Thermal electro-hydrodynamic heat transfer augmentation in vertical annuli by the use of dielectrophoretic forces through a.c. electric field

详细信息    查看全文

• 作者：B. Futterer ; ^{birgit.futterer@web.de" class="auth_mail" title="E-mail the corresponding author} ; N. Dahley ; C. Egbers
• 关键词：Natural convection ; Vertical annulus ; Cylindrical enclosures ; Thermal electro-hydrodynamic convection TEHD ; Dielectrophoretic DEP forces ; Experiments ; Flow visualization ; Heating power measurement ; Nusselt number calculation
• 刊名：International Journal of Heat and Mass Transfer
• 出版年：2016
• 出版时间：February 2016
• 年：2016
• 卷：93
• 期：Complete
• 页码：144-154
• 全文大小：2509 K

文摘

We consider a fluid-filled cylindrical enclosure with an inner heated cylinder of radius r_i$r_i$ maintained at temperature T_i$T_i$ and an outer cooled cylinder of radius r_o$r_o$ maintained at temperature T_o$T_o$. This vertical annulus is of height H with adiabatic top and bottom boundaries. The temperature difference ΔT=T_o-T_i$\mathrm{\Delta }T=T_o-T_i$ induces natural convection in the gap width d=r_o-r_i$d=r_o-r_i$ at small values of ΔT$\mathrm{\Delta }T$. This base flow experiences transition to instabilities depending on the radius ratio η=r_i/r_o$\eta =r_i/r_o$, aspect ratio Γ=H/(r_o-r_i)$\mathrm{\Gamma }=H/(r_o-r_i)$, physical properties of the fluids (weighted with the Prandtl number) and on the driving force (weighted with the Rayleigh number). In this work, we study experimentally the heat transfer enhancement by the dielectrophoretic force induced by the application of an alternating (a.c.) electric field superposing natural convection in the vertical annulus. This procedure allows to introduce an electric Rayleigh number for the system. We will show a clear distortion of the base flow via flow visualization, and we quantify heat transfer by measurements of the Nusselt number for the inner cylinder. For low values of the electric Rayleigh number the superposed electric field damps the heat transfer, whereas for large values we observe a clear increase via an increase of the Nusselt number.