Optimum structured adsorbents for gas separation processes

Laminate zeolite structure prepared using papermaking techniques for carbon dioxide capture: synthesis, characterisation and performance

In conventional packed beds, mass transfer and flooding limitations lower the productivity of many processes. The almost zero sensitivity to variations in gravitational force has made centrifugal processes to have great potential for enhancing heterogeneous catalytic reactions. We studied a rotating packed bed (RPB) reactor as a gas/liquid contactor for multi-phase catalytic reactions. The scarcity of fundamental data on the hydrodynamics and mass transfer of the reactor limits the design, scale-up, and retrofitting of RPB reactors. Hence, we focused on the hydrodynamic behavior of the device. Previous studies on RPB reactor flooding and operating limits dwelled on visual observations and pressure drop variations only. However, physical visualizations are subjective because RPB reactor pressure drop variations are too inconsistent to be used to determine the upper operating limit during their operations. A robust quantitative method of obtaining RPB reactor flooding limits based on the flow rate of the ejected liquid, supported by visual observation and pressure drop measurement, was presented. The aim was to identify, with greater certainty, RPB reactor hydrodynamic characteristics and provide a more standard method of identifying it. The average increase in single-phase pressure drop per unit increase in rotation speed in the range investigated was 0.75Pa/rpm, and the average increase in pressure drop per unit increase in gas flow rate was 4.11Pa/Nm3h-1 within the operating range investigated.

Today many manufacturing firms are focusing on cycle or throughput time reduction to gain a competitive advantage. In many instances, cycle times at individual workstations are adversely affected by unscheduled machine breakdowns. In this paper, existing closed-form approximations for the expected cycle time at a parallel machine workstation with general process and interarrival times and for the variability in departures from the workstation are used to demonstrate how the mean and variance of machine repair or downtime affects cycle times at a given workstation and downstream workstations. Results from the machine interference literature are used to characterize the dependence of repair time on a base stock inventory policy used for the replenishment of spare components. Expressions for the mean and approximations for the variance of repair times are obtained for machines with either a single critical component or a series of critical components when such components fail exponentially. Numerical examples are given to illustrate the effect that spare component inventory levels have on the average station cycle time and departure variability. A methodology for base stock parameter selection that considers the trade-off between reduced cycle times and inventory investment is also presented.

Laminar flow and heat transfer in a finned tube annulus

Most approaches to increasing heat transfer rates in the convection sections of gas-fired process heaters involve the incorporation of fins, baffles, turbulizers, etc. to increase either the heat transfer surface area or turbulence or both. Although these approaches are effective in increasing the heat transfer rates, this increase is invariably accompanied by an associated increase in convection section pressure drop as well as, for heaters firing ‘dirty’ fuel mixtures, increased fouling of the tubes – both of which are highly undesirable. GTI has identified an approach that will increase heat transfer rates without a significant increase in pressure drop or fouling rate. Compared to other types of heat transfer enhancement approaches, the proposed dimpled tube approach achieves very high heat transfer rates at the lowest pressure drops. Incorporating this approach into convection sections of chemical industry fired process heaters may increase energy efficiency by 3-5%. The energy efficiency increase will allow reducing firing rates to provide the required heating duty while reducing the emissions of CO2 and NOx.

Flow field design is critical to improving the overall performance of high-temperature proton exchange membrane fuel cells. Adding baffles in the flow channel has been proven to be effective in enhancing mass transfer. In this study, fuel cells with different baffle numbers, heights, and arrangements are numerically simulated to investigate the effects of reactant velocity, concentration distribution, and pressure drop on mass transfer and output performance. The results show that baffles are beneficial in improving cell performance, especially under high current density. With the increase in baffle number and height, the concentration of the reactant at the outlet decreases and the output power increases with the increase in pressure drop. The net power density growth rate is defined to characterize the cell performance. A lower pressure drop reduces the pumping power loss generated during reactant transfer, resulting in a staggered baffle structure with the highest net power density of 4329.65 W/m2. Compared with the traditional and parallel baffle channels, this value is improved by about 11.74% and 4.83%, respectively. Therefore, the optimized baffle channel can enhance the mass transfer, reduce the pumping power, and further improve the cell performance, providing an effective guide for the optimal design and development direction of the orientated flow channel.

A number of grid-generation and CFD-process software tools have been developed which greatly improve the ability to perform overset CFD analysis of complex con gurations. These tools have been applied to the task of generating grids and computing the ow eld about two di erent high-lift aircraft con gured for landing: a Boeing 777-200, and a High-Wing Transport with externally blown aps. The high-lift owelds of both aircraft were simulated using the OVERFLOW solver. A Navier-Stokes simulation of a complete Boeing 777-200 aircraft con gured for landing was obtained in less than 50 labor days with a lift coe cient which di ers from experimental data by only 1.2%. This is an order of magnitude reduction in the cycle time for the entire computational process compared to a similar high-lift simulation e ort that took place two years earlier. The new software was utilized to perform a oweld analysis of a ap-rigging modi cation for the Boeing 777-200 aircraft in only four days. The software was also utilized to simplify Aerospace Engineer. yChief, Aerospace Operations Modeling O ce. Senior Member AIAA. zResearch Engineer. xPrincipal Engineer. Senior Member AIAA. {Engineer/Scientist Specialist. Member AIAA. kPrincipal Engineer. Copyright c 2000 by the American Institute of Aeronautics and Astronautics, Inc. No copyright is asserted in the United States under Title 17, U.S. Code. The U.S. Government has a royalty-free license to exercise all rights under the copyright claimed herein for Governmental Purposes. All other rights are reserved by the copyright owner. grid generation of the High-Wing Transport for many di erent geometric con gurations. The reductions in computational cycle time are primarily the result of the use of an automatic script system that streamlines the overset grid preparation process. Analysis of the process shows that over-setting the the grid system is now the most labor-intensive part of a single-point analysis; however, for multi-point analyses, multiple viscous ow-solver runs are costly.

Asphaltenes are complex molecular entities, which together with resins, aromatic hydrocarbons and saturates forms the crude oil. Asphaltenes and resins are in the thermodynamic equilibrium at static reservoir condition. However, asphaltene can precipitate due to changes in thermodynamic condition. Asphaltene deposition in production tubings has been an outstanding problem with wide economic impact on the oil industry. Meanwhile, the use of real-time tools to monitor depositions along the well is of great difficulty. In this work, the asphaltene precipitation region in a single phase flow wellbore is predicted for an oil well of the Iranian oil field. Then, asphaltene deposition thickness along the well is predicted for three time intervals. The simulation results indicated that asphaltene thickness exceeded more than 50% of tubing radius; therefore, a reduction in flow rate, an increase in pressure drop and tubing blockage are expected. Moreover, it is shown the deposits thickness along the wellbore has approximately a skew normal distribution shape, which could be the result of increases in velocity and excess pressure drop.

Background and Objective: This study was conducted with the aim of determining the effect of different disinfection methods on the efficiency, pressure drop, and quality of medical masks used by medical staff. The filtration efficiency of medical masks was also investigated in the present study. Materials and Methods: In the present study, four models of medical masks used by the treatment staff were selected. The masks were then disinfected with the disinfection methods recommended by the disease control and prevention centers, including heat methods, autoclaves, ultraviolet rays, immersion in 70% alcohol, and immersion in sodium hypochlorite. Finally, the effect of each disinfection method on the efficiency, pressure drop, and quality of the masks was checked using the test system. Results: Based on the results obtained from the study, disinfecting masks using thermal methods, autoclaving, ultraviolet radiation, immersion in sodium hypochlorite, and immersion in 70% alcohol caused changes in efficiency by 5.58%, 9.83%, 8.15%, 13.34%, and 20.38%, respectively. Additionally, changes in pressure drop were observed at rates of 12.9, 7, 6.92, 183.75, and 16.13 Pa, respectively. Moreover, the quality factor of masks improved after disinfection using thermal methods and autoclaving, in contrast to other methods. Furthermore, the assessment of filtration efficiency indicated that three out of four types of masks examined had efficiencies lower than 85%. Conclusion: Disinfection of medical masks using the heat method was chosen as the best disinfection method due to the least change in efficiency, a slight increase in pressure drop, and availability, and the 70% alcohol immersion method was chosen as the weakest disinfection method due to the decrease in efficiency, increase in pressure drop, and destruction of the mask's structure.

Accelerated product development is a competitive strategy that seeks to reduce the development cycle time of new products. However, there has been little theoretical advancement and empirical model testing in the identification of the conditions under which cycle time reduction is appropriate, the organizational characteristics and practices that accelerate product development, and the precise manner by which cycle time reduction affects project outcomes. Since cycle time reduction has become widely accepted as a key element in managing new‐product development, this contribution organizes and integrates the literature on accelerated product development. Specifically, we argue that the antecedents associated with shorter development cycle time are well known, but that there are inconsistencies with respect to the contextual applicability of cycle time reduction, and contradictory empirical evidence for its alleged merits in achieving lower development costs, better product quality, and greater chance of new‐product success. We attribute these inconclusive results to methodological differences in measurement approach, trade‐offs in cycle time reduction, and the hidden costs of accelerated product development. Moreover, we discuss that it is essential to take the new product's window of opportunity into account while investigating the outcomes of accelerated product development. For scholars, we provide a theoretical foundation for rigorous, empirical research. For practitioners, we list the merits of cycle time reduction, describe the situations in which it is appropriate, and delineate ways how interventions can be applied.

As the longitudinal vortex is known to be effective in enhancing heat transfer, a three-dimensional unsteady numerical analysis has been made especially for the flow and thermal fields in a unit element of flat tube heat exchanger with vortex generator (VG) in so-called middle Reynolds number range. Both staggered and in-lined arrangements of the tubes with VG are considered and results obtained from the case with VG are compared with those without VG. The study was aimed at the influence of Reynolds number and some geometrical parameters on the heat transfer and the pressure drop. Moreover, as little research has been considered the interaction between transverse vortices and longitudinal vortices in the literatures, the effect is also investigated. It is found that the longitudinal vortex plays an important role in enhancing the local heat transfer by exchanging the fluid from the tube surface region to the fresh fluid of the main flow region and lasts over long distances. Moreover, the longitudinal vortices restrain unsteady transverse vortex shedding. As a result, heat transfer rate for the flat tube with VG case is larger compared to that without VG case. From the view point of pressure drop, increase in pressure drop for the case with VG is not so much larger due to the restraint of transverse vortex shedding. Finally, heat transfer performance becomes higher for the flat tube with VG case compared to that without VG case for the same pumping power.

In the present study laminar forced convective flow of nanofluid through a converging minichannel is investigated numerically by employing two phase mixture model. The heat transfer enhancement and the corresponding pressure drop are analyzed for the following range of parameters: Reynolds number (700 ≤ Re ≤ 1650), particle volume concentration (0% ≤ ϕ ≤ 4%) and converging angle (θ = 0.029°, 0.043° and 0.05°). The results indicate that there is a considerable increase in pressure drop coupled with enhancement in heat transfer rate with particle loading due to the improvement in the thermal properties of the resulting mixture. The pressure drop in the converging channel increases with the converging angle. The pressure drop augments as high as 2 times by advancing the particle loading from 0% to 4%. The wall temperature decreases appreciably by 34 K and heat transfer coefficient is enhanced by as high as 98% from Re = 700, ϕ = 0% and straight channel to Re =1650, Hout = 2.75mm and ϕ = 4%. The enhancement in heat transfer and corresponding increase in pressure drop as compared to equivalent straight channel is presented by the performance factor, which increases with decrease in converging angle. There is a significant concern of the pumping power with increase in converging angle, volume fraction and Reynolds number.

Convection heat transfer in a shell-and-tube heat exchanger using sheet fins for effective utilization of energy

Direct contact membrane distillation with heat recovery: Thermodynamic insights from module scale modeling

This article presents two area/latency optimized gate level asynchronous full adder designs which correspond to early output logic. The proposed full adders are constructed using the delay-insensitive dual-rail code and adhere to the four-phase return-to-zero handshaking. For an asynchronous ripple carry adder (RCA) constructed using the proposed early output full adders, the relative-timing assumption becomes necessary and the inherent advantages of the relative-timed RCA are: (1) computation with valid inputs, i.e., forward latency is data-dependent, and (2) computation with spacer inputs involves a bare minimum constant reverse latency of just one full adder delay, thus resulting in the optimal cycle time. With respect to different 32-bit RCA implementations, and in comparison with the optimized strong-indication, weak-indication, and early output full adder designs, one of the proposed early output full adders achieves respective reductions in latency by 67.8, 12.3 and 6.1 %, while the other proposed early output full adder achieves corresponding reductions in area by 32.6, 24.6 and 6.9 %, with practically no power penalty. Further, the proposed early output full adders based asynchronous RCAs enable minimum reductions in cycle time by 83.4, 15, and 8.8 % when considering carry-propagation over the entire RCA width of 32-bits, and maximum reductions in cycle time by 97.5, 27.4, and 22.4 % for the consideration of a typical carry chain length of 4 full adder stages, when compared to the least of the cycle time estimates of various strong-indication, weak-indication, and early output asynchronous RCAs of similar size. All the asynchronous full adders and RCAs were realized using standard cells in a semi-custom design fashion based on a 32/28 nm CMOS process technology.