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Abstract
Improving the working fluid transport properties is a way to enhance the thermal performance of heat transfer equipment. In this research work, a two-dimensional numerical simulation is used to investigate the thermal performance of a nanofluid-filled cylindrical heat pipe. The considered nanofluid is pure water as the base fluid with dispersed Al2O3 nanoparticles. Effects of particle volume fractions, particle diameters, various heat inputs, and wick structures on thermal performance of the heat pipe are investigated and the results are compared with that of the pure water. A comparison is made for the first time between the results of a simulation by considering fluid flow in the liquid-wick region and treating this region as pure conduction. The results show the heat pipe thermal performance enhancement and a decrease in thermal resistance for about 31% when 5% particle volume fraction with a particle diameter of 10 nm is used. Also, an insignificant effect of heat input on thermal resistance and variation of pressure distribution in the presence of nanoparticles are observed.
NOMENCLATURE
| A | = | area (m2) |
| c | = | inertia coefficient |
| Cp | = | specific heat capacity (kJ/kg-K) |
| dp | = | particle diameter (nm) |
| h | = | convective heat transfer coefficient (W/m2-K) |
| hfg | = | latent heat of vaporization (kJ/kg) |
| K | = | permeability of the wick (m2) |
| k | = | thermal conductivity (W/m-K) |
| keff | = | effective thermal conductivity of the porous wick (W/m-K) |
| klayer | = | nanolayer thermal conductivity (W/m-K) |
| kwall | = | thermal conductivity of the heat pipe wall (W/m-K) |
| L | = | length of heat pipe (m) |
| La | = | adiabatic section length (m) |
| Lc | = | condenser section length (m) |
| Le | = | evaporator section length (m) |
| m | = | mass flux (kg/m2s) |
| P | = | pressure (Pa) |
| Q | = | heat transfer rate (W) |
| Qc | = | heat transfer rate at the condenser section (W) |
| Qe | = | heat transfer rate at the evaporator section (W) |
| r | = | radial coordinate (m) |
| rp | = | particle radius (nm) |
| R | = | thermal resistance (K/W), water vapor specific gas constant (0.4615 kJ/kg-K) |
| Ro | = | heat pipe wall outer radius (m) |
| Rv | = | vapor region radius (m) |
| Rw | = | heat pipe wall inner radius (m) |
| S | = | source term (W/m3) |
| T | = | temperature (K) |
| Tb | = | bulk temperature of the coolant (K) |
| Twall | = | heat pipe wall temperature (K) |
| u | = | axial velocity (m/s) |
| v | = | radial velocity (m/s) |
| V | = | velocity vector (m/s) |
| w | = | nanolayer thickness (nm) |
| x | = | axial coordinate (m) |
Greek Symbols
| φ | = | particle volume fraction |
| ϵ | = | porosity of the wick |
| μ | = | dynamic viscosity (N-s/m2) |
| ρ | = | density (kg/m3) |
Subscripts
| b | = | bulk |
| bf | = | base fluid |
| c | = | condenser |
| e | = | evaporator |
| eff | = | effective |
| int | = | liquid-wick/vapor interface |
| l | = | liqud-wick region |
| max | = | maximum |
| nf | = | nanofluid |
| o | = | outer wall region |
| p | = | particle |
| s | = | solid wick structure |
| sat | = | saturated |
| v | = | vapor |
| w | = | inner wall region |
Additional information
Notes on contributors
Mohammad Hasan Shojaeefard
Mohammad Hasan Shojaeefard is a professor in the Department of Mechanical Engineering, Iran University of Science and Technology, Narmak, Tehran, Iran. He obtained his B.Sc. at the Iran University of Science and Technology, and M.Sc. and Ph.D. at Birmingham University, United Kingdom. His fields of research are fluid mechanics, heat transfer, turbomachinery, and automotive engineering.
Javad Zare
Javad Zare is a Ph.D. student in the Department of Mechanical Engineering, Iran University of Science and Technology, Narmak, Tehran, Iran. He obtained his M.Sc. at Iran University of Science and Technology. His fields of research are CFD, heat transfer, nanofluidics, thermodynamics, and turbulence.
Mojtaba Tahani
Mojtaba Tahani is an assistant professor in the Faculty of New Sciences and Technologies, University of Tehran, Amirabad shomali, Tehran, Iran. He obtained his Ph.D. at Iran University of Science and Technology. His fields of research are CFD, turbulence, aerodynamics, fluid mechanics, and thermodynamics.