The influence of the injectors with swirling flow generating on the heat transfer in the concentric heat exchanger ☆ Gülşah Çakmak ⁎ , Cengiz Yıldız Department of Mechanical Engineering, Firat University, 23119 Elazig, Turkey Available online 19 April 2007 Abstract In this paper, undertaken to enhance heat transfer rates, swirling motion was imposed on the hot air by placing injectors with various diameters and numbers in triangle line rows on the entrance section of the inner pipe of the concentric heat exchanger. With this aim various the injectors were prepared to test in the experiments. These elements can be placed and removed easily on the entrance section of the inner pipe. The experiments were carried out for counter current flow models of the fluids at different Reynolds numbers. The heat transfer rates increased with decreasing diameter and with increasing number of the injectors used in the experiments. The results showed that up to 93% enhancements could be accomplished in heat transfer rates with this kind of swirl generators compared to heat exchanger without these elements. In the end of the study, the results showed that a rather smaller size but the same capacity heat exchanger could be proposed by using these elements imposing swirling to the fluid flowing through inner pipe. © 2007 Elsevier Ltd. All rights reserved. Keywords: Heat exchanger; Swirling flow; Injectors 1. Introduction Heat exchangers are applied to heat transfer between the fluids in the different temperatures. Heat exchangers have been widely used in many areas of the industry from the quenching of request to save the energy and energy sources to air conditioning and cooling. The most effective method for the heat transfer in the heat exchanger is improved of the heat convection coefficients in hot and cold fluid sides. In the literature, the improvement of the heat transfer is received as in order to increase in the heat convection coefficient obtained in the new system according to the heat convection coefficient in a smooth or an annular tube [1]. Production of the effective heat exchangers has been being studied to taking into consideration the energy and material saving for years. The general aim of heat transfer is reduced the dimension of the heat exchanger for the desired heat passing. The efficiency of the heat exchangers is affected from the parameters such as the physical properties of the fluids, the input temperatures of the fluids, the physical properties of the heat exchanger material, the surface area, kind shape of the interface, whether the fluid flow is laminar or turbulence and the environmental conditions. By taking into consideration these parameters, the improvement of the heat transfer in the heat exchanger could be made by using one from the active and passive methods [2]. The active methods are included the methods International Communications in Heat and Mass Transfer 34 (2007) 728 – 739 www.elsevier.com/locate/ichmt ☆ Communicated by W.J. Minkowycz. ⁎ Corresponding author. E-mail addresses: gulcakmak@firat.edu.tr (G. Çakmak), cyildiz@firat.edu.tr (C. Yıldız). 0735-1933/$ - see front matter © 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.icheatmasstransfer.2007.03.007