Changfeng Guan

Experimental Study of Heat Transfer Enhancement and Friction Loss Induced by Inserted Rotor-assembled Strand (I) Water

Abstract The single-phase pressure drop and heat transfer in a rotor-assembled strand inserted tube were measured using water as the working fluid. Experiment using a smooth tube was carried out to calibrate the experimental system and the data reduction method. In the experiment, fixed mounts were used to eliminate the entrance effect. The experimental results of smooth tube show that employment of fixed mounts leads to a visible bias of friction factor at relative low Reynolds numbers, although it does not significantly affect the Nusselt numbers. The measured data of inserted tube reveal that rotor-assembled strand can significantly improve heat transfer with the Nusselt number increased by 101.6%-106.6% and the overall heat transfer coefficient increased by 58.1%-67.4% within the Reynolds number range of 20000 to 36000. Meanwhile, friction factor increases by 52.2%-84.2% within the same Reynolds number range. The correlations of Nusselt number and friction factor as function of the Reynolds number and Prandtl number were determined through multivariant linear normal regression.

Microalgal cultivation and hydrodynamic characterization using a novel tubular photobioreactor with helical blade rotors

Industrial-scale microalgal cultivation for food, feedstocks and biofuel production is limited by several engineering factors, such as cultivation systems. As a closed microalgal growth system, tubular photobioreactors are the most preferred ones in the mass algae production. In this work, microalgal cultivation and hydrodynamic characterization using a novel tubular photobioreactor equipped with helical blade rotors (HBRs) were investigated, with the aid of computational fluid dynamics and cultivation experiments to evaluate the effect of HBRs on the performance of tubular photobioreactor and growth of the Chlorella sp. The results showed that the use of HBRs in tubular photobioreactors would result in swirl flow and increase of radial velocity and circumferential velocity; it also indicated that the HBRs would enable microalgal cells to move forward helically and to be shuttled alternatively between the light zone and the dark zone. This has led to the faster growth rate of Chlorella sp. and no attachment on the tube surface in the tubular photobioreactor during the whole cultivation cycle. In conclusion, the HBRs could improve the performance of tubular photobioreactors and thus impact positively on the cultivation of microalgae cells for biotechnological industry.

Experimental Study of Heat Transfer Enhancement and Friction Loss Induced by Inserted Rotor-assembled Strand (II) Lubricant Oil 22 *

Abstract The paper described experimental investigation of heat transfer and single-phase pressure drop through tubes with different rotor-assembled strands inserted in the Reynolds number range of 800–9000 with lubricant as working fluid. In the experiment, fixed mounts were employed to eliminate the entrance effect. The experimental results showed that the employment of fixed mounts led to a visible bias of friction factor in the laminar regime while it could not affect the Nusselt numbers significantly. Experiment for the tube inserted with rotors-assembled strand showed remarkable improvement for heat transfer with the Nusselt number increased by 200%–225% in the laminar regime and 125%–160% in the transitional regime. Meanwhile, the friction factor increased inevitably by 200%–300% within the same range of Reynolds number. The comparison of different rotor-assembled strands inserted tubes and plain tube showed that the heat transfer benefited from the increase of the diameter of rotor-assembled strand with the same lead and the decrease of the lead of rotor-assembled strand, so does the friction factor. Based on experimental data and thorough multivariant linear normal regression method, the correlations of average Nusselt number and friction factor are established.

Numerical Simulation on the Anti-fouling Property of Helical Blade Rotors in Circular Tube

Inferior heat transfer efficiency and severe fouling precipitation have been the troublesome problems for shell-and-tube heat exchangers. As a typical type of tube insert, the helical blade rotors (HBRs) can achieve heat transfer augmentation and fouling mitigation in heat exchanger. In this work, the numerical simulation regarding to the anti-fouling property of HBRs in circular tube was conducted. The numerical method was verified accurate in comparison with the results in literature prior to the simulation. The results showed that in the process of the crystallization of the fouling the deposition rate decreased and the removal rate increased, and eventually they tended to be stable and reached a dynamic balance; the deposition rate, the removal rate, the net rate and the thermal resistance in tube with HBRs was lower than that in smooth tube, which means that inserting HBRs into the circular tube can effectively prevent the deposition of crystallization fouling; moreover, the mass fraction of CaCl2 in tube with HBRs was lower than that in smooth tube, and in tube with HBRs it was not just lower near the tube wall but also near the HBRs, which illustrate that the HBRs can enhance the mass transfer of Ca in circular tube, and the mass transfer of Ca towards the HBRs is enhanced, while the mass transfer towards the tube wall is weakened.

Heat transfer and pressure drop in tubes fitted with grooved lobe rotor-assembled strands

The heat transfer enhancement of grooved lobe rotors and smooth tube were investigated in the integrated heat transfer performance test bench of shell-and-tube heat exchanger. The results indicated that heat transfer rate of tube with the grooved lobe rotors increased about 80-120% compared with that of smooth tube, but the coefficients of resistance also increased about 65-75%. It would be necessary to modify the structure of grooved lobe rotors in the future in order to obtain high heat transfer coefficient and a relatively low friction factor.