Abstract
Alternating current electroosmotic flow and associated heat transfer under constant surface heat flux conditions are numerically examined in a micro-annular channel. The channel surfaces are arbitrarily heated and/or cooled, while the resultant heating is normally transferred downstream by the advection mechanism. An important feature of time-periodic electrokinetic flow is that there is not any preferential axial direction. If the excitation frequency is sufficiently small and/or the liquid kinematic viscosity is sufficiently large, momentum diffuses far into the bulk fluid and thus the advection mechanism is intensified. The reverse is true for relatively large frequency and small kinematic viscosity values. Mean Nusselt number fluctuates over a period of time; its time-averaged magnitude is dependent on the electrokinetic diameter and the dimensionless frequency. This quantity approaches a specific value regardless of the thermal scale and the wall heat flux ratios. The system may attain optimal effectiveness for particular magnitudes of the frequency and electrokinetic diameter. An interesting case may exist in the cooling mode where the axial variation of the mean fluid temperature vanishes temporarily while the state of constant surface temperature is instantly satisfied; at the particular points in time, the advection mechanism does not contribute to the development of the liquid temperature field.
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Abbreviations
- \(A_{\text{c}}\) :
-
Dimensionless cross-sectional area
- \(c_{\text{p}}\) :
-
Specific heat (J kg−1 K−1)
- \(D_{\text{h}}\) :
-
Hydraulic diameter
- \(e\) :
-
Fundamental charge of an electron (C)
- \(E\) :
-
Time-periodic axial electric field strength (V m−1)
- \(E_{\text{th}}\) :
-
Thermal scale ratio
- \(f\) :
-
Fanning friction factor
- \(F\) :
-
Time-periodic function of unit magnitude
- \(h\) :
-
Mean convective heat transfer coefficient (W m−2 K−1)
- \(k_{\text{B}}\) :
-
Boltzmann constant (J K−1)
- \(k_{{{\text{th}} .}}\) :
-
Thermal conductivity of the fluid (W m−1 K−1)
- \(n_{\infty }\) :
-
Bulk ionic concentration (m−3)
- \(P\) :
-
Peripheral ratio
- \(P_{\text{ad}}\) :
-
Advection coefficient
- \({\text{Po}}\) :
-
Poiseuille number
- Pr:
-
Prandtl number
- \(q^{\prime\prime}\) :
-
Surface heat flux (W m−2)
- Q :
-
Dimensionless volumetric flow rate
- \(r\) :
-
Radial coordinate (m)
- \(R\) :
-
Dimensionless radial coordinate
- \(\Re\) :
-
Radius of the outer cylinder (m)
- \(\text{Re}\) :
-
Reynolds number
- \(t\) :
-
Time (s)
- T :
-
Temperature (K)
- \({\text{TF}}_{\text{ix}}\) :
-
Thermal/frictional index
- \(U_{\text{HS}}\) :
-
Helmholtz–Smoluchowski reference velocity (m s−1)
- \(V_{\text{z}}\) :
-
Axial velocity in the annulus (m s−1)
- \(V\) :
-
Dimensionless axial velocity
- \(z\) :
-
Axial coordinate (m)
- \({\mathbb{Z}}\) :
-
Absolute value of the ionic valence
- \(Z\) :
-
Dimensionless potential
- \(\chi\) :
-
Electrokinetic diameter
- \(\delta\) :
-
Wall heat flux ratio
- \(\varepsilon\) :
-
Electric permittivity of solution (F m−1)
- \(\varPhi\) :
-
Dimensionless temperature
- \(\gamma\) :
-
Radius ratio
- \(\kappa\) :
-
Debye–Hückel parameter (m−1)
- \(\mu\) :
-
Dynamic viscosity of the fluid (Ns m−2)
- \(\theta\) :
-
Dimensionless time
- \(\rho\) :
-
Fluid density (kg m−3)
- \(\rho_{\text{e}}\) :
-
Net volume charge density (C m−3)
- \(\sigma\) :
-
Electrical conductivity of the liquid (S m−1)
- \(\tau\) :
-
Shear stress (Pa)
- \(\omega\) :
-
Frequency (s−1)
- \(\varOmega\) :
-
Dimensionless frequency
- \(\psi\) :
-
Electrical potential (V)
- \(\varPsi\) :
-
Dimensionless electrical potential
- \(\zeta\) :
-
Zeta potential (V)
- i:
-
Inner wall
- m:
-
Mean value
- o:
-
Outer wall
- w:
-
Wall
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Moghadam, A.J. Thermal transport characteristics of AC electrokinetic flow in a micro-annulus. J Therm Anal Calorim 145, 2727–2740 (2021). https://doi.org/10.1007/s10973-020-09793-7
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DOI: https://doi.org/10.1007/s10973-020-09793-7