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Nusselt Number (nusselt + number)

Distribution by Scientific Domains

Engineering	61%
Chemistry	25%
Mathematics and Statistics	9%

Kinds of Nusselt Number

average nusselt number

Selected Abstracts

Numerical simulation of heat transfer and fluid flow over two rotating circular cylinders at low Reynolds number

HEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 4 2010
Nikolay Pavlovich Moshkin
Abstract This paper presents a numerical investigation of the characteristics of two-dimensional heat transfer in a steady laminar flow around two rotating circular cylinders in a side-by-side arrangement. The simulation is validated by comparing our computational results for the large gap-spacing between cylinder surfaces with the available numerical and experimental data for a single cylinder. Numerical simulations were carried out for the Reynolds number range 10,Re ,40, for the Prandtl number range 0.7,Pr ,50, and for a variety of absolute rotational speeds (|,|,2.5) at different gap spacings. The study revealed that for the range of parameters considered the rate of heat transfer decreases with the increasing speed of rotation. An increase of the Prandtl number resulted in an increase in the average Nusselt number. The streamlines and isotherms are plotted for a numbers of cases to show the details of the velocity and thermal fields. © 2010 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20293 [source]

Heat and fluid flow characteristics inside differentially heated square enclosures with single and multiple sliding walls

HEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 7 2009
E.M. Wahba
Abstract Fluid flow and heat transfer characteristics of differentially heated lid driven cavities are numerically modeled and analyzed in the present study. One-, two-, and four-sided lid driven cavity configurations are considered with the vertical walls being maintained at different temperatures and the horizontal walls being thermally insulated. Eight different cavity configurations are considered depending on the direction of wall motion. The Prandtl number Pr is taken to be 0.7, the Grashof number is taken to be 104, while two values for the Richardson number Ri are considered, 0.1 and 10. It is found that both the Richardson number and the cavity configuration affect the heat and fluid flow characteristics in the cavity. It is concluded that for Ri=0.1, a four-sided driven cavity configuration with all walls rotating in the same direction would triple the value of the average Nusselt number at the cold wall when compared to a one-sided driven cavity configuration. However, for Ri=10, the cavity configuration has minimal effect and all eight cases result in an average Nusselt number value at the cold wall ranging between 1.3 and 1.9. © 2009 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience (www.interscience. wiley.com). DOI 10.1002/htj.20264 [source]

Study on heat transfer characteristics of porous metallic heat sink with conductive pipe under bypass effect

HEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 3 2009
Sheng-Chung Tzeng
Abstract The work investigated the forced convection heat transfer of the heat sink situated in a rectangular channel by considering the bypass effect. The fluid medium was air. The relevant parameters were the Reynolds number (Re), the relative top by-pass gap (C/H), and the relative side by-pass gap (S/L). The size of the heat sink was 60 mm (L)×60 mm(W)×24 mm(H). Two heat sinks were employed as test specimens: (A) the 0.9-porosity aluminum foam heat sink and (B) the 0.9-porosity aluminum foam heat sink with a 20 mm diameter copper cylinder. The copper cylinder was used as a conductive pipe of heat sink. The average Nusselt number was examined under various forced convection conditions. Experimental results demonstrate that increasing by-pass space decreased the Nusselt number. Besides, the average Nusselt number of mode B heat sink was higher than that of mode A heat sink by 30% for the case without by-pass flow. The heat transfer enhancement by the copper cylinder would decline as the by-pass space grew. © 2009 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20247 [source]

Convective heat transfer and pressure drop of annular tubes with three different internal longitudinal fins

HEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 1 2008
Lin Tian
Abstract Pressure drop and heat transfer characteristics of air in three annular tubes with different internal longitudinal fins were investigated experimentally at uniform wall heat flux. The tested tubes have a double-pipe structure with the inner blocked tube as an insertion. Three different kinds of fins, plain rectangle fin, plain rectangle fin with periodical ridges and wave-like fin, were located peripherally in the annulus. The friction factor and Nusselt number can be corrected by a power-law correction in the Reynolds number range tested. It was found that the tube with periodical ridges on the plain fin or with wave-like fin could augment heat transfer; however, the pressure drop was increased simultaneously. In order to evaluate the comprehensive heat transfer characteristics of the tested tubes, two criteria for evaluating the comprehensive thermal performance of tested tubes were adopted. They are: 1) evaluating the comprehensive heat transfer performance under three conditions: identical mass flow, identical pumping power, and identical pressure drop; 2) the second law of thermodynamics, i.e., the entropy generation. According to the two different evaluating methods, it was found that the tube with wave-like fins provided the most excellent comprehensive heat transfer performance among the three tubes, especially when it was used under higher Reynolds number conditions. © 2007 Wiley Periodicals, Inc. Heat Trans Asian Res, 37(1): 29,40, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20186 [source]

Internal gravity wave resonance of thermal convection fields in rectangular cavities with heat-flux vibration (effects of aspect ratio on the fields)

HEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 3 2007
Shota Matsumura
Abstract In this paper the thermal convection field and its resonance phenomena in a rectangular cavity with heat-flux vibration are numerically examined and the results are compared with those of a square cavity. As in the case of ,=1, the critical angular velocity at which the relative amplitude of the midplane Nusselt number ,m has a local maximum agrees very well with the resonance angular velocity of the internal gravity wave ,r, estimated by the theoretical equation proposed by Thorpe, even when the aspect ratio is ,=5 and the Prandtl number is Pr=0.71 for a range of the Rayleigh number Ra. However, ,m has two local maxima for a larger Ra, which is peculiar to the case of larger ,. The time variation of sub-components of the fluctuating component of the midplane Nusselt number shows that the phase at the maximum value of ,m agrees well with that of the sub-component of velocity for the first resonance angular velocity ,r. For the other angular velocity ,r2, the phase of ,m agrees with that of the sub-component of temperature. Moreover, we found that the boundary angular velocity ,0 between the first two of the five , regions, which classify the thermal convection fields against ,, can be expressed by a function of ,, Ra, and Pr and that ,m is independent of , and Ra for a relatively wide range of ,/,0. © 2007 Wiley Periodicals, Inc. Heat Trans Asian Res, 36(3): 158, 171, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20149 [source]

An investigation on thermal-recycling of recycled plastic resin (spherically symmetric analysis of abrupt heating processes of a micro plastic-resin particle)

HEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 4 2006
Ryuji Yamakita
Abstract A fundamental understanding of the physical properties of a micro plastic-resin particle subjected suddenly to hot combustion gas, such as the temperature history in the micro particle and its lifetime, is necessary for effectively realizing thermal recycling of recycled plastic resin. However, micro plastic particles have such small diameters, ranging from 100 µm to 200 µm, that the measurement of temperature histories within them is extremely difficult. In this paper, therefore, a spherically symmetric one-dimensional analysis is applied to the abrupt heating process of a micro plastic resin particle in a high temperature inert atmosphere. Variations of the temperature history and the lifetime with the ambient gas temperature and the initial particle diameter are numerically analyzed, by dividing the entire heating process into four independent periods; the solid heating period, the melting period, the liquid heating period, and the vaporization period. Effects of the Nusselt number on the particle lifetime are also discussed. It is found that, by suitably taking account of the influences of heat transfer properties, the proposed simplified analysis is useful for estimating the fundamental and overall temperature characteristics of a micro plastic resin particle under abrupt heating. © 2006 Wiley Periodicals, Inc. Heat Trans Asian Res, 35(4): 279,293, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20113 [source]

Heat transfer and fluid flow characteristics in a swirling impinging jet

HEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 5 2005
Mamoru Senda
Abstract An experimental study on heat transfer and fluid flow has been carried out for a swirling round impinging jet. A thermosensitive liquid crystal sheet was used for the heat transfer measurements and the three velocity components were measured with LDV in the stagnation region for cases where the Swirl number Sw = 0.0, 0.22, and 0.45 at the Reynolds number Re = 8100. The formation of recirculation flow due to a swirl near the impinging wall was found to deteriorate the heat transfer coefficient in the stagnation region and results in a more uniform distribution of the Nusselt number with an increasing Swirl number. The heat transfer mechanism of the swirling impinging jet is discussed based on the flow characteristics of the mean velocities and turbulence quantities. © 2005 Wiley Periodicals, Inc. Heat Trans Asian Res, 34(5): 324,335, 2005; Published online in Wiley InterScience (www.interscience. wiley.com). DOI 10.1002/htj.20068 [source]

Heat transfer for Marangoni-driven boundary layer flow

HEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 2 2002
David M. Christopher
Abstract Marangoni convection induced by variation of the surface tension with temperature along a surface influences crystal growth melts and other processes with liquid,vapor interfaces, such as boiling in both microgravity and normal gravity in some cases. This paper presents the Nusselt number for Marangoni flow over a flat surface calculated using a similarity solution for both the momentum equations and the energy equation assuming developing boundary layer flow along a surface. Solutions are presented for the surface velocity, the total flow rate, and the Nusselt number for various temperature profiles, Marangoni numbers, and Prandtl numbers. For large bubbles, the predicted boundary layer thickness would be less than the bubble diameter, so the curvature effects could be neglected and this analysis could be used as a first estimate of the effect of Marangoni flow around a vapor bubble. © 2002 Scripta Technica, Heat Trans Asian Res, 31(2): 105,116, 2002; DOI 10.1002/htj.10019 [source]

Unsteady free convection,radiation flow over a vertical wall embedded in a porous medium

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 11 2008
Joaquín Zueco
Abstract A numerical solution for the transient two-dimensional free convection flow of viscous dissipative fluid over an infinite vertical plate through a porous medium bounded, taking into account the thermal radiation, is analysed. The fluid is grey, and acts as a radiation emitting and absorbing (but non-scattering) medium. The influence of the non-dimensional parameters such as the Forchheimer coefficient (Fo), the permeability parameter (P), the Eckert number (Ec) and the radiation parameter (R) on the velocity, temperature, Nusselt number and on the time taken to reach the steady state is studied. The possibility of non-Darcy flow is also analysed. The numerical method employed, network simulation method, is based on an electro-thermal analogy and permits the direct visualization and evolution of the local and/or integrated transport variables (velocities, temperatures and fluxes) at any point or section of the medium. The numerical solutions of this work have been compared with the existing information in the literature with good agreement. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Volumetric methods for evaluating energy loss and heat transfer in cavity flows,

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 12 2007
Stuart Norris
Abstract Methods have been developed for calculating irreversible energy losses and rates of heat transfer from computational fluid dynamics solutions using volume integrations of energy dissipation or entropy production functions. These methods contrast with the more usual approach of performing first law energy balances over the boundaries of a flow domain. Advantages of the volumetric approach are that the estimates involve the whole flow domain and are hence based on more information than would otherwise be used, and that the energy dissipation or entropy production functions allow for detailed assessment of the mechanisms and regions of energy loss or entropy production. Volume integrations are applied to the calculation of viscous losses in a lid-driven cavity flow, and to the viscous losses and heat transfer due to natural convection in a side-heated cavity. In the convection problem comparison with the entropy increase across a stationary heat conducting layer leads to a novel volume integral expression for the Nusselt number. The predictions using this method compare well with traditional surface integrals and benchmark results. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Calculation of turbulent fluid flow and heat transfer in ducts by a full Reynolds stress model

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 2 2003
Masoud Rokni
Abstract A computational method has been developed to predict the turbulent Reynolds stresses and turbulent heat fluxes in ducts by different turbulence models. The turbulent Reynolds stresses and other turbulent flow quantities are predicted with a full Reynolds stress model (RSM). The turbulent heat fluxes are modelled by a SED concept, the GGDH and the WET methods. Two wall functions are used, one for the velocity field and one for the temperature field. All the models are implemented for an arbitrary three-dimensional channel. Fully developed condition is achieved by imposing cyclic boundary conditions in the main flow direction. The numerical approach is based on the finite volume technique with a non-staggered grid arrangement. The pressure,velocity coupling is handled by using the SIMPLEC-algorithm. The convective terms are treated by the van Leer scheme while the diffusive terms are handled by the central-difference scheme. The hybrid scheme is used for solving the , equation. The secondary flow generation using the RSM model is compared with a non-linear k,, model (non-linear eddy viscosity model). The overall comparison between the models is presented in terms of the friction factor and Nusselt number. Copyright © 2003 John Wiley & Sons, Ltd. [source]

The effect of condenser heat transfer on the energy performance of a plate heat pipe solar collector

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 10 2005
Jorge Facão
Abstract For a novel prototype solar collector, using a plate heat pipe, condenser heat transfer was analysed in detail. The condenser has the shape of a rectangular channel. Flow and heat transfer of water in the rectangular channel was modelled and the heat transfer coefficient assessed, using the Fluent code. Under typical operating conditions a mixed convection situation occurs. The channel is inclined and heating is through one wall only (upper channel surface). The range of temperature differences considered was similar to the one verified under real operating conditions, covering a wide range of Grashof numbers. Results showed that the Nusselt number is significantly higher than the one for forced convection in a rectangular channel with fully developed boundary layers. In order to enhance heat transfer, a modification to the rectangular channel was analysed, using baffles to improve flow distribution and increase velocity. The effect of this modification on collector energy performance (efficiency) was assessed. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Heat transfer from a plate impinging swirl jet

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 4 2002
Kadir Bilen
Abstract Heat transfer and flow visualization experiments were conducted to investigate the performance of swirling and multi-channel impinging jets and compare the results with those of a multi-channel impinging jet (MCIJ) and conventional impinging jet (CIJ) for the present work at the same conditions. Swirling impinging jets (SIJs) employed the fixed blade lengths of 12.3 mm with four blades at the exit of the housing tube to divert the air flow through four narrow channels with a desired swirl angle (, of 22.5, 41 and 50°). The MCIJ jet had the same dimensions as the SIJs, except that the narrow channels in the solid insert were vertical (,=0°). The local and surface average Nusselt numbers of MCIJ were generally higher than those of the CIJ and SIJs. The SIJs, however, demonstrated significant improvement in radial uniformity of heat transfer compared to the MCIJ and CIJ. In the region of 2.7,X/D,0 for H/D=8 and Re=20 000, the average Nusselt number for the MCIJ was 11, 33, 72 and 98 per cent higher than that of the CIJ, ,=22.5, ,=41 and ,=50°, respectively. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Thermal performance analysis of a tube finned surface

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 4 2002
Kadir Bilen
Abstract The present work submits an experimental work on the heat transfer and friction loss characteristic, employing a tube finned heating surface kept at a constant temperature in a rectangular channel. The tube fins attached on the surface (o.d.=29 mm) were arranged as either in-line or staggered. The parameters for the study were Reynolds number (3700,30 000), depending on hydraulic diameter, the distance between the tube fins in the flow direction (Sy/D=1.72,3.45) and the fin arrangement. The change in the Nusselt number with these parameters was determined. For both tube fin arrangements, it was observed that increasing Reynolds number increased Nusselt number, and maximum heat transfer occurred at Sy/D=2.59. Thermal performances for both arrangements were also determined and compared with respect to heat transfer from the same surface without fins. With staggered array, a heat transfer enhancement up to 25 per cent for Sy/D=3.45 in staggered array was achieved in constant pumping power. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Online temperature measurement and simultaneous diameter estimation of fibers by thermography of the spinline in the melt spinning process

ADVANCES IN POLYMER TECHNOLOGY, Issue 3 2004
M. Golzar
Abstract Online measurements of the temperature and the diameter of fibers in the melt spinning process of thermoplastics are discussed. The temperature and the diameter of fibers can be applied in many fields such as fiber formation modelling, cooling rate behavior (Nusselt number), and rheological investigations (apparent extensional viscosity) of polymers. The online measurements along the spinline were carried out with an infrared camera during the melt spinning process. Two different experiments were designed and carried out to find the correction factor, i.e., the emissivity. The results show that the emissivity correction factor depends on the polymer type and the fiber diameter. Usually the diameter of the fibers is measured by an instrument or by direct velocity measurements invoking the continuity equation. In this new approach the diameter is found directly by the evaluation of the measured temperature. Therefore only one apparatus, namely an infrared camera taking snapshots, is required to find the fiber diameter. The key of this method can be seen in the temperature difference between the fiber and the environment. A mathematical procedure was developed to estimate the diameter of the fiber from the distribution curve. © 2004 Wiley Periodicals, Inc. Adv Polym Techn 23: 176,185, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20008 [source]

Effect of filament drawdown on aerodynamic drag and heat transfer in fiber spinning

AICHE JOURNAL, Issue 5 2004
C. Miller
Abstract The momentum and thermal boundary layer equations are solved numerically to assess the effects of filament drawdown on aerodynamic drag and heat transfer in melt fiber spinning. It is found that, relative to the case without drawdown (constant filament velocity and diameter), the aerodynamic drag on the filament increases substantially, but the heat transfer rate is suppressed. Moreover, the air velocity profile eventually becomes fully developed (unlike the zero drawdown case), and the (velocity) boundary layer thickness, rather than continuing to grow with distance beneath the spinneret, eventually becomes proportional to the filament diameter, and thus decreases with increasing axial distance. Quantitative results are presented for the dimensionless drag force per unit length along the filament (the Drag number) and the Nusselt number as functions of the dimensionless axial distance and a new dimensionless parameter, the Drawdown Reynolds number. © 2004 American Institute of Chemical Engineers AIChE J, 50: 898,905, 2004 [source]

CFD modeling of heat transfer in turbulent pipe flows

AICHE JOURNAL, Issue 9 2000
S. S. Thakre
Twelve versions of low Reynolds number k-, and two low Reynolds number Reynolds stress turbulence models for heat transfer were analyzed comparatively. Predictions of the mean axial temperature, the radial and axial turbulent heat fluxes, and the effect of Prandtl number on Nusselt number were compared with the experimental data. The model by Lai and So from the k-, group and Lai and So from the Reynolds stress group had the best overall predictive ability for heat transfer in turbulent pipe flow. The Lai and So model was attributed to its success in the predictions of flow parameters such as mean axial velocity, turbulent kinetic energy, eddy diffusivity, and the overall energy dissipation rate. The k-, models performed relatively better than the Reynolds stress models for predicting the mean axial temperature and the Nusselt number. This qualitative and quantitative study found the need for more sophisticated near-wall experimental measurements and the accuracy of the dissipation (of turbulent energy) and the pressure-scrambling models. [source]

Momentum and heat transfer over a continuously moving surface with a parallel free stream in a viscoelastic fluid

NUMERICAL METHODS FOR PARTIAL DIFFERENTIAL EQUATIONS, Issue 2 2010
T. Hayat
Abstract The flow and heat transfer characteristics for a continuous moving surface in a viscoelastic fluid are investigated. Constitutive equations of viscoelastic fluid obey the second-grade model. Analytic expressions to velocity and temperature have been developed by employing homotopy analysis method. The criterion to the convergence of the solution is properly discussed. Furthermore, the values of skin friction coefficient and the local Nusselt number have been computed and discussed. © 2009 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2010 [source]

Stretching a plane surface in a viscoelastic fluid with prescribed skin friction

NUMERICAL METHODS FOR PARTIAL DIFFERENTIAL EQUATIONS, Issue 6 2009
M. Sajid
Abstract A model of forced convection flow due to stretching surface is derived to represent the physical system with prescribed skin friction. To achieve the similar solutions, the partial differential equations are reduced into ordinary differential equations. The analytic solutions of the resulting problems have been obtained by a homotopy analysis method. The convergence of the developed series solution is seen. Finally, the results of velocity, temperature, the stretching velocity, and Nusselt number are analyzed. © 2008 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2009 [source]

Heat transfer behavior of melting polymers in laminar flow field

POLYMER ENGINEERING & SCIENCE, Issue 3 2004
Sadao Sato
Heat transfer coefficients were investigated by insertion of a probe into melting polymers under laminar flow at 200,240°C and a flow velocity of 0.5,2.7 mm/sec. The average heat transfer coefficients of melting polypropylene (PP) and polystyrene (PS) were found to be 160,220 W/m·°C and 180,270 W/m·°C, respectively. These coefficients show remarkable dependence on flow velocity, and the average heat transfer coefficient of PS is about 13%,23% higher than that of PP. When the flow velocity of flowing melting PP and PS exceeds about 0.078mm/sec, heat transfer by convection becomes dominant, whereas under lower flow velocities, since the equivalent conduction layer thickness ,, in which the quiescent state without flow approaches infinity, heat transfer by conduction becomes dominant. The Prandtl number (Pr) and Nusselt number (Nu) of melting PP are 125,133 × 106 and 38.6,51.4, respectively, and those of melting PS are 63,64 × 106 and 42.3,61.3. In the case of constant flow velocity, the Peclet number (Pe) and Stanton number (St) are dependent on the specific heat of melting polymer. Polym. Eng. Sci. 44:423,432, 2004. © 2004 Society of Plastics Engineers. [source]

Experimental and Numerical Simulation Study of Heat Transfer Due to Confined Impinging Circular Jet

CHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 10 2007
L. Chang-geng
Abstract An experimental and numerical simulation study of heat transfer due to a confined impinging circular jet is presented. In this research, a stainless steel foil heated disk was used as the heat transfer surface of a simulated chip, and the thermocouples were mounted symmetrically along the diameter of the foil to measure the temperature distribution on the surface. Driven by a small pump, a circular air jet (1.5,mm and 1,mm in diameter) impinged on the heat-transfer surface with middle and low Reynolds numbers. The parameters, such as Reynolds number and ratio of height-to-diameter, were changed to investigate the radial distribution of the Nusselt number and the characteristics of heat transfer in the stagnation region. Numerical computations were performed by using several different turbulence models. In wall bounded turbulent flows, near-wall modeling is crucial. Therefore, the turbulence models enhanced wall treatment, such as the RNG ,-, model, may be superior for modeling impingement flows. The numerical results showed reasonable agreement with the experimental data for local heat transfer coefficient distributions. The impinging jet may be an effective method to solve the cooling problem of high power density electronic packaging. [source]

Vapor Condensation Heat Transfer in a Thermoplate Heat Exchanger

CHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 7 2007
J. Mitrovic
Abstract The heat transfer and pressure drop in a thermoplate heat exchanger operating as a condenser have been investigated experimentally. In order to separate the heat transfer resistances in the condensation process, the single phase forced convection has been studied using distilled water and Marlotherm oil in the thermoplate and correlations developed for the Nusselt number and the friction factor. For the condensation experiments, an apparatus has been constructed comprising two identical condensers composed of the same thermoplate type as employed in the single phase experiments. Isopropanol is used as a test fluid at pressures below atmospheric pressure. The heat transfer resistances in the condensation experiments are separated and expressions for the condensation heat transfer and pressure drop are developed with the aid of the results obtained in the single phase studies. [source]

Effect of Thermal Asymmetry on Heat Transfer in a Laminar Annular Flow

CHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 10 2005
J. Mitrovi
Abstract The effect of thermal asymmetry on heat transfer in a hydrodynamically developed annular flow has been investigated numerically. The surfaces confining the fluid space are kept at constant but different temperatures. Depending on the fluid inlet temperature, the thermal asymmetry can lead to a discontinuity of the Nusselt number on one surface. With the thermally developed flow the exact expressions for the Nusselt numbers have been obtained. [source]

Fronts in reactive convection: Bounds, stability, and instability

COMMUNICATIONS ON PURE & APPLIED MATHEMATICS, Issue 12 2003
Peter Constantin
This paper examines a simplified active combustion model in which the reaction influences the flow. We consider front propagation in a reactive Boussinesq system in an infinite vertical strip. Nonlinear stability of planar fronts is established for narrow domains when the Rayleigh number is not too large. Planar fronts are shown to be linearly unstable with respect to long-wavelength perturbations if the Rayleigh number is sufficiently large. We also prove uniform bounds on the bulk burning rate and the Nusselt number in the KPP reaction case. © 2003 Wiley Periodicals, Inc. [source]

Melting of a vertical ice cylinder inside a rotating cylindrical cavity filled with binary aqueous solution

HEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 6 2008
Yoshimi Komatsu
Abstract The melting of a vertical ice cylinder into a homogeneous calcium chloride aqueous solution inside a rotating cylindrical cavity with several rotating speeds is considered experimentally. The melting mass and temperature are measured on four initial conditions of the solution and four rotating speeds of the cavity. The temperature of the liquid layer becomes uniform by the mixing effect resulting from cavity rotation and it enhances the melting rate of the ice cylinder. As the cavity-rotating speed increases, the melting rate increases. The dimensionless melting mass is related to the Fourier number and the rotating Reynolds number in each initial condition, therefore an experimental equation that is able to quantitatively calculate the dimensionless melting mass is presented. It is seen that the melting Nusselt numbers increase again in the middle of the melting process. The ice cylinder continues to melt in spite of the small temperature difference between the ice cylinder and the solution. © 2008 Wiley Periodicals, Inc. Heat Trans Asian Res, 37(6): 359,373, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20211 [source]

Heat transfer of combined forced and natural convection from horizontal cylinder to air

HEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 8 2007
Kenzo Kitamura
Abstract Experimental investigations have been carried out for combined convective flows of air induced around uniformly heated, horizontal cylinders. Three cases of aiding, opposing, and cross flows were examined. The experiments covered the ranges of the Reynolds and modified Rayleigh numbers of Red=50 to 900 and Rad*=5×104 to 3×106. The flow fields around the cylinders were visualized with smoke. The results showed that separation points gradually shift from those of the forced convection to the top edge of the cylinder with increasing wall heat fluxes. The local heat transfer coefficients of the cylinders were also measured. Although the local coefficients show complex variations with the forced flow velocities and the wall heat fluxes, the overall coefficients become higher than those estimated from pure forced and natural convections throughout the cases of aiding, opposing, and cross flows. Moreover, it was confirmed that the overall Nusselt numbers as well as the separation points can be predicted with the non-dimensional parameter (Grd*/NudRed2). © 2007 Wiley Periodicals, Inc. Heat Trans Asian Res, 36(8): 474,488, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20180 [source]

Numerical simulation of natural convection heat transfer in the open space between two horizontal circular planes

HEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 6 2001
Hideki Tokanai
Abstract Numerical simulations were conducted for natural convection heat transfer in a narrow gap between two horizontal plates in air. The lower plate is an infinite plate with a circular heating zone. The upper one is the bottom of a vertical cylinder, which is placed right above the circular heated plate and kept at room temperature. A set of Navier,Stokes equations and an energy equation are analyzed for a variety of combinations of gap clearance and Rayleigh number. The calculated average heat transfer values are shown to be in good agreement with the experimentally obtained ones reported in a previous paper. From the obtained isotherms, streamlines, and local Nusselt numbers, it is found that two types of convection appear in the gap space according to the conditions of Rayleigh number and gap clearance: one is a simple convection due to a single renewal flow which replaces heated air with ambient air and the other is a combined convection due to several vortex flows and a renewal flow. Furthermore, the flow rate of each flow controls the rate of heat transfer from the limited area which is covered by each flow. From this fact, the validity of the previously proposed heat transfer correlation is briefly discussed. © 2001 Scripta Technica, Heat Trans Asian Res, 30(6): 485,502, 2001 [source]

Heat transfer from a plate impinging swirl jet

Effects of Viscous Dissipation on Heat Transfer between an Array of Long Circular Cylinders and Power Law Fluids

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 6 2007
R. P. Chhabra
Abstract The free surface model has been combined with the equations of motion and of thermal energy to investigate the role of viscous dissipation on heat transfer between banks of long cylinders and power law (shear-thinning and shear-thickening) fluids. The equations of motion cast in the stream function/vorticity formulation have been solved numerically using a second-order accurate finite difference method to obtain extensive information on the behaviour of local and surface-averaged Nusselt numbers over a range of Reynolds numbers 1 , 500, for a wide range of power law indices (0.4 , n , 2.0), Brinkman numbers (0 , Br , 5) and Prandtl numbers (Pr = 1, 1000) at two representative solid volume fractions corresponding to the porosities of e = 0.4 and 0.9. Two different thermal boundary conditions are considered at the cylinder surface: constant temperature (CT) and constant heat flux (CHF). The results presented herein provide a fundamental knowledge about the influence of viscous dissipation on the heat transfer characteristics. The results reported herein further show that the effect of Brinkman number on heat transfer is strongly conditioned by the thermal boundary condition, Prandtl number and the power law index. On a combiné le modèle de surface libre aux équations de mouvement et de transfert de chaleur afin d'étudier le rôle de la dissipation visqueuse sur le transfert de chaleur entre des rangées de cylindres longs pour des fluides de loi de puissance (rhéofluidifiants et rhéoépaississants). Les équations de mouvement formulées en fonction de courant/vorticité ont été résolues numériquement à l'aide d'une méthode de différences finies du second ordre, afin d'obtenir des informations détaillées sur le comportement des nombres de Nusselt locaux et moyennés en surface pour une gamme de nombres de Reynolds compris entre 1 et 500, une large gamme d'indices de loi de puissance (0,4 , n , 2,0), de nombres de Brinkman (0 , Br , 5) et de nombres de Prandtl (Pr = 1,1000) à deux fractions de volume de solides correspondant à une porosité de e = 0,4 et 0,9. Deux conditions aux limites thermiques ont été considérées à la surface du cylindre: la température constante (CT) et le flux de chaleur constant (CHF). Les résultats présentés permettent de rendre compte de l'influence de la dissipation visqueuse sur les caractéristiques du transfert de chaleur et l'effet du nombre de Brinkman sur le transfert de chaleur qui est fortement influencé par la condition aux limites thermique, le nombre de Prandtl et l'indice de loi de puissance. [source]