was followed in shutting down the test at the end of the day. That was to switch on the trace heater when the main heater was turned off thereby allowing the evaporator to cool down before the condenser. This procedure ensured repriming of the evaporator and a uniform prestarting condition for all the power levels tested. Experimental Uncertainty The experimental data were subject to the following uncertainty in measurement due to systematic or instrumental errors. Results and Discussion Heat Losses and Calorimetry All of the heat input (QJ to the evaporator was not transported to the condenser due to radial losses through the shields in the evaporator and adiabatic sections. Under steady state conditions: The quantities QE, QK and Qo are the portions of the heat lost from the evaporator, adiabatic and condenser zones respectively. These losses were obtained through the calorimetric measurements and tallied with the input power for every steady state test. At low heat inputs (100-600 W) the losses in the evaporator and adiabatic zones (Qe+Qa) varied from 80% to 40% of Q, and at high inputs (>600 W) the losses were almost constant at 40% of Q,. The actual heat transported through the heat pipe is Qo and this value is given along with Q, for all the transient and steady state test profiles. Vacuum Mode Test Results Steady State. The steady state axial temperature profiles for different transported power levels (Qo= 129-515 W) are shown in Fig. 4. The pipe operated nearisothermal from end-to-end at QO = 467 W and 515 W. The average temperatures of the evaporator and condenser for QO = 515 W were 558.1 °C and 534.6°C respectively and the overall temperature drop was 23.5°C. At power levels below QO = 467 W, the hot front did not reach the condenser end. It was suspected that a trace amount of gas could be present in the pipe. This trace amount of gas could be argon trapped within the pipe during sodium filling which could not be pumped out thoroughly subsequent to the filling. Transient State. In the vacuum mode, the pipe was nearly free of noncondensible gas. The pipe was started from the frozen state at room temperature. Figs 5 and 6 show the axial temperature profiles at 20, 30, 60 and 150 min after the application of the power input for Qo=289.6 W and 354.4 W respectively. Figs 7 and 8 show the corresponding transient temperature profiles at a few specified axial locations for the same power levels. It may be observed that the hot zone was not isothermal during
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