Effect of low heat and mass fluxes on the boiling heat transfer coefficient of R-245fa

Abstract The nucleate pool is a useful technique of heat dissipation in a variety of thermal applications. This study investigates the effect of the gridded metal surface (GMS) with and without protrusions on the heat transfer from a surface maintained at a temperature above the saturation temperature of water. The experimental data have been collected pertaining to boiling heat transfer at atmospheric pressure by varying the grid size of gridded metal surface with protrusions from 6 mm to 22.5 mm placed over a boiling surface having microporous coating. The mean particle diameter of coating is varied as 11, 24, and 66 μm during the experimentation. It is observed that the increase in the boiling heat transfer coefficient of the aluminum disk with GMS with protrusions of grid size 11.5 mm compared to that of the smooth boiling surface is found to be 10.7%. Furthermore, the effect of GMS having protrusions with coated surface on the heat transfer is studied. The results showed that by using GMS having protrusions and with coated surface, the heat transfer is further enhanced. The boiling heat transfer coefficient obtained in case of GMS with protrusions (grid size = 11.5 mm) and microporous-coated surface (dm = 66 μm) shows the maximum enhancement of 39.93% in comparison to the smooth surface.

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Steady State Film Boiling Heat Transfer Simulated With TRACE V4.160

Volume 2: Thermal Hydraulics ◽

10.1115/icone14-89494 ◽

2006 ◽

Author(s):

Audrius Jasiulevicius ◽

Rafael Macian-Juan

Keyword(s):

Heat Transfer ◽

Heat Flux ◽

Heat Transfer Coefficient ◽

Transfer Coefficient ◽

Mass Flux ◽

Boiling Heat Transfer ◽

High Mass ◽

Film Boiling ◽

Experimental Database ◽

Boiling Heat Transfer Coefficient

This paper presents the results of the assessment and analysis of TRACE v4.160 heat transfer predictions in the post-CHF (critical heat flux) region and discusses the possibilities to improve the TRACE v4.160 code predictions in the film boiling heat transfer when applying different film boiling correlations. For this purpose, the TRACE v4.160-calculated film boiling heat flux and the resulting maximum inner wall temperatures during film boiling in single tubes were compared with experimental data obtained at the Royal Institute of Technology (KTH) in Stockholm, Sweden. The experimental database included measurements for pressures ranging from 30 to 200 bar and coolant mass fluxes from 500 to 3000 kg/m2s. It was found that TRACE v4.160 does not produce correct predictions of the film boiling heat flux, and consequently of the maximum inner wall temperature in the test section, under the wide range of conditions documented in the KTH experiments. In particular, it was found that the standard TRACE v4.160 underpredicts the film boiling heat transfer coefficient at low pressure-low mass flux and high pressure-high mass flux conditions. For most of the rest of the investigated range of parameters, TRACE v4.160 overpredicts the film boiling heat transfer coefficient, which can lead to non-conservative predictions in applications to nuclear power plant analyses. Since no satisfactory agreement with the experimental database was obtained with the standard TRACE v4.160 film boiling heat transfer correlations, we have added seven film boiling correlations to TRACE v4.160 in order to investigate the possibility to improve the code predictions for the conditions similar to the KTH tests. The film boiling correlations were selected among the most commonly used film boiling correlations found in the open literature, namely Groeneveld 5.7, Bishop (2 correlations), Tong, Konkov, Miropolskii and Groeneveld-Delorme correlations. The only correlation among the investigated, which resulted in a significant improvement of TRACE predictions, was the Groeneveld 5.7. It was found, that replacing the current film boiling correlation (Dougall-Rohsenow) for the wall-togas heat transfer with Groeneveld 5.7 improves the code predictions for the film boiling heat transfer at high qualities in single tubes in the entire range of pressure and coolant mass flux considered.

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Experimental Study of Flow Boiling Heat Transfer Coefficient of FC-72 Over Micro-Pin-Finned Surfaces

2010 14th International Heat Transfer Conference, Volume 1 ◽

10.1115/ihtc14-22282 ◽

2010 ◽

Author(s):

Y. F. Xue ◽

M. Z. Yuan ◽

J. J. Wei

Keyword(s):

Heat Transfer ◽

Heat Transfer Coefficient ◽

Transfer Coefficient ◽

Boiling Heat Transfer ◽

Flow Boiling ◽

Fluid Velocity ◽

Nucleate Boiling ◽

Flow Boiling Heat Transfer ◽

Nucleate Boiling Heat Transfer ◽

Boiling Heat Transfer Coefficient

Experiments of flow boiling heat transfer coefficient of FC-72 were carried out over simulated silicon chip of 10×10×0.5 mm3 for electronic cooling. Four kinds of micro-pin-fins with the dimensions of 30×60, 30×120, 50×60, 50×120 μm2 (thickness, t × height, h) respectively, were fabricated on the chip surfaces by the dry etching technique to enhance boiling heat transfer. A smooth chip was also tested for comparison. The experiments were conducted at three different fluid velocities (0.5, 1 and 2m/s) and three different liquid subcoolings (15, 25 and 35K). All micro-pin-finned surfaces show a considerable heat transfer enhancement compared to the smooth surface. Both the forced convection and nucleate boiling heat transfer contribute to the total heat transfer performance. The contribution of each factor to the total heat transfer has been clearly presented in the flow boiling heat transfer coefficient curves. In a lower heat flux region, the heat transfer coefficient increases greatly with increasing fluid velocity, but increases slightly with increasing heat flux, indicating that the single-phase forced convection dominates the heat transfer process. With further increasing heat flux to the onset of nucleate boiling, the heat transfer coefficient increases remarkably. For a given liquid subcooling, the curves of flow boiling heat transfer coefficient at fluid velocities of 0.5 and 1 m/s almost follow one line for each surface, showing insensitivity of nucleate boiling heat transfer to fluid velocity. However, at the largest fluid velocity of 2 m/s, the slope of the flow boiling heat transfer coefficient curves for micro-pin-finned surfaces becomes smaller, indicating that the forced convection also plays an important role besides the nucleate boiling heat transfer. The curves of the flow boiling heat transfer coefficient can be used to determine the boiling incipience at different fluid velocities, which provides a basis for the suitable fluid velocity selection in designing highly efficient cooling scheme for electronic devices.

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