Showing papers in "Heat and Mass Transfer in 1997"
TL;DR: In this paper, the shape-stabilized paraffin can be used in a latent heat storage system without encapsulation using a transient hot wire method, a differential scanning calorimeter (DSC), a water and a volume expansion meter.
Abstract: This report deals with thermophysical properties and measuring methods of shape-stabilized paraffin as a new type of latent heat storage material, which keeps the same shape in a solid state when the paraffin melts Therefore, this type paraffin can be used in a latent heat storage system without encapsulation A transient hot wire method, a differential scanning calorimeter (DSC), a water calorimeter and a volume expansion meter, which were developed in the present study, were used to measure effective thermal conductivity, latent heat, specific heat and density of the shape-stabilized paraffin, respectively From the obtained data, useful correlation equations of the above-mentioned thermophysical properties of the shape-stabilized paraffin were expressed as functions of physical property and mass fraction of each constituent of the shape-stabilized paraffin
252 citations
TL;DR: In this article, the effects of arrangement of pin fins on heat transfer and resistance are discussed and the row-by-row variations of the mean Nusselt numbers are presented.
Abstract: It has been experimentally researched that convective heat transfer and pressure loss characteristics in rectangular channels with staggered arrays of drop-shaped pin fins in crossflow of air. The effects of arrangements of pin fins on heat transfer and resistance are discussed and the row-by-row variations of the mean Nusselt numbers are presented. By means of the heat/mass transfer analogy and the naphthalene sublimation technique, the heat transfer coefficients on pin fins and on endwall (base plate) of the channel have been achieved respectively. The total mean heat transfer coefficients of pin fin channels are calculated and the resistance coefficients are also investigated. The experimental results show that heat transfer of a channel with drop-shaped pin fins is higher than that with circular pin fins while the resistance of the former is much lower than that of the latter in the Reynolds number range from 900 to 9000.
73 citations
TL;DR: In this article, a breadboard prototype of an absorption system for truck refrigeration using heat from the exhaust-gases was designed, built and tested, and the results show that the system is promising for long distance driving on flat roads.
Abstract: A breadboard prototype of an absorption system for truck refrigeration using heat from the exhaust-gases was designed, built and tested. Measured COP values of the unoptimized single-stage ammonia-water absorption cycle varied between 23 and 30%, but system modeling shows that this can be improved to values considerably over 30%. Computer simulation for the system included cycle analysis as well as component modeling, using a detailed two-fluid model for flow of the ammonia-water mixture in the condenser and absorber. This detailed model was also validated using test data. In addition, the recoverable energy of the exhaust gases was analyzed for representative truck-driving conditions for city traffic, mountain roads and flat roads. The results show that the system is promising for long distance driving on flat roads.
72 citations
TL;DR: In this paper, a free convertion flow of an optically dense viscous incompressible fluid along a vertical thin circular cylinder has been studied with effect of radiation when the surface temperature is uniform.
Abstract: A free convertion flow of an optically dense viscous incompressible fluid along a vertical thin circular cylinder has been studied with effect of radiation when the surface temperature is uniform. With appropriate transformations, the boundary layer equations governing the flow are reduced to local nonsimilarity equations. Solutions of the governing equations are obtained employing the implicit finite difference methods together with Keller box scheme as well the local nonsimilarity method with second order truncation for all ξ (nondimensional transverse curvature parameter) in the interval [0,10] and are expressed in terms of local Nusselt number for a range of values of the pertinent parameters. Effects of pertinent parameters, such as, the radiation parameter, R d , the surface temperature parameter, θ w , taking Prandtl number, Pr, equals 0.7 on the velocity and temperature field are also presented graphically. From the solution it is seen that increase of R d , or θ w leads to increase in the local rate of heat transfer coefficients. Results obtained by both the methods are obtained in excellent agreement between each other upto ξ = 10.
68 citations
TL;DR: In this paper, the authors studied the convection heat transfer in inclined rectangular enclosures with perfectly conducting fins attached to the heated wall and found that the heat transfer through the cover is considerably affected by the presence of the fins.
Abstract: The natural convection heat transfer in inclined rectangular enclosures with perfectly conducting fins attached to the heated wall is numerically studied. The parameters governing this problem are the Rayleigh number (102≤Ra≤2×105), the aspect ratio of the enclosures (2.5≤A=H′/L′≤∞), the dimensionless lengths of the partitions (0≤B=l′/L′≤1), the aspect ratio of micro-cavities (A≤C=h′/L′≤0.33), the inclination angle (0≤φ≤60∘) and the Prandtl number (Pr=0.72). The results indicate that the heat transfer through the cover is considerably affected by the presence of the fins. At low Rayleigh numbers, the heat transfer regime is dominated by conduction. When B≈0.75 and C≈0.33, the heat transfer through the cold wall decreases considerably. This trend is enhanced when the enclosure is inclined. Useful engineering correlations are derived for practical applications.
58 citations
TL;DR: In this paper, an exact solution for fully developed natural convection in open-ended vertical concentric annuli under a radial magnetic field is presented, where expressions for velocity field, temperature field, mass flow rate and skin-friction are given.
Abstract: Exact solutions for fully developed natural convection in open-ended vertical concentric annuli under a radial magnetic field are presented. Expressions for velocity field, temperature field, mass flow rate and skin-friction are given, under more general thermal boundary conditions. It is observed that both velocity as well as temperature of the fluid is more in case of isothermal condition compared with constant heat flux case when gap between cylinders is less or equal to radius of inner cylinder while reverse phenomena occur when the gap between cylinders is greater than radius of inner cylinder.
47 citations
TL;DR: In this paper, a finite difference method was used to solve the conservation of mass, momentum and energy in Laminar convection in enclosures bounded by a solid wall with its outer boundary at constant temperature while the opposing side has a constant heat flux.
Abstract: Laminar natural convection has been studied in enclosures bounded by a solid wall with its outer boundary at constant temperature while the opposing side has a constant heat flux. Two-dimensional equations of conservation of mass, momentum and energy, with the Boussinesq approximation are solved using a finite difference method. The numerical procedure adopted is based on the SIMPLER algorithm. Various parameters were: Rayleigh number (from 103 to 106), dimensionless conductivity of bounding wall (from 1 to 10) and dimensionless wall width (from 0.15 to 0.5), aspect ratio (from 0.5 to 1) and the inclination angle (from 30∘ to 180∘). The results are reduced in terms of the normalized Nusselt number as a function of the Rayleigh number, and other dimensionless parameters. The isotherms and streamlines are produced for various Rayleigh numbers and geometrical conditions. It is found that the heat transfer is an increasing function of the Rayleigh number, wall to fluid conductivity ratio, enclosure aspect ratio and a decreasing function of the wall thickness. It passes from a maximum for the inclination angle of about 80∘.
47 citations
TL;DR: In this paper, a-C,:H-Si films of different thickness were applied on the surface of copper discs which were coated by silicon-modified amorpheous hydrogenated carbon (a-C) films.
Abstract: At atmospheric pressure filmwise (FWC) and dropwise (DWC) condensation have been studied on the surface of copper discs which were coated by silicon-modified amorpheous hydrogenated carbon (a-C : H-Si) films of different thickness. On vertically oriented surfaces the DWC heat transfer coefficients were found to be larger by a factor of about 10 than the FWC coefficients which follow as function of surface subcooling temperature quite well Nusselt’s theory. Varying the angle of surface inclination, the DWC coefficient decreased down to about 40% of the vertical-surface values for 180° (face down orientation). The mean value for all inclination angles between 30° and 180° was calculated to be 87.6% of the maximum value for the 90°-orientation. Partly coating of the copper surface indicates a strong heat transfer enhancement of DWC over FWC even for relative small coated parts (e.g., 19%-coating yields an enhancement by a factor 2.3 for a cooling water flow rate of 4 m3/h). The diamond like properties of the a-C : H-coatings promise long stand times and thus application also in real technical condensation systems.
43 citations
TL;DR: In this article, a generalised porous medium model is used to study both Darcy and non-Darcy flow regimes in an axisymmetric cavity, and it is observed that an increase in radius ratio leads to higher Nusselt and Sherwood numbers along the inner wall.
Abstract: Double-diffusive natural convection in a fluid saturated porous medium has been investigated using the finite element method. A generalised porous medium model is used to study both Darcy and non-Darcy flow regimes in an axisymmetric cavity. Results indicate that the Darcy number should be a separate parameter to understand flow characteristics in non-Darcy regime. The influence of porosity on heat and mass transfer is significant and the transport rates may differ by 25% or more, at higher Darcy and Rayleigh numbers. When compared with the Darcy and other specialised models of Brinkman and Forchheimer, the present generalised model predicts the least heat and mass transfer rates. It is also observed that an increase in radius ratio leads to higher Nusselt and Sherwood numbers along the inner wall.
38 citations
TL;DR: In this study the true-colour image processing of the liquid crystal images was developed successfully and applied to the study of heat and mass transfer problems.
Abstract: In the last five years or so, true-colour image processing has gone being available mainly to highly technical users on expensive image processing systems to being used by virtually anyone who can use a desktop computer. Also, during the past 25 years, liquid crystals have emerged as reliable temperature sensors for heat transfer research, and have been applied in a number of situations to visualise the temperature distribution under complex flow fields. In this study the true-colour image processing of the liquid crystal (LC) images was developed successfully and applied to the study of heat and mass transfer problems. The history of this technique is reviewed and principal methods are described and some examples are presented.
38 citations
TL;DR: In this article, the incompressible laminar flow of air and heat transfer in a channel with a backward-facing step is studied for steady cases and for pulsatile inlet conditions.
Abstract: The incompressible laminar flow of air and heat transfer in a channel with a backward-facing step is studied for steady cases and for pulsatile inlet conditions. For steady flows the influence of the inlet velocity profile, the height of the step and the Reynolds number on the reattachment length is investigated. A parabolic entrance profile was used for pulsatile flow. It was found with amplitude of oscillation of one by Re=100 that the primary vortex breakdown through one pulsatile cycle. The wall shear rate in the separation zone varied markedly with pulsatile flows and the wall heat transfer remained relatively constant. The time-average pulsatile heat transfer at the walls was greater as with steady flow with the same mean Reynolds number.
TL;DR: In this paper, the influence of lateral mass flux and thermal dispersion on non-Darcy natural convection over a vertical flat plate in a fluid saturated porous medium was studied. And the authors showed that the boundary layer thickness decreases where as the heat transfer rate increases as the mass flux parameter passes from injection domain to the suction domain.
Abstract: The method of similarity solution is used to study the influence of lateral mass flux and thermal dispersion on non-Darcy natural convection over a vertical flat plate in a fluid saturated porous medium. Forchheimer extension is considered in the flow equations and the coefficient of thermal diffusivity has been assumed to be the sum of molecular diffusivity and the dispersion thermal diffusivity due to mechanical dispersion. The suction/injection velocity distribution has been assumed to have power function form Axl, where x is the distance from the leading edge and the wall temperature distribution is assumed to be uniform. When l=−1/2, similarity solution is possible, and the results indicate that the boundary layer thickness decreases where as the heat transfer rate increases as the mass flux parameter passes from injection domain to the suction domain. The increase in the thermal dispersion parameter is observed to enhance the heat transfer. The combined effect of thermal dispersion and fluid suction/injection on the heat transfer rate is discussed.
TL;DR: In this paper, the horizontal exchanger steam-water exposed to vibrations with frequency 20≤f≤120 [Hz] and amplitude 0.2≤A≤0.5 [mm] in the same direction as flow of medium was investigated.
Abstract: Investigation concerns the horizontal exchanger steam-water exposed to vibrations with frequency 20≤f≤120 [Hz] and amplitude 0.2≤A≤0.5 [mm] in the same direction as flow of medium. Experiments were executed for laminar flow in range of 430≤ Re≤2300. For the examined range the correlation equation was worked out:
where (Ka) represents the new nondimensional modulus, which takes into account the influence of vibration frequency on heat transfer:
Vibrations with high acceleration coefficient improve in general heat transfer, but nearing the resonance frequency can be harmful to the construction of the equipment.
TL;DR: In this article, the effect of radiation on Darcy's buoyancy induced flow of an optically dense viscous incompressible fluid along a heated inclined flat surface maintained at uniform temperature placed in a saturated porous medium with Rosseland diffusion approximation employing the implicit finite difference method together with Keller box elimination technique.
Abstract: The paper investigates the effect of radiation on Darcy's buoyancy induced flow of an optically dense viscous incompressible fluid along a heated inclined flat surface maintained at uniform temperature placed in a saturated porous medium with Rosseland diffusion approximation employing the implicit finite difference method together with Keller box elimination technique. Both the streamwise and normal components of the buoyancy force are retained in the momentum equations. The numerical results show that as the buoyancy parameter, ξ, increases the local Nusselt number increases. The results for the locally nonsimilar solutions are compared with the locally similar solutions for small angle of inclination and approximate similar solutions along vertical surface. The effect of the conduction-radiation parameter, Rd, and the surface temperature excess ration, θw, on the local Nusselt number, the tangential velocity distribution and the temperature distribution are also shown graphically.
TL;DR: In this paper, a model of the absorption process in a vertical tubular bubble absorber working with R22-DMF, R 22-DMA, R22 -DMETEG and R 22 -NMP is developed using finite element method employing Galerkin's technique.
Abstract: A model of the absorption process in a vertical tubular bubble absorber working with R22-DMF, R22-DMA, R22-DMETEG, R22-DMEDEG and R22-NMP is developed using finite element method employing Galerkin's technique. The objective of this paper is to study the influence of the liquid and gas properties on the volumetric mass transfer coefficient. Analysis have also been done using ammonia-water as working fluid, the results obtained are compared with those in the literature and the agreement is found to be good. A correlation for mass transfer coefficient is proposed as a function of Reynolds number, Schmidt number and length to diameter ratio. The correlation can be used either in estimating the mass transfer rates or in fixing up any of the major design parameters namely length required for complete absorption and diameter.
TL;DR: In this paper, a boundary layer analysis has been presented for the combined convection along a vertical non-isothermal wedge embedded in a fluid-saturated porous medium, and the transformed conservation laws are solved numerically for the case of variable surface temperature.
Abstract: A boundary layer analysis has been presented for the combined convection along a vertical non-isothermal wedge embedded in a fluid-saturated porous medium. The transformed conservation laws are solved numerically for the case of variable surface temperature. Results are presented for the details of the velocity and temperature fields as well as the Nusselt number. The wedge angle geometry parameter m ranged from 0 to 1.
TL;DR: In this article, the authors combined heat and mass transfer by laminar natural convection from a vertical plate maintained with uniform surface heat flux and species concentration and obtained very accurate finite-difference solutions of a set of nonsimilarity equations.
Abstract: This paper studies combined heat and mass transfer by laminar natural convection from a vertical plate maintained with uniform surface heat flux and species concentration. Very accurate finite-difference solutions of a set of nonsimilarity equations have been obtained for most practical gaseous solutions (Pr = 0.7, 0.21 ≤ Sc ≤ 2.1) and aqueous solutions (Pr = 7, 140 ≤ Sc ≤ 1400). Variations of heat and mass transfer rates with buoyancy ratio and Lewis number are presented. Precise correlations have been developed for predicting heat and mass transfer rates of natural convection arising from single (solutal or thermal) buoyancy force and dual buoyancy forces.
TL;DR: In this article, a heat transfer from a vertically moving plate to a flowing free stream is investigated, where the plate moves either in parallel or reversely to the free stream; and the buoyancy force accelerates or retards the flow.
Abstract: Mixed convection heat transfer from a vertically moving plate to a flowing free stream is investigated. The plate moves either in parallel or reversely to the free stream; and the buoyancy force accelerates or retards the flow. An universal formulation can be obtained from which similarity and nonsimilarity equations for six limiting cases of forced, natural, and mixed convection can be readily reduced. Accurate finite-difference solutions and comprehensive correlations of heat transfer rate for 0.01 ≤ Pr ≤ 10000 are presented over the entire domains of mixed convection and relative velocity.
TL;DR: In this paper, a finite-difference solution of transient free convection flow of a viscous dissipative fluid past an infinite vertical plate, on taking into account viscous heat is presented, and the numerical values of the skin-friction and the rate of heat transfer are entered in a Table.
Abstract: A finite-difference solution of transient free convection flow of a viscous dissipative fluid past an infinite vertical plate, on taking into account viscous dissipative heat is presented. Velocity profiles, temperature profiles are shown for different values of Pr, the Prandtl number and E, the Eckert number. The numerical values of the skin-friction and the rate of heat transfer are entered in a Table. It is observed that greater viscous dissipative heat causes a rise in the velocity, temperature and the skin-friction and a fall in the rate of heat transfer. An increase in Pr leads to a fall in the velocity, temperature and the skin-friction but the rate of heat transfer increases with increasing Pr.
TL;DR: In this paper, the authors give an overview of the recent developments in research on freezing phenomena in forced convection flows inside ducts and present some new experimental and numerical results on solidification in duct flows.
Abstract: The present work gives an overview about the recent developments in research on freezing phenomena in forced convection flows inside ducts. Emphasis is given to the fundamental aspects of the phenomena observed in the solidification processes as well as on the analytical and numerical modelling aspects for this kind of problems. The paper deals with solidification problems inside tubes, parallel plate channels, curved rectangular channels and in diverging rectangular channels. Additionally, some new experimental and numerical results on solidification in duct flows are shown from the current research program in Darmstadt on freezing phenomena.
TL;DR: In this paper, the results of natural convection heat transfer between inclined parallel plates were presented. But the authors did not consider the effect of plate spacing and plate inclination on heat transfer.
Abstract: Presented in this paper are the results of natural convection heat transfer between inclined parallel plates. Lower plate is heated isothermally while the upper plate is both unheated and insulated. Plate inclinations were 0∘, 30∘, 45∘ measured from vertical position. Experiments were carried out for different temperature differences in air to determine the effect of plate spacing and plate inclination on heat transfer. It was found that heat transfer rate depends on plate spacing and inclination.
TL;DR: In this article, a semi-empirical model for pool boiling over porous surfaces is presented, where the pressure drop across the porous surface is estimated using Darcy's law.
Abstract: A semi-empirical model for pool boiling over porous surfaces is presented. The pressure drop across the porous surface is estimated using Darcy 's law. The significance of the latent heat flux contribution for highly porous surfaces is examined. Two nucleation factors are defined and correlated in terms of measurable quantities using literature data. An expression for the total heat flux in terms of the wall superheat, pore geometry and the physical properties of the liquid is presented. The present model matches well with literature data on pool boiling over porous surfaces, both flat surfaces and tubes from four different sources, thus validating the present approach.
TL;DR: In this article, the two-dimensional thermal problem due to relative motion of a medium and a suddenly activated circular heat source is solved for several boundary conditions, such as uniform and non-uniform temperature, uniform heat flux boundary conditions and the effect of radial direction on the temperature distribution.
Abstract: The two-dimensional thermal problem due to relative motion of a medium and a suddenly activated circular heat source is solved for several boundary conditions. The solutions can be interpreted as for a moving heat source in a stationary medium or a medium moving past a stationary heat source. Uniform and non-uniform temperature, and uniform and non-uniform heat flux boundary conditions are considered. The effect of velocity and radial direction on the temperature distribution is examined. Average, steady-state Nusselt numbers are derived. The transient response of a continuous line source is obtained as a limiting case of the prescribed heat flux solution.
TL;DR: In this paper, the authors applied transformation group theory to analysis of the governing equations of continuity, momentum, energy and diffusion of convective heat and mass transfer over a horizontal plate.
Abstract: Investigation to the mixed convective heat and mass transfer over a horizontal plate has been carried out. By applying transformation group theory to analysis of the governing equations of continuity, momentum, energy and diffusion, we show the existence of similarity solution for the problem provided that the temperature and concentration at the wall are proportional to x
4/(7-5n) and that the moving speed of the plate is proportional to x
(3-n)/(7-5n), and further obtain a similarity representation of the problem. The similarity equations have been solved numerically by a fourth-order Runge–Kutta scheme. The numerical results obtained for Pr=0.72 and various values of the parameters Sc, K
1, K
2 and K
3 reveals the influence of the parameters on the flow, heat and mass transfer behavior.
TL;DR: In this article, the hydrodynamic and heat transfer characteristics of a porous medium consisting of 20 wire screen meshes are examined theoretically and experimentally for the range of Reynolds number based on mean velocity and wire diameter from 1.5 to 12.
Abstract: The hydrodynamic and heat transfer characteristics of a porous medium consisting of 20 wire screen meshes are examined theoretically and experimentally. The hydrodynamic experiments are conducted for the range of Reynolds number based on mean velocity and wire diameter from 1.5 to 12. The Ergun's constants and thermal dispersion coefficients are calculated in this range. Nusselt number variation is determined in both thermally developing and fully developed flows by the help of forced convection heat transfer experiments conducted for the uniform heat flux boundary condition. Correlation functions of Nusselt number in the range of fully developed and thermally developing, and of thermal entrance length are obtained from experimental data. Solutions of momentum and energy equations simulating the experimental model are obtained numerically with variable porosity and the anticipated thermal dispersion coefficients. The thermal dispersion coefficients well-adjusted to the experimental data are determined by numerical solution of the energy equation.
TL;DR: In this paper, a mathematical modeling of CO2 laser cutting process is introduced and numerical solution of the heat transfer equation is obtained, the melting front velocities at different laser output power and workpiece thicknesses are predicted.
Abstract: To improve the laser cutting process, the modeling of the heating mechanism is essential. In the present study a mathematical modeling of CO2 laser cutting process is introduced and numerical solution of the heat transfer equation is obtained. The melting front velocities at different laser output power and workpiece thicknesses are predicted. The temporal development of the melting front profile is computed. The study is extended to include the experimental study of the transient behavior of the vapor ejected from the kerf in the initial stage of the cutting process. To achieve this two methods namely He–Ne laser transmittance and fiber-optic methods are introduced. It is found that the melting front velocity is high in the early stage of the cutting process which agrees with the experimental findings.
TL;DR: In this article, heat transfer characteristics of a turbulent, dilute air-solids suspension flow in thermally developing/developed regions were experimentally studied, using a uniformly heated, horizontal 54.5 mm-ID pipe and 43-μm-diameter glass beads.
Abstract: Heat transfer characteristics of a turbulent, dilute air-solids suspension flow in thermally developing/developed regions were experimentally studied, using a uniformly heated, horizontal 54.5 mm-ID pipe and 43-μm-diameter glass beads. The local heat transfer was measured at 27 locations from the inlet to 120-dia downstream of the heated section over a range of Reynolds numbers 3×104−1.2×105 and solids loading ratio 0–3, and the fully developed profiles of air velocity/temperature and particle mass flux were measured at a location 140-dia downstream of the heated section using specially designed probes, inserted into the suspension flow. The effects of the Reynolds number, solids loading ratio, and azimuthal/longitudinal locations on the heat transfer characteristics and their interactions are discussed through comparison of the present results with the data obtained by other investigators.
TL;DR: In this article, the propagation of thermal waves in a solid cylinder which undergoes a change of its boundary temperature is studied by assuming the validity of Cattaneo-Vernotte's constitutive equation for the heat flux.
Abstract: The propagation of thermal waves in a solid cylinder which undergoes a change of its boundary temperature is studied by assuming the validity of Cattaneo-Vernotte's constitutive equation for the heat flux. The hyperbolic energy equation, together with its boundary and initial conditions, is written in a dimensionless form and solved analytically by the Laplace transform method. It is shown that, if the boundary temperature undergoes a step change, the temperature field presents singularities. On the other hand, no singularity is present if the temperature change is achieved by a continuous monotonic evolution of the boundary temperature. However, even in this case, the absolute value of the temperature change in internal points of the cylinder can be greater than that prescribed at the boundary.
TL;DR: In this article, a generalized thermal boundary condition is derived to include all thermal effects of a thin layer which is in thermal contact with an adjacent domain, such as thermal capacity of the thin layer, thermal diffusion, enthalpy flow, viscous dissipation within the layer, convective losses from the layer and other effects.
Abstract: A generalized thermal boundary condition is derived to include all thermal effects of a thin layer which is in thermal contact with an adjacent domain. The thin layer may be a stationary or moving solid-skin or fluid-film. The included thermal effects of the thin layer are the thermal capacity of the layer, thermal diffusion, enthalpy flow, viscous dissipation within the layer, convective losses from the layer, and other effects. Six different kinds of thermal boundary conditions can be obtained as special cases of the generalized boundary condition. The generalized boundary condition is given for perfect and imperfect thermal contact between the thin layer and its adjacent domain. The importance of the generalized boundary condition is demonstrated in an example.
TL;DR: In this paper, experimental and numerical investigations of turbulent flow and heat transfer have been performed in a concentric annulus between independently rotating tubes, and the results showed that due to different superimpositions of centrifugal force and additional shear stress there is a wide variation of effects on fluid flow caused by the rotation of the inner and the outer tube.
Abstract: Experimental and numerical investigations of turbulent flow and heat transfer have been performed in a concentric annulus between independently rotating tubes. Numerical predictions, applying a Reynolds stress turbulence model, are compared with experimental fluid flow and heat transfer results for the case of a heated outer tube and an adiabatic inner tube. Compared to the above mentioned boundary conditions for the conservation equation of energy, differences in heat transfer in case of a heated inner tube and an adiabatic outer one, are examined by analysis, applying a mixing length turbulence model. Numerical investigations with both kinds of models about the influence of annulus radius ratio make evident that due to different superimpositions of centrifugal force and additional shear stress there is a wide variation of effects on fluid flow and heat transfer caused by the rotation of the inner and the outer tube.