Raed Kafafy

Enhancing the efficiency of polymerase chain reaction using graphene nanoflakes

The effect of the recently developed graphene nanoflakes (GNFs) on the polymerase chain reaction (PCR) has been investigated in this paper. The rationale behind the use of GNFs is their unique physical and thermal properties. Experiments show that GNFs can enhance the thermal conductivity of base fluids and results also revealed that GNFs are a potential enhancer of PCR efficiency; moreover, the PCR enhancements are strongly dependent on GNF concentration. It was found that GNFs yield DNA product equivalent to positive control with up to 65% reduction in the PCR cycles. It was also observed that the PCR yield is dependent on the GNF size, wherein the surface area increases and augments thermal conductivity. Computational fluid dynamics (CFD) simulations were performed to analyze the heat transfer through the PCR tube model in the presence and absence of GNFs. The results suggest that the superior thermal conductivity effect of GNFs may be the main cause of the PCR enhancement.

Vehicle Fuel Consumption and Emission Modelling: An In-Depth Literature Review

Modelling of vehicle fuel consumption and emissions has emerged as an effective tool to help develop and assess vehicle technologies and to help predict vehicle fuel consumption and emissions. A review to identify the current state-of-the-art on vehicle fuel consumption and emissions modelling is elucidated. This review categorises vehicle fuel consumption and emissions models into five classifications. The relevant main models to each of these classifications are presented. These models are then compared with regard to assumptions, limitations, merits, drawbacks, characteristic parameters, data collection techniques, accuracy, and relevance to road traffic. The study demonstrates that the trends of vehicle fuel consumption and emissions provided by current models generally do satisfactorily replicate field data trends. In addition, the paper demonstrates that mesoscopic models, empirical models, mean value-based models, and quasi dimensional models strike a balance between accuracy and simplicity and thus are very suitable for transportation and control applications. The study shows as well that no one model as yet fully meets the needs of transportation applications.

Vaporization Characteristics of Ethanol Droplets: Influence of the Environment Humidity

The study of the gasification of a droplet via vaporization, which involves heat, mass and momentum transfer processes in gas and liquid phases, and their coupling at the droplet interface, is necessary for better understanding and modeling of complex spray and mixture formation issues. A detailed description of the vaporization of an isolated droplet has been realized in this experimental study aimed at investigating the impact of the water vapor contained in the surrounding gas on the evaporation of an ethanol droplet. The experimental set-up consists of a heated chamber with a cross quartz fibers configuration as droplet support. An ethanol droplet is located at the intersection of the cross with a controlled initial diameter (300–550μm). Ambient temperature is varied from 350 to 850 K. The real impact of the water concentration on the vaporization rate of an ethanol droplet in a large range of temperature is examined, showing that the vaporization of an ethanol droplet is accompanied by the simultaneous condensation of water vapour on the droplet surface and thus the temporal evolution of the droplet squared diameter exhibits an unsteady behaviour. The histories of the instantaneous vaporisation rates calculated from the d2 (t) curves confirms this non-stationary aspect of the phenomenon.Copyright

Air supply system transient model for proton exchange membrane fuel cell

Proton exchange membrane (PEM) fuel cells are considered one of the best potential alternative power sources. It has both high efficiency and high power density. The air supply system dictates the performance of the fuel cell. It is responsible for supplying the correct amount of mass flow rate which is essential for ensuring efficient reaction of hydrogen and controlling the pressure inside the cathode. Pressure has a direct effect on the water balance characteristics and efficiency. In this work, a dynamic model for the air delivery system, including compressor and supply manifold, is developed. The model can capture both flow and inertia dynamics of the compressor. The model is tested by simulating the transient performance of the air supply system for a transportation-size fuel cell. A feedforward control method based on the compressor map is developed. Results show the success of the model in predicting the transient behaviour of the air supply system. The model can be used to implement and test different control strategies.

Improving the efficiency of micronozzle by heated sidewalls

Heat developing by electrical field within a uniform side wall of micronozzle is established and its effect on nozzle flow parameters is tested. The continuum two-dimensional flow analysis of gas and onedimensional thermal analysis of the uniform sidewall are solved numerically and simultaneously for different configurations of heat supplying. Heat developing in the convergent-divergent sidewall shows improvement of thrust level and specific impulse due to an increase in both density and pressure at the exit section, although there is a degradation of Mach number and velocity and increase in the thickness of the subsonic boundary layer. Heat generation rate can be increased under limitations of the base metal structural properties. It is observed that heat exchange at convergent and divergent sections is more effective than preheating at the straight section before the entrance of the nozzle. It is found that; choosing the inlet boundary condition at the starting point of convergence shows additional pres...

Assessment of free-rotating air swirling device to reduce SI engine emissions and improve fuel economy

Claims are furnished in several patents; that swirling the intake air in SI engines can improve fuel economy and reduce environmental impact. In this paper, we investigate the effect of a free rotating air swirling device (FRASD) installed in the air intake hose on the overall performance and emission characteristics of an SI engine. FRASDs with three vane angles were tested; 6, 9 and 12 degrees. The baseline engine was tested without FRASD at selected loads. Then, the engine was tested at the same loads with each FRASD and results were compared with the baseline engine. Experiments show that all tested FRASDs exhibit some degree of enhancement in the overall performance and reduction in exhaust emissions. It was found that enhancement greatly depends on the engine operating condition in addition to the FRASD vane angle. Specifically, best enhancement in performance and highest reduction in emissions was observed with the 9-degrees which reduced specific fuel consumption by 12%, hydrocarbon (HC) emissions by 20% and carbon monoxide emissions by 12%. Suggestions are made to modify the FRASD design to magnify its impact on engine performance.

Modeling of Non-Uniform Thermoelement Devices Subject to Lateral Heat Convection

In this paper, we draw attention to the importance of the lateral convection heat transfer effect on the operation of thermoelements with variable cross-sectional area. The significance of lateral heat convection arises from a new application, in which thermoelements form the walls of a MEMS-based convergent-divergent micronozzle in order to pump heat from the divergent part of the micronozzle to the convergent part to enhance overall performance. To assess the effect of thermoelement, we develop a quasi-one-dimensional model for thermoelements, in which, the physical phenomena of Peltier effect, Joule heating, Seebeck effect, longitudinal heat conduction, and lateral heat convection are considered. The general energy equation of the thermoelement with variable material properties is formulated with heat convection modeled as a lateral heat source. We used the model to study thermoelements with rectangular cross section and uniform thickness, but variable width. The width of the element is maximum at the location forming the micronozzle throat. Several geometries have been investigated; a piece-wise linear, parabolic and piece-wise sine wave. Two parameters which play important role in the thermal performance of thermoelement are identified. These are the thermal resistance ratio; ratio of longitudinal conduction resistance to lateral convection resistance, and heating ratio; ratio of Joule heating to Fourier conducted heat. The effects of varying these two parameters as well as thermoelement geometry have been investigated thoroughly and the results are presented in the form of charts to assist the design and material selection of the thermoelement.

Two-dimensional flow properties of micronozzle under varied isothermal wall conditions

A new technology, which uses thermoelectric elements as side-walls of microthrusters for heating and cooling purpose, is emerging. This technique can improve the performance of low-Reynolds-number microthrusters as a result of increasing the flow momentum forces or decreasing the viscous forces. In the present paper, we focus on the effect of using heated or cooled walls to control the properties of the flow through a micronozzle. Viscous compressible laminar flow is solved in the micronozzle. Different isothermal divergent-wall temperatures are tested to study the impact of wall temperature on the fundamental properties of momentum forces. The temperature difference between the wall and the gas effects the static temperature and static pressure profile, Mach number is increased, density near the wall is increased due to cooling. Alleviation of viscous losses by cooling the supersonic flow in the expander is demonstrated by the reduction of the thickness of the subsonic boundary layer.

Hybrid rocket performance with varying additive concentrations

A hybrid rocket motor represents a compromise between a solid rocket motor and a liquid rocket motor in terms of its performance. In addition, hybrid rockets are featured by throttling capability, increased safety, moderate cost and benign environmental impact. However, low regression rate is a major drawback of hybrid rocket performance. Adding additives to the hybrid rocket fuel is one possible solution to this matter. To investigate the characteristics of hybrid rocket performance we develop a generic simulation algorithm based on a legacy interior ballistic model. MATLAB® environment was used to develop the design and performance analysis codes, and visualize the temporal variation of performance characteristics. The simulation algorithm is used to predict the performance of hybrid rocket using different types of fuels with varying metallic additive concentrations. To increase heat conduction at localized head, higher additives intensity is doped, giving adequate burning throughout the fuel. This paper also presents experimental results obtained from a laboratory scale hybrid rocket motor which employs paraffin wax fuel doped with metallic additives with varying concentrations along the hybrid rocket motor axis and gaseous oxygen as an oxidizer. Experiments are carried out to investigate how varying the additive concentration affects the regression rate and overall performance. Initial investigation reveals that varying the distribution of metallic additive concentration can improve the regression rate.

Experimental investigation of the performance of flutter-based microgenerators

Many wind harvesters have a high cut-in speed which is not available in many locations over long periods of time. The average wind speed round the year at most locations is 3-5 m/s. A novel and inexpensive low wind speed harvester design is proposed and tested in this work, winds and artificial airflows with speeds as low as 1 m/s can be harvested to generate usable electric voltage which is fed into a power conditioning and storage circuit. A commercially available micropower step up booster, conditioning and storage circuit is used and the harvester’s ability to integrate is demonstrated. Voltage and power outputs for various wind speeds are studied at different resistive loads