VOF two phase thermosyphon heat pipe. "No pressure Rise"
 

I am simulating two-phase thermosyphon heat pipe with VOF model, k-e Realizable, primary phase water vapor, secondary phase is water liquid,
I have tried both SIMPLE and PISO with PRESTO solution methods.
My thermosyphon specifications are:
Three sections - Evaporator, condenser and adiabatic,
Constant heat flux is given at evaporator and convection at condenser section.
I am doing transient analysis with Explicit formulation. with very small variable time steps.
Everything is fine, my temperature contour, velocity profile, residuals are also good, but there is no significant change in pressure. The pressure is the same as what I give as the operating pressure. As the temperature is increasing inside the thermosyphon, there should be a rise in pressure also. But it is not rising, Please can anyone help?

I assume you are using Pressure-based solver not density based. In that case, you should check velocity contour, if its not changing much, then pressure change is also correct.