Awad, M.M. (2015), "Comments on “New correlations for wavy plate-fin heat exchangers: different working fluids” ", International Journal of Numerical Methods for Heat & Fluid Flow, Vol. 25 No. 2. https://doi.org/10.1108/HFF-10-2014-0321
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Comments on “New correlations for wavy plate-fin heat exchangers: different working fluids”
Article Type: Letter to the Editor From: International Journal of Numerical Methods for Heat & Fluid Flow, Volume 25, Issue 2
Khoshvaght Aliabadi et al. (2014) presented new correlations for wavy plate-fin heat exchangers (WPFHEs) using three working fluids: air, water, and ethylene glycol (Pr=0.7, 7, and 150). The researchers used the computational fluid dynamics (CFD) to obtain the numerical results. They compared and validated the simulation results with an available experimental data. They found that the mean deviations of the Fanning friction factor (f) and Colburn factor (j) values between the simulation results and the experimental data were 9.07 and 3.74 percent, respectively. The presented air correlations and experimental data were in a good agreement, so that approximately 95 percent of the experimental data were correlated within ±12 percent. The (f) factor values did not sensibly change, while the (j) factor values varied for the various working fluids.
It should be noted that there are other correlations for WPFHEs using air (Pr=0.7) in literature. For example, Awad and Muzychka (2011) proposed new models that simplified the prediction of the Fanning friction factor (f) and the Colburn (j) factor. These new models were developed by combining the asymptotic behavior for the low Reynolds number and laminar boundary layer regions. In these two regions, the models are developed by taking into account the geometric variables like: fin height (H), fin spacing (S), wave amplitude (A), fin wavelength (λ), Reynolds number (Re), and Prandtl number (Pr). The fitting parameter of pressure drop and heat transfer models was equal to two and five, respectively. For more details, the readers can see the equations of pressure drop and heat transfer models in the paper of Awad and Muzychka (2011). The proposed models were compared with numerical and experimental data for air at different values of the geometric variables obtained from the published literature such as the three data sets of Kays and London (1984). The new models for (f) and (j) covered a wide range of the Reynolds number. Since the model was based analytically, it would also allow for proper design assessment of heat exchanger performance.
It should be noted that Mahmud (2009) used also the asymptotic method to model the pressure drop and the heat transfer in compact wavy fin heat exchangers for large Prandtl number liquids (318<Pr<573). The advantage of these pressure drop and heat transfer models using the asymptotic method is that they have only one fitting parameter. The fitting parameter of pressure drop and heat transfer models was equal to two and five, respectively. Therefore, calibration of these pressure drop and heat transfer models to experimental data is greatly simplified. For more details, the readers can see the equations of pressure drop and heat transfer models in the thesis of Mahmud (2009).
Recently, Asadi and Xie (2014) presented an experimental study on heat transfer surface area of wavy-fin heat exchangers. The researchers observed the wavy-fins surface area effects on thermal-hydraulic performance of a heat exchanger. They introduced first a new method to calculate the heat transfer area of wavy-fin surfaces. Their results showed that their proposed method was accurate enough to be used in the analysis of heat exchanger performance. Their method was a direct method compared with the experimental method introduced by Kays and London (1984), and thus might be a strong tool in the optimization of heat exchangers based on various objective functions. Also, they investigated influences of some nondimensional parameters, like amplitude-to-wavelength ratio, fin space ratio, and channel cross-section ratio on the heat transfer characteristics and pressure drop.
At the end, Xie and co-workers (Song et al., 2014; Xie et al., 2014) used their model (Asadi and Xie, 2014) with the help of Constructal Theory to improve the thermal performance of a corrugated-wall channel. More information can be found in the papers of Xie and co-workers (Song et al., 2014; Xie et al., 2014).
M.M. Awad Mechanical Power Engineering Department, Faculty of Engineering, Mansoura University, Mansoura, Egypt
Asadi, M. and Xie, G. (2014), “An experimental study on heat transfer surface area of wavy-fin heat exchangers”, ASME Journal of Thermal Science and Engineering Applications, Vol. 6 No. 3, 9pp
Awad, M.M. and Muzychka, Y.S. (2011), “Models for pressure drop and heat transfer in air cooled compact wavy fin heat exchangers”, Journal of Enhanced Heat Transfer, Vol. 18 No. 3, pp. 191-207
Kays, W.M. and London, A.L. (1984), Compact Heat Exchangers, 3rd ed., Kreiger Publishing, Melbourne
Khoshvaght Aliabadi, M., Hormozi, F. and Rad, E.H. (2014), “New correlations for wavy plate-fin heat exchangers: different working fluids”, International Journal of Numerical Methods for Heat & Fluid Flow, Vol. 24 No. 5, pp. 1086-1108
Mahmud, F.B.A. (2009), “Experimental measurements and models for the thermal-hydraulic characteristics in wavy fin heat exchangers for large Prandtl number liquids”, MSc thesis, Memorial University of Newfoundland, St. John’s
Song, Y., Asadi, M., Xie, G. and Rocha, L.A.O. (2014), “Constructal wavy-fin channels of a compact heat exchanger with heat transfer rate maximization and pressure losses minimization”, Applied Thermal Engineering, Vol. 75, pp. 23-32
Xie, G., Asadi, M., Sunden, B. and Zheng, S. (2014), “Constructal theory based geometric optimization of wavy channels in the low reynolds number regime”, ASME Journal of Electronic Packaging, Vol. 136 No. 3