Two Phase Flow of Carbon Dioxide in Micropipe Heat Exchangers

In recent years, the research in the field of thermal hydraulic at a microscale level has been constantly increasing due to the rapid growth of the technology applications that require the transfer of high heat rates in a relatively small space and volume. Such applications spread from compact heat exchangers to cooling systems for computer CPU to micro fluidic devices. Generally, the classical thermal and fluid dynamic theories developed for macro systems are not applicable to fluids in a microscale structure. Investigations on the heat transfer in a capillary are the basis for designing micro- and high-efficiency heat transfer equipment, such as micro heat pipes (MHPs). Two-phase flow Patterns are also greatly affecting the design and prediction of performance of the refrigeration cycle. Properties such as density, heat capacity, viscosity, thermal conductivity, enthalpy, entropy¿etc, must be known in order to design the cycle and for dimensioning heat exchangers. One of the major challenges for CO2 refrigeration systems is to improve the performance of heat exchangers. It is worth mentioning that most of these early works on flow boiling of CO2 were performed for large diamete