolute pressure (I think I'm right there) The water wouldnt boil and turn to vapour at this surely but it is cavitating( air bubbles forming). The water is stored in sand in a sealed container (the reason for all this is I am a Geotehnical Engineer and I'm trying to understand a certain ground condition). Air bubbles appear to be created and rise and form an air pocket at the top. With an air pocket created now at the top of the container would you expect a change in pressure. Another question is does anyone know where I could find information on the effect of Time. I mean if negative pressure is created slowly or fast does it make a difference? Thanks for any help

Hi Guys, If water is in a sealed unit and some of the water is pumped out until it reached a certain negative pressure say-100kPa. At this point the water cavitates and air comes out of the water. what will happen the pressure as the air comes out? Thanks a million for any help

Cheers I am going to try and read up with regards it occurring in those situations, I'm afraid I was unaware of them so thank you very much. Currently I have set up an experiment and I have lowered the pressure in a soil profile completely saturated with water. The soil profile is resting on a mesh. Below the sample is a reservoir of water and above there is a reservoir of water. I have gone to -80kPa. I lowered the pressure by pumping water out of the sample reservoir below. Cavitation is occurring and there appears to be an air pocket forming on the top. I was wondering though what would you expect to happen to the pressure as cavitation occurs. In two tests I ran so far I have got conflicting responses. In the first the pressure lowered and in the second it stayed the same. When air comes out of the water and fills the vacuum what will happen the overall pressure?

Really interesting reply thank you

Problem: Drilling in London and high pressure Nitrogen gas pockets are hit killing two workers due to lack of ventilation. Background and proposed theory: Underneath London in the 1940s the water table was lowered underneath an impermeable layer of clay. This created a vacuum in certain areas Due to the vacuum the water cavitated Air came out of the water and formed above the water and below the clay. Iron present in the clay oxidised causing the removal of Oxygen in this air and resulted in Nitrogen rich air Water table increased (due to less demand officially) and resulted in the Nitrogen under high pressure. Question: Does this theory make sense to scientists? Thanks for your help regardless I really appreciate it Mahony