Flow characterization in T-shaped and cross-shaped micromixers

The understanding of physical phenomena such as flow behaviour and mass transfer performance is needed in order to develop appropriate micromixers for industrial or biomedical applications. In this article, the flow behaviour of the T-shaped and the cross-shaped micromixers with square cross-section are studied through numerical and experimental investigations. The comparisons are based on identical treated fluxes. From the particle image velocimetry (PIV) measurements, the flow topologies in the T-shaped and cross-shaped micromixers are very different. After liquid impact, it is observed that the vortex structures cover a longer part of the outlet channel in the case of the cross geometry. This result indicates that the cross-shaped micromixer could improve the mixing process in comparison with the micromixers having T geometry. A second experimental technique has been used, the electrochemical one, involving microelectrodes placed at several wall positions of the cross-shaped micromixer. The electrochemical method can locally characterize the formation of swirling flows. The high values of wall shear rate, in the impact zone, confirm the near wall disturbance created by the impingement of the flow and also the appearance of vortices that could enhance fluid mixing.     

Pressure drop optimisation in debottlenecking of heat exchanger networks

Process integration technology is now widely applied in grass-roots design, energy saving retrofit and the debottlenecking of heat exchanger networks. This technology has been used in a variety of industries and proved to be reliable and applicable in engineering design. Debottlenecking may apply to a specific part or entire unit, whether it is due to increased throughput or process modifications. One of the advanced methods for debottlenecking that is currently used is based upon fixed allowable pressure drops, through which a retrofit can be achieved without a need for pump and/or compressor replacement. This research is trying to develop a new procedure for pressure drop optimisation in debottlenecking. This procedure enables the designer to study pump and/or compressor replacement whilst at the same time optimising the additional area and operating cost of the network. It deals with the problem of optimal debottlenecking of heat exchanger networks considering minimum total cost. Moreover, one can consider the possibility of the replacement of a given pump with a smaller one. The new procedure has been effectively applied to a crude oil pre-heat train, which was subject to some 20% increase in throughput, and the corresponding results proved to be accurate enough.     

Analytical Analysis of Applying Packet Fragmentation Mechanism on Both Basic and RTS/CTS Access Methods of the IEEE 802.11b DCF Network Under Imperfect Channel and Finite Load Conditions

The mathematical modeling and performance evaluation of the IEEE 802.11 network in all its various extensions (802.11b, 802.11a, 802.11g, 802.11e, 802.11n, etc.) have already been widely explored over the past years. However, the Packet Fragmentation Mechanism (PFM), which is proposed by the IEEE work group to enhance the MAC sub-layer of the IEEE 802.11 standard in an error-prone channel, has been missed in the available literature. Yet, the PFM is the only existing solution to reduce the influence of bit error rate and the length of data packets on the packet error rate, and consequently on the performances of IEEE 802.11 networks. In this paper, we propose a new three-dimensional Markov chain in order to model, for the first time in the literature, the PFM in both Basic and RTS/CTS access methods of the IEEE 802.11b DCF network under imperfect channel and finite load conditions. Then, we develop mathematical models to derive a variety of performance metrics, such as: the overall throughput, the average packet delay successfully transmitted, the average packet drop time, the delay jitter and the packet delay distribution. Performance analysis of applying PFM on both Basic and RTS/CTS access methods of the IEEE 802.11b DCF network under imperfect channel and finite load conditions shows original results and leads to new conclusions that could not be intuitively expected.     

Application of Fuzzy C-means algorithm as a novel approach to predict solubility of hydrocarbons in carbon dioxide

In the recent years, declination of oil reservoir causes the importance of researches on enhancement of oil recovery processes become more important. One of wide applicable approaches in enhancement of oil recovery is carbon dioxide injection which becomes interested because of relative low cost, good displacement and environmentally aspects. The injection of carbon dioxide to oil reservoir causes the lighter hydrocarbons of crude oil are extracted by CO₂. This phenomena can be affected by various factors such the solubility of hydrocarbons in carbon dioxide so in the present investigation Fuzzy c-means (FCM) as a novel approach for estimation of solubility of alkanes in carbon dioxide in terms of temperature, pressure and carbon number of alkane were utilized. The predicting algorithm FCM has reliable ability to estimate solubility based on graphical and statistical results. The coefficient of determination (R²) for training and testing data are calculated as 0.9856 and 0.9529 respectively.     

Inertial preintegration for VI-SLAM by the screw motion theory

Most smoothing-based visual-inertial simultaneous localization and mapping algorithms (VI-SLAM) rely on the Lie algebra processing of the inertial measurements. This approach is limited in its decoupled update of the attitude by using SO₃ and velocity increments by SE₃. In addition to limitations on only point transformation between frames. We present a novel approach to handling inertial measurement unit (IMU) measurements between two camera frames by the screw motion theory. Where rigid body dynamics are concisely represented by the compact unit dual quaternion. With this approach, the limitations of point transformation are mitigated by the superior Plücker line transformation and the states update is achieved by a single coupled operation. To harness this consistent framework for a smoothing-based VI-SLAM, the screw motion twist parameter is based on the raw IMU measurements. Then, a consistent residual cost function with the corresponding Jacobian and covariance updates is derived for graph-optimization algorithm respecting the screw motion paradigm. A transition method is proposed to overcome the issues of over-parametrization by the unit dual quaternion. solving all singularity threats while saving the advantages of adopting the twist operator. Finally, the loftier performance of the proposed algorithms is attested by simulation and real-world experiments.