Steady, Forced Convection Boiling in Micro Ducts

Abstract

Convective boiling is defined as the addition of heat to a flowing liquid in such a way that generation of vapour occurs while, conversely, convective condensation is defined as the removal of heat from the fluid in such a way that vapour is converted into liquid. This definition, therefore, excludes the process of flashing where vapour generation occurs solely as the result of a reduction in flow pressure. However, in many systems, the two processes do occur simultaneously and, hence, cannot be clearly distinguished. This chapter will be concerned with only single-component microsystems, i.e. a pure liquid and its vapour. Furthermore, much of the information presented will be devoted to one such system, namely the water/steam system. Many other fluid systems of industrial importance, however, involve the use of multi-component systems such as refrigerants, organic liquids, cryogenic liquids and liquid metals. Very limited information is available on the processes of boiling and condensation with multi-component macrosystems and practically none with multi-component microsystems.