https://orcid.org/0000-0003-3225-3670
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ABSTRACT
A comparative experimental investigation in order to evaluate the hydrothermal characteristics of a heat exchanger tube fitted with varied types of twisted tape is performed using graphene nanoplatelets (GNP) and water nanofluid. The experiment is carried out for three varied weight concentrations (ω = 0.05%, 0.075% and 0.1%) of GNP/water nanofluids flowing in a tube fitted with various twisted tapes of three different twist ratios (x/b = 3, 4 and 5) for the Reynolds number of 6700 –33,200 and a nanofluid flow rate of 5 to 25 lpm. The results showed the heat transfer rate and pressure loss increased with rising Reynolds numbers, a decrease in the twist ratio of tapes, and an increase in nanofluid concentration. The specially designed anti-clockwise clockwise twisted tape (ACCT) insert provides a 67.8% greater heat transfer coefficient than typical twisted tape. The addition of GNP nanoparticles to water has a significant impact on the increase in heat transfer rate. The best hydrothermal performance factors achieved are 2.03, 1.93, and 1.84 for ACCT tape (x/b = 3) fitted tube at Reynolds number of 26,600 for 0.1%, 0.075%, and 0.05% weight concentration of GNP/water nanofluids, respectively. Nusselt number and friction factor correlations are also established in terms of twist ratio, Reynolds number, and nanofluid concentration parameters.
Nomenclature
| A | = | Surface area of heat transfer (m2) |
| b | = | Tape width (m) |
| cp | = | Fluid specific heat capacity (J.kg−1.K−1) |
| D | = | Tube inner diameter (m) |
| ƒ | = | Friction factor |
| k | = | Fluid thermal conductivity (W.m−1.K−1) |
| h | = | Heat transfer coefficient (W.m−2.K−1) |
| L | = | Length of test section (m) |
| Nu | = | Nusselt number |
| ṁ | = | Mass flow rate (Kg.s−1) |
| Pr | = | Prandtl number |
| P | = | Pressure (Pa) |
| Re | = | Reynolds number |
| Q | = | Heat rate(W) |
| t | = | Tape thickness (m) |
| T | = | Temperature (K) |
| U | = | Mean velocity (m.s−1) |
| x | = | Twist pitch of tape (m) |
| x/b | = | Twist ratio |
| Greek Symbols | = | |
| µ | = | Absolute viscosity (kg.m−1.s−1) |
| △ | = | Exact difference |
| ρ | = | Density (kg.m−3) |
| φ | = | Volume concentration (%) |
| ω | = | Weight concentration (%) |
| Abbreviations | = | |
| ACCT | = | Anti-clockwise clockwise twisted |
| HEX | = | Heat Exchanger |
| TT | = | Twisted tape |
| lpm | = | Litre per minute |
| TPF | = | Thermal performance factor |
| TR | = | Twist ratio |
| Subscripts | = | |
| bf | = | Base fluid (water) |
| b | = | Bulk |
| c | = | Convection |
| f | = | fluid |
| h | = | Wall surface of tube |
| i | = | Inlet |
| insert | = | Insert fitted in a tube |
| nf | = | nanofluid |
| o | = | Outlet |
| p | = | Nano-particles |
| plain | = | Plain tube |
Acknowledgements
The authors are grateful to the Maulana Azad National Institute of Technology (MANIT) in India for providing the necessary technical assistance to carry out this research.
Disclosure statement
No potential conflict of interest was reported by the author(s).
Authors contribution
Bhavik V. Patel is a Ph.D. scholar in Department of Mechanical Engineering, Maulana Azad National Institute of Technology (MANIT), Bhopal, India. He has received an M.Tech. degree in Thermal Engineering from MANIT, Bhopal, India. He has worked on the experimental and numerical investigation of heat transfer enhancement in a heat exchanger tube by suggesting novel insert and using nanofluids.
R. M. Sarviya is a Professor in Department of Mechanical Engineering, MANIT, Bhopal, India. He received his doctorate degree from the Indian Institute of Technology, Roorkee, India. His field of expertise includes thermal engineering, heat and mass transfer and solar energy.
S. P. S. Rajput is a Professor in Department of Mechanical Engineering, MANIT, Bhopal, India. His field of expertise includes refrigeration, thermal engineering, human thermal comfort, and energy conversion cycles.