Greetings,

I seem to missing something here. It is likely a fundamentals issue and I am not recalling something.

If I put a gP transmitter on the bottom of a tank filled 90% full of mineral oil will I be able to measure the weight of the oil over a range of temperatures? Assume the tank is vented to atmosphere.

The argument is that as the temperature goes up the volume goes up However, the density goes down so the pressure on the transmitter should remain the same since the mass of the oil is rho * V the mass should remain constant. Yes the volume increases so the level does increase but the density goes down so the mass remains constant.
Regardless of the temperature, volume, and density changes the mass must be staying the same.

Questions; How would I detect a leak if the level (volume) is constantly changing? Is the pressure measured by the gP transmitter going to be affected by the density of the oil (I say yes)? If so why does a temperature induced change in volume/density cause the pressure on the transmitter to change?

Thanks,
Ron

 

Ron,

I agree the pressure will remain constant regardless of temperature. However it will drop with a leak (l4ess Mass).

Gas stations often use a magneto restrictive transmitter for their underground storage that is very accurate and capable of detecting a small leak or theft from the tank. They also have double walled tanks with a liquid sensor in the interstitial space.

Google pneumicator

Roy

 

> Is the pressure measured by the gP transmitter going to be affected by the density of the oil?

It depends.

In context of your discussion, if the volume of oil in the tank is constant (no leaks, no removal, no addition), the changing temperature changes the density and a pressure measurement is not affected (assuming a vertical walled tank, not a horizontal round tank); the answer is no. The pressure measurement will remain the same for varying temperatures/densities of a constant volume.

A different oil with a different density will yield a different DP value at any given level.

> If so why does a temperature induced change in volume/density cause the pressure on the transmitter to change?

It doesn't in an open system (open, straight wall, vertical tank). The temperature induced density change of liquid in a horizontal round tank will produce pressure measurement changes because the associated volumetric change occurs over varying tank geometry.

If the liquid is trapped in a closed system, like capillary tubing in a remote seal pressure measurement, then a temperature change causes a pressure change.