bluuebunny/crossref_metadata_2025 huggingface dataset:
A Correlation for Nusselt Number Under Turbulent Mixed Convection Using Transient Heat Transfer Experiments
Authors: Gnanasekaran N. , Balaji C.
Published: March 2011

This paper reports the results of an experimental investigation of transient, turbulent mixed convection in a vertical channel in which one of the walls is heated and the other is adiabatic. The goal is to simultaneously estimate the constants in a Nusselt number correlation whose form is assumed a priori by synergistically marrying the experimental results with repeated numerical calculations that assume guess values of the constants. The convective heat transfer coefficient “h” is replaced by the Nusselt number (Nu) which is then assumed to have a form Nu = a (1+RiD) b ReDc where a, b and c are the constants to be evaluated. From the experimentally obtained temperature time history and the simulated temperature time history, based on some guess values of a, b, and c, one can define the objective function or the residue as the sum of the square of the difference between experimentally obtained and simulated temperatures. Using Bayesian inference driven by the Markov chain Monte Carlo method, one, more or all of the constants a, b and c are retrieved together with the uncertainty involved in these estimates. Additionally, the estimated parameters are compared with experimental benchmarks.
Influence on Convection Heat Transfer of Unsteady Flow in a Tube
Authors: Chen Lei
Published: March 2011

Turbulent convection heat transfer with monotonously time-increasing mass flux in a tube with consideration of variable thermophysical properties was investigated numerically. The turbulent heat transfer model was based on the equation of eddy shear stress and for unsteady process. The numerical calculations were compared with experimental data. It is shown that the basic features of the processes discussed in the present paper are the same as for the fluids with constant properties investigated earlier. However variable thermophysical properties increase the transient effects especially at high temperature factors.
Similarity Theory Including Variable Property Effects: A Complex Benchmark Problem
Authors: Jin Y. , Herwig H.
Published: March 2011

An asymptotic computational method (ACFD) to account for variable property effects is applied to a complex benchmark geometry. The method is based on the Taylor series expansion of all properties with respect to temperature and provides general results, applicable to specific problems with different fluids and heating rates. It can take into account the temperature dependence of all physical properties involved in momentum and heat transfer problems. The benchmark is a room which is ventilated by forced convection through inlet and outlet slit nozzles at the top and bottom of the side walls. Four heating elements standing on the ground floor add heat with constant heat flux density of variable strength. CFD solutions with the full coverage of all property temperature dependencies of air and SF6 are compared with the general ACFD results, applied to these fluids.
Earth-Air and Earth-Water Heat Exchanger Design for Ventilation Systems in Buildings
Authors: De Paepe Michel , T’Joen Christophe , Janssens Arnold , Steeman Marijke
Published: March 2011

Earth-air heat exchangers are often used for (pre)heating or (pre)cooling of ventilation air in low energy or passive house standard buildings. Several studies have been published in the passed about the performance of these earth-air heat exchangers [1–8]. Often this is done in relation to the building energy use. Several software codes are available with which the behaviour of the earth-air heat exchanger can be simulated. De Paepe and Janssens published a simplified design methodology for earth-air heat exchangers, based on thermal to hydraulic performance optimisation [7]. Through dynamic simulations and measurements it was shown that the methodology is quite conservative [9–10]. Hollmu¨ller added an earth-air heat exchanger model to TRNSYS [11]. In stead of using earth-air heat exchangers, earth-water heat exchangers are now getting more attention. In this system the ventilation air is indirectly cooled/heated with the water flow in a fin-tube heat exchanger in the inlet of the ventilation channel. The water-glycol mixture transfers heat with the earth by flowing through e.g. a polyethylene tube. In the second part of this paper a design methodology is first derived and then applied to this type of system.
Temperature Field Prediction of a Multilayered Composite Pipeline Based on the Particle Filter Method
Authors: Vianna Flavio L. V. , Orlande Helcio R. B. , Dulikravich George S.
Published: March 2011

Thermal management of subsea oil production systems in deep water environments is one of the main issues for petroleum exploitation operations. Thermal monitoring is crucial to avoid and control the formation of solid deposits, which in adverse operating conditions can result in blockages inside the production systems and consequently incur large financial losses. This paper aims to demonstrate the robustness of a Bayesian approach for accurate estimation of the produced fluid temperature field in a typical multilayered composite pipeline. The physical problem consists of a pipeline represented by a circular domain filled by a stagnant fluid (petroleum) with temperature dependent thermal properties, which is bounded by a multilayered composite pipe wall. The mathematical model governing the heat conduction problem in the multilayered wall and in the stagnant fluid was solved with the finite volume method. The Particle Filter method was used for the solution of the inverse transient problem involving the prediction of the temperature field in the medium, from limited temperature data available at one single location in the pipeline composite wall. The aim of this method is to represent the required posterior density function by a set of random samples with associated weights, and to compute the estimates based on these samples and weights. Results are presented in this paper by taking into account uncertainties in the state evolution and measurement models. Simulated temperature data is used in the inverse analysis for typical conditions observed during production shutdown periods.
Quantitative Evaluation of Skin Lesions Using Transient Thermal Imaging
Authors: Pirtini C¸etingu¨l Mu¨ge , Alani Rhoda M. , Herman Cila
Published: March 2011

We have recently developed a thermal (infrared - IR) imaging system that allows accurate measurements of transient temperature distributions of the skin surface. It relies on active infrared imaging for the characterization of skin lesions. We hypothesize that lesions with increased proliferative potential or inflammatory processes in the skin generate quantifiable amounts of heat and possess an ability to reheat more quickly than the surrounding normal skin. We demonstrate that the visualization and measurement of the transient thermal response of the skin to a cooling excitation can aid the identification of skin lesions of different origin. In the preliminary studies we focused on optimizing this high-resolution infrared scanning system in order to evaluate thermal images of the skin with the aim to distinguish benign from malignant pigmented lesions. Such an imaging tool is expected to improve the diagnostic accuracy and sensitivity for melanoma as well as other skin cancers, while decreasing the number of unnecessary biopsies. Therefore, we are currently conducting a pilot clinical trial of our transient thermal imaging system to verify the feasibility of the described approach in distinguishing pigmented lesions of varying malignant potential. In our trial patients who possess a pigmented lesion with a clinical indication for biopsy are selected to participate in the study. After scanning the lesions, they are biopsied and graded for malignant potential. Biopsy results are correlated with thermal images and bright light images in order to evaluate thermal associations with malignant potential.
Unstable Thermal Modes in Fischer-Tropsch Reactors With Fixed Pelletized Catalytic Bed
Authors: Derevich I. V. , Ermolaev V. S. , Mordkovich V. Z.
Published: March 2011

Investigation of oscillation of temperature and synthesis gas concentration inside spherical catalytic particle it is executed. Approximate distributions of temperature and concentrations in a particle with internal heat release and synthesis gas consumption are obtained. Stationary distributions of thermal and gaseous parameters are found. In the frame of small disturbances of temperature and concentrations thermal stability is investigated. It is revealed, that diffusion resistance synthesis gas inside a porous particle can lead to occurrence oscillation regime.
Non-Orthogonal Transformation of Irregular Geometry for Particle Based Simulation
Authors: Kumar Anurag , Abu-Nada Eiyad , Yamada Toru , Asako Yutako , Faghri Mohammad
Published: March 2011

Simulations of irregular geometries using non-orthogonal transformation is widely used in grid based methodology such as computational fluid dynamics. However, this approach is not utilized for particle based models. In this paper we introduce non-orthogonal transformation to simulate fluid flow in irregular geometry using dissipative particle dynamics (DPD). Applying boundary condition is not trivial in DPD methodology and problem becomes more complicated for irregular boundary. In the present work, irregular (physical) domain is transformed into a rectangular domain and boundary particles are frozen along the wall. Transformation for position and velocity is used to relate physical and computational domains. As particle’s position and velocity change with time, transformation matrices are determined for each DPD particle at every time step. In DPD, forces are function of actual distance between the particles and acts within a cutoff radius, which change in transformed domain at every location. To solve this problem, firstly, interacting particles are identified in the physical domain and then forces are calculated in the transformed domain. This approach is described by simulating fluid flow inside a convergent-divergent nozzle, whose geometry is controlled by the contraction ratio (CR) in the middle of the nozzle. The DPD results were validated against in-house computational fluid dynamic (CFD) finite volume code based on the stream function vorticity approach. The range of Reynolds number and CR, under study here, is Re = 10–200 and CR = 0.8 and 0.6, respectively. The results revealed an excellent agreement between the DPD and CFD. The maximum deviation between the DPD and CFD results is within 2%. It is found that using large values of dissipative force parameter velocity fluctuations are less.
Optical Measurements of the Thermal Conductivity of Porous SiO2 Films
Authors: Hopkins Patrick E. , Kaehr Bryan J. , Phinney Leslie M. , Koehler Timothy P. , Grillet Anne M. , Dunphy Darren , Garcia Fred , Brinker C. Jeffrey
Published: March 2011

Nanocomposites offer unique capabilities of controlling thermal transport through the manipulation of various structural aspects of the material. However, measurements of the thermal properties of these composites are often difficult, especially porous nanomaterials. Optical measurements of these properties, although ideal due to the noncontact nature, are challenging due to the large surface variability of nanoporous structures. Recently, a novel pump-probe geometry was used in Time Domain Thermoreflectance (TDTR) to determine the thermal conductivity of liquids. In this work, we develop a thermal algorithm to solve for the temperature change and heat transfer in this TDTR geometry in which a thin film which is subjected to a modulated heat source is sandwiched between two thermally conductive pathways. We validate our thermal algorithm with TDTR measurements of the thermal conductivity and on a series of porous SiO2-based nanostructured films.
Numerical Studies on Heat Transfer and Friction Factor Characteristics of a Tube Fitted With Helical Twisted Tape Without Core-Rod Inserts
Authors: Liu Zhichun , Zhang Xiaoyu , Liu Wei
Published: March 2011

The principles of heat transfer enhancement in the core flow of tube have been proposed to improve the temperature uniformity and reduce flow resistance, which is different from that of heat transfer enhancement in the boundary flow of tube. Helical twisted tape inserts with four different widths (w = 7.5mm, 12mm, 15mm and 20mm) have been investigated for different inlet volume-flow rates ranging from 200L/h to 500L/h. A three-dimensional turbulence analysis of heat transfer and fluid flow is performed by numerical simulation. The simulation results show that the average overall heat transfer coefficients in circular plain tubes are enhanced with helical twisted tape of different widths by as much as 220∼390% at a constant tube-side temperature and the friction factor are enhanced by as much as 50% to 790%. The PEC value of the helical twisted tape inserts of different width varies between 1.60 and 3.15. Physical quantity synergy analysis is also performed. The synergy angles α, β, γ and θ are calculated, and the numerical results verify the synergy regulation among physical quantities of fluid particle in the flow field of convective heat transfer, which can guide the optimum design for better heat transfer units and high-efficiency heat exchangers.
An Investigation of Concentration Dependency of Mass Diffusion Coefficients in Multi-Component Diffusion
Authors: Komiya Atsuki , Torres Juan F. , Okajima Junnosuke , Moriya Shuichi , Maruyama Shigenao , Behnia Masud
Published: March 2011

In this paper the concentration dependency of mass diffusion coefficients in binary system was investigated. We have developed a novel and accurate visualization system using a small area of transient diffusion fields by adopting a phase shifting technique. Through accurate visualization of the transient diffusion field, it is possible to determine the mass diffusion coefficient. Unlike a conventional interferometer, the proposed system provides high spatial resolution profiles of concentration even though the target area is less than 1.0 mm. This allows the measurement of local transient diffusion field with a high accuracy. The determination of mass diffusion coefficient of each component in multi-component system was also conducted. For the accurate and reliable measurement of mass diffusion coefficient, the experimental error should be taken into account. The experimental data usually contains unexpected accidental error and inherent errors of the measurement system. In this study, an optimization technique using conjugate gradient method is developed for the precise determination of the mass diffusion coefficients. The difference between the experimental and numerical concentration distribution is set as the objective function for the optimization method. The conjugate gradient method searches the optimal value by minimizing the objective function. For the concentration dependency evaluation, sodium chloride (NaCl) in pure water was selected as solute. For determination of each mass diffusion coefficient in multi-component system, NaCl and lysozyme in buffer solution was selected. The experiments were performed under isothermal conditions. The proposed measurement method was validated by comparing the measured data with those available in the literature. The results indicated that the concentration dependency was successfully investigated from the experimental data. The mass diffusion coefficient of each component also could be determined from the experimental data as evidenced by good agreement with the published data. The difference between the reference and determined value of mass diffusion coefficient was less than 10%. It can be said that the diffusion of each solute inside the cell progresses independently within the dilute concentration ranges and the superposition principle of concentration of NaCl and lysozyme was satisfied. The influence of concentration of solution on the diffusion process and allowable concentration range of the superposition principle are determined and discussed.
Preliminary Study of Natural Convection Due to a Small Heat Source on an Isothermal Wall
Authors: Dias Tito , Milanez Luiz Fernando
Published: March 2011

In this work, we simulated a flow over a point heat source flush-mounted on a vertical uniform temperature wall. Our numerical study was accomplished by integrating the governing equations by the finite volume control method. The flow was assumed to be incompressible and laminar, with constant temperature properties except for the Boussinesq assumption of the dependence of specific mass on temperature. The results are presented for two- and three-dimensional cases for Rayleigh number equal to 106. The numerical results confirm the theoretical scales, provided by similarity methods in literature, for the decay of the centerplane-to-normal temperature excess ratio with the downstream coordinate. We also show that these scales are valid not only for the region far downstream from the heat source, as stated in similarity analyses, but also for the region near the discrete heat source. The spanwise-surface temperature excess ratio is also presented. In this plane, a transition from two- to three-dimensional behavior can be seen in the similarity scales close to and far from the heat source, although this transition occurred closer than in the case of a flow over an adiabatic wall.
Integral Transforms, Bayesian Inference, and Infrared Thermography in the Simultaneous Identification of Variable Thermal Conductivity and Diffusivity in Heterogeneous Media
Authors: Naveira-Cotta Carolina P. , Orlande Helcio R. B. , Cotta Renato M. , Nunes Jeziel S.
Published: March 2011

This work deals with the simultaneous estimation of spatially variable thermal conductivity and diffusivity for one-dimensional heat conduction in heterogeneous media. The direct problem solution is analytically obtained via integral transforms and the related eigenvalue problem is solved by the Generalized Integral Transform Technique (GITT). The inverse problem is handled by Bayesian inference through a Markov Chain Monte Carlo (MCMC) method. Instead of seeking the function estimation in the form of a sequence of local values for the thermal properties, an alternative approach is utilized here, which is based on the eigenfunction expansion of the thermal conductivity and diffusivity themselves. Then, the unknown parameters become the corresponding expansion coefficients. In addition, the inverse analysis is performed on the transformed temperature field, instead of employing the actual local temperature measurements, thus promoting a significant data reduction through the integral transformation of the experimental measurements. A demonstration experiment is built involving a partially heated thin bakelite plate. Temperature measurements obtained via infrared thermography are used in the inverse analysis.
Laminar Flow Forced Convection Heat Transfer Behavior of Phase Change Material Fluid in Microchannels With Staggered Pins
Authors: Kondle Satyanarayana , Alvarado Jorge L. , Marsh Charles , Ravi Gurunarayana
Published: March 2011

Microchannels have been extensively studied for electronic cooling applications ever since they were found to be effective in removing high heat flux from small areas. Many configurations of microchannels have been studied and compared for their effectiveness in heat removal. However, there is little data available in the literature on the use of pins in microchannels. Staggered pins in microchannels have higher heat removal characteristics because of the continuous breaking and formation of the boundary layer, but they also exhibit higher pressure drop because pins act as flow obstructions. This paper presents numerical results of two characteristic staggered pins (square and circular) in microchannels. The heat transfer performance of a single phase fluid in microchannels with staggered pins, and the corresponding pressure drop characteristics are also presented. An effective specific heat capacity model was used to account for the phase change process of PCM fluid. Comparison of heat transfer characteristics of single phase fluid and PCM fluid are made for two pins geometries for three different Reynolds numbers. Circular pins were found to be more effective in terms of heat transfer by exhibiting higher Nusselt number. Circular pin microchannels were also found to have lower pressure drop compared to the square pin microchannels.
Experimental Study on Counter-Gravity Effect of Non-Phase Change Heat Pipes
Authors: Lee Suvit , Yuan Dazhong , Wu Bangxian
Published: March 2011

An innovative concept of Non-Phase Change Heat Pipe (NPC-HP) was recently proposed by the present authors. Different shapes of NPC-HP with different structures have been successfully developed in our laboratory. The heat transfer in NPC-HP is not dependent on phase change, but on pressure response to temperature change. With the external heat source as the driving force, the remarkable pressure rise of the working medium inside NPC-HP resulting from the heat input precedes the rise of the saturated vapor pressure, thus effectively restrains the phase change in the loop pipe and finally results in a special heat transfer mode with phase change suppressed. NPC-HP has much higher heat flux (as high as 104 W/cm2) and much higher heat transfer rate compared to traditional heat transfer components. Besides, NPC-HP overcomes the deficiencies or limitations of conventional heat pipes, such as the dry-up phenomenon, the difficulty of heat transfer in counter-gravitational direction, etc. It is, in fact, a new generation of heat transfer components with a completely new mechanism. In order to testify the counter-gravity effect of NPC-HP, an experiment for downward heat transmission in NPC-HP is arranged. The test result demonstrates the superior capability of downward heat transfer of NPC-HP. For heating power of 275W, heat effectively transmits downwards to the cooling end of the pipe at the vertical distance of 1.68m from the heating position. The temperature difference is about 7°C from the top to the bottom of the pipe. This result is hardly realizable in conventional heat pipes. A preliminary analysis on the mechanism of downward heat transfer is then made. For an effective downward heat transfer, it is essential for NPC-HP to keep phase change effectively and opportunely suppressed in the loop pipe as well as to further keep natural convection restrained. Because of its superior performance, NPC-HP will undoubtedly become a new generation of heat transfer components, and have wide applications in different industries.
Thermal Conductivity Enhancement of Binary Nanoemulsions (O/S)
Authors: Sul Hea Youn , Jung Jung-Yeul , Kang Yong Tae
Published: March 2011

Binary nanoemulsions, nano-sized oil-droplet suspensions in binary solution (H2O/LiBr), are developed to enhance the heat and mass transfer performance of absorption refrigeration systems. In this study, a novel four-step method is proposed to prepare the stable oil-in-binary solution (O/S) emulsion. To stabilize the nanoemulsions in a strong electrolyte, a polymeric stabilizer (Gum Arabic) is used as a steric stabilizer. The droplet size and the thermal conductivity of binary nanoemulsions are measured by the dynamic light scattering method and the transient hot-wire method, respectively. It is concluded that the ratio of 2:1 (oil:surfactant) is the best condition for distribution stability. It is also found that the measured thermal conductivity of the oil-in-water nanoemulsion enhances up to 6.4% at 0.1 vol% of oil, and the binary nanoemulsion enhances up to 3.6% at 1.0 vol% of oil in 30 wt% H2O/LiBr compared with the estimated one from the Maxwell’s model. This result is compared with electric conductivity of LiBr solution and it is found both conductivities have similar trend. It is finally proposed that the thermal conductivity of the binary nanoemulsion could be enhanced by adding nano-sized droplets of n-decane oil, which has a lower thermal conductivity than that of the base fluid.
Numerical Analysis of Temperature Distribution in a Three-Dimensional Image-Based Hand Model
Authors: Shao Hongwei , He Ying , Mu Lizhong
Published: March 2011

In the present study, a simulation has been developed to investigate the blood and temperature distribution in the human hand. The simulation consists of image-based mesh generation, blood flow modeling in large vessels, and finite element analysis of heat transfer in tissues based on the porous media theory. In order to reconstruct a real geometric mesh model of the human hand, sequential MR images of a volunteer’s hand was taken firstly. Furthermore, a MATLAB program was developed to detect the edge information of the target by applying several image preprocessing operators. Finally, a FORTRAN program based on the transfinite interpolation method was developed to generate mesh from the preprocessed images automatically, and the positions of simplified bones and vessels were set according to the anatomic structure. The blood flow in large vessels adopted in this study was provided from the one-dimensional simulation of blood circulation in the upper limb, which was completed by He [1]. On the other hand, blood flow perfused in solid tissues through the micro vessels was expressed by Darcy model. The heat transfer in tissues was described by the energy equation for porous media with assuming that a local equilibrium was achieved between the blood and tissue phase. The primary results for the distribution of the blood flow perfused in tissues and temperature were obtained in this study, and they were similar to the real state of the human hand. The improvement of this simulation will be the next work.
Flow Pattern and Boiling Heat Transfer of CO2 at High Pressure in Horizontal Mini-Channels
Authors: Ami Takeyuki , Nakamura Noriko , Umekawa Hisashi , Ozawa Mamoru , Shoji Masahiro
Published: March 2011

Experimental investigation was conducted with CO2 at high pressure, ranging 5.0 to 6.5 MPa, in horizontal mini-channels of 0.51, 1.0 and 2.0 mm in diameters. In smaller bores tube, e.g. 0.51 and 1.0 mm, the phase stratification is not serious and the flow pattern becomes quasi-axi-symmetric, while in 2.0 mm or larger tubes phase stratification becomes significant as in conventional sized tubes. This phase stratification, together with the intermittent flow behavior, causes the heat transfer deterioration at the upper wall. Existing criteria as a whole were insufficient in predicting flow patterns. In order to predict complicated two-phase flow behavior, including inherent void fraction fluctuation and flow patterns, the discrete bubble model based on a pattern dynamics approach was developed, so as to be applicable to the horizontal mini-channels. The simulated void fraction fluctuations successfully provided not only the flow pattern maps in terms of statistical properties, but also quantitative estimation of the heat transfer deterioration at the upper wall of the tube of 2.0 mm in diameter. Existing correlations were evaluated through the comparison with the present experimental data, and a nucleate boiling mode was found a dominant mode over the boiling heat transfer at high pressure in mini-channels.
Heat and Mass Transfer With Phase Change and Chemical Reactions in Microscale
Authors: Kuznetsov Vladimir V.
Published: March 2011

In recent years considerable attention has been paid to the study of microscale flow and heat transfer with phase change and chemical reactions. This article reviews the patterns of the microscale two-phase gas-liquid flow, the statistical parameters of slug flow and capillary phenomena in annular flow for a rectangular microchannel. The evaporative and condensing heat transfer model for the curved liquid microfilm in microchannel and near contact line is developed and discussed. The influence of forced convection, nucleate boiling and thin film evaporation on microscale flow boiling heat transfer is reviewed and analyzed. The model of forced boiling heat transfer in microchannel is developed and compared with the existing experimental data. The mechanism and patterns of microscale explosive evaporation in the MEMS system is determined at high external heat flux density and the acousto-thermal model of the explosive evaporation is considered. The results of calculations are compared with the experimental data. The peculiarities of heat and mass transfer in a micro channel with surface catalytic reactions producing the hydrogen are presented. The kinetics of sequence of chemical reactions at nanoscale catalyst under conditions of significant nonuniformity of temperature and species concentration fields is considered.
Experimental Study on CHF Characteristics of R134a Flow Boiling in Horizontal Helically-Coiled Tubes
Authors: Chen Chang-Nian , Han Ji-Tian , Shao Li , Chen Wen-Wen , Jen Tien-Chien
Published: March 2011

An experimental study of critical heat flux (CHF) was performed to investigate the CHF characteristics of R134a flow boiling in horizontal helically-coiled tubes. The test sections made of stainless steel were directly heated by high-power DC power sources to maintain constant heat-fluxes. The experimental parameters are the outlet pressures of 0.30–1.10 MPa, mass fluxes of 60–480 kg/m2s, inlet qualities of −0.32–0.36 and heat fluxes of 6–90 kW/2m. Thirteen helically-coiled tubes were tested with the outer diameters of 6–14 mm, inner diameters of 3.8–11 mm, coil diameters of 135–370 mm, helical pitches of 40–105 mm and valid heated lengths of 0.85–7.54 m. The detection for CHF occurrence was based on the event-driven method of Agilent BenchLink Data Logger Pro with a total of thirty-two 0.2mm T-type thermocouples set in every coil to measure the wall temperatures accurately. It was found that the wall temperatures jumped abruptly once the CHF occurred. The magnitude of CHF decreases with increasing valid heated length, coil diameter and inner diameter to some extent, while the DNB (departure from nucleate boiling) CHF seems independent when length-to-diameter L/di>200. Coil-to-diameter ratio is considered more important for CHF than length-to-diameter ratio in helically coiled tubes. The helical pitch has little effect on CHF. While CHF value increases much with increasing mass flux and decreases little with increasing absolute pressure, it decreases nearly linearly with increasing inlet qualities and critical qualities in different levels. But the CHF values at xcr<0.5 vary acutely than those at higher critical qualities. New experimental correlations for the DNB and the dry-out CHF of R134a flow boiling in horizontal helically-coiled tubes were developed.
Film Cooling Efficiency in the Supersonic Flow With Foreign Gas Injection
Authors: Zditovets A. G. , Leontiev A. I. , Vinogradov U. A. , Strongin M. M. , Titov A. A.
Published: March 2011

Numerical investigation (A.I.Leontiev, V.G.Lushchik, A.E.Jakubenko «PARADOXES OF HEAT TRANSFER ON A PERMEABLE WALL») shows that adiabatic wall temperature in the region of the gas film may be lower than the injected gas (coolant) temperature. It occurs in case of foreign light-gas injection and it does not occur in case of uniform gas injection under the same conditions. This paper is devoted to the experimental investigation of this conclusion. Experimental researches have been conducted in the low flow-rate supersonic wind tunnel (Mach number of 3) located in the Institute of Mechanics of the Moscow State University. Argon was used as a primary stream, helium and argon as coolant. The coolant was blown in through the porous permeable part of a model and injected into the supersonic boundary layer. The surface temperature of the model was gained with use of the infrared scanning device ThermaCAM SC 3000. As a result following data have been obtained. It is shown in particular that the adiabatic wall temperature in the region of the gas film may be lower than the injected gas (coolant) temperature. This effect does not take place in case of uniform (air-air, argon-argon etc.) gas injection, for this effect is especially essential for gas mixtures with low values of the Prandtl number.
Experimental Investigation of Skin Friction Drag and Heat Transfer on the Surfaces With Concavities in Compressible Fluid Flow
Authors: Titov Alexander A. , Leontiev Alexander I. , Vinogradov Uriy A. , Zditovets Andrey G. , Strongin Mark M.
Published: March 2011

This experimental study has been performed to investigate the surface heat transfer enhancement in compressible fluid flow by using hemispherical concavities (dimples). The experiments were carrying out in supersonic wind-tunnel with free-stream Mach number 2,8. Using the IR-imager the temperature fields of the testing plates were obtained at any time of experiments. The studying of these fields at unsteady conditions allowed to obtain the area-averaged heat transfer coefficient. The skin friction drag of the test plates was found by direct weight measurement with using a “smoothing element”. The skin friction drag and heat transfer were measured simultaneously (at the same conditions) in each experiment. The plate with dimples with ratio of dimple depth to dimple print diameter 0,14 was investigated. It was shown that the tested surface with concavities (vortex generation relief) intensified the heat transfer and decreased the recovery factor in supersonic flow. The ratio of the heat transfer enhancement to the skin friction drag increasing for the dimpled surface in compressible flow is equal to 0,7.
Study on Fluid-to-Fluid Modeling of CHF of R134a-Water in Horizontal Helically-Coiled Tubes
Authors: Chen Chang-Nian , Han Ji-Tian , Shao Li , Chen Wen-Wen , Jen Tien-Chien
Published: March 2011

The new similarity laws for fluid-to-fluid modeling of critical heat flux (CHF) in horizontal helically-coiled tubes were derived based on the dimensional analysis and similarity theory considering the effect of the geometrical parameters on CHF. A generalized factor Dn was introduced to the new similarity laws, and all the new dimensionless numbers were derived from the classical theorem of Buckingham π for dimensional analysis. The obtained dimensionless parameter sets were a reasonable extension to Ahmad’s compensated distortion model, which may be considered as a special case of the new dimensionless parameter sets when the variable n is equal to unity. Based on the experimental data, the specific similarity numbers were determined for CHF phenomena in horizontal helically-coiled tubes. A new equivalent characteristic parameter De-helix was developed, which could reflect the influence of complex flow channels on the occurrence of CHF. The equivalent characteristic parameter consists of the essential geometrical parameters of tubes and the fluid thermophysical properties. The new fluid-to-fluid modeling methods were proposed for CHF of R134a-water in horizontal helically-coiled tubes, which could be used readily to derive the CHF data of water through the CHF data of R134a at the corresponding experimental conditions.
Research and Development of Compact Heat Exchangers of Gas Turbine Power Conversion Unit for Nuclear Power Plant With High Temperature Gas-Cooled Reactor
Authors: Golovko V. F. , Dmitrieva I. V. , Kodochigov N. G.
Published: March 2011

The NPP design that integrates a high temperature helium cooled nuclear reactor with a gas-turbine power conversion unit requires investigations and development of high-efficiency heat-exchange equipment operating in the closed primary circuit. The equipment must be very compact, which implies highly efficient heat transfer at minimum pressure loss. This paper presents an analysis of optimal heat-exchange surface selection, as well as design and layout features of recuperators, precoolers and intercoolers. Considered are tube (made of straight, helical, including those with the small bending radius, finned tubes etc.), plate-and-fin and matrix heat-exchange surfaces combined as separate modules or as a single bundle. Suggested are methods and criteria to select rational heat-exchange surfaces with account of critical factors and limitations. Given are results of the comparative analysis and computational and experimental investigations of surfaces; design and layout solutions for heat-exchange apparatuses arranged in the vertical high-pressure vessel with limited dimensions.
Paradoxes of Heat Transfer on a Permeable Wall
Authors: Leontiev A. I. , Lushchik V. G. , Yakubenko A. E.
Published: March 2011

Numerical modeling of a turbulent boundary layer on a permeable wall with gas injection is performed. New effects are discovered. It is shown in particular that the wall temperature in the region of the gas film may be lower than the injected gas temperature. This effect is especially essential for gas mixtures with low values of the Prandtl number.
Impact of the Anticorrosion Films on the Condensing Heat Transfer of Flue Gas in Fin-Tube Heat Exchangers
Authors: Wang Sui-lin , Wu Yuan-yuan , Pan Shu yuan , Shi Yong zheng
Published: March 2011

The forced convective heat transfer with condensing was experimentally investigated when wet flue gas was flowing in the fin-tube heat exchangers with three anticorrosion films respectively, including the nickel-phosphorus amorphous composite eletroless and organic compound (NPACE&OC) surface, the nickel-phosphorus amorphous composite eletroless (NPACE) surface, and the organic compound (OC) surface. The experimental results indicate the convection heat transfer characteristics as following: Among the three heat exchangers, the convection heat transfer for the heat exchanger with NPACE&OC surface is the best, the convection heat transfer coefficient is about 18%∼25% higher than that of the other two heat exchangers. It could be caused by the lower surface energy of the NPACE&OC surface that forms the drop condensate. The experimental results of heat transfer coefficient relative to Reynolds Number and Jakob Number were also presented in this paper. Based on the experimental results and the analysis, the correlation of the measurements was achieved.
Study of Flow Instabilities in a Natural Circulation Boiling System
Authors: Kazem Arrdaneh , Asad allah Ahmadi , Farahi Mohsen , Salman Zaferanlouei
Published: March 2011

The purpose of this paper is to develop a nonlinear model to investigate the instabilities of a two-phase natural circulation loop. We obtain a stability map to explore the unstable regions of this natural circulation loop. The results show that the considered loop has two unstable regions, instability type-I in the low power region and instability type-II in the high power region. Then the parametric study is carried out to understand the relation between the parameters of system and two types of instability. The parametric study reveals that lengthening the riser has an unstable effect on system stability. Thus, lengthening the riser causes a reduction in the stability region in the both low power and high power levels. Also it can be observed that by increasing the form loss coefficient at the inlet of heated section or in the downcomer section, the stability region expands, however by increasing the form loss coefficient at the outlet of heated section or in the upper horizontal section, the stability region decreases consequently.
Numerical Simulation of Multiwalled Carbon Nanotube Growth in a Tube Flow Chemical Vapor Deposition Reactor
Authors: Lombardo Jeffrey J. , Chiu Wilson K. S.
Published: March 2011

The deposition rate of carbon nanotubes in a tube flow CVD reactor was studied over different temperatures and inlet gas concentrations with a focus on particle size and the number nanotube walls per particle. It was found that larger particles and higher numbers of walls increased the use of carbon and required a higher concentration of the carbon feedstock gas, methane. These results show that optimizing reactor conditions will require tailoring the feedstock gas concentrations according to the particle size and expected number of walls per nanotube in order to ensure that there is enough carbon to facilitate nanotube forming reactions.
Modeling of Thermal Contact Conductance
Authors: Murashov Mikhail V. , Panin Sergey D.
Published: March 2011

Nowadays a new science direction has arisen from decades of experimental work carried out in 20th century — micromechanics of contact processes (deformation, heat transfer, electric conduction). To determine contact area a dynamic elastic-plastic deformation problem is to be solved even in the simplest case — butt contact of two rough surfaces under pressure. It is followed by the solution of spatial boundary heat transfer problem to obtain nonstationary temperature distribution for two bodies. In principal, this stage is not difficult to perform with finite element program ANSYS. Meanwhile the questions concerning deformation and conduction through oxide films of metals as well as directional effect remain. In the literature there are attempts to simulate thermal contact conductance numerically of such authors as M.K.Thompson, S.Lee et al, M. Ciavarella, M.M.Yovanovich and others. The disadvantages of existing spatial models are: - surfaces profiles has no random component; - only elastic or only plastic material behavior; - microroughness is not considered. In the present work the roughness before contact of two rough surfaces of copper bodies was presented as spatial two-level (roughness and microroughness) model with the use of fractal Weierstrass–Mandelbrot function. In quasistatic approach the 3D deformation and heat transfer problems of contacting bodies under pressure were solved within elastic-plastic material behavior. Contact ANSYS elements were used. Copper compression diagram was replaced by multilinear model of isotropic hardening. From the cycle of calculations real contact areas, shapes of contact spots, temperature and stress distributions were determined for the range of pressures. Good agreement with experimental data took place only when microroughness is considered.
Fire Suppression by Water-Mist Sprays: Experimental and Numerical Analysis
Authors: Santangelo Paolo E. , Tartarini Paolo , Pulvirenti Beatrice , Valdiserri Paolo , Marshall Andre´ W.
Published: March 2011

Water-mist systems have become a promising technology in the fire-fighting field over the last twenty years. The present work is aimed at employing the available knowledge on water-mist sprays in an experimental and numerical analysis of the suppression mechanism. Therefore, a water-mist system has been operated within a typical fire case. Most notably, this latter is constituted by a heptane pool fire: experiments have been carried out inside a test chamber, where a set of thermocouples has conveniently been placed to evaluate the thermal transient at different locations of interest. Some free-combustion tests have been run as a benchmark to validate combustion models. Then, a typical water-mist nozzle has been inserted and activated to realize control, suppression and potential extinction of the generated fire. The recognized FDS (Fire Dynamics Simulator) and Fluent® codes have been challenged in reproducing the test case: thermal transient and suppression time have been considered as parameters for validation. Therefore, the water-mist spray has been modeled and the already mentioned results about its characterization have been implemented as initial or boundary conditions. Moreover, the fire scenario has been modeled as well. A good agreement between experimental and numerical results has been obtained, even under some approximations, with specific reference to combustion mechanisms.
Convective Thermal Transfer From a Heated Surface to an Impinging Multiphase Incompressible Turbulent Liquid Jet
Authors: Osmar Ludovic , Vincent Ste´phane , Caltagirone Jean-Paul , Cavallaro Gabriel
Published: March 2011

The cooling process controlled by an impinging unsubmerged jet on a heated surface is tackled. Numerical studies about cooling by a two-phase incompressible turbulent flow have not been significantly treated in the literature and are considered here. The liquid jet cooling method is modelled by associating the energy equation with a multiphase incompressible turbulent flow model, the final objective being to be able to predict the heat transfer coefficient between the cooling liquid jet and the impinged surface. Turbulence is modelled by Large Eddy Simulation (LES). It is coupled with an Eulerian Volume of Fluid (VOF) method to follow the evolution of the interface between two fluids. In a first part, a work of validation is led and the model is compared to experimental results available in the literature [1]. Convective heat transfer induced by a planar jet of water impinging normally onto a flat heated surface is simulated. Knowing the imposed heat flux, local heat transfer coefficients are deduced from predicted surface temperatures. The next step will be to study cooling due to a cylindrical jet of water impinging onto a heated semi-hemispherical concave surface.
Flow Rate Maldistribution in Multi Heated Parallel Pipes
Authors: Baikin Mordechai , Taitel Yehuda , Barnea Dvora
Published: March 2011

Fluids flowing in parallel pipes, undergoing evaporation, take place in heat exchangers, boilers, power plants, cooling systems and in the nuclear industry. Evaporating two-phase flow in parallel micro-channels is considered for heat removal in microelectronic devices. The main motivation of the present work is associated with the use of solar energy collected in long lines. In this technology, an array of parallel pipes is located at the focal center of parabolic mirrors that focus solar radiation on the pipes to generate steam. It is a common knowledge that maldistribution may occur in evaporating liquid flowing in parallel pipes with common inlet and outlet manifolds. This phenomenon occurs due to multiple steady state solutions some of which are unstable. One may obtain uneven flow rate distribution even for the case of equal heating of the pipes. For non equal heating higher flow rates may take place in the less heated pipes. This is quite an unfavorable phenomenon. The theoretical model developed by Minzer et al. [1] for the flow rate distribution is extended to a larger number of pipes and different heating conditions. Stable and unstable solutions are identified and the model predictions are experimentally validated for different configurations involving three pipes. It is shown that the behavior of the system may depend on the history of the process exhibiting a hysteresis phenomenon. Transient simulations are carried out using this model in order to study the time dependent system response to finite disturbances and to changes in operational conditions.
Heat Transfer Characteristics of Flow Boiling of R134a in Uniformly Heated Horizontal Circular Microtubes
Authors: Basu Saptarshi , Ndao Sidy , Michna Gregory J. , Peles Yoav , Jensen Michael K.
Published: March 2011

An experimental study of two-phase heat transfer coefficients was carried out using R134a in uniformly heated horizontal circular microtubes with diameters of 0.50 mm and 1.60 mm. The effects of mass flux, heat flux, saturation pressure, and vapor quality on heat transfer coefficients were studied. The flow parameters investigated were as follows: exit pressures of 490, 670, 890, and 1160 kPa; mass fluxes of 300–1500 kg/m2s; heat fluxes of 0–350 kW/m2; inlet subcooling of 5, 20, and 40 °C; and exit qualities of 0 to 1.0. The parametric trends presented in the study are consistent with published literature. Heat transfer coefficients increased with increasing heat flux and saturation pressure while they were independent of variations in mass flux. Vapor quality had a negligible influence on heat transfer coefficients. For the conditions studied, the trends indicated that the dominant heat transfer mechanism was nucleate boiling. The experimental data was compared to three microchannel correlations — the Lazarek-Black, the Kandlikar, and the Tran Correlations. None of the correlations predicted the experimental data very well, although they all predicted the correct trend within limits of experimental error.