Linear Temperature Gradient Research Articles

A computational study of multiple surface-directed phase separation in polymer blends under a temperature gradient

The surface-directed phase separation (SDPS) phenomena of a model binary polymer blend quenched into the unstable region of its binary symmetric upper critical solution temperature phase diagram is numerically investigated using a mathematical model composed of the nonlinear Cahn–Hilliard (CH) theory for phase separation along with the Flory–Huggins–de Gennes (FHdG) free energy functional. The SDPS occurs in a square domain with a linear temperature gradient along the horizontal direction and with all sides having short range surface potential h1. The effects of different quench depth, diffusion coefficient, surface potential, and temperature gradient were studied numerically. The numerical results indicate that there is a simultaneous competition between the four surfaces in attracting the preferred polymer. The side with a higher surface potential would win the competition against the side with a lower surface attraction in the case of a uniform quench. The numerical results also indicated a later transition time for higher values of h1. As surface potential increased, the transition time from complete wetting to partial wetting occurred at a later time on the surface. The impact of different temperature gradient ΔT*/Δx* values on the surface enrichment rate with fixed temperature at one surface and higher temperature at the opposite surface was studied for the first time within a multiple surface potential set up. The results showed that higher values of ΔT*/Δx* increased the growth rate of the preferred polymer on the surface adding to the thickness of the wetting layer. The transition time from complete wetting to partial wetting occurred slightly later at the lower temperature side.

Out-of-Plane Buckling of Beams Having In-Plane Elastic Restraints under Gradient Thermal Action

AbstractWhen a beam is subjected to an in-plane linear temperature gradient field, the thermal effects of the temperature gradient field tend to change the curvature of the beam in the transverse direction and to expand the beam in the axial direction. The rotation and expansion of the ends of the beam may be restrained elastically by its supports or by adjacent members such as columns. The restrained thermal actions will produce bending moments and compressive forces in the beam, and when these actions reach critical values the elastically restrained beam may bifurcate from its primary in-plane equilibrium configuration to an out-of-plane buckled equilibrium configuration. This paper investigates the thermoelastic out-of-plane buckling of an elastically restrained beam with a doubly symmetric cross section that is subjected to an in-plane linear temperature gradient field. The analytical solution for the critical temperature gradient for thermoelastic out-of-plane buckling of the beam is derived. It is f...

A computational study of short-range surface-directed phase separation in polymer blends under a linear temperature gradient

The nonlinear Cahn–Hilliard theory and the Flory-Huggins-de-Gennes theory were used to study numerically the surface-directed phase separation phenomena of a model binary polymer blend quenched into the unstable region of its binary symmetric upper critical solution temperature phase diagram. Short-range surface potential within a square geometry, where one side of the binary polymer blend is exposed to a surface with preferential attraction to one component of the blend that is under a linear temperature gradient along the direction perpendicular to the surface, was integrated into the model. The structure factor analysis showed a faster exponential growth at the early stage of phase separation and a slower growth rate at the intermediate stage with a slope of 0.31 within the bulk, which is consistent with the Lifshitz–Slyozov growth law. The investigation of surface enrichment rate at the surface wall demonstrated faster growth rate at the early stage with the slope of 0.5. This growth rate became slower at the intermediate stage with a slope of 0.13 near the surface. The effect of various temperature gradient values on the surface enrichment rate with constant temperature T1* at the surface preferentially attracting one of the polymer components and different temperature T2* at the opposite surface, where T1*>T2*, was studied for the first time. The results showed that the thickness of the wetting layer increased with increasing temperature difference ΔT*, where ΔT*=T1*−T2*. The structure factor analysis of the surface potential h1 effect on the phase separation within the bulk close to the surface showed earlier transition time for higher values of h1. However, there was no difference observed for transition time within the bulk at distances farther away from the surface. As the surface potential increased, spinodal wave became more visible in the bulk and the transition time from complete wetting to partial wetting occurred at a later time on the surface.

Translational thermophoresis and rotational movement of peanut-like colloids under temperature gradient

Thermophoresis can be used for particle manipulation and separation in microfluidics. This work reports an experimental investigation on thermophoresis and the associated rotational patterns of dilute peanut-like colloids in DI water and SDS surfactant solutions. A microfluidic device is utilized for generating a linear temperature gradient and for directly visualizing the thermophoretic motion and rotation of peanut-like particles. Thermophilic behavior was observed for the peanut-like particles, and their thermophoretic mobilities were found smaller than those of the spherical particles of similar sizes. The peanut-like particles’ rotation characterized by the rotational diffusion coefficient is found to be free diffusive dominated. A very small orientation order toward a preferred direction is distinguished along with the random Brownian rotation.

Characteristic transport lengths (CTLs) in porous medium evaluated with classic diffusion solutions under infinite Biot number condition

In process engineering practice, including those in food industry, simple mathematical solutions are more useful. Learned assumptions are necessary to support effective simplifications. Previously it has been suggested that for a conduction and convection coupled system, there is an approximately linear temperature or concentration gradient between the surface and the average temperature, which occurs at a ‘fixed location’ within the conduction domain. The local temperature at the point is also said to be similar as the average temperature. This gradient is thus approximately the same as the temperature gradient at the interface between the conduction domain and the convection medium when thermal properties are considered constants. The distance from the surface to this ‘fixed location’ is marked as the characteristic transport length (CTL), which is a fraction of the size of the conduction medium. The previous findings were based on the agreements between the numerical solutions and compartmental, and then integral solutions in different occasions The argument has been validated among moderate Biot numbers (Bi) of <10 and moderate Fourier numbers (Fo) of >0.3. Similarly, one should find that the diffusional mass transfer process has the same property due to the same mathematical nature involved. Here, the mass diffusion process has been analyzed to yield the CTLs for the cases of infinite Biot number, where the analytical solutions for longer times for semi-infinite slab, infinite cylinder and sphere are available which can be put to great use. When applying these classical solutions for the above purpose, there are still new discoveries, which are interesting to report here.

Using a local gyrokinetic code to study global ion temperature gradient modes in tokamaks

In this paper the global eigenmode structures of linear ion temperature gradient (ITG) modes in tokamak plasmas are obtained using a novel technique which combines results from the local gyrokinetic code GS2 with analytical theory to reconstruct global properties. Local gyrokinetic calculations are performed for a range of radial flux surfaces, x, and ballooning phase angles, p, to map out the local complex mode frequency, Ω0(x, p) = ω0(x, p) + iγ0(x, p) for a single toroidal mode number, n. Taylor expanding Ω0 about a reference surface at x = 0, and employing the Fourier-ballooning representation leads to a second order ODE for the amplitude envelope, A(p), which describes how the local results are combined to form the global mode. The equilibrium profiles impact on the variation of Ω0(x, p) and hence influence the global mode structure. The simulations presented here are based upon a global extension to the CYCLONE base case and employ the circular Miller equilibrium model. In an equilibrium with radially varying profiles of a/LT and a/Ln, peaked at x = 0, and with all other equilibrium profiles held constant, including ηi = Ln/LT, Ω0(x, p) is found to have a stationary point. The reconstructed global mode sits at the outboard mid-plane of the tokamak, with global growth rate, γ ∼ Max[γ0]. Including the radial variation of other equilibrium profiles like safety factor and magnetic shear, leads to a mode that peaks away from the outboard mid-plane, with a reduced global growth rate. Finally, the influence of toroidal flow shear has also been investigated through the introduction of a Doppler shift, , where Ωϕ is the equilibrium toroidal flow, and a prime denotes the radial derivative. The equilibrium profile variations introduce an asymmetry into the global growth rate spectrum with respect to the sign of , such that the maximum growth rate is achieved with non-zero shearing, consistent with recent global gyrokinetic calculations.

‘Weighing’ a gas with microwave and acoustic resonances

With calibrations of large flow meters in mind, we established the feasibility of determining the mass M of argon gas contained within a 0.3 m3 commercially manufactured pressure vessel (‘tank’) with a relative standard uncertainty of ur(M) = 0.0016 at 0.6 MPa by combining the measured argon pressure and the measured microwave and acoustic resonance frequencies within the pressure vessel with an accurate equation of state for argon. (All stated uncertainties correspond to the 68% confidence level.) Previously, we used microwaves to determine the tank’s internal volume Vmicro with ur(V) = 0.0006 and to determine the thermal expansion of the volume (Moldover et al 2015 Meas. Sci. Tech. 26 015304). Here, we show that the microwave results accurately predict the wavenumbers kcalc of the four lowest-frequency acoustic modes of the gas. When we compared kcalc to the measured wavenumbers kmeas, which included corrections for known perturbations, such as the tank’s calculated pressure-dependent center-of-mass motion (but not the tank’s vibrational modes), the inconsistency of the ratio kmeas/kcalc among the modes was the largest component of ur(M). Because the resonance frequencies f calc of the acoustic modes depend on the average speed of sound (and therefore the average temperature) of the gas in the tank, first-order perturbation theory predicts that f calc for a rigid cylindrical cavity is independent of linear temperature gradients. Consistent with this prediction, the average of f meas for the 3 lowest-frequency, non-degenerate longitudinal modes changed only Δfmeas / f meas = (0.2 ± 1.3) × 10−4 when, near ambient temperature, we heated the tank’s top 13 K warmer than its bottom. However, we observed a linear dependence on ΔT for the average of f meas for the nearly-degenerate doublet modes, which the rigid cylinder theory does not predict. We argue that the linear dependence on ΔT was caused by anisotropic changes in the tank’s shape in response to the applied temperature gradient. We conclude that resonance frequencies can be used to ‘weigh’ the compressed gas in much larger tanks, which are possibly made from ferromagnetic steel and possibly at high pressures in un-thermostatted environments; therefore, resonance measurements will have many applications in gas metrology.

Solid–liquid interfacial energy of solid succinonitrile in equilibrium with succinonitrile-1,4-diiodobenzene eutectic liquid

The grain boundary groove shapes for equilibrated solid SCN in equilibrium with the SCN-0.5 mol% DIB eutectic liquid have been directly observed by using a horizontal linear temperature gradient apparatus. The ratio of thermal conductivity of equilibrated liquid to thermal conductivity of solid SCN has also been determined to be 0.90. From the observed grain boundary groove shapes and measured thermal conductivity ratio, the Gibbs–Thomson coefficient (Г) of solid SCN has been determined to be (5.46 ± 0.55) × 10−8 K m. The solid–liquid interfacial energy (σ SL) and the grain boundary energy of solid SCN have also been determined to be (8.25 ± 1.24) × 10−3 J m−2 and (15.84 ± 2.53) × 10−3 J m−2, respectively.

Acoustic timescale characterisation of symmetric and asymmetric multidimensional hot spots

In this work, two-dimensional hot spots are modelled by combining a linear temperature gradient with a constant temperature plateau. This approach retains the simplicity of a linear temperature gradient, but captures the effects of a local temperature maximum of finite size. Symmetric and asymmetric plateau regions are modelled using both rectangular and elliptical geometries. A one-step Arrhenius reaction for H2–air is used to model the reactive mixture. Plateaus with different ratios of excitation to acoustic timescales, spanning two orders of magnitude, are simulated. Even with clear differences in behaviour between one and two dimensions, the a priori prescribed hot spot timescale ratio is shown to characterise the 2-D gasdynamic response. The relationship between one and two dimensions is explored using asymmetric plateau regions. It is shown that 1-D behaviour is recovered over a finite time. Furthermore, the duration of this 1-D behaviour is directly related to the asymmetry of the plateau.

Frost flowers on young Arctic sea ice: The climatic, chemical, and microbial significance of an emerging ice type

Ongoing changes in Arctic sea ice are increasing the spatial and temporal range of young sea ice types over which frost flowers can occur, yet the significance of frost flowers to ocean-sea ice-atmosphere exchange processes remains poorly understood. Frost flowers form when moisture from seawater becomes available to a cold atmosphere and surface winds are low, allowing for supersaturation of the near-surface boundary layer. Ice grown in a pond cut in young ice at the mouth of Young Sound, NE Greenland, in March 2012, showed that expanding frost flower clusters began forming as soon as the ice formed. The new ice and frost flowers dramatically changed the radiative and thermal environment. The frost flowers were about 5°C colder than the brine surface, with an approximately linear temperature gradient from their base to their upper tips. Salinity and δ18O values indicated that frost flowers primarily originated from the surface brine skim. Ikaite crystals were observed to form within an hour in both frost flowers and the thin pond ice. Average ikaite concentrations were 1013 µmol kg−1 in frost flowers and 1061 µmol kg−1 in the surface slush layer. Chamber flux measurements confirmed an efflux of CO2 at the brine-wetted sea ice surface, in line with expectations from the brine chemistry. Bacteria concentrations generally increased with salinity in frost flowers and the surface slush layer. Bacterial densities and taxa indicated that a selective process occurred at the ice surface and confirmed the general pattern of primary oceanic origin versus negligible atmospheric deposition.

Acoustic timescale characterisation of a one-dimensional model hot spot

Hot spots have been shown to be the autoignition centre in reactive mixtures. Linear temperature gradients and thermal stratification are used to characterise their behaviour. In this work, a model hot spot is considered by combining a linear temperature gradient with a constant temperature plateau. This approach retains the simplicity of a linear temperature gradient, but captures the effects of a local temperature maximum of finite size. A one-step Arrhenius reaction for H2–air is used to model the reactive mixture. Plateaus of three different initial sizes spanning two orders of magnitude are simulated. Each length corresponds to a different ratio of excitation time to acoustic time. It is shown that ratios less than unity react at nearly isochoric conditions while ratios greater than unity react at nearly isobaric conditions. Furthermore, it is demonstrated that the gasdynamic response is characterised by the a priori prescribed hot spot acoustic timescale ratio. Based upon the prescribed timescale ratio, it is shown that the plateau can have either a substantial or negligible impact on the reaction of a surrounding temperature gradient. This is explored further as the slope of the temperature gradient is varied. Based upon the heating-to-acoustic timescale ratio, plateaus of a particular size are shown to facilitate detonation formation inside gradients that would otherwise not detonate.

Plane-parallel advective flow in a horizontal incompressible fluid layer with rigid boundaries

The exact solution of the Navier-Stokes equations that describes the plane-parallel advective flow in a plane incompressible fluid layer with rigid boundaries at which either the linear distribution of temperature of different signs or the linear horizontal temperature gradient is given is presented.

Finite ballooning angle effects on ion temperature gradient driven mode in gyrokinetic flux tube simulations

This paper presents effects of finite ballooning angles on linear ion temperature gradient (ITG) driven mode and associated heat and momentum flux in Gyrokinetic flux tube simulation GENE. It is found that zero ballooning angle is not always the one at which the linear growth rate is maximum. The ITG mode acquires a short wavelength (SW) branch (k⊥ρi &amp;gt; 1) when growth rates maximized over all ballooning angles are considered. However, the SW branch disappears on reducing temperature gradient showing characteristics of zero ballooning angle SWITG in case of extremely high temperature gradient. Associated heat flux is even with respect to ballooning angle and maximizes at nonzero ballooning angle while the parallel momentum flux is odd with respect to the ballooning angle.

Mechanistic Analysis of Rigid Pavement for Temperature Stresses Using Ansys

Finite-element analysis is not new to the pavement design and research community. Two- dimensional finite-element programs have been in use for the past two decades to analyze rigid pavement response. In recent years three dimensional finite-element (3DFE) analyses emerged as a powerful tool capable of capturing pavement response. The study of the effect of temperature variation on concrete pavement using ANSYS software was presented. ANSYS is finite element method based software. Analysis for temperature stresses has been done using both linear and non-linear temperature gradient between top and bottom of pavement slab. The results obtained using the linear temperature gradient has shown reasonable agreement with the results obtained from the three other mechanistic models: given by software KENSLABS, ILLI-SLAB and JSLAB. The result also matches with the analytical solution proposed by Bradbury. The model was used to perform parametric studies involving effect of slab length and thickness on curling stresses. High curling stresses were not only observed for long slab but also for the short slab that has a thickness of 30cm. Frictional stress value obtained by ANSYS showed reasonable agreement with the stress value given by the software package ABAQUS, and but its value was less than that given by Westergaard's solution. The temperature stresses obtained for non-linear temperature gradient were compared with the linear temperature distribution. Non-linear temperature distribution cause higher stresses as compared with the linear temperature distribution.

Experimentally-aided Simulation of Directional Solidification of Steel

Dendritic microstructures are most dominant patterns in solidified alloys. The microstructural features of these structures control the segregation profiles of solute elements in the interdendritic regions, thus determining the mechanical properties of cast structures. In this study, a 2D model of solid/liquid interface instability in a low carbon steel was introduced, using the multi-phase-field software code MICRESS® combined with an in-situ study of solidification in a laser-scanning confocal microscope. The use of a moving-frame boundary condition and a linear temperature gradient within the simulation allows further optimization of the solidification studies in the laser-scanning confocal microscope. By analysing the shape of the delta-ferrite grain boundary at the solid/liquid interface, in-situ and at temperature, it was possible to experimentally determine the Gibbs-Thomson coefficient and the solid/liquid interfacial energy of the alloy. The interface mobility of the solid/liquid interface was calibrated in the model so as to reproduce the experimentally measured interface velocity at the onset of interface instability. The proposed model was used to describe the morphological transitions from planar to cellular to dendritic modes during solidification and solute segregation under a variety of processing conditions such as cooling rate and temperature gradient. The importance of this approach is that the verified model has been used to extend the prediction of microstructural development to cooling rates well beyond what can be achieved experimentally and into the regime pertinent to high-speed continuous casting. Significant microstructural differences that arise as a result of varying processing conditions are discussed.

Measurement of Soret and Fickian diffusion coefficients by orthogonal phase-shifting interferometry and its application to protein aqueous solutions

We have developed a method to measure thermodiffusion and Fickian diffusion in transparent binary solutions. The measuring instrument consists of two orthogonally aligned phase-shifting interferometers coupled with a single rotating polarizer. This high-resolution interferometer, initially developed to measure isothermal diffusion coefficients in liquid systems [J. F. Torres, A. Komiya, E. Shoji, J. Okajima, and S. Maruyama, Opt. Lasers Eng. 50, 1287 (2012)], was modified to measure transient concentration profiles in binary solutions subject to a linear temperature gradient. A convectionless thermodiffusion field was created in a binary solution sample that is placed inside a Soret cell. This cell consists of a parallelepiped cavity with a horizontal cross-section area of 10 × 20 mm(2), a variable height of 1-2 mm, and transparent lateral walls. The small height of the cell reduces the volume of the sample, shortens the measurement time, and increases the hydrodynamic stability of the system. An additional free diffusion experiment with the same optical apparatus provides the so-called contrast factors that relate the unwrapped phase and concentration gradients, i.e., the measurement technique is independent and robust. The Soret coefficient is determined from the concentration and temperature differences between the upper and lower boundaries measured by the interferometer and thermocouples, respectively. The Fickian diffusion coefficient is obtained by fitting a numerical solution to the experimental concentration profile. The method is validated through the measurement of thermodiffusion in the well-known liquid pairs of ethanol-water (ethanol 39.12 wt.%) and isobutylbenzene-dodecane (50.0 wt.%). The obtained coefficients agree with the literature values within 5.0%. Finally, the developed technique is applied to visualize biomolecular thermophoresis. Two protein aqueous solutions at 3 mg∕ml were used as samples: aprotinin (6.5 kDa)-water and lysozyme (14.3 kDa)-water. It was found that the former protein molecules are thermophilic and the latter thermophobic. In contrast to previously reported methods, this technique is suitable for both short time and negative Soret coefficient measurements.

Solid–liquid interfacial energy of solid succinonitrile solution in equilibrium with succinonitrile–neopentylglycol eutectic liquid

The grain boundary groove shapes for solid succinonitrile solution (SCN–5mole% NPG) in equilibrium with the succinonitrile (SCN)–neopentylglycol (NPG) eutectic liquid (SCN–9.55mole% NPG) have been directly observed by using a horizontal linear temperature gradient apparatus at 317.1K equilibrium temperature. From the observed grain boundary groove shapes, the Gibbs–Thomson coefficient (Г) and solid-liquid interfacial energy (σSL) of solid SCN solution have been determined to be (5.43±0.50)×10−8Km and (8.09±1.21)×10−3Jm−2, respectively. The grain boundary energy of solid SCN solution has been determined to be (14.22±2.28)×10−3Jm−2 from the observed grain boundary groove shapes. The thermal conductivity for SCN–9.55mole% NPG eutectic solid phase and the thermal conductivity ratio of eutectic liquid phase to eutectic solid phase at the melting temperature have also been measured with a radial heat flow apparatus and Bridgman type growth apparatus, respectively.

Analytical Model To Predict the Effect of Pipe Friction on Downhole Fluid Temperatures

Summary The advent of deviated, horizontal, and extended-reach drilling has led to increased frictional forces acting between the drillstring and the wellbore wall. Wellbore mechanical friction attributable to pipe rotation or to torque and drag plays a significant role in drilling operations and is considered to influence the downhole temperatures of the drilling fluid. An analytical model to estimate the influence of this pipe friction will help in providing a better physical insight to understand the downhole borehole conditions as well as in realizing the effect of its underlying parameters. This study aims to develop a simple mathematical model to analyze the heat generated downhole from the drillstring and borehole contact and then predict its influence on the temperature of the drilling fluid during a drilling operation at any depth in the well. The model presents a steady-state solution for heat transfer between the drillstring and the fluids in the drillpipe and annulus, as well as for heat transfer between the annular fluid and the formation. The heat generated from friction has been modeled by use of the torque acting on the drillstring as a result of contact forces. A linear temperature gradient for the formation and a constant borehole-wall temperature has been assumed to simplify the model. Frictional pressure losses in the drillpipe, in the annulus, and across the bit have been incorporated in the model because they contribute to the heat generated downhole. The temperature profile of the drilling fluid has been estimated both in the annulus and inside the drillpipe for the entire well profile under consideration. This paper will present the derivations of the generalized heat-transfer model and its validation by use of two practical drilling scenarios. Two different field cases, one for a deviated well and the other for a horizontal well, have been presented, and the estimated temperature profile by use of the model is compared with the actual temperature measured downhole by use of measurement-while-drilling (MWD) tools. The increase in temperature for a particular depth in the well for the entire bit run has also been presented as another successful application of this model. The impact of drilling parameters on temperatures has also been analyzed and can be used effectively to maintain a better check on undesired temperatures. This simple analytical model can be suitably applied to field cases on the basis of the well profile and can be effectively used to predict the maximal temperatures to be encountered downhole while drilling ahead as planned. An accurate estimation of maximal temperatures will help us prevent severe downhole friction heating in the future.

Global gyrokinetic simulations of TEM microturbulence

Global gyrokinetic simulations of electrostatic temperature-gradient-driven trapped-electron-mode (TEM) turbulence using the δf particle-in-cell code ORB5 are presented. The electron response is either fully kinetic or hybrid, i.e. considering kinetic trapped and adiabatic passing electrons. A linear benchmark in the TEM regime against the Eulerian-based code GENE is presented. Two different methods for controlling the numerical noise, based, respectively, on a Krook operator and a so-called coarse-graining approach, are discussed and successfully compared. Both linear and non-linear studies are carried out for addressing the issue of finite-ρ*-effects and finite electron collisionality on TEM turbulence. Electron collisions are found to damp TEMs through the detrapping process, while finite-ρ*-effects turn out to be important in the non-linear regime but very small in the linear regime. Finally, the effects of zonal flows on TEM turbulence are briefly considered as well and shown to be unimportant in the temperature-gradient-driven TEM regime. Consistently, basically no difference is found between linear and non-linear critical electron temperature gradients in the TEM regime.

Global gyrokinetic ion temperature gradient turbulence simulations of ITER

Global gyrokinetic simulations of ion temperature gradient (ITG) driven turbulence in an ideal MHD ITER equilibrium plasma are performed with the ORB5 code. The noise control and field-aligned Fourier filtering procedures implemented in ORB5 are essential in obtaining numerically healthy results with a reasonable amount of computational effort: typical simulations require 109 grid points, 109 particles and, despite a particle per cell ratio of unity, achieve a signal to noise ratio larger than 50. As compared with a circular concentric configuration with otherwise similar parameters (same ρ* = 1/720), the effective heat diffusivity is considerably reduced for the ITER MHD equilibrium. A self-organized radial structure appears, with long-lived zonal flows (ZF), modulating turbulence heat transport and resulting in a corrugated temperature gradient profile. The ratio of long-lived ZF to the fluctuating ZF is markedly higher for the ITER MHD equilibrium as compared with circular configurations, thereby producing a more effective ITG turbulence suppression, in spite of a higher linear growth rate. As a result, the nonlinear critical temperature gradient, R/LTcrit,NL, is about twice the linear critical temperature gradient, R/LTcrit,lin. Moreover, the heat transport stiffness above the nonlinear threshold is considerably reduced as compared with circular cases. Plasma elongation is probably one of the essential causes of this behaviour: indeed, undamped ZF residual levels and geodesic acoustic mode damping are both increasing with elongation. Other possible causes of the difference, such as magnetic shear profile effects, are also investigated.