Boiling Heat Transfer Of Water Research Articles

Study of a flat-surface, high-pressure, pool boiling test instrument

A study has been conducted of a newly developed high-pressure instrument, capable of pool boiling testing on multiple flat surfaces without instrumentation of each sample tested. The instrument has a unique design for testing flat samples with instrumentation only in the instrument and a data reduction procedure appropriate for the design. The validity of the instrument design and data reduction procedure was verified through boiling water heat transfer testing on a flat stainless-steel surface at atmospheric and 0.69-MPa pressures. The boiling heat transfer results obtained were shown to be in reasonable agreement with predicted values from correlations in the engineering literature. This test instrument is especially useful for evaluating the performance of newly engineered surfaces, such as textured and coated surfaces, compared to that of the base surface, where experimental testing on the base and engineered surfaces under the same operation conditions is required, and instrumentation of the surfaces would be detrimental to them.

Investigation of Nucleate Pool Boiling Heat Transfer of Water on Platinum Wire Under Hypergravity and Earth’s Gravity

Investigation of Nucleate Pool Boiling Heat Transfer of Water on Platinum Wire Under Hypergravity and Earth’s Gravity

Transient Flow Boiling Heat Transfer in Water

Transient Flow Boiling Heat Transfer in Water

Advanced Process Simulation of Low Pressure Die Cast A356 Aluminum Automotive Wheels—Part I, Process Characterization

In this work, a plant trial was conducted on an industrial low pressure die casting (LPDC) manufacturing process for the production of aluminum alloy wheels. Various types of data have been acquired, including extensive measurements of temperature at different locations (die, wheel and cooling channels), pressure in cooling channels and size/location of shrinkage porosity in the produced wheels. Moreover, two process conditions were tested in the trial—one was the standard production process condition and the other was designed to generate shrinkage porosity in wheels by altering the die temperature. The large amount of quantitative data acquired in this study helped us to understand the key transport phenomena occurring in the process, which include: (1) a thorough picture of the evolution in temperature at a large number of discrete locations in the die and the casting; (2) the dynamic and complicated heat transfer in the cooling channels both water-on and water-off stages, associated with boiling water heat transfer. This paper (Part I) presents the results and findings obtained from the process characterization. The follow-on paper (Part II) will introduce the developed modeling methodology based on the data produced from this work.

Enhancement in Boiling Heat Transfer for Water Using a Polished Plate Surface

The thermal characteristic of a plate evaporator for boiling water have been experimentally investigated. Stainless-steel plates with five kinds of surface roughness (a mirror-polished surface and four kinds of polished plate surface, F2, F0, F-1, and F-2 polishing) were used for the investigation. The roughness order is F-2 > F-1 > F0 > F2 > mirror. The local boiling heat transfers were measured on the evaporator surface using ten thermocouples inside the evaporator. For a comparison of the heat transfer characteristic of the evaporator, the local boiling heat transfer coefficient was measured when the polishing direction was perpendicular or parallel to the water flow at a range of pressures (0.3–0.4 MPa) and flow rates (20–60 mL/min). The results indicate that the local heat transfer coefficient increased with increasing vapor quality at all surface conditions. For F0 polishing, the heat transfer coefficient on the surface with perpendicular polishing was much larger than that on the surfaces with parallel and mirror polishing. In particular, the heat transfer coefficient of the perpendicularly polished surface (F2 and F0 polishing) was increased six-fold in comparison with that of the mirror surface at a vapor quality of 0.35. However, for the F-1 and F-2 perpendicularly polishing plates, the heat transfer coefficients were smaller than those of the F0 and F2 perpendicularly polishing plates. For the F2 perpendicularly polished plate, heat transfer enhancement was confirmed, along with an increase in the number of bubbling points, on increasing the system pressure. For the polished surface, the heat transfer coefficient increased with increasing flow rate. This indicates that the bubble formation cycle was promoted by an increased flow rate.

Effect of Surface Roughness on Pool Boiling Heat Transfer of Water on a Superhydrophilic Aluminum Surface

The effect of surface roughness on the pool boiling heat transfer of water was investigated on superhydrophilic aluminum surfaces. The formation of nanoscale protrusions on the aluminum surface was confirmed after immersing it in boiling water, which modified surface wettability to form a superhydrophilic surface. The effect of surface roughness was examined at different average roughness (Ra) values ranging from 0.11 to 2.93 μm. The boiling heat transfer coefficients increased with an increase in roughness owing to the increased number of cavities. However, the superhydrophilic aluminum surfaces exhibited degradation of the heat transfer coefficients when compared with copper surfaces owing to the flooding of promising cavities. The superhydrophilic aluminum surfaces exhibited a higher critical heat flux (CHF) than the copper surfaces. The CHF was 1650 kW/m2 for Ra = 0.11 μm, and it increased to 2150 kW/m2 for Ra = 0.35 μm. Surface roughness is considered to affect CHF as it improves the capillary wicking on the superhydrophilic surface. However, further increase in surface roughness above 0.35 μm did not augment the CHF, even at Ra = 2.93 μm. This upper limit of the CHF appears to result from the hydrodynamic limit on the superhydrophilic surface, because the roughest surface with Ra = 2.93 μm still showed a faster liquid spreading speed.

Enhancement of Pool Boiling Heat Transfer in Water Using Sintered Copper Microporous Coatings

Abstract Pool boiling heat transfer of water saturated at atmospheric pressure was investigated experimentally on Cu surfaces with high-temperature, thermally-conductive, microporous coatings (HTCMC). The coatings were created by sintering Cu powders on Cu surfaces in a nitrogen gas environment. A parametric study of the effects of particle size and coating thickness was conducted using three average particle sizes (APSs) of 10 μm, 25 μm, and 67 μm and various coating thicknesses. It was found that nucleate boiling heat transfer (NBHT) and critical heat flux (CHF) were enhanced significantly for sintered microporous coatings. This is believed to have resulted from the random porous structures that appear to include reentrant type cavities. The maximum NBHT coefficient was measured to be approximately 400 kW/m2k with APS 67 μm and 296 μm coating thicknesses. This value is approximately eight times higher than that of a plain Cu surface. The maximum CHF observed was 2.1 MW/m2 at APS 67 μm and 428 μm coating thicknesses, which is approximately double the CHF of a plain Cu surface. The enhancement of NBHT and CHF appeared to increase as the particle size increased in the tested range. However, two larger particle sizes (25 μm and 67 μm) showed a similar level of enhancement.

Gallium-Cooled Target for Compact Accelerator-Based Neutron Sources

This paper discusses the motivation for gallium cooling of targets of compact accelerator-based neutron sources (CANS); summarizes features of the low-power alternative, i.e., water cooling, and the limitations of boiling water heat transfer; lists the properties of liquid gallium; and cites its low hazards potential. I set out working equations for heat transport and fluid flow in liquid gallium and present a concept for a gallium-cooled system, including a scoping calculation of temperatures and pressure drops, and present conclusions and a recommendation.

Film Boiling and Water Film Ejection in the Secondary Cooling Zone of the Direct-Chill Casting Process

Accurate thermal modeling of the direct-chill casting process relies nowadays on increasingly complex boundary conditions for the secondary cooling zone. A two-dimensional axisymmetric finite-element model of the direct-chill casting process was developed to quantify the importance of secondary cooling at the surface compared with internal heat conduction within the billet. Boiling water heat transfer at the surface was found to dominate and be the governing factor only when stable film boiling or water film ejection take place; all other cases were dominated by internal heat conduction. The influence of various parameters (casting speed, cooling water flow rate, and thermophysical properties of the cast material) on the occurrence of water film ejection was analyzed. An exponential relationship was found between the cooling water flow rate and the minimum casting speed at which water film ejection takes place.

Gallium-cooled target for compact accelerator-based neutron sources

This paper discusses the motivation for gallium-cooling of targets of compact accelerator-based neutron sources (CANS); summarizes features of the low-power alternative, i.e., water cooling, and the limitations of boiling water heat transfer; lists the properties of liquid gallium; and cites its low hazards potential. I set out working equations for heat transport and fluid flow in liquid gallium and present a concept for a gallium-cooled system, including a scoping calculation of temperatures and pressure drops, and present conclusions and a recommendation.

Numerical Simulation of Boiling Heat Transfer of Water in Vertical Rectangular Mini-Channels

Boiling heat transfer in vertical rectangular mini-channels with a width of 1mm and 0.1mm is studied in this paper. The course of bubble generation, growth and departure is numerically simulated and analyzed, and the influence of the movement of phase interfaces on pressure difference and average surface heat transfer coefficient is investigated by using geometry reconstruction and interface tracking. All the calculation is conducted taken into account the gravity, surface tension and wall adhesion. This paper presents that the width of channels plays a significant role in the course of bubble generation, growth and motion, which also leads to changes of critical heat flux. In addition, it is found that surface tension is much more important than gravity in the process of boiling heat transfer. As the channel size is decreased, the boiling heat transfer coefficient increases significantly, which proves that mini-channels can enhance the heat transfer. However, the boiling heat transfer coefficient obtained through numerical simulation is higher than the existing experimental data due to the ideal assumptions adopted in simulation.

Pool Boiling Heat Transfer of Water on Finned Surfaces at Near Vacuum Pressures

This research paper presents a study of boiling heat transfer from longitudinal rectangular-finned surfaces immersed in saturated water at low vapor pressures. Finned surfaces with assorted fin spacing, fin thicknesses, and fin heights on a copper based surface have been investigated. All the finned surfaces were found to increase both boiling heat transfer coefficients and critical heat fluxes. An optimal fin thickness was found for a configuration, and heat transfer coefficients have been obtained at the pressures. Factors affecting the boiling characteristics have been identified and the optimal enhancement requires a balance of the active nucleation sites, bubble flow resistance, natural convection, thin film evaporation, liquid superheating, heat transfer area, bubble coalescence, and liquid reflux resistance. High speed visualization of vapor plug and vapor film generation on the boiling surfaces has revealed significant insights into the boiling mechanisms at low saturation pressures.

Accurate Determination of Surface Heat Fluxes During Quenching Characterized by Boiling Water Heat Transfer

Abstract Mathematical models play a critical role in design, optimization, and control of water quenching treatment in metals processing. Modeling these processes correctly is predicated on accurately characterizing the heat transfer at the product surface throughout the quench operation, usually with a boiling curve. These curves are most often generated from time-resolved subsurface temperature measurements carried out during quenching, although data analysis is complicated by the ill-posed nature of the underlying problem. This paper reviews the best experimental and analytical practices that have been developed for recovering the boiling water curve through an inverse heat conduction analysis.

Quantification of the Surface Temperature Discrepancy Caused by Subsurface Thermocouples and Methods for Compensation

In the study of boiling water heat transfer, temperature measurements via subsurface thermocouples are often used in conjunction with inverse heat conduction (IHC) models to evaluate the heat-transfer boundary conditions at the surface. It has been documented in previous studies that the presence of a subsurface thermocouple causes a disturbance in the local temperature field surrounding the thermocouple. If not accounted for, such discrepancies will lead to errors when evaluating the surface heat flux histories and surface temperatures via IHC models. A technique called the “equivalent depth” technique is proposed as a method to offset the location of the thermocouple and thereby compensate for the effect the thermocouple hole has on the measured temperature. Although the use of the equivalent depth technique results in the correct prediction of the surface heat flux without including the thermocouple hole in the IHC analysis, it does not allow the correct calculation of the surface temperature. This article outlines the simulations and procedure to derive a correlation to determine the correct surface temperature. By quantifying the surface temperature discrepancy between regions with thermocouples and regions without, a correlation is developed and can be used in conjunction with an IHC analysis to correctly predict the surface temperature. A verification of this technique for the characterization of the surface boundary condition using an IHC model with experimentally measured thermal history data is also presented.

Effect of Sample Start Temperature during Transient Boiling Water Heat Transfer

The influence of the initial sample start temperature (400 °C to 1000 °C) on the boiling water heat-transfer behavior during quenching of AISI 316 stainless steel plates has been examined. The study involved instrumenting 280-mm-diameter, 12.7-mm- (0.5- in.-) thick plates with seven subsurface thermocouples (TCs) placed at various locations across the diameter and spraying water onto the surface using a circular cone spray nozzle placed directly above the plate surface. The measured temperature-time history at each location was then input to a two-dimensional (2-D) axisymmetric inverse heat conduction (IHC) model so that the boiling curves for each test condition could be determined. The study has demonstrated that the initial sample temperature has a significant effect on the shape and magnitude of the boiling curve during transient cooling conditions. A simple method is proposed to approximately capture the influence of sample start temperature on transient boiling water behavior that alleviates the need to conduct multiple measurements.

Effect of Advanced Cooling Front (ACF) Phenomena on Film Boiling and Transition Boiling Regimes in the Secondary Cooling Zone during the Direct-Chill Casting of Aluminium Alloys

Accurate knowledge of the boundary conditions is essential when modeling the Direct-Chill (DC) casting process. Determining the surface heat flux in the secondary cooling zone, where the greater part of the heat removal takes place, is therefore of critical importance. Boiling water heat transfer phenomena are quantified with boiling curves which express the heat flux density as a function of the surface temperature. Compilations of boiling curves for the DC casting of aluminum alloys present a good agreement at low surface temperatures but a very poor agreement at higher surface temperatures, in the transition boiling and film boiling modes. Secondary cooling was simulated by spraying instrumented samples with jets of cooling water. Quenching tests were conducted first with a stationary sample, and then with a sample moving at a constant “casting speed” in order to better simulate the DC casting process. The ejection of the water film in quenching tests with a stationary sample and the relative motion between the sample and the water jets both lead to an Advanced Cooling Front (ACF) effect, in which cooling occurs through axial conduction within the sample rather than through boiling water heat transfer at the surface. The heat flux density and surface temperature were evaluated using the measured thermal history data in conjunction with a two-dimensional inverse heat conduction (IHC) model. The IHC model developed at the University of British Columbia was able to take into account the advanced cooling front effect. The effect of various parameters (initial sample temperature, casting speed, water flow rate) on the rate of heat removal in the film boiling and transition boiling regimes was investigated.

EFFECT OF WATER FLOW RATE, WATER TEMPERATURE, NOZZLE SIZE AND NOZZLE STAND-OFF DISTANCE ON THE BOILING WATER HEAT TRANSFER OF AISI 316 STAINLESS STEEL PLATE

During boiling water heat transfer, large non-linear variations in the rate of heat extraction at the surface of the component are experienced as its surface temperature changes during cooling. Many factors can impact on the rate of heat extraction and include factors related to the water and how it is delivered to the surface of the component. This study has examined the effect of water flow rate (0.63 to 3.15 L/s), water temperature (13 to 40 °C), stand-off distance or distance between the nozzle and surface of the sample (81 to 158 mm) and a large and small diameter cone spray nozzle on the boiling water behaviour during quenching of AISI 316 12.7 mm stainless steel circular plate samples. For the analysis, the measured temperature/time history at specific locations in the stainless steel plates was input to a 2- D axisymmetric Inverse Heat Conduction (IHC) model so that the boiling curves for each test condition could be determined.Lors de la transmission de chaleur de l’eau bouillante, de grandes variations non linéaires du taux d’extraction de chaleur à la surface de la pièce sont éprouvées à mesure que la température de sa surface change lors du refroidissement. Plusieurs facteurs peuvent influencer le taux d’extraction de chaleur, incluant les facteurs reliés à l’eau et la façon dont elle est délivrée à la surface de la pièce. Dans cette étude, on a examiné l’effet du débit d’eau (0.63 à 3.15 L/s), de la température de l’eau (13 à 40 °C), de la distance d’aspersion ou distance entre la buse et la surface de l’échantillon (81 mm à 158 mm) et d’une buse d’aspersion à cône de grand ou petit diamètre sur le comportement de l’eau bouillante lors de la trempe d’échantillons circulaires de 12.7 mm de tôle d’acier inoxydable AISI 316. Pour l’analyse, on a entré dans un modèle axisymétrique à 2-D “Conduction Thermique Inverse” [Inverse Heat Conduction (IHC)], l’histoire mesurée température–temps à des positions spécifiques des tôles d’acier inoxydable, de telle sorte que l’on pouvait déterminer les courbes d’ébullition de chaque condition d’évaluation.

Inverse determination of boundary conditions during boiling water heat transfer in quenching operation

Heat transfer equations describe in most general terms the relationship of temperature, time and space coordinates. In order to achieve a solution matching a given phenomenon, unicity conditions of the solution have to be determined. One of them is the heat transfer coefficient. In complex heat transfer processes, to which belong quenching operation, that coefficient is being determined experimentally or numerically.This paper presents a technique for identifying the local heat transfer coefficient when cooling hot bodies in water during quenching. A dynamic method was applied, using inverse solution of the heat transfer equation. In that solution, a temperature experimentally determined during sensor cooling is set in the equation. The paper presents the results of measurements and calculations as well as a discussion of results for various cooling conditions and positions of the active surface of the sensor.

Enhancement of Pool Boiling Heat Transfer in Water and Alcohol/Water Mixtures (Effect of Surface-active Agent)

Surface tension of alcohol/water mixtures has been measured over the whole fraction range and then it has been measured when a surface-active agent was added into the mixtures. The effect of the concentration of alcohol and the surface-active agent on surface tension was experimentally clarified, in order to gain base data related to enhancement of a heat transfer coefficient in the mixtures and water. The experiment has also been carried out to enhance the boiling heat transfer coefficients of water and alcohol/water mixtures on a horizontal heated fine wire at pressure of 0.1 Mpa by adding the surface-active agent into the tested liquid. As a result, the coefficients were enhanced in lower alcohol concentration (C≤O.5) and low heat flux range which is just after onset of boiling. It was also found that the enhancement effect by the surfactant disappears in concentrations over 1000 ppm. Finally, we clarified that the surface tension remarkably affects the heat transfer coefficients in nucleate pool boiling.

Flow Film Boiling Heat Transfer in Water and Freon-113.

Experimental apparatus and method for film boiling heat transfer measurement on a horizontal cylinder in forced flow of water and Freon-113 under pressurized and subcooled conditions were developed. The experiments of film boiling heat transfer from single horizontal cylinders with diameters ranging from 0.7 to 5 mm in saturated and subcooled water and Freon-113 flowing upward perpendicular to the cylinders were carried out for the flow velocities ranging from 0 to 1 m/s under system pressures ranging from 100 to 500 kPa. Liquid subcoolings ranged from 0 to 50 K, and the cylinder surface superheats were raised up to 800 K for water and 400 K for Freon-113. The film boiling heat transfer coefficients obtained were depended on surface superheats, flow velocities, liquid subcoolings, system pressures and cylinder diameters. The effects of these parameters were systematically investigated under wider ranges of experimental conditions. It was found that the heat transfer coefficients are higher for higher flow velocities, subcoolings, system pressures, and for smaller cylinder diameters. The observation results of film boiling phenomena were obtained by a high-speed video camera. A new correlation for subcooled flow film boiling heat transfer was derived by modifying authors' correlation for saturated flow film boiling heat transfer with authors' experimental data under wide subcooled conditions.