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.

Boiling of Dilute Emulsions on a Heated Strip

2013 ◽  
Author(s):  
Matthew L. Roesle ◽  
David L. Lunde ◽  
Francis A. Kulacki
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Free Convection ◽  
Transfer Coefficient ◽  
Volume Fraction ◽  
Small Diameter ◽  
Vertical Surface ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
The Wire

Measurements of heat transfer coefficients in 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 and FC-72 in water. Single phase and boiling heat transfer coefficients are measured for emulsions with a volume fraction of the dispersed component of 0.1 and 0.5 percent in an isothermal pool at approximately 25 degrees Centigrade. 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 slightly decreases the overall heat transfer coefficient, but when boiling commences, an enhancement of the heat transfer coefficient 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. Heat transfer coefficients are compared to recently published measurements of boiling in similar emulsions on a small diameter horizontal wire. Quantitative comparison of the boiling curves for the wire and plate geometries is made and discussed. The magnitude of the increase in heat transfer coefficient is smaller for emulsion boiling on the surface of the heated strip than is reported for boiling on the wire. The shape of the boiling curve is nearly the same for both geometries.

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.

Comparison of the Three–Zone Evaporation Model with Boiling Heat Transfer in a Compact Tube Bundle

2011 ◽  
Vol 5 ◽  
pp. 53-63
Author(s):  
Ebenezer Adom ◽  
Peter Kew ◽  
Keith Cornwell
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Tube Bundle ◽  
Small Diameter ◽  
Heat Fluxes ◽  
Evaporation Model ◽  
Mass Fluxes ◽  
Micro Channels ◽  
Three State Model ◽  
Outside Diameter

The recent interest in boiling heat transfer in small diameter tubes has led to the study of boiling heat transfer outside a compact tube bundle of diameter 3mm. The bank comprised 3 columns each of 10 stainless steel electrically heated tubes of 3mm outside diameter, with pitch to diameter ratio of 1.5 in an in-line arrangement. These tests were carried out using distilled water and R113 at nominal atmospheric pressure over a range of heat fluxes between 4-21 kW/m2 for mass fluxes from G=5.6 - 32.8 kg/m2s. The recent three-zone evaporation model developed by Thome, Dupont and Jacobi for boiling inside micro channels was used to compare with experimental results as photographic study showed that bubbles confined within the bundle were responsible for the heat transfer enhancement observed. It was observed that the three state model was promising in its application to the bundle arrangement as the confinement number Co for bundle has been shown to be in the order of 0.63

Effect of Al2O3 Nanolubricant on a Turbo-BII R134a Pool Boiling Surface

2012 ◽  
Author(s):  
M. A. Kedzierski
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Volume Fraction ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Heat Fluxes ◽  
Al2o3 Nanoparticles ◽  
Surface Wetting ◽  
Mass Fractions ◽  
Heat Transfer Degradation

This paper quantifies the influence of Al2O3 nanoparticles on the pool boiling performance of R134a/polyolester mixtures on a Turbo-BII-HP boiling surface. An Al2O3 nanolubricant (a lubricant containing dispersed nano-size particles) was made by suspending nominally 10 nm diameter Al2O3 particles in a synthetic polyolester to roughly a 1.0% volume fraction. The nanoparticles caused, on average, a 12% degradation in the boiling heat transfer relative to that for R134a/polyolester mixtures without nanoparticles for the three lubricant mass fractions that were tested. The degradation was nearly constant for heat fluxes between 20 kW/m2 and 120 kW/m2. It was speculated that the boiling heat transfer degradation was primarily due to a combination of (1) film boiling in the reentrant cavity rendering the nucleate boiling enhancement mechanism of the nanoparticles ineffective and (2) a reduction in bubble frequency due to the increased surface wetting as caused by the nanoparticles. In addition, these degradation factors might be mitigated with increased nanoparticle loading.

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.

Experimental Study of Horizontal Flow Boiling Heat Transfer of R134a at a Saturation Temperature of 18.6 °C

2017 ◽  
Vol 139 (11) ◽  
Author(s):  
Carlos A. Dorao ◽  
Oscar Blanco Fernandez ◽  
Maria Fernandino
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Small Diameter ◽  
Saturation Temperature ◽  
Local Heat Transfer ◽  
High Heat ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Flow Boiling Heat Transfer

In spite of the extensive work in flow boiling in small-diameter tubes, the general characteristics and dominant mechanisms remain elusive. In this study, flow boiling heat transfer of R134a inside a 5 mm I.D., smooth horizontal stainless steel pipe is experimentally studied. Local heat transfer coefficients (HTCs) were measured for heat fluxes from 3.9 to 47 kW/m2 and mass fluxes from 200 to 400 kg/m2 s at a saturation temperature of 18.6 °C. The studied cases have shown different behaviors at low and high heat fluxes. At low heat fluxes, the convective contribution looks to control the HTC, while at high heat fluxes the nucleation of vapor looks to be the dominant mechanism. Reducing the heat flux, the HTC approaches asymptotically a limit equivalent to the single-phase HTC defined in terms of the sum of the superficial liquid and vapor Reynolds numbers. A new correlation for dominant convective flow boiling is proposed and evaluated against experimental data from the literature.

Boiling Heat Transfer in a Horizontal Small-Diameter Tube

1993 ◽  
Vol 115 (4) ◽  
pp. 963-972 ◽  
Author(s):  
M. W. Wambsganss ◽  
D. M. France ◽  
J. A. Jendrzejczyk ◽  
T. N. Tran
Keyword(s):  
Heat Transfer ◽  
Flow Pattern ◽  
Slug Flow ◽  
Boiling Heat Transfer ◽  
Small Diameter ◽  
Heat Fluxes ◽  
Mean Deviation ◽  
Physical Parameters ◽  
Transfer Coefficients ◽  
Two Phase

Results of a study on boiling heat transfer of refrigerant R-113 in a small-diameter (2.92 mm) tube are reported. Local heat transfer coefficients are measured for a range of heat flux (8.8–90.75 kW/m2), mass flux (50–300 kg/m2s), and equilibrium mass quality (0–0.9). The measured coefficients are used to evaluate 10 different heat transfer correlations, some of which have been developed specifically for refrigerants. High heat fluxes and low mass fluxes are inherent in small channels, and this combination results in high boiling numbers. In addition, based on a flow pattern map developed from adiabatic experiments with air-water mixtures, it has been shown that small-diameter channels produce a slug flow pattern over a large range of parameters when compared with larger-diameter channels. The effects of high boiling number and slug flow pattern lead to domination by a nucleation mechanism. As a result, the two-phase correlations that predicted this dominance also predicted the data the best when they properly modeled the physical parameters. The correlation of Lazarek and Black (1982) predicted the data very well. It is also shown that a simple form, suggested by Stephan and Abdelsalam (1980) for nucleate pool boiling, correlates the data equally well; both correlations are within a mean deviation of less than 13 percent. Results are applicable to boiling in compact heat exchangers.

Improvement Of Free Convection From Three horizontal Finned Cylinders Fixed Between Two Walls

2018 ◽  
Vol 6 (2) ◽  
pp. 98-114 ◽  
Author(s):  
Hassan K. Abdullah ◽  
Haneen H. Rahman
Keyword(s):  
Heat Transfer ◽  
Free Convection ◽  
Prandtl Number ◽  
Convection Heat Transfer ◽  
Constant Heat Flux ◽  
Heat Fluxes ◽  
Head Orientation ◽  
Outer Diameter ◽  
Gravitational Acceleration ◽  
Convection Heat

Improvement of  free convection heat transfer from three finned cylinders arranged at a triangle shape fixed between two walls has been investigated in this study. Three mild steel finned cylinders fixed between two walls from Pyrex glass have been used as a test rig. It has been changed the spacing between the cylinders (X/D=1,2,3 & S/D=2,4,6) and the head orientation of a triangle to the top under constant heat flux values (38, 254, 660, 1268) W/m2 and compare with case of three finned cylinders arranged in vertical array in line fixed between two wall. The experiments are carried for Rayleigh number (Ra) from (15x103 to 14 x104 ) and Prandtl  number from (0.706-0.714 ). The results indicated an increase in Nu with increasing Ra for all cylinders. Furthermore,hx and Nu increased proportionally with the increasing of cylinder spacings for all heat fluxes. Also the experimental results show the case of triangle arrangement is improvement the heat transfer more than case of vertical arrangement. Heat transfer dimensionless correlating equation is also proposed.              Nomeclature: Ax: surface area(m2), T∞: surrounding temperature(k), D: the outer diameter of fin (m), Kf: the thermal conductivity for air at film temperature(W/m.k), hx: Local convection heat transfer(W/m2.k),  Gravitational acceleration(m/s2), I: Electric current (Amp), Nu: Nusselt number, Pr: Prandtl number

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