Keywords

Jet impingement, pseudo-boiling, flow boiling, two-phase heat transfer, pressure drop, thermal modeling

Subject Categories

Heat Transfer, Combustion | Mechanical Engineering

Abstract

Carbon dioxide (CO2) is gaining attention as a low-toxicity, zero-ozone-depletion refrigerant with a global warming potential of 1, making it an attractive alternative to synthetic HFCs/HFOs. Near its critical point, CO2's thermophysical properties change sharply with small shifts in temperature and pressure — a behavior that can be exploited to enhance heat transfer in trans-critical power cycles and electronics cooling. This dissertation experimentally investigates heat transfer during the pseudo-boiling of supercritical CO2 in a parallel-flow microchannel and a micro-jet impingement device, alongside CO2 flow boiling and single-phase water heat transfer in micro-jet impingement. Using microfluidic devices instrumented with embedded resistance temperature detectors and a LabVIEW data-acquisition system, heat transfer coefficients were measured across mass fluxes of 1825–8080 kg/m²·s, reduced pressures of 1.02–1.143, and heat fluxes up to 98 W/cm². A pseudo-boiling mass quality, x_pb, is introduced to characterize heat transfer behavior across the Widom-line transition, derived from the enthalpy change through the pseudocritical region via an equation of state, alongside a dimensionless enhancement coefficient, E = hpb/hl, evaluated for both geometries. A second study examines flow boiling of an array of 13 CO2 micro-jets (206 µm diameter) at high reduced pressures, over mass fluxes of 880–2360 kg/m²·s, pressures of 5.86–6.895 MPa, and heat fluxes of 3–58 W/cm². Results show that boiling curves, heat transfer coefficients, and critical heat flux depend on radial position, heat flux, mass flux, and pressure, and are benchmarked against existing correlations and single-jet studies, offering new design guidance for CO2-based thermal management systems.

Completion Date

2026

Semester

Summer

Committee Chair

Yoav Peles

Degree

Doctor of Philosophy (Ph.D.)

College

College of Engineering and Computer Science

Department

Mechanical and Aerospace Engineering

Format

PDF

Document Type

Dissertation

Language

English

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