Vibration Characteristics of a Vertical Round Tube According to Heat Transfer Regimes

2002 ◽  
Author(s):  
Yong Ho Lee ◽  
Soon Heung Chang ◽  
Won-Pil Baek
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Heated Surface ◽  
Nucleate Boiling ◽  
Nucleation Site ◽  
Vibration Characteristics ◽  
Flow Induced Vibration ◽  
Round Tube ◽  
Tube Exit ◽  
Saturated Boiling

This paper presents the results of an experimental work on the effects of boiling heat transfer regimes on the flow-induced vibration (FIV). The experiment has been performed using an electrically heated vertical round tube through which water flows at atmospheric pressure. Vibration characteristics of the heated tube are changed significantly by heat transfer regimes and flow patterns. For single-phase liquid convection, the rod vibrations are negligible. However, on the beginning of subcooled nucleate boiling at tube exit, vibration level becomes very large. As bubble departure occurs at the nucleation site of heated surface, the vibration decreases to saturated boiling region where thermal equilibrium quality becomes 0.0 at tube exit. In saturated boiling region, vibration amplitude increases with exit quality up to a certain maximum value due to the reinforced turbulence then decreases. At liquid film dryout condition, vibration could be regarded as negligible, however, these results cannot be extended to DNB-type CHF mechanism. Frequency analysis results of vibration signals suggested that excitation sources be different with heat transfer regimes. This study would contribute to improve the understanding of the relationship between boiling heat transfer and FIV.

scholarly journals Flow Boiling Heat Transfer in Microchannels

2006 ◽  
Vol 129 (10) ◽  
pp. 1321-1332 ◽  
Author(s):  
Dong Liu ◽  
Suresh V. Garimella
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Transfer Coefficients ◽  
Convective Boiling ◽  
Maximum Heat ◽  
Flow Boiling Heat Transfer ◽  
Microchannel Flows ◽  
Saturated Boiling

Flow boiling heat transfer to water in microchannels is experimentally investigated. The dimensions of the microchannels considered are 275×636 and 406×1063μm2. The experiments are conducted at inlet water temperatures in the range of 67–95°C and mass fluxes of 221–1283kg∕m2s. The maximum heat flux investigated in the tests is 129W∕cm2 and the maximum exit quality is 0.2. Convective boiling heat transfer coefficients are measured and compared to predictions from existing correlations for larger channels. While an existing correlation was found to provide satisfactory prediction of the heat transfer coefficient in subcooled boiling in microchannels, saturated boiling was not well predicted by the correlations for macrochannels. A new superposition model is developed to correlate the heat transfer data in the saturated boiling regime in microchannel flows. In this model, specific features of flow boiling in microchannels are incorporated while deriving analytical solutions for the convection enhancement factor and nucleate boiling suppression factor. Good agreement with the experimental measurements indicates that this model is suitable for use in analyzing boiling heat transfer in microchannel flows.

Wall Thermal Conductivity Effects on Nucleation Site Interaction During Boiling: An Experimental Study

2010 ◽  
Author(s):  
Yu Yan Jiang ◽  
Hiroshi Osada ◽  
Masahide Inagaki ◽  
Nariaki Horinouchi
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Flux ◽  
Stainless Steel ◽  
Boiling Heat Transfer ◽  
Bubble Diameter ◽  
Nucleate Boiling ◽  
Nucleation Site ◽  
Uniform Heat Flux ◽  
Stainless Steel Surface

The past decades have witnessed the diverse applications of boiling heat transfer enhancement in the removal of high density heat flux released by electronic components or power devices. People have developed many enhanced surfaces to obtain the highest heat transfer coefficient in nucleate boiling or to raise the CHF. In the boiling arena bubbling and nucleation site density play core parts, and hence it is crucial to correlate them quantitatively with surface structure and heat transfer conditions. For example one can determine by that correlation the best arrangement of boiling cavities for a given heat flux. However, the bubbling is highly influenced by inter-bubble actions. It has been found that the interactions can considerably change the bubble’s size, frequency and spatial distribution. The interactions are needed to be taken accounts of for a good correlation. Researchers tried to formulate the interactions as a single function of the inter-site spacing but have obtained contradictory conclusions, as suggests that they depend also on other parameters. In the present study we conducted a saturated boiling heat transfer experiment to investigate the interactions with respects to both the inter-site spacing and the wall thermal conductivity. The test section was fabricated by both copper and stainless steel, whose surface has two cylindrical artificial cavities of 50μm in diameter. It was heated with a uniform heat flux. The results show that both the bubble diameter Db and frequency f are functions of the inter-cavity distance s, but they vary in different manners in the copper and the stainless steel surfaces. In the copper surface, we observed evident enhancement of the boiling heat transfer at 1> S >0.4 and a slight inhibitive effect at 1.6> S >1, where S = s/Db. On the contrary the two nucleate sites in the stainless steel surface interfere with each other giving rise to evident suppression of boiling heat transfer at 1.6> S >0.65 and only slight enhancement at 0.65> S >0.3. Note that the copper’s thermal conductivity is 22 times larger than the stainless steel. Numerical simulation has revealed that the temperature variation beneath the copper cavities is much less than the stainless steel, which partly explains the differences in our experimental results. It is suggested that modeling the bubble interactions should take accounts of not only the distance-to-diameter ratio but also the fluid and wall properties.

Generalized Correlation of Boiling Heat Transfer

1959 ◽  
Vol 81 (1) ◽  
pp. 37-42 ◽  
Author(s):  
S. Levy
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Heated Surface ◽  
Heating Surface ◽  
Nucleate Boiling ◽  
Generalized Equation ◽  
Test Results ◽  
Nucleate Boiling Heat Transfer ◽  
Generalized Correlation ◽  
Good Agreement

A generalized equation to describe surface boiling of liquids is derived. The expression which correlates all fluid independently of pressure and heating surface-fluid combination is QA=kLCLρL2σTsρL-ρV1BLΔT3 The form of the relation was obtained from a simplified model of heat transfer to the bubbles close to the heated surface. The coefficient BL, determined empirically, was found to be a function only of the product ρVhfg and is shown in Fig. 4. Good agreement between test results and the derived equation was obtained for pool boiling and nucleate boiling heat transfer of subcooled and vapor-containing liquids.

Boiling Heat Transfer Enhancement Using a Submerged, Vibration-Induced Jet

2006 ◽  
Vol 128 (2) ◽  
pp. 145-149 ◽  
Author(s):  
Steven W. Tillery ◽  
Samuel N. Heffington ◽  
Marc K. Smith ◽  
Ari Glezer
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Heated Surface ◽  
Horizontal Cell ◽  
Cross Flow ◽  
Nucleate Boiling ◽  
Heat Fluxes ◽  
Bulk Liquid ◽  
Liquid Jet ◽  
Vapor Bubbles

In this paper we describe a new two-phase cooling cell based on channel boiling and a vibration-induced liquid jet whose collective purpose is to delay the onset of critical heat flux by forcibly dislodging the small vapor bubbles that form on the heated surface during nucleate boiling and propelling them into the cooler bulk liquid within the cell. The submerged turbulent vibration-induced jet is generated by a vibrating piezoelectric diaphragm operating at resonance. The piezoelectric driver induces pressure oscillations in the liquid near the surface of the diaphragm, resulting in the time-periodic formation and collapse of cavitation bubbles that entrain surrounding liquid and generate a strong liquid jet. The resultant jet is directed at the heated surface in the channel. The jet enhances boiling heat transfer by removing attached vapor bubbles that insulate the surface and provides additional forced convection heat transfer on the surface. A small cross flow maintained within the cell increases heat transfer even further by sweeping the bubbles downstream, where they condense. In addition, the cross flow keeps the temperature of the liquid within the cell regulated. In the present experiments, the cell dimensions were 51×25×76mm and water was the working liquid. Heat fluxes above 300W∕cm2 were obtained at surface temperatures near 150°C for a horizontal cell.

Numerical Investigation on Saturated Boiling Heat Transfer in a Vertical Rectangular Minichannel

2015 ◽  
Author(s):  
Weihua Cai ◽  
Hongqiang Ma ◽  
Yang Yao ◽  
Yiqiang Jiang
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Numerical Method ◽  
Boiling Heat Transfer ◽  
Nucleate Boiling ◽  
Transfer Mechanism ◽  
Heat Transfer Mechanism ◽  
Vapor Quality ◽  
High Vapor ◽  
Saturated Boiling

A numerical method based on the Euler-Euler model was developed to investigate the mechanism of saturated boiling heat transfer mechanism on upward flow in a vertical rectangular minichannel. This method validated by the experimental data from literature. At the same time, the mechanism of saturated boiling heat transfer was also investigated by ANSYS CFX for Freon R21 at high vapor quality in a vertical rectangular minichannel based on the above numerical method. The results show that the simulation results are good agreement with experimental data from reference and the deviation is within ±15%. The main boiling mechanism is forced convective boiling while the contribution of nucleate boiling is slight for saturated boiling heat transfer at high vapor quality. The evaporation of dispersed liquid phase should be also a main boiling heat transfer mechanism. These results will provide some constructive instructions for the understanding of saturated boiling heat transfer phenomenon in a vertical rectangular minichannel of PFHE.

An Investigation of Local Degassing Effects on Heat Transfer During Gas-Saturated Boiling From a Small Cylinder

1999 ◽  
Author(s):  
Y. S. Hong ◽  
C. N. Ammerman ◽  
S. M. You
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Nucleate Boiling ◽  
Gas Content ◽  
Working Fluid ◽  
Dissolved Gas ◽  
System Pressure ◽  
Boiling Enhancement ◽  
Nucleate Boiling Heat Transfer ◽  
Saturated Boiling

Abstract Boiling heat transfer from a 50-μm-diameter wire immersed in FC-72 is examined. Effects of pressure, subcooling, and dissolved gas concentration on nucleate boiling heat transfer and critical heat flux (CHF) are investigated. The current study is an ongoing effort to systematically quantify dissolved gas content effects on boiling heat transfer. The present investigators previously determined that gas-saturated boiling efficiency is affected by local degassing of the working fluid near the heater surface. This local degassing effect is further investigated in the present study using helium, air, and carbon dioxide as dissolved gases. In addition, the limits of gas-saturated boiling enhancement are determined by varying system pressure.

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