bluuebunny/crossref_metadata_2025 huggingface dataset:
Measurement of Concentration and Temperature Gradients at Binary Mixture Boiling Bubbles
Authors: Knauer Oliver S. , Braeuer Andreas , Lang Matthias C. , Leipertz Alfred
Published: March 2011

Due to the high heat flux available, nucleate boiling is one of the most utilized processes for the transfer of large amounts of heat in chemical or power engineering applications. Nevertheless, the basic physical phenomena of this kind of heat transfer are physically not well understood, especially for multi-component mixtures in which the heat transfer coefficient is a function of the mixture composition. To apprehend the binary mixture boiling phenomena, the knowledge of the composition and temperature field surrounding a boiling bubble near the heater surface is of great impact. These quantities are measured at individual boiling bubbles by means of laser-optical methods without disturbing the system and with high spatial resolution. An optical accessible and temperature adjustable boiling chamber for the generation of single bubbles of acetone-isopropanol mixtures was constructed. As the vapor-liquid equilibriums (VLE) of these mixtures show a large gap between the saturated liquid and vapor line, significant composition alterations occur during the phase transition. Concentration and temperature gradients have been measured along a line by linear Raman spectroscopy. Due to the species specific Raman shift and the linear superposition of the inelastic scattered light intensities, qualitative and quantitative composition information can be achieved. In alcohols, e.g. isopropanol, the molecules can develop hydrogen bonds, which have an impact on the shape of the O-H bind signal in the Raman spectrum. As the ratio of molecules with and without hydrogen bonds changes with temperature, the temperature of the liquid phase can be derived from the spectra as well. The results show an enhancement of isopropanol, the less volatile component, near the phase boundary due to preferential evaporation of acetone. Furthermore, a not expected depletion of isopropanol approximately 0.75 mm away from the bubble was measured. The detected temperature increases near the boiling bubble, indicating a heat transfer from the gas phase to the surrounding liquid. The temperature distribution also has a minimum at the same position as the isopropanol distribution. A species conservation calculation with simplified assumptions was carried out and validated the measured composition distribution in the liquid surrounding a boiling bubble.
Capillary Flow Separation in 2- and 3-Dimensional Laminar Falling Liquid Films
Authors: Dietze Georg F. , Kneer Reinhold
Published: March 2011

Due to the selective use of liquid films in specialized technical equipment (e.g. new generation nuclear reactors), a fundamental understanding of underlying momentum and heat transport processes inside these thin liquid layers (with a thickness of approximately 0.5 mm) is required. In particular, the influence of surface waves (which develop due to the film’s natural instability) on these transport processes is of interest. For a number of years, experimental and numerical observations in wavy falling liquid films have suggested that momentum and heat transfer in the capillary wave region, preceding large wave humps, undergo drastic modulations. Indeed, some results have indicated that upward flow, i.e. counter to the gravitational acceleration, takes place in this region. Further, evidence of a substantial increase in wall-side and interfacial transfer coefficients has also been noted. Recently, Dietze et al. [1,2] have established that flow separation takes place in the capillary wave region of 2-dimensional laminar falling liquid films, partially explaining the above mentioned observations. Thereby, it was shown that the strong third order deformation (i.e. change in curvature) of the liquid-gas interface in the capillary wave region causes an adverse pressure gradient sufficiently large to induce flow detachment from the wall. In the present paper, a detailed experimental and numerical account of the capillary flow separation’s kinematics and governing dynamics as well as its effect on heat transfer for two different 2-dimensional flow conditions is presented. Experimentally, velocity measurements (using Laser Doppler Velocimetry (LDV) and Particle Image Velocimetry (PIV)) and film thickness measurements (using a Confocal Chromatic Imaging technique) were performed in a specifically designed optical test setup. On the numerical side, simulations of the full Navier-Stokes equations as well as the energy equation using the Volume of Fluid (VOF) method were performed. In addition to the 2-dimensional investigations, the characteristics of capillary flow separation under 3-dimensional wave dynamics were studied based on the 3-dimensional numerical simulation of a water film, which was previously investigated experimentally by Park and Nosoko [3]. Results show that flow separation persists over a wide area of the 3-dimensional capillary wave region, with multiple capillary separation eddies occurring in the shape of vortex tubes. In addition, strong spanwise flow induced by the same governing mechanism is shown to occur in this region, which could explain the drastic intensification of transfer to 3-dimensional liquid films.
A Human Energy Balance Model With Clothing Effects for Estimating Human Thermal Comfort
Authors: Yoshida Atsumasa , Shimazaki Yasuhiro , Kinoshita Shinichi , Suzuki Ryota
Published: March 2011

There is an increased world attention on environmental issues with the global trend of environmental degradation. Especially thermal environment was highly concerned as human safety. We have been focused on creation of amenity environment with energy-saving way. This study is uncommonly dealing with human feeling for human thermal comfort, that is to say quantification of environment has been done. The feeling of comfort is mixed sense and can be totally easier to improve compared with straightforward way, and this may lead to energy and cost saving way of improvement. Moreover, this is human-oriented and can reflect humans’ wishes. Since thermal comfort index is useful tool for understanding the present state and evaluating the impact of countermeasures, effectiveness of human thermal load which is thermal comfort index based on energy balance of human body was examined. The human thermal comfort around the human body in outdoor is influenced by six dominant factors; air temperature, humidity, solar radiation, wind speed, metabolism and clothing. The difference between indoor and outdoor is expressed mainly as non-uniform and unsteady. Therefore, the unsteady responses of each dominant factors were examined and clarified human thermal load is quite good estimation of human thermal comfort. In steady state and even in unsteady state, thermal comfort can be obtained by using human thermal load on the whole. The reason is human thermal load consider the amount of physiology and also weather parameters. In the process of creating energy balance model of human, clothing material was deeply considered. For establishing better thermal environment, clothing material is of great use, because clothing material has an impact on thermal exchange between exterior environment and human body and more easy way to improve in 6 factors. The traditional treatment of clothing in human science was only resistance of heat transfer and this was not enough for all clothing effects. In daily life, effect of humidity exists and moisture property is required. Moreover color of material has impact on energy balance in clothing material. In order to show a way of better thermal environment, the heat and the moisture transfer coefficients on clothing material, radiative properties, and additional properties such as convection heat transfer coefficient were measured, and energy flow of clothing material was totally investigated. Finally, the effects of clothing material for human thermal comfort were predicted and this energy balance human model has become much better model.
An Overview: Analysis of Heat and Mass Transfer in Fractal Media by Fractal Geometry and Technique
Authors: Yu Boming
Published: March 2011

In the past three decades, fractal geometry and technique have received considerable attention due to its wide applications in sciences and technologies such as in physics, mathematics, geophysics, oil recovery, material science and engineering, flow and heat and mass transfer in porous media etc. The fractal geometry and technique may become particularly powerful when they are applied to deal with random and disordered media such as porous media, nanofluids, nucleate boiling heat transfer. In this paper, a summary of recent advances is presented in the areas of heat and mass transfer in fractal media by fractal geometry technique. The present overview includes a brief summary of the fractal geometry technique applied in the areas of heat and mass transfer; thermal conductivities of porous media and nanofluids; nucleate boiling heat transfer. A few comments are made with respect to the theoretical studies that should be made in the future.
Large Eddy Simulation of Turbulent Flow and Heat Transfer Characteristics in Rectangle Channel With Vortex Generators
Authors: Wen Juan , Yang Li , Qi Cheng Ying
Published: March 2011

The flow structures and heat transfer characteristics of rectangle channel with the new type of vortex generators are obtained using large eddy simulation (LES) and by the application of the hydromechanics software FLUENT6.3. The bevel-cut half-elliptical column vortex generators, which is one model of the passive heat transfer enhancement, are laid on the three-dimensional rectangle channel. The instantaneous characteristic and the variational law of various parameters, such as the velocity, the temperature, the pressure and the vorticity magnitude, is analyzed to find out the temperature stripe structure that is similar with the velocity stripe in the temperature field. A turbulent boundary layer interacting with the disturbance of the vortex generators, is investigated using a “coherent structure” type of approach. The coherent structure and the streak structure of turbulent boundary layer flow are showed and the characteristic of vortex induced by vortex generator and its influence on turbulent coherent structure are analyzed. The control of the coherent structure induced by vortex generator plays more important role in heat transfer enhancement and drag reduction. And this fow configuration is of interest in terms of both heat transfer and skin friction control. The result of simulation indicates that the turbulence coherent structure directly affects the temperature gradient at the wall and the heat transfer enhancement mechanism of vortex generator is explained. Then we can seek suitable form of vortex generator and structure parameters, in order to achieve enhanced heat transfer and flow of drag reduction.
Optimized Utilization of Liquefied Natural Gas (LNG) Cold Energy
Authors: Si Hongyu , Mei Ning , Wang Xiaoyan
Published: March 2011

There is possibility of the effective utilization of the cold energy in the process of LNG vaporization. The purpose of this paper is to propose a cascade utilization scheme to recycle LNG cold energy on the basis of comprehensively considering of thermophysical and actual factors. The optimized utilization scheme includes three cascade grades: separating the air with the deep-cool cold, the cold storage as the second grade, generating power as the last one. This scheme not only pays attention to the thermophysical rationality, but also considers of the fittingness between two cascade grades. This scheme overall considers the theoretic rationality and the actual feasibility. But basing on the principle of adaptation to local conditions, we should comprehensively consider all factors and the process ought to match the circumambient industry. This paper provides crucial references for optimized utilization of LNG cold energy.
Experimental Study on Cooling-Air Grinding for 40Cr
Authors: Zhang Hua , Liu Yefeng , Chen Xi , Zhao Huanhuan , Cai Yulin , Yao Jun , Huang Haitao , Zhu Dairu
Published: March 2011

Cooling-air grinding is one of important green grinding. Cooling-air grinding performances for 40Cr are test in this paper using cooling-air generator. Main performance influencing factors are test and analyzed, such as air temperature, wheel granularity, amount of feed and so on. Cooling-air grinding results shows that roughness of surface of test pieces can reach precise grinding standard. So cooling-air grinding can replace traditional grinding in this experiment. This study for the promotion of cooling-air grinding application technology has important significance for reference.
Analysis of Local Heat Transfer in Direct Fired Rotary Kilns
Authors: Herz Fabian , Sonavane Yogesh , Specht Eckehard
Published: March 2011

Heat transfer in the rotary kiln is a complex phenomenon due to the different modes of heat transfer. In the first part of this study, the local heat transfer coefficients are analysed theoretically, to describe the heat transfer mechanisms in the cross section of the rotary kiln. Furthermore, the axial solid motion along the length of the kiln is considered in the local surfaces which exchanges the heat. A pilot plant drum of length 0.45 m and internal diameter of 0.6 m has been designed and fabricated to measure the contact heat transfer coefficient from the kiln wall to the covered solid bed. The cylinder is heated continuously by means of three electrical heaters fixed externally around the cylinder at various positions. K-type thermocouples have been used to measure the wall and solid bed temperature along the circumferential and the radial direction. Experiments are performed with various materials such as Quartz sand and Copper pellets of different size, shape and thermal conductivity. The effect of the material properties, the rotational speed (1–6 rpm) and the filling degree (10–20%) on the contact heat transfer have been studied thoroughly.
Application of Water-Cooled Air-Conditioning for High-Rise Residential Buildings
Authors: Chen Hua , Di Qianqian
Published: March 2011

To improve the applicability of water-cooled air-conditioners in the domestic sector, the development of a prediction model for energy performance analysis is needed. This paper addressed the development of an empirical model for predicting the operation performance and the annual energy consumption for the use of water-cooled air-conditioners. An experimental prototype was set up and tested in an environmental chamber in validating the empirical model. The predictions compared well with the experimental results. Furthermore, a high-rise residential building whole-year energy consumption simulation on applications of water-cooled air conditioners in South china was also analyzed. The results show 20.4% energy savings over air-cooled units while the increase in water-side consumption is 31.1%. The overall energy savings were estimated at 16.2% when including the additional water costs.
Numerical Analysis of Natural Convection of Suspension With Particle Sedimentation
Authors: Asaoka Tatsunori , Okada Masashi , Teraoka Yoshikazu , Tsumura Akihiro
Published: March 2011

A new method for the numerical analysis of natural convection of suspension was proposed. Natural convection phenomena of suspension appear in some industrial fields, such as water disposal process and food engineering process. It is difficult to comprehend the behavior of the natural convection of the suspensions, because the convection of the suspension is caused by the interactive effects of the temperature distribution and particle-concentration distribution in the suspension. In this study, a numerical model for the natural convection phenomena of the suspension accompanied by particle sedimentation was constructed. In this model, since the limited number of particles is tracked individually, the movement of each particle which has varied sizes can be achieved. Then the effect of distribution of particle size on the particle-concentration in the suspension can be considered. As a result, it was confirmed that the typical behavior of the natural convection of suspension can be expressed by using this model. Additionally, it was found that the mean Nusselt number of the natural convection of the suspension obtained by using this model shows the same tendency as that of the previous experiments.
Nusselt Number Data Scattering in Natural Convection in Porous Media
Authors: Vadasz Peter
Published: March 2011

Analytical solutions derived in this paper confirm the experimental and numerical results revealing widespread Nusselt number data scattering in natural convection in porous media. The weak non-linear method of solution is used to evaluate the Nusselt number in a porous layer heated from below and subject to weak boundary and domain imperfections. Little attention has been paid so far to the effect that the lower branch of the imperfect bifurcation has on the average Nusselt number. The results presented in this paper demonstrate the latter effect and explain the reason behind the scattering of data. The comparison of the results with existing experimental and numerical data confirms the findings. In addition the latter effect is shown to be essential in ones ability to control heat transfer enhancement via natural convection in porous metal foams, for example.
Thermal Radiation From the Zone of Melt-Water Interaction: Computational Model and Some Numerical Results
Authors: Dombrovsky Leonid A. , Davydov Mikhail V.
Published: March 2011

This paper is concerned with numerical modeling of thermal radiation from the zone of interaction of a melt jet with a water pool. This particular problem is a part of the analysis of complex interaction of the core melt with water in the case of a hypothetical severe accident in light-water nuclear reactors. The energetic contribution of thermal radiation has been studied in some details in recent papers by the authors. In the present paper, we focus on a solution related with possible optical diagnostics of the physical parameters of the process. This diagnostics can be based on comparison of the measured and calculated thermal radiation in the small-scale laboratory experiments. The sensitivity of the numerical data to some important parameters of the computational model is expected to be important to validate and improve the multiphase flow model. The radiation transfer model employed is based on the transport approximation. The numerical procedure includes ray-tracing calculations in the range of water semi-transparency with a source function determined using the large-cell radiation model. It is shown that the visible radiation of the interaction zone contains important information on the process parameters and these parameters might be identified on the basis of the developed computational procedure for the direct problem.
Microporous Layer Consisting of Alternating Porous Material With Different Wettability for Controlling Moisture in Gas Diffusion Layer of PEFC
Authors: Utaka Yoshio , Hirose Ikunori
Published: March 2011

The oxygen transfer characteristics of the gas diffusion layer are closely related to the cell performance of a polymer electrolyte fuel cell. In this study, a new hybrid gas diffusion layer is proposed in which two porous media with different wettabilities are arranged alternately for augmentation of the oxygen diffusivity in the gas diffusion layer. Since the movement of water from hydrophobic to hydrophilic media due to the difference in capillary pressure, the oxygen diffusion paths in the porous media can be maintained. The oxygen diffusion characteristics with respect to water saturation were measured using an experimental apparatus that uses a galvanic battery oxygen sensor as an oxygen absorber. The experimental results demonstrate that the hybrid structure has superior oxygen diffusion characteristics than a conventional gas diffusion layer with a single porous material with moisture. That is, the effective oxygen diffusivity of the hybrid configuration was almost five times larger than that of the single type at water saturation S = 0.2.
Combined Experimental and Numerical Study for Multiple Microchannel Heat Transfer System
Authors: Zhang Jingru , Jaluria Yogesh , Zhang Tiantian , Jia Li
Published: March 2011

Multiple microchannel heat sinks for potential use for electronic chip cooling are studied experimentally and numerically to characterize their thermal performance. The numerical simulation is driven by experimental data, which are obtained concurrently, to obtain realistic, accurate and validated numerical models. The ultimate goal is to design and optimize thermal systems. The experimental setup was established and liquid flow in the multiple microchannels was studied under different flow rates and heat influx. The temperature variation versus time was recorded by thermocouples, from which the time needed to reach steady state was determined. Temperature variations under steady state conditions were compared with three-dimensional steady state numerical simulation for the same boundary and initial conditions. The experimental data served as input parameters for the validation of the numerical model. In case of discrepancy, the numerical model was improved. A fairly good agreement between the experimental and simulation results was obtained. The numerical model also served to provide input that could be employed to improve and modify the experimental arrangement.
Ballistic-Diffusive Heat Conduction Model
Authors: Xu Mingtian , Cheng Lin
Published: March 2011

In the present work, the heat flux and high order fluxes as well as their time derivatives are taken as independent variables and a new type of extended irreversible thermodynamics is developed. In the framework of this extended irreversible thermodynamics, the size dependence of the effective conductivity is investigated and a generalized single phase lagging heat conduction model including the size effect is established. Theoretically, it covers the diffusive to ballistic regime of heat conduction. The comparison with the experimental and theoretical results of silicon nanowires and thin films shows a good agreement in nano-scale regime.
Numerical Investigation and Thermodynamic Analysis on a Novel Regular Hexagonal Plate Heat Exchanger
Authors: Du Wenjing , Wang Fei , Xin Gongming , Zhang Shihu , Cheng Lin
Published: March 2011

In conventional Plate Heat Exchangers (PHEs), a good heat transfer performance is usually obtained at the cost of much pumping power consumption. In order to address this dilemma, a novel Regular Hexagonal Plate Heat Exchanger (RHPHE) is proposed in this paper. Specially-shaped spherical ribs and quasi-spiral flow paths are designed on plates with the purpose of achieving a best trade-off between the heat transfer and fluid flow performance. Because of its regular hexagonal structure with 3 inlets and 3 outlets, three or at least two kinds of fluids with different temperatures can exchange heat in a single set of heat exchanger. It is an innovation that multiple fluids heat transfer in a PHE without the assistance of supplementary baffles. Numerical investigation is carried out on the RHPHE and water is the working fluid. The heat transfer and flow performance of the RHPHE in a series of working conditions are investigated. Results show that heat transfer coefficient per unit pressure drop of the RHPHE is much better than that of the widely accepted PHE with 60° chevron corrugations. Also studied is the influence of various combinations of inlet and outlet positions on heat transfer and fluid flow performance. For the thermodynamic analysis, the entropy generation caused by heat conduction under finite temperature difference and fluid friction is obtained numerically. The variation of the entropy generation number with respect to the Reynolds number is depicted, which provides reference for the future optimization design of the RHPHE.
The New Method for Simulation of Bulk Condensation of Supersaturated Vapor
Authors: Kortsenshteyn N. M. , Yastrebov A. K.
Published: March 2011

The method of direct numerical solution of the kinetic equation for the droplet size distribution function is presented. This new method which is not restricted by the Knudsen number was developed using the analogy with a similar method of solution of the Boltzmann kinetic equation. The simulation of vapor behavior at fast creation of supersaturation state in vapor-gas mixture by means of adiabatic expansion was carried out for the verification of the method. The results obtained by this method were compared with those which were obtained by using the method of moments over a broad range of Knudsen number. The effect of the interphase heat transfer and dependence between saturation pressure and droplet size on the dynamics of condensation relaxation was studied.
Heat Transfer to a Ducted, Semiconfined Impinging Synthetic Air Jet
Authors: Rylatt Daniel , O’Donovan Tadhg S.
Published: March 2011

Heat transfer to confined impinging synthetic air jets is investigated experimentally. The influence of ducting on the cooling performance of synthetic air jets is of particular interest. Heat transfer to the jets is reported for a wide range of experimental parameters including nozzle to impingement surface spacings (0.5 to 5 jet diameters), Reynolds numbers (2000, 3000 and 4000) and non-dimensional Stroke lengths, L0/D (10 15 and 20 respectively). A range of ducting outlet sizes were also investigated (1, 1.2, 1.4 jet diameters). It has been found that ducting can have the effect of reducing the turbulent mixing of the flow but overall enhances the rate of heat transfer to the jet at low H/D < 2. The largest ducting outlet of 1.4 jet diameters has also been shown to outperform the others across the whole range of variables tested.
Predicting the Phonon Properties of Carbon Nanotubes Using the Spectra Energy Density
Authors: Thomas J. A. , Turney J. E. , Iutzi R. M. , McGaughey A. J. H. , Amon C. H.
Published: March 2011

Thermal transport by phonons in water/carbon nanotube (CNT) composite systems is investigated using molecular dynamics (MD) simulation. We calculate the spectral energy density of empty and water-filled CNTs and use it to extract the mode-specific phonon group velocities, relaxation times, and thermal conductivities. The total thermal conductivity predicted from the spectral energy density is consistent with what we predict using a direct application of the Fourier law in an MD simulation. The number of atoms and simulation runtime required to predict the spectral energy density, however, are both at least one order-of-magnitude smaller.
Experimental Investigation of Micro-Scale Heat Transfer at an Evaporating Moving 3-Phase Contact Line
Authors: Ibrahem K. , Abd Rabbo M. F. , Gambaryan-Roisman T. , Stephan P.
Published: March 2011

An experimental study is conducted to investigate the micro-scale heat transfer at an evaporating moving 3-phase contact line. The moving evaporating meniscus is formed by pushing or sucking a liquid column of HFE7100 in a vertical channel of 600 μm width using a syringe pump. The gas atmosphere is pure HFE7100 vapor. This channel is built using two parallel flat plates. A 10 μm thick stainless steel heating foil forms a part of one of the flat plates. Two-dimensional micro-scale temperature field at the back side of the heating foil is observed with a high speed infrared camera with a spatial resolution of 14.8 μm × 14.8 μm and an in-situ calibration procedure is used at each pixel element. A high speed CMOS camera is used to capture the shape of the moving meniscus, the images are post-processed to track the free surface of the meniscus. Local heat fluxes from the heater to the evaporating meniscus are calculated from the measured transient wall temperature distributions using an energy balance for each pixel element. In the vicinity of the 3-phase contact line the heat flux distribution shows a local maximum due to high evaporation rates at this small region. The local maximum heat flux at the 3-phase contact line area is found to be dependent on the input heat flux, the velocity and the direction of the meniscus movement. The results give detailed insight into the specific dynamic micro-scale heat and fluid transport process.
Experimental Study of Flow Boiling Heat Transfer Coefficient of FC-72 Over Micro-Pin-Finned Surfaces
Authors: Xue Y. F. , Yuan M. Z. , Wei J. J.
Published: March 2011

Experiments of flow boiling heat transfer coefficient of FC-72 were carried out over simulated silicon chip of 10×10×0.5 mm3 for electronic cooling. Four kinds of micro-pin-fins with the dimensions of 30×60, 30×120, 50×60, 50×120 μm2 (thickness, t × height, h) respectively, were fabricated on the chip surfaces by the dry etching technique to enhance boiling heat transfer. A smooth chip was also tested for comparison. The experiments were conducted at three different fluid velocities (0.5, 1 and 2m/s) and three different liquid subcoolings (15, 25 and 35K). All micro-pin-finned surfaces show a considerable heat transfer enhancement compared to the smooth surface. Both the forced convection and nucleate boiling heat transfer contribute to the total heat transfer performance. The contribution of each factor to the total heat transfer has been clearly presented in the flow boiling heat transfer coefficient curves. In a lower heat flux region, the heat transfer coefficient increases greatly with increasing fluid velocity, but increases slightly with increasing heat flux, indicating that the single-phase forced convection dominates the heat transfer process. With further increasing heat flux to the onset of nucleate boiling, the heat transfer coefficient increases remarkably. For a given liquid subcooling, the curves of flow boiling heat transfer coefficient at fluid velocities of 0.5 and 1 m/s almost follow one line for each surface, showing insensitivity of nucleate boiling heat transfer to fluid velocity. However, at the largest fluid velocity of 2 m/s, the slope of the flow boiling heat transfer coefficient curves for micro-pin-finned surfaces becomes smaller, indicating that the forced convection also plays an important role besides the nucleate boiling heat transfer. The curves of the flow boiling heat transfer coefficient can be used to determine the boiling incipience at different fluid velocities, which provides a basis for the suitable fluid velocity selection in designing highly efficient cooling scheme for electronic devices.
Effect of Metallic Ion on the Formation of Calcium Carbonate Fouling
Authors: Zou Yong , Zhao Liang , Xin Gongming , Cheng Lin
Published: March 2011

Calcium carbonate (CaCO3) is the most common fouling adhering on the surface of heat exchanger. But metallic ion in natural water could affect the crystalline type of calcium carbonate. In this study, the effect of sodium ion, magnesium ion and aluminum ion on crystalline type and morphology of CaCO3 were reported. The experimental results indicate that the addition of sodium ion has no obvious role for changing the crystalline type of CaCO3, only calcite was obtained and the lattice parameter of calcite has a little variation depending on the concentration of sodium ion. However, the addition of magnesium and aluminum ion prompts obviously the formation of aragonite. In order to clarify the mechanism about the effect of metallic ion on lattice stability of calcium carbonate, the energies and electronic structures for the calcite with sodium, magnesium or aluminum inclusion have been determined from first-principle calculations. The calculated results indicate magnesium and aluminum inclusion has more effects on the stability of calcite than that of sodium inclusion.
Effect of Surface Conditions on the Adhesion of Crystallization Fouling
Authors: Zou Yong , Liu Yida , Xin Gongming , Liu Wen , Cheng Lin
Published: March 2011

In this study, effects of surface conditions in terms of surface roughness and oxide layer, on adhesion of crystallization fouling on heat transfer surfaces were investigated. The experimental results showed that the surface roughness has no obvious effect on the adhesion of crystallization fouling. The polished sample did not present better anti-fouling properties compared to other rough samples. While the formation of Fe2O3 layer on the surface is proved to be able to accelerate the adhesion of calcite fouling with hexagonal structure, because there are similar crystalline structure and lattice parameter between the Fe2O3 and calcite fouling. Therefore, in order to improve the anti-fouling property of heat transfer surfaces, inhibiting the formation of oxide layer is more important than efforts to improve surface roughness.
Fuel Droplet Heating and Evaporation: New Hydrodynamic and Kinetic Models
Authors: Sazhin Sergei S. , Shishkova Irina N. , Gusev Ivan G. , Elwardany Ahmed , Krutitskii Pavel , Heikal Morgan
Published: March 2011

Recently developed approaches to the hydrodynamic and kinetic modelling of fuel droplet heating and evaporation are reviewed. Two new solutions to the heat conduction equation, taking into account the effect of the moving boundary during transient heating of an evaporating droplet, are discussed. The first solution is the explicit analytical solution to this equation, while the second one reduces the solution of the differential transient heat conduction equation to the solution of the Volterra integral equation of the second kind. It has been pointed out that the new approach predicts lower droplet surface temperatures and slower evaporation rates compared with the traditional approach. A simplified model for multi-component droplet heating and evaporation, based on the analytical solution of the species diffusion equation inside droplets, is discussed. A new algorithm, based on simple approximations of the kinetic results for droplet radii and temperatures, suitable for engineering applications, is discussed.
Single-Phase Heat Transfer and Pressure Drop of Water Cooled Inside Horizontal Smooth Tubes in the Transitional Flow Regime
Authors: Meyer Josua P. , Liebenberg Leon , Olivier Jonathan A.
Published: March 2011

Heat exchangers are usually designed in such a way that they do not operate in the transition region. This is usually due to a lack of information in this region. However, due to design constraints, energy efficiency requirements or change of operating conditions, heat exchangers are often forced to operate in this region. It is also well known that entrance disturbances influence where transition occurs. The purpose of this paper is to present experimental heat transfer and pressure drop data in the transition region for fully developed and developing flows inside smooth tubes using water as the working fluid. The use of different inlet disturbances were used to investigate its effect on transition. A tube-in-tube heat exchanger was used to perform the experiments, which ranged in Reynolds numbers from 1 000 to 20 000, with Prandtl numbers being between 4 and 6 while Grashof numbers were in the order of 105. Results showed that the type of inlet disturbance could delay transition to a Reynolds number as high as 7 000, while other inlets expedited it, confirming results of others. For heat transfer, though, it was found that transition was independent of the inlet disturbance and all commenced at the same Reynolds number, 2 000–3 000, which was attributed to secondary flow effects.
Heat Transfer During Condensation Inside Small Channels: Applicability of General Correlation for Macrochannels
Authors: Shah Mirza Mohammed
Published: March 2011

Prediction of heat transfer during film condensation in mini and microchannels is of much practical interest. No well-verified method for this purpose is available. The applicability of the author’s well-validated general correlation (Shah 2009) for condensation in tubes to small channels is investigated in this paper. A wide range of data for condensation in horizontal micro and mini channels were compared with it. This correlation was found to predict 500 data points from 15 studies on small diameter channels with a mean deviation of 15.9 percent. These data included single round and rectangular channels as well as multiport channels with round and rectangular ports with equivalent diameters from 0.49 to 5.3 mm, 8 fluids, reduced pressures from 0.048 to 0.52, and mass flux from 50 to 1400 kg/m2s. This indicates its applicability to minichannels. However, a large amount of data for diameters from 0.114 to 2.6 mm showed large deviations from this correlation. The discrepancy in the overlapping range of data could be due to difficulties in accurate measurements on small channels.
Experimental Investigation by IR-Thermography of Heat Transfer Over Rib-Roughened Surfaces
Authors: Fustinoni Damiano , Niro Alfonso
Published: March 2011

This paper presents experimental results on convective heat transfer of air flows over a not-thin plate with different rib-roughness patterns; data over a flat plate are also reported for comparisons. The paper first reviews the technique principles, the experimental setup, and the data processing to recover heat transfer characteristics from IR-thermographic images. Then, thermal performances of three differently ribbed surfaces, namely, with ribs tilted of 90° and 60° angles over flow direction, as well as with 60° V-shape ones are presented and discussed. In all the configurations, the plate is 200 mm long and 150 mm wide, whereas ribs have a square cross-section with 3-mm side, and a corrugation-pitch to rib-side ratio of 13.3. Air flows at room temperature with speed ranging from 2.3 to 11.6 m/s, corresponding to Reynolds numbers at the end of the heated-length between 50000 and 250000, and for a heat flux of near 650 W/m2. For all three enhanced surfaces, the average Nusselt number over the plate horizontal midline shows the same dependence on the Reynolds number as the flat plate, but its values are from 50% to 130% higher with slight differences between the different tested configurations.
Application of Pulsed Spark Discharge for Mitigation of Mineral Fouling in a Heat Exchanger
Authors: Yang Yong , Kim Hyoungsup , Jung Jin M. , Fridman Alexander , Cho Young I.
Published: March 2011

One of the challenges in the production of electricity is the cooling water management because the calcium content in circulating cooling water continues to increase with time as pure water evaporates. Thus, the excessive mineral contents in water circulation systems could cause severe fouling in heat transfer equipment. To avoid the catastrophic failure in condensers, the cooling water is discharged after 3 cycles at a rate of 10 million gallons a day in a 1,000-MW thermoelectric power plant. The present study investigated the effect of pulsed spark discharges on the mitigation of mineral fouling in a concentric counterflow heat exchanger. Artificial hard water with calcium carbonate hardness ranging from 250 to 500 ppm was used with velocity varying over a range of 0.1–0.5 m/s and zero blowdown. Fouling resistances decreased by 50–88% for the plasma treated cases compared with the values for no-treatment cases. SEM photographs showed particle with larger sizes for the plasma treated cases comparing to smaller but more organized particles for the no-treatment cases. The different structures of particles were associated with pulsed spark discharge assisted precipitation of calcium carbonate in oversaturated hard water. X-ray diffraction data showed calcite crystal structures for all cases.
Investigation of Flow and Mass Transfer on a Flat Plate Downstream of a Shear Inducing Moving Wall
Authors: Ghosh Kalyanjit , Goldstein R. J.
Published: March 2011

The effects of an opposing (upstream-moving) wall-shear on a two-dimensional turbulent boundary layer are investigated. The shear at the boundary is imparted by a moving belt, flush with the wall. Boundary layer measurements are reported for four surface-to-freestream velocity ratios (0, −0.38, −0.51, −0.63) with the Reynolds number (based on the momentum thickness) between 922 and 1951. Velocity profiles downstream of the moving surface show an increased velocity deficit near the wall, which is more pronounced at higher (negative) belt velocity. Streamwise turbulence values downstream of the belt show the growth of a second peak in the logarithmic region of the boundary layer in addition to the normally-observed peak in the buffer region. This suggests the presence of larger length-scale turbulent eddies at locations away from the wall in the boundary layer. Spectral measurements indicate that the turbulent energy content is distributed over a wide portion of the logarithmic region. Mass transfer measurements using naphthalene sublimation provide the variation of Stanton with Reynolds number on the plate downstream of the moving belt. It shows little difference from the stationary belt case, which suggests that increased wall turbulence is balanced by an increase in the boundary layer thickness.
Natural Convection Ventilation in Fully Open Enclosures
Authors: Nateghi Morteza , Armfield Steven W.
Published: March 2011

The present study is concerned with natural convection ventilation in a two dimensional fully open enclosure (cavity) with thermally stratified ambient for both transient and steady-state flow. The left hand vertical wall of the enclosure is heated and the right hand facing boundary is open, with the top and bottom boundaries insulated. The numerical solutions will be obtained by solving the Navier-Stokes equations and the temperature transport equation on a non-staggered grid using an unsteady second-order finite-volume scheme with a pressure correction equation used to simultaneously provide an update for the pressure field and enforce the divergence free condition. Results will be presented for Rayleigh numbers in the range 1 × 105 to 1 × 1010 with Prandtl numbers in the range 0.2 to 1.0. It will be shown that the flow transits from steady to unsteady, at full development, with increasing Rayleigh number for Pr <= 1.0, as observed for the similar closed enclosure flow. For higher Prandtl numbers the flow is steady at full development for the full range of Rayleigh numbers considered, again as for the similar fully closed enclosure. Streamline and temperature contour plots will be presented to illustrate the basic flow behaviours and to demonstrate the effect of the Prandtl number.
Airside Performance of Wavy Fin-and-Tube Heat Exchangers: Data With Larger Diameter Tube
Authors: Lo Huau Pao , Hung Chinghua , Wang Chi-Chuan
Published: March 2011

This study examines the airside fin-and-tube heat exchangers having a larger diameter tube Dc = 16.59 mm) with the tube row ranging from 1 to 16. It is found that the effect of tube row on the heat transfer performance is quite significant, and the heat transfer performance deteriorates with the rise of tube row. The performance deteriorates with the rise of tube row. The performance drop is especially pronounced at the low Reynolds number region. Actually more than 85% drop of heat transfer performance is seen for Fp ∼ 1.7 mm as the row number is increased from 1 to 16. Upon the influence of tube row on the frictional performance, an unexpected row dependence of the friction factor is encountered. The effect of fin pitch on the airside performance is comparatively small for N = 1 or N = 2. However, a notable drop of heat transfer performance is seen when the number of tube row is increased, and normally higher heat transfer and frictional performance is associated with that of the larger fin pitch.
Study on a Cooling System for a Concentrating Photovoltaic Module
Authors: Do Kyu Hyung , Kim Tae Hoon , Kim Sung Jin , Jang Seok Pil
Published: March 2011

A concentrating photovoltaic (CPV) module, which mainly consists of optical concentrator or collector, solar cell, cooling system, can produce electricity from sunlight at a lower cost than conventional photovoltaic system by the replacement of expensive photovoltaic area with less expensive concentrating mirrors or lenses. However, concentration of sunlight onto photovoltaic cells causes the cell temperature to rise unless the heat is efficiently dissipated to the environment. Therefore, a cooling system is an essential part to prevent both short-term and long-term degradation of the CPV module. In this paper, a cooling system which consists of a heat spreader and a natural convective heat sink is proposed. Based on the previous studies, the heat spreader and the natural convective heat sink are designed. Experimentally, the thermal performance of the proposed cooling system is evaluated. Also, the effect of an inclined angle on the thermal performance of the natural convective heat sink is investigated. Finally, the proposed cooling system satisfies design constraints for well operating the CPV module for energy harvesting.
Thermal Analysis in Phase Change Materials (PCMs) Embedded With Metal Foams
Authors: Tian Y. , Zhao C. Y.
Published: March 2011

The heat transfer enhancement for phase change materials (PCMs) has received increasing attention nowadays, since most of PCMs have low thermal conductivities which prolong the charging and discharging processes. Metal foams, as a sort of novel material with high thermal conductivity, are believed to be a promising solution to enhance the heat transfer performance of PCMs for thermal energy storage systems. The effects of natural convection on heat transfer enhancement for PCMs embedded with metal foams are investigated in this paper. The numerical investigation is based on the two-equation non-equilibrium heat transfer model, where the coupled heat conduction and natural convection in PCMs are considered at phase transition and liquid zones. The numerical results are validated by experimental data. In order to investigate the effect of metal foams on heat transfer, two different cases are compared in this study, which are the Case A (PCMs embedded with metal foams) and the Case B (pure PCMs). At the solid zone, heat conduction plays a dominant part because of natural convection’s absence, thus metal foams achieve much higher heat conduction rate than pure PCMs, and this can be attributed to the high thermal conductivity of metal foams skeleton and the heat can be quickly transferred through the foam solid structure to the whole domain of PCMs. At the two-phase zone and liquid zone, natural convection takes place and becomes the dominant heat transfer mode, but metal foam structures suppress the natural convection inside the PCMs owing to big flow resistance in metal foams. In spite of this suppression caused by metal foams, the overall heat transfer performance of Case A is still superior to the counterpart of Case B (pure PCMs), implying the enhancement of heat conduction offsets or exceeds the natural convection loss. The results show that the heat transfer enhancement due to the natural convection in PCMs embedded with metal foams is not as strong as expected, since metal foams have big flow resistance and the natural convection is suppressed. It also shows that better heat transfer performance can be achieved by using the metal foams of smaller porosity and bigger pore density. Last but not least, a series of detailed velocity and temperature profiles are given through numerical solutions, in order to present a vivid evolution of flow field and temperature profiles in the whole melting process.
Visual Observation of Fine-Scale Mixing Morphology During Vapor Explosion and Droplet Entrapping Processes
Authors: Furuya Masahiro , Arai Takahiro
Published: March 2011

The successive stages of vapor explosion were video-framed with an exposure time of 500 ns. In order to attain good repeatability and visibility, a smooth round water droplet was impinged onto a molten alloy surface. This configuration suppresses pre-mixing process prior to triggering of vapor explosion. The cluster of bubble generated by spontaneous bubble-nucleation covered the whole contact area at 0.1 ms after the impingement. Prominent fine mixing between two liquids were found to start at 0.6 ms that resulting in vapor explosion. Droplet entrapping phenomenon frequently occurred on an oxide layer, since coherent mixing was prevented due to unevenly formed oxide layer.