Transition Boiling Heat Transfer on a Vertical Surface

1985 ◽  
Vol 107 (4) ◽  
pp. 756-763 ◽  
Author(s):  
T. D. Bui ◽  
V. K. Dhir
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Boiling Heat Transfer ◽  
Initial Conditions ◽  
Vertical Surface ◽  
Heat Fluxes ◽  
Rate Of Change ◽  
Transient Heating ◽  
Maximum Heat ◽  
Heating And Cooling

Transition boiling heat transfer on a vertical surface in a pool of saturated water is investigated experimentally. Local heat transfer rates are obtained on a 6.3-cm-wide and 10.3-cm-high surface which was machined from a large block of copper. Experiments conducted with water show that even for relatively slow transient cooling rates (|dT/dt| < 11 K/s), the transient maximum heat fluxes are as much as 60 percent lower than the maximum steady-state heat fluxes. It is found that transition boiling heat transfer is very sensitive to the surface condition as well as to the history of the process. Two distinct transition boiling curves are observed during transient heating and cooling of clean surfaces. However, the difference between the two curves diminishes as the wettability of the surface increases. A correlation is developed to relate the transient quenching and steady-state peak heat fluxes for the range of temperature transient rates and surface conditions used in this investigation. Although the transient transition boiling curves obtained during heating and cooling are distinct because of different initial conditions, it is found that they possess the same rate of change of heat transfer coefficient with surface temperature when a correction factor equal to the ratio of steady to transient maximum heat fluxes is used.

Boiling Heat Transfer Performance in a Spiraling Radial Inflow Microchannel Cold Plate

2015 ◽  
Author(s):  
Maritza Ruiz ◽  
Claire M. Kunkle ◽  
Jorge Padilla ◽  
Van P. Carey
Keyword(s):  
Heat Transfer ◽  
Heat Sink ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Contact Angles ◽  
Heat Fluxes ◽  
Working Fluid ◽  
Maximum Heat ◽  
Flow Boiling Heat Transfer

This study presents an experimental exploration of flow boiling heat transfer in a spiraling radial inflow microchannel heat sink. The effect of surface wettability, fluid subcooling levels, and mass fluxes are considered in this type of heat sink for use in applications with high fluxes up to 300 W/cm2. The design of the heat sink provides an inward radial swirl flow between parallel, coaxial disks that form a microchannel of 300 μm and 1 cm radius with a single inlet and a single outlet. The channel is heated on one side through a copper conducting surface, while the opposite side is essentially adiabatic to simulate a heat sink scenario for electronics cooling. Flow boiling heat transfer and pressure drop data were obtained for this heat sink device using water at near atmospheric pressure as the working fluid for inlet subcooling levels from 20 to 81°C and mean mass flux levels ranging from 184 to 716 kg/m2s. To explore the effects of varying surface wetting, experiments were conducted with two different heated surfaces. One was a clean, machined copper surface with water equilibrium contact angles in the range of 14–40°, typical of common metal surfaces. The other was a surface coated with zinc oxide nanostructures that are superhydrophilic with equilibrium contact angles measured below 10°. During boiling, increased wettability resulted in quicker rewetting and smaller bubble departure diameter as indicated by reduced temperature oscillations during boiling and achieving higher maximum heat flux without dryout. Reducing inlet subcooling levels was also found to reduce the magnitude of oscillations in the oscillatory boiling regime. The highest heat transfer coefficients were seen in fully developed boiling with low subcooling levels as a result of heat transfer being dominated by nucleate boiling. The highest heat fluxes achieved were during partial subcooled flow boiling at 300 W/cm2 with an average surface temperature of 134 °C and requiring a pumping power to heat rate ratio of 0.01%. The hydrophilic surface retained wettability after a series of boiling tests. Recommendations for use of this heat sink design in high flux applications is also discussed.

Boiling Heat Transfer to Dilute Emulsions From a Vertical Heated Strip

2015 ◽  
Vol 137 (4) ◽  
Author(s):  
Matthew L. Roesle ◽  
David L. Lunde ◽  
Francis A. Kulacki
Keyword(s):  
Heat Transfer ◽  
Free Convection ◽  
Boiling Heat Transfer ◽  
Volume Fraction ◽  
Small Diameter ◽  
Lower Surface ◽  
Vertical Surface ◽  
Heat Fluxes ◽  
Convection Boundary Layer ◽  
Direct Current Resistance

Heat transfer measurements for nucleate pool boiling of a dilute emulsion on a short vertical surface are reported. The vertical surface is a thin steel ribbon of 1.35 mm height × 101 mm length. Direct current resistance heating produces boiling either on the surface or in the free convection boundary layer of dilute emulsions of pentane in water and FC-72 in water. Single phase and boiling heat transfer is measured for emulsions with a volume fraction of the dispersed component of 0.1% and 0.5% in a pool at approximately 25 °C. The dispersed component is created by a simple atomization process and no surfactants are employed to maintain the droplets of the dispersed phase in suspension. In free convection, the presence of the dispersed component somewhat impedes heat transfer, but when boiling commences enhancement of heat transfer is observed. Boiling is observed in the emulsions at lower surface temperatures than for water alone, and significantly more superheat is required to initiate boiling of the dispersed component than would be needed for a pool of the dispersed component alone. Consequently, a temperature over shoot is observed prior to initiation of boiling, and such an over shoot has been observed in several prior studies. Boiling heat fluxes are compared to recently published measurements of boiling in similar emulsions on a small diameter horizontal wire. Boiling generally occurs at a slightly higher degree of superheat of the dispersed component on the heated strip as compared to thin wires.

Transient Pool Boiling of Water on a Vertical Surface With a Step in Heat Generation

1962 ◽  
Vol 84 (3) ◽  
pp. 217-224 ◽  
Author(s):  
Henry Lurie ◽  
H. A. Johnson
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Heat Generation ◽  
Boiling Heat Transfer ◽  
Nucleate Boiling ◽  
Vertical Surface ◽  
Steady State Temperature ◽  
Nucleate Boiling Heat Transfer ◽  
Time Required ◽  
Phd Thesis

This paper is based on the PhD thesis investigation by H. Lurie [1] on the transient heat transfer from a vertical submerged metallic ribbon undergoing a step in Joule heating leading to boiling on its surface. The tests were made in deaerated distilled water at atmospheric pressure with pool temperatures at saturation and 112 deg F subcooled, and with heat generation rates per unit of ribbon surface area from nonboiling to 1.6 × 106 Btu/ft2hr. Although the heat capacity of the ribbon is low, the surface temperature overshoot compared to the steady-state temperature is minor with values of less than 10 deg F. The time required to reach this overshoot, or the time required to reach steady state, is very short and decreases with increasing heat flux. These values are short compared to Goldstein and Eckert [2] and Siegel’s [3] estimates of the time required to develop the hydro-dynamic and thermal boundary layers in natural convection, and indicate that nucleate boiling heat transfer is probably a weak function of the fluid circulation. Some further support for this is evidenced by calculated transient temperatures based on steady nucleate boiling heat transfer which are in reasonable agreement with the measured performance.

Experimental Study of Boiling Heat Transfer From a Sphere Embedded in a Liquid-Saturated Porous Medium

1990 ◽  
Vol 112 (3) ◽  
pp. 736-743 ◽  
Author(s):  
V. X. Tung ◽  
V. K. Dhir
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Particle Size ◽  
Porous Medium ◽  
Heat Transfer Coefficient ◽  
Steady State ◽  
Transfer Coefficient ◽  
Boiling Heat Transfer ◽  
Maximum Heat ◽  
Maximum Heat Flux

Boiling heat transfer from a sphere embedded in a porous medium composed of nonheated glass particles was studied under steady-state and transient quenching conditions. In the experiments, the diameter of the nonheated glass particles forming the porous layers was varied parametrically. Freon-113 was used as the test liquid. Experimental results showed that the maximum heat flux increased monotonically with increasing glass particle diameter and approached an asymptotic value corresponding to the maximum heat flux obtained in a pool free of glass particles. It was also observed that the minimum heat flux was nearly insensitive to the particle size and the film boiling heat transfer coefficient increased slightly with decreasing particle size. In the nucleate boiling region, the heat transfer coefficient showed a much weaker dependence on wall superheat in the presence of particles. Transient data indicated that the surface temperature was not uniform during quenching. Therefore, different maximum heat fluxes were obtained depending on the location of the thermocouple whose temperature history was employed in recovering the transient boiling curve. However, for some applications, cooling rates predicted by imposing the steady-state boiling curve may not be in large error.

Pool Boiling Heat Transfer Enhancement Through Nanostructures on Silicon Microchannels

2012 ◽  
Vol 3 (3) ◽  
Author(s):  
Z. Yao ◽  
Y.-W. Lu ◽  
S. G. Kandlikar
Keyword(s):  
Heat Transfer ◽  
Silicon Nanowires ◽  
Boiling Heat Transfer ◽  
Bubble Dynamics ◽  
Pool Boiling ◽  
Hierarchical Structures ◽  
Heat Fluxes ◽  
Average Height ◽  
Maximum Heat ◽  
Maximum Heat Flux

Uniform silicon nanowires (SiNW) were successfully fabricated on the top, bottom, and sidewall surfaces of silicon microchannels by using a two-step electroless etching process. Different microchannel patterns with the channel width from 100 to 300 μm were first fabricated in a 10 mm × 10 mm silicon chip and then covered by SiNW with an average height of 10–20 μm. The effects of the microchannel geometry, micro/nano-hierarchical structures on pool boiling were studied and the bubble dynamics on different sample surfaces were compared. It was found that the combination of the micro/nanostructures promoted microbubble emission boiling under moderate heat fluxes, and yielded superior boiling heat transfer performance. At given wall superheats, the maximum heat flux of the microchannel with SiNW was improved by 120% over the microchannel-only surface, and more than 400% over a plain silicon surface. These results provide a new insight into the boiling mechanism for micro/nano-hierarchical structures and demonstrate their potential in improving pool boiling performance for microchannels.

Heat Transfer Coefficient Measurements on the Film-Cooled Pressure Surface of a Transonic Airfoil

2013 ◽  
Vol 135 (6) ◽  
Author(s):  
Paul M. Kodzwa ◽  
John K. Eaton
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Steady State ◽  
Transfer Coefficient ◽  
Film Cooling ◽  
Wide Band ◽  
Heat Fluxes ◽  
Pressure Surface ◽  
Lift Off ◽  
Transonic Airfoil

This paper presents isoenergetic temperature and steady-state film-cooled heat transfer coefficient measurements on the pressure surface of a modern, highly cambered transonic airfoil. A single passage model simulated the idealized two-dimensional flow path between blades in a modern transonic turbine. This set up offered a simpler construction than a linear cascade but produced an equivalent flow condition. Furthermore, this model allowed the use of steady-state, constant surface heat fluxes. We used wide-band thermochromic liquid crystals (TLCs) viewed through a novel miniature periscope system to perform high-accuracy (±0.2 °C) thermography. The peak Mach number along the pressure surface was 1.5, and maximum turbulence intensity was 30%. We used air and carbon dioxide as injectant to simulate the density ratios characteristic of the film cooling problem. We found significant differences between isoenergetic and recovery temperature distributions with a strongly accelerated mainstream and detached coolant jets. Our heat transfer data showed some general similarities with lower-speed data immediately downstream of injection; however, we also observed significant heat transfer attenuation far downstream at high blowing conditions. Our measurements suggested that the momentum ratio was the most appropriate variable to parameterize the effect of injectant density once jet lift-off occurred. We noted several nonintuitive results in our turbulence effect studies. First, we found that increased mainstream turbulence can be overwhelmed by the local augmentation of coolant injection. Second, we observed complex interactions between turbulence level, coolant density, and blowing rate with an accelerating mainstream.

Pool Boiling Characteristics of Metallic Nanofluids

2011 ◽  
Vol 133 (11) ◽  
Author(s):  
K. Hari Krishna ◽  
Harish Ganapathy ◽  
G. Sateesh ◽  
Sarit K. Das
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Boiling Heat Transfer ◽  
Volume Fraction ◽  
Pool Boiling ◽  
Heat Fluxes ◽  
Solid Particles ◽  
Heater Surface ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics

Nanofluids, solid-liquid suspensions with solid particles of size of the order of few nanometers, have created interest in many researchers because of their enhancement in thermal conductivity and convective heat transfer characteristics. Many studies have been done on the pool boiling characteristics of nanofluids, most of which have been with nanofluids containing oxide nanoparticles owing to the ease in their preparation. Deterioration in boiling heat transfer was observed in some studies. Metallic nanofluids having metal nanoparticles, which are known for their good heat transfer characteristics in bulk regime, reported drastic enhancement in thermal conductivity. The present paper investigates into the pool boiling characteristics of metallic nanofluids, in particular of Cu-H2O nanofluids, on flat copper heater surface. The results indicate that at comparatively low heat fluxes, there is deterioration in boiling heat transfer with very low particle volume fraction of 0.01%, and it increases with volume fraction and shows enhancement with 0.1%. However, the behavior is the other way around at high heat fluxes. The enhancement at low heat fluxes is due to the fact that the effect of formation of thin sorption layer of nanoparticles on heater surface, which causes deterioration by trapping the nucleation sites, is overshadowed by the increase in microlayer evaporation, which is due to enhancement in thermal conductivity. Same trend has been observed with variation in the surface roughness of the heater as well.

High Heat Flux Boiling Heat Transfer for Laser Diode Arrays

2016 ◽  
Author(s):  
Todd M. Bandhauer ◽  
Taylor A. Bevis
Keyword(s):  
Heat Transfer ◽  
Thermal Management ◽  
Laser Diode ◽  
Boiling Heat Transfer ◽  
Single Phase ◽  
Laser Diodes ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Laser Diode Arrays

The principle limit for achieving higher brightness of laser diode arrays is thermal management. State of the art laser diodes generate heat at fluxes in excess of 1 kW cm−2 on a plane parallel to the light emitting edge. As the laser diode bars are packed closer together, it becomes increasingly difficult to remove large amounts of heat in the diminishing space between neighboring diode bars. Thermal management of these diode arrays using conduction and natural convection is practically impossible, and, therefore, some form of forced convective cooling must be utilized. Cooling large arrays of laser diodes using single-phase convection heat transfer has been investigated for more than two decades by multiple investigators. Unfortunately, either large fluid temperature increases or very high flow velocities must be utilized to reject heat to a single phase fluid, and the practical threshold for single phase convective cooling of laser diodes appears to have been reached. In contrast, liquid-vapor phase change heat transport can occur with a negligible increase in temperature and, due to a high enthalpy of vaporization, at comparatively low mass flow rates. However, there have been no prior investigations at the conditions required for high brightness edge emitting laser diode arrays: >1 kW cm−2 and >10 kW cm−3. In the current investigation, flow boiling heat transfer at heat fluxes up to 1.1 kW cm−2 was studied in a microchannel heat sink with plurality of very small channels (45 × 200 microns) using R134a as the phase change fluid. The high aspect ratio channels (4.4:1) were manufactured using MEMS fabrication techniques, which yielded a large heat transfer surface area to volume ratio in the vicinity of the laser diode. To characterize the heat transfer performance, a test facility was constructed that enabled testing over a range of fluid saturation temperatures (15°C to 25°C). Due to the very small geometric features, significant heat spreading was observed, necessitating numerical methods to determine the average heat transfer coefficient from test data. This technique is crucial to accurately calculate the heat transfer coefficients for the current investigation, and it is shown that the analytical approach used by many previous investigations requires assumptions that are inadequate for the very small dimensions and heat fluxes observed in the present study. During the tests, the calculated outlet vapor quality exceeded 0.6 and the base heat flux reached a maximum of 1.1 kW cm−2. The resulting experimental heat transfer coefficients are found to be as large a 58.1 kW m−2 K−1 with an average uncertainty of ±11.1%, which includes uncertainty from all measured and calculated values, required assumptions, and geometric discretization error from meshing.

Heat Transfer Enhancement in Compact Phase Change Microchannel Heat Exchangers for High Flux Laser Diodes

2018 ◽  
Author(s):  
Jensen Hoke ◽  
Todd Bandhauer ◽  
Jack Kotovsky ◽  
Julie Hamilton ◽  
Paul Fontejon
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Phase Change ◽  
Flow Boiling ◽  
Laser Diodes ◽  
High Heat ◽  
Heat Fluxes ◽  
High Heat Flux ◽  
Maximum Heat ◽  
Average Maximum

Liquid-vapor phase change heat transfer in microchannels offers a number of significant advantages for thermal management of high heat flux laser diodes, including reduced flow rates and near constant temperature heat rejection. Modern laser diode bars can produce waste heat loads >1 kW cm−2, and prior studies show that microchannel flow boiling heat transfer at these heat fluxes is possible in very compact heat exchanger geometries. This paper describes further performance improvements through area enhancement of microchannels using a pyramid etching scheme that increases heat transfer area by ∼40% over straight walled channels, which works to promote heat spreading and suppress dry-out phenomenon when exposed to high heat fluxes. The device is constructed from a reactive ion etched silicon wafer bonded to borosilicate to allow flow visualization. The silicon layer is etched to contain an inlet and outlet manifold and a plurality of 40μm wide, 200μm deep, 2mm long channels separated by 40μm wide fins. 15μm wide 150μm long restrictions are placed at the inlet of each channel to promote uniform flow rate in each channel as well as flow stability in each channel. In the area enhanced parts either a 3μm or 6μm sawtooth pattern was etched vertically into the walls, which were also scalloped along the flow path with the a 3μm periodicity. The experimental results showed that the 6μm area-enhanced device increased the average maximum heat flux at the heater to 1.26 kW cm2 using R134a, which compares favorably to a maximum of 0.95 kw cm2 dissipated by the plain walled test section. The 3μm area enhanced test sections, which dissipated a maximum of 1.02 kW cm2 showed only a modest increase in performance over the plain walled test sections. Both area enhancement schemes delayed the onset of critical heat flux to higher heat inputs.

Nucleate Boiling Heat Transfer of Binary Mixtures at Low to Moderate Heat Fluxes

1999 ◽  
Vol 121 (2) ◽  
pp. 365-375 ◽  
Author(s):  
R. J. Benjamin ◽  
A. R. Balakrishnan
Keyword(s):  
Heat Transfer ◽  
Stainless Steel ◽  
Binary Mixtures ◽  
Boiling Heat Transfer ◽  
Heating Surface ◽  
Nucleate Boiling ◽  
Steel Tube ◽  
Heat Fluxes ◽  
Stainless Steel Tube ◽  
Turbulent Natural Convection

A model for nucleate pool boiling heat transfer of binary mixtures has been proposed based on an additive mechanism. The contributing modes of heat transfer are (i) the heat transferred by microlayer evaporation, (ii) the heat transferred by transient conduction during the reformation of the thermal boundary layer, and (iii) the heat transferred by turbulent natural convection. The model takes into account the microroughness of the heating surface which has been defined quantitatively. The model compares satisfactorily with data obtained in the present study and in the literature. These data were obtained on a variety of heating surfaces such as a vertical platinum wire, a horizontal stainless steel tube and flat horizontal aluminium, and stainless steel surfaces (with various surface finishes) thereby demonstrating the validity of the model.

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