Fluid Rotation Research Articles

Optimizing turning logic of glass curtain wall cleaning robot

Abstract. In contemporary urban environments, there has been a notable increase in the construction of high-rise edifices with glass curtain walls. While glass curtain walls contribute to the aesthetic appeal of buildings, they also give rise to a number of challenges. In recent decades, cleaning robots have been developed to address the issue of maintaining glass curtain walls. However, the challenge of efficiently avoiding obstacles and gaps on the glass curtain remains. The research aims to optimize the trajectory of glass curtain wall cleaning robots. A series of simulations were conducted using MATLAB 2024b and the RobotCraft Robotics Playgrounds add-on. The robot is required to traverse a defined maze, which features a 90-degree turn. The time required for each operational logic to traverse the entire route from the initial point to the final destination has been meticulously documented. The results of these simulations are compared in a chart in order to identify a logic that will result in a faster average speed for the robot. The initial experiment yielded results indicating that the turning is excessively sharp and rigid. Accordingly, the distance detection has been increased in the subsequent iteration to facilitate an earlier turning point. Moreover, an increase in the rotational speed of the motor on the corresponding side was implemented to expand the turning radius, thereby facilitating a more seamless and fluid rotation. In essence, the robot has been optimized to achieve a balance between spatial utilization and high average speed. The refinement of the turning path has been shown to enhance the overall cleaning efficiency while maintaining an exceptional ability to avoid obstacles.

Orientation of inertialess spheroidal particles in turbulent channel flow with spanwise rotation

The orientation dynamics of inertialess prolate and oblate spheroidal particles in a directly simulated spanwise-rotating turbulent channel flow has been investigated by means of an Eulerian–Lagrangian point-particle approach. The channel rotation and the particle shape were parameterized using a rotation number Ro and the aspect ratio λ, respectively. Eleven particle shapes 0.05 ≤ λ ≤ 20 and four rotation rates 0 ≤ Ro ≤ 10 have been examined. The spheroidal particles retained their almost isotropic orientation in the core region of the channel, despite the significant mean shear rate set up by the Coriolis force. Irrespective of channel rotation rate Ro, rod-like spheroids tend to align in the streamwise direction, while disk-like particles are oriented in the wall-normal direction. These trends were accentuated with increasing departure from sphericity λ = 1. The changeover from the isotropic orientation mode in the centre to the highly anisotropic near-wall orientation mode commenced further away from the suction-side wall with increasing Ro, whereas the particle orientations on the pressure side of the rotating channel remained essentially unaffected by Ro. We observed that the alignments of the fluid rotation vector with the Lagrangian stretching direction were similarly unaffected by the imposed system rotation, except that the de-alignment set in deeper into the core at high Ro. This contrasts with the well-known substantial impact of system rotation on the velocity and vorticity fields. Similarly, slender rods and flatter disks were aligned with the Lagrangian stretching and compression directions, respectively, for all Ro considered, except in the vicinity of the walls. The typical near-wall de-alignment extended considerably further away from the suction-side wall at high Ro. We conjecture that this phenomenon reflects a change in the relative importance of mean shear and small-scale turbulence caused by the Coriolis force. Preferential particle alignment with Lagrangian stretching and compression directions are known from isotropic and anisotropic turbulence in inertial reference systems. The present results demonstrate the validity of this principle also in a non-inertial system.

Precessing non-axisymmetric ellipsoids: bi-stability and fluid instabilities

This study explores precession-driven flows in a non-axisymmetric ellipsoid spinning around its medium axis. Using an experimental approach, we focus on two aspects of the flow: the base flow of uniform vorticity and the development of fluid instabilities. In contrast to a preceding paper (J. Fluid. Mech., vol. 932, 2022, A24), where the ellipsoid rotated around its shortest axis, we do not observe bi-stability or hysteresis of the base flow, but a continuous transition from small to large differential rotation and tilt of the fluid rotation axis. We then use the model developed by Noir & Cébron (J. Fluid. Mech., vol. 737, 2013, pp. 412–439) to numerically determine regions in the parameter space of axial and equatorial deformations for which bi-stability may exist. Concerning fluid instabilities, we use three independent observations to track the onset of both boundary layer and parametric instabilities. Our results clearly show the presence of a parametric instability, yet the exact nature of the underlying mechanism (conical shear layer instability, shear instability and elliptical instability) is not unambiguously identified. A coexisting boundary layer instability, although unlikely, cannot be ruled out based on our experimental data. To make further progress on this topic, a new generation of experiments at significantly lower Ekman numbers (ratio of rotation and viscous time scales) is clearly needed.

Experimental Analysis of Shale Cuttings Migration in Horizontal Wells

The extraction of shale gas via horizontal drilling presents considerable challenges, primarily due to the accumulation of cuttings within the annular space, resulting in increased friction, torque, and potential drilling complications. To address this issue, the study proposes an experimental setup aimed at simulating cuttings transport under various operational conditions, with a particular emphasis on gas wells. The methodology encompasses the modulation of the drilling fluid flow rate and the drill’s rotational speed to examine the transport velocity of cuttings. Furthermore, the study analyzes the impact of annular eccentricity on return volume, transport time, and cuttings bed height. Critical initiation velocities for cuttings across different motion modes were also determined, and theoretical calculations were compared with empirical data. The findings indicate that an increased flow rate of drilling fluid and higher rotation speed substantially improve the transport of cuttings, thereby minimizing bed formation, whereas increased eccentricity hinders this process. The results revealed that the theoretical model showed a greater overestimation of the start-up velocity for spherical particles, with average errors ranging from 15.50% to 17.56%. In contrast, the model exhibited better accuracy for non-spherical (flaky) particles, with errors between 8.63% and 9.61%. Under non-rotating conditions, the average error of the model was approximately 8.32%, while the introduction of drill tool rotation increased the average error to 11.94%. These results have the potential to optimize operational parameters in shale gas well drilling and may contribute to the development of specialized borehole purification tools.

Investigation of the effect of elbow pipes of Ti6Al4V, 304 stainless steel, AZ91 materials on erosion corrosion by finite element analysis

Corrosion is the degradation of metals caused by chemical or electrochemical reactions with their environment. As a result of these reactions, undesirable conditions occur in the physical, chemical, mechanical and electrical properties of metals. These conditions cause parts made of metallic materials to become unusable. Erosion corrosion is one of the most common types of corrosion in fluid transfer. There are several methods for preventing erosion corrosion. First of all, some precautions should be taken to prevent wear. Intervention is very important in terms of cost, especially at the design stage. Measures such as wide angle bends, wall thickness of wear-resistant material and corrosion allowance can be taken, especially in applications where the flow direction needs to be changed. The aim of this study was to determine the effect of liquid fluid on erosion corrosion in Ti6Al4V, 304 stainless steel and MgAz91 elbow pipes by using the computer aided and finite element based AnsysWorkbench Explicit Dynamics module. For the design of the elbow pipe, SolidWorks was used for 3D studies. In the analysis of the pipe, the suitability of the pipe for the 3D model was examined. The effect of fluid rotation on the pipe walls and the effect of the pipe material on the flow along the pipe were determined. The standard k-e model based on the velocity-pressure relationship in continuous and steady flow was used for the flow calculations. The flow simulation showed that for all models the flow accumulation after rotation was more concentrated on the opposite walls of the pipe, as expected. The results obtained showed that the deformation in MgAZ91 material had the highest value at 9.14 × 10−8 mm. This situation has been interpreted to mean that it may vary depending on the flow rate automation. Designs on the old designs in the erosion structure of the liquid that occurs in the pipes with a new product design in the analysis design.

Analytical Analysis of the Bladeless Rotor Turbine Design for Enhanced Performance

The growing desire for clean and efficient energy solutions has fueled considerable advances in turbine technology. This study proposed a conceptual approach to enhancing the performance of bladeless turbines using an analytical technique, and the analytical solutions bear a resemblance to the experimental setup for a fluid dynamics investigation of a rotor for real-flow effects. The Navier-Stokes equations for fluid flow in cylindrical coordinates were simplified to two-dimensional flow by ignoring axial direction and velocity, and direct integration was used in conjunction with series expansion solutions. The experiment data were used to verify the rotor's fluid dynamics analytical solutions. The model's result was compared to previously calculated solutions of the fluid dynamics of a disc rotor in a bladeless turbine. The disc turbine models were used to predict radial velocity, tangential velocity, pressure gradient, volumetric flow rate, rotor torque, shear stress on the inner and outer disc walls, and rotor efficiency. The model was validated using experimental data with an efficiency of 23.9%, the theoretical solution model was 34%, and the analytical efficiency was 24.3%. The efficiency comparison of the analytical solutions model to the theoretical solutions model revealed a substantial difference, however, the correlation between computed theoretical and analytical results is significant. Previous studies used computed solutions for models, but current analytical solutions outperformed them. The model's output will be valuable to engineers building the disc turbine. It demonstrates a strong link between the analytical and experimental research of the bladeless turbine.

Mixed convection hybrid nanofluid flow over a rotating cone in a rotating fluid environment with interfacial nanolayer effect

This study explores the dynamics of a mixed magneto-hybrid nanofluid (HNF) flowing over a rotating cone within a rotational fluid flow, focusing on the effects of joule heating and thermal radiation. Employing water as a base fluid, enhanced with nanoparticles like molybdenum disulfide (MoS2) and graphene oxide (GO), we examine the critical role of liquid–solid interfacial layers on thermal integrity and boundary conditions. The governing model integrates joule heating, thermal radiation, mixed convection, and magnetic effects to fully represent the complexities of the flow dynamics. A system of partial differential equations (PDEs), simplified under boundary layer assumptions, is transformed into ordinary differential equations (ODEs) through similarity transformations. These ODEs are then solved using the Homotopy Analysis Method (HAM) in Mathematica. Notably, our results demonstrate an improvement in heat transfer rates under combined magnetic and rotational influences, compared to conventional fluids. This enhanced cooling efficiency is critical for applications like aeronautical gas turbines and power production turbines, where higher thermal regulation directly correlates with improved performance, durability, and operational efficiency. Moreover, the study reveals a significant sensitivity of the thermal boundary layer to variations in the Prandtl number, indicating that higher Prandtl numbers lead to a lower temperature profile. This finding is vital for optimizing heat transfer processes, particularly in engineering applications where precise control over thermal properties is required. Furthermore, the study provides detailed insights into the friction factors for azimuthal and tangential directions, alongside local Nusselt numbers, offering substantial agreement with prior research. These findings contribute significantly to the design and optimization of modern cooling systems, emphasizing the potential of HNFs in high-temperature environments.

Interfacial dynamics of two immiscible second-grade and couple stress fluids in rotating and counter-rotating scenarios

This article aims to examine the dynamics of interfacial flow that occurs when a layer of second-grade fluid rotates over another layer of uniformly rotating immiscible couple stress fluid. Fluid models with different densities, pressures, velocities, and viscosities exhibit intriguing flow properties. Under the restriction of parameter σ2ρ=1 , where σ=ω2/ω1 (angular velocities ratio) and ρ=ρ2/ρ1 (densities ratio), the occurrence of similarity solutions under coupling and viscoelastic effects across the interface for both cases of co-and-counter rotation is investigated. In contrast to the rotation of upper fluid, the couple stress fluid layer can counter-rotate. An advanced numerical method known as the Keller box is employed to thoroughly analyze the multiple aspects of the flow. The dominance of the couple stress fluid has been observed in shaping the dynamics of interfacial flow, significantly impacting phenomena such as the generation of inward/outward jets, Ekman pumping/suction, and the development of recirculation regions. Lower-layer far-field flow demonstrates transitions, oscillating between inflow and outflow, depending on parameters μ and σ . These findings illustrate an interesting interplay between rheological parameters, providing perspectives into the complicated behaviors of immiscible rotating fluids under different characteristics and useful implications for a variety of practical applications.

On dark energy effects on the accretion physics around a Kiselev spinning black hole

Kiselev metric in the static and rotating form is widely used to test different aspects of the dark energy (DE) effects. We consider a DE Kiselev spacetime, predicting the reduction to the Kerr black hole (BH) solution under suitable conditions on the DE parameters and in this frame we study the effects of the dark energy on BHs and disks accretion. Elaborating a close comparison with the limiting vacuum Kerr spacetime, we focus on thick accretion disks around the central BH in the Kiselev solution, both co-rotating and counter-rotating with respect the central BH. We examine different aspects of BH accretion energetics by focusing on quantities related to the accretion rates and cusp luminosity, when considered the DE presence, related to the pure Kerr central BH. Our findings show that in these conditions heavy divergences with respect to the vacuum case are expected for the DE metrics. A known effect of the Kiselev metric is to lead to a false estimation the BH spin, we confirm this characteristic from the fluids dynamics analysis. Remarkably our results show that DE is affecting differently the accretion physics, and particularly the accretion rate, according to the fluid rotation orientation with respect to the central spinning attractor, leading in some cases to an under-estimation of the BH spin mass ratio. These contrasting aspects emerging in dependence on the fluids rotational orientation can be a distinguishing general DE feature which could lead to a revised observational paradigm where DE existence is considered.

Heat transfer performance study of fluid rotating microchannel heat sink

The study presents a novel fluid rotating microchannel heat sink (FR-MC) and reports its heat transfer performance. The FR-MC features two cross ribs positioned in the channel. These cross ribs are inclined in the direction of fluid flow, with each rib inclining in opposite directions. This design enables the fluid to ascend or descend along the ribs, creating rotation after passing through the center to alter the flow direction. Experimental validation confirms the accuracy of the model and numerical simulations. The study investigates the heat transfer capability of FR-MC through comparative analysis, and explores the reasons for the improved performance. The results indicate a 45 % reduction in thermal resistance compared to a rectangular microchannel (R-MC). This improvement is attributed to the rotation of fluid promoting the exchange between the upper and lower parts and the mixing of hot and cold portions, effectively disrupting the thermal boundary layer near the wall. Further exploration into the impact of microchannel dimensions on heat transfer performance indicates that the FR-MC outperforms the R-MC across various heights and widths, achieving thermal resistance reductions ranging from 16 % to 50 %, illustrating the superior heat transfer performance of FR-MC.

Supercritical Operation of Bearingless Cross-Flow Fan

This paper presents a decoupled bearingless cross-flow fan (CFF) that operates at a supercritical speed, thereby increasing the maximum achievable rotational speed and fluid dynamic power. In magnetically levitated CFF rotors, the rotational speed and fan performance are limited by the bending resonance frequency. This is primarily defined by the low mechanical bending stiffness of the CFF blades, which are optimised for fluid dynamic performance, and the heavy rotor magnets on both rotor sides, which add significant mass but a minimal contribution to the overall rotor stiffness. This results in detrimental deformations of the CFF blades in the vicinity of the rotor bending resonance frequency; hence, the CFF is speed-limited to subcritical rotational speeds. The novel CFF rotor presented in this study features additional mechanical decoupling elements with low bending stiffness between the fan blades and the rotor magnets. Thus, the unbalance forces primarily deform the soft decoupling elements, which enables them to pass resonances without CFF blade damage and allows rotor operation in the supercritical speed region due to the self-centring effect of the rotor. The effects of the novel rotor design on the rotor dynamic behaviour are investigated by means of a mass-spring-damper model. The influence of different decoupling elements on the magnetic bearing is experimentally tested and evaluated, from which an optimised decoupled CFF rotor is derived. The final prototype enables a stable operation at 7000 rpm in the supercritical speed region. This corresponds to a rotational speed increase of 40%, resulting in a 28% higher, validated fluid flow and a 100% higher static pressure compared to the previously presented bearingless CFF without decoupling elements.

Flow and Heat Transfer of CoFe2O4-Blood Due to a Rotating Stretchable Cylinder under the Influence of a Magnetic Field.

The flow and heat transfer of a steady, viscous biomagnetic fluid containing magnetic particles caused by the swirling and stretching motion of a three-dimensional cylinder has been investigated numerically in this study. Because fluid and particle rotation are different, a magnetic field is applied in both radial and tangential directions to counteract the effects of rotational viscosity in the flow domain. Partial differential equations are used to represent the governing three-dimensional modeled equations. With the aid of customary similarity transformations, this system of partial differential equations is transformed into a set of ordinary differential equations. They are then numerically resolved utilizing a common finite differences technique that includes iterative processing and the manipulation of tridiagonal matrices. Graphs are used to depict the physical effects of imperative parameters on the swirling velocity, temperature distributions, skin friction coefficient, and the rate of heat transfer. For higher values of the ferromagnetic interaction parameter, it is discovered that the axial velocity increases, whereas temperature and tangential velocity drop. With rising levels of the ferromagnetic interaction parameter, the size of the axial skin friction coefficient and the rate of heat transfer are both accelerated. In some limited circumstances, a comparison with previously published work is also handled and found to be acceptably accurate.

Circulation of hydraulically ponded turbidity currents and the filling of continental slope minibasins

Natural depressions on continental margins termed minibasins trap turbidity currents, a class of sediment-laden seafloor density driven flow. These currents are the primary downslope vectors for clastic sediment, particulate organic carbon, and microplastics. Here, we establish a method that facilitates long-distance self-suspension of dilute sediment-laden flows, enabling study of turbidity currents with appropriately scaled natural topography. We show that flow dynamics in three-dimensional minibasins are dominated by circulation cell structures. While fluid rotation is mainly along a horizontal plane, inwards spiraling flow results in strong upwelling jets that reduce the ability of minibasins to trap particulate organic carbon, microplastics, and fine-grained clastic sediment. Circulation cells are the prime mechanism for distributing particulates in minibasins and set the geometry of deposits, which are often intricate and below the resolution of geophysical surveys. Fluid and sediment are delivered to circulation cells by turbidity currents that runup the distal wall of minibasins. The magnitude of runup increases with the discharge rate of currents entering minibasins, which influences the amount of sediment that is either trapped in minibasins or spills to downslope environs and determines the height that deposits onlap against minibasin walls.

Finite element modeling of the rotational dynamics of a single magnetic particle in a strong magnetic field and liquid medium

We have performed a comparative computational study of magnetic particle alignment in a strong magnetic field and ambient viscous fluid using the first-principles Navier–Stokes equation as well as numerical modeling using the finite element method (FEM). FEM solution has been compared with the solution of the unsteady rotations of a magnetic particle in a viscous fluid during the alignment process described with nonlocal integro-differential equations (IDEs) for torque and angular velocity. The assumption of nonlocality comes from the history term of acceleration torque with a non-Basset kernel function, which has its origin in the presence of vortices in the flow of a particle fluid environment due to its unsteady rotation and ambient fluid inertia and friction. The flow vortices of the ambient fluid are explicitly shown in the solution of the FEM model. Moreover, the solution of the time evolution of the alignment angle and angular velocity for the FEM model are in good agreement with an IDE model which we have recently developed. The obtained results are justification for interchangeability of the FEM and IDE models, which may have important consequences for large-scale simulations of magnetic microparticles.

Research progress of thermoregulating textiles based on spinning of organic phase change fiber of energy storage

Thermal energy storage can contribute to the reduction of carbon emissions, motivating the applications in aerospace, construction, textiles and so on. Phase change materials have been investigated extensively in the field of high-performance intelligent thermoregulating fabrics for energy storage. Advances toward fibers or fabrics for thermo regulation are developed, but leakage of phase change medium is a concern when directly coated or filled with fibers or fabrics. Thus, different spinning methods have appeared to integrate phase change materials into copolymer fiber to prepare phase change fiber. The present review has been divided into three parts and first deals with spinning technologies such as wet spinning, melt spinning, electrostatic spinning, and centrifugal spinning with the thermal properties and mechanical properties of phase change fiber. Among them, the phase change medium loading in the phase change fiber with wet spinning is up to 70 wt.%, while the fiber strength is below 2.12 cN/dtex. In contrast, phase change fiber prepared by melt spinning achieves a breaking strength of up to 37.31 cN/dtex, but with an enthalpy of only 8.48 kJ/kg. Considering electrostatic spinning, not only enthalpies are satisfactory but the fiber diameters are mostly below 1000 nm, matching with the softness requirement for fabric. Moreover, centrifugal spinning enables efficient production of phase change fiber of large enthalpy by controlling spinning parameters such as rotational speed and spinning fluid concentration. The second part reports that the thermal management effects of different intelligent thermo regulating fabrics are evaluated by designed experiments or simulations to investigate further the more comfortable conditions of thermal comfort of humans. Simulation and experimental results show that the energy storage of smart fabrics extends the time duration of thermal comfort by more than 300 s. In the last part, multifunctional intelligent thermoregulating fabrics are systematically discussed, such as light and heat response, ultraviolet resistance, air permeability, and water resistance. Practical applications of phase change fibers and intelligent thermoregulating fabrics should be further studied and broadened in the future.

Rotational Stagnation Point Non-Newtonian Second-Grade Fluid Flowing over Spiraling Disk

Rotational Stagnation Point Non-Newtonian Second-Grade Fluid Flowing over Spiraling Disk

Describing geophysical turbulence with a Schrödinger–Coriolis equation in velocity space

In this paper, we examine the predictions of the scale-relativity approach for a turbulent fluid in rotation. We first show that the time derivative of the governing Navier–Stokes equation in the usual x-space can be transformed into a Schrödinger-like equation in velocity space with an external vectorial field to account for the rotation, together with a local velocity harmonic oscillator (VHO) potential in the v-space. The coefficients of this VHO are given by the second order x-derivatives of the pressure. We can then give formulas for the velocity and acceleration probability distribution functions (PDF). Using a simple model of anisotropic harmonic oscillator, we compare our predictions with relevant data from both direct numerical simulations (DNS) and oceanic drifter velocity measurements. We find a good agreement of the predicted acceleration PDF with that observed from drifters and some possible support in DNS for the existence of gaps in the local velocity PDF, expected in the presence of a Coriolis force.

Action mechanism of axial flow on windage loss in open shaft‐type gap with CO2

AbstractThe windage loss in rotor‐stator gap has an important effect on rotating machinery, especially with higher rotational speed and fluid density. However, the mechanism of axial flow on windage loss in open shaft‐type gap is hardly studied in most literature. To clarify it, the influences of axial Reynolds number Reu and rotational Reynolds number Reω on skin friction coefficient Cf are investigated, and flow characteristics are analyzed with different gap geometry, radius ratio η. First, the results reveal that the Cf remains constant when Reu is less than 2.8 × 104 and increases rapidly as Reu when Reu ≥ 2.8 × 104, which indicates that the effect of axial velocity u on Cf is negligible for low Reu. The positive relative deviation Δ suggests that the axial flow makes windage loss and Cf rise. Besides, a larger number of Taylor vortexes fill with gap when the effect of the centrifugal force is larger than that of the inertial force, but they gradually disappear as Reu. Subsequently, the Cf and Δ increase as η, highlighting that the effect of u on windage loss and Cf is more prominent for larger η. The fact that vorticity near walls is larger than that at the center of gap reveals that windage loss arises from the interaction between walls and fluid rather than the dissipation with fluid itself. Finally, the model of Cf in shaft‐type gap is proposed in different Reω ranges based on numerical results, and the maximum sum of squares error of 1.02 × 10−5 and minimal R2 of 0.969 satisfy the requirement of fitting accuracy and indicate that the fitting model can accurately predict Cf. The conclusions significantly help predict windage loss in open shaft‐type gap with axial flow, and further improve the design for generators of supercritical CO2 turbine‐alternator‐compressor unit.

Experimental and simulated studies on the distribution law of rotational–perforated fluid in tridimensional rotational flow sieve tray

The distribution law of the rotational and perforated fluid in tridimensional rotational flow sieve trays (TRST) is the key point for revealing its working mechanism and engineering application. Due to complex issues such as overlapping blades, rotational fluid accumulation, and centrifugal force within TRST, it is very difficult to accurately calculate the flow ratio. In this paper, the flowable interior mesh faces were constructed at all sieve holes on a blade, and the velocity distribution on the interior faces was simulated as the fluid perforated through the different sieves, thus calculating the volume flow rate and ratio of the flow through perforations. And the three-blade unit experiment was designed to calculate the perforated ratio of the entire blade. Compared with the simulated values, the relative differences of the gas and liquid phases were within 25% and 10%, respectively, which were in good agreement.

Unsteady micropolar nanofluid flow past a variable riga stretchable surface with variable thermal conductivity

In this study, we considered the flow of a micropolar fluid over a vertical Riga sheet. The non linear stretching sheet is considered. The effects of variable thermal conductivity and radiation on the Riga sheet are taken into account. Additionally, we also debated the Brownian motion and thermophoretic. To simplify the partial differential equations, we converted them into dimensionless ordinary differential equations using suitable similarity variables and solved dimensionless system numerically using the bvp4c function. The impact of some intended parameters on the dimensionless velocity, microrotation, temperature, and concentration distributions graphically are presented and the numerical outcomes of physical quantities like skin friction, Nusselt number, Sherwood number, and couple stress have been presented in tabular form. The micropolar parameter increased which increased the couple stress and friction at surface. Because, the fluid rotation increased which increased friction at surface and also increased the couple stress. The transfer of mass decayed and transfer of heat heightened by larger values of variable thermal conductivity. Thermal conductivity improved which improved the heat transfer phenomena, so transfer of heat at surface becomes larger while also reducing the transfer of mass.