Download or read book Heat Transfer and Pressure Drop for Flow of Supercritical and Subcritical CO2 in Microchannel Tubes written by and published by . This book was released on 2000 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Within this project, the heat transfer and pressure drop characteristics of CO2 (R-744) were investigated at supercritical pressures (cooling) and subcritical pressures (evaporation). The measurements were carried out with a microchannel type (MPE) tube with 25 parallel ports and a port diameter of 0.787 mm. The experimental data collected confirm that CO2 offers high heat transfer coefficients at supercritical pressures. The comparison of these data with common correlations shows good correspondence. The comparison of the measured pressure drop data with calculation models is satisfactory as well. At evaporation the situation is not as clear. The experiments at high mass fluxes have shown a strongly decreasing heat transfer coefficient from a certain vapour fraction upwards. A comparison with a calculation model for dry-out has shown that this drop has to be expected. On the contrary, at low mass fluxes no influence of the velocity was detected. None of the heat transfer calculation models investigated takes this phenomenon into account. The two-phase pressure drop correlations yield too low values in general, but for a first estimation models from the literature can be taken.