bluuebunny/crossref_metadata_2025 huggingface dataset:
Discrete Investigation of Thermal Relaxation in Packed Beds
Authors: Weigler Fabian , Peglow Mirko , Tsotsas Evangelos
Published: March 2011

Granular materials are of great importance industrially, yet not completely understood in regard of their thermal behavior in mixers, dryers, reactors and other types of contact processing equipment. In such equipment heat is supplied to a mechanically agitated bed of particles from heating surfaces. Continuum models are used traditionally for the description of the process. An example is the penetration model (PM) which describes the heating process of the particles as a sequence of penetration periods and mixing steps. As an alternative to the PM the thermal discrete element method (DEM) was applied in newer work. To validate the DEM simulation an experimental set-up and a new contactless measurement method were developed, and applied to the thermal relaxation in packed beds composed by a fraction of warm and a fraction of cold particles. In these thermal investigations aluminum spheres which are coated with thermochromic pigments are used. Thermochromic pigments are pigments that change color with heat supply as a result of a structural phase transition. Such a measuring technology allows for the experimental determination of temperature distributions in the disperse phase and thus, for a quantitative comparison with the results of the thermal DEM simulation. In this work the experimental results of 2D, 3D, stagnant and agitated beds are presented and compared with corresponding numerical computations using the discrete element method. Still existing deviations are partially caused by undesired heat losses and will be discussed in the contribution.
Modeling Mass Transfer and Nanoparticle Capture in Electrostatically Charged Monolith Filters
Authors: Wu M. , Kuznetsov A. V. , Jasper W.
Published: March 2011

Analyzing trajectories of particles in monolith filters is important for predicting the capture efficiency and improving the design of this class of filters. Modeling and simulations of the particle trajectories are carried out to evaluate the probability of capture by the filter’s front surface and filter channel’s inner wall. Due to Brownian motion and electrostatic attraction, the particles exhibit a random walk and their trajectories deviate from the streamlines of the fluid flow. Particle trajectories are computed by the integration of Newton’s second law, where the electrostatic force, the Brownian motion force resulting from random collisions of the particle with air molecules, and the drag force from the surrounding fluid are all taken into account. A computer simulation for computing the particle trajectories and evaluating the probability of particle capture by the filter was developed. For this model, both flow field and electric field must be provided. The electric charge was assumed to be uniformly distributed along the edge of the channels of the filter and calculated numerically. The flow field is difficult to obtain due to the complex geometry of the model. The commercial CFD package ANSYS CFX [1] is used to compute the flow field. The resulting velocity flow field is then used to evaluate the drag force on the particles. We assume a one-way coupling between the fluid flow and the particle motion. Although there can be over one million uniformly distributed channels per square centimeter in the monolith filter, for simulation purposes, a single unit cell which models only one channel is used. The single unit model effectively describes the behavior of particles outside and inside the channels of monolith filter. The effects of different forces and different particle sizes were analyzed to investigate which factors affect the capture efficiency.
Improved Regimes in High Pressure Magnetic Discharges
Authors: Ryzhkov Sergei V. , Anikeev Andrey V.
Published: March 2011

Field-Reversed Configuration (FRC) [1] and Gas-Dynamic Trap (GDT) [2] represent compact system, which is a special magnetic geometry for plasma confinement. Theoretical and experimental study of gas-dynamic regimes with high energy content is carried out. The approach to a high beta (β is the ratio of plasma pressure to magnetic pressure) magnetic systems assumed different regimes of plasma with beta > 0.5 that is proper to compact devices such as tori and mirror traps. Both FRC and GDT traps are axial symmetric configurations, has open field lines and poloidal magnetic field only. Last experimental results on GDT have shown the possibility to build the stationary system with high beta. Analysis of the global energy and particle balance together with the Monte-Carlo equilibrium modelling allowed to conclude that two-component plasma confined in a steady-state regime. The characteristic plasma lifetimes are 4 to 5 times less then the experiment duration. A peripheral gas-puff near the mirror region enabled to maintain the radial profile of background plasma during the all neutral beam injection (NBI) pulse. This report is focused mainly on ambipolar effect and the possibility of further increasing the fast ion energy content and β. Improved gas-dynamic regimes in high pressure magnetic discharges and microinstabilities arising are described. Synthesized hot ion plasmoid (SHIP) experiment in the compact mirror section attached to the GDT central cell and the scheme of compact tori (FRC formation) for the compact mirror cell of GDT device are presented. Fusion prospects (reactor, neutron source, material studies) of such systems with high-energy (fast) particles [3, 4] and hybrid FRC + GDT scheme proposed by author from Bauman Moscow State Technical University (BMSTU) are discussed.
Transient Characteristics of a Two-Phase Thermosyphon Loop for Cooling Telecommunication Outdoor Cabinets
Authors: Louahlia-Gualous H. , Mecheri B. , Nortershauser D. , Le Masson S.
Published: March 2011

In this paper, experimental investigations of a two-phase thermosyphon loop are presented in order to keep telecommunication equipments temperature below 55°C. The experimental setup consists of a thermosyphon loop containing an evaporator and a condenser connected by two flexible tubes. Tests are performed firstly in transient state using the thermosyphon loop prototype inside telecommunication cabinet. The n-pentane is used as the working fluid. Firstly, transient thermal characteristics of the thermosyphon loop are measured. In the other way, the thermosyphon loop is tested for different power input up to 450W. Operating temperatures of the telecommunication equipments cooled with forced air convection and two-phase thermosyphon loop are compared.
The Effect of Directional Radiative Surface Properties on the Performance of Mutually Irradiating Conducting Fins
Authors: Ambirajan Amrit , Prasanna S. , Venkateshan S. P.
Published: March 2011

The problem of mutually irradiating conducting fins is considered in this paper. The problem is analyzed under two types of surface models, namely, diffuse-specular (D-S) model and a directional (Dir) radiative surface property model, for various surface roughnesses and RMS slopes. Metal (aluminum) coated and dielectric (Aluminum oxide) coated surfaces are considered as the two extreme cases. Analysis indicates that dielectric coated surfaces are sensitive to the radiative surface property model while metal coated surfaces are insensitive to the surface property model. Irrespective of the surface property model used metal coated surface show a drastic drop in heat flux for even a slight increase in surface roughness.
Dropwise Condensation Heat Transfer on Superhydrophobic Surface in the Presence of Non-Condensable Gas
Authors: Ma Xuehu , Wang Sifang , Lan Zhong , Wang Aili , Peng Benli
Published: March 2011

Roughness-induced superhydrophobic surface was applied to promote dropwise condensation (DWC) on a vertical plate in the presence of non-condensable gas (NCG). The DWC heat transfer characteristics were investigated and the wetting behaviors of the condensate droplets were observed visually. The experimental results have shown that the roughness-induced superhydrophobic surface would enhance the heat transfer characteristics of steam condensation in the presence of NCG with high concentration. The underlined mechanism is analyzed in terms of the droplet wetting modes.
A Droplet Model in Dropwise Condensation With the Presence of Non-Condensable Gases
Authors: Lan Zhong , Wang Aili , Peng Benli , Wang Sifang , Ma Xuehu
Published: March 2011

A droplet model is proposed with respect to molecular clustering to describe the state of steam molecules before condensing on the cooled solid surface in steam condensation process, and also the model is used to account for the mechanism of steam dropwise condensation in the presence of non-condensable gases (NCG). The mathematical model is presented based on the Dillmann and Meier’s homogeneous nucleation theory. Correction of surface tension term is conducted to match the physical and chemical characteristics of condensation process, and the heat transfer model considering the effect of interfacial effects was used to calculate the mean temperature of clusters. The model predicted results of Gibbs free energy at different subcooling degrees and different saturated temperatures were given. And the ratio of heat transfer coefficient with to that without NCG with different fractions of NCG was also obtained. The results show that the non-condensable gases reduce the condensation rates in the same way as shown by experimental results in the literature. That confirms the validity of the model.
A Numerical Study of the Plate Heat Exchanger With Compound Corrugations in the Condition of Low Reynolds Number and High Prandtl Number
Authors: Cao Xing , Du Wenjing , Zhang Guanmin , Cheng Lin
Published: March 2011

In general the conventional plate heat exchanger has good heat transfer performance on the one hand and high pressure drop on the other hand. In order to deal with this dilemma, a novel plate heat exchanger with compound corrugations is proposed in this paper. Comparisons with the traditional plate heat exchanger indicate that the new heat exchanger can reduce flow resistance and simultaneously improve its heat transfer performance. The heat-transfer oil with a relatively high dynamic viscosity is selected as the working fluid. The performance in the newly-proposed plate heat exchanger with compound corrugations in the condition of low Reynolds number and high Prandtl number is numerically investigated. In the process of numerical simulations, variations are made on one geometric parameter of the plates and keep invariant for the others. Through comparisons on the j-factor, the friction factor and their ratio j/f for various plate geometries, the influence of geometry parameters on heat transfer performance, flow resistance characteristics and comprehensive heat exchanger performance is thoroughly examined. Based on numerical results, the geometric parameters which have significant impact on heat transfer and flow resistance of the proposed plate heat exchanger are determined. And the Nusselt number and friction factor correlations of the plate heat exchanger with compound corrugations are obtained, which are applicable for the laminar flow mode when the working fluid is with low Reynolds number and high Prandtl number.
On the Correlation Between Vorticity Strength and Convective Heat Transfer
Authors: Habchi Charbel , Lemenand Thierry , Della Valle Dominique , Peerhossaini Hassan
Published: March 2011

Vorticity is an inherent feature of fluid flow and has an essential role in the convective heat and mass transfer. The present study aims at determining quantitatively the relationship between the streamwise vorticity flux Ω, and the convective heat transfer, characterized by Nusselt number Nu. Physical vortices are created by using a vorticity generator inserted on the wall of a heated straight channel. It is shown that the streamwise variations of Ω and Nu are related through a power law of the type Nu ≈ α(Ω − C1)β + C2.
Experimental Investigation of Effective Thermal Conductivity for LHP Wicks
Authors: Xin Gongming , Cui Kehang , Chen Yan , Du Wenjing , Zou Yong , Cheng Lin
Published: March 2011

In this study, the effective thermal conductivity (ETC) of sintered loop heat pipe wicks, with pure nickel powders, pure copper powders, Ni-10wt%Cu powders and Ni-20wt%Cu powders were experimentally investigated. The ETC of sintered Ni-Cu wicks is found less than those of sintered pure nickel wick and sintered pure copper wicks. In the same porosity level, addition of copper into nickel will reduce ETC of the sintered Ni-Cu wicks. The sintered Ni-20wt%Cu wick presents the lowest ETC among the tested wick samples. Compared to experimental results, Alexander model can provide a reasonable prediction in some wick samples.
A Graphene Chain Acts as a Long-Distance Ballistic Heat Conductor
Authors: Takahashi Koji , Ito Yohei , Ikuta Tatsuya
Published: March 2011

A carbon nanofiber material, consisting of bottomless graphene cups inside on each other in a line, like a set of soft-drink cups, has been discovered to have the potential to conduct heat ballistically over a long distance. Its longitudinal heat transport ability had been forecast to be extremely poor due to the weak van der Waals force operating between the graphene cups, but our measurements using nano thermal sensor showed that its thermal conductivity is much higher than that along the c-axis of bulk graphite. This unexpected result can be understood by its similarity to a one-dimensional (1D) harmonic-chain where no phonon is scattered even for an infinite length. The current graphene-based nanofiber resembles this type of “superconductive” chain due to the huge difference between the stiff covalent bonding in each cup and the weak inter-cup interaction. A non-equilibrium molecular dynamics simulation is conducted to explore the phonon transport in this fiber. The simulation results show that the thermal conductivity varies with the fiber length in a power law fashion with an exponent as large as 0.7. The calculated phonon density of states and atomic motions indicate that a low-frequency quasi-1D oscillation occurs there. Our investigations show that treating the current nanofiber as a 1D chain with three-dimensional oscillations explains well why this material has the most effective ballistic phonon transport ever observed.
SLW-1 Modeling of Radiative Heat Transfer in Non-Isothermal Non-Homogeneous Gas Mixtures With Soot
Authors: Solovjov Vladimir P. , Lemonnier Denis , Webb Brent W.
Published: March 2011

The Spectral Line Weighted-sum-of-gray-gases (SLW) model consisting only of a single gray gas and of one clear gas is developed as an efficient spectral method for modeling radiation transfer in gaseous medium. The model is applied here in prediction of radiative transfer in non-isothermal and non-homogeneous gas mixtures with non-gray soot. The absorption spectrum of the gas mixture and soot particles is treated as a spectrum of a single effective gas reducing the problem to the simplest case of the SLW model with a single gray gas. Good accuracy can be achieved by the optimal choice of the model’s gray gas absorption coefficient and its weight by application of the Absorption-Line Blackbody Distribution Functions of individual species in the mixture calculated with a high-resolution spectral database. The SLW-1 model is validated by comparison with benchmark solutions using the Line-by-Line method, the SLW method with a large number of gray gases, and the SNB model.
Study on Comparison Experiment of the Bidirectional Reflectance Distribution Function (BRDF) of the Surface of Exterior Decorative Materials for Buildings Under Dry and Wet Condition
Authors: Xie Ming , Xie Xiaochen , Zhao Huanhuan , Wang Xiaochun , Tan Heping
Published: March 2011

As Bidirectional Reflectance Distribution Function (BRDF) can describe the reflection and scattering characteristic of solid material surface better, an experiment which is based on the basic concept of BRDF and combined with the effects on surface profile from surface wettability theory and wet condition, was carried out for comparison. Using the white standard plate as a single sample for reference on a self-built experiment table, the BRDF values of the surface of three exterior decorative materials for buildings, namely granite, coated glass and Ethylene-Propylene-Diene-Monomer (EPDM), were measured under the conditions of dry and wet, on two wavebands (visible light band 0.6328μm and near infrared band 1.34μm) and at different incident angles. After the comparison of distribution, the results indicate that if forming stable water-film, which has the function of translucent smooth interface, above the surface of the three materials, their BRDF values will demonstrate obvious specular reflection component to different degree.
Boiling Heat Transfer Enhancement by Controllable Tailoring of the TPL
Authors: Ustinov Alexander , Mitrovic Jovan
Published: March 2011

Novel surface treatment technology was developed in the University of Paderborn in partnership with MiCryon Technik GmbH, Quedlinburg, Germany. The technology allows creation of micro-pin structures, which enhance the boiling heat transfer up to 18 times in comparison with a smooth surface, and provide an independency of the surface superheat on the applied heat flux [1–6]. The micro pins as basic structure elements can be created with the diameters of 0.1 μm to 25 μm at pins density ranging up to 109 pins/cm2. Such pin structures are created by electro-deposition of metallic ions on the basic surface. The microstructure provides for the very first time in thermal engineering a possibility to adjust the available length of the three phase line (TPL) on demand, correspondingly tailoring the shape of a boiling curve. The TPL, formed by the micro pins piercing the vapor-liquid interface, acts as an extremely efficient heat sink, providing high heat transfer coefficients and the constancy of the wall superheat at heat fluxes up to 125 kW/m2. Present article delivers the summary on boiling experiments performed with the novel microstructure, and reveals the quantitative dependencies of the heat transfer enhancement rate on the TPL length, having the pressure and the liquid type as further parameters. A newly discovered phenomenon of the vapor bubble chains formation on microstructured surfaces is discussed as well. Experiments were conducted with the refrigerants R134a, R141b and the fluorocarbon liquid FC-3284 at pressures, ranging between 0.5 bar and 9 bar.
Numerical Modeling of Thermal and Hydrodynamic Processes During the Bubble Compression Due to the Ambient Pressure Rise in a Liquid
Authors: Cherkasov S. G. , Desyatov A. V. , Il’mov D. N.
Published: March 2011

Recent attention has been focused on the use of the cavitation in developing the new type of chemical reactor. The idea is based on the hypothesis that temperature increase in collapsing bubbles is significant and sufficient for successful high-temperature chemical reactions of a certain types. The direct experimental determination of temperature inside cavitation bubbles is an extremely difficult task. The theoretical estimates, that do not take into account heat- and mass transfer mechanisms in “bubble-ambience” system, lead to enormous magnitudes of temperatures, up to a few thousands degrees. In this study, we report on numerical simulations of the processes occurring during the compression of a single spherical vapor bubble in infinite incompressible medium. The reduction of initially equilibrated bubble is provoked by abrupt pressure rise in a liquid. The mathematical model used for calculations is aimed to take into account heat transfer and phase transitions on the bubble/liquid interface in full details. It is shown that the heat absorption by liquid and vapor condensation on the bubble interface can significantly, by one or two orders of magnitude, reduce the rate of the temperature and pressure increase in the bubble. In particular, the regime, named Rayleigh-regime, has been detected. The pressure rise inside the bubble is very slow in this regime due to intense condensation of the vapor. As the result, the dynamic of the bubble collapse is basically unresponsive to the pressure rise inside the bubble. Virtually all external work contributes to the increase of the kinetic energy of the liquid in this case and the system is warmed up by the heat released during the condensation. The obtained results show that idea of mandatory significant temperature rise in collapsing bubbles during cavitation might be only a hypothesis that requires additional investigations involving careful consideration of thermal aspects of the problem.
Thermoelectricity of Double Doped Strontium Titanate
Authors: Ravichandran Jayakanth , Siemons Wolter , Kardel Justin , Heijmerikx Herman , Chari Arvind , Oh Dongwook , Cahill David , Ramesh Ramamoorthy , Majumdar Arun
Published: March 2011

Lanthanum (La) doped Strontium Titanate (SrTiO3) is amongst the most promising n-type thermoelectric materials for power generation. We report a double doping method for thin films of SrTiO3 (STO), grown by Pulsed Laser Deposition (PLD), where doping of STO in the Sr-site by Lanthanum is accompanied by doping with oxygen vacancies. In the past theoretical predictions have shown that introducing oxygen vacancies in STO produces a high-effective mass defect band just below the conduction band edge, explaining the high seebeck coefficient observed in oxygen deficient STO. Based on careful transport measurements, we show that it is possible to obtain enhanced thermoelectric power factor by double doping, using La and oxygen vacancies in these thin films. With the aid of optical spectroscopic measurements, we establish the presence of the impurity band created by the vacancies and validate their role in the enhanced thermoelectric performance with structural and transport measurements. The presence of oxygen vacancies also serves to decrease the thermal conductivity due to effective phonon scattering.
Non-Intrusive Heat Transfer Coefficient Determination in a Packed Bed of Spheres
Authors: Geb David J. , Catton Ivan
Published: March 2011

Non-intrusive measurements of the internal average heat transfer coefficient [1] in a randomly packed bed of spherical particles are made. It is desired to establish accurate results for this simple geometry so that the method used can then be extended to determine the heat transfer characteristics in any porous medium, such as a compact heat exchanger. Under steady, one-dimensional flow the spherical particles are subjected to a step change in volumetric heat generation rate via induction heating. The fluid temperature response is measured. The average heat transfer coefficient is determined by comparing the results of a numerical simulation based on volume averaging theory with the experimental results. More specifically, the average heat transfer coefficient is adjusted within the computational procedure until the predicted values of the fluid outlet temperature match the experimental values. The only information needed is the basic material properties, the flow rate, and the experimental data. The computational procedure alleviates the need for solid and fluid phase temperature measurements, which are difficult to make and can disturb the solid-fluid interaction. Moreover, a simple analysis allows us to proceed without knowledge of the heat generation rate, which is difficult to determine due to challenges associated with calibrating an inductively-coupled, sample specific, heat generation system. The average heat transfer coefficient was determined, and expressed in terms of the Nusselt number, over a Reynolds number range of 20–600. The results compared favorably to the work of Whitaker [2] and Kays and London [3]. The success of this method, in determining the average heat transfer coefficient in a randomly packed bed of spheres, suggests that it can be used to determine the average heat transfer coefficient in other porous media.
Experimental Study on Gas Cooler Heat Transfer Characteristics Applied in CO2 Supercritical Cycle Heat Pump Water Heater
Authors: Liu Yefeng , Zhang Hua , Cai Caoping , Wu Weidong , Qi Yingxia
Published: March 2011

One CO2 heat pump water heater test apparatus was built in the paper. The heat transfer characteristics of CO2 in gas cooler with water in double-pipe heat exchanger was experimentally investigated. The effects of variation of cooling water flux on heat transfer characteristics, outlet temperature of water, COP and CO2 temperature were analyzed. The influences of cooling water flux to heat exchange about CO2 side, water side, and the CO2 and water temperature matching was analyzed. Experimental results showed that the supercritical CO2 heat pump water heater can acquire higher temperature of outlet water up to 80°C than those conventional Freon heat pump water heater, and the COP of the system increased with the increase of water flow rate through gas cooler. All the work was valuable for the application of CO2 heat pump water heater.
Mass Nature of Heat and Its Applications III: Thermomass Model Based Damped Wave in Dielectrics
Authors: Hou Quan-Wen , Wang Hai-Dong
Published: March 2011

The character of wave model for heat conduction is studied by numerical simulation of heat conduction in silicon heated by laser pulse. Based on the damping of the temperature peak, the penetration depth of thermal wave can be defined which gives a new division of heat conduction regime for experiments. The thermal wave is expected to be observed when the system is shorter than the penetration depth. In the thermomass model, the penetration depth is about one magnitude larger than that in CV model. Consequently, it gives a wider region to observe thermal wave phenomena.
Heat Transfer Characteristics of Low Reynolds Number Turbulent Swirling LPG/Air Flame Impinging on a Flat Surface
Authors: Kaushal Arun , Singh Gurpreet , Chander Subhash , Ray Anjan
Published: March 2011

An experimental study has been conducted to determine the heat transfer characteristics for low Reynolds number turbulent swirling LPG/Air flames impinging on a flat surface. Effect of variation of Reynolds number (3000–7000), dimensionless separation distance (H/d = 1 to 6) and equivalence ratio (φ = 0.8 to 2) on heat transfer characteristics has been determined at constant swirl number of 4. Further, experiments were also conducted to investigate the effect of swirl number on heat transfer characteristics at Re = 7000, φ = 1.0 and H/d = 5. It has been concluded that the major drawback of flame impingement i.e., non-uniformity in the heating can be resolved by using swirling flames in place of non-swirling flames. With increase in Reynolds number the flame becomes longer and broader. Also, at higher Re the flame becomes noisy and violent because of the enhanced turbulences in the flame. A dip in the temperature was observed at the stagnation point at all Re and this dip was more significant at higher Re. At small separation distances (H/d = 1 and 2) and at large Reynolds numbers (Re = 7000) heating is comparatively more non-uniform because of close proximity of the visible reaction zone to the plate resulting in intense heating in the stagnation region. High average heat fluxes were obtained at low separation distances and at larger Reynolds numbers.
Heat Transfer in Vapour-Liquid Flow at High Reduced Pressures
Authors: Yagov Victor , Minko Maria
Published: March 2011

During the last decade a number of studies of boiling heat transfer in carbon dioxide notably increase. As a field of CO2 practical using corresponds to high reduced pressures, and a majority of available experimental data on CO2 flow boiling even in submillimetric channels relate to turbulent liquid flow regimes, a possibility arises to develop sufficiently general method for HTC predicting. Under the above conditions nucleate boiling occurs up to rather high flow quality, even in annular flow regime due to extremely small size of an equilibrium vapour bubble. This conclusion is in agreement with the available experimental data. The predicting equation for nucleate boiling heat transfer developed by one of the present authors in 1988 is valid for any nonmetallic liquid. A contribution of forced convection in heat transfer is calculated according to the Petukhov et al. equation with correction factor, which accounted for an effect of velocity increase due to evaporation. This effect can be essential at relatively small heat fluxes and rather high mass flow rates. The Reynolds analogy and homogeneous model are used in order to account for the convective heat transfer augmentation in two-phase flow. Due to low ratio of liquid and vapour densities at high reduced pressures the homogeneous approximation of two-phase flow seems to be warranted. A total heat transfer coefficient is calculated as an interpolated value of boiling and convective HTCs. The experimental data on CO2 flow boiling related to regimes before heated wall dryout incipience are in rather good agreement with the calculations. Besides the data on carbon dioxide flow boiling, the results on water, helium, nitrogen and some refrigerants were used for comparison; at rather high reduced pressures the computed and the measured values of HTCs are in a good agreement. The data include results obtained in the channels of a diameter from 0.6mm up to 18mm. It is clear that at high reduced pressures there is no strong variation in boiling heat transfer with channel size decrease, it means that a classification on channel size has no sense if it does not consider liquid/vapour densities ratio.
Numerical Investigation of Heat Transfer for Laminar and Turbulent Flow in a Plate Heat Exchanger
Authors: Gherasim Iulian , Galanis Nicolas , Nguyen Cong Tam
Published: March 2011

The problem of turbulent flow and heat transfer in a two-channel plate heat exchanger was numerically investigated, considering its complex geometry as well as inlet and outlet ports effects. Results obtained for the flow and thermal field have clearly shown their asymmetrical behavior, which has important influence on the local heat transfer. Friction factor are found to be in good agreement with theoretical correlation.
Numerical Simulation of Heterogeneous Flows and Heat-Mass Transfer in Complex Domains on Rectangular Grids
Authors: Ershova T. V. , Mikhatulin D. S. , Reviznikov D. L. , Sposobin A. V. , Vinnikov V. V.
Published: March 2011

This paper is concerned with numerical simulation of two-phase flows in complex computational regions. Both nozzle flow and jet-obstacle interaction are considered. The presence of dispersed phase (solid or liquid particles) may lead to specific thermal and erosional interaction of inertial particles with the nozzle walls and the obstacle material. The latter makes the conjugated problem much more complicated. Therefore, we consider the complete flow field in the nozzle-jet-obstacle system. The present work is a continuation of the recent study by the authors [1, 2]. A unified approach to the general problem of a two-phase nozzle-jet-obstacle flow is suggested. In this approach, both the continuous and dispersed phase behavior is calculated using the fixed rectangular grids. The solution of transient conduction equation in the solid is also carried out on rectangular grids. Both dynamics and heating/cooling of particles are calculated using the discrete-element method in Lagrangian variables. The computational model includes many mechanical effects such as collisions of particles with each other, reflection of particles from the wall surface and the feedback effect of the dispersed phase on the gas flow. The distinctive feature is the direct numerical simulation of dispersed phase dynamics, where each single real particle in the flow has its computational counterpart. All governing equations for continuous fields are solved on rectangular grids using a ghost-cell immersed boundary method. This method provides discretization of the appropriate boundary conditions via a procedure of polynomial approximation. Such approach works well for both the incompressible and compressible flows. Rectangular grids allow a straightforward implementation of high order TVD and ENO schemes for the numerical simulation of gas flows. The immersed boundary method is perfectly suited for the problems within a computational domain of varying geometry, since it doesn’t require rebuilding the grid after each boundary movement. This feature was successfully used in the numerical simulation of erosive destruction of the circular cylinder in the two-phase flow [2], where the mass carried away from the body resulted in moving boundaries. The current work incorporates the previous methods and algorithms into the software package allowing the numerical investigation of heterogeneous flows in more complex configurations.
Thermo-Hydraulic Performance of a Heat Exchanger Consisting of Metal Foam Covered Tubes
Authors: T’Joen Christophe , De Jaeger Peter , Huisseune Henk , De Paepe Michel
Published: March 2011

Open cell metal foam offers an interesting combination of materials properties from a heat exchanger point of view such as a high specific surface area, tortuous flow paths for flow mixing and low weight. A heat exchanger design with metal foams is studied in this work, aimed at low airside pressure drop. It consists of a single row of Al tubes covered with thin layers (4–8 mm) of metal foam. Through wind tunnel testing the impact of various parameters on the thermo-hydraulic performance was considered, including the Reynolds number, the tube spacing, the foam height and the type of foam. The results indicated that if a good metallic bonding between the foam and the tubes can be achieved, metal foam covered tubes with a small tube spacing, small foam heights and made of foam with a high specific surface area potentially offer strong benefits at higher air velocities (> 4 m/s) compared to helically finned tubes. The bonding was done by conductive epoxy glue and was found to have a strong impact on the final results, showing a strong need for a cost-effective and efficient brazing process to connect metal foams to the tube surfaces.
Use of Optimum Seeking Method in Test of Heat Transfer Performance of Finned Tubes
Authors: Ouyang Xinping , Zhang Hua , Liu Ni , Wu Guomei
Published: March 2011

Curve fitting method is often used in the test of heat transfer performance of heat exchangers. The convective heat transfer coefficient may be obtained with the method. However, there are defects with the method. A New Curve fitting method is introduced in this paper. Optimum seeking method is adopted in the New Curve fitting method. The new method is a practical method for test of convective heat transfer coefficient. There are few constraint with the method. Moreover, the results are more precise and the test is more convenient. The method is especially suitable for test of convective heat transfer coefficient of finned tubes outer surface. Two instances of use of the method are given.
Analysis of Local Heat Transfer in Plate Heat Exchangers for Flow Pattern Optimisation
Authors: Kabelac Stephan
Published: March 2011

Plate heat exchangers are already very effective and successful in liquid to liquid heat transfer. Nevertheless there is still room for improvement if more details about flow maldistribution and specifically about the coupling between flow interactions and heat transfer mechanisms on a local scale would be accessible. The relation between surface corrugation of the plates and thermal effectiveness is known, if at all, to the manufactors only. This contribution will report on an experimental study of local heat transfer within corrugated plate heat exchangers. The resolution of the experimental procedure is better than 0.5 × 0.5 mm. The measurements are performed using the Temperature Oscillation InfraRed Thermography (TOIRT) method, which can resolve a local heat transfer coefficient behind a surface with an uncertainty of less than 10% if the flow is turbulent. The outer surface is periodically heated by means of sinodial laser radiation, the temperature response of the plate surface to this excitement is recorded by a lockin IR-camera. The phase shift between heat flux excitement and temperature response as seen by the IR camera is depending, among other parameters, on the heat transfer coefficient on the back side of the plate. This can be extracted using a numerical model based signal evaluation, thus enabling an intrusion free measurement. Plates with different corrugation angles and different flow fields have been analysed in detail. The result of this analysis gives rise to an understanding of the distribution of the local heat transfer coefficient as a function of topology of the plate and as a function of flow parameters. These results will be discussed on behalf of improvement potential for corrugated plates.
The Ground Source Heat Pump: A System Analysis With a Particular Focus on The U-Pipe Borehole Heat Exchanger
Authors: Madani Hatef , Acun˜a Jose , Claesson Joachim , Lundqvist Per , Palm Bjo¨rn
Published: March 2011

The mass flow rate of the secondary refrigerant flowing in the borehole heat exchanger of a ground source heat pump is an influential system parameter whose variation can influence the pumping power, efficiency of the pump, heat distribution in the borehole, heat pump heat capacity, and above all, the system Overall Coefficient Of Performance (COP). The present paper uses both in-situ field measurements and modeling to evaluate these effects. From the field measurements, it can be concluded that the thermal contact between U-pipe channels increases as the brine mass flow rate decreases. Furthermore, the modeling results show that there is a certain optimum brine mass flow rate which gives a maximum overall system COP. Different optimum mass flow rates are obtained for different compressor speed and it is shown that their relation is almost linear. However, concerning system COP maximization, it can be concluded that a constant but carefully-selected brine mass flow rate can still be an appropriate option for the variable capacity heat pump unit studied in the present paper where the compressor frequency changes between 30Hz and 75Hz. Concerning the heat capacity maximization in the system, a variable speed brine pump can be used to help the insufficiently-sized compressor to cover the peak heat demand of the building.
Unified Integral Transform Approach in the Hybrid Solution of Multidimensional Nonlinear Convection-Diffusion Problems
Authors: Cotta Renato M. , Quaresma Joa˜o N. N. , Sphaier Leandro A. , Naveira-Cotta Carolina P.
Published: March 2011

The present work summarizes the theory and describes the algorithm related to the construction of an open source mixed symbolic-numerical computational code named UNIT — Unified Integral Transforms, that provides a development platform for finding solutions of linear and nonlinear partial differential equations via integral transforms. The reported research was performed by making use of the symbolic computational system Mathematica v.7.0 and the hybrid numerical-analytical methodology Generalized Integral Transform Technique — GITT. The aim here is to illustrate the robust and precision controlled simulation of multidimensional nonlinear transient convection-diffusion problems, while providing a brief introduction of this open source code. Test cases are selected based on nonlinear multi-dimensional formulations of the Burgers equations, with the establishment of reference results for specific numerical values of the governing parameters. Special aspects and computational behaviors of the algorithm are then discussed, demonstrating the implemented possibilities within the present version of the UNIT code.
Numerical Study of Laminar Flow and Mass Transfer for In-Line Spacer-Filled Passages
Authors: Beale S. B. , Pharoah J. G. , Kumar A. , Mojab S. M.
Published: March 2011

Performance calculations for laminar fluid flow and mass transfer are presented for a spacer-filled passage containing cylindrical spacers configured in an inline-square arrangement, typical of those employed in the process industries. Numerical calculations are performed for fully-developed flow, based on stream-wise periodic conditions for a ‘unit cell’ and compared with those obtained for developing regime in a row of 10 such units. The method is validated for an empty passage (i.e. a plane duct). Results are presented for the normalized mass transfer coefficient and driving force, as function of mean flow Reynolds number, and also the wall mass flux, or blowing parameter. Both constant and variable wall velocities were considered, the latter being typical of those found in many practical membrane assemblies.
Influence of Adsorbent Properties on Enthalpy Wheel Performance
Authors: Sphaier L. A. , Worek W. M.
Published: March 2011

Enthalpy wheels are regenerative heat exchangers capable of both latent and sensible heat transfer and, thereby, have a variety of industrial applications. Due to the relevance of these type of exchangers, a notable number of studies were presented over the last decades, and different levels of improvement on problem formulation were obtained. This paper presents simulations results using a unified formulation for heat and mass transfer regenerators and generalized effectiveness-NTU methodology, both developed in recent years. The presented analysis focuses on examining the effects of adsorbent properties, such as the water uptake and heat of sorption, on exchanger performance. The results show, as expected, that the performance is worse for materials with higher heat of sorption. On the other hand, when examining the adsorption isotherm form, it is seen that the employment of a favorable isotherm not necessarily results in better energy and mass exchange performance.
Mass Nature of Heat and Its Application VII: Coupled Heat and Mass Transfer Optimization Based on the Entransy Theory
Authors: Chen Qun , Wang Moran , Pan Ning , Guo Zeng-Yuan
Published: March 2011

Using the analogy between heat and mass transfer processes, the recently developed entransy theory is extended in this paper to tackle the coupled heat and mass transfer processes so as to analyze and optimize the performance of evaporative cooling systems. We first introduce a few new concepts including the moisture entransy, moisture entransy dissipation, and the thermal resistance in terms of the moisture entransy dissipation. Thereinafter, the moisture entransy is employed to describe the endothermic ability of a moist air. The moisture entransy dissipation on the other hand is used to measure the loss of the endothermic ability, i.e. the irreversibility, in the coupled heat and mass transfer processes, which consists of three parts: (1) the sensible heat entransy dissipation, (2) the latent heat entransy dissipation, and (3) the entransy dissipation induced by a temperature potential. And then the new thermal resistance, defined as the moisture entransy dissipation rate divided by the squared refrigerating effect output rate, is recommended as an index to effectively reflect the performance of the evaporative cooling system. Meanwhile, a minimum thermal resistance law for optimizing the evaporative cooling systems is developed. In the end, several direct and indirect evaporative cooling processes are analyzed to illustrate the applications of the proposed concepts.
Analysis of Influences of Soil Characteristics on the Underground Heat Exchanger With a Novel Heat and Mass Transfer Model
Authors: Li Sufen , Li Haijun , Wang Jinxiang , Shang Yan , Dai Lanhua , Dong Ming
Published: March 2011

In this paper, a novel heat and mass transfer model was used to simulate the temperature field of both the U-tube heat exchanger and soil around it. Beside two-dimensional N-S equations were solved to consider the seepage of groundwater, an energy equation coupling thermal conduction and groundwater advection was enclosed in the model as well. The energy equation was built according to the real conditions of the U-tube and seepage flow in the soil. Through analyzing the simulation results, the effects of groundwater seepage to the heat transfer process and thermal short-circuiting among U-tube legs are obtained. The influences of soil type, soil physical aspects and backfill on the soil temperature field around the single U-tube of an underground heat exchanger were studied at the same time. The conclusions had great academic significance to the analysis and designing of the underground heat exchanger.
Numerical Simulation of Gas/Oil Co-Combustion Process and Thermal NOx Formation in a Retrofitted Oil-Burning Boiler
Authors: Li Haijun , Li Sufen , Pan Xinxiang , Pu Jianguo , Wang Xudong
Published: March 2011

The purpose of this paper is to realize oil/gas co-combustion in an oil-burning boiler and to examine the effect of co-combustion of heavy fuel oil and refinery gas on the thermal NOx formation. The analysis was carried out by means of 3-D numerical simulation. Comprehensive mathematical model of the furnace was setup to include all relevant aerodynamic and thermo-chemical processes in the furnace. Heat transferred to the furnace walls and temperature field in the furnace were also examined in order to establish regions of safe and efficient boiler operation for different operational conditions. Realization of oil/gas co-firing safely, efficiently and with lower NOx emission in many old oil-burning boilers by retrofitting does not only deal with combustible waste gas, but also take advantage of thermal energy from the refinery gas.
Heat Transfer Enhancement in a Double Pipe Heat Exchanger by Insertion of Propeller-Type Swirl Generators
Authors: Wongcharee Khwanchit , Pethkool Somsak , Thianpong Chinaruk
Published: March 2011

This paper describes an experimental study of turbulent convective heat transfer and flow friction characteristics in a double tube heat exchanger equipped with propellers (2 blade-type). The propellers are used as the decaying swirl generators in the inner tube. The experiments were performed using the propellers with four different interval lengths (l = 1D, 2D, 3D and 4D where D is diameter of the inner tube), for the Reynolds number ranging from 5000 to 32,000, using water with temperature of 27°C and 70°C as cold and hot working fluids, respectively. The data of the tube equipped with the propellers are reported together with those of the plain tube, for comparison. The obtained results demonstrate that the heat transfer rate in term of Nusselt number (Nu) and friction factor (f) in the tube with propellers are higher than those in the plain tube at the similar operating conditions. This is due to the chaotic mixing and efficient interruption of thermal boundary layer caused by the propellers. In addition, the Nusselt number and friction factor in the tube fitted with the propellers increase as the interval length decreases. Depending on Reynolds number and interval length, Nusselt numbers and friction factors in the tube fitted with the propellers are augmented to 1.95 to 2.3 times and 5.8 to 13.2 times of those in the plain tube. In addition, the correlations of the Nusselt number (Nu) and the friction factor (f) for tube fitted with the propellers are reported and the performance evaluation to access the real benefits of using the turbulators is also determined.