Correlations for heat transfer coefficient and friction factor for turbulent flow of air through square and hexagonal ducts with twisted tape insert

Heat transfer and overall heat transfer in a double pipe heat exchanger fitted with twisted-tape elements and titanium dioxide nanofluid were studied experimentally. The inner and outer diameters of the inner tube were 8 and 16 mm, respectively, and cold and hot water were used as working fluids in shell side and tube side. The twisted tapes were made from aluminum sheet with tape thickness (d) of 1 mm, width (W) of 5 mm, and length of 120 cm. Titanium dioxide nanoparticles with a diameter of 30 nm and a volume concentration of 0.01% (v/v) were prepared. The effects of temperature, mass flow rate, and concentration of nanoparticles on the overall heat transfer coefficient, heat transfer changes in the turbulent flow regimeRe≥2300, and counter current flow were investigated. When using twisted tape and nanofluid, heat transfer coefficient was about 10 to 25 percent higher than when they were not used. It was also observed that the heat transfer coefficient increases with operating temperature and mass flow rate. The experimental results also showed that 0.01% TiO2/water nanofluid with twisted tape has slightly higher friction factor and pressure drop when compared to 0.01% TiO2/water nanofluid without twisted tape. The empirical correlations proposed for friction factor are in good agreement with the experimental data.

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Comparison of convective heat transfer coefficient and friction factor of TiO2 nanofluid flow in a tube with twisted tape inserts

International Journal of Thermal Sciences ◽

10.1016/j.ijthermalsci.2014.03.002 ◽

2014 ◽

Vol 81 ◽

pp. 84-93 ◽

Cited By ~ 84

Author(s):

W.H. Azmi ◽

K.V. Sharma ◽

P.K. Sarma ◽

Rizalman Mamat ◽

Shahrani Anuar

Keyword(s):

Heat Transfer ◽

Heat Transfer Coefficient ◽

Transfer Coefficient ◽

Convective Heat Transfer ◽

Friction Factor ◽

Convective Heat ◽

Convective Heat Transfer Coefficient ◽

Twisted Tape ◽

Nanofluid Flow

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Local Heat Transfer Measurements in Turbulent Flow Around a 180-deg Pipe Bend

Journal of Heat Transfer ◽

10.1115/1.3248065 ◽

1987 ◽

Vol 109 (1) ◽

pp. 43-48 ◽

Cited By ~ 12

Author(s):

J. W. Baughn ◽

H. Iacovides ◽

D. C. Jackson ◽

B. E. Launder

Keyword(s):

Heat Transfer ◽

Heat Transfer Coefficient ◽

Turbulent Flow ◽

Transfer Coefficient ◽

Secondary Flow ◽

Local Heat Transfer ◽

Reynolds Numbers ◽

Local Heat ◽

Pipe Bend ◽

Streamline Curvature

The paper reports extensive connective heat transfer data for turbulent flow of air around a U-bend with a ratio of bend radius:pipe diameter of 3.375:1. Experiments cover Reynolds numbers from 2 × 104 to 1.1 × 105. Measurements of local heat transfer coefficient are made at six stations and at five circumferential positions at each station. At Re = 6 × 104 a detailed mapping of the temperature field within the air is made at the same stations. The experiment duplicates the flow configuration for which Azzola and Humphrey [3] have recently reported laser-Doppler measurements of the mean and turbulent velocity field. The measurements show a strong augmentation of heat transfer coefficient on the outside of the bend and relatively low levels on the inside associated with the combined effects of secondary flow and the amplification/suppression of turbulent mixing by streamline curvature. The peak level of Nu occurs halfway around the bend at which position the heat transfer coefficient on the outside is about three times that on the inside. Another feature of interest is that a strongly nonuniform Nu persists six diameters downstream of the bend even though secondary flow and streamline curvature are negligible there. At the entry to the bend there are signs of partial laminarization on the inside of the bend, an effect that is more pronounced at lower Reynolds numbers.

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Heat Transfer Performance of Different Nanofluids Flows in a Helically Coiled Heat Exchanger

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.832.160 ◽

2013 ◽

Vol 832 ◽

pp. 160-165 ◽

Cited By ~ 16

Author(s):

Mohammad Alam Khairul ◽

Rahman Saidur ◽

Altab Hossain ◽

Mohammad Abdul Alim ◽

Islam Mohammed Mahbubul

Keyword(s):

Heat Transfer ◽

Heat Transfer Coefficient ◽

Heat Exchanger ◽

Pressure Drop ◽

Transfer Coefficient ◽

Friction Factor ◽

Heat Exchangers ◽

Heat Transfer Performance ◽

Volume Concentration ◽

Transfer Performance

Helically coiled heat exchangers are globally used in various industrial applications for their high heat transfer performance and compact size. Nanofluids can provide excellent thermal performance of this type of heat exchangers. In the present study, the effect of different nanofluids on the heat transfer performance in a helically coiled heat exchanger is examined. Four different types of nanofluids CuO/water, Al2O3/water, SiO2/water, and ZnO/water with volume fractions 1 vol.% to 4 vol.% was used throughout this analysis and volume flow rate was remained constant at 3 LPM. Results show that the heat transfer coefficient is high for higher particle volume concentration of CuO/water, Al2O3/water and ZnO/water nanofluids, while the values of the friction factor and pressure drop significantly increase with the increase of nanoparticle volume concentration. On the contrary, low heat transfer coefficient was found in higher concentration of SiO2/water nanofluids. The highest enhancement of heat transfer coefficient and lowest friction factor occurred for CuO/water nanofluids among the four nanofluids. However, highest friction factor and lowest heat transfer coefficient were found for SiO2/water nanofluids. The results reveal that, CuO/water nanofluids indicate significant heat transfer performance for helically coiled heat exchanger systems though this nanofluids exhibits higher pressure drop.

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