Experimental study of ethylene glycol-based Al₂O₃ nanofluid turbulent heat transfer enhancement in the corrugated tube with twisted tapes

Abstract

In this study, fluid flow of the Al₂O₃/ethylene glycol (EG) nanofluid in a corrugated tube fitted with twisted tapes were experimentally studied under turbulent flow conditions. The experiments with different twists ratio and different nanofluid concentration were performed under similar operation condition. The investigated ranges are (1) three different Al₂O₃ concentrations: 0.5, 1 and 1.5 % by volume (2) three different twist ratios of twisted tape: y/w = 2, 3.6 and 5 and (3) Reynolds number from 6000 to 30,000. Regarding the experimental data, utilization of twists together with nanofluids tends to increase heat transfer and friction factor as compared with the base fluid. In addition, heat transfer performances were weakened by using for high nanoparticle concentration. The thermal performances of the heat exchanger with nanofluid and twisted tapes were evaluated for the assessment of overall improvement in thermal behavior. Over the range studied, the maximum thermal performance factor 4.2 is found with the use of Al₂O₃/EG nanofluid at concentration of 0.5 % by volume in corrugated tube together with twisted tape at twist ratio of 2.

Appendix: Uncertainty analysis

The uncertainty table for different instruments used in experiment is given in Table 2. The maximum possible error for the parameters involved in the analysis are estimated and summarized in Table 3.

Table 2 Uncertainties of instruments and properties

Table 3 Uncertainties of parameters and variables

Reynolds number, Re:

$$\text{Re} = \frac{{4\dot{m}}}{\pi D\mu },\frac{{U_{\text{Re}} }}{\text{Re}} = \left( {\left( {\frac{{U_{{\dot{m}}} }}{{\dot{m}}}} \right)^{2} + \left( {\frac{{U_{\mu } }}{\mu }} \right)^{2} } \right)^{1/2} = 1.4\;\%$$

Heat transfer rate of the nanofluid:

$$Q_{nf} = \dot{m}_{nf} cp_{nf} (T_{out} - T_{in} )_{nf} ,\quad \frac{{U_{{Q_{nf} }} }}{{Q_{nf} }} = \left( {\left( {\frac{{U_{{\dot{m}_{nf} }} }}{{\dot{m}_{nf} }}} \right)^{{^{2} }} + \left( {\frac{{U_{{cp_{nf} }} }}{{cp_{nf} }}} \right)^{2} + \left( {\frac{{U_{{T_{out} - T_{in} }} }}{{T_{out} - T_{in} }}} \right)^{2} } \right)^{1/2} = 0.17\;\%$$

Heat transfer rate of the water:

$$Q_{w} = \dot{m}_{w} cp_{w} (T_{out} - T_{in} )_{w} ,\quad \frac{{U_{{Q_{w} }} }}{{Q_{w} }} = \left( {\left( {\frac{{U_{w} }}{{\dot{m}_{w} }}} \right)^{2} + \left( {\frac{{U_{{cp_{w} }} }}{{cp_{w} }}} \right)^{2} + \left( {\frac{{U_{{T_{out} - T_{in} }} }}{{T_{out} - T_{in} }}} \right)^{2} } \right)^{1/2} = 0.5\;\%$$

Nusselt number, Nu:

$$Nu = \frac{hD}{K},\frac{{U_{Nu} }}{Nu} = \left( {\left( {\frac{{U_{h} }}{h}} \right)^{2} + \left( {\frac{{U_{K} }}{K}} \right)^{2} } \right)^{1/2} = 0.26\;\%$$

Friction factor, f:

$$f = \frac{\varDelta P}{{\left( \frac{l}{D} \right)\left( {\frac{{\rho V^{2} }}{2}} \right)}},U_{f} = \left( {\left( {\frac{{U_{\varDelta P} }}{\varDelta P}} \right)^{2} + \left( {\frac{{U_{\rho } }}{\rho }} \right)^{2} + \left( {\frac{{2U_{V} }}{V}} \right)^{2} } \right)^{1/2} = 0.42\;\%$$