This work proposes a new method for the determination of the mass diffusion coefficient in hygroscopic materials. The experiment consisted of submitting one face of the sample to a variation in time of the relative humidity (RH) and measuring the RH on its back face. The imposed RH and temperature were measured during the test and served as boundary conditions in a comprehensive computational code to solve heat and mass transfer in porous media. This model uses a physical engine embedded in the inverse procedure to determine the mass diffusion coefficient. Compared with classical methods, this new method has several advantages:It allows several samples to be measured simultaneously, simply by multiplexing the RH sensors. Accurate values can be obtained even when starting and ending out of equilibrium, which allows the characterization time to be drastically reduced. The external mass transfer coefficient has a negligible effect on the identified value. Nonstandard Fickian behaviors can be detected by the disagreement between the measured and simulated curves.The results show that the diffusivity obtained for spruce wood is in good agreement with those found with classical methods. In contrast, the fiber board results differed between the experiment and model, or yielded unrealistic values, which confirms the dual-scale nature of mass transfer that occurs in this kind of material.

This paper presents an experimental device specially designed for the continuous measurement of mass and dimensions of samples submitted to convective drying. This experimental device consists of a magnetic suspension balance and an image acquisition system. The sample deformation is determined by image correlation using a custom software. The entire system is able to achieve accurate mass and dimension measurements over a wide range of temperature and relative humidity. In order to present the potential of this equipment, experimental data of highly deformable food products (potato and apple) submitted to several drying conditions are presented. The obtained results confirm that it is required to consider the actual sample surface to 2 determine the mass flux. This allowed a first drying stage to be observed for potato.Clear differences in physical behavior of these two vegetable products were also observed, for example, an isotropic shrinkage behavior for potato and an anisotropic behavior for apple. These results were explained by the anatomical structure of the products.

We experimentally study drops formed from a nozzle into an immiscible, crossflowing phase. Depending on the operating conditions, drops are generated either in dripping or jetting mode. We investigate the impact of the continuous and dispersed phase velocities, dispersed phase viscosity and interfacial tension on the drop generation mode and size. We find that a dripping to jetting transition (DJT) takes place at a critical inner Weber number, function of the outer capillary and Ohnesorge numbers. Two jetting regimes occur depending on the phase velocity ratio. When the continuous phase velocity is significantly greater (resp. lower) than the dispersed phase velocity, jet narrowing (resp. widening) occurs. In jet widening, the critical inner Weber number depends little on the outer capillary number whereas in jet narrowing, it sharply decreases as the outer capillary number increases. We propose a comprehensive model to describe the DJT based on the attached drop equation of motion. The model satisfactorily predicts the DJT and the effect of the outer capillary number on the critical inner Weber number. It also well accounts for the drop diameter in jet narrowing. I. INTRODUCTION Membrane emulsification is an industrial process used to generate emulsions by forcing a dispersed phase through an inorganic, porous membrane into a continuous cross-flowing phase. 1 This process is usually operated in dripping (drop by drop) mode. The shear stress exerted by the continuous phase controls drop formation, so drag and the retaining capillary force are the main forces involved. In dripping mode, the drop diameter decreases with increasing shear stress, while remaining greater than the membrane pore size. A first estimate of the drop diameter may be given by a simple torque balance about the pore edge. 2 More recently, alternative fabrication methods based on microfluidics have appeared, such as flow-focusing and coflowing devices. These devices commonly operate in dripping or jetting (continuous jet) mode. 3-6 In jetting mode, the liquid thread breaks up by Plateau-Rayleigh instabilities. In certain operating conditions, drops much smaller than the nozzle diameter may be produced. The same trend is expected for membrane emulsification operated in jetting mode. Thus, it is of high interest to study the dripping to jetting transition (DJT) in this process. A DJT can occur if the liquid thread exiting the nozzle grows to a length comparable to its radius and if the pinch-off time is larger than the thread growth time. 7 The simplest case is the dripping faucet, where a dispersed phase flows from a nozzle into a stagnant, immiscible outer phase. Smith and Moss 8 studied mercury jets into gases and found that above a critical velocity (named the jetting velocity), the liquid exits the nozzle as a jet. They proposed an empirical expression for the jetting velocity, which can be recovered from a simple balance between the jet momentum flux and the retaining capillary force. Scheele and Meister 9 investigated the DJT for fifteen l...