Flat Plate Pulsating Heat Pipes with and without separating grooves: experimental investigation on adiabatic length, coolant temperature and orientation

Two Flat Plate Closed Loop Pulsating Heat Pipes have been tested under various operating conditions, working fluids and different evaporator-to-condenser distances. The devices have the same geometrical features; nevertheless, on one FPPHP plate external grooves between adjacent channels have been engraved to minimize the transversal thermal conductive spreading whilst the other is a simple smooth plate. The working fluids are ethanol and FC72. Both FPPHPs have shown better performances when tilted in favorable vertical position. It has been found that higher secondary fluid temperatures within the condenser provide better thermal performances. The fluids’ different thermophysical properties and critical diameters have remarkable effects on FPPHPs behavior. Moving the condenser towards evaporator increases the heat transfer capabilities, reducing the influence of gravity. Finally, the higher thermal insulation between adjacent channels, provided by the external grooves, seems to degrade the thermal performance, especially on horizontal position and on the edge.