Outer Cylindrical Wall Research Articles

Mixed convection flows from a revolving cylindrical cavity

Efforts are made to describe the thermofluidic behavior around a spinning hot cylindrical open cavity with negligible wall thickness suspended in air within the laminar regime. Several important input parameters, such as, Rayleigh number ( 10 2 ≤ Ra ≤ 10 6 ) , aspect ratio ( 0.5 ≤ H / D ≤ 10 ) , and Reynolds number ( 0 ≤ Re D ≤ 300 ) are considered to carry out the ongoing numerical analysis. Firstly, thermal plumes are provided to describe the pattern of flow and heat transfer around the heated surfaces of shell by considering the effect of Ra , H / D , and Re D . It is predicted that the heated plume is thrown radially due to the presence of swirling motion ( Re D ≠ 0 ) of the cylindrical shell unlike the pattern of thermal plume around the stationary vessel. Furthermore, the influence of Re D on behavior of cooling rate from inner ( Q iw ) and outer ( Q ow ) surfaces has also been predicted by considering both stationary and swirling conditions. A substantial growth in Q iw is noticed with the growth of Re D for a constant H / D . This effect is substantially greater at lower H / D compared to higher H / D . Again, attempts are made to elucidate the influence of Re D on Nusselt number for cylindrical inner wall ( Nu cyl − iw ) , cylindrical outer wall ( Nu cyl − ow ) , base inner wall ( Nu base − iw ) , and base outer wall ( Nu base − ow ) . Fluid flow behavior around the stationary and revolving cylindrical open cavity is also explained by employing velocity vectors. Finally, an appropriate correlation demonstrating a reasonable agreement with numerical data is found for average Nusselt number in terms of Ra , H / D , and Re D .

Mitigation of gas entrainment in swirling free surface flows

Gas entrainment presents a safety challenge within sodium-cooled fast reactors. This problem is similar to two-phase free surface interactions in a Taylor–Couette flow characterized by a large annulus gap (small radius ratio, η≈0.333) and highly turbulent swirling flows (Re≈105). The aim of the current work is to test strategies that could mitigate this phenomenon. A three-dimensional numerical model of the primary sodium pump annulus region involved in gas entrainment due to shaft rotation was developed, and turbulent swirling flow that occurs in the annular gap between the vessel and the shaft is investigated. The influence of baffle plates mounted on the stationary vessel with and without porosity was examined during the study. The simulation results revealed that submerged porous plates placed on the outer cylindrical wall both delayed vortex breakdown and suppressed shear waves near the surface. Both these effects substantially delayed gas entrainment into the liquid.

Angular momentum Based-Analysis of Gas-Solid fluidized beds in vortex chambers

Gas-solid vortex chambers are a promising alternative for reactive and non-reactive processes requiring enhanced heat and mass transfer rates and order-of-milliseconds contact time. The conservation of angular momentum is instrumental in understanding how the interactions between gas, particulate solids, and chamber walls influence the formation of a rotating solids bed. Therefore, this work applies the conservation of angular momentum to derive a model that gives the average angular velocity of solids in terms of gas injection velocity, wall-solids bed drag coefficient, gas and particle properties, and chamber geometry. Three datasets from published studies, comprising 1 g-Geldart B- and d-type particles in different vortex chambers, validate the model results. Using a sensitivity analysis, we assessed the effect of input variables on the average angular velocity of solids, average void fraction, and average bed height. Results indicate that the top and bottom end-wall boundaries exert the most significant braking effect on the rotating solids bed compared with the cylindrical outer wall and gas injection boundaries. The wall-solids bed drag coefficient appears independent of the gas injection velocity for a wide range of operating conditions. The proposed model is a valuable tool for analyzing and comparing gas–solid vortex typologies, unraveling improvement opportunities, and scale-up.

Experimental observation on flow patterns of thermocapillary-buoyancy convection in shallow annular pools with a heated inner cylinder

Experimental observations on flow patterns of thermocapillary-buoyancy convection in shallow annular pools with a hot inner cylindrical wall have been carried out to understand the effect of Prandtl number on the flow pattern bifurcation. The results reveal that the flow could be weakened and the critical Marangoni number increases with the increasing aspect ratio and Prandtl number. With the increasing Marangoni number, both the transition from a stable multicellular flow to an oscillating multicellular flow and the pulsating pattern have been observed. Because the pulsating pattern is superimposed on an oscillating multicellular flow, thermocapillary convection evolves from periodic oscillatory state to quasi-periodic bifurcation state. As Prandtl number increases, both the oscillating multicellular flow and the pulsating pattern become difficult to be observed. Moreover, the pulsating pattern propagates radially from the hot inner cylindrical wall to the colder outer cylindrical wall, which is opposite to the direction of the surface-tension gradient. The underlying physical mechanism of the pulsating pattern is discussed.

Numerical study of detonation flows in a supersonic annular chamber

The presented paper is devoted to the study of detonation structures in a flow-type supersonic chamber of a new design, previously proposed by us. The detonation chamber is an annular cylindrical channel located between the inner and outer cylindrical walls. The oblique detonation wave is formed by a compression body inside the annular channel, shaped as a continuous monofilar helix with a constant pitch angle. Numerical simulations are performed for a supersonic flow of a stoichiometric hydrogen-air mixture with inflow Mach number M0=3 and the pitch angle a<aCJ. A mathematical model of the reacting flow in the combustor is developed in a two-dimensional unsteady formulation. A two-stage model of the detonation kinetics is used to describe the chemical process in reacting gas. The flow evolution for the different conditions for starting the detonation chamber operation is numerically studied. The final structures of the steady flow in the combustor are obtained. The bifurcation effect of a stationary solution according to the initial conditions of the problem is discovered for some combinations of the geometric parameters of the detonation combustor.

The mechanism of vortex instability in electromagnetically driven flow in an annular thin layer of electrolyte

A circumferential flow of a conducting fluid in an annular channel can be created by the action of a Lorentz force arising as a result of the interaction between an applied vertical magnetic field and a radial electric current flowing through the electrolyte. Quite unexpectedly, experiments revealed that a robust vortex system appears near the outer cylindrical wall in such flows. McCloughan and Suslov (J. Fluid Mech. 887:A23, 2020) (McCS) reported comprehensive linear stability results of such a flow for variable Lorentz forcing. Here we complement that study by investigating the flow structure as a function of the channel aspect ratio. Remarkably, despite the completely different physical nature of parametric dependences, dynamic in McCS and purely geometric here, we show that in both scenarios vortices appear on a background of a steady axisymmetric flow at the boundary between two counter-rotating toroidal structures and have a similar energy distributions. The two studies demonstrate the robustness of the mechanism responsible for the vortex formation: Rayleigh's inviscid centrifugal instability aided by radial shear in the boundary layer near the outer cylindrical wall.

Mean flow generation due to longitudinal librations of sidewalls of a rotating annulus

Laboratory experiments with a rotating cylindrical annulus are reported that reveal a prograde jet, which is adjacent to a (longitudinally) librating inner straight cylindrical wall. Here, wall libration is realised as a time-harmonic modulation of the inner cylinder's rotation rate. The outer cylindrical wall and bottom and top lids rotate with constant angular velocity. The main purpose of our study is to contribute to a qualitative and quantitative understanding of non-linearities that are present in oscillating, but centrifugally stable, vertical boundary layers frequently encountered in rotating wall-bounded flows. We consider a problem that is in a sense complementary to that of previous works that focused on oscillating Ekman layers but neglected the vertical Stokes−Stewartson layers. A simple analytical model is proposed that is able to predict the magnitude and spatial structure of the emerging prograde near-wall jet in terms of nonlinearity inherent in the inner cylinder's boundary layer dynamics.

Numerical Study of Laminar Natural Convection Heat Transfer in Inclined Trapezoidal Enclosure

In this paper, fluid flow pattern and heat transfer behavior are numerically studied in a trapezoidal enclosure inclined at different tilt angles. The enclosure has isothermally heated cylindrical inner wall and cooled cylindrical outer wall, whereas sidewalls have linearly varying temperature profile. The numerical analysis is performed at different Rayleigh numbers (103 ≤ Ra ≤106) and Prandtl numbers (0.71 ≤ Pr ≤ 40) assuming steady, incompressible, laminar, Newtonian, and two-dimensional flow. The angle between two nonparallel sidewalls is varied from 10 deg to 90 deg, while the tilt angle is varied from 5 deg to 175 deg. Governing equations along with the Poisson type equation for heatfunctions are solved to obtain fluid flow and direction of heat flow in the trapezoidal enclosure. At low Raleigh number, the isotherms are smooth, indicating the dominance of conduction heat transfer dominates. The streamlines, isotherms, and heatlines in high Prandtl number (Pr = 6.99 ad 40) fluids show a similar pattern as that in the air (Pr = 0.71) at Ra = 106; however, the strength of heatfunctions increases. With the increase in the aspect ratio of the enclosure, thermally stratified region is found to increase in size. Stronger convection is present in the enclosure with a higher angle between two nonparallel sidewalls.

Three-Dimensional Numerical Simulation on Thermocapillary Convection of Moderate Prandtl Number Fluid in an Annular Shallow Pool with Surface Heat Dissipation

In order to understand the effect of surface heat dissipation on thermocapillary convection of moderate Prandtl number fluid in an annular shallow pool, we performed a series of three-dimensional numerical simulations by using the finite volume method. An annular shallow pool is full of 0.65cSt silicone oil with Prandtl number of 6.7. The radius ratio and the aspect ratio of the pool are respectively fixed at 0.5 and 0.1. Surface heat dissipation Biot number is varied from 0 to 50. Results indicate that the critical Marangoni number of flow destabilization mainly depends on the coupling effect of the thermocapillary force and surface heat dissipation on the free surface, which decreases first, and then increases gradually. When Biot number is small, the steady axisymmetric flow after the flow destabilization will bifurcate to the hydrothermal wave. With the increase of Marangoni number, the flow pattern evolution at a small Biot number is similar to that of an adiabatic free surface, and the fundamental oscillatory frequency increases gradually. With the increase of Biot number, the radial roll cells near the outer cylindrical wall gradually extend to the inner wall, and eventually occupy the whole liquid pool. When Biot number is large, the flow pattern after the flow destabilization is a radial rolling cell pattern with alternating azimuthal direction. Then it gradually evolves into azimuthal waves, and the fundamental oscillatory frequency has a slight decrease.

Effect of surface heat dissipation on thermocapillary convection of moderate Prandtl number fluid in a shallow annular pool

This paper presents a series of three-dimensional numerical simulations on the effect of surface heat dissipation on thermocapillary convection of moderate Prandtl number fluid in a shallow annular pool. The annular pool with a fixed aspect ratio of 0.05 and radius ratio of 0.5 is filled with 0.65 cSt silicone oil. Its Prandtl number is 6.7. Biot number of surface heat dissipation ranges from 0 to 50. The results show that when Marangoni number is small, thermocapillary convection is the axisymmetric steady flow. When Marangoni number exceeds the critical value, the basic flow will destabilize and transit to the hydrothermal waves that propagate along the clockwise or anticlockwise direction. The critical Marangoni number of the flow destabilization increases with the increase of Biot number. Furthermore, when Biot number increases, the radial temperature gradient on the free surface decreases near the inner cylindrical wall, but increases near the outer cylindrical wall, which results in the thermocapillary convective cell moving gradually from the inner to the outer cylindrical walls. After the flow destabilizes, the temperature fluctuation on the free surface mainly appears near the outer cylinder at a large Biot number.

Surface Heat Dissipation Dependence of Thermocapillary Convection of Moderate Prandtl Number Fluid in an Annular Pool

In order to understand surface heat dissipation dependence of thermocapillary convection for moderate Prandtl number fluid in a deep annular pool, a series of three-dimensional numerical simulations have been carried out by using the finite volume method. The radius ratio and the aspect ratio of an annular pool are fixed at 0.5 and 1.0, respectively. The working fluid is 0.65cSt silicone oil with Prandtl number of 6.7. Surface heat dissipation Biot (Bi) number is varied from 0 to 50. Results indicate that with the increase of Biot number, the radial temperature gradient near the inner cylindrical wall decreases, and near the outer cylindrical wall it increases, so the flow is enhanced. When 0 < Bi < 10, with the increase of Marangoni number, the axisymmetric steady flow first transits to the standing wave, and then to the azimuthal waves. The standing wave should be attributed to Marangoni-Benard instability. However, the azimuthal waves should be corresponded to hydraulic instability, which is mainly driven by the azimuthal motion of temperature fluctuation from the sudden change of flow direction near the bottom and the inner cylindrical wall. When Bi ≥ 10, when the flow destabilizes, the axisymmetric steady flow transits directly to the azimuthal waves. With the increase of Biot number, the critical Marangoni number of the flow destabilization increases. Furthermore, the fundamental frequency and the wave number of three-dimensional oscillatory flow increase gradually with the increase of Biot number.

New Measurement Method of Broadband Permittivity and Permeability of Non-Solid Materials in Small Quantity

Evaluation of permittivity (e) and permeability (μ) of magnetic/dielectric material in microwave band becomes more important with the rapid expansion of microwave technologies. Transmission/reflection line method is well known as a simultaneous measurement method of e and μ in the band. However in this method material under test (MUT) is limited to solid state. On the other hand, for measuring liquid material open ended coaxial probe method was proposed. The method is disadvantageous in terms of requiring deciliter volumes of MUT for approximating a semi-space filled by MUT. We propose a new measurement method with the aim of simultaneous measuring both of permittivity and permeability of not only solid material but also a small amount of liquid, powder, and gel state material. A plastic toroidal case was utilized to encapsulate non-solid state MUT and whole the case was evaluated by coaxial line method. In this study the cases were modeled using Acrylic 3-D printer (Stratasys, Objet 260 Connex). An example of the plastic case with a cap fabricated is shown in Fig. 1. Outer and inner diameter (7.00 and 3.00 mm) of the case was designed to fit to a coaxial sample holder (KEAD Inc., CSH2-APC7). The length of the case including a cap thickness measured by digital vernier caliper was 5.00 mm. In the same way, thickness of wall, bottom, and cap was 0.45, 0.50, and 0.50 mm, respectively. Accordingly the volume of MUT required for the case was about 70 microliters. The specimen which MUT was encapsulated was inserted to the coaxial sample holder and complex scattering (S) parameters from 1–10 GHz were taken using a vector network analyzer (Hewlett-Packard, HP 8720D). S-parameters whose reference planes were both upper and lower surface of the specimen were obtained by shifting reference planes of the measured S-parameters. After that we obtained S-parameters of MUT in numerical calculations mentioned below in order to take away unwanted plastic case portions. The specimen can be divided into three coaxial portions: Inner cylindrical wall, outer cylindrical wall, and middle core including MUT between their walls. From the viewpoint of electric circuit it corresponds to a series connection of the three two-port networks. Impedance (Z) parameters of the middle core were obtained using the relationship: Z-matrix of the specimen equals to the sum of their three Z-matrices. Z-matrix of the specimen was obtained by converting S-matrix of it by a reference impedance. Z-matrix of outer and inner wall was obtained from e and μ measured in advance using solid specimens of the plastic material and outer and inner diameters of their cylindrical walls. Z-matrix of the middle core was converted S-matrix again. The middle slender core can be divided into three coaxial portions: a part of cap, a part of bottom, and MUT. The core corresponds to a cascaded connection of the three two-port networks. Transfer (T) parameters of MUT were obtained using the relationship: T-matrix of the core equals to the product of their three T-matrices. T-matrix of the core was obtained by converting S-matrix of it. T-matrix of a part of bottom and cap was obtained from e and μ of the plastic material used and bottom and cap thickness. Finally e and μ of MUT were calculated from S-parameters of it using Nicolson-Ross-Wier algorithm [1, 2]. In this study, the air at the volume was measured as MUT in order to confirm a validity of the proposed method. The dependences of real and imaginary part of relative permittivity of air obtained by this method on frequency were shown in Fig. 2(a) and Fig. 2(b). Although the both values had a margin of error of plus or minus 10% a constant and nearly ideal relative permittivity of air was confirmed in the band measured from these figures. This result indicates that the proposed method is effective for measuring non-solid materials.

Effects of annular-cylindrical combined channel Hall thruster length on the discharge characteristics

In order to increase the degree of ionization and improve the efficiency, the effects of different cylindrical outer wall lengths on the discharge characteristics of the annular-cylindrical combined channel Hall thruster are studied. The cylindrical outer wall is set to the following positions: 95% (with positive magnetic field gradient), and 100%, 95%, 90%, 75%, and 50% (with negative magnetic field gradient) of the maximum magnetic field. The ionization gain and wall energy loss under different positions are analyzed through numerical simulations. The simulation result shows that when the cylindrical outer wall is set to the position where it is 100%–90% of the maximum magnetic field (negative magnetic field gradient zone), the power deposition on the channel wall is small, the propellant utilization can be largely improved, and the comprehensive performance is optimal for the annular-cylindrical combined channel Hall thruster.

Numerical Investigation of Developing Natural Convection in Vertical Double-Passage Porous Annuli

The present study deals with the numerically investigation of developing laminar natural convection in the vertical double-passage porous annuli formed by three vertical concentric cylinders of which the middle cylinder is a thin and perfectly conductive known as baffle. In this analysis, two thermal conditions are considered namely, either inner or outer cylindrical wall is constantly heated while the opposite wall is insulated. An implicit finite difference technique is employed to solve the boundary layer equations in both the annular passages. The temperature profiles and velocity profiles in axial as well as radial directions have been presented for different values of Grashof number, Darcy number, baffle position and radius ratio. The results reveal that both physical and geometrical parameters have profound influence on the development of velocity and thermal fields as well as heat transfer rate.

A study of continuous rotation modes of detonation in an annular chamber with constant or increasing section

The detonation regime is an alternative to the conventional constant-pressure combustion mode typically used for propulsive systems because of its higher thermal efficiency and temperature and pressure of products, and shorter characteristic combustion time and length. The classic implementation is the rotating detonation engine, with the combustion chamber consisting of the annular space between a center-body and an outer cylindrical wall. This experimental study focuses on the effects of the chamber inner geometry, the total mass flow rate, and the detonation cell width on the conditions for detonation rotation. Cylindrical and conical center-bodies with several lengths and half-apex angles are considered to approach the hollow configuration of the RDE chamber. The cell width is varied by testing with mixtures of ethylene and enriched air, with several equivalence ratios and nitrogen dilutions. The combustion modes and the detonation velocities and pressures are characterized by analyzing pressure signals and high-speed camera visualizations. Three detonation regimes are identified, characterized by one or two fronts propagating in the same or opposite directions. Decreasing the center-body length and increasing the half-apex angle increases the measured detonation velocity and pressure. Velocities range between 53 and 89% of the Chapman–Jouguet value, and the pressure reaches about 11 bar. For the conditions tested, higher detonation velocity and pressure are obtained for the conical center-body configuration. Our interpretation is that center-bodies that are too long, or channels that are too narrow, hinder the exhaust of the burned gas. As a result, the proportion of products in the unburned gas mixture ahead of the detonation wave (consisting of fresh and burned gas) increases, resulting in a decrease in the magnitude of the detonation properties.

Newtonian Poiseuille flow in ducts of annular-sector cross-sections with Navier slip

We consider the Newtonian Poiseuille flow in a duct the cross section of which is either a circular or an annular sector assuming that Navier slip occurs either along both the cylindrical walls or only along the outer cylindrical wall. A general analytical solution is derived and the results for the latter case are discussed and the effects of the angle of the sector, the radii ratio and the slip number are analysed.

Flow visualization using heat lines for unsteady radiative hydromagnetic micropolar convection from a vertical slender hollow cylinder

The present study aims to investigate the thermal radiation heat transfer effect on unsteady magnetohydrodynamic flow of micropolar fluid over a uniformly heated vertical hollow cylinder using Bejan's heat function concept. The normalized conservation equations emerge as a system of time-dependent non-linear coupled partial differential equations. Under appropriate wall and free stream conditions these equations are solved with an efficient unconditionally stable implicit scheme of Crank-Nicolson type. Important thermo-physical parameters featured include the magnetic body force parameter (M), Grashof (free convection) parameter (Gr), Eringen micropolar material parameter (K), Prandtl number (Pr), conjugate heat transfer parameter (P) and radiative-conductive Rosseland parameter (N), are analyzed on the flow-field with ranges 0–3, 105–106, 0–1.2, 0.7–7.0, 0–0.5 and 0–15, respectively. The time-histories of average values of momentum and heat transport coefficients, as well as the steady-state flow variables are presented for selected values of these non-dimensional parameters. With elevation in magnetic parameter or radiation parameter, the time taken for the flow-field variables to attain the time-independent state increases. The dimensionless thermal radiative heat function values are closely correlated with the overall rate of heat transfer on the outer hot cylindrical wall. Bejan's heat flow visualization implies that the thermal radiative heat function contours are compact in the neighbourhood of leading edge of the boundary layer on the outer hot cylindrical wall. Increasing radiation or magnetic parameter values result in an increase in the deviation of heat lines from the hot wall. Also, the heat lines are observed to depart slightly away from the hot wall with greater values of vortex viscosity. Furthermore, the deviations of flow variables from the hot wall for a micropolar fluid are significant compared to the Newtonian fluid (vanishing micropolar vortex viscosity).

Numerical study of double-diffusive convection in a vertical annular enclosure with a baffle

This paper numerically examines the influence of a circular thin baffle on thermosolutal convection in a vertical annular enclosure. The inner and outer cylindrical walls, and the baffle are retained with different temperatures and concentrations, while the upper and lower boundaries are kept at adiabatic and impermeable. The model equations are solved using an implicit finite difference scheme consisting of ADI and SLOR methods. Numerical simulations are performed to understand the size and position effects of the baffle on the thermosolutal convection and are successfully captured through our results. It has been observed that the baffle size and location has very important role in controlling the thermosolutal convective flow and the corresponding heat and mass transport characteristics. Further, our results are in good agreement with the available benchmark results for limiting cases.

Electromagnetically driven flow of electrolyte in a thin annular layer: axisymmetric solutions

Experimental observations of an azimuthal electrolyte flow driven by Lorentz force in a thin annular fluid layer placed on top of a magnet show that it develops a robust vortical system near the outer cylindrical wall. It appears to be a result of instabilities developing on a background of steady axisymmetric flow. Therefore, the goal of this paper is to establish a scene for a future comprehensive stability analysis of such a flow. We discuss popular depth-averaged and quasi-two-dimensional approximate solutions that take advantage of the thin-layer assumption first, and argue that they cannot lead to the observed flow patterns. Thus, three-dimensional toroidal flows are considered. Their similarities to various other well-studied rotating flow configurations are outlined, but no close match is found. Multiple axisymmetric solutions are detected numerically for the same governing parameters, indicating the possibility of subcritical bifurcations, namely type 1, consisting of a single torus, and type 2, developing a second counter-rotating toroidal flow near the outer cylinder. It is suggested that the transition between these two axisymmetric solutions is likely to be caused by the centrifugal instability, while the shear-type instability of the type 2 solution may be responsible for the observed vortex structures. However, a dedicated stability analysis which is currently underway and will be reported in a separate publication is required to confirm these hypotheses.

A new curved boundary treatment in lattice Boltzmann method for micro gas flow in the slip regime

A new curved boundary treatment in lattice Boltzmann method is developed for micro gas flow in the slip regime. The proposed treatment is a combination of the nonequilibrium extrapolation scheme for curved boundary with no-slip velocity condition and the counter-extrapolation method for the velocity and its normal gradient on the curved boundary. Taking into consideration the effect of the offset between the physical boundary and the closest grid line, the new treatment is proved to be more accurate than the traditional half-way diffusive bounce-back (DBB) scheme. The present treatment is also more applicable than the modified DBB scheme because the specific gas-wall interaction parameters need to be determined to ensure the validation of the modified DBB scheme.The proposed boundary treatment is implemented to simulate the benchmark problems, which include a Poiseuille flow in the aligned/inclined micro-channel, a flow past a microcylinder and a microcylindrical Couette flow. The results and conclusions are summarized as follows.1) The force-driven Poiseuille flow in an aligned microchannel is simulated separately with different values of wall-grid offset qδx (q=0.25, 0.5, 0.75, 1.0). With the consideration of the wall-grid offset, the numerical results with the new boundary treatment show good agreement with the analytical solutions. However, the results obtained by using the half-way DBB scheme only accord well with the analytical solutions under the condition of a fixed wall-grid offset (q=0.5).2) To demonstrate the capability of the present treatment in dealing with gas flow in a more complex geometry, the force-driven Poiseuille flow in a micro-channel is investigated separately with different inclined angles. The present numerical results fit well with the analytical solutions. However, the discrepancy between the results obtained with the half-way DBB scheme and the analytical solutions can be clearly observed near the inclined boundaries.3) The gas flow past a microcylinder is simulated to prove that the present treatment can deal with the curved boundary. The slip velocity profile along the micro cylinder periphery obtained with the present treatment accords well with the available data in the published literature. However, the results obtained with the half-way DBB scheme show lower values than the results from the published work.4) In the simulations of the microcylindrical Couette flow between two coaxial rotating cylinders for different Knudsen numbers the results obtained by using the present treatment show excellent agreement with the analytical solutions. However, the results obtained with the half-way DBB scheme and the modified DBB scheme deviate obviously from the analytical solutions near the inner and outer cylindrical walls, respectively.In summary, the new boundary treatment proposed in this work is capable of dealing with the complex gas-solid boundary in the slip regime. The new treatment has a higher accuracy than the half-way DBB scheme and shows a better applicability than the modified DBB scheme.