Browsing by Author "Rehena Nasrin, Dr."

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Numerical analysis of turbulent flow through a shell and tube heat exchanger using kays-crawford model
(Department of Mathematics(Math), BUET, 2020-11-22) Shamima Airin Sweety; Rehena Nasrin, Dr.
Shell and tube heat exchangers are considered as the most effective type of heat exchangers. These are used in various industrial process applications for performing tasks such as removal of process heat and feed water preheating, cooling of hydraulic and lube oil, cooling of turbine, compressor and engine, condensing process vapor or steam and evaporating process liquid or steam. In this research, a numerical analysis of turbulent flow has been carried out in a shell and tube heat exchanger using Kays-Crawford model to investigate the heat transfer performance of water and different concentrated water-MWCNT (Multi Walled Carbon Nanotube) nanofluids. A two-dimensional model of a part of shell and tube heat exchanger has been used which consists of a bundle of tubes through which the cooling fluid will flow in abundant supply entering from one side and maintaining a constant temperature. Hot fluid will enter from above the tubes and the tubes will be assumed to be made of stainless steel. The Reynold-Averaged Navier-Stokes (RANS) equations and heat transport equations with appropriate boundary conditions have been solved using finite element method. The implications of solid concentration, velocity and temperature of water- MWCNT nanofluid on the flow structure and heat transfer characteristics have been investigated in details. In addition, the present numerical result has been compared with that of Yang and Liu [44]. The numerical results indicate that the occurring solid volume fraction of nanoparticles, inflow velocity variation and inlet temperature variation characteristic significant changes in the flow and heat transfer performance. Moreover, it is noticed that using 3% concentrated water-MWCNT nanofluid, higher rate of heat transfer (12.24%) is achieved compared that of water (base fluid) and therefore to enhance the efficiency of shell and tube heat exchanger.
Numerical modeling of heat and mass transfer using nanofluid in a tubular reactor
(Department of Mathematics(Math), BUET, 2020-12-15) Sadikul Islam; Rehena Nasrin, Dr.
Chemical reactions occur everywhere in our everyday life, for example, in the human body, in cell phone batteries, in a rocket engine and in the pharmaceutical and chemical industry. Optimizing chemical reactors, filtration equipment, mixers, and other processes is made easy with the chemical reaction engineering. In this researchthe model provides a study of an elementary, exothermic, 2nd-order reversible reaction in a tubular reactor (liquid phase, laminar flow regime). The aim of this research is to study numerically the effect of convective heat and mass transfer flow of a viscous fluid in the reactor. Assuming that the variations in angular direction around the central axis are negligible makes it possible to reduce the model to a 2D axisymmetric model.The numerical procedure to solve the governing equations with appropriate boundary conditions will be conducted by finite element formulation based on the Galerkin weighted residual approach.The investigation of forced convection flow, heat and mass transfer phenomena through a tubular reactor is carried. The implications of heat of reaction (H), rate of reaction (R) and solid volume fraction of water-copper nanofluid () on the flow structure, heat transfer and mass transfer characteristics are presented. The results are presented in the form of isothermal lines, iso-concentrations and stream function, average Nusselt number and Sherwood number. Present numerical results have also been compared with published result and found good agreement. The rates of forced convective heat transfer and mass transfer enhance 14 and 20%, respectively for rising volume fraction (ϕ) upto 3% with compared to base fluid.