Effects of sample rheology on the equilibrium position of particles and cells within a spiral microfluidic channel

Elasto-inertial migration in non-Newtonian fluids is a rapidly growing field with tremendous potentials for manipulating micron to submicron particles. Previous research attempts were mainly carried out in straight channels due to the complexity of particle migration, solution tuning, and data analysis in elasto-inertial microfluidics. Consequently, the combined effects of Dean drag force and solution rheology on coupled Dean drag elasto-inertial focusing phenomena have not been carefully analyzed. This study delved thoroughly into the combined effects of solution rheology and Dean drag force on elasto-inertial focusing of particles and cells within a spiral microchannel. Polyethylene oxide (PEO) of 1MDa, 2MDa, and 4MDa molecular weights were used to prepare 250, 500, and 1000 ppm non-Newtonian solutions to investigate the focusing behavior of particles and cells over a wide range of flow rates and solution rheologies. Dean coupled elasto-inertial effects were systematically investigated to demonstrate its potentials for position-adjustable and size-tunable particle and cell focusing phenomenon. Various cells and microbeads with diameters ranging from 1 to 17 μm were employed to carefully study the equilibrium position, focusing band, and migration behavior under different elastic, inertial, and Dean conditions. Following the focusing, cell viability, morphology, and growth rate were evaluated which showed cells remained undamaged from viscosity, shear rate, and chemical properties of PEO solutions. We are of the opinion that the current study can provide scientists with a better understanding of focusing phenomena in viscoelastic fluids within spiral microfluidic channels

Flow boiling heat transfer and pressure drop characteristics of Isobutane in horizontal channels with twisted tapes

© 2020 Elsevier Ltd Using twisted tapes as a passive method for heat transfer improvement in a two-phase flow heat exchanger is experimentally studied. The test evaporator is a copper channel with a length of 1000 mm and an internal diameter of 8.1 mm which is installed horizontally. Three twisted tapes with twist ratios of 4, 10, and 15 are used at refrigerant vapor qualities in the range of 0.1–0.8 and refrigerant mass velocities between 160-350 kgm−2s−1. The natural refrigerant Isobutane (R600a) is chosen as the working fluid because it is environmentally friendly. According to the experiments, installing twisted tapes inside the channel augments both heat transfer rate and pressure drops over the plain channel. It is also observed that for both plain and twisted tape inserted channels, the values of heat transfer coefficients and pressure losses grow by giving rise to the refrigerant mass velocity and vapor quality. Results showed that the system performance factor varied between 0.44–1.09 offering that using twisted tapes as a turbulator is beneficial under specific operating conditions. The empirical data showed that there is an optimum value of the working fluid mass velocity at which the performance of twisted tape inserted channels is higher