Page 217 - Managing Global Warming

178 Managing Global Warming

of Pr is governed by the more significantly changing property of the coolant. We have
established that the specific heat is nearly constant for all of the Generation IV reactors
coolants except for SCW. Therefore, for most of the coolants, it is the ratio of the vis-
cosity to the thermal conductivity that influences the shape of the Pr/temperature
curve.
As we see from Fig. 4.45, the changes in the viscosity and thermal conductivity of
the gases are such that they compensate each other, and the Pr of gases is virtually
constant over most of the 750°C temperature span. However, for the liquid metals,
the viscosity drops more significantly than the thermal conductivity increases. As a
result, the Pr of liquid metals drops almost linearly with temperature. Due to an
increase in viscosity of LBE at high temperatures, the corresponding value of Pr
for Pb-Bi also increases. Since the specific heat of SCW goes through the most rapid
changes compared with its other thermophysical properties, the Pr of SCW behaves
similar to its specific heat. At high temperatures (>500°C), the Pr of SCW behaves
similar to that of the gases.
The volumetric expansivity of liquid metals is much smaller than that of the
remaining coolants and stays almost constant (see Fig. 4.46). The volumetric

Fig. 4.46 Volume or volumetric expansivity of selected coolants vs temperature [1].