# How to calculate vapor quality in a heated annular channel

Say I have a pipe of length L and an inner diameter of ID. Inside is a heated rod of diameter OD that is uniformly heated with power P. I have water flowing through the pipe with mass flow rate G under pressure p. The specific enthalpy at the inlet is H. I want to calculate the vapor quality x at the inlet and outlet.

I believe the correct way to do this for the inlet is: $$x_{in}=\frac{H-h_f}{h_{fg}}$$

And for the outlet it would be something like: $$x_{out}=x_{in}+\frac{P}{G\times h_{fg}}$$

I mostly want to check that this makes sense.

• Is the pressure approximately constant over the length of the pipe? – Chet Miller Aug 26 at 17:00
• Yes, it is approximately constant. – twalker Aug 26 at 17:16
• I confirm your result – Chet Miller Aug 26 at 18:06