Condensation of carbon dioxide in microchannels

Heat transfer coefficients and pressure drops during condensation of carbon dioxide (CO₂) are measured in small quality increments in rectangular microchannels of 0.10 ≤ D_h ≤ 0.16 mm and aspect ratios from 1 to 4. Channels are fabricated on a copper substrate by electroforming copper onto a mask patterned by X-ray lithography, and sealed by diffusion bonding. The test section is cooled by chilled water circulating at a high flow rate to ensure that the thermal resistance on the condensation side dominates. A conjugate heat transfer analysis, in conjunction with local pressure drop profiles allows driving temperature differences, heat transfer rates, and condensation heat transfer coefficients to be determined accurately. Condensation heat transfer coefficients and pressure drops are measured for G = 400, 600 and 800 kg m^-2 s^-1, for 0 < x < 1, and saturation temperatures of 15, 20 and 25 °C (P_r = 0.69, 0.78 and 0.87). The data are used to evaluate the applicability of correlations developed for larger hydraulic diameters and different fluids for predicting condensation heat transfer and pressure drop of CO₂.