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Abstract
This paper deals with pool boiling of water–Al2O3 and water–Cu nanofluids on porous coated, horizontal tubes. Commercially available stainless-steel tubes having 10 mm outside diameter and 0.6 mm wall thickness were used to fabricate a test heater. Aluminum porous coatings 0.15 mm thick with porosity of about 40% were produced by plasma spraying. A smooth tube served as a reference tube. The experiments were conducted under different absolute operating pressures of 200 kPa, 100 kPa, and 10 kPa. Nanoparticles were tested at concentrations of 0.01%, 0.1%, and 1% by weight. In all cases tested, enhancement heat transfer was always observed during boiling of water–Al2O3 and water–Cu nanofluids on smooth tubes compared to boiling of distilled water. Contrary to smooth tubes, addition of even a small amount of nanoparticles resulted in deterioration of heat transfer during pool boiling of water–Al2O3 and water–Cu nanofluids on porous coated tubes in comparison with boiling of distilled water.
NOMENCLATURE
| = | mean pore radius (m) | |
| Bo | = | boiling number, |
| Csf | = | surface/liquid parameter in EquationEq. (13) |
| D | = | diameter (m) |
| g | = | acceleration due to gravity (m/s2) |
| hfg | = | latent heat of vaporization (kJ/kg) |
| I | = | current (A) |
| keff | = | enhancement factor, |
| L | = | active length of the tube (m) |
| M | = | molecular weight (kg/kmol) |
| MAD | = | mean absolute deviation, MAD = 1/n∑|αcor − αexp |/αexp ( %) |
| n | = | number of experimental points () |
| N | = | electrical power (W) |
| Nu | = | Nusselt number, |
| P | = | pressure (kPa) |
| Pr | = | Prandtl number |
| q | = | heat flux (W/m2) |
| Re | = | Reynolds number |
| Ra | = | roughness arithmetic average (nm) |
| Rp | = | surface roughness parameter (μm) |
| S | = | constant, |
| T | = | temperature (K) |
| U | = | voltage (V) |
Greek Symbols
| α | = | average heat transfer coefficient (W/m2K) |
| λ | = | thermal conductivity (W/mK) |
| ρ | = | density (kg/m3) |
| σ | = | surface tension coefficient (N/m) |
| Φ | = | concentration of nanoparticles by weight (%) |
| μ | = | dynamic viscosity (Pa) |
Subscripts
| bf | = | base fluid |
| f | = | fluid |
| cor | = | correlation (EquationEq. 13 |
| cr | = | critical |
| exp | = | experimental |
| i | = | inside |
| l | = | liquid |
| loc | = | local |
| m | = | mass |
| nano | = | nanofluid |
| o | = | outside |
| p | = | particle |
| r | = | reduced |
| t | = | tube |
| v | = | vapor |
| vol | = | volume |
| w | = | wall |
Additional information
Funding
Notes on contributors
Janusz T. Cieśliński
Janusz T. Cieśliński received his M.Sc. degree in mechanical engineering from Gdańsk University of Technology in 1978 and his Ph.D. degree in 1986. He also received his D.Sc. degree (habilitation) from Gdańsk University of Technology in 1997. In 2002–2008 he served as a vice dean of the Faculty of Mechanical Engineering. In 2006–2010 he was head of the group of Ecoengineering and Process Apparatus and since 2010 he has been head of the Ecoengineering and Combustion Engines Division. In 2002–2007 he was a chairman of the Multi-Phase Flow and Non-Newtonian Fluids Section of the Polish Academy of Sciences. Since 2008 he has been full professor at Gdańsk University of Technology.
Tomasz Z. Kaczmarczyk
Tomasz Z. Kaczmarczyk received his M.Sc. degree in mechanical engineering from Gdańsk University of Technology in 2005 and M.Sc. degree in electrical and control engineering from Gdańsk University of Technology in 2008, as well as his Ph.D. degree in 2012. Since 2008 he has been a specialist at Gdańsk University of Technology. Since 2013 he has been a research fellow at the Szewalski Institute of Fluid-Flow Machinery of the Polish Academy of Sciences.