Critical Heat Flux for Subcooled Water Flowing Normal to a Cylinder

1964 ◽  
Vol 86 (1) ◽  
pp. 68-74 ◽  
Author(s):  
G. C. Vliet ◽  
G. Leppert
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Atmospheric Pressure ◽  
Marked Effect ◽  
Fractional Power ◽  
Nucleate Boiling ◽  
Water Velocity ◽  
Critical Flux ◽  
Vapor Cavity ◽  
Saturated Water

Empirical data are presented which show the effects of diameter, water velocity, and subcooling on the critical heat flux from an electrically heated, cylindrical lube or wire. The maximum flux which can be accommodated in subcooled nucleate boiling is found to vary directly with the water velocity and subcooling and inversely with a fractional power of the heater diameter. The exponent which describes the diameter dependence is itself a function of both velocity and subcooling. Measurements of the critical flux are reported for water at atmospheric pressure over a range of subcooling from 3 to 100 deg F, velocity from 0.5 to 11 ft/sec, and heater diameter from 0.010 to 0.189 in. Visual and photographic observations indicate a marked effect of subcooling on the flow mechanism near the critical heat flux. High subcooling prevents the formation of the vapor cavity which was described in the previous paper [1] for nearly saturated water, although the failure of nucleate boiling still occurs at the rear of the cylinder and is accompanied by a concentration of vapor in that region.

Critical Heat Flux for Nearly Saturated Water Flowing Normal to a Cylinder

1964 ◽  
Vol 86 (1) ◽  
pp. 59-66 ◽  
Author(s):  
G. C. Vliet ◽  
G. Leppert
Keyword(s):  
Heat Flux ◽  
Atmospheric Pressure ◽  
Saturation Temperature ◽  
Nucleate Boiling ◽  
Companion Paper ◽  
Critical Flux ◽  
Steel Wires ◽  
Saturated Water ◽  
Peak Flux ◽  
Heater Wall

Visual and photographic observations are used to construct a physical model of the mechanism of transition from nucleate to film boiling on a cylindrical heater. In this paper, interest is focused on forced-convection boiling of a liquid which is near its saturation temperature, while a companion paper deals with the effects of various degrees of liquid subcooling on the peak flux. An approximate analysis is presented of the saturated nucleate-boiling model which predicts the critical flux, and comparisons are made with experimental observations. Measurements of the peak nucleate-boiling heat flux are reported for water at atmospheric pressure over a velocity range of 1.2 to 9.5 feet per second. Resistively heated, stainless-steel wires and tubes of 0.010 to 0.189-inch diameter, the latter with wall thicknesses of 0.006 to 0.028 in., were used. Within these ranges of variables, the critical flux is found to increase with the square root of the velocity and to be independent of heater wall thickness. Only a weak dependence on the heater diameter is observable, but the tendency is for the peak flux to diminish for larger tubes.

Parametric Effects of Heater Size, Contact Angle, and Surrounding Vessel Size On Pool Boiling Critical Heat Flux From Horizontal Surfaces

2021 ◽  
Author(s):  
Zhenyu She ◽  
Vijay K. Dhir
Keyword(s):  
Heat Flux ◽  
Contact Angle ◽  
Critical Heat Flux ◽  
Nucleate Boiling ◽  
Flat Plates ◽  
Vessel Size ◽  
Saturated Water ◽  
Nucleate Boiling Heat Transfer ◽  
Parametric Effects ◽  
Glass Tubes

Abstract Saturated water at one atmosphere pressure was boiled on horizontal copper discs of diameters 1.0,1.5 and 2.0 cm. respectively. The contact angle was varied from 10 to 80 degrees by controlling thermal oxidation of the discs, while the surrounding vessel size was changed by placing glass tubes of different inner diameters around the discs. Nucleate boiling heat transfer data were obtained up to critical heat flux (CHF), where vapor removal patterns were photographed. Dominant wavelengths at vapor jet interface and vapor jet diameters were measured from the photographs of the well wetted discs. For a well wetted surface, the magnitude of CHF increased when the heater size was reduced from 2.0 to 1.0 cm. Improving the wettability enhanced the CHF substantially, whereas the increased size of the liquid holding vessel had a smaller effect. The highest measured CHF is 233 W/cm2 or 2.11 times Zuber's CHF prediction for infinite horizontal flat plates. It was obtained on a 1.0 cm. disc of contact angle about 10 degrees surrounded by a large vessel. The CHF for this surface was increased from 201 to 233 W/cm2 when the ratio of heater size to surrounding vessel size was reduced from 1 to about 0.

Pool Boiling of FC-72 and HFE-7100

1999 ◽  
Vol 123 (2) ◽  
pp. 399-400 ◽  
Author(s):  
Z. W. Liu ◽  
W. W. Lin ◽  
D. J. Lee ◽  
X. F. Peng
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Atmospheric Pressure ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Film Boiling ◽  
Boiling Mode

This work reported the boiling characteristics of FC-72 and HFE-7100 at atmospheric pressure and at a liquid subcooling of 0–20 K. The FC-72 exhibits a more efficient nucleate boiling mode and a higher critical heat flux (CHF) than the HFE-7100. For film boiling mode, HFE-7100 becomes more efficient.

Boiling Heat Transfer and Critical Heat Flux Enhancement of Upward- and Downward-Facing Heater in Nanofluids

2013 ◽  
Vol 135 (7) ◽  
Author(s):  
Muhamad Zuhairi Sulaiman ◽  
Masahiro Takamura ◽  
Kazuki Nakahashi ◽  
Tomio Okawa
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Boiling Heat Transfer ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Flux Enhancement ◽  
Optimum Configuration ◽  
Wall Superheat ◽  
Nucleate Boiling Heat Transfer

Boiling heat transfer (BHT) and critical heat flux (CHF) performance were experimentally studied for saturated pool boiling of water-based nanofluids. In present experimental works, copper heaters of 20 mm diameter with titanium-oxide (TiO2) nanocoated surface were produced in pool boiling of nanofluid. Experiments were performed in both upward and downward facing nanofluid coated heater surface. TiO2 nanoparticle was used with concentration ranging from 0.004 until 0.4 kg/m3 and boiling time of tb = 1, 3, 10, 20, 40, and 60 mins. Distilled water was used to observed BHT and CHF performance of different nanofluids boiling time and concentration configurations. Nucleate boiling heat transfer observed to deteriorate in upward facing heater, however; in contrast effect of enhancement for downward. Maximum enhancements of CHF for upward- and downward-facing heater are 2.1 and 1.9 times, respectively. Reduction of mean contact angle demonstrate enhancement on the critical heat flux for both upward-facing and downward-facing heater configuration. However, nucleate boiling heat transfer shows inconsistency in similar concentration with sequence of boiling time. For both downward- and upward-facing nanocoated heater's BHT and CHF, the optimum configuration denotes by C = 400 kg/m3 with tb = 1 min which shows the best increment of boiling curve trend with lowest wall superheat ΔT = 25 K and critical heat flux enhancement of 2.02 times.

Study on Subcooled-Forced Flow Boiling Heat Transfer and Critical Heat Flux of Solid-Water Two-Phase Mixture

1999 ◽  
Author(s):  
Yasuo Koizumi ◽  
Hiroyasu Ohtake ◽  
Manabu Mochizuki
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Liquid Layer ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Forced Flow ◽  
Superheated Liquid ◽  
Flow Boiling Heat Transfer

Abstract The effect of solid particle introduction on subcooled-forced flow boiling heat transfer and a critical heat flux was examined experimentally. In the experiment, glass beads of 0.6 mm diameter were mixed in subcooled water. Experiments were conducted in a range of the subcooling of 40 K, a velocity of 0.17–6.7 m/s, a volumetric particle ratio of 0–17%. When particles were introduced, the growth of a superheated liquid layer near a heat trasnsfer surface seemed to be suppressed and the onset of nucleate boiling was delayed. The particles promoted the condensation of bubbles on the heat transfer surface, which shifted the initiation of a net vapor generation to a high heat flux region. Boiling heat trasnfer was augmented by the particle introduction. The suppression of the growth of the superheated liquid layer and the promotion of bubble condensation and dissipation by the particles seemed to contribute that heat transfer augmentation. The wall superheat at the critical heat flux was elevated by the particle introduction and the critical heat flux itself was also enhanced. However, the degree of the critical heat flux improvement was not drastic.

scholarly journals Determination of Pool Boiling Critical Heat Flux Enhancement in Nanofluids

2007 ◽  
Author(s):  
Bao H. Truong
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Porous Coating ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Sem Images ◽  
Heat Transfer Coefficients ◽  
Nucleate Boiling Heat Transfer

Nanofluids are engineered colloids composed of nano-size particles dispersed in common fluids such as water or refrigerants. Using an electrically controlled wire heater, pool boiling Critical Heat Flux (CHF) of Alumina and Silica water-based nanofluids of concentration less than or equal to 0.1 percent by volume were measured. Silica nanofluids showed a CHF enhancement up to 68% and there seems to be a monotonic relationship between the nanoparticle concentration and the magnitude of enhancement. Alumina nanofluids had a CHF enhancement up to 56% but the peak occurred at the intermediate concentration. The boiling curves in nanofluid were found to shift to the left of that of water and correspond to higher nucleate boiling heat transfer coefficients in the two-phase flow regime. Scanning Electron Microscopy (SEM) images show a porous coating layer of nanoparticles on wires subjected to nanofluid CHF tests. These coating layers change the morphology of the heater’s surface, and are responsible for the CHF enhancement. The thickness of the coating was estimated using SEM and was found ranging from 3.0 to 6.0 micrometers for Alumina, and 3.0 to 15.0 micrometers for Silica.

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