Passive Control of Base Pressure in a Converging-Diverging Nozzle with Area Ratio 2.56 at Mach 1.8

In this study,a duct is considered and special attention is paid to a passive method for the control of the base pressure relying on the use of a cavity with a variable aspect ratio.The Mach number considered is 1.8,and the area ratio of the duct is 2.56.In particular,two cavities are examined,their sizes being 3:3 and 6:3.The used L/D spans the interval 1–10 while the NPRs(nozzle pressure ratio)range from 2 to 9.The results show that the control becomes effective once the nozzles are correctly expanded or under-expanded.The pressure contours at different NPR and L/D are presented.It is shown that the NPR and cavity location strongly influence the base pressure.The NPR,Mach number,and cavity aspect ratio have a strong effect on the base pressure in the wake region.

Computational Analysis of Surface Pressure Distribution over a 2D Wedge in the Supersonic and Hypersonic Flow Regimes

The complex fluid-dynamic instabilities and shock waves occurring along the surface of a two-dimensional wedge at high values of the Mach number are studied here through numerical solution of the governing equations.Moreover,a regression model is implemented to determine the pressure distribution for various Mach numbers and angles of incidence.The Mach number spans the interval from 1.5 to 12.The wedge angles(θ)are from 5°to 25°.The pressure ratio(P2/P1)is reported at various locations(x/L)along the 2D wedge.The results of the numerical simulations are compared with the regression model showing good agreement.

A review of chemical absorption of carbon dioxide for biogas upgrading

Significant attention has been given to biogas production, purification and upgrading as a renewable and clean fuel supplement. Biogas is a product of an anaerobic digestion process comprising methane, carbon dioxide,and trace amounts of other gases. Biogas purification removes trace gases in biogas for safe utilisation. Biogas upgrading produces methane-rich biogas by removing bulk carbon dioxide from the gas mixture. Several carbon dioxide removal techniques can be applied for biogas upgrading. However, chemical absorption of carbon dioxide for biogas upgrading is of special significance due to its operation at ambient or near ambient temperature and pressure, thus reducing energy consumption. This paper reviews the chemical absorption of carbon dioxide using amine scrubbing, caustic solvent scrubbing, and amino acid salt solution scrubbing. Each of these techniques for biogas upgrading is discussed. The paper concludes that an optimised implementation of the chemical absorption techniques for biogas upgrading requires further research.

Genetic Algorithm Routing Protocol for Mobile Ad Hoc Network

Mobile ad hoc network(MANET)is a dynamically reconfigurable wireless network with time-variable infrastructure.Given that nodes are highly mobile,MANET’s topology often changes.These changes increase the difficulty in finding the routes that the packets use when they are routed.This study proposes an algorithm called genetic algorithm-based location-aided routing(GALAR)to enhance the MANET routing protocol efficiency.The GALAR algorithm maintains an adaptive update of the node location information by adding the transmitting node location information to the routing packet and selecting the transmitting node to carry the packets to their destination.The GALAR was constructed based on a genetic optimization scheme that considers all contributing factors in the delivery behavior using criterion function optimization.Simulation results showed that the GALAR algorithm can make the probability of packet delivery ratio more than 99%with less network overhead.Moreover,GALAR was compared to other algorithms in terms of different network evaluation measures.The GALAR algorithm significantly outperformed the other algorithms that were used in the study.

Assessment of engine's power budget for hydrogen powered hybrid buoyant aircraft

It is well known that hydrogen has less undesirable exhaust emissions as compared with other types of liquid fuels.It can be used as an altemative fuel for a hybnid buoyant aircraft in which half of the gross takeoff weight is balanced by the aerostatic lift.In the present study,weight advantage of liquid hydrogen as an ideal fuel has been explored for its further utilization in such aircraft.Existing relationships for the estimation of zero lift drag of airship is discussed with special focus on the utilization of such analytical relationships for the aircraft whose fuselage resembles with the hull of an airship.Taking the analytical relationship of aircraft and airship design as a reference,existing relationships for estimation of power budget are systematically re-derived for defined constraints of rate of climb,maximum velocity and takeoff ground roll.It is perceived that when the propulsion sizing for liquid hydrogen is required,then the presented framework for estimation of its power budget will provide a stating point for the analysis.An example for estimation of the power requirement is also presented as a test case.

Chemical resistance tests on PP-ternary nanocomposite for its application in bioreactor liner fabrication

Continuous usage of bioreactor causes early degradation of most bioreactor liner materials due to the effects of various chemicals, consequently resulting in contamination in the bioprocess. Performance of PP-ternary nanocomposite (PPTN) for its potential application in the fabrication of bioreactor liner material was investigated in this study. The chemical resistance of the composite samples obtained was tested by exposing them to chemicals such as acid, alkaline, water and bacterial solutions, according to ASTM 543-06, and their effects on the composite samples were carefully observed. Specifically, the investigation focused on the changes in the physico-mechanical properties of PPTN following long term of exposure to these chemicals. The results show slight increase in the weight and dimensions of samples in the first few days, followed by constant reading for the period of 4 weeks. The performance in terms of physical properties was in the range of PPTN with 0.61% MWCNT > PPTN 0.45% > PPTN 0.17%. The maximum percentage change in tensile properties, observed in this study, was approximately 10% against PPTN (0.17%), which indicates stable mechanical properties of the composite and invariably suggests that the nanocomposites could serve as a better alternative for bioreactor liner fabrication.