Flow Instability (FI) for subcooled flow boiling through a narrow rectangular channel under transversely uniform and non-uniform heat flux

Abstract In the development of plasma-facing components (PFC) for fusion reactors and high heat flux heat sinks (or components) for electronic applications, the components are usually subjected to a peripherally non-uniform heat flux. Even if the applied heat flux is uniform in the axial direction [which is unlikely], both intuition and recent investigations have clearly shown that both the local heat flux and the eventual critical heat flux (CHF) in this three-dimensional case will differ significantly from similar quantities found in the voluminous body of data for uniformly heated tubes and flow channels. Although this latter case has been used in the past as an estimate for the former case, more study has become necessary to examine the three-dimensional temperature and heat flux distributions and related CHF. Work thus far has shown that the non-uniform peripheral heat flux condition enhances CHF in some cases. In order to avoid the excess costs associated with using electron- or ion-beams to produce the non-uniform heat flux, a new facility was developed which will allow three-dimensional conjugate heat transfer measurements and two-dimensional local subcooled flow boiling heat flux and related critical heat flux measurements. The configurations under study consist of: (1) a non-uniformly heated cylindrical-like test section with a circular coolant channel bored through the center, and (2) a monoblock which is a square cross-section parallelepiped with a circular drilled flow channel through the center line along its length. The theoretical or idealization of the cylindrical-like test section would be a circular cylinder with half (−90 degrees to +90 degrees) of its outside boundary subjected to a uniform heat flux and the remaining half insulated. For the monoblock, a uniform heat flux is applied to one of the outside surfaces and the remaining surfaces are insulated. The outside diameter of the cylindrical-like test section is 30.0 mm and its length is 200.0 mm. The monoblock square has lengths 30.0 mm. The inside diameter of the flow channel for both types of test sections is 10.0 mm. Water is the coolant. The inlet water temperature can be set at any level in the range from 26.0 °C to 130.0 °C and the exit pressure can be set at any level in the range from 0.4 MPa to 4.0 MPa. Thermocouples are placed at forty-eight locations inside the solid cylindrical-like or monoblock test section. For each of four axial stations, three thermocouples are embedded at four circumferential locations (0, 45, 135, and 180 degrees, where 0 degrees corresponds to that portion of the axis of symmetry close to the heated surface) in the wall of the test section. Finally, the mass velocity can be set at any level in the range from 0.6 to 10.0 Mg/m2s.

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Critical heat flux in subcooled flow boiling of fluorocarbon liquid on a simulated electronic chip in a vertical rectangular channel

International Journal of Heat and Mass Transfer ◽

10.1016/0017-9310(89)90184-1 ◽

1989 ◽

Vol 32 (2) ◽

pp. 379-394 ◽

Cited By ~ 61

Author(s):

I. Mudawar ◽

D.E. Maddox

Keyword(s):

Heat Flux ◽

Critical Heat Flux ◽

Flow Boiling ◽

Rectangular Channel ◽

Subcooled Flow Boiling ◽

Subcooled Flow

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Enhancement of Subcooled Flow Boiling Heat Transfer with High Porosity Sintered Fiber Metal

Applied Sciences ◽

10.3390/app11031237 ◽

2021 ◽

Vol 11 (3) ◽

pp. 1237

Author(s):

Yusuke Otomo ◽

Edgar Santiago Galicia ◽

Koji Enoki

Keyword(s):

Heat Flux ◽

Mass Flux ◽

High Speed ◽

Flow Boiling ◽

Rectangular Channel ◽

Working Fluid ◽

High Porosity ◽

Subcooled Flow Boiling ◽

Subcooled Flow ◽

Porous Surfaces

We conducted experimental research using high-porosity sintered fiber attached on the surface, as a passive method to increase the heat flux for subcooled flow boiling. Two different porous thicknesses (1 and 0.5 mm) and one bare surface (0 mm) were compared under three different inlet subcooling temperatures (30, 50 and 70 K) and low mass flux (150–600 kg·m−2·s−1) using deionized water as the working fluid under atmospheric pressure. The test section was a rectangular channel, and the hydraulic diameter was 10 mm. The results showed that the heat flux on porous surfaces with a thickness of 1 and 0.5 mm increased by 60% and 40%, respectively, compared to bare surfaces at ΔTsat = 40 K at a subcooled temperature of 50 K and mass flux of 300 kg·m−2·s−1. An abrupt increase in the wall superheat was avoided, and critical heat flux (CHF) was not reached on the porous surfaces. The flow pattern and bubble were recorded with a high-speed camera, and the bubble dynamics are discussed.

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Onset of flow instability with one-side heated swirl tube for fusion reactor safety

Nuclear Fusion ◽

10.1088/1741-4326/ac3c83 ◽

2021 ◽

Author(s):

Ji Hwan Lim ◽

Su Won Lee ◽

Hoongyo Oh ◽

Minkyu Park ◽

Donkoan Hwang ◽

...

Keyword(s):

Heat Flux ◽

Flow Rate ◽

Error Rate ◽

Flow Instability ◽

Mean Absolute Error ◽

Flow Boiling ◽

Absolute Error ◽

Subcooled Flow Boiling ◽

Subcooled Flow ◽

The Impact

Abstract In this study, the onset of flow instability (OFI) heat flux of a one-side heated swirl tube is experimentally investigated. The OFI heat flux means the minimum heat flux that can cause flow instability by the vapor generated in the flow path. An analysis of the effect of system parameters on the OFI heat flux indicates that as the pressure increases, the bubble size decreases. Therefore, the void fraction decreases and, consequently, the OFI heat flux tends to increase. Similarly, the higher the flow rate and degree of subcooling, the faster the vapor can be removed; thus, the OFI heat flux increases. In addition, the prediction performances of the existing OFI correlations developed under the subcooled flow-boiling condition are evaluated. Therefore, although the Wang correlation indicates the lowest error rate, it yields a high mean absolute error rate of 87.75%. Thus, it is difficult to predict the OFI heat flux of a one-side heated swirl tube using the existing OFI correlations. Therefore, in this study, a new correlation is developed using a Python code created by employing an artificial intelligence regression method. The developed correlation incorporates the impact of one-side heating, swirl tape, mass flow rate, subcooling, and pressure (mean absolute error = 12.17%, root mean square error = 14.99%).

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