  Citation: Ferdows, M.; Alam, J.; Murtaza, G.; Tzirtzilakis, E.E.; Sun, S. Biomagnetic Flow with CoFe 2 O 4 Magnetic Particles through an Unsteady Stretching/Shrinking Cylinder. Magnetochemistry 2022, 8, 27. https://doi.org/10.3390/ magnetochemistry8030027 Academic Editors: Dimitri Stanicki and Sophie Laurent Received: 29 November 2021 Accepted: 8 January 2022 Published: 25 February 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). magnetochemistry Article Biomagnetic Flow with CoFe 2 O 4 Magnetic Particles through an Unsteady Stretching/Shrinking Cylinder Mohammad Ferdows 1, *, Jahangir Alam 1 , Ghulam Murtaza 2 , Efstratios E. Tzirtzilakis 3 and Shuyu Sun 4 1 Research Group of Fluid Flow Modeling and Simulation, Department of Applied Mathematics, University of Dhaka, Dhaka 1000, Bangladesh; jahangircu1994@gmail.com 2 Department of Mathematics, Comilla University, Cumilla 3506, Bangladesh; limonn@yahoo.com 3 Fluid Mechanics and Turbomachinery Laboratory, Department of Mechanical Engineering, University of the Peloponnese, 22100 Tripoli, Greece; etzirtzilakis@uop.gr 4 Computational Transport Phenomena Laboratory, Division of Physical Science and Engineering, King Abdullah University of Science and Technology, Thuwal 23955-6900, Saudi Arabia; shuyu.sun@kaust.edu.sa * Correspondence: ferdows@du.ac.bd Abstract: The study of biomagnetic fluid flow and heat transfer containing magnetic particles through an unsteady stretching/shrinking cylinder was numerically investigated in this manuscript. Biomagnetic fluid namely blood taken as base fluid and CoFe 2 O 4 as magnetic particles. Where blood acts as an electrically conducting fluid along with magnetization/polarization. The main concentration is to study a time-dependent biomagnetic fluid flow with magnetic particles that passed through a two dimensional stretching/shrinking cylinder under the influence of thermal radiation, heat source and partial slip condition which has not been studied yet as far as best knowledge of authors. This model is consistent with the principles of magnetohydrodynamic and ferrohydrodynamic. The flow equations, such as momentum, energy which is described physically by a system of coupled, nonlinear partial differential equation with appropriate boundary conditions and converted into a nonlinear system of ordinary differential equations by using suitable similarity transformations. The resultant ODEs numerically solved by applying by applying an efficient numerical technique based on a common finite differencing method along with central differencing, tridiagonal matrix manipulation and an iterative procedure. The values assigned to the parameters are compatible with human body conditions. The numerous results concerning velocity, temperature and pressure field, as well as the skin friction and the rate of heat transfer, are presented for the parameters exhibiting physical significance, such as ferromagnetic interaction parameter, magnetic field parameter, volume fraction, unsteady parameter, curvature parameter, etc. The main numerical findings are that the fluid velocity is decreased as the ferromagnetic number is enhanced gradually in both stretching or shrinking cases whereas, the opposite behavior is found for the skin friction coefficient. The rate of heat transfer with ferromagnetic interaction parameter was also monitored and found that opposite behavior occurs for stretching and shrinking cases. Comparisons were made to check the accuracy of the present numerical results with published literature and found to be in excellent agreement. Hopefully, this proposed model will control the blood flow rate, as well as the rate of heat transfer, such as magnetic hyperthermia. Keywords: biomagnetic fluid dynamics; blood; magnetic particles; stretching/shrinking cylinder; magnetic dipole; finite difference method; magnetohydrodynamic; ferrohydrodynamic; thermal radiation; heat source 1. Introduction The study of biomagnetic fluid dynamic (BFD) has attained serious attention from researchers over the last few decades because of its wide range of applications in the biomedical and bioengineering sector including magnetic resonance imaging (MRI), in Magnetochemistry 2022, 8, 27. https://doi.org/10.3390/magnetochemistry8030027 https://www.mdpi.com/journal/magnetochemistry