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One common feature noted about the velocities measured as a function of pressure at given loading densities was the tendency of the velocity to reach a constant value after a certain given heat input. This can be regarded as the deterioration of the heat transfer according to fluid flow and proximity to the critical point. With the introduction of an internal heater instead of the external heater as noted in Figure 28, effect of actual heat input could be studied.
Figure 30. Dependence of velocity on heat input, Qh,
for various reduced densities, rr = rload/rc. Tcooler = 50.
Figure 30shows some of the results for a range of reduced densities and for a fixed cooler temperature of 50 oC.
To conclude, high flow velocities of almost 7 m/min are attainable with supercritical carbon dioxide in a prototype closed-loop circulation system. Flow velocities depended on system loading density and the temperature difference between heating and cooling sources. Simulation could predict velocities generally to within 35%. Velocities could be correlated to within about 10%. Internal heating gave higher velocities than external heating probably since a larger percentage of the energy input could be imparted to the fluid. Loading densities that were somewhat lower than the critical density allowed higher velocities to be |