Numerical analysis of the surface and geometry of plate fin heat exchangers for increasing heat transfer rate

International Journal of Energy and Environmental Engineering https://doi.org/10.1007/s40095-018-0270-z ORIGINAL RESEARCH Numerical analysis of the surface and geometry of plate fin heat exchangers for increasing heat transfer rate Iman Shahdad1 · Farivar Fazelpour2 Received: 20 January 2018 / Accepted: 12 March 2018 © The Author(s) 2018 Abstract This paper investigates the flow field and turbulent flow heat transfer around an array of plain and perforated fin using Fluent software within the range of 20,000–50,000 Reynolds. Regarding the turbulent flow, the k-ε RNG turbulence model was implemented, and SIMPLE algorithm was used for solving the equations of three-dimensional, steady, and incompressible flow. In the simulation process, air was considered as the working fluid with consistent physical properties. The results revealed that perforated fins increase the heat transfer coefficient as well as Nusselt number. The highest heat transfer coefficient and Nusselt number was achieved for perforated fins with two square holes. Moreover, it was concluded that increase of Reynolds number notably increases the heat transfer coefficient and Nusselt number. The total drag force imposed to plain fins was higher than the force imposed to perforated fins. As a result, by changing plain fins into perforated fins, the pressure decreases due to passage of the flow through the pins, and accordingly, the total drag force imposed to the fins decreases. Finally, it was revealed that attaching some pins on the plain fins along the passing flow will decrease the pressure, while notably increase the heat transfer. Furthermore, it can reduce the fins’ weight and price. Keywords Convection heat transfer · Reynolds number · Nusselt number · Total drag force · Turbulent flow Introduction Since 1973 oil crisis (when the members of the Organization of Arab Petroleum Exporting Countries announced an oil sanction), environmental issues including energy saving has increasingly found importance. Moreover, world population growth has led to increase of energy demand. Although energy consumption has brought about great profits, such issues as environmental pollution and the effects of consuming energy resources over human health has caused a number of concerns to emerge. One of the keys to resolve this problem is “Meaningful Energy Conservation”, and a precondition of realizing this concept is design and definition of operational conditions for heat exchangers. * Farivar Fazelpour 1 Department of Mechanical Engineering, Faculty of Engineering, Islamic Azad University, South Tehran Branch, Tehran, Iran 2 Department of Energy Systems Engineering, Faculty of Engineering, Islamic Azad University, South Tehran Branch, Tehran, Iran A heat exchanger is a machine that transfers the heat of a fluid to one or more other fluids with different temperatures. As a result, the heat exchangers are implemented in all industrial and commercial usages, and even those aspects of normal life that are related to energy transfer. Each living creature is somehow equipped with a heat exchanger. Heat exchangers are manufactured in very small and very huge sizes. The smallest heat exchangers (less than 1 W) are used for superconductor electronic applications, guiding missiles controlled by the thermal source, etc. The biggest heat exchangers (more than 1000 mW) are implemented in large power plants as boiler, condenser or cooling tower. Heat exchangers are widely used in different industrial units like power plants, refineries, metal molding and glass industries, food and medicine industries, paper making, petro chemistry, cold storage, heating and cooling systems for buildings, gas congestion industries, land, sea and space vehicles, and finally electronic industries. Smaller size of a heat exchanger is a measurement of industrial growth at present [1]. Regarding the increasing growth of cryogenics, plate fin heat exchangers are usually appropriate for implementation in a wide range of industries. The plate fin units are usually used in counter flow 13 Vol.:(0123456789) International Journal of Energy and Environmental Engineering heat exchangers. This type of heat exchangers have thin corrugated fins or corrugated heat transfer surface of the plates [2]. The density of small heat exchangers’ surface 2 is very high, and it can be as much as 1800 m . Due to its m3 high heat transfer rate, plate fin heat exchangers are highly important now, and are widely used [3]. Regarding the energy transfer, efficiency of heat exchangers in satisfaction of the requirements for energy standards (based on low cost and environmental impact) is highly important [4]. In this paper, first, the plate fin heat exchangers and their performance has been considered, and then a plate fin heat exchanger in Ansys-Fluent was simulated to analyze the geometry of different fins, heat transfer, and pressure drop in different Reynolds numbers. Finally, the simulation results will be compared with each other to obtain the highest rate of heat transfer among Reynolds numbers. There are well-cited researches in this regard. Johnson and Moshfegh made an experiment on seven different types of thermal performance of plate fin, strip fin, and pin fin heat sinks in a wind tunnel with turbulent flow. The authors investigated thermal resistance and pressure drop [5]. Kays and London conducted a number of integrated experiments to obtain such factors as friction and heat transfer for different types of plate fin heat exchangers [6]. Velayati and Yaghoubi conducted a numerical study on an array of parallel fins, and calculated the Nusselt number and pressure drop in the turbulent flow by changing the width of the fins and the distance among them. By decreasing the proportion of fins’ width to the distance among them, the Nusselt number and friction coefficient increased both [7]. Razelos and Kakatsios obtained the optimal dimensions of the fins with Heat transfer and radiation heat transfer. The authors investigated hyperbolic fins and achieved the results by simplifying the equations [8]. Computational fluid dynamics has a good flexibility in formation of computational models, in a way that required physical conditions will be prepared for the model, without any need to construct an experimental model. Wang, et al. conducted a numerical study on fluid flow and heat transfer in plain and offset plate fin heat exchangers within the quiet Reynolds number range. The researchers compared the results of their study with the results of Kays and London [6] at the end [9]. Asako and Faghri analyzed the heat transfer characteristics in a turbulent flow around arrays of heated blocks encountered on the wall of two parallel sheets on a channel. A wide range of geometrical parameters were considered in this study, and k-ε turbulence model was implemented to solve the equations [10]. Flow behavior in plate fin heat exchangers has been analytically and experimentally (...truncated)