A. Al-Sarkhi

EFFICIENCY OF MILLER ENGINE AT MAXIMUM POWER DENSITY

Thermodynamic analysis of an ideal air-standard Miller cycle is presented in this paper. The paper outlines the effect of maximizing power density on the performance of the cycle efficiency. The power density defined as the ratio of the power to the maximum cycle specific volume. Although the efficiency of Atkinson and Joule-Brayton cycles at maximum power density is greater than that of Miller cycle, it is important to note that the total cycle volume and pressure ratio at maximum power density of Miller is smaller. The results obtained from this work can be helpful in the thermodynamic modeling and in evaluation of Miller engines over Atkinson and Joule-Brayton engines.

Effect of pipe diameter on the drop size in a horizontal annular gas–liquid flow

Abstract Measurements of the drop size distributions were obtained for air and water flowing in an annular pattern in a 2.54 cm horizontal pipe. A laser diffraction technique was used. The data were obtained at the centerline. These are compared with measurements obtained previously for annular flow of air and water in a horizontal 9.53 cm pipe in the same flow loop and with the same instrumentation. The volume median drop diameter for these two flows was found to increase with pipe diameter and to vary with D0.5 for superficial gas velocities larger than 30 m/s.

Effect of Piston Friction on the Performance of SI Engine: A New Thermodynamic Approach

This paper presents thermodynamic analysis of piston friction in spark-ignition internal combustion engines. The general effect of piston friction on engine performance was examined during cold starting and normal working conditions. Considerations were made using temperature-dependent specific heat model in order to make the analysis more realistic. A parametric study was performed covering wide range of dependent variables such as engine speed, taking into consideration piston friction combined with the variation of the specific heat with temperature, and heat loss from the cylinder. The results are presented for skirt friction only, and then for total piston friction (skirt and rings). The effect of oil viscosity is investigated over a wide range of engine speeds and oil temperatures. In general, it is found that oils with higher viscosities result in lower efficiency values. Using high viscosity oil can reduce the efficiency by more than 50% at cold oil temperatures. The efficiency maps for SAE 10, SAE 30, and SAE 50 are reported. The results of this model can be practically utilized to obtain optimized efficiency results either by selecting the optimum operating speed for a given oil type (viscosity) and temperature or by selecting the optimum oil type for a given operating speed and temperature. The effect of different piston ring configurations on the efficiency is also presented. Finally, the oil film thickness on the engine performance is studied in this paper.

Medium-range planning economics of future electrical-power generation options

In their continuous planning for load growth, electricity utilities search for the most economic generation schemes. But this will be subject to a number of constraints, such as the type of fuel available and compliance with national environmental standards. In this paper, medium-range planning economics of using alternative fuels options for electrical-power generation systems in Jordan is discussed. Imported natural gas, heavy fuel oil, coal and local oil shale are compared. A net-present-value model was used to compare electricity generation cost for different types of thermal power plants. Sensitivity analysis was performed to determine the influence of the most important variables, such as unit capital and fuel prices, discount and inflation rates. It was found that imported natural gas, as a future primary fuel, to supply new combined cycle and/or upgraded existing gas turbine stations, in Jordan, represents the best option during the study period.

Heat Transfer and Fluid Flow Characteristics of Separated Flows Encountered in a Backward-Facing Step Under the Effect of Suction and Blowing

Numerical investigation of heat transfer and fluid flow over a backward-facing step (BFS), under the effect of suction and blowing, is presented. Here, suction/blowing is implemented on the bottom wall (adjacent to the step). The finite volume technique is used. The distribution of the modified coefficient of friction and Nusselt number at the top and bottom walls of the BFS are obtained. On the bottom wall, and inside the primary recirculation bubble, suction increases the modified coefficient of friction and blowing reduces it. However, after the point of reattachment, mass augmentation causes an increase in the modified coefficient of friction and mass reduction causes a decrease in modified coefficient of friction. On the top wall, suction decreases the modified coefficient of friction and blowing increases it. Local Nusselt number on the bottom wall is increased by suction and is decreased by blowing, and the contrary occurs on the top wall. The maximum local Nusselt number on the bottom wall coincides with the point of reattachment. High values of average Nusselt number on the bottom wall are identified at high Reynolds numbers and high suction bleed rates. However, the low values correspond to high blowing rates. The reattachment length and the length of the top secondary recirculation bubble are computed under the effect of suction and blowing. The reattachment length is increased by increasing blowing bleed rate and is decreased by increasing suction bleed rate. The spots of high Nusselt number, and low coefficient of friction, are identified by using contour maps.

Effects of High Oil Viscosity on Drift Velocity for Horizontal and Upward Inclined Pipes

This paper (SPE 115342) was accepted for presentation at the 2008 SPE Annual Technical Conference and Exhibition, Denver, 21–24 September, and revised for publication. Original manuscript received for review 6 July 2008. Revised manuscript received for review 24 November 2008. Paper peer approved 6 December 2008. Summary The translational velocity, velocity of slug units, is one of the key closure relationships in two-phase flow mechanistic modeling. It is described as the summation of the maximum mixture velocity in the slug body and the drift velocity. The existing equation for the drift velocity is developed by using potential flow theory. Surface tension and viscosity are neglected. However, the drift velocity is expected to be affected with high oil viscosity. In this study, the effects of high oil viscosity on drift velocity for horizontal and upward inclined pipes are experimentally observed. The experiments are performed on a flow loop with a test section 50.8 mm ID for inclination angles of 0° to 90°. Water and viscous oil are used as test fluids. Liquid viscosities vary from 0.001 to 1.237 Pa·s. A new drift velocity model is proposed for high oil viscosity for horizontal and upward inclined pipes. The experimental results are used to evaluate the performances of proposed model for drift velocity. The calculated drift velocities are compared very well with the experimental results. The proposed model could be easily implemented into translational velocity equation. It should improve the existing two-phase flow models in the development and maintenance of heavy oil fields.

NUMERICAL INVESTIGATION OF SHROUDED FIN ARRAY UNDER COMBINED FREE AND FORCED CONVECTION

The influence of combined free and forced convection in a vertical shrouded fin is . considered in this paper. Nusselt number, Nu. and friction factor multiplied by Reynolds number. fRe, are functions of the buoyancy force which is associated strongly with the geometry of the shrouded fin the clearance above the fin tip and the spacing between adjacent fins). Nu and fRe increase nonlinearly with increasing the clearance above the fin tip. The results obtained from this work can be helpful in the characteristics evaluation of shrouded fins.

Image Adaptive Thresholding for Multiphase Wavy Flow

Multiphase flow measurement is a very challenging issue in process industry. One of the promising approaches for multiphase flow analysis is image processing. Image segmentation is very important step in multiphase flow analysis. Determination of appropriate threshold value is very critical step for correct identification of the liquid and gas phases. There are two main thresholding techniques: Global and Adaptive. Adaptive thresholding is more suitable for multiphase flow case due to it’s adaptability to image conditions such non-uniform illumination and noise. In this work, six adaptive thresholding techniques are examined for the case of wavy flow regime. These algorithms are used to estimate the wave shape and mix region between liquid and gas. In general, the adaptive algorithms are able to compensate for non-uniform illumination and they are able to estimate wave shape and mix region correctly. The execution time for the adaptive techniques is higher than global thresholding technique, but with the availability of new powerful PCs, it will become a minor issue.© 2014 ASME

THE EFFECT OF SUCTION BOUNDARY CONDITION ON THE LOCAL AND AVERAGE NUSSELT NUMBERS FOR A FREE CONVECTION FLOW REGIME

We study the effect of suction on local and average Nusselt number around a cylinder surface subjected to natural convection. The complete Navier-Stokes and energy equations are formulated in terms of stream function and vorticity. They are solved using the finite difference technique. The Rayleigh number is ranged between 1 x 10 3 to 1 x 10 5 in the current simulations. An increase in the overall Nusselt number with an increase in the suction flow rate for the three simulated Rayleigh numbers is reported. For the lowest simulated flow rate, i.e. Q = 5, the average Nusslet number difference between the three Ralyeigh number modeled cases is relatively significant. However for the maximum simulated suction flow rate, i.e. Q =40, the difference is relatively small