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Abstract
In this study, the optimal location of baffle in the header of air-to-air plate heat exchangers and the geometry of the header and the effects of triangular fins arrays on the effectiveness were numerically investigated for different flow rates and Reynolds numbers on different models. The main purpose of inlet baffle and geometry changes is to improve the pattern of flow distribution and assist flow uniformity. The investigations show that the optimal location of the inlet baffle with high Reynolds numbers has an insignificant effect on effectiveness, while with Reynolds numbers 250–3000, the effectiveness is affected significantly by baffle location. On the other hand, the reduction in flow gradients by changes in geometry can improve flow distribution. Moreover, investigations show that the increase in fin density (fins/mm) up to a specific value can enhance the effectiveness. In the present study, the Colburn j-factor behavior versus different Reynolds numbers, velocity distributions, pressure drops, and velocity vectors is examined.
NOMENCLATURE
| C | = | heat capacity rate, J s−1 K−1 |
| Cp | = | pressure coefficient, dimensionless |
| Cp | = | specific heat capacity, J kg−1 K−1 |
| D | = | diameter of inlet duct, m |
| H | = | distance between the heat transfer plates, m |
| h | = | heat transfer coefficient, W m−2 K−1 |
| hw | = | height of inlet duct studied by Wen et al. [Citation6], m |
| j | = | Colburn j-factor, dimensionless |
| L | = | distance between inlet duct and heat transfer plates, m |
| l | = | distance between inlet duct and baffle, m |
| lw | = | length of header studied by Wen et al. [Citation6], m |
| n | = | fin density, m−1 |
| Pr | = | Prantdl number, dimensionless |
| q | = | heat transfer rate, W |
| Re | = | Reynolds number, dimensionless |
| rw | = | radius of header studied by Wen et al. [Citation6], m |
| Sg | = | global flow maldistribution parameter, m s−1 |
| T | = | temperature, K |
| t | = | fins thickness, m |
| V | = | velocity, m s−1 |
| Vi | = | local velocity, m s−1 |
Greek Symbols
| α | = | angle between the fins and heat transfer plates, dimensionless |
| ϵ | = | effectiveness, dimensionless |
| θ | = | velocity ratio, dimensionless |
| ρ | = | density, kg m−3 |
Subscripts
| ave | = | average |
| c | = | cold fluid |
| h | = | hot fluid |
| i | = | inlet |
| max | = | maximum |
| min | = | minimum |
| o | = | outlet |
Additional information
Notes on contributors
Sina Salehi
Sina Salehi is a Ph.D. student under the supervision of Dr. Mohammad Seyyed Mahmoodi at University of Tabriz, Tabriz, Iran. He received his B.Sc. in mechanical engineering in 2010 from Amirkabir University of Technology, Tehran, Iran. Moreover, he received his M.Sc. in mechanical engineering in 2012 under the supervision of Prof. Hossein Afshin and Prof. Bijan Farhanieh from Sharif University of Technology, Tehran, Iran.
Hossein Afshin
Hossein Afshin is an assistant professor in the Mechanical Engineering Department at Sharif University of Technology, Tehran, Iran. He received his M.Sc. and Ph.D. degrees from Sharif University of Technology. He has been teaching at Sharif University since 2010. He directs the research group of process integration in the Center of Excellence in Energy Conversion. His main research interests include heat exchangers, renewable energy, computational fluid dynamics, and two-phase flow. He is currently working on enhanced heat transfer in heat exchangers. He has co-authored more than 20 journal papers.
Bijan Farhanieh
Bijan Farhanieh is a professor of mechanical engineering at Sharif University of Technology in Tehran, Iran. He earned his B.Sc. from Sussex University at Brighton, England, in 1981. He worked as a project engineer for about 4 years in power generation industries. He received his Ph.D. from Chalmers University of Technology in Sweden in 1991. He directs the research group of process integration in the Center of Excellence in Energy Conversion. His main research interests are thermal fluid dynamics, computational fluid dynamics (CFD), thermal systems, and stochastic processes. He has co-authored more than 80 journal papers. He has also authored three books, on physics of turbulence, dynamics of heat fluxes, and viscous fluid flows.