Physics Van 3-site Navigational Menu

Physics Van Navigational Menu

Q & A: Cool Bunsen Burner Needle Valves

Learn more physics!

Most recent answer: 10/22/2007
Q:
Why does the needle valve in a bunsen burner remain cool? And also, what kind of energy is released by the reaction between the gas and the oxygen in the air when a bunsen burner is used?
- Clarissa (age 14)
Anglec JHS, USA
A:
The needle valve in a bunsen burner is not right near the flame. The flame burns where the gas and air (with oxygen in it) mix, in the hollow tube held above the needle valve. In addition, the needle valve is below the flame. The burning gases already are moving upwards through the tube because the gas comes out of a jet at the bottom pointing up into the tube. So all the hot gas comes out of the top of the tube, in a nice, controlled fashion and there is no "flickering" of the flame and little chance that there will be unburned gas at the end of the reaction.

There may be a little warming up of the needle valve in a bunsen burner when it operates because the flame emits visible and infrared light in all directions, some of which goes downwards towards the valve and gets absorbed. But air comes in from the sides to mix in with the gas (the Venturi effect, using Bernoulli's principle), and this flowing air helps to keep the bottom of the burner cool.

Tom

(published on 10/22/2007)

Follow-up on this answer.