Two-dimensional vapor flow analysis in heat pipes

The computer code AGATHE which is intended to evaluate axially symmetric heat pipes with compressible vapor flow at Mach numbers up to one and at all radial Reynolds numbers is discussed. The code evaluates empirical factors which describes turbulence. Heat input and output are modeled by describing liquid heat transfer loops. The method leads to nonuniform heating and cooling rates typical of actual heat pipes. The code is adapted to evaluate heat pipes in tubular geometry composed of a series of heat transfer and adiabatic zones of cylindrical or conical shape. The two dimensional mathematical problem is reduced to a number of ordinary differential equations, which are integrated by a Runge-Kutta scheme. The reduction is achieved by starting from the Navier-Stokes equation using the boundary layer approximation; this approximation introduces the main limitation of the code, restricting its use to the calculation of vapor ducts with large length to diameter ratios. The velocity profile is simulated by a power series; the n-coefficients of this series are determined such that at each axial position the radial pressure gradient is approximately zero, as specified by the boundary layer approximation.