- Nano Express
- Open Access
Experimental Research on Stability and Natural Convection of TiO2-Water Nanofluid in Enclosures with Different Rotation Angles
© The Author(s). 2017
- Received: 21 March 2017
- Accepted: 29 May 2017
- Published: 8 June 2017
The stability and natural convection heat transfer characteristics of TiO2-water nanofluid in enclosures with different rotation angles (α = −45°, α = 0°, α = 45°, and α = 90°) are experimentally investigated. The effects of different pH values and doses (m) of dispersant agent on the stability of TiO2-water nanofluid are investigated. It is found that TiO2-water nanofluid with m = 6 wt% and pH = 8 has the lowest transmittance and has the best stability. The effects of different rotation angles (α = −45°, α = 0°, α = 45°, and α = 90°), nanoparticle mass fractions (wt% = 0.1%, wt% = 0.3%, and wt% = 0.5%) and heating powers (Q = 1 W, Q = 5 W, Q = 10 W, Q = 15 W, and Q = 20 W) on the natural convection heat transfer characteristics are also studied. It is found that the enclosure with rotation angle α = 0° has the highest Nusselt number, followed by the enclosure with rotation angles α = 45° and α = 90°, the enclosure with rotation angle α = −45° has the lowest Nusselt number. It is also found that natural convection heat transfer performance increases with the nanoparticle mass fraction and heating power, but the enhancement ratio decreases with the heating power.
- Natural convection
- Rotation angle
Natural convection heat transfer characteristics of nanofluid are numerically investigated by many researchers. He et al. [10, 11] applied a single-phase and a two-phase lattice Boltzmann methods to numerically study the natural convection heat transfer of Al2O3-water nanofluid in a square cavity, respectively. Sheikholeslami et al.  investigated the magnetohydrodynamic natural convection heat transfer characteristics of a horizontal cylindrical enclosure with an inner triangular cylinder filled with Al2O3-water nanofluid by a lattice Boltzmann simulation method. Uddin et al.  studied the natural convection heat transfer of various nanofluids along a vertical plate embedded in porous medium based on the Darcy-Forchheimer model. Meng et al.  numerically investigated the natural convection of a horizontal cylinder filled with Al2O3-water nanofluid. Ahmed et al.  used a two-phase lattice Boltzmann method to study the natural convection of CuO-water nanofluid in an inclined enclosure. Qi et al.  numerically simulated the natural convection of Cu-Ga nanofluid in an enclosure.
In addition to above numerical simulations on the natural convection of nanofluid, the experimental studies on natural convection of nanofluid are done by more and more researchers. Li et al.  experimentally investigated the natural convection heat transfer of ZnO-EG/water nanofluid. Hu et al. [18, 19] experimentally studied the natural convection heat transfer enhancement of a square enclosure filled with TiO2-water and Al2O3-water nanofluids respectively. Ho et al.  experimentally studied the natural convection heat transfer of vertical square enclosures with different sizes filled with Al2O3-water nanofluid. Heris et al. [21–23] experimentally investigated the convective heat transfer characteristics of different kinds of nanofluid (Cu/water, Al2O3-water, and CuO-water) in circular tubes, respectively. Mansour et al.  experimentally investigated the mixed convection of an inclined tube filled with Al2O3-water nanofluid. Chang et al.  experimentally investigated the natural convection of Al2O3-water nanofluid in thin enclosures. Wen et al. [26, 27] experimentally investigated the convective heat transfer characteristics of Al2O3-water nanofluids and TiO2-water nanofluids under laminar flow conditions, respectively. Xuan et al.  experimentally studied the convection heat transfer of Cu-water nanofluid in a straight brass tube.
Above literatures made a great contribution in the natural convection heat transfer characteristics of nanofluid. However, the natural convection heat transfer enhancement of enclosures with different rotation angles filled with nanofluid is needed to be investigated further. Hence, the stability and natural convection heat transfer characteristics of TiO2-water nanofluid in enclosures with different rotation angles (α = −45°, α = 0°, α = 45°, and α = 90°) are experimentally investigated in this paper.
Preparation of Nanofluid and its Stability
Information of materials and equipments. Information of some materials and equipments in the preparation of nanofluids
Materials and equipments
Nanjing Tansail Advanced Materials Co., Ltd.
Crystal form: anatase;
Particle diameter:10 nm
Base fluid (deionized water)
Prepared by ultrapure water device
Resistivity: 16–18.2 MΩ•cm@25 °C
Ultrapure water device
Nanjing Yeap Esselte Technology Development Co., Ltd.
Nanjing Tansail Advanced Materials Co., Ltd.
Element: macromolecule polymers;
Scope of application: water or solvent (base fluid)
Ultrasonic oscillation device
Shenzhen Jeken Ultrasonic Technology Co., Ltd.
Ultrasonic frequency: 40,000 HZ
Magnetic stirring apparatus
Shanghai MeiYingPu Instrument Manufacturing Co., Ltd.
Rotate speed: 50 ~ 1500 r/min
Electronic analytical balance
Shanghai Hengping Instrument and Meter Factory
Precision: 0.1 mg
where U and I are the voltage and electricity of the DC power respectively.
where Q loss is the heat loss measured by a heat flow meter.
where T 1, T 2, …, T 6 are the temperatures of thermocouples.
where δ = 0.005m is the thickness of the copper plate, A is the area of the copper plate, λ w is the thermal conductivity of the copper plate.
where T 7, T 8, …, T 12 are the temperatures of thermocouples in the right side of the enclosure.
where λ f is the thermal conductivity of the fluid in the enclosure.
Based on the Eqs. (10) and (11), the errors of the convective heat transfer coefficient and Nusselt number are 5.65 and 6.34%, respectively, in this experiment. It can be found that the errors of the experimental sets are small, which can ensure the reliability and accuracy of the experimental results.
Enclosure with A = 1:2
Enclosure with A = 1:4
Comparison Between A = 1:2, A = 1:4, and A = 1:1
Nusselt numbers (A = 1:1). Nusselt number values based on Fig. 14 (A = 1:1)
Nusselt numbers (A = 1:2). Nusselt number values based on Fig. 14 (A = 1:2)
Nusselt numbers (A = 1:4). Nusselt number values based on Fig. 14 (A = 1:4)
TiO2-water nanofluid with m = 6 wt% and pH = 8 has the lowest transmittance and has the best stability.
The enclosure with rotation angle α = 0° has the highest Nusselt number followed by the enclosure with rotation angles α = 45° and α = 90°; the enclosure with rotation angle α = −45° has the lowest Nusselt number.
There is a higher heat transfer performance in a bigger aspect ratio enclosure. The Nusselt numbers of enclosure (A = 1:1 and A = 1:2) can be enhanced by 190.6% ~ 224.4% and 103.6% ~ 172.0% compared with the Nusselt numbers of enclosure (A = 1:4) at the same conditions.
Nusselt numbers increase with nanoparticle mass fractions, but the enhancement ratio decreases with the heating power.
Average Nusselt numbers increase with the heating power. Average Nusselt numbers of nanofluid can be enhanced by 701.5% compared with water at the best.
This work is financially supported by “National Natural Science Foundation of China” (Grant No. 51606214) and by “the Fundamental Research Funds for the Central Universities” (Grant No. 2015XKMS063).
CQ participated in the design of the experiment set and drafted the manuscript. GQW carried out the experiment of nanofluid and processed with the data. YFM and LXG carried out the experiment of nanofluid. All authors read and approved the final manuscript.
The authors declare that they have no competing interests.
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