Heat Transfer In Annular Channels Research Articles

Heat Transfer in Annular Channels with the Inner Rotating Cylinder and the Radial Array of Cylinders

Numerical investigations of heat transfer for forced, mixed, and natural convection conditions within an annular channel are carried out. The main objective was to investigate, for the first time, the effect of the radial cylinder array on heat transfer in the annular channel with the rotating cylinder. The governing equations for velocity and temperature with the Boussinesq approximation were solved using the finite-volume method. The heat transfer quantities were obtained for different Rayleigh numbers (104–106), the radius ratios (1.4–2.6), the radial cylinder spacing, and for different rotating velocities in the form of the Richardson number (10−2–104). The Prandtl number was 0.7. It has been shown that radial cylinders do not influence significantly the intensity and the local distribution of heat transfer on the inner rotating cylinder. The Nusselt number was 1.4–2.0 times higher on the radial cylinder array for all convection modes relative to the outer flat surface. For all annuli gaps with radial cylinders, the maximal values of the Nusselt number were observed with an increase of the radial spacing of cylinders.

Numerical study on heat transfer characteristics of molten salt in annular channel with wire coil

• Annular channel with wire coil is firstly proposed to heat molten salt. • Wire coil inserts are used to enhance the heat transfer in annular channel. • Overall performance is evaluated using the thermal performance factor. • The correlations for Nusselt number and friction factor are presented. In order to develop a heat transfer enhancement technique for molten salt heat exchanger, Fluent simulation is carried out to investigate the molten salt flow and heat transfer performances in annular channels with wire coil. Two experimental set-ups were built to measure the temperature distribution of the test section, and the maximum relative deviation between the simulated temperature and experimental one is 3.27%. The effects of the wire width and helical pitch on heat transfer and flow characteristics, and the mechanism of heat transfer enhancement in wire coil inserted annular channels are discussed in the light of numerical results. It is found that adding coiled wire inserts in an annular channel can enhance the heat transfer performance by up to eight times as compared to a smooth annular channel, at a cost of higher flow resistance. The thermal performance factor is evaluated, which is greater than 3.7 at a constant pumping power. Finally, the heat transfer and friction factor correlations for annular channels with wire coil are proposed.

Evaporation Heat Transfer of R134a on outside of Smooth and Enhanced Tubes

Increasing attention has been paid to the flow and heat transfer in annular channels since their intensive applications in engineering. In this study, evaporation of the outer surface of two enhanced heat transfer tubes (2EHT) was compared to the performance of a smooth surface copper tube through experimental research. The refrigerant flowed in an annular space between the outer tube and the test tube. The outside and inside diameters of tubes used in this study were 19.05 and 17.10 mm, respectively. Tests were performed using refrigerant R134a as the working fluid, over the saturation temperature of 6 °C for evaporation, the quality range of 0.1–0.8 and the mass fluxes is from 30 to 58 kg/m2s. It is observed that through different surface structures, the heat transfer area increased, while both the nucleate boiling and convective boiling were improved, leading to the heat transfer coefficient of 2EHT being significantly enhanced. According to the evaluation, the evaporation enhanced tube had better enhancement effect. Finally, correlation analysis was conducted based on experimental data. The results from correlation analysis can be implemented to predict the experimental heat transfer coefficients within a deviation of ±10%.

Size control synthesis and characterization of ZnO nanoparticles and its application as ZnO-water based nanofluid in heat transfer enhancement in light water nuclear reactor

Abstract A novel and facile approach for size-tunable synthesis of ZnO nanoparticle (NPs) is reported. Size-tuning was attained by using PEG (polyethylene glycol) of molecular weights 400 and 4 000. ZnO NPs was synthesized using homogeneous chemical precipitation followed by hydrothermal. Here triethylamine (TEA) was used as a hydroxylating agent. As-synthesized ZnO NPs were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM) and Energy Dispersive Spectroscopy (EDS) analysis. Synthesized ZnO nanoparticle was used for the preparation of ZnO-water based nanofluid and its application in heat transfer enhancement in light water nuclear reactor. In this work, ZnO-water based nanofluid of different volume concentration (1 percnt;, 2 percnt; and 3 percnt;) and particle size of 10 nm and 20 nm is used for enhancement in heat transfer in annular channel by using two phase approach. The particle size of 10 nm gives better result for enhancing the heat transfer rate in comparison to 20 nm particle size in nuclear reactor.

Физико-технические проблемы управляемого термоядерного синтеза

The lines of scientific activity and the results of investigations carried out at the MPEI Department of General Physics and Nuclear Fusion are briefly reviewed. The conducted activities are mainly focused on the problems of controlled thermonuclear fusion and plasma technologies. Efforts are taken to study heat transfer and hydrodynamics in the plasma-facing structural components of thermonuclear reactors, one-sided heating of which results in essentially nonuniform distributions of heat flux density and wall temperature over the pipe inner perimeter. Another line of research activities is concerned with experimental investigations of nucleate boiling and heat transfer in essentially subcooled flow, of enhanced heat transfer in annular channels and models of pebble fuel element beds, and of heat transfer enhancement as applied to the problems concerned with cooling the International thermonuclear experimental reactor (ITER). A large-scale test bench for studying thermal-hydraulic processes in the models of advanced nuclear fuel assemblies operating with the parameters of a VVER-type reactor has been constructed. Activities are underway on studying the resistance of refractory metals to the effect of powerful plasma and heat fluxes expected to take place in a tokamak-type thermonuclear reactor. A plasma installation equipped with a linear multicusp magnetic system featuring uniquely high parameters has been constructed, which is used to perform tests of materials exposed to megawatt-scale hot plasma. The unique plasma installation has been constructed for studying plasma-to-surface interaction and high-temperature plasma testing of refractory materials like tungsten, molybdenum, steel, etc. The experiments to be performed on the installation are aimed at developing a new technology for producing a highly porous surface nanostructure of refractory metal, including tungsten “fuzz”. Such investigations are topical for inventing new materials that are of considerable interest for nuclear, chemical, power, and biomedical technologies. The main lines of activities on nanotechnologies include obtaining, studying and using carbon nanostructures such as fullerenes, carbon nanotubes, graphene, and their derivatives. Within the framework of studying the strengthening phenomenon, the extent of steel surface strengthening as a function of the type and intensity of incident radiation, and the type of nanocarbon material is considered. The interaction of charged particles and radiation with structural materials is investigated. Experimental and theoretical investigations of the interaction of electrons and light ions with inhomogeneous solid bodies are continued to solve the problems concerned with scattering ion beams in inhomogeneous media. Innovative methods for destructive and non-destructive analysis of thin films are developed, including layer-wise analysis techniques. Unique plasma installations have been constructed at the department, such as a high-frequency induction plasmatron for carrying out chemical spectral analysis, an arc plasmatron for studying the free plasma burning processes, a high-voltage installation for studying streamer and arc discharges with electrolysis, and a cold plasma installation for studying the effect of discharge on biological tissues. All these installations are successfully used for carrying out both research activities and student training laboratory works.

Experimental and Numerical Study of Axial Turbulent Fluid Flow and Heat Transfer in a Rotating Annulus

The present work is an experimental and a numerical investigation of the turbulent fluid flow and heat transfer in an annular channel between two concentric cylinders with heated stationary outer cylinder (constant heat flux) and adiabatic rotating inner cylinder. Numerically, the governing equations are discretized in a finite volume fashion using a non-staggered (collocated) arrangement of the variables. The solutions were obtained using the SIMPLE algorithm with upwind scheme. A computer program in FORTRAN 90 was build to solve a set of partial differential equations that govern the fluid flow and heat transfer in annular channels. The experimental results are obtained for an inlet air velocity range of 2–6 m/s, for a wall heat flux range of 600–1200 W/m2 and a rotational speed range of inner cylinder of 0–1500 rpm with a gap width of 1.5 cm. Finally, the relationships between the average Nusselt number and the effective Reynolds number for experimental and numerical results were proposed and compared with those in the existing literature.

Heat transfer in annular channels with flow swirling

We present results from an analysis of experimental data on heat transfer in channels with one- and two-sided heating and with flow swirling by means of screw-type inserts or by winding a thin-walled capillary with a thickness equal to the annular gap. We also propose generalizing relations for calculating heat transfer in annular channels with flow swirling and with different operating and design parameters.

Heat transfer in annular channels with flow twisting

The results of the experimental study of heat transfer in one-and two-phase regions at a pressure p = (98–103)105 Pa in annular channels with twisting by means of a wire spiral and two-way heat supply are presented. We consider problems of determining the boiling point temperatures and heat transfer intensity at convection and boiling on convex and concave surfaces of an annular channel with twisting.

Investigations on post-dryout heat transfer in bilaterally heated annular channels

Post-dryout heat transfer in bilaterally heated vertical narrow annular channels with 1.0, 1.5 and 2.0 mm gap size has been experimentally investigated with deionized water under the condition of pressure ranging from 1.38 to 5.9 MPa and low mass flow rate from 42.9 to 150.2 kg/m 2s. The experimental data was compared with well known empirical correlations including Groeneveld, Mattson, etc., and none of them gave an ideal prediction. Theoretical investigations were also carried out on post-dryout heat transfer in annular channels. Based on analysis of heat exchange processes arising among the droplets, the vapor and two tube walls of annular channel, a non-equilibrium mechanistic heat transfer model was developed. Comparison indicated that the present model prediction showed a good agreement with our experimental data. Theoretical calculation result showed that the forced convective heat transfer between the heated wall and vapor dominate the overall heat transfer. The heat transfer caused by the droplets direct contact to the wall and the interfacial convection/evaporation of droplets in superheated vapors also had an indispensable contribution. The radiation heat transfer would be neglected because of its small contribution (less than 0.11%) to the total heat transfer.

Correlations of the Convection Heat Transfer in Annular Channels With Rotating Inner Cylinder

In the internal air system of gas turbine engines or generators, a large variety of different types of annular channels with rotating cylinders are found. Even though the geometry is very simple, the flow field in such channels can be completely three-dimensional and also unsteady. From the literature it is well-known that the basic two-dimensional flow field breaks up into a pattern of counter-rotating vortices as soon as the critical speed of the inner cylinder is exceeded. The presence of a superimposed axial flow leads to a helical shape of the vortex pairs that are moving through the channel. For the designer of cooling air systems there are several open questions. Does the formation of a Taylor-vortex flow field significantly affect the convective heat transfer behavior of the channel flow? Is there a stability problem even for high axial Reynolds-numbers and where is the location of the stability boundary? After all, the general influence of rotation on the heat transfer characteristics has to be known. By the results of flow field and heat transfer measurements, the impact of rotation and the additional influence of Taylor-vortex formation on the heat transfer characteristics in annular channels with axial throughflow will be discussed. The flow field was investigated by time-dependant LDA-measurements, which revealed detailed information about the flow conditions. By a spectral analysis of the measured data, the different flow regimes could be identified. Based on these results, the heat transfer from the hot gas to the rotating inner shaft was determined with a steady-state method. Thus, the influence of the different physical phenomena such as rotation with and without Taylor-vortex formation or the flow development could be separated and quantified. Finally, correlations of the measured results were derived for technical applications.

Supercritical heat transfer in an annular channel with bilateral heating

This paper presents the experimental investigation of the degradation of heat transfer accompanying an ascending flow of a steam-water mixture and the development of an engineering method for calculating supercritical heat transfer in a vertical annular channel with bilateral heating. The experimental setup is described. The temperature of the exothermic surfaces from the indications of the thermocouples are determined taking into account their individual calibration, the temperature drops in the wall, and thermal losses. The temperature distribution along the length and periphery of the exothermic surfaces of the annular channel is shown and the dependence of the critical steam content on the power fed to the outer wall of the channel with different mass velocities is presented.

Experimental investigation of heat transfer in the annular channel of a circulation loop

The results of an experimental investigation of heat transfer in the vertical annular channel of a closed circulation heat exchanger are given.

Improving the heat transfer in annular channels

Results are shown of a study concerning an improvement of the heat transfer by means of circumferential grooves around an annular channel with a diameter ratio d2/d1=1.455.