• International Journal of Air-Conditioning and Refrigeration
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• v.7
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• pp.79-90
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• 1999

This investigation presents the experimental results of forced convection boiling heat transfer around a circular, electrically heated horizontal cylinder to subcooled water in cross flow. In these experiments, the following primary variables were included: heat flux, flow velocity, pressure and degree of subcooling at inlet. Local surface temperatures were measured at nine peripheral positions. Local surface temperature distributions are classified into four categories depending on the supplied heat flux. The effects of the boiling curve depending on the fluid velocity, degree of subcooling at inlet and pressure are presented.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.10 no.5
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• pp.558-568
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• 1998

This paper presents the results of experiments involving external forced convection on boiling heat transfer from electrically heated horizontal tube to water in cross flow. In these experiments, all of the following primary variables were varied: heat flux, cross flow velocity, pressure and degree of subcooling. Local surface temperatures were measured at nine peripheral positions. Surface temperature distributions are classified into four groups as a function of heat flux. The characteristics of the boiling curve at different velocity, degree of subcooling and pressure are examined.

• Journal of ILASS-Korea
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• v.13 no.3
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• pp.143-148
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• 2008

In the present study, the correlation between the Nusselt number and Reynolds number was developed for forced convection and nucleate boiling region in spray cooling. Also the effect of droplet subcooling on spray cooling heat transfer was investigated. Full cone spray nozzles were employed for spray cooling experiment, and water and FC-77 were used for developing the correlation. From the experimental results, the correlation between the Nusselt number and Reynolds number based on droplet-flow-rate was developed. The correlation shows good predictions with ${\pm}30%$ error for water and FC-77.

• Nuclear Engineering and Technology
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• v.44 no.8
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• pp.889-896
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• 2012

Recent progress in the computational fluid dynamics methods of two- and multiphase phase flows has already started opening up new exciting possibilities for using complete multidimensional models to simulate boiling systems. Combining this new theoretical and computational approach with novel experimental methods should dramatically improve both our understanding of the physics of boiling and the predictive capabilities of models at various scale levels. However, for the multidimensional modeling framework to become an effective predictive tool, it must be complemented with accurate mechanistic closure laws of local boiling mechanisms. Boiling heat transfer has been studied quite extensively before. However, it turns out that the prevailing approach to the analysis of experimental data for both pool boiling and forced-convection boiling has been associated with formulating correlations which normally included several adjustable coefficients rather than based on first principle models of the underlying physical phenomena. One reason for this has been the tendency (driven by practical applications and industrial needs) to formulate single expressions which encompass a broad range of conditions and fluids. This, in turn, makes it difficult to identify various specific factors which can be independently modeled for different situations. The objective of this paper is to present a mechanistic modeling concept for both pool boiling and forced-convection boiling. The proposed approach is based on theoretical first-principle concepts, and uses a minimal number of coefficients which require calibration against experimental data. The proposed models have been validated against experimental data for water and parametrically tested. Model predictions are shown for a broad range of conditions.

• Journal of Advanced Marine Engineering and Technology
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• v.39 no.7
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• pp.702-708
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• 2015

Two-phase flow boiling experiments were conducted using FC-72 as the working fluid. The micro-channels consisted of 15 channels with a depth of 0.2 mm, width of 0.45 mm, and length of 60 mm. Tests were performed over a mass flux range of $200-400kg/m^2s$, heat flux range of $5.6-49.0kW/m^2$, and vapor quality range of 0.02-0.93. Based on the results of the experiment, the heat transfer mechanism by nucleate boiling was dominant at a lower vapor quality (x<0.2), whereas that in the region of a vapor quality greater than 0.2 was complexly influenced by nucleate boiling and forced convection boiling. The nucleate boiling and forced convection boiling could be expressed as functions of the boiling number and convection number, respectively. In addition, the heat transfer coefficient obtained by the experiment was compared with the heat transfer coefficient by the existing correlation.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.12 no.5
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• pp.502-510
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• 2000

Evaporation heat transfer characteristics were studied in a horizontal tube using R22/R114 non-azotropic refrigerant mixture. the heat transfer coefficient was high in the upper part for pure refrigerants, and heat transfer coefficient was low in the lower part for refrigerant mixtures. In the low quality region where nucleate boiling was dominant, the average heat transfer coefficient was low. In the region where forced convection was dominant, heat transfer coefficient was high. Results show that the heat transfer coefficient for pure refrigerants obtained by experiments were lower than those of Yoshida et al. but agreed well with Jung et al., and Chen et al. data. But the heat transfer coefficients for refrigerant mixtures were lower about 20% than those predicted by the equation for pure refrigerant.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.11
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• pp.983-990
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• 2010

In the present study, spray cooling heat transfer was experimentally investigated for the case in which water is sprayed onto the surfaces of micro-fins in forced convection and nucleate boiling regions. The experimental results show that an increase in the droplet flow rate improves heat transfer due to forced convection and nucleate boiling in the both case of smooth surface and surfaces of micro-fins. However, the effect of subcooling for fixed droplet flow rate is very weak. Micro-fins surfaces enhance the spray cooling heat transfer significantly. In the dilute spray region, the micro-fin structure has a significant effect on the spray cooling heat transfer. However, this effect is weak in the dense spray region. A previously determined correlation between the Nusselt number and Reynolds number shows good agreement with the present experimental data for a smooth surface.

• Nuclear Engineering and Technology
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• v.52 no.7
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• pp.1417-1428
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• 2020

The design of a nuclear reactor core requires basic thermal-hydraulic information concerning the heat transfer regime at which onset of nucleate boiling (ONB) will occur, the pressure drop and flow rate through the reactor core, the temperature and power distributions in the reactor core, the departure from nucleate boiling (DNB), the condition for onset of flow instability (OFI), in addition to, the critical velocity beyond which the fuel elements will collapse. These values depend on coolant velocity, fuel element geometry, inlet temperature, flow direction and water column above the top of the reactor core. Enough safety margins to ONB, DNB and OFI must-emphasized. A heat transfer package is used for calculating convection heat transfer coefficient in single phase turbulent, transition and laminar regimes. The main objective of this paper is to study the possibility of power upgrading of WWR-S research reactor from 2 to 10 MW_th. This study presents a one-dimensional mathematical model (axial direction) for steady-state thermal-hydraulic design and analysis of the upgraded WWR-S reactor in which two types of plate fuel elements are employed. FOR-CONV computer program is developed for the needs of the power upgrading of WWR-S reactor up to 10 MW_th.

• Journal of the Korean Society of Propulsion Engineers
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• v.24 no.3
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• pp.59-70
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• 2020

Obtaining external forced convection heat transfer from bubble boiling and validating it with experimental results using cryogenic liquids are suggested to derive total heat transfer coefficient with pool boiling condition in the case of coil type heat exchanger with a bundle of tubes and to overcome the limitation of using the empirical correlation. Experiment is conducted with pool boiling heat transfer of saturate liquid nitrogen with helical coil type heat exchanger using liquid oxygen as hot stream fluid. Experimentally measured heat transfer coefficient is well-agreed with the estimated curve considering nucleate boiling and forced convection induced by bubble rise.

• Journal of Fisheries and Marine Sciences Education
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• v.28 no.5
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• pp.1388-1394
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• 2016

This paper presents a experimental study of two-phase flow boiling of FC-72 in multi channels. Flow boiling heat transfer coefficients are obtained with mass flux ranging from 152.9 to $353.9kg/m^2s$ and heat flux from 5.6 to $46.1kW/m^2$. The experimental results show that the heat transfer is governed by nucleate boiling mechanism in the low heat flux region. However, it is found that the effects of nucleate boiling and forced convection boiling are combined as the heat flux increases. A new correlation to predict the heat transfer coefficient is developed by using the dimensionless number such as Reynolds number, Weber number, boiling number. This correlation shows good predictive accuracy against the measured data.