Concentric Annular Channel Research Articles

Pulsating non-Newtonian heat and fluid flow in a concentric annular duct: An analysis using perturbation series method

In the current study, an analytical analysis is conducted to examine laminar pulsating flow and heat transfer of power-law fluid in a concentric annular channel that is uniformly heated. The momentum and energy balance equations are solved analytically using the perturbation series method under the assumption that fully developed hydrodynamic and thermal conditions exist. Nondimensional frequency and amplitude effects on periodic and period-averaged friction factor and Nusselt number are obtained for various power-law index values, representing pseudoplastic, Newtonian, and dilatant fluids. The results from the present study are compared to those from the literature for some specific cases, and an excellent agreement is observed.

Modeling of Turbulent Convective Heat-Transfer Characteristics in a Concentric Annular Channel

Turbulent convective heat-transfer characteristics in a concentric annular channel with both walls heated are theoretically modeled and numerically computed in this article. Generalized algebraic predictive models and equations for heating over a single wall are first reviewed by summarizing the well-known methods in the literature. These methods are then scrutinized according to the most recent investigations such that new viewpoints and corrections are introduced accordingly. Moreover, the application of superposition in temperature is used in the current work instead of the Nusselt number as seen in the literature. The numerical integration method is applied to the generalized equations to obtain the solutions, which are found to be in decent agreement with the direct numerical simulation (DNS) data in the literature. The results in this work also indicate that the wall heat flux density ratio and the annular radius ratio are two key factors that have a great influence on the heat-transfer characteristics of the case with both walls heated.

Mass Flux and Gas Pressure Distribution in a Long Concentric Annular Channel in the Case of Incomplete Accommodation of Gas Molecules

Mass Flux and Gas Pressure Distribution in a Long Concentric Annular Channel in the Case of Incomplete Accommodation of Gas Molecules

Critical heat flux characteristics of flow boiling on a heater rod under inclined and rolling conditions

Offshore floating nuclear power plants have been developed to supply power to remote regions. Since they are operated in an ocean environment, the thermal–hydraulic phenomena in the reactor core may be different from those in the land-based reactors. However, the experimental study on critical heat flux (CHF) under ocean condition is limited and its mechanism is unclear. In this study, an experiment was performed to measure CHF in a single heater rod under inclined and rolling conditions. To create the required environment to simulate the conditions of inclination and rolling, a rolling platform was designed and constructed. It could provide an inclination of up to 45° and rolling of up to 45° with a minimum period of 6 s. In the CHF test loop, the experimental conditions were set up to correspond to pressurized water reactor conditions, using the fluid-to-fluid scaling method. The working fluid used was R134a. The test section was a concentric annular channel composed of a heater rod and an unheated tube housing. The result of the inclination experiment suggested that in the most cases, the CHF was enhanced when compared with the vertical condition. In a limited number of cases of low-pressure and high-flow conditions, the CHF was degraded as compared to the vertical condition. These variations were proportional to the inclination angle and inversely proportional to the mass flux. From the results of the rolling experiment, a precursor of CHF was observed with a large fluctuation in temperature before the CHF, and its trigger was related to the CHF value of the inclined case. Based on this observation, the overall relations between the vertical, inclined, and rolling CHF values were derived. It was concluded that the rolling motion weakened the CHF enhancement and degradation effects of the inclination.

Dynamic recoil response of tensioner and riser coupled in an emergency disconnection scenario

As the tension force provider for the riser system, the hydro-pneumatic tensioner system plays an essential role in riser recoil. However, Existing riser recoil analyses rarely adopt hydro-pneumatic tensioner, and main nonlinear characteristics of the tensioner, including internal friction, pressure loss of hydraulic oil flowing, and stroke limit, are almost ignored. In this paper, a recoil model that couples the nonlinear hydro-pneumatic tensioner and riser system is proposed to explore the recoil response under the action of these characteristics. A non-Newtonian mud discharge model in the concentric annular channel is developed and incorporated into the coupled model. Effects of the nonlinear characteristics of the tensioner on recoil behaviors are analyzed. Results show that internal friction and pressure loss increase the peak-to-peak value of the top tension, inhibit the recoil displacement in the recoil early stage, and advance the phase of recoil behaviors. The piston rod reaching the stroke limit will produce impact loads on the riser system, intensify the riser oscillation and result in dynamic compression of the riser. Some factors affecting the riser recoil involving the heave phase point, opening of the anti-recoil control valve, and mud density are identified on the basis of the proposed model.

Study of the pressure distribution along a concentric annular channel

A study of an isothermal rarefied gas flow through a long concentric annular channel is carried out. The solution is based on the linearized BGK model with diffuse boundary conditions and it is valid in the whole range of the rarefaction parameter. The pressure distribution along the channel is obtained and investigated depending on the values of the pressure maintained at the channel ends.

Investigation of the influence of Taylor-Gortler vortexes on heat transfer of annular channel

This article is about the influence of Taylor-Gortler vortices on heat transfer in concentric annular channels with turbulent decaying swirling flows. The study shows that the occurrence and transformation of secondary vortex structures has a significant effect on the distribution of heat flux over the annular channel surface. An explicit is relationship between the radial velocity fluctuations and the heat flux density distribution. The highest intensity of heat transfer on the outer surface is observed in the areas of positive radial velocity values, while on the inner surface it is observed in the areas of negative radial velocity values.

An application of the Chebyshev collocation method for the calculation of a mass flux in a long concentric annular channel

An application of the Chebyshev collocation method for the calculation of a mass flux in a long concentric annular channel

Numerical Simulations of Natural Convective Heat Transfer in Vertical Concentric and Eccentric Annular Channels

Natural convective heat transfer in a concentric and a highly eccentric, vertical, open ended, annular channel has been investigated numerically. The inner to outer diameter ratio was 0.61, and the height to hydraulic diameter ratio was 18:1. Three heating modes were considered, all having uniform heat flux applied to one or both of the two walls, while the unheated wall was kept adiabatic. The wall temperature distribution, mass flow rate, and midchannel Nusselt number for the case with both walls heated were found to be in excellent agreement with available experimental results. For the same heating conditions, the heat transfer rate in the concentric annular channel was found to be greater than that in the highly eccentric channel, while the mass flow rate was higher in the eccentric channel. A novel finding for the eccentric channel was that the location of maximum velocity was intermediate between the narrow and wide gaps. Another novel observation, which was attributed to radiation effects, was that the fluid temperature in the wide gap region was lower than that of an adiabatic wall. The paper contains additional observations that would be of interest to designers of systems containing annular channels.

Enhancement of forced convection in wide cylindrical annular channel using rotating inner pipe with interrupted helical fins

This paper presents the results of heat transfer and pressure drop in concentric annular wide channel with inner plain or finned pipe under stationary and rotating conditions in Taylor–Couette–Poiseuille flow. The experiments are conducted for one plain pipe and three finned pipes with helical fin spacing of 75, 110 and 150mm at rotating speeds of 0, 200, 250, 300, 350 and 400rpm. The experiments cover axial Reynolds number of 8.07×104–1.82×105, rotational Reynolds number of 0 and from 1428 to 3008, corresponds to Taylor number of 0 and from 1.22×106 to 8.32×106. The reported results in the form of Nusselt numbers and friction factors are correlated in terms of Re, Ta, Pr and fin geometrical parameters. The results proved that at Re=1.5×105, the wide annular channel with inner pipe of helical fin spacing 75mm that rotates at 400rpm enhances Nu by a factor of 7.5 and also boosts the ratio of heat exchange to pumping power by a factor of 7.6, compared to the case for plain stationary pipe.

Heat transfer of water flowing upward in vertical annuli with spacers at high pressure conditions

Experimental studies on heat transfer to water flowing upward in a concentric annular channel are carried out at the SWAMUP test facility at both subcritical and supercritical pressure conditions. The vertical annuli contain a heated inner tube of 8mm outer diameter and an unheated outer tube of 15.3mm inner diameter with spacers without mixing-vane. More than 500 test data were obtained with the following test conditions: pressure from 15.5 to 26.0MPa, mass flux from 500 to 1600kg/m2s, heat flux from 0.45 to 1.4MW/m2 and bulk temperature from 310 to 390°C. Test data are also compared with those obtained in tubes of similar hydraulic diameter. The results show that heat transfer coefficient in annuli without spacer effect is slightly lower than that in circular tubes, whereas a significant enhancement of heat transfer is obtained in annuli with spacer effect. The phenomenon of heat transfer enhancement and its decay behavior downstream of spacers were investigated and analyzed. A new correlation was developed to predict the local heat transfer enhancement due to spacers at supercritical pressure condition.

An Experimental Study of Forced Heat Convection in Concentric and Eccentric Annular Channels

An experimental study of the effect of eccentricity on forced convective heat transfer was conducted for upward flows in vertical, open-ended annular channels with a diameter ratio of 0.61, a length to outer diameter ratio of 18:1, and both internal surfaces heated uniformly. Flows with Reynolds numbers Re = 5450, 10,000, and 27,500 and eccentricities varying from 0 to 0.9 were examined. These results are deemed to be mostly in the forced convection regime with some possible overlap with the mixed convection regime at the lowest Reynolds number considered. This work complements our previous work on natural and mixed convection using the same facility. The effect of eccentricity was not significant at lower eccentricities, but, in highly eccentric cases, the wall temperature in the narrow gap was much higher than in the wide gap and the average heat transfer coefficient was as low as one-fifth of the concentric value. For Re > 10,000, the average Nusselt number for the concentric case was nearly four times higher than the value predicted by the Dittus–Boelter correlation.

Thermodynamic analysis of a solid nuclear fuel element surrounded by flow of coolant through a concentric annular channel

A continuous quest for efficient utilization of energy resources has motivated the researchers to search for optimal design and operating conditions during various energy conversion techniques. These conditions for such systems are often proposed by minimizing the destroyed exergy potential in course of the process. In the present paper a second law analysis is done for a nuclear fuel element inside a concentric annular coolant passage. The entropy generation analysis has been carried out through a conjugate approach, with steady state temperature profiles within the fuel element and a thermodynamic approach within fluid. The effect of solid core heat generation and the temperature gradients inside solid core, fuel-clad gap and cladding are considered as well along with the irreversibilities arising out of fluid flow under turbulent condition. The effect of Reynolds number, duty parameter, diameter ratio, Biot number, dimensionless heat flux and thermal conductivity ratios on overall entropy generation characteristics have been investigated and interpreted physically. The validation of the present calculations was confirmed by best-estimate thermal-hydraulic code RELAP. The new thermodynamic design methodology presented in this paper adheres to the safety limits in temperature. The present analysis can be extended for complex fuel pellet arrangements in subchannel structures by an “equivalent annulus model”.

Critical heat flux for water boiling in channels. Modern state, typical regularities, unsolved problems, and ways for solving them (a review)

Some general matters concerned with description of burnout in channels are outlined. Data obtained from experimental investigations on critical heat fluxes (CHF) in different channels, CHF data banks, the main determining parameters, CHF basic dependences, and a system of correction functions are discussed. Two methods for estimating the CHF description errors are analyzed. The influence of operating parameters, transverse sizes of channels, and conditions at their inlet are analyzed. The effects of heat-transfer surface shape and heat supply arrangement are considered for concentric annular channels. The notions of a thermal boundary layer and an elementary thermal cell during burnout in channels with an intricate cross section are defined. New notions for describing CHF in rod assemblies are introduced: bundle effect, thermal misalignment, assembly-section-averaged and local parameters (for an elementary cell), cell-wise CHF analysis in bundles, and standard and nonstandard cells. Possible influence of wall thermophysical properties on CHF in dense assemblies and other effects are considered. Thermal interaction of nonequivalent cells and the effect of heat supply arrangement over the cell perimeter are analyzed. Special attention is paid to description of the effect the heat release nonuniformity along the channels has on CHF. Objectives to be pursued by studies of CHF in channels of different cross-section shapes are formulated.

General pure convection residence time distribution theory of fully developed laminar flows in straight planar and axisymmetric channels

In literature, the diffusion-free residence time distribution (RTD) of laminar flows – the so-called convection model – has been determined for various velocity profiles mostly on a case-by-case basis. In this analytical paper, we derive general mathematical relations which allow computing the diffusion-free differential and cumulative RTD in straight planar, circular and concentric annular channels for arbitrary monotonic and piece-wise monotonic one-dimensional velocity profiles. The theory is used to determine the RTD of plane Couette–Poiseuille flow with non-monotonic velocity profile, and the optimal value of the volumetric flow rate where the RTD becomes most narrow. It is shown that any velocity profile that depends in a sub-layer linearly on the distance from a stationary or moving no-slip wall has a differential RTD which follows a −3 power law as the residence time approaches its maximum. The variance of the RTD is directly associated with the asymptotic behavior of the RTD and can be finite or infinite.

Thermal Analysis of Immersed Heat Source during Flow Reduction Transient

and experimental study of transient heat transfer parameters related to downward flowing water in a circular concentric annular channel is conducted. The cooling channel is exposed internally to sinusoidal heat flux and has an adiabatic outer surface. The present theoretical study investigated the heat transfer and thermodynamic parameters during of 25%, 50%, and 75% flow reduction transients. The related experiments to such flow reductions simulates the loss of flow accidents (LOFA) in the research nuclear reactors initiated by loss of main power supply, pump failure, heat exchanger blockage, pipe blockage or valve closing. The results of steady state condition set as an initial condition for the transient model which is evaluated by using M-file- MatlabR2013a written computer program. The theoretical transient approach involved a mathematical model based on the analytical solution for first order ordinary differential equations supported by experimental correlations for axially, symmetric, simultaneously developing laminar water flow in a vertical annulus cooling channel which takes under consideration the nucleate boiling, film boiling and two phase flow formulation. The mathematical model is based on one dimensional downward flow. Unit step flow reduction function is implemented in the present model to simulate the flow reduction transient. It is noteworthy that the unit step reduction function is used first time in the recent study among the related previous study. The present experimental investigation included a set of experiments carried out to investigate the thermal-hydraulic behavior and evaluate their boiling safety factor, K. The present work is based on the following initial and boundary conditions: heat flux of 50 kW/m 2 , mass flux values of 192.6, 128.4, and 64.2 kg/m 2 .s to simulate the 25%, 50% and 75% flow reduction transients as the nominal mass flux is 256.8 kg/m 2 .s accompanied with

A method for describing and calculating critical heat fluxes in annular channels in a wide range of parameters

The paper presents a method for describing and calculating critical heat fluxes during flow of boiling water in concentric and eccentric annular channels heated on one and two sides for different ratios of heat fluxes on opposite walls and for different ratios of annular channel radiuses and eccentricities.

An Experimental Study of Natural Convection in Vertical, Open-Ended, Concentric, and Eccentric Annular Channels

The effects of eccentricity on the natural convection heat transfer from a vertical open-ended cylindrical annulus with diameter ratio of 1.63 and aspect ratio of 18:1 have been investigated experimentally. Within the range of present conditions, and with the possible exclusion of the highest eccentricities, it was found that the flow was thermally fully developed in a considerable section of the apparatus, as indicated by the linear variation of wall temperature with height. This made it possible to estimate the mass flow rate from the wall temperature gradient in the mid-section of the annulus, and use it to calculate the bulk Reynolds number, which was found to be weakly sensitive to eccentricity for a constant wall heat flux and to increase with increased wall heat flux. With the exception of the very low eccentricity range in which it was insensitive to eccentricity, the overall heat transfer rate diminished monotonically with increasing eccentricity. Plots of the local azimuthal variation of the Nusselt number showed that, at low eccentricities, the heat transfer rate increased near the wider gap but decreased near the narrower gap. The average Nusselt number was found to decrease measurably with increasing eccentricity and to increase slightly with increasing heat flux within the examined range. In contrast, the Grashof number was found to be much more sensitive to changes in heat flux and only had a weak dependence on eccentricity.

Shear driven two-phase flows in vertical cylindrical duct

Experiments and numerical simulations were carried out for shear-driven two-phase flows in a confined volume of liquid under conditions of normal gravity. The geometry corresponds to a cylindrical liquid bridge surrounded by a concentric annular gas channel with external solid walls. The internal part consists of solid supports at the bottom and top, while the central part is a liquid zone filled with a viscous liquid and kept in its position by surface tension. Gas enters into the annular duct, flows between solid walls and upon reaching the liquid zone entrains initially quiescent liquid. The flow dynamics is governed by the Navier–Stokes equations in both fluids, which are numerically solved in the exact experimental geometry taking into account interface deformation by gravity. In the experiments 5 cSt silicone oil and air were used as test fluids and the flow was monitored by means of particle tracking velocimetry. The experiments were performed for unit aspect ratio (the ratio of liquid zone length to its radius), while the simulations of shear-driven flow were carried out for a wide range of parameters. A particular attention is focused on the effect of free surface shape and fluids viscosity contrast on the interfacial flow dynamics. The current study suggests a linear dependence between velocities of gas and liquid when the viscosity of the liquid is larger by two orders of magnitude than that of gas. Another relation is proposed when the fluids viscosity ratio, μ l / μ g , is less than 50.

Numerical simulation for designing tuned liquid dampers to damp out double-pendulum oscillations

This paper presents a simplified dynamic analytical model based on the Lagrangian formalism to describe the annular sloshing damper behavior used to damp out free oscillations of a double-pendulum system. A simulation program using this model has been developed with the mathematical software MATLAB®. This simulation method is applied to design dampers for the mass and coil suspensions of the French watt balance experiment. The motion of each suspension is equivalent to a double-pendulum motion having two main natural frequencies for each configuration considered. The shape of the damper used is a ring composed of one or two concentric annular channels partially filled with a liquid (water for instance). The depth of the liquid must be adjusted in each channel in order to tune the resonance frequency of the liquid to a natural frequency of the suspension. Two corrective parameters determined experimentally have been added to our model in order to yield results in fair agreement with experiment. The numerical simulation based on our analytical model has provided useful information for designing annular sloshing dampers as efficient as possible for the experiment concerned. Furthermore, this method can be used to study any pendulous load system behavior and to design appropriate sloshing dampers.