Energy and exergy analysis of ferrofluid flow in a triple tube heat exchanger under the influence of an external magnetic field

•The performance of triple tube heat exchanger is enhanced by applying magnetic field.•A minor increase in pressure drop is observed due to the induced swirling flow.•The effect of magnetic field is substantial at low Reynolds numbers.•The magnetic field is most effective when it is applied to all flow zones of the heat exchanger. A numerical study is carried out to investigate the performance of a triple tube heat exchanger exposed to a uniform magnetic field in various possible configurations. The simulations are performed for the Reynolds number range of 400–2000, under a magnetic field with 800 G, 1600 G, and 2400 G intensities, and nanoparticle volume fractions of φ = 0, 1.5, 3, and 4.5%. Swirling flows are formed in the zones containing ferrofluid due to the presence of the magnetic field. These flows cause an increase in the heat transfer coefficient (HTC) and a slight increase in the pumping power. However, the overall performance is generally improved due to applying the magnetic field. The effect of the magnetic field on the thermofluid characteristics is weakened by increasing the Reynolds number. The overall performance is highest when the magnetic field influences all flow zones. From the exergy viewpoint, a rise in entropy generation in the presence of the magnetic field leads to an overall decrease in second-law efficiency. For this case, a 5% decrease in exergy efficiency is well compensated by the considerable rise of the overall performance index, up to 68% at the intensity of 2400 G and a Reynolds number of 400. The effect of nanoparticle concentration on the performance index and pumping power is also considered. Both factors increase with augmenting the concentration of nanoparticles. It can be concluded that applying a magnetic field is beneficial for enhancing the heat transfer rate and efficiency of the triple tube heat exchanger.