Heat transfer by boiling coolant

At the point D, the coolant enters a regime known as annular flow, where a thin film of water flows along the wall of the tube while the center of the channel is filled with high-velocity vapor carrying small droplets of water with it. 

With further increase of heat flux a situation is reached where the bubble density becomes so great that the bubbles coalesce and blanket a portion of 

For the case of liquid flowing through a round tube with a uniformly heated wall, for example, it is found that the burnout heat flux, can be represented by an expression of the form 

The enthalpy of subcooling is the amount by which the specific enthalpy of the coolant entering the channel is below the specific enthalpy of the saturated liquid at the system pressure. The specific enthalpy (enthalpy per unit mass) is defined by the relation 

The only one of the five parameters listed above for which the burnout flux shows an approximately linear dependence is the inlet subcooling. A typical set of experimental data illustrating the linear relation between burnout flux and inlet subcooling for water in a uniformly heated tube is shown in Fig. 6.12. A commonly used correlation formula for burnout flux is 

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