Onset of electroconvection of homeotropically aligned nematic liquid crystals

Zhou, Sheng‐Qi; Éber, Nándor; Buka, Ágnes; Pesch, Werner; Ahlers, Guenter

doi:10.1103/physreve.74.046211

Cited by 13 publications

(5 citation statements)

References 39 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In order to identify them we adopt the plumes identification procedure used in Refs. [22,44], which is based on a threshold analysis on the intensity variance of the shadowgraph images, and we then calculate the area fraction of the plumes, A p appearing in one of the corner of the experiment (inside the red square frame shown in Fig. 2g).…”

Section: Flow Patternsmentioning

confidence: 99%

Robustness of heat transfer in confined inclined convection at high Prandtl number

2019

View full text Add to dashboard Cite

We investigate the dependency of the magnitude of heat transfer in a convection cell as a function of its inclination by means of experiments and simulations. The study is performed with a working fluid of large Prandtl number, Pr ≃ 480, and at Rayleigh numbers Ra ≃ 10 8 and Ra ≃ 5 × 10 8 in a quasi-two-dimensional rectangular cell with unit aspect ratio. By changing the inclination angle (β) of the convection cell, the character of the flow can be changed from moderately turbulent, for β = 0 o , to laminar and steady at β = 90 o . The global heat transfer is found to be insensitive to the drastic reduction of turbulent intensity, with maximal relative variations of the order of 20% at Ra ≃ 10 8 and 10% at Ra ≃ 5 × 10 8 , while the Reynolds number, based on the global root-meansquare velocity, is strongly affected with a decay of more than 85% occurring in the laminar regime. We show that the intensity of the heat flux in the turbulent regime can be only weakly enhanced by establishing a large scale circulation flow by means of small inclinations. On the other hand, in the laminar regime the heat is transported solely by a slow large scale circulation flow which exhibits large correlations between the velocity and temperature fields. For inclination angles close to the transition regime in-between the turbulent-like and laminar state, a quasi-periodic heat-flow bursting phenomenon is observed.

show abstract

Section: Flow Patternsmentioning

confidence: 99%

Robustness of heat transfer in confined inclined convection at high Prandtl number

2019

View full text Add to dashboard Cite

show abstract

“…The minimum of the neutral surface [µ(q, U ) = 0] provided the threshold voltage U c . The numerical calculations have been carried out with a Fortran code developed at the University of Bayreuth, using the same set of known material parameters (permittivities, conductivities, elastic moduli, viscosities), as for earlier calculations with the SM (for Phase 5 and Phase 5A in [34], and for MBBA in [7,35,36]). The original measurements of these parameters have been reported in [34,37,38] for Phase 5 and in [39,40,41,42,43,44] for MBBA.…”

Section: Substances Experimental Set-up and Details Of Calculationsmentioning

confidence: 99%

Flexoelectricity and competition of time scales in electroconvection

et al. 2008

Self Cite

View full text Add to dashboard Cite

An unexpected type of behavior in electroconvection (EC) has been detected in nematic liquid crystals (NLCs) under the condition of comparable time scales of the director relaxation and the period of the driving ac voltage. The studied NLCs exhibit standard EC (s-EC) at the onset of the instability, except one compound in which nonstandard EC (ns-EC) has been detected. In the relevant frequency region, the threshold voltage for conductive s-EC bends down considerably, while for dielectric s-EC it bends up strongly with the decrease of the driving frequency. We show that inclusion of the flexoelectric effect into the theoretical description of conductive s-EC leads to quantitative agreement, while for dielectric s-EC a qualitative agreement is achieved. The frequency dependence of the threshold voltage for ns-EC strongly resembles that of the dielectric s-EC.

show abstract

“…In equation (8), parameters J, J, J and J have the dimensions of the material flux. The terms J and J are designed to yield the concentration field of equation ( 7) under the constraint of equation ( 6) (Fig.…”

Section: Simplification Of Flow Director and Concentration Fieldsmentioning

confidence: 99%

“…In addition to the fluid-structure interaction, the migration of the charge carriers should be analysed as they interact with both flow and structure. Therefore, it is generally complicated and challenging to describe the mechanisms of the phenomena related to electroconvection, as seen in the generation of travelling waves including solitons [4][5][6][7][8][9][10][11][12][13][14], bifurcation between turbulent states [15][16][17][18], and the appearance of negative viscosity [19,20].…”

Section: Introductionmentioning

confidence: 99%

Propagation of periodic director and flow patterns in a cholesteric liquid crystal under electroconvection

Yoshioka,

Nobori,

Fukao

et al. 2024

Preprint

View full text Add to dashboard Cite

The electroconvection of liquid crystals is a typical example of a dissipative structure generated by complicated interactions between three factors: convective flow, structural deformation, and the migration of charge carriers. In this study, we found that the periodic structural deformation of a cholesteric liquid crystal propagates in space, like a wave, under an alternating-current electric field. The existence of convection and charge carriers was confirmed by flow-field measurements and dielectric relaxation spectroscopy. Given that the wave phenomenon results from electroconvection, we suggest a possible model for describing the mechanism of wave generation. The validity of the model was examined using the Onsager variational principle. Consequently, it was suggested that wave generation can be described by four effects: the electrostatic potential, mixing entropy, anisotropic friction due to charge migration, and viscous dissipation of the liquid crystal.

show abstract

Onset of electroconvection of homeotropically aligned nematic liquid crystals

Cited by 13 publications

References 39 publications

Robustness of heat transfer in confined inclined convection at high Prandtl number

Robustness of heat transfer in confined inclined convection at high Prandtl number

Flexoelectricity and competition of time scales in electroconvection

Propagation of periodic director and flow patterns in a cholesteric liquid crystal under electroconvection

Contact Info

Product

Resources

About