Longitudinal Heat Transfer Research Articles

Non-uniformity of heat transfer in a shuttle kiln

A numerical investigation of the flow and heat transfer characteristics in a shuttle kiln is performed using the CFD software FLUENT with non-conformal grids and the standard κ-e turbulence model. The integral and local heat transfer non-uniformities of stacks are evaluated, and furthermore, the formation mechanism of such non-uniformities is analyzed. The results show much greater heat transfer intensity among the peripheral stacks than that among the internal ones, which contributes to the integral non-uniformity. The longitudinal heat transfer non-uniformity is primarily caused by the layer-like nozzle jets and bottom outlet, which form three layer-style surrounding streams converging to outlet. The periodical arrangement of stacks together with the strong impingement of jets, leads to the peripheral heat transfer non-uniformity. Based on the comprehensive understanding of flow and heat transfer, innovative efforts are made to improve heat transfer performance by adjusting flowrate distribution among nozzles

Thermal profiling for optical characterization of waveguide devices

We demonstrate a thermal profiling technique for wafer-scale testing of the optical power distribution in photonic integrated circuits. Radiative cooling of the lattice of a semiconductor optical amplifier is observed in response to an optical signal; likewise, lattice heating occurs in an optically injected absorber. We develop a total energy balance model that can be used to quantify modal gain or absorption within these devices, along with longitudinal and vertical thermal impedances and heat transfer coefficients. Spatially resolved thermal profiling in conjunction with our energy balance model accurately describes the optical power distribution inside optoelectronic devices, without recourse to direct optical measurement.

Longitudinal Heat Transfer Enhanced by Fluid Oscillation in a Circular Pipe with Conductive Wall.

The longitudinal heat transfer in capillary pipes is enhanced by fluid oscillation. The analytical solution to this phenomenon is obtained considering the wall thermal conductivities. Based on this solution, the effects of wall conductivity and thickness are investigated for the case of large amplitude of fluid motion. The longitudinal heat transfer through the fluid part is more enhanced with highly conductive thick pipes. This is because the radial region where the heat is transferred backward is smaller with these pipes. The direction of longitudinal heat transfer depends on the phase difference of temporal change between the velocity and temperature; whether it exceeds π/2, or not. From this point of view, the most effective wall to this problem is presented, where the wall temperature does not change preserving the mean temperature of the location during the oscillation.

1108 管壁の熱伝導を考慮した円管内脈動流による長手方向熱拡散の促進

1108 管壁の熱伝導を考慮した円管内脈動流による長手方向熱拡散の促進

1016 管壁の熱伝導を含めた円管内脈動流による長手方向熱拡散の解析解(GS-5 管内流れ)

The longitudinal heat transfer in capillary pipes is enhanced by fluid pulsation. The analytical solution to this phenomenon is obtained considering the wall conductance. The longitudinal heal transfer through fluid part is also more enhanced with highly conductive walls. The effect of thickness of highly conductive wall is investigated showing that heat transfer is most enhanced with pipes of thickness of 10 - 20 % of the outer radius.

Longitudinal Heat Transfer in Oscillatory Flows in Pipe Bundles of Various Cross Sections.

The effect of the sectional shape of pipes on the enhancement of longitudinal heat transfer by fluid pulsation in pipe bundles has been investigated. Bundles of circular, triangular, square and hexagonal pipes are considered. Heat transfer characteristics of each pipe and the gross performance as a pipe bundle including the heat conduction in pipe walls, are discussed. The local distribution of longitudinal heat transfer in pipe section reveals the existence of a region where heat is transferred toward the higher temperature end when the pulsation frequency is sufficiently high. As a pipe bundle, only a circular one has narrow gaps among each three pipes, which deteriorate the gross performance of heat transfer. But in the case of the present investigation which assumes acrylic pipes of the same wall thickness, the circular pipe bundle is advantageous to other ones as for the global performance of longitudinal heat transfer including the wall thermal conduction, because the area ratio of pipe walls, whose low thermal conductivity lowers the performance, is least when the pipes are circular.

The Effect of the Pipe Cross-Sectional Shape on the Longitudinal Heat Transfer in Oscillatory Flows in Pipe Bundles.

The enhancement of longitudinal heat transfer by means of fluid pulsation in pipe bundles has been investigated. Bundles of circular, triangular, square and hexagonal pipes are considered. Heat transfer characterisitics of each pipe and the gross performance as pipe bundles including the heat conductance in pipe walls are discussed. The distribution of the longitudinal heat transfer intensity across the pipe section reveals the existance of a region where heat is transferred toward the high temperature end when the pulsation frequency is high. Although the gaps between three circular pipes deteriorate the heat transfer characteristics by fluid in a circular pipe bundle, when acrylic pipes are assumed, the gross performance is the best with a circular pipe bundle, because the area ratio occupied by pipe wall in a cross-section, where the low thermal conductance deteriorates the performance, is least when the pipes are circular.

Discussion: “Analysis of Matrix Heat Exchanger Performance” (Venkatarathnam, G., and Sarangi, S., 1991, ASME J. Heat Transfer, 113, pp. 830–836)

Recently, a new numerical scheme for solving the equations governing matrix heat exchanger thermal performance was published in this journal. It was found that this scheme does not include the full effect of longitudinal heat transfer in the said heat exchangers. This effect is demonstrated by correcting the parameter related to longitudinal heat transfer in the approximate analytical solution for the balanced flow case and finding it to deviate considerably from the numerically calculated result.

管断面形状が軸方向熱輸送特性に及ぼす影響

管断面形状が軸方向熱輸送特性に及ぼす影響

Longitudinal Heat Transfer in Oscillatory Flows in Pipes With Thermally Permeable Wall

The effect of a thermally permeable wall on the enhanced longitudinal heat transfer by fluid pulsation in a pipe has been investigated. An analytical solution is obtained for the case when heat loss through the wall over a cycle of fluid pulsation is uniform along the pipe. The distribution of time-averaged sectional mean temperature is expressed by a quadratic curve. The rate of longitudinal heat transfer decreases linearly toward the lower temperature end. The amplitude of time-varying sectional mean temperature also decreases toward the same end. The effect of the value of Womersley number on this temperature field is discussed.

Longitudinal Heat Transfer in Oscillatory Flows in Circular Pipes with Heat Loss.

The enhancement of longitudinal heat transfer by means of fluid pulsation in a circular pipe with heat loss through the pipe wall has been investigated. An analytical solution is obtained for the case that heat loss through the pipe wall during one cycle of fluid pulsation is uniform along the pipe. Based on the analytical solution, some characteristics of the phenomenon are discussed. These include the effect of heat loss on longitudinal heat transfer and temperature distributions, as well as the effect of pulsation frequency on the amplitude of temperature pulsation.

Enhanced Heat Transfer through Oscillatory Flow.

The enhancement of longitudinal heat transfer by means of fluid pulsation in a pipe has been investigated analytically and numerically, including the transient state. The effects of pulsation amplitude, frequency and pipe length on thermal properties such as effective thermal diffusivity and delay time are clarified. Their effects on numerical calculations are also presented, and suggestions for efficient numerical calculations of this problem are made concerning the combination of parameters.

Longitudinal vortex structures and heat transfer in the region of attachment of a supersonic turbulent boundary layer

Longitudinal vortex structures and heat transfer in the region of attachment of a supersonic turbulent boundary layer

Contribution to the theory of nonisothermal flow through porous media with phase transitions

Nonisothermal three-velocity flow through porous media is investigated numerically with allowance for phase transitions. The modeling is based on the following common assumptions: it is possible to neglect the diffusive process of mixture component transport, longitudinal heat transfer due to heat conduction, and the transport of the liquid and gas phases as a result of the capillary pressure difference in the phases as compared with convective transport; the porous medium is in local thermodynamic equilibrium (equality of the temperatures, pressures and chemical potentials of the phases); and, moreover, the problems of heat transfer along and across the reservoir can be treated separately (Leverrier model).

Enhanced heat conduction in oscillating viscous flows within parallel-plate channels

The hydrodynamics of enhanced longitudinal heat transfer through a sinusoidally oscillating viscous fluid in an array of parallel-plate channels with conducting sidewalls is examined analytically. Results show that for fixed frequency the corresponding effective thermal diffusivity reaches a maximum when the product of the Prandtl number and the square of the Womersley number is approximately equal to α2Pr = π Under such tuned conditions the axial heat transfer achievable is considerable and can exceed that possible with heat pipes by several orders of magnitude. The heat flux between different temperature reservoirs connecting the parallel-plate-channel configuration is shown, under tuned conditions, to be proportional to the first power of both the axial temperature gradient and the flow oscillation frequency and to the square of the tidal displacements. A large value for the fluid density and specific heat is also found to be beneficial when large heat-transfer rates are desired. The process discussed involves no net convection and hence achieves large heat-transfer rates (in excess of 106 W/cm2) without a corresponding net convective mass transfer. A discussion of the physical origin for this new heat-transfer process is given and suggestions for applications are presented.

Two-phase heat transfer in a one-dimensional channel

The problems of heat transfer in a flow of continuous medium in a channel filled with dispersed material, and of the unsteady operation of a straight-through heat regenerator are examined; longitudinal heat transfer is ignored.

Bouyancy Effects on Forced Convection Along a Vertical Cylinder

The effects of buoyancy forces on the longitudinal forced convective flow and heat transfer along an isothermal vertical cylinder are studied analytically. This problem does not admit similarity solutions, the nonsimilarity arising both from the transverse curvature ξ = (4/r0) (νx/u∞)1/2 of the cylindrical surface and from the buoyancy effect expressible as Ω = Grx/Rex2 where Grx and Rex are, respectively, the Grashof and Reynolds numbers. The governing equations are solved by the local nonsimilarity method in which all the nonsimilar terms are retained in the conservation equations and only in the derived subsidiary equations are terms selectively neglected according to the two-equation or three-equation model. Numerical results for the velocity and temperature profiles, wall shear stress, and surface heat transfer for the case of assisting flow are presented for gases having a Prandtl number of 0.7 over a wide range of values of ξ from 0 (i.e., a flat plate) to 4.0 and Ω from 0 (i.e., pure forced convection) to 2.0. It is found that the wall shear and surface heat transfer rate increase with increasing buoyancy force and increasing curvature of the surface.

190. A method for predicting the longitudinal temperature distribution and heat transfer rate at the exit end of high-temperature continuous graphite furnaces

190. A method for predicting the longitudinal temperature distribution and heat transfer rate at the exit end of high-temperature continuous graphite furnaces

An Experimental and Analytical Investigation of the Gas Exchange Process in a Multi-Cylinder Pressure-Charged Two-Stroke Engine

The results are given of a comprehensive investigation of the pressure and temperature diagrams in a multi-cylinder two-stroke engine during the gas-exchange process. A six-cylinder turbocharged two-stroke diesel engine was fully instrumented to record transient pressures in three cylinders, in the scavenge belt, and in a number of positions in a specially designed exhaust pipe. Transient-temperature records were taken in the exhaust pipe. Steady-flow tests were carried out on the inlet ports, the exhaust valves, and the exhaust pipe. The steady-flow data were then used in a computer programme (see references (9) (12)‡) to predict the pressure in the cylinder and the pressures and temperatures in the exhaust pipe. Discounting some measured cylinder-pressure records, which were suspect, the investigation showed good agreement between the predicted and measured pressures in the cylinders and exhaust pipe. The analysis of the temperature records showed there was evidence of mixing and longitudinal heat transfer in the exhaust pipe; however, the mean computed temperature in the exhaust pipe at the nozzle end agreed with the measured temperature. Comparison of the measured and computed mass flows at the nozzle end of the pipe using the theoretical diagrams gave good agreement. It was concluded that the computer programme was a satisfactory method for calculating the pressures in the cylinder and exhaust pipe during the gas-exchange process.

Weak locally homogeneous turbulence and heat transfer with uniform normal strain

AbstractTurbulence and longitudinal heat transfer for an axisymmetric accelerating or decelerating flow are analyzed. The analysis is based on generalized two‐point correlation equations which are obtained from the incompressible Navier‐Stokes, continuity, and energy equations. Viscosity, thermal conductivity, and the effects of mean strain are retained in the analysis, but the turbulence is assumed to be weak enough to neglect the triple correlation terms in the equations in comparison with the other terms. The calculated longitudinal turbulent heat transfer in the decelerating case is discussed in connection with the heat transfer at a stagnation point.