Imagine that you are filling a cryogenic tank sitting on weight scales. You fill it to the proper fill density from a tank supplying very cold zero psi liquid and record the weight. You then use your Superman X-ray vision and make a mark on the outside of the tank at the level of the liquid inside the tank.
A few weeks later, and not having used any product from the tank, you notice that the pressure in the tank has increased. Using your X-ray vision again, you look inside the tank and see that, amazingly, the tank has more product in it than when you filled it. The level has risen! You look at the scales, however, and the weight is still the same as the original value you recorded. How can this be?
Most substances expand in length and volume as they warm, and contract as they cool (there are a few exceptions). The sidewalk in front of your home has expansion joints to permit the concrete sections to expand in the summertime and contract in the wintertime. When you fill your car’s tanks with gasoline the nozzle trips off before the tank is 100% full, ensuring a bit of volume for the gas to expand into as it warms. If you have kept topping off your car you may have seen gasoline later weeping out of the tank and onto the ground on a hot day.
... to continue reading you must be subscribed
