This work revealed the thermo physical characteristics of near critical and supercritical carbon dioxide at the micro scale. The results include the extension of flow boiling heat transfer correlations, boiling inception, near critical bubble dynamics, thermalization mode shift, Joule Thomson effect and pressure drop evaluation. It was found that extremely low superheat temperatures are required for boiling inception near the critical conditions (i.e., T=31.4 °C, and P=7.37 MPa), and boiling heat transfer correlations were extended up to a reduced pressure of 0.99. The work also revealed a significant enhancement of the heat transfer coefficient as the critical conditions approached, which was partially attributed to a shift of the thermalization mode (i.e., up to x 3 higher compared to lower reduced pressures). For the first time, the thermalization shift in convective micro scale flows was visualized and measured using marker-less technique. Additionally, it was found that near the critical conditions the growth and translation of bubbles slowed down and were driven by thermal diffusion (i.e., asymptotical thermally driven models described the bubble dynamics well). Moreover, the interactions between the bubbles had major influence on the bubbles' growth rate. Subsequently, a micro-orifice was integrated into the microchannel to demonstrate the importance and applicability of the Joule Thomson coefficient (JTh) in the vicinity of the critical point of CO2. In the experiments the fluid's temperature was reduced to -10.8 °C, which is 34 °C below ambient, without complicated thermal insulation due to the sustainable Joule-Thomson effect. Lastly, pressure drop for the micro-orifice were compared with different models (i.e., homogeneous and separated two phase flow, capillary tube, and short tube orifice correlation). The capillary tube model best predicted the measured pressure drop. To conclude, this work presents a major advancement in understanding the thermophysical behavior of carbon dioxide and will lay the foundation to its wider utilization in the future.
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Doctor of Philosophy (Ph.D.)
College of Engineering and Computer Science
Mechanical and Aerospace Engineering
Length of Campus-only Access
Doctoral Dissertation (Open Access)
Parahovnik, Anatoly, "Thermofluidic Characterization of Carbon Dioxide Near Critical Conditions at Microscale" (2022). Electronic Theses and Dissertations, 2020-. 1064.
Restricted to the UCF community until May 2022; it will then be open access.