Effect of conjugate heat transfer on the thermo-electro-hydrodynamics of nanofluids: entropy optimization analysis
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Effect of conjugate heat transfer on the thermo‑electro‑hydrodynamics of nanofluids: entropy optimization analysis Rajkumar Sarma1 · Abhay Kumar Shukla1 · Harshad S. Gaikwad1 · Pranab Kumar Mondal1 · Somchai Wongwises2 Received: 28 May 2020 / Accepted: 5 October 2020 © Akadémiai Kiadó, Budapest, Hungary 2020
Abstract We investigate, in this analysis, the entropy generation characteristics associated with the transport of nanofluid in a microfluidic channel under the combined influences of applied pressure gradient and electrical forcing. In our study, the nanofluid is subjected to an asymmetric cooling at the channel walls, while the conductive transport of heat through the channel walls is also taken into account. We show that the underlying thermo-electro-hydrodynamics of nanofluids in the channel lead to entropy generation, attributed to the irreversibilities associated with heat transfer, viscous dissipation, and Joule heating effects. We establish that a non-trivial interplay among these irreversibilities gives rise to an optimum value of the geometrical parameter, viz. the channel wall thickness ( 𝛿 ), and the thermophysical parameters, viz. the thermal conductivity of the wall (𝛾) , Biot number (Bi), and the modified Peclet number ( Pe ), leading to a minimum entropy generation rate of the system. Also, we unveil through this study that changes in the electroosmotic parameter 𝜅̄ (representative of the EDL thickness) or the composition of the fluid ( 𝜙 , the volume fraction of nanoparticles agglomerates) non trivially alter the optimum values of these parameters. Inferences drawn from this analysis may have consequences in the optimum design of thermal systems/ devices, typically used for thermal management in micro-heat exchangers, micro-reactors, and micro heat pipes. Keywords Nanofluid · Microfluidic channel · Ionic liquids · Entropy · Electroosmotic transport List of symbols Bi Biot number Br Brinkman number Cp Specific heat at constant pressure ( J kg−1 K−1) d Channel wall thickness (m) e Elementary electronic charge (= 1.6022 × 10−19 C) Ex Applied electric field strength ( = V m−1) G Dimensionless axial temperature gradient (= 𝜕𝜃∕ 𝜕x) H Half height of the channel (m) h External convective heat transfer coefficient ( = W m−2 K−1) J Dimensionless Joule heating parameter * Pranab Kumar Mondal [email protected]; [email protected] 1
Department of Mechanical Engineering, Indian Institute of Technology Guwahati, Guwahati 781039, India
Fluid Mechanics Thermal Engineering and Multiphase Flow Research Laboratory (FUTURE), Department of Mechanical Engineering, Faculty of Engineering, King Mongkut’s University of Technology Thonburi, Bangmod, Bangkok 10140, Thailand
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kB Boltzmann constant k Thermal conductivity ( W m−1 s−1) k̄ Thermal conductivity ratio ( = knf ∕ kf ) L Channel length (m) n∞ Bulk concentration of ions p Pressure (Pa) number ⟨Pe Peclet ⟩ Ṡ Dimensionless volumetric entropy generation rate T Temperature (K) u Axial velocity ( m s−1) ū Dimensionless axial velo
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