Augmentation of Heat Transfer in a Circular Channel with Inline and Staggered Baffles

This numerical investigation presents the effects of the position of baffles in the shape of a circle’s segment placed inside a circular channel to improve the thermal and flow performance of a solar air heater. Three different baffles’ positions with Reynolds number varying between 10,000 to 50,000 were investigated computationally. The k-omega SST model was used for solving the governing equations. Air was taken as the working fluid. Three pitch ratios (Y = 3, 4, and 5) were considered, while the height of the baffles remained fixed. The result showed an enhancement in Nusselt number, friction factor, j-factor, and thermal performance factor. Staggered exit-length baffles showed maximum enhancement in heat transfer and pressure drop, while inline inlet-length baffles showed the least enhancement. For a pitch ratio of Y = 3.0, the enhancement in all parameters was the highest, while for Y = 5.0, the enhancement in all parameters was the least. The highest thermal performance factor of 1.6 was found for SEL at Y = 3.0.

Study of hydraulic resistance of tangential swirlers

This article presents the results of experimental research and simulation of the hydraulic drag of tangential swirlers. Three types of swirler devices made with straight, profiled, and circular channel walls were studied within a wide range of design and process parameters. Simulation modelling on the Comsol Multiphysics platform was used to calculate hydraulic drag and determine the velocity and pressure fields. This allowed obtaining a dependence of the hydraulic drag coefficient of the investigated swirlers and identifying parameters affecting their hydraulic drag.

Numerical investigation of simultaneous effects of nanofluid flow and porous baffle on thermal energy transfer and flow features in a circular channel

In the present work, the forced-convection heat transfer features of different nanofluids in a circular channel with porous baffles are numerically investigated. Nanofluid flow in the porous area is simulated by the simultaneous use of Darcy-Brinkman-Forchheimer and two-phase mixture models. The flow is considered to be laminar, two-dimensionall, steady, axially symmetric, and incompressible. The simulations are conducted in Fluent software and by using the finite volume method and SIMPLE algorithm. The influences of various parameters, including Reynolds number, volume fractions of nanoparticles, Darcy number, porous region height, and various nanofluid types on the nanofluid flows and their thermal energy transfer features, are investigated. Results show that porous blocks significantly change the flow characteristics and thermal energy transfer features. For instance, at low Darcy numbers, the permeability of the porous region decreases, and the porous baffles have greater resistance against the nanofluid flow. As a result, the vortex area becomes stronger and taller, and streamlines near obstacles are tighter. However, in high Darcy numbers, due to the high permeability of the porous medium, the flow will be the same as the flow in the channel without barriers, and the porous baffles will not have much influence on the flow. For example, at Darcy number Da = 10-4 the vortex area almost disappears. The growth of conductivity ratio increases the local Nu in the vicinity of the barriers. Properties of the porous medium and nanofluid flow affect the thermal energy transfer rate, and it can be improved by making appropriate changes to these features.

Simulation of Oldroyd-B Viscoelastic Fluid in Axisymmetric Straight Channel by Using a Hybrid Finite Element/Volume Method

In this study, incompressible viscoelastic fluid through the axisymmetric circular channel is simulated with Oldroyd-B model. The simulation is performed based on a hybrid finite volume/element method, which consists of Taylor-Galerkin finite element discretisation, and a cell vertex fluctuation-distribution finite volume method. In this context, the momentum and continuity equations are treated with a finite element method, while a finite volume approach is applied to solve the Oldroyd-B constitutive model. Analytical expressions are presented for the velocity and stress components in fully developed channel flow of Oldroyd-B fluid. For this complex fluid, we see an excellent agreement between the analytic and the numerical solutions. The study of axisymmetric circular channel problem based on a hybrid numerical method represents a great challenge. The novelty here is to study the temporal convergence-rate of the system solution that is taken to be steady state, incompressible, axisymmetric, and laminar, which did not address by researchers previously. Here, the rate of convergence for all solution components is presented, where a large level of convergence is appeared for stress compared to the other solution components. Moreover, the pressure drops and stress response across the flow are provided with respect to difference in solvent-fraction and Weissenberg number . A significant effect from the viscoelastic parameters upon the level of the stress has been detected, while for the pressure response the change is semi-modest. For the stress response the findings reveal that, with decreasing solvent-fraction , the maxima level of stress components are strongly amplifies.

Water wave resonance in a circular oscillating channel

<p>Nonlinear surface waves in the form of tidal bores can have a profound impact on the flow in rivers and estauries. The waves can also be studied experimentally in a specially designed periodic channel at BTU Cottbus-Senftenberg [1],[2]. We hence analyze these surface waves in this narrow circular channel partially filled with water and compare the data with numerical simulations. The flow in the channel is blocked by a barrier and the channel oscillates in azimuthal direction with variable frequency,  maintaining the same maximum velocity. The response in terms of wave shape, maximum amplitude and root mean square of the surface deviations are numerically investigated and compared with experiments. Note that for the experimental setup a number of maximum eight ultrasound sensors can provide the local height evolution. Due to the oscillations, the barrier produces wave trains or hydraulic jumps which then propagate inside the channel. Reflections, damping and collisions take place. Some frequencies are  favourised and in the first approximation can also be calculated using a shallow water model. How will be seen, only the odd multiples of the basic frequency produce high answers (resonances).<br><br>[1] I.D. Borcia, R. Borcia, Wenchao Xu, M. Bestehorn, S. Richter, and U. Harlander. Undular bores in a large circular channel. European Journal of Mechanics - B/Fluids, 79, 67-73, 2020.<br><br>[2] I.D. Borcia, R. Borcia, S. Richter, Wenchao Xu, M. Bestehorn, and U. Harlander. Horizontal Faraday instability in a circular channel. Proceedings in Applied Mathematics and Mechanics (PAMM), 19, , 2019.</p>