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ABSTRACT
In this study, numerical simulation was used to investigate the effect of adding different nano-particles into the fluid on the performance of a baffled shell-and-tube heat exchanger. A three-dimensional modeling approach was followed to analyze the effect of different nano-fluids, at various volume fractions, as applied in a baffled shell-and-tube heat exchanger. Once finished with validating the grid independency and results, we proceeded to obtain heat transfer rate, pressure drop, outlet shell temperature and exchanger effectiveness for different volume fractions and particle size of different nano-fluids. The studied nano-particles in the present work included Al2O3, CuO, Fe2O3, Cu, Fe, SiO2, and Au, with water and ethylene glycol employed as base fluids. With constant mass flow rate for all cases, the results indicated that, the addition of nano-particles had reduced the heat transfer coefficient, pressure drop and the rate of heat transfer through the shell, even though it had increased outlet shell temperature. In other words, considering a constant heat transfer rate, the presence of nano-fluids in a baffled shell-and-tube heat exchanger is likely to be associated with increased outlet shell temperature. Another consequence presents that using ethylene glycol as base fluid leads to higher effectiveness compared with water as a base fluid in exchanger.
Nomenclature
| A | = | total heat transfer area (m2) |
| cp | = | heat capacity (J/kg K) |
| Bc | = | Baffle cut |
| B | = | central baffle spacing (m) |
| Ds | = | shell size (m) |
| do | = | tube outer diameter (m) |
| dp | = | nano-particle size (m) |
| df | = | molecular diameter of the base liquid (m) |
| E | = | total energy (J) |
| f | = | friction coefficient |
| Δh | = | head loss (m) |
| k | = | thermal conductivity (W/m K) |
| kg | = | Boltzmann constant |
| L | = | heat exchanger length (m) |
| N | = | Avogadro constant |
| Nt | = | number of tubes |
| Nb | = | number of baffles |
| Nu | = | Nusselt number |
| M | = | molecular weight (kg) |
| = | mass flow rate (kg/s) | |
| p | = | pressure (Pa) |
| Pr | = | Prandtl number |
| = | heat transfer rate (W) | |
| Sij | = | strain tensor (s−1) |
| T | = | temperature (K) |
| ΔTm | = | mean logarithmic temperature difference (K) |
| U | = | heat transfer coefficient (W/m2K) |
| = | Reynolds stress component (m2/s2) | |
| ui | = | velocity component (m/s) |
| xi | = | direction component |
Greek symbols
| φ | = | volume fractions (%) |
| ρ | = | density (kg/m3) |
| δij | = | Kronecker delta |
| μ | = | viscosity (kg/m s) |
| ϵth | = | thermal effectiveness |
| k-ϵ | = | turbulent model |
| τij | = | stress tensor (Pa) |
Subscripts
| ave | = | average |
| b | = | base fluid |
| c | = | cold fluid |
| eff | = | effective |
| f | = | base fluid |
| f0 | = | base fluid calculated at 293 K |
| h | = | hot fluid |
| in | = | inlet |
| out | = | outlet |
| np | = | nano-particles |
| nf | = | nano-fluid |
| p | = | particle |
Additional information
Notes on contributors
Ali Heydari
Ali Heydari is an assistant professor in the Mechanical Engineering Department at Semnan Islamic Azad University (IAU), Semnan, Iran. His research interests include computational fluid dynamics, unsteady aerodynamics, boundary layer characteristics, solar energy and nano-fluid heat transfer. He received a BS degree in Mechanical engineering and MS and PhD degrees in Energy Conversion from the Mechanical Engineering Department of Ferdowsi University, Iran. He is a reviewer for journals such as Environmental Progress & Sustainable Energy and Journal of Aerospace Engineering. He is a board founder of strategic research center of energy and sustainable development in Semnan IAU.
Mostafa Shateri
Mostafa Shateri graduated in Mechanical Engineering and Energy Conversion with a BS and MS degree respectively from the Islamic Azad University of Semnan, Iran. He is now a Ph.D. student there. His intrests include heat and mass transfer, vortex tubes and static mixers.
Sina Sanjari
Sina Sanjari graduated with a Master's degree in Materials Engineering (identification and selection of materials) from slamic Azad University of Semnan, Iran. He research intersrs are manufacturing process optimization and improved properties of materials by using nano-particles.