A flow boiling critical heat flux correlation for water and Freon-12 at low mass fluxes

1982 ◽  
Vol 72 (3) ◽  
pp. 381-389 ◽  
Author(s):  
W.J. Green
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Flow Boiling ◽  
Mass Fluxes ◽  
Low Mass

Effect of Inlet Restriction on Flow Boiling Heat Transfer in a Horizontal Microtube

2013 ◽  
Vol 135 (2) ◽  
Author(s):  
YanFeng Fan ◽  
Ibrahim Hassan
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Pressure Drop ◽  
Critical Heat Flux ◽  
Mass Flux ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Mass Fluxes ◽  
Flow Boiling Heat Transfer ◽  
Low Mass

Flow boiling heat transfer in a horizontal microtube with inlet restriction (orifice) under uniform heating condition is experimentally investigated using FC-72 as working fluid. A stainless steel microtube with an inner diameter of 889 μm is selected as main microtube. Two microtubes with smaller diameters are assembled at the inlet of main microtube to achieve the restriction ratios of 50% and 20%. The experimental measurement is carried out at mass fluxes ranging from 160 to 870 kg/m2·s, heat fluxes varying from 6 to 170 kW/m2, inlet temperatures of 23 and 35 °C, and saturation pressures of 10 and 45 kPa. The effects of the orifices on two-phase pressure drop, critical heat flux (CHF), and flow boiling heat transfer coefficient are studied. The results show that the pressure drop caused by the orifice takes a considerable portion in the total pressure drop at low mass fluxes. This ratio decreases as the vapor quality or mass flux increases. The difference of normal critical heat flux in the microtubes with different orifice sizes is negligible. In the aspect of flow boiling heat transfer, the orifice is able to enhance the heat transfer at low mass flux and high saturation pressure, which indicates the contribution of orifice in the nucleate boiling dominated regime. However, the effect of orifice on flow boiling heat transfer is negligible in the forced convective boiling dominated regime.

Experimental Investigation of Flow Boiling Instability in a Single Horizontal Microtube With and Without Inlet Restriction

2012 ◽  
Vol 134 (8) ◽  
Author(s):  
YanFeng Fan ◽  
Ibrahim Hassan
Keyword(s):  
Heat Flux ◽  
Flow Instability ◽  
Flow Boiling ◽  
Area Ratio ◽  
High Mass ◽  
Working Fluid ◽  
Stainless Steel Tube ◽  
Operating Condition ◽  
Mass Fluxes ◽  
Low Mass

An experimental study is conducted to investigate the effects of inlet restriction (orifice) on flow boiling instability in a single horizontal microtube. The test-section is composed of a stainless steel tube with an inner diameter of 889 μm, and a length of 150 mm. Experiments are performed for three different orifice configurations with 20%, 35%, and 50% area ratio. Mass flux is varied from 700 to 3000 kg/m2 · s, whereas the heat flux is varied from 6 to 27 W/cm2. The dielectric coolant FC-72 is selected as the working fluid. In the absence of an orifice at the inlet, four oscillation types are observed at the onset of flow instability; it is also noticed that the frequency of the oscillations increases with increasing heat flux, while the amplitude remains constant. The addition of an orifice at the inlet helps stabilizing the flow without generating significant pressure drop at the same operating condition as the microtube without orifice. The 20% area ratio orifice shows better performance at low mass fluxes (<1000 kg/m2 · s). Whereas, at high mass fluxes (>2000 kg/m2 · s), 50% and 35% area ratio orifices are efficient in stabilizing the flow or delaying the onset of flow instability. Therefore, selecting the area ratio of the orifice depends on the operating condition. A small area ratio orifice is preferably used at low mass fluxes, whereas a large area ratio orifice is more suitable for high mass fluxes.

Critical Heat Flux in Horizontal Tube Bundles in Vertical Crossflow of R113

1992 ◽  
Vol 114 (1) ◽  
pp. 179-184 ◽  
Author(s):  
K. M. Leroux ◽  
M. K. Jensen
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Mass Flux ◽  
Horizontal Tube ◽  
High Mass ◽  
Intermediate Mass ◽  
Average Value ◽  
Mass Fluxes ◽  
Local Quality ◽  
Low Mass

The critical heat flux (CHF) on a single tube in a horizontal bundle subject to an upward crossflow of R113 has been studied in three bundle geometries. Effects of local quality, mass flux, pressure, and bundle geometry on the CHF were investigated. The shapes of the CHF-quality curves display three distinct patterns, which progress from one to another as mass flux increases. At low mass fluxes, the CHF data monotonically decreased with increasing quality. At intermediate mass fluxes with increasing quality, the CHF data initially decreased to a relative minimum, then increased to a relative maximum, and finally began to decrease again as the higher qualities were reached. At high mass fluxes, as quality increased, the CHF rose gradually from the zero quality value to a maximum and then began to decrease. For all mass fluxes, the zero-quality CHF points clustered around an average value, which varied slightly with test section geometry. Mechanisms for the CHF condition are suggested.

scholarly journals EXPERIMENTAL INVESTIGATION OF CRITICAL HEAT FLUX IN ANNULUS AT LOW PRESSURE AND LOW FLOW PARAMETERS

2020 ◽  
Vol 28 ◽  
pp. 50-58
Author(s):  
Daniel Vlček ◽  
Ladislav Suk ◽  
Kamil Števanka ◽  
Taron Petrosyan
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Flow Boiling ◽  
Low Pressure ◽  
Low Flow ◽  
Inconel 625 ◽  
Outer Diameter ◽  
Flow Parameters ◽  
Low Mass ◽  
Vertically Aligned

Steady state flow boiling experiments were conducted on a technically smooth Inconel 625 tube with outer diameter 9.1 mm at inlet pressures 131, 220 and 323 kPa, inlet temperatures 62, 78 and 94 °C and approximately 400, 600 and 1000 kg/(m2.s) mass flow. Water of these parameters was entering into the vertically aligned annulus, where the uniformly heated tube was placed until the critical heat flux (CHF) appeared. The experimental data were compared to estimations of CHF by local PGT tube correlation and Groeneveld’s look-up tables for tubes. The results imply that in the region of low pressure and low mass flux, the differences between calculations and experiments are substantial (more than 50 % of CHF). The calculations further imply that look-up tables and tube correlations should be corrected to the annulus geometry. Here, the Doerffer’s approach was chosen and led to a substantial enhancement of CHF estimation. Yet, a new correlation for the region of low pressure and flow is needed.

Experimental Study of Flow Critical Heat Flux in Alumina-Water, Zinc-Oxide-Water, and Diamond-Water Nanofluids

2009 ◽  
Vol 131 (4) ◽  
Author(s):  
Sung Joong Kim ◽  
Tom McKrell ◽  
Jacopo Buongiorno ◽  
Lin-Wen Hu
Keyword(s):  
Experimental Study ◽  
Heat Flux ◽  
Zinc Oxide ◽  
Critical Heat Flux ◽  
Mass Flux ◽  
Flow Boiling ◽  
Thermal Conditions ◽  
Nanometer Range ◽  
Low Concentration ◽  
Mass Fluxes

It is shown that addition of alumina, zinc-oxide, and diamond particles can enhance the critical heat flux (CHF) limit of water in flow boiling. The particles used here were in the nanometer range (<100 nm) and at low concentration (≤0.1 vol %). The CHF tests were conducted at 0.1 MPa and at three different mass fluxes (1500 kg/m2 s, 2000 kg/m2 s, and 2500 kg/m2 s). The thermal conditions at CHF were subcooled. The maximum CHF enhancement was 53%, 53%, and 38% for alumina, zinc oxide, and diamond, respectively, always obtained at the highest mass flux. A postmortem analysis of the boiling surface reveals that its morphology is altered by deposition of the particles during boiling. Additionally, the wettability of the surface is substantially increased, which seems to correlate well with the observed CHF enhancement.

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