Thermal performance of a circular tube embedded with TBVG inserts: an experimental study

Abstract

The results of various geometrical and flow parameters on thermal energy transfer and performance of tube heat exchangers with solid and perforated "triple-blade vortex generator" insert are presented in this study. Pitch ratio = 1,2,3,4, blade angle = 45°, and perforation index = 0%, 25% are the parameters used in the experiment. The experiments are carried out over a wide range of Reynolds numbers, ranging from 6000 to 24,000. A three-dimensional numerical analysis is also performed to gain a better understanding of fluid flow behavior and heat transfer mechanisms. The results show that using the triple-blade vortex generator insert improves the performance of a heat exchanger. The heat transfer escalation detected in comparison with a simple heat exchanger with a plain tube is in the range of 2.4–4.35, maximum for pitch ratio of 1 and 0% perforation index and a minimum for pitch ratio of 4 and 25% perforation index. The friction factor varies from 0.43 to 3.15, lowest for pitch ratio of 4 and a 25% perforation index and the highest for pitch ratio of 1 and 0% perforation index. The maximum thermal performance of 1.16 is achieved with a pitch ratio of 1 and a perforation index of 25%. For the prediction of Nusselt number, friction factor, and the thermal performance factor of the tubular heat exchanger with triple-blade vortex generator inserts, statistical correlations are developed using experimental data.

Appendix: Uncertainty analysis

Reynolds number

$$\mathrm{Re}=\frac{\rho \mathrm{VD}}{\mu }$$

$$\frac{\delta \mathrm{Re}}{\mathrm{Re}}={\left[{\left(\frac{\delta \rho }{\rho }\right)}^{2}+{\left(\frac{\delta V}{V}\right)}^{2}+{\left(\frac{\delta D}{D}\right)}^{2}+{\left(\frac{\delta \mu }{\mu }\right)}^{2}\right]}^{0.5}$$

$$\frac{\delta \mathrm{Re}}{Re}={\left[{{\left(8.18\times {10}^{-4}\right)}^{2}}+{{\left(7.43\times {10}^{-2}\right)}^{2}}+{{\left(9.34\times {10}^{-4}\right)}^{2}}+{{\left(5.042\times {10}^{-4}\right)}^{2}}\right]}^{0.5}$$

$$\frac{\delta \mathrm{Re}}{\mathrm{Re}}=0.0742$$

Hence, the uncertainty in Reynolds number is 7.42%.

Nusselt number

$$\mathrm{Nu}=\frac{h\mathrm{D}}{K}$$

$$\frac{\delta \mathrm{Nu}}{\mathrm{Nu}}={\left[{\left(\frac{\delta h}{h}\right)}^{2}+{\left(\frac{\delta D}{D}\right)}^{2}+{\left(\frac{\delta K}{K}\right)}^{2}\right]}^{0.5}$$

$$\frac{\delta \mathrm{Nu}}{\mathrm{Nu}}={\left[{\left(0.0283\right)}^{2}+{\left(0.000941\right)}^{2}+{\left(0.00527\right)}^{2}\right]}^{0.5}$$

$$\frac{\delta \mathrm{Nu}}{\mathrm{Nu}}=0.0287$$

Hence, uncertainty in the Nusselt number is 2.87%.

Friction factor

$$f=\frac{2{\left({\Delta }_{\text{p}}\right)}_{\text{d}}D}{4\rho L{V}^{2}}$$

$$\frac{\delta f}{f}={\left[{{\left(\frac{\delta V}{V}\right)}^{2}+{\left(\frac{\delta \rho }{\rho }\right)}^{2}+\left(\frac{\delta D}{D}\right)}^{2}+{\left(\frac{\delta L}{L}\right)}^{2}+{\left(\frac{\delta {\left({\Delta }_{\text{p}}\right)}_{\text{d}}}{{\left({\Delta }_{\text{p}}\right)}_{\text{d}}}\right)}^{2}\right]}^{0.5}$$

$$\frac{\delta f}{f}={\left[{\left(0.0742\right)}^{2}+{\left(0.000821\right)}^{2}+{\left(0.000939\right)}^{2}+{\left(0.0000667\right)}^{2}+{\left(0.00767\right)}^{2}\right]}^{0.5}$$

$$\frac{\delta f}{f}=0.0744$$

Hence, uncertainty in the friction factor is 7.45%.