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Abstract
In the process of heat transfer, the fluid type and external parameters have a significant impact on heat transfer performance. For this reason, the physical properties, pressure differences, and heat transfer rates of SiO2–water nanofluids have been experimentally investigated in a straight circular pipe. Experimental results revealed a great difference in physical properties between SiO2–water nanofluids and purified water. The friction factor of low-volume-concentration nanofluids was slightly increased for laminar flow and tended to be almost independent of the Reynolds number for turbulent flow. The heat transfer coefficient can be enhanced either by adding nanoparticles to purified water or by imposing a transverse vibration on the heat transfer surface. Using these two methods at the same time (compound heat transfer enhancement), heat transfer performance is much better than that with either method alone. The largest increase of about 182% was observed under conditions of compound heat transfer enhancement.
NOMENCLATURE
| A | = | the inner surface area of test section (m2) |
| a | = | vibration amplitudes(mm) |
| Cp | = | specific heat capacity of SiO2–water nanofluids (J/(kg·K)) |
| Cp,0 | = | specific heat capacity of purified water (J/(kg·K)) |
| Cp,s | = | specific heat capacity of SiO2 nanoparticles (J/(kg·K)) |
| d | = | inner diameter of the straight circular pipe (m) |
| En | = | nano enhancement coefficient |
| Ev | = | vibration enhancement coefficient |
| E(n+v) | = | composed enhancement coefficient |
| f | = | friction factor |
| fr | = | vibration frequency (Hz) |
| g | = | gravitational acceleration (m/s2) |
| Δh | = | liquid surface height difference (m) |
| h | = | average convective heat transfer coefficient of water and nanofluids (W/(m2·K)) |
| hn | = | average convective heat transfer coefficient of water for steady flow (W/(m2·K)) |
| hs | = | average convective heat transfer coefficient of nanofluids for steady flow (W/(m2·K)) |
| hv | = | average convective heat transfer coefficient of water under vibration state (W/(m2·K)) |
| h(n+v) | = | average convective heat transfer coefficient of nanofluids under vibration state (W/(m2·K)) |
| k | = | thermal conductivity of working fluid(W/(m·K)) |
| l | = | tap distance of the manometer (m) |
| m0 | = | mass of SiO2 nanoparticles (kg) |
| mp | = | mass of water (kg) |
| Nu | = | Nusselt number of water |
| Nunf | = | Nusselt number of nanofluids |
| Δp | = | overall pressure drop (Pa) |
| Prf | = | Prandtl number of water at average temperature of itself |
| Prnf | = | Prandtl number of nanofluids at average temperature of itself |
| Prw | = | Prandtl number of working fluid at wall temperature |
| Ped | = | Peclet number of the nanoparticles |
| qm | = | average mass flow rate (kg/s) |
| qv | = | volume rate of working fluid (m3/s) |
| Q | = | average heat transfer rate of test section (W) |
| Re | = | Reynolds number for steady flow and the flow of vibration state |
| Renf | = | Reynolds number of nanofluids |
| tw | = | average wall temperature of test section (°C) |
| tf | = | average temperature of working fluid in the test section (°C) |
| tin | = | temperature of inlet of working fluid (°C) |
| tout | = | temperature of outlet of working fluid (°C) |
| T | = | average temperature of working fluid in the state of nature (°C) |
| u | = | axial average velocity of working fluid (m/s) |
Greek Symbols
| φ | = | volume concentration of SiO2–water nanofluids |
| μ | = | viscosity of working fluid (Pa·s) |
| ρnf | = | density of nanofluids (kg/m3) |
| ρc | = | density of CCl4 (kg/m3) |
| ρ0 | = | the density of water(kg/m3) |
| ρs | = | density of SiO2 nanoparticles (kg/m3) |
Additional information
Funding
Notes on contributors
Liang Zhang
Liang Zhang is a Ph.D. student in the Heat Transfer Laboratory, School of Energy and Power Engineering, Dalian University of Technology, Dalian, China. He received his MASTER’S degree from the same University in 2007 and bachelor's degree from WeiFang University in 2000, Shandong, China. Currently, he is working on the experimental and theoretical analysis of the heat transfer behavior of nanofluids. He has published 13 research papers in international journals and conferences.
Jizu Lv
Jizu Lv is an associate professor in the School of Energy and Power Engineering, Dalian University of Technology, Dalian, China. He received his M.E. and Ph.D. degrees from Dalian University of Technology, Dalian, China, in 2006 and 2009. His research interests include heat transfer enhancement in internal combustion engines, combustion and heat transfer in nanofluids.
Minli Bai
Minli Bai is a professor in the School of Energy and Power Engineering, Dalian University of Technology, Dalian, China. She received her M.E. and Ph.D. degrees from Dalian University of Technology, Dalian, China, in 1984 and 1996. She has published about 100 research papers in international journals and conferences. She is an evaluation expert in the National Natural Science Foundation, Division of Engineering, Thermal Physics. Her research interests include heat exchangers, two-phase heat transfer, heat transfer in nanofluids, and computational fluid dynamics.
Detian Guo
Detian Guo is a bachelor's degree student in the Heat Transfer Laboratory, School of Energy and Power Engineering, Dalian University of Technology, Dalian, China. Currently, he is working on the experimental and theoretical analysis of the heat transfer behavior of nanofluids.