SUMMARY

Flow boiling in micro scale systems was studied intensively in the past two decades and is still attracting the interest of many researchers. Possible improvement in heat transfer over single phase flow at the same mass flux, due to latent heat of vaporization makes it a promising thermal management method for high power dissipation electronics. Moreover, two phase flow may offer better temperature uniformity than single phase flow, if dryout and instabilities can be mitigated. This work studies flow boiling of deionized (D.I.) water in microgap and microgap with pin fin enhancement. This study investigates flow boiling in a closed flow loop system experimentally with a wide range of heat fluxes, mass fluxes and inlet temperatures. The closed flow loop consists of a gear pump to deliver liquid flow with a volume flow rate up to 506 mL/min, a flow meter to measure flow rate, a preheater to control inlet temperature, a filter of 2 μm pore size to remove particles that may be present inside the flow system, the test section, a heat exchanger to condense vaporized fluid, and a 300 mL fluid reservoir. The microgap and microgap with pin fin enhancement both have footprint area of 1 cm2, and height of 200 μm. Pin fin designs of different longitudinal and transverse pitches, and pin diameters are studied. High seed camera is utilized to visualize boiling. Pressure drop, heat transfer coefficient, boiling regimes, two phase flow instabilities are studied in this work. A numerical model of flow boiling of water in microgap using volume of fluid method will be developed and compared with experimental data.