Effect of geometrical parameters on the evaporative heat transfer and pressure drop of R-134a flowing in dimpled tubes
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ORIGINAL
Effect of geometrical parameters on the evaporative heat transfer and pressure drop of R-134a flowing in dimpled tubes Kanit Aroonrat 1 & Lazarus Godson Asirvatham 2 & Ahmet Selim Dalkılıç 3 & Omid Mahian 4,5 & Ho Seon Ahn 6 & Somchai Wongwises 1,7 Received: 5 January 2020 / Accepted: 4 September 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract An investigation was experimentally performed to explore the influence of geometrical parameters on the evaporative heat transfer coefficient and pressure drop of R-134a in dimpled tubes. The test sections were the counter-flow tube-in-tube heat exchanger, where the refrigerant was evaporated in the inner tube and hot water flows in the annulus. Seven dimpled tubes with various helical pitches (p), dimpled pitches (z), and dimpled depths (e) were used as the test tubes. The test runs were carried out over mass fluxes of 300, 400, and 500 kg/m2s; heat fluxes of 20, 25, and 30 kW/m2; and evaporating temperatures of 7, 10, and 13 °C. The results show the heat transfer enhancement factor (HF) and pressure drop penalty factor (PF) increase with a rise in e and a decrease in p and z. The HF and PF range between 1.03–1.7 and 1.76–9.00, respectively. The correlations for predicting the Nusselt number and the friction factor of R-134a during evaporation in dimpled tubes are proposed. Keywords Evaporation . Heat transfer . Pressure drop . Dimpled tube
liquid only Froude number, Frlo = G2/gDρl2 friction factor interfacial friction factor mass flux, kg/m2 s earth gravity, g = 9.81 m/s2 heat transfer enhancement factor heat transfer coefficient, W/m2 K single-phase liquid heat transfer coefficient specific enthalpy, J/kg specific enthalpy of vaporization, J/kg thermal conductivity, W/m K length of test tube, m
Nomenclature Ai inner surface area of the test section, m2 Bd Bond number, Bd = g(ρl-ρg)D2/σ Bo Boiling number, Bo = q”/Gifg CT corrugated tube cp specific heat at constant pressure, J/kg K D tube diameter, mm DT dimpled tube EHT Enhanced heat transfer tube EI efficiency index e depth of dimple, mm Ff Fluid-dependent parameter, Ff = 1845 for R-134a
Frlo f fi G g HF HTC HTCl i ifg k L
* Somchai Wongwises [email protected]
4
School of Chemical Engineering and Technology, Xi’an Jiaotong University, Xi’an, China
1
Fluid Mechanics, Thermal Engineering and Multiphase Flow Research Lab (FUTURE), Department of Mechanical Engineering, Faculty of Engineering, King Mongkut’s University of Technology Thonburi, Bangmod, Bangkok, Thailand
5
Renewable Energy and Micro/Nano Sciences Lab., Department of Mechanical Engineering, Ferdowsi University of Mashhad, Mashhad, Iran
2
Department of Mechanical Engineering, Karunya Institute of Technology and Sciences, Coimbatore, Tamil Nadu, India
6
Department of Mechanical Engineering, Incheon National University, Incheon, Republic of Korea
3
Heat and Thermodynamics Division, Department of Mechanical Engineering, Yildiz Technical University, Yildiz, Istanbul, Besiktas, Turkey
7
National Science and
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