Theoretical analysis1 has predicted that the driving factors in flow stagnation of a radiator panel in a pumped fluid loop system are:
the viscosity of the working fluid,
the temperature drop between the fluid inlet and outlet on the panel (limiting the amount of heat rejection achievable with a single radiator panel), and
the magnitude of the cooling differential between the tubes on the panel.
Historically, manned spaceflight has used high viscosity, non-toxic glycol/water mix working fluids for pumped fluid loop radiators where panel fluid outlet temperatures are in a range where flow stagnation due to viscosity increases becomes a serious issue. Radiator panel flow stagnation occurs when fluid stops flowing through some of the panel fluid tubes, effectively reducing radiator size and heat rejection capability. If this phenomenon can be adequately understood, stagnation can be used advantageously as system heat rejection needs vary.
The focus of this paper is to evaluate the effect of radiator design parameters on the panel fluid tube flow stagnation point in a man-rated pumped fluid loop system with a goal of maximizing radiator panel heat rejection while increasing fluid system stability and stagnation predictability.
Using a Thermal Desktop® (
www.crtech.com) model of a radiator panel with fluid tubes, the sensitivity of the radiator fluid stagnation point to uniform changes in sink temperature, fluid inlet temperature to the radiator panel, radiator panel thickness, fluid tube internal diameter, fluid tube length, and working fluid viscosity is evaluated.