# Measuring the gas temperature inside a vessel on the outside of the vessel

1. Nov 6, 2008

### Sierra1934

Hello,

I got a pratical problem; I want to know the gas temperature of SF6 gas inside a vessel. I can't insert a temperature probe to measure the temp. What i can do is clamp a temp. probe to the ouside of the vessel. Does this gives me a realistic reading, bare in mind the wetter conditions, sun shine ect...? I need the temperature to measure the density of the gas, i do know the gas and pressure.

2. Nov 6, 2008

### mgb_phys

In equilibrium the temperature of the tank must equal the temperature of the gas - since the gas in contact with the walls will heat or cool to the same temperature.
Dependign on how conductive thewalls are(assume it's a metal tank?) you might have to measure the temperature at a few places and average them. You might also have to remove any paint or coating when you apply the thermometers.

If the tank is a part of a process and new gas is entering and exiting all the time then this won't work as it won't have time to reach equalise.

3. Nov 6, 2008

### FredGarvin

To do it with that method, you need to look at two things:

1) Define how much variance you can accept in your density calculation. You will already have some due to instrumentation. However, the method of application of the thermocouple and the length of time you average out the temperature readings will all contribute to that variance.

2) You need to pay very particular attention to how the TC or whatever you use, is adhered to the vessel. You can induce quite a bit of error from the junction interface alone.