Heat (mass) transfer and friction loss in two-pass ducts with various parallel rib arrangements

The present study investigated the effects of four parallel rib arrangements on heat/mass transfer and pressure drop characteristics in rotating two-pass ducts. The experiments of mass transfer and pressure measurement are performed to obtain heat transfer distributions and friction losses. The highest averaged heat (mass) transfer and friction loss in each region appeared in the turning region in the stationary cases, but appeared in the upstream region of the second pass in the rotating cases. Among the tested rib arrangements, the averaged heat (mass) transfer and the friction factor in the second pass in the stationary ducts were high in the cases with the NN- and PP-type ribs; however, in the rotating ducts, they were high in the cases with the NN- and PN-type ribs. The thermal performance in the four different rib arrangements was almost the same.     

Pressure drop and thermal performance in rotating two-pass ducts with various cross rib arrangements

The present study investigates the pressure drop characteristics of rotating two-pass ducts. The duct has an aspect ratio (W/H) of 0.5 and a hydraulic diameter (D _h ) of 26.67 mm. Rib turbulators are attached in the four different cross arrangements on the leading and trailing surfaces of the test ducts. The ribs have a rectangular cross section of 2 mm (e) × 3 mm (w) and a rib angle-of-attack of 70°. The pitch-to-rib-height ratio (p/e) is 7.5 and the rib-height-to-hydraulic-diameter ratio (e/D _h ) is 0.075. The measured results for each region show that the highest pressure drop appears in the turning region in the stationary case, but appears in the upstream region of the second pass in the rotating case. The heat transfer and the pressure coefficients in the first pass are similar for the stationary and rotating cases in all the tested rib arrangements. After the turning region, however, the heat transfer and pressure drop are high in the cases with the cross NN- and PP-type ribs in the stationary ducts. In the rotating ducts, they are high in the cases with the cross NP- and PP-type ribs.     

Heat transfer characteristics of rotating triangular thermosyphon

An experimental investigation is carried out to study heat transfer characteristics of a rotating triangular thermosyphon, using R-134a refrigerant as the working fluid. The tested thermosyphon is an equilateral triangular tube made from copper material of 11?mm triangular length, 2?mm thickness, and a total length of 1,500?mm. The length of the evaporator section is 600?mm, adiabatic section is 300?mm, and condenser section is 600?mm. The effects of the rotational speed, filling ratio, and the evaporator heat flux on each of the evaporator heat transfer coefficient, h_e, condenser heat transfer coefficient, h_c, and the overall effective thermal conductance, C_t are studied. Experiments are performed with a vertical position of thermosyphon within heat flux ranges from 11 to 23?W/m² for the three selected filling ratios of 10, 30 and 50?% of the evaporator section volume. The results indicated that the maximum values of the tested heat transfer parameters of the rotational equilateral triangular thermosyphon are obtained at the filling ratio of 30?%. Also, it is found that the heat transfer coefficient of the condensation is increased with increasing the rotational speed. The tested heat transfer parameters of the thermosyphon are correlated as a function of the evaporator heat flux and angular velocity.     

Heat transfer by laminar flow from a rotating sphere

Summary The heat transfer problem for the flow of an incompressible viscous, heat-conducting fluid, due to uniform rotation about a diameter of a sphere, which is kept at a constant temperature, has been solved with viscous dissipation included. Due to inflow at the poles the cooler liquid is drawn from infinity towards the rotating sphere and this causes a lowering of the temperature there. After flowing in the boundary layer of the sphere the liquid gets heated up and causes a rise in temperature near the equator. Numerical results are given in case of water (Prandtl number σ=5), and it is found that the isothermals are surfaces of revolution flattened at the poles and elongated near the equator. The thermal and the velocity boundary layers turn out to be of the same order of magnitude.     

Heat transfer peaks on a blunt-nosed triangular plate in hypersonic flow

An experimental investigation [1] of hypersonic flow over a blunt-nosed triangular plate revealed anomalies — the presence on the windward side of narrow bands of intensified heat transfer. Below, this effect is related to the appearance in the flow near the surface of regions of gas spreading induced, in its turn, by the interference between the bow shock (due to the blunt nose) and the leading edges of the plate. This spreading is called inertial, since it takes place at almost constant pressure. Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 2, pp. 131–137, March–April, 1994.     

Heat transfer experiments in rotating boundary layer flow

The influence of Coriolis force on heat transfer in a rotating transitional boundary layer has been experimentally investigated. The experiments have been conducted for local Görtler numbers up to 150. Heat transfer measurements have been performed for a flat plate with nearly uniform heat flux applied to the surface, where the temperature was measured by the thermochromic liquid crystal method. The results indicate that heat transfer is enhanced when Coriolis force acts towards the wall, i.e., on the pressure surface. The velocity measurements under equivalent conditions show that Coriolis instability induces counter-rotating longitudinal vortices which augment the lateral transport of the fluid on the pressure surface. On the other hand, the heat transfer on the suction surface remains at the same level as compared to the case without system rotation. As a consequence, the heat transfer coefficient on the pressure surface is 1.8 times higher than that measured on the suction surface when averaged over the measured surface.     

Heat transfer analysis of a particle-containing channel flow

This paper describes an analytical model of heat transfer in a two-dimensional, steady, nonreacting particle-containing channel flow. An idealized gas flow of specified uniform velocity between insulated parallel plates is assumed and the nonvaporizing particles are conceptualized as contained within an thin sheet injected at the symmetry plane. Two dimensionless parameters that affect the solution are described. These are the effective gas diffusivityK and the dimensionless particle number densityP. The linear, coupled differential equations governing the energy exchange between the gas and liquid phases are solved by means of the Green's function technique. This procedure yields a Volterra integral-series equation as the solution of the gas-phase energy equation. A series solution of this integral equation is obtained by the method of successive substitutions and terms up to second order are calculated.     

Heat transfer in unsteady laminar flow through a channel

The temperature distribution in unsteady laminar flow of a viscous incompressible fluid in a flat channel is investigated, when the pressure gradient is an arbitrary function of time. Two techniques are presented (i) explicit finite difference scheme, and (ii) Chebyshev polynomial solution. Using both the techniques, several cases of pressure gradient are considered, with special attention paid to the linearly varying case.     

Heat transfer in a radiating fluid with slug flow in a parallel-plate channel

Summary As a step towards a better understanding of combined conduction, convection, and radiation, fully developed heat transfer in slug flow in a flat duct between two parallel plates is considered. The flat duct consists of two diffuse, nonblack, isothermal surfaces. The gray radiating fluid between them is capable of emitting and absorbing thermal radiation. The problem is formulated in terms of a nonlinear integrodifferential equation, and the solution is obtained by an approximate method. The differences between heating and cooling the fluid are examined. The effects of the optical thickness of the fluid, the ratio which determines the relative role of energy transport by conduction to that by radiation, and the emissivity of the duct surfaces on the temperature distribution and the heat transfer characteristics are investigated. An approximate method for calculating the radiant heat flux at the wall is presented, and the accuracy of the approximation is tested.Work done under the auspices of the U.S. Atomic Energy Commission.     

Heat transfer in a flow past a semi-in-finite plate with oscillating temperature

The response of laminar boundary layer flow past a semi-infinite flat plate to harmonic oscillations in the plate temperature in the form of a travelling wave convected in the direction of the free-stream has been studied here. Series solutions in terms of the small amplitude and the small oscillations to the non-linear system have been derived and the resulting nonlinear ordinary equations due to usual similarity transformations are solved numerically. The function affecting the temperature is shown on a graph. Due to greater viscous dissipative heat the function K ₁, increases and it decreases with increasing Prandtl number. Also the time averaged heat flux function K ₁(0) increases with Prandtl number and decreases due to greater viscous dissipative heat.     

Hydromagnetic flow in a rotating channel

The steady flow in a parallel plate channel rotating with an angular velocity Ω and subjected to a constant transverse magnetic field is analysed. An exact solution of the governing equations is obtained. The solution in the dimensionless form contains two parameters: the Hartmann number, M ², and K ² which is the reciprocal of the Ekman number. The effects of these parameters on the velocity and magnetic field distributions are studied. For large values of the parameters, there arise thin boundary layers on the walls of the channel.     

Heat transfer in magnetohydrodynamic laminar radial channel flow

Heat transfer in the steady axisymetrical laminar source flow of an incompressible electrically conducting fluid between two parallel disks in the presence of a transverse applied magnetic field is analyzed. The energy equation is solved numerically for the temperature distribution, where both Joulean and viscous heating are included. Both local and average Nusselt numbers for the case of constant wall temperature are evaluated. For fluids of moderate and high Prandtl numbers, Nusselt number is seen to be a strong function of both Hartmann number and a heat generation parameter together with a modified Peclet number. However, for fluids of small Prandtl number, Joulean heating and viscous dissipation can be neglected without appreciable error.     

Heat transfer analysis of MHD and electroosmotic flow of non-Newtonian fluid in a rotating microfluidic channel: an exact solution

The heat transfer of the combined magnetohydrodynamic(MHD) and electroosmotic flow(EOF) of non-Newtonian fluid in a rotating microchannel is analyzed. A couple stress fluid model is scrutinized to simulate the rheological characteristics of the fluid. The exact solution for the energy transport equation is achieved. Subsequently,this solution is utilized to obtain the flow velocity and volume flow rates within the flow domain under appropriate boundary conditions. The obtained analytical solution results are compared with the previous data in the literature, and good agreement is obtained.A detailed parametric study of the effects of several factors, e.g., the rotational Reynolds number, the Joule heating parameter, the couple stress parameter, the Hartmann number, and the buoyancy parameter, on the flow velocities and temperature is explored. It is unveiled that the elevation in a couple stress parameter enhances the EOF velocity in the axial direction.     

Heat transfer associated with viscous two-dimensional channel flow in a transverse acoustic field

An analytic solution is proposed for the problem of the effect of a transverse resonant acoustic field on the heat transfer process in laminar two-dimensional channel flow.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 3, pp. 41–49, May–June, 1985.The author wishes to thank V. E. Nakoryakov for formulating the problem and discussing the results.     

Heat transfer in flow past a continuous moving plate with variable temperature

A study of thermal boundary layer on a continuously moving semi-infinite flat plate, whose temperature varies as Axⁿ, where A is a constant and x is measured from the leading edge of the plate, has been presented. Similarity solutions have been derived and the resulting equations are integrated numerically. It has been observed that the value of the Nusselt number increases with increasing n.

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Wärmeübertragung in einer Strömung längs einer kontinuierlich bewegten Platte mit variabler Temperatur

Zusammenfassung Es wird die thermische Grenzschicht an einer gleichförmig bewegten halbunendlichen Platte, deren Temperatur sich nach der Gleichung Axⁿ ändert, betrachtet. A ist eine Konstante und x ist der Abstand von der Vorderkante. Ähnlichkeitslösungen wurden abgeleitet und die entstehenden Gleichungen numerisch integriert. Aus den Ergebnissen ergibt sich ein Anstieg der Nusselt-Zahlen mit steigendem Exponenten n.

     

Heat exchange in a laminar channel flow with temperature gradients at the walls: possibility for heat transfer reversal

This paper presents a detailed numerical study of the heat exchange between two parallel plates with prescribed temperature gradients along the plates and a fluid circulating between them. The interplay between the bulk temperature, the heat flow and the Nusselt number has been clarified.     

Heat flow in a channel with discontinuity of the temperature on the wall

We study the temperature field in the flow of a viscous fluid in a circular tube when there is an abrupt change in the boundary condition for the temperature on the walls at a section of the channel. Following the classical studies [1, 2], this problem has often been considered (for example, in [3, 4, 5]) under different assumptions about the type of flow, the form of the boundary conditions, and the values of the Péclet number. The solutions hitherto obtained are frequently cumbersome and do not exhaust all situations of physical interest. In the present paper, we find the solution to the problem for the case of Poiseuille flow, boundary conditions of the first kind for the temperature, and arbitrary values of the Péclet number. We establish an expression that determines the Nusselt number at different sections of the channel. The results of calculations based on the obtained formulas are given.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Shidkosti i Gaza, No. 5, pp. 194–198, September–October, 1979.     

Direct numerical simulation of turbulent heat transfer in a wall-normal rotating channel flow

Investigations into the characteristics of turbulent heat transfer and coherent flow structures in a plane-channel subjected to wall-normal system rotation are conducted using direct numerical simulation (DNS). In order to investigate the influence of system rotation on the temperature field, a wide range of rotation numbers are tested, with the flow pattern transitioning from being fully turbulent to being quasilaminar, and eventually, fully laminar. In response to the Coriolis force, secondary flows appear as large vortical structures, which interact intensely with the wall shear layers and have a significant impact on the distribution of turbulence kinetic energy (TKE), turbulence scalar energy (TSE), temperature statistics, and turbulent heat fluxes. The characteristic length scales of turbulence structures responsible for the transport of TSE are the largest at the quasilaminar state, which demands a very large computational domain in order to capture the two-dimensional spectra of temperature fluctuations. The effects of the Coriolis force on the turbulent transport processes of the temperature variance and turbulent heat fluxes are thoroughly examined in terms of their respective budget balances.