Abstract
The heat transfer and pressure drop characteristics of SiO2/water nanofluids flowing through a horizontal circular stainless steel tube equipped with free rotating swirl generators (FRSGs) at the entrance of a test tube are reported in this article. The experimental studies were performed with a Reynolds number ranging from 3500 to 13,000; volume concentrations of 0.5, 1, and 2 vol%; and inlet temperatures of 25, 30, and 35 °C, where a constant heat flux was imposed on a test tube. FRSGs made from aluminum, with three different twisted angles (30°, 60°, and 90°) and a length of 2.3 cm, were located at the entrance of the test tube. The results indicated that FRSGs had significant effects on heat transfer and pressure drop characteristics for the flow of both water and nanofluids in the tube. The Nusselt number increased with increasing volume concentration, inlet temperature, and Reynolds number. However, the friction factor of nanofluids flowing through FRSGs was significantly greater than that of water when the Reynolds number was lower than 6000. This is because FRSGs do not rotate under the given conditions. A maximum efficiency index of 1.57–1.7 was obtained when using SiO2/water nanofluids with FRSGs at a volume concentration of 2 vol%, inlet temperature of 35 °C, and Reynolds number greater than 7000. On the other hand, the efficiency index value was lower than unity when the Reynolds number was lower than 7000 and with volume concentrations of 0.5 and 1 vol%. No significant differences were found among twisted angles of FRSGs on heat transfer, pressure drop, and efficiency index.
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Abbreviations
- A:
-
Surface area of test section (m2)
- Cp:
-
Specific heat at constant pressure (J/kg.K)
- Di :
-
Inside tube diameter (m)
- d:
-
Diameter (m)
- f :
-
Friction factor
- h:
-
Heat transfer coefficient (W/m2.K)
- I:
-
Electric current (A)
- k:
-
Thermal conductivity (W/m.K)
- L:
-
Length of test section (m)
- ṁ:
-
Mass flow rate (kg/s)
- Nu:
-
Nusselt number
- Pr:
-
Prandtl number
- Q:
-
Heat transfer rate (W)
- Re:
-
Reynolds number
- r:
-
radius (m)
- SMT:
-
Smooth tube
- FRSG:
-
Free rotating swirl generator
- T:
-
Temperature (°C)
- u:
-
Velocity (m/s)
- V:
-
Electric voltage (V)
- α:
-
Thermal diffusivity (m2/s)
- ε:
-
Tube roughness (m)
- η:
-
Efficiency index
- μ:
-
Dynamic viscosity (kg/m.s)
- ϕ:
-
Volume concentration (%)
- ρ:
-
Density (kg/m3)
- ΔP:
-
Pressure drop (Pa)
- ave:
-
Average
- bf:
-
Base fluid
- in:
-
Inlet
- nf:
-
Nanofluids
- out :
-
Outlet
- p:
-
Particle
- ss:
-
Stainless steel
- sup:
-
Supply
- SMT:
-
Smooth tube
- FRSG:
-
Free rotating swirl generator
- wi:
-
Inner wall
- wo:
-
Outer wall
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Acknowledgments
The authors acknowledge the support provided by the “Research Chair Grant” National Science and Technology Development Agency (NSTDA), and King Mongkut’s University of Technology Thonburi through the “KMUTT 55th Anniversary Commemorative Fund”.
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Jumpholkul, C., Asirvatham, L.G., Dalkılıç, A.S. et al. Experimental investigation of the heat transfer and pressure drop characteristics of SiO2/water nanofluids flowing through a circular tube equipped with free rotating swirl generators. Heat Mass Transfer 56, 1613–1626 (2020). https://doi.org/10.1007/s00231-019-02782-z
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DOI: https://doi.org/10.1007/s00231-019-02782-z