Experimental study on thermo-hydraulic performance of nanofluids in diverse axial ratio elliptical tubes with a built-in
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pISSN: 0256-1115 eISSN: 1975-7220
INVITED REVIEW PAPER
INVITED REVIEW PAPER
Experimental study on thermo-hydraulic performance of nanofluids in diverse axial ratio elliptical tubes with a built-in turbulator Cong Qi*,**,†, Tiantian Chen*,**, Yuxing Wang*,**, and Liyuan Yang*,** *Jiangsu Province Engineering Laboratory of High Efficient Energy Storage Technology and Equipment, China University of Mining and Technology, Xuzhou 221116, China **School of Electrical and Power Engineering, China University of Mining and Technology, Xuzhou 221116, China (Received 21 February 2020 • Revised 17 April 2020 • Accepted 30 April 2020) AbstractDue to the low heat transfer efficiency of common heat exchange systems, an improved heat exchange system was developed. Enhanced tubes (elliptical tubes with a built-in turbulator) instead of a smooth tube were used and TiO2-water nanofluids were substituted for water to intensify the heat transfer. The influences of turbulator (presence or absence), axial ratios of elliptical tubes (Z=1.235, 1.471, 1.706), nanoparticle concentration (=0.0 wt%, 0.1 wt%, 0.3 wt%, 0.5 wt%), and Reynolds number (Re=400-12,000) on the flow and heat transfer properties of TiO2-water nanofluids were studied. Thermal and exergy efficiency were used to research the comprehensive thermo-hydraulic characteristics of these heat transfer enhancement technologies. The thermo-hydraulic properties of nanofluids all showed an increasing trend with the growing axial ratio, nanoparticle concentration and Reynolds number. Nanofluids (=0.5 wt%) in an elliptical tube (Z=1.706) with a built-in turbulator showed the best thermal performance, which could be increased by 33.8% in comparison with water at best. The thermal efficiency index increased first and then decreased with the Re. Nanofluids in elliptical tubes with a built-in turbulator can clearly promote heat transfer under the identical condition. Keywords: Nanofluids, Forced Convection, Elliptical Tube, Thermal Efficiency, Exergy Efficiency
intensity requirements. For the high heat transfer intensity field, especially the heat exchanger system, the turbulent flow is widely adopted instead of the natural convection to achieve high-intensity heat transfer. Turbulent flow heat transfer, as a main heat transfer model, is of great significance in the design of the heat exchange system. Numerous researches on the turbulent flow of nanofluids are being carried out. Hu et al. [18] conducted a numerical simulation on the turbulent flow of salt-based nanofluids among the solar energy system. Results indicated that the heat transmission characteristic of salt-based nanofluids firstly increases with nanoparticle concentration and then decreases, and the crucial concentration of nanoparticle is 1.0 wt%. Li et al. conducted a number of studies about the turbulent flow of nanofluids [19,20] in cavities [21-23], a pipe with modified turbulators [24], and a round duct with volute turbulators [25]. It was presented that the magnetic field, porous media, and turbulator play a posit
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