Annular Pipe Research Articles

Validation and Visualization of Decaying Vortex Flow in an Annulus

Swirling jets produced using inlet swirlers are often used to increase the heat or mass diffusion rates in heat exchangers or reactors, separation of smoke and dust suspended in the air in ventilation ducts etc. The aim of this work is to validate a CFD model through streak-line comparison and to define the fully laminar and turbulent regime for decaying vortex flow produced using a set of axial swirlers in an annular pipe. Flow visualization was conducted using fluorescent dye to visualize on eddy formation along the pipe. Decaying vortex flow was produced using static axial swirlers fitted at the inlet of the annular pipe. In this study, three different swirl angles were investigated: 30°, 45° and 60°. In addition, the Reynolds number (Re) was varied from 10 to 1800. Results shows that the flow regimes for decaying vortex flow in annuli can be defined with reference to axial annular pipe flow.

Simulation of laminar flow through eccentric annuli using isogeometric variational multiscale method

We present an application of the Residual-based variational multiscale (RBVMS) methodology to the computation of laminar eccentric annular pipe flow with eccentricities of 0.5 and 1. Isogeometric analysis is utilized for higher order approximation of the geometry and solution using Non-uniform rational B-splines (NURBS) functions. The ability of NURBS exactly representing curved circular geometries makes NURBS-based isogeometric analysis attractive for the application to the flow through the eccentric annuli. By using the exact representation of circular boundary, the limiting case of the eccentricity, i.e. the inner circular wall actually touches the outer circular wall, is successfully demonstrated.

Numerical investigation of roll heat pipe type for heat exchangers thermal management

Heat pipes cooling technology is currently spreading out for many applications such as electronic, solar energy, air conditioning systems, space applications, telecommunications, food industries, geothermal systems, heat recovery etc.In this work, two numerical studies have been developed to investigate the thermal performance of a novel type of heat pipe called “Roll heat pipe (RHP)”. Results show that RHP performs better than annular pipes often used in heat exchangers. The effect of boundary conditions on the heat pipe thermal resistance is investigated. Results reveal that the RHP thermal resistance decreases with the heat input and RHP thermal performance is controlled by the outer surface temperature. Heat transfer inside RHP can be enhanced when heat is extracted quickly from the condenser region. Result reveals also that a higher grade of isothermalisation can be obtained compared with conventional tubular heat exchanger for uniform or localized heat inputs in the evaporator region. The objective of this study is to better understand the thermal performance of RHP type for further heat exchanger applications or other designs processes that are transient or steady.

Stability of centrifugal convection in a rotating pipe

This numerical study reveals that the thermal convection, induced by the axial gradient of temperature in a rotating pipe, suffers from the shear-layer instability if the Prandtl number, Pr, is small. As Pr increases, this instability is suppressed by the stable density stratification in the field of centrifugal force. In an annular pipe, the thermal instability develops for large Pr if a temperature of walls is prescribed. For a narrow annulus, these features agree with the known results for a planar flow driven by gravity and a horizontal gradient of temperature. It is shown here that the thermal instability does not develop if the walls are adiabatic. The centrifugal and Marangoni convection of a liquid, partially filling the pipe, also suffers from the shear-layer instability for small Pr and has no thermal instability. These features agree with the experiments for the planar flow performed by Kirdyashkin. The obtained results are of fundamental interest and can be relevant for the development of centrifugal heat exchangers.

Forced, natural and mixed-convection heat transfer and fluid flow in annulus: A review

The enhancement of the thermal performance of heat exchanging equipment transport energy at low financial cost by various techniques is presented in this review. Heat transfer is classified into three forms, namely, conduction, convection, and radiation. Convection is one of the major modes of heat transfer that can be qualified in terms of being natural, forced, gravitational, granular, or thermomagnetic. In the past decade, several studies on convection heat transfer in annular pipes with nanofluids have been reported. The effect of eccentricity in horizontal, inclined and vertical directions on heat transfer rate in most numerical and experimental investigations for horizontal, inclined and vertical annular tubes is studied. The effects of heater length, as well as the Darcy, Prandtl, Reynolds, Grashof and Rayleigh numbers on heat transfer in concentric and eccentric annular tubes are also investigated. This paper reviews various researches on fluid flow and heat transfer behavior in an annulus. A basic description of the convection heat transfer is given. Numerical and experimental investigations are conducted according to the concentric and eccentric annuli. Finally, conclusions and important summaries are presented according to the collected data.

MHD mixed convection in a vertical annulus filled with Al2O3–water nanofluid considering nanoparticle migration

In the current study, an MHD mixed convection of alumina/water nanofluid inside a vertical annular pipe is investigated theoretically. The model used for the nanofluid mixture involves Brownian motion and thermophoretic diffusivities in order to take into account the effects of nanoparticle migration. Since the thermophoresis is the main mechanism of the nanoparticle migration, different temperature gradients have been imposed using the asymmetric heating. Considering hydrodynamically and thermally fully developed flow, the governing equations have been reduced to two-point ordinary boundary value differential equations and they have been solved numerically. It is revealed that the imposed thermal asymmetry would change the direction of nanoparticle migration and distorts the velocity, temperature and nanoparticle concentration profiles. Moreover, it is shown that the advantage of nanofluids in heat transfer enhancement is reduced in the presence of a magnetic field.

Mathematical Modeling of Water Flow for Irrigation in a Permeable Pipe of Elliptical Cross-section

An unsteady incompressible fully developed flow in a horizontal flexible and permeable annular pipe of elliptic cross-section under the action of gravity is studied. The solution is obtained through a homogenization method by employing a small scale separation parameter that approximates the pipe in the form of a series. The results in terms of velocity and pressure distributions and mass flow rate inside the pipe and through the pipe wall are presented and discussed. It is shown that the pipe thickness has no influence on the water flow through the pores. We also propose that for the efficient use of water for irrigation, the elliptical pipe should be laid in a vertical position.

1513 二重円管内乱流の亜臨界遷移に関する直接数値シミュレーション

We perform direct numerical simulation (DNS) for annular pipe flow and report localized structures in subcritical transition. Our flow system is the simplest fundamental annular pipe flow which is a flow between two concentric cylinders and is driven by a constant uniform pressure gradient in the axial direction. By changing Reynolds number (Re_τ = uτδ/ν) and radius ratio (η = r_<in>/r_<ou>) systematically, we found several localized intermittent turbulent states. To observe the effect of η, we choose low to high radius ratios, which are 0.1, 0.3, 0.5, and 0.8. At η &ge; 0.5, we confirmed stripe pattern similar to that in the plane Poiseuille flow. In contrast, with a low η of 0.1, localized structures corresponding to equilibrium puffs and splitting puffs arise. The moderate η of 0.3 gives rise to localized turbulence taking a form of finite (like a puff) and helical shape (like a stripe pattern).

Numerical simulation of heat transfer to separation tio2/water nanofluids flow in an asymmetric abrupt expansion

Abstract. Flow separation and reattachment of 0.2% TiO2 nanofluid in an asymmetric abrupt expansion is studied in this paper. Such flows occur in various engineering and heat transfer applications. Computational fluid dynamics package (FLUENT) is used to investigate turbulent nanofluid flow in the horizontal double-tube heat exchanger. The meshing of this model consists of 43383 nodes and 74891 elements. Only a quarter of the annular pipe is developed and simulated as it has symmetrical geometry. Standard k-epsilon second order implicit, pressure based-solver equation is applied. Reynolds numbers between 17050 and 44545, step height ratio of 1 and 1.82 and constant heat flux of 49050 W/m2 was utilized in the simulation. Water was used as a working fluid to benchmark the study of the heat transfer enhancement in this case. Numerical simulation results show that the increase in the Reynolds number increases the heat transfer coefficient and Nusselt number of the flowing fluid. Moreover, the surface temperature will drop to its lowest value after the expansion and then gradually increase along the pipe. Finally, the chaotic movement and higher thermal conductivity of the TiO2 nanoparticles have contributed to the overall heat transfer enhancement of the nanofluid compare to the water.

Thermal management of double-pipe air to water heat exchanger

In this study, turbulent flow and heat transfer in an air to water double-pipe heat exchanger is investigated experimentally. The working fluids were air, flowing in the annular pipe, and water through the inner circular tube. To attain fully developed conditions, the heat exchanger was built with additional lengths before and after the test section. The inner tube was made from copper. The external tube was made of an industrial plastic which was insulated from the environment. In this manner, the outer surface of the annular channel can be considered adiabatic. The experiments are conducted in the range of flow rate of water from 120 to 200 (L/h) and in the temperature of water in upper tank range from 70 to 90°C. Correlations for Nusselt number and friction factor are presented for according to experimental data. Results show that velocity boundary layer thickness in air side increases with increase of the temperature of the water in the upper tank and flow rate of water on heat transfer. Nusselt number in water side is an increasing function of inlet temperature and inlet velocity of water while opposite tend is observed for Nusselt number in air side. Inserting agitator improves the rate of heat transfer. Enhancement of heat transfer has reverse relationship with Reynolds number.

The effects of wall roughness on erosion rate in gas–solid turbulent annular pipe flow

In the present study, the effects of wall roughness on erosion rate for gas–solid flows in horizontal annular pipes for different ratios of inner to outer radii and also for different values of solid particle concentration are investigated. The results are compared with earlier studies, and the effect of various parameters is discussed. The impingement angles and impact velocities of solid particles, which are needed for using the comprehensive erosion model, are evaluated using a four-way coupled Eulerian–Lagrangian simulation approach of gas–solid flows. The turbulent gas phase flow is solved using the k–ε model. For the simulation of particle movement, the fluctuations of gas phase velocity are evaluated by the eddy interaction method. The numerical results indicate that the solid particle induced erosion rate at the outer wall of annular pipes is considerably larger in comparison with a simple circular pipe with the same outer radius, and the erosion rate further increases as the radius ratio increases. The results also show that the erosion rates at both inner and outer walls increase as wall roughness increases and are much higher compared with those for smooth walls or walls with a small roughness.

Investigation of turbulent flow and heat transfer in an air to water double-pipe heat exchanger

In this study, turbulent flow and heat transfer in an air to water double-pipe heat exchanger is investigated experimentally. The working fluids are air, flowing in the annular pipe, and water through the inner circular tube. To achieve fully developed conditions, the heat exchanger was built with additional lengths before and after the test section. The inner tube was made from copper. The external tube was made of an industrial plastic which was insulated from the environment. In this manner, the outer surface of the annular pipe can be considered adiabatic. The experiments are conducted in the range of water flow rate (water inlet velocity) from 120 to 200 (L/h) and temperature of water in upper tank range (water inlet temperature) from 70 to 90 °C. Correlations for Nusselt number and friction factor are presented according to experimental data. Results show that velocity boundary layer thickness in air side increases with increase in the water inlet temperature and water flow rate. Nusselt number in water side is an increasing function of water inlet temperature, and water inlet temperature while opposite tend is observed for Nusselt number in air side.

An Experimental Study of Heat Transfer Coefficient in a Bubble Flow throughout an Annulus Pipe Heated at Inner Wall

The aim of the research work describe in this paper is to investigate correlation of water, air massflow rate and calor fluks to heat transfer coefficient. The investigation was carried out toward a pipe section test developed from acrylic with diameter of 60 mm and 210 mm length, therefore, the buble can be easier to shoot. A concurrent water were flowed upward and air was injected from the bottom. The wall of the heater was heated using two thermocouple installed at the outer surfece of the heater. The fluid flow was measured using thermocouple installed along the annulus pipe. A heater with transparent tube diameter of 50 mm and 1800 mm length was also installed, and supplied with 1000 Watt electric power. Result of the experiment showed that heat transfer coefficient incresed along with the air massflow rate increased, and its decreased with the increasing of water mass flow rate. The maximum heat transfer coefficient of 4340,602 W/m2 °C at electric fluck calor of 29582,448 W/m2 was echieved on water volume flow rate of 3 lpm and 9 lpm of air volume rate.

Using Taguchi and ANOVA methods to study the combined effects of drilling parameters on dynamic barite sag

Abstract The settling of barite particles in drilling fluids under no-flow conditions and under flow conditions is still a major problem in drilling. The separation of barite particles out of the drilling fluids causes a variety of problems, such as stuck pipe, lost circulation, and poor cement jobs. Furthermore, several severe well-controlled incidents have been caused by barite sag. This paper presents the quantitatively combined effects of the drilling parameters on dynamic barite sag in oil-based drilling fluids. The drilling parameters include annular velocity, pipe rotation, inclination angle, and eccentricity. Two levels for each parameter were considered to develop the test matrix in this study. For example, the parameter of inclination angle has two levels including concentric drill pipe (e=0) and eccentric drill pipe (e=1). The Barite Sag Flow Loop (BSFL), which utilized a coriolis mass flow meter to measure the circulating density of the fluid, was used to conduct tests. The Taguchi method was used to design the test matrix, which greatly reduces the number of experiments required and offers the optimum settings of the control parameters. Based on the two levels of the analyzed parameters, the annular velocity and pipe rotation contribute almost 60% and 21%, respectively, to the prevention of sag. The results also indicate that changing the inclination angle in the range from 60° to 45° from the vertical has the least impact on the prevention of barite sag. The results of this study enable drillers and designers to operate and design wells with fewer problems related to barite sag.

Investigation of Flow and Heat Transfer Characteristics of Annular Impinging Jet

Flow and heat transfer characteristics of impinging jet from annular pipe were experimentally and numerically investigated. To generate annular jet, the cylindrical rod with 12.7 mm in diameter was inserted at center of pipe nozzle which has inner diameter (D) of 28.6 mm. The jet-to-plate distance (H) was examined in the range of 2D, 4D, 6D and 8D. The jet Reynolds number was fixed for all experiments at Re=20,000 based on averaged velocity and pipe inner diameter. The conventional jet was also studied for comparison. The temperature distribution on the impingement surface was measured using an infrared camera. The numerical simulation was carried out to visualize the flow behavior. The results show that the heat transfer of annular jet is higher than that the case of conventional pipe jet at low jet-to-plate distance (H=2D); however, the ones of annular and conventional jet are comparable when jet-to-plate distance becomes higher than H=6D.

Fully developed flow and heat transfer of nanofluids inside a vertical annulus

Thermally fully developed mixed convection flow of nanofluids in a vertical annular pipe was investigated. Because of the non-adherence of the fluid–solid interface in the presence of nanoparticles, known as slip condition, the Navier’s slip condition was considered at the pipe walls. The Buongiorno’s model was employed for nanofluids that incorporate the effects of Brownian motion Nb and thermophoresis Nt numbers. Using the similarity variables, the governing partial differential equations were transformed into a system of ordinary ones with a constraint parameter and a solution was prepared via a reciprocal numerical algorithm. The effects of Grashof number Gr and slip parameter λ on nanoparticle volume fraction, velocity, temperature, average Nusselt number Nuavg, and pressure coefficient σ have been investigated in details. Results indicate that an increase in Gr and λ reduces the peak value of the dimensionless velocity profile in the core region of the annulus, away from the pipe walls, however, the velocity closer to the pipe walls increases. Furthermore, it was shown that nanofluids can transfer heat more efficiently in a slip condition than in a no-slip condition.

Validation of heat transfer and friction loss data for fibre suspensions in a circular and a coaxial pipe heat exchanger

Heat transfer data obtained previously in a pipe heat exchanger were validated using an annular test unit with longer calming section and axial entry flow levels. Water and two suspensions of long-fibre softwood Kraft pulps with fibres having different coarseness (mass/unit fibre length) were used. Data in both systems were accumulated and compared over a range of flow rates with the fibre concentrations up to 0.4%. Heat transfer coefficient hc increased with increasing velocity for both water and fibre suspension flow. Various fibre dimensions and fibre characteristics are shown to vary systematically with hc at the same experimental conditions in both flow systems. The data from a pipe and an annular coaxial pipe heat exchanger for fibre suspensions of concentrations 0.2 and 0.4% show that the relationships among heat and momentum transfer and fibre characteristics and specific properties of paper can be obtained with confidence from either type of heat exchanger.

A Two-Phase CFD Modeling Approach to Investigate the Flow Characteristics in Radial Flow Moving-Bed Reactors

Abstract Based on a complete CFD Eulerian–Eulerian two-fluid approach, a comprehensive three-dimensional (3D) two-phase reactor model was suggested to describe the flow behavior in radial flow moving-bed reactors (RFMBRs). A porous media model was incorporated into the reactor model in order to describe the flow resistance provided by the porous walls of the center and annular pipes. Compared with these previous reactor models, the reactor model considers the solid-phase movement instead of immobilization, which benefits for predicting the formation of cavity practically. The simulation results are agreement with the published experimental data. By employing the verified model, the flow field parameters in the reactors such as pressure drop and flow velocity were obtained. Besides, the simulations were then carried out to investigate the effect of the bed voidage on the flow behavior and to understand the phenomenon of cavity in the RFMBRs. The simulation results showed that both the centripetal and the centrifugal flow configurations have the inhomogeneous flow distribution and the phenomenon of cavity. Furthermore, the inhomogeneous distribution increases with the increase of the bed voidage, whereas the phenomenon of cavity is more obvious with the increase of gas inlet velocity. As a whole, this work provided a realistic modeling and a useful approach for the understanding of RFMBRs.

Study of Charging Nitrogen to External Floating Roof Tank to Prevent Rim-seal Fires from Lightning

It is estimated that 95% of rim seal fires are caused by lightning strikes. To avoid rim-seal fires caused by lightning, the existing methods mainly focus on the use of secondary sealing to reduce volatilization of oil and the electrical connections measures such as air terminals, deflectors, grounding device, discharge shunts and scalable grounding device to avoid sparks caused by lightning current. But these devices can’t eliminate the spark generation thoroughly. A new method charging nitrogen to external floating roof tank seal ring is proposed to prevent rim-seal fires from lightning. In this paper, the safe oxygen content is set as the goal to charge nitrogen. An annular nitrogen charging pipe network is designed and its reliability is verified by experiment. The time of filling nitrogen to the seal ring of an external floating roof tank with the capacity of 10×104 m3 at the rate of 63.38 m3/h to reach the nitrogen charging goal is proved within the time of lightning warning through experiment. And this experiment can provide some reference to the application of nitrogen charging.

The influence of the tangential velocity of inner rotating wall on axial velocity profile of flow through vertical annular pipe with rotating inner surface

In the oil and gas industries, understanding the behaviour of a flow through an annulus gap in a vertical position, whose outer wall is stationary whilst the inner wall rotates, is a significantly important issue in drilling wells. The main emphasis is placed on experimental (using an available rig) and computational (employing CFD software) investigations into the effects of the rotation speed of the inner pipe on the axial velocity profiles. The measured axial velocity profiles, in the cases of low axial flow, show that the axial velocity is influenced by the rotation speed of the inner pipe in the region of almost 33% of the annulus near the inner pipe, and influenced inversely in the rest of the annulus. The position of the maximum axial velocity is shifted from the centre to be nearer the inner pipe, by increasing the rotation speed. However, in the case of higher flow, as the rotation speed increases, the axial velocity is reduced and the position of the maximum axial velocity is skewed towards the centre of the annulus. There is a reduction of the swirl velocity corresponding to the rise of the volumetric flow rate.