Nucleate Boiling Heat Transfer Research Articles

Pool boiling heat transfer in binary mixtures of ammonia/water: Effect of heat of dilution and dissolution on heat transfer coefficient

AbstractNucleate boiling heat transfer coefficients were measured on a horizontal heated wire during the pool boiling of non‐azeotropic mixtures of ammonia/water. The experiment was carried out at pressures of 0.4 and 0.7 MPa, at heat fluxes below 2.0 × 106 W/m2, and over a range of mass fraction. The heat transfer coefficients in the mixtures were smaller than those in single‐component substances. No existing correlation is found to predict boiling heat transfer coefficients over the range of mass fraction of interest. In the mixtures of the ammonia/water, the heats of dilution and dissolution were generated near a liquid surface while vapor with a rich concentration of ammonia was condensed and then was diffused into the bulk liquid; while in most other mixtures, little heat was generated during any dilution and dissolution. In relation to the heat generated, the effect of the heats of dilution and dissolution on pressure and temperature in a system (pressure vessel) is shown herein. © 2002 Wiley Periodicals, Inc. Heat Trans Asian Res, 31(4): 272–283, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.10034

Mechanism of Nucleate Boiling Heat Transfer Enhancement From Microporous Surfaces in Saturated FC-72

Abstract The present study is an experimental investigation of the nucleate pool boiling heat transfer enhancement mechanism of microporous surfaces immersed in saturated FC-72. Measurements of bubble size, frequency, and vapor flow rate from a plain and microporous coated 390 μm diameter platinum wire using the consecutive-photo method were taken to determine the effects of the coating on the convective and latent heat transfer mechanisms. Results of the study showed that the microporous coating augments nucleate boiling performance through increased latent heat transfer in the low heat flux region and through increased convection heat transfer in the high heat flux region. The critical heat flux for the microporous coated surface is significantly enhanced over the plain surface due to decreased latent heat transfer (decreased vapor generation rate) and/or increased hydrodynamic stability from increased vapor inertia; both of which are a direct result of increased nucleation site density.

Pool boiling heat transfer to binary mixtures with miscibility gap

Nucleate boiling heat transfer has been investigated from a horizontal copper tube (4.35 mm O.D.) to mixtures of water/1-butanol and to the pure components at saturation temperatures between 100 °C and 150 °C and at compositions within and beyond the miscibility gap of this binary system. Simultaneously, the vapour–liquid or vapour–liquid–liquid equilibrium has been investigated. The results of the heat transfer measurements do not exhibit any peculiarities due to partial miscibility.

Bubble Behavior and Nucleate Boiling Heat Transfer in Saturated FC-72 Spray Cooling

Bubble behavior during saturated FC-72 spray cooling was experimentally investigated. A heater previously used for pool boiling was used to allow direct comparison. The results are analyzed to reveal the interaction between bubbles and impinging droplets. The following are presented: (1) the importance of secondary nuclei entrained by impingement droplets, (2) the role of impinging droplets on bubble parameters such as growth, diameter at puncture, lifetime, life cycle and bubble number density, and (3) the relative contribution of nucleation, especially that of secondary nuclei, to the heat transfer. It is concluded that increasing the droplet flux increases the number of secondary nuclei, helps to lower surface temperature for a given heat flux, increases the overall heat transfer coefficient, and increases heat transfer due to both nucleate boiling and enhanced convection. Increasing the droplet flux also shortens the bubble growth time (i.e., resulting in earlier bubble removal) and life cycle. However, increasing the droplet flux (and, therefore, secondary nucleation) for each of the three heat flux values does not affect the percentage of either nucleate or convection heat transfer. This suggests that both the nucleate and convection heat transfer are enhanced, as a result of increased secondary nuclei and turbulent mixing due to the impinging droplets.

Pool Boiling in Binary Mixtures of Ammonia/Water. Effect of Heat of Dilution and Dissolution and Heat Transfer Coefficient.

Nucleate boiling heat transfer coefficients have been measured during pool boiling of non-azeotropic mixtures of ammonia/water on a horizontal heated wire. The experiment was carried out at pressures of 0.4 and 0.7 MPa and at heat fluxes below 2.0×106 W/m2 and in overall range of mass fraction. The heat transfer coefficients in the mixtures are smaller than those in single component substances. No existing correlation is found to predict boiling heat transfer data over the range of mass fraction. In the mixtures of ammonia/water, heat of dilution and dissolution is generated near vapor-liquid interface, when vapor of higher concentration of ammonia is condensed and then is diffused into the bulk liquid, while in the most of mixtures, little heat is generated during any dilution and dissolution. In relation to this heat generated, the effect of the heat of dilution and dissolution on pressure and temperature in a system (pressure vessel) is shown.

414 細線を用いた核沸騰伝熱の画像計測(熱工学II)

414 細線を用いた核沸騰伝熱の画像計測(熱工学II)

INFLUENCE OF MICROSCALE CONCENTRATION GRADIENTS IN NUCLEATE BOILING HEAT TRANSFER OF BINARY MIXTURES

Nucleate boiling heat transfer coefficients of binary mixtures can be calculated using a micro region model. The model is described and assessed by comparing calculated heat transfer coefficients with experimental values. The model includes the governing physical phenomena, such as the meniscus curvature, the adhesion pressure, and the interfacial thermal resistance as well as the local variation of composition and liquid-vapor equilibrium and the Marangoni effect. Due to the preferential evaporation of one component of the mixture, strong concentration gradients occur close to the heated wall. The influence of these microscale concentration gradients is investigated. By means of various calculations the physical phenomena are quantified and their relevance in the nucleate boiling process is evaluated.

211 画像計測による水平細線からの核沸騰熱伝達(熱工学III)

211 画像計測による水平細線からの核沸騰熱伝達(熱工学III)

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

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.

Study on Nucleate Boiling Heat Transfer to Slush Hydrogen and Slush Nitrogen.

Slush hydrogen is a mixture of liquid hydrogen and solid hydrogen particles, and is being considered as a spaceplane fuel or as a means of transport for hydrogen used as a source of clean energy. This paper describes nucleate boiling heat transfer characteristics to slush hydrogen and slush nitrogen. For visual observation of heat transfer states, a heat transfer unit was placed in a glass dewar designed to minimize the heat leak from atmospheric environment. The heat transfer unit used was a circular fiat plate 0.025 m diameter made of electrolytic tough pitch copper. For orientations of the heat transfer surface during testing, three different orientations were used; horizontal facing up, vertical, and horizontal facing down. In addition to that for slush hydrogen and nitrogen, heat transfer data for normal boiling point (NBP) liquid hydrogen, triple point (TP) liquid hydrogen, NBP liquid nitrogen and TP liquid nitrogen was obtained up to the critical heat flux (burnout). Comparison of these data with the slush hydrogen and nitrogen data, including the results of observation of the heat transfer surface, clarified nuclear boiling heat transfer characteristics to slush hydrogen and slush nitrogen, which have hardly ever been investigated.

Spray Cooling Enhancement by Addition of a Surfactant

An experimental study was done on the effect of dissolving a surfactant in water sprays used to cool a hot surface. A copper surface was heated to an initial temperature of 240°C and then rapidly cooled using a spray of either pure water or an aqueous solution containing 100 ppm by weight of sodium dodecyl sulfate. The variation of surface temperature was measured during cooling, and spray impact was photographed. Addition of the surfactant was found to enhance nucleate boiling heat flux by up to 300 percent. The surface temperature required to initiate vapor bubble nucleation was reduced from 118°C to 103°C. These effects were attributed to the surfactant promoting bubble nucleation and foaming in spray droplets. Nucleate boiling heat transfer enhancement was observed at all liquid mass fluxes and droplet velocities in the range of our experiments. The surfactant slightly reduced transition boiling heat transfer, and also reduced the temperature at which spray droplets started to wet the surface. Changing the orientation of the surface with respect to gravity had no effect on heat transfer.

Concentration Dependence of Pool Nucleate Boiling Heat Transfer Coefficients for R134a and Polyolester Oil System

Concentration Dependence of Pool Nucleate Boiling Heat Transfer Coefficients for R134a and Polyolester Oil System

蒸気泡発生頻度を変化させた場合の飽和プール核沸騰の液体流動の可視化

蒸気泡発生頻度を変化させた場合の飽和プール核沸騰の液体流動の可視化

Study on the Depression of Incipient Boiling Temperature Induced by Ultrasonic Wave.

The effects of an ultrasonic wave on nucleate-boiling heat transfer, focusing on depression of the incipient boiling temperature were examined. Experiments were conducted using a copper thin film and saturated R-113 liquid for a pool condition at 0.10 MPa. The incipient boiling temperature was depressed by ultrasonic wave incidence up to 10 K in reheating experiments where the heat transfer surface had been immersed in the liquid following the previous boiling experiment. On the other hand, it was minimally affected when the boiling experiment started immediately after the test surface was immersed into the liquid. These results were considered to be related to the number of active nucleation sites available. The decrease of the incipient boiling temperature as the power of the ultrasonic wave was increased, however, did not depend on the frequency. It was pointed out that the depression of the incipient boiling temperature was caused by the local pressure increase caused by the ultrasonic wave incidence.

Nucleate Boiling Heat Transfer in Spray Cooling

An experimental study to determine the effect of liquid and secondary gas flow in droplet impingement cooling is presented. The nucleate boiling regime in particular is analyzed. A correlation to predict the Nusselt number based on the liquid film thickness is derived and compared with the experimental data.

Nonlinear Aspects of High Heat Flux Nucleate Boiling Heat Transfer

This paper deals with potential nonlinear effects in nucleate boiling systems as a result of the behavior of individual nucleation sites on the heater surface. This requires detailed microscopic modeling of the surface. A computational model has been formulated for this purpose. The model addresses the three-dimensional transient conduction heat transfer process within the problem domain comprised of the macrolayer and heater. Hydrodynamic effects are represented through boundary conditions. Individual nucleation sites are activated or deactivated depending on the thermal conditions that prevail at the site. The model has been used to examine the behavior of sites on a realistic heater surface. The results indicate that significant spatial and temporal temperature variations can occur on the surface, and that thermal interactions among sites can result in some sites operating intermittently. Surface-averaged temperatures show nonlinear period-doubling behavior. A chaotic case was found. Qualitative comparisons are made to both local instantaneous temperature measurements and recent experiments that showed chaotic behavior. We believe that such nonlinear behavior is one of the reasons that mechanistic predictive capabilities for the boiling process have remained elusive.

Enhancement of Nucleate Boiling Heat Transfer and Depression of Surface Tension by Surfactant Additives

Enhancement of Nucleate Boiling Heat Transfer and Depression of Surface Tension by Surfactant Additives

Induced Convective Enhancement of the Critical Heat Flux From Partially Heated Horizontal Flat Plates in Saturated Pool Boiling

Current developments in high-power electronics and other energy-intensive applications have accentuated the need for higher performance heat transfer. Nucleate boiling heat transfer is one of the most effective modes of heat transfer, with pool boiling being perhaps the simplest type of passive two-phase cooling. Unfortunately, the maximum heat flux attainable in nucleate pool boiling is limited by the relatively low critical heat flux at the onset of film boiling. Several methods have been suggested to enhance the critical heat flux. In particular, Costello et al. showed that the critical heat flux in saturated pool boiling could be enhanced by simply increasing the width of the pool while maintaining a fixed heater size. Elkassabgi and Lienhard examined the combined effects of immersion depth and pool size on the critical heat flux for a small-diameter horizontal cylinder in saturated pool boiling. No similar study for flat plate heaters appears in the literature. While as noted above the effect of heater appears in the literature. While as noted above the effect of heater appears in the literature. While as noted above the effect of heater size and immersion depth have been studied independently, no systematic investigation of the combined effects has been conductedmore » previously. This paper presents the results of such a study.« less

Enhancement of a saturated-pool nucleate-boiling heat transfer by ultrasonic vibrations.

Enhancement of a saturated-pool nucleate-boiling heat transfer by ultrasonic vibrations.

Nucleate boiling heat transfer and critical heat flux in narrow space between rectangular surfaces

Pool boiling heat transfer in a confined narrow space is systematically investigated for saturated water at atmospheric pressure between heated and unheated parallel rectangular plates. Experiments are performed at heat flux from boiling inception to the critical heat flux on heating surfaces with a width of 30 mm, lengths of 30 and 120 mm, and gap sizes of 5, 2, 0.6 and 0.15 mm under three surface peripheral conditions. They are all edges open, closed side edges, and closed side and bottom edges. Space inclination is also changed from vertical to facing downwards nearly to the horizontal. On the basis of measurements and observation, boiling behavior and mechanisms in a narrow space are discussed. Measured critical heat flux under two different periphery conditions are also compared with predictions on corresponding burnout models.