Prediction of Pressure Drop in a Boiling Channel.
The pressure drop in a boiling channel is an important consideration for a number of applications where parallel flow channels exist, e.g., nuclear reactors, and internal combustion engines. The formation of bubbles in a heated channel can have a significant effect on the overall pressure drop along the channel. For fully developed single-phase flow, the pressure drop is comprised primarily of effects due to wall friction, associated with tube surface roughness, which decreases with velocity. For cases where the wall temperature is greater than the saturation temperature of the fluid, as the velocity decreases, the applied heat flux causes the formation of vapor in the fluid. Boiling causes an increase in frictional drag due to the presence of bubbles, and also acts to affect pressure drop through acceleration and buoyancy effects. At some velocity, the increase in pressure drop due to boiling completely offsets the decrease in pressure drop due to channel frictional components. Further velocity reductions cause the pressure drop to rise which results in a minimum point, the onset of flow instability (OFI) point, in the pressure drop versus velocity curve (demand curve). If parallel flow paths exist, this increase in pressure drop in one channel may cause flow to be diverted to alternate channels, destabilizing the system, and resulting in an excursive or Ledinegg instability. The present study was undertaken to develop a simple model for predicting the pressure drop in a boiling channel which would be applicable from single phase to saturated boiling conditions. The objective was to obtain an accurate simple model that could be used by designers.
|Main Author:||Fleischer, A. S.|
|Other Authors:||McAssey, Jr., E. V., Jones, G. F.|