Contents lists available at ScienceDirect Journal of Energy Storage journal homepage: www.elsevier.com/locate/est Multi-objective optimization of thermal and flow characteristics of R-404A evaporation through corrugated tubes Sina Yarmohammadi a , Kazem Mohammadzadeh b, ⁎ , Mousa Farhadi a , Hossein Hajimiri c , Alireza Modir d a Faculty of Mechanical Engineering, Babol University of Technology, P.O. Box 484, Babol, Iran, b Department of Energy Engineering, Quchan university of technology, P.O. Box 94771-67335, Quchan, Iran c Azerbaijan State Agricultural University, Faculty of Engineering, Department of Information Technologies and Systems, Azerbaijan d Department of Mechanical and Materials Engineering, Florida International University, 10555 W Flagler St, Miami FL 33174, United States ARTICLE INFO Keywords: Evaporation Corrugated tube Pressure drop Genetic algorithm Artificial neural network ABSTRACT Experimental investigation and multiobjective optimization are used to find optimum combinations of pressure drop and heat transfer coefficient during R-404A evaporation inside corrugated tubes. The mass velocity of refrigerant was between 280.5 and 561 kg m -2 s -1 , the evaporating pressure kept in the range of 4–8 bar, and the heat flux was between 10 and 20 kW m -2 . Results indicate that using corrugated tubes enhance both heat transfer coefficient and pressure drop simultaneously. Artificial neural networks and multi-objective genetic algorithm have been employed in this study to detect an optimal working condition. This will be achieved by finding an optimum combination of heat transfer coefficient and pressure drop. The design variables were corrugation pitch, corrugation depth, refrigerant mass velocity, and quality of vapor. It is shown in the results that some informative design aspects involved in the performance of corrugated tube evaporators can be ob- served by multi-objective Pareto optimization. 1. Introduction The high cost of energy in recent years caused many efforts for manufacturing high performance heat exchangers. Increasing the effi- ciency of heat exchangers by techniques for increasing the heat transfer has a great effect on reducing the size of them and reducing the man- ufacturing cost. On the other hand, regardless of the size, methods for increasing the heat transfer rate in heat exchangers working with low thermal conductive material like gases and oils are so demanding. Furthermore, implementing the techniques for increasing the heat transfer in heat exchangers, help them to work properly at lower tem- peratures while having the same or higher heat transfer coefficient. Evaporators are one of the most used heat exchangers in engineering processes such as steam power plant, chemical industries and re- frigeration and air conditioning systems that experience forced boiling in their tubes. For designing a high-performance refrigeration system, pressure drop and heat transfer characteristics in the flow boiling mechanism are major concerns [1–2]. Different heat transfer improvement methods which increase the convective heat transfer rate and simultaneously increase the pressure drop have been used in heat exchangers in different industries [3–6]. Corrugated tube is one of the passive methods of heat transfer improvement which enhances heat transfer rate using mixing and restricting the fluid boundary layers near the tube surface [7]. Table 1 shows some experimental studies which have been conducted on the two phase heat transfer improvement inside the corrugated tubes. Employing the heat transfer enhancement methods in the re- frigeration units results in a remarkable decrement of the refrigeration cycle volume, the amount of refrigerant needed for running, and also the direct refrigerant emissions. Enhancement methods also result in a remarkable decrease in volume the carbon dioxide emissions due to a lower energy consumption [16]. R-404A (4% R-134a, 44% R-125, 52% R-143a), which is the con- sidered refrigerant in this paper, is a high-pressure near-azeotropic re- frigerant blend with a low point of boiling (-45.5 °C at 1 atm) and high volatility [17]. R-404A is an alternative for R-22 and R-502 in low and medium temperature refrigeration applications, including super- markets, transport, and commercial refrigeration systems. There are a few studies done on the R-404A inside the plain and enhanced tubes [18–22]. Literature review reveals that no investigation has been done so far https://doi.org/10.1016/j.est.2019.101137 Received 15 August 2019; Received in revised form 4 December 2019; Accepted 4 December 2019 ⁎ Corresponding author. E-mail address: Kazem.Mohammadzadeh@modares.ac.ir (K. Mohammadzadeh). Journal of Energy Storage 27 (2020) 101137 2352-152X/ © 2019 Elsevier Ltd. All rights reserved. T