Film Boiling Collapse Temperature of Hot Dry Surface by Using Measuring Two Dimensional Temperature Field:
The behavior of rewetting on a high superheated and dry surface, focusing on rewetting temperature just as collapse of saturated and subcooled film boiling was investigated experimentally. Saturated and subcooled impingement jet experiments were conducted by using a Silicon and silver wafer with 20 mm length and 20 mm width and pure water at atmospheric condition. Temperature of the test heater was measured by using a commercial separated-type infrared thermometer from a back side of it. The present experimental results showed that sputtering temperature was close to the value given by Nishio's correlation, 200oC, for silver plate case. For case of Si wafer with low thermal conductivity, sputtering temperature was close to the thermodynamics limit of superheat of water.
Subcooled Flow Boiling Heat Transfer under Vibration Conditions of Sinusoids and Seismic Shock Waves:
Critical heat flux –CHF- on subcooled flow boiling under vibration conditions, focusing on liquid velocity, acceleration and frequency of vibrations was investigated experimentally. Experiments were conducted using a copper thin-film and subcooled water in a range of the liquid velocity from 0.3 to 4.1 m/s at 0.10MPa. The liquid subcooling was 20K. The acceleration was 0.4, 1.3 and 4.15 m/s2, respectively; the frequency was 2, 4 and 20 Hz, respectively. The present experimental results showed that critical heat fluxes under the vibration conditions of both vibration directions, i.e., horizontal and vertical vibrations to the heater, were higher than those for steady flow. According to present observations, coalesced bubble on the heater was frequently released by vibration of the test heater: the characteristic length of coalesced bubble decreased. This behavior causes the CHF to become higher under the vibration condition. Some experiments were demonstrated under vibration condition of seismic shock wave. It was confirmed that thermal limit of heater was a conservative evaluation during earthquake. Furthermore, the CHF under vibration condition was examined analytically by using velocity profiles in channel under the vibration condition and a liquid sub-layer model.
Condensation Heat Transfer of Micro Structured Surfaces:
The present study was intended to examine how the condensation heat transfer, especially the drop-wise condensation, was affected by modifying the surface nature. In the present study, condensation heat transfer experiments for steam were performed by using mirror-finished copper surface, mirror-finished silicon surface and some mirror-finished silicon surfaces with very thin metal films by using spattering. The silicon surfaces with the thin metal films were created by the MEMS technology. The film- and also the drop-wise condensation were observed on the copper surface. The film-wise condensation heat flux was in good agreement with the values of the Nusselt’s equation. It was approximately one-tenth of the drop-wise condensation heat flux. The condensation on the mirror-finished silicon surface was the drop-wise condensation. The heat flux was approximately one-tenth of the drop-wise condensation heat flux on the copper surface. The condensation on silicon surfaces with thin Copper(Cu), Chromium(Cr), Lead(Pb) and Gold(Au) films were drop-wise. The condensation on silicon surfaces with thin Nickel(Ni), Titanium(Ti) and Aluminum(Al) films were film-wise.
Study on Flow Characteristics and Frictional Pressure Drop of Gas-Liquid Two-Phase Flow in Min-Micro Pipes and at Vena Contracta and Expansion:
The pressure drop of single-phase and two-phase flows in min pipes and at vena contracta and expansion ( form losses ) were investigated experimentally. Diameter of test section of mini pipes was 0.12-0.57 mm, respectively. Test section of vena contracta and expansion were a cylinder of 0.4 mm diameter and two tanks of 5 mm diameter. In the present experiments, the superficial gas velocity was 2.1 < Ug < 92.5 m/s, the superficial liquid velocity was 0.03 < Ul < 10 m/s. Based on the present experimental results, new correlations were obtained for the enlargement and the contraction pressure losses in mini-channel. The two-phase friction multiplier data for D > 0.5 mm showed to be in good agreement with the conventional correlations. On the other hand, the two-phase friction multiplier data for D < 0.25 mm differed from the calculated values by the conventional correlations. The effect of mini-pipe was rarefaction effects, Kn<0.1. The mini pipe was D/λc < 0.02. New correlation of mini pipes is obtained for frictional pressure drop of gas-liquid two-phase flow.
Film Cooling of Gas Turbine Blade with Water Mist:
In order to improve the thermal efficiency of a gas turbine, an attempt to operate the gas turbine at higher gas temperature has been made. Although the film cooling of the turbine blade by blowing out the air flow of low temperature along the blade surface is the most effective method, the improvement is approaching in the limit. In the present paper, the introduction of the mist flow into the film cooling is proposed to break through the limitation. The feasibility of the film cooling of the mist flow was experimentally examined. The present experimental results showed that the maximum cooling efficiency was 26 % under the mist flow.
|Topics of research||
|keyword||Heat Transfer / Multi-phase Flow / Boiling / Microfluidics|