A Systematic Approach to Predicting Critical Heat Flux for Inclined Sprays

2007 ◽  
Vol 129 (4) ◽  
pp. 452-459 ◽  
Author(s):  
Milan Visaria ◽  
Issam Mudawar
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Inclination Angle ◽  
High Speed ◽  
Systematic Approach ◽  
Test Surface ◽  
Great Success ◽  
Spray Formation ◽  
Inclination Angles ◽  
The Impact

This study provides a new systematic approach to predicting the effects of spray inclination on critical heat flux (CHF). Experiments were performed with three pressure spray nozzles over a broad range of inclination angles at five flow rates and subcoolings of 15°C and 25°C. These experiments also included high-speed video analysis of spray formation, impact, and recoil for a 1.0×1.0cm2 test surface. Inclined sprays produced elliptical impact areas, distorted by lateral liquid flow that provided partial resistance to dryout along the downstream edge of the impact ellipse. These observations are used to determine the locations of CHF commencement along the test surface. A new theoretical model shows that increasing inclination angle away from normal decreases both the spray impact area and the volumetric flux. These trends explain the observed trend of decreasing CHF with increasing inclination angle. Combining the new model with a previous point-based CHF correlation shows great success in predicting the effects of spray inclination on CHF.

An Investigation of the Effect of Inclination on Critical Heat Flux of PF-5060 Dielectric Liquid on Microporous Copper Surfaces

2013 ◽  
Author(s):  
Amir F. Ali ◽  
Mohamed S. El-Genk
Keyword(s):  
Experimental Data ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Inclination Angle ◽  
Pool Boiling ◽  
Dielectric Liquid ◽  
Copper Surfaces ◽  
Electrochemical Processes ◽  
Inclination Angles

Pool boiling experiments investigated the effect of inclination angle on the Critical Heat Flux (CHF) for saturation boiling of PF-5060 dielectric liquid on MicroPorous Copper (MPC) surfaces of different thicknesses (80 to 230 μm). The morphology of the surfaces, deposited using electrochemical processes, vary with the thickness, and hence CHF. The inclination angles investigated are 0° (upward facing), 60°, 90° (vertical), 120°, 150°, 160°, 170° and 180° (downward facing). CHF decreases with decreasing MPC thickness and/or increasing inclination angle. The CHF values in the upward facing orientation are 39%–67% higher than on smooth, polished Cu. For all MPC surfaces, CHF values in the downward facing orientation are ∼ 28% of those in the upward facing orientation (0°). The developed CHF correlation accounts for the effects of MPC thickness and inclination angle and is in agreement with experimental data to within ± 8%.

Saturation Boiling Critical Heat Flux of PF-5060 Dielectric Liquid on Microporous Copper Surfaces

2015 ◽  
Vol 137 (4) ◽  
Author(s):  
Mohamed S. El-Genk ◽  
Amir F. Ali
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Inclination Angle ◽  
Nucleate Boiling ◽  
Dielectric Liquid ◽  
Copper Surfaces ◽  
Inclination Angles ◽  
Surface Inclination ◽  
Effect Of Surface ◽  
Good Agreement

Pool boiling experiments are performed to investigate potential enhancement of critical heat flux (CHF) of PF-5060 dielectric liquid on microporous copper (MPC) surfaces and the effect of surface inclination angle. The morphology and microstructure of the MPC surfaces change with thickness. The experiments tested seven 10 × 10 mm MPC surfaces with thicknesses from 80 to 230 μm at inclination angles of 0 deg (upward facing), 60 deg, 90 deg (vertical), 120 deg, 150 deg, 160 deg, 170 deg, and 180 deg (downward facing). CHF increases as the thickness of the surface increases and/or the inclination angle decreases. The values in the upward facing orientation are 36–59% higher than on smooth Cu. For all surfaces, CHF values in the downward facing orientation are approximately 28% of those in the upward facing orientation. A developed CHF correlation, similar to those of Zuber and Kutateladze, accounts for the effects of inclination angle and thickness of the MPC surfaces. It is in good agreement with experimental data to within ±8%. Still photographs of nucleate boiling on the MPC surfaces at different inclinations help the interpretation of the experimental results.

Prediction of Subcooled Water Flow Boiling Critical Heat Flux (CHF) at Low Pressure

2017 ◽  
Author(s):  
Fangxin Hou ◽  
Huajian Chang ◽  
Yufeng Zhao ◽  
Ming Zhang ◽  
Peipei Chen ◽  
...  
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Water Flow ◽  
Pressure Vessel ◽  
High Speed ◽  
Flow Boiling ◽  
Reactor Vessel ◽  
Lower Head ◽  
Inclination Angles ◽  
Reactor Pressure

In vessel retention (IVR) is one of the key severe accident mitigation strategies to maintain reactor pressure vessel (RPV) integrity. IVR designs utilize the reactor pressure vessel lower head to contain molten fuel and rely on external reactor vessel cooling (ERVC) to remove decay heat. The capacity of ERVC is limited by the critical heat flux (CHF) of flow boiling on the outside of the reactor vessel surface. Therefore, the determination of critical heat flux (CHF) is crucial to predict whether the adoption of IVR would be successful in mitigating severe accidents. In 1999, Celeta et.al proposed a superheated layer vapor replenishment model. In this model they postulated that CHF would occur when the superheated layer was occupied by the vapor blanket coming into contact with the heated wall and they successfully predicted the critical heat flux in subcooled water flow boiling under high mass flux, high liquid subcooling and low/medium pressure conditions. To evaluate the practicability of this model in predicting CHF under IVR conditions, CHF experiments were performed under natural circulation conditions on the experiment facility “Test of External Vessel Surface with Enhanced Cooling” (TESEC). Experiments are conducted in a 30 mm wide, 61mm high rectangular flow channel with a 200 mm long heated surface along the flow direction. Two quartz windows are installed at the sidewalls of the flow channel for visualization. In order to simulate various positions of the reactor lower head, experiments at different inclination angles of the test section were conducted. The high speed visualization data at CHF point at various inclination angles were processed and analyzed by a MATLAB code developed by the author. The vapor blanket thickness at various inclination angles was measured from the visualization data and was also predicted by the Celeta model. By using geometry data from high speed images, CHF values were calculated by Celeta model and compared with the experimental results at various inclination angles. Limitations of the Celeta model in adaptation of predicting CHF under IVR conditions were further discussed.

Nozzle Track and CHF Prediction of Spray Cooling for Inclined Sprays

2008 ◽  
Author(s):  
Yongxian Guo ◽  
Jianyuan Jia ◽  
Weidong Wang ◽  
Shaorong Zhou
Keyword(s):  
Heat Flux ◽  
Inclination Angle ◽  
Spray Cooling ◽  
Test Surface ◽  
Volume Flux ◽  
Maximum Difference ◽  
Impact Area ◽  
Inclination Angles ◽  
Simulation Results ◽  
The Difference

The tracks of the nozzles were studied during spray cooling with different inclination angles, based on the study of Visaria [1,2] and the critical heat flux (CHF) criterion, which means that CHF will be achieved when the spray is configured on the condition that the spray impact area just inscribes a square test surface. The predictions of the tracks of the nozzles were made. It indicates that the nozzle tracks are parts of some ellipses as keeping the four borderline of the square test surface being the tangent line of the elliptical spray impact area. A new CHF model was established and new expression of CHF was derived based on the nozzle track model and the study of Visaria. The effects of spray inclination angle on CHF were predicted. Three different nozzles with different cone angles and volume flux were used. Simulation results indicate that CHF increases slightly with increasing inclination angle. The maximum difference of CHF of the three nozzles is about 13.1%. One reason for the difference between the established model and the results derived by Visaria is attributed to the difference of the spray impact area.

The Experimental Study of Single Droplet Impinging on an Inclined Heated Wall

2020 ◽  
Author(s):  
Wenlong Tian ◽  
Huang Zhang ◽  
Qianfeng Liu ◽  
Guang Hu ◽  
Wen He
Keyword(s):  
Inclination Angle ◽  
Wall Temperature ◽  
Weber Number ◽  
High Speed ◽  
Conservation Equation ◽  
Heated Wall ◽  
Single Droplet ◽  
Droplet Spreading ◽  
Energy Conservation Equation ◽  
Inclination Angles

Abstract We investigated a single droplet impinging on an inclined heated wall with different inclination angles. A high-speed camera was used to observe this impinging process at 10000 frames / second. The phenomena of the droplet spreading, shrinking, rebounding, boiling, break-up and splashing were observed. The effects of the wall temperature (Tw, 40–262 °C), the Weber number of the droplet (Wed, 0.66–589) and the wall inclination angle (α, 0–45.6°) on the spreading behavior of the droplet after impinging on the wall were analyzed. Energy conservation equation was used to analyze experimental results. The results show that increasing the inclination angle of the wall is beneficial to the forward spreading of the droplet along the wall, but not to the downward spreading. When α > 45.6°, the droplet will break through the flow resistance of the wall and slide down all the time. The increase of the wall temperature and the Weber number of the droplet is beneficial to the backward and forward spreading of the droplet. Increasing α, increasing Tw and decreasing Wed will promote the shrinking of the droplet after spreading. In addition, the experimental phenomenon also shows that the larger the wall inclination and the higher the wall temperature, the easier the droplet will break away from the wall.

Study on Enhancement of Critical Heat Flux by Supplying Liquid-Jets to Heating Surface

1999 ◽  
Author(s):  
Hiroyasu Ohtake ◽  
Noriyuki Yamamoto ◽  
Yasuo Koizumi
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Flow Rate ◽  
Liquid Flow ◽  
Liquid Flow Rate ◽  
Heated Surface ◽  
Pure Copper ◽  
Liquid Jets ◽  
Test Surface ◽  
Jet Velocity

Abstract The enhancement of a critical heat flux in pool boiling was investigated by supplying liquid-jets to a heated surface, as a proposal of the high heat removal technology for future. Experiments were conducted using a pure copper block and saturated water for a pool condition at atmospheric conditions. Two or three jet-nozzles were set away a certain distance from the test surface for supplying liquid-jets to the heated surface. In the present study, the effects of the distance between the nozzles and the test surface, the diameter of jet-nozzles, the liquid flow rate and the jet-velocity on the enhancement rate of the critical heat flux were examined experimentally. The critical heat flux obtained in the present experiments was enhanced a factor of about two for the flow rate per nozzle of 2.5 × 10−6 m3/s by supplying two liquid-jets. However, it was little affected for the supplied liquid when the distance between the jet-nozzles and the heated surface was 15 mm. The enhancement rate increased with the liquid flow rate and liquid jet velocity except for the 15 mm nozzle distance. The dependency of the enhancement rate on the flow rate for the nozzle-diameter of 0.9 mm was similar to that for the 0.5 mm in diameter. The dependency on the jet-velocity for the case of 0.9 mm, however, was difference to that of 0.5 mm. In other words, the enhancement rate of the critical heat flux is related to the flow rate of the liquid-jets. These results suggest that the enhancement of the critical heat flux is affected additionally by the quantity of supplied liquid to the macrolayer on the heated surface.

Critical Heat Flux Measurement and Model for Refrigerant-123 Under Stabilized Flow Conditions in Microchannels

2006 ◽  
Author(s):  
Wai Keat Kuan ◽  
Satish G. Kandlikar
Keyword(s):  
Experimental Data ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
High Speed ◽  
Flow Boiling ◽  
Flux Measurement ◽  
Absolute Error ◽  
Cross Sectional ◽  
Boiling Process ◽  
Parallel Microchannels

The present work is aimed toward understanding the effect of flow boiling stability on critical heat flux (CHF) with Refrigerant-123 (R-123) in microchannel passages. Experimental data and theoretical model to predict the CHF are the focus of this work. The experimental test section has six parallel microchannels with each having a cross sectional area of 1054 × 157 μm2. The effect of flow instabilities in microchannels is investigated using flow restrictors at the inlet of each microchannel to stabilize the flow boiling process and avoid the backflow phenomena. This technique resulted in successfully stabilizing the flow boiling process as seen through a high-speed camera. The present CHF result is found to correlate to mean absolute error (MAE) of 24.1% with a macroscale empirical equation by Katto [13]. A theoretical analysis of flow boiling phenomena revealed that the ratio of evaporation momentum to surface tension forces is an important parameter. For the first time, a theoretical CHF model is proposed using these underlying forces to represent CHF mechanism in microchannels, and its correlation agrees with the experimental data with MAE of 2.5%.

Effect of Tube Wall Wettability on the Onset of Churning in Upward Gas-Liquid Annular Flow

2014 ◽  
Author(s):  
S. P. C. Belfroid ◽  
V. Khosla ◽  
E. D. Nennie ◽  
G. J. N. Alberts ◽  
C. A. M. Veeken
Keyword(s):  
Pressure Drop ◽  
High Speed ◽  
Tube Wall ◽  
Liquid Content ◽  
Liquid Loading ◽  
Hydrophobic Coating ◽  
Inclination Angles ◽  
Different Diameters ◽  
The Impact ◽  
Wall Wettability

The influence of hydrophobic and hydrophilic tube walls on the pressure drop and liquid loading behavior was investigated in previous projects in the past. In this paper, results of visualization experiments and of experiments at different liquid-to-gas ratios and inclination angles are presented for hydrophobic tube walls. Experiments were performed in coated and uncoated steel and Perspex pipes of different diameters: 20 mm and 50 mm. Experiments with different deviation angles ranging from 0° (vertical) to close to horizontal (≈80°) were performed for the 20mm diameter tube. The impact of the wall wettability on the flow patterns was examined by performing flow visualizations with a high speed camera in coated and uncoated Perspex tubes. From the experiments it becomes clear that the hydrophobic coating prevents the formation of a liquid film on the tube wall. As a result, the transport of the liquid phase is solely in the form of droplets/ligaments. In the hydrophobic coated tube, the onset of churning is at a lower gas velocity than in the uncoated tube. The presence of the coating reduces the critical gas rate corresponding to the minimum pressure drop by as much as 40%. This decrease reduces for high liquid rates and for larger inclination angles. However, for a liquid content of LGR = 1000 Sm3/106 Sm3, the benefit is still 33% at a vertical flow and a reduction in the critical rate remains up to a deviation angle of 80°. The hydrophobic coating increases the friction at higher gas rate but reduces the hydrostatic head at lower gas rate with a 70% reduction at low liquid content.

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