ABSTRACT
The process of flow boiling of a liquid in heated confined passages is commonly encountered in many applications. Steam generators in power plants and evaporators in refrigeration and air conditioning equipment are some commonly encountered examples. This chapter covers the flow boiling inside smooth circular tubes. Consider a subcooled liquid flowing in a heated channel. As long as the channel wall is below the local saturation temperature of the liquid, heat transfer is by single-phase mode. As the wall temperature exceeds the saturation temperature, boiling may be initiated, depending on the wall, heater surface, and flow conditions. The first bubbles appear on the wall at location C, which is identified as the onset of nucleate boiling, or ONB. The wall temperature begins to level off as more nucleation sites are activated beyond ONB. Further downstream, as more sites are activated, the contribution to heat transfer from nucleate boiling continues to rise, while the single-phase convective contribution diminishes.
