Pressure recovery in a cylindrical heat pipe at high radial Reynolds numbers and at high Mach numbers

Pressure recovery in a cylindrical heat pipe at average radial Reynolds number Re(r) between 5 and 150 and average Mach number between 0.1 and nearly 1.0 was investigated. The observed flow phenomena are described, and the basic features of a modular heat pipe design based on these observations is shown. The pressure recovery increases with Re(r) from a value of about 50 percent at Re(r) of roughly five to a maximum of 93 percent at Re(r) of about 50. At Re(r) between 50 and 130, the pressure recovery remains practically constant at 93 percent. A strong decrease in pressure recovery occurs independently of Re(r) if the local Mach numbers reach or exceed 1.0. This indicates an additional energy dissipation at a supersonic core flow. Measurements of pressure recovery for subsonic flow compared well with a laminar two-dimensional model at Re(r) up to 30 and with a turbulent model at Re(r) above about 80.