Numerical study of an individual Taylor bubble rising through stagnant liquids under laminar flow regime

Slug flow is one of the main flow regimes encountered in multiphase flow systems especially in oil and gas production systems. In the present study, the rise of single Taylor bubble through vertical stagnant Newtonian liquid is investigated by performing complete dimensionless treatment followed by an order of magnitude analysis of the terms of equations of motion. Based on this analysis, it is concluded that Froude, E€otv€os and Reynolds numbers are the sole physical parameters influencing the dimensionless slug flow equations. Using the guidelines of the order of magnitude analysis, computational fluid dynamics simulation is carried out to investigate the dynamics of Taylor bubbles in vertical pipe using the volume-of-fluid (VOF) method. Good agreement with previous experimental data and models available in the literature is established confirming that the density ratio, viscosity ratio and the initial ratio of bubble size to pipe diameter ðLTB=DÞ have minimal effect on the main hydrodynamic features of slug flow. Based on the developed results, correlations for the terminal velocity of the Taylor bubble and the dimensionless wall shear stress are proposed showing the significance of these main dimensionless parameters and support other important theoretical and experimental work available in the literature

Wet front propagation for water jet impingement on flat surface

A casted leaded-bronze block was impinged by a circular water jet. A 30-fps digital camera was used to video record the wet front propagation process on the surface of the block. The video frames were analyzed to illustrate the effect of different key parameters on the wetting front propagation. Regression correlations were developed to describe the effect of the jet Reynolds number (Red), the ratio of the degree of jet subcooling to the initial temperature of the block ΔTsubTi and the nozzle-to-surface spacing (H) on the wetting front propagation. The correlation is applicable for the experimental ranges investigated; 12,155 ≤ Red ≤ 36,460, 0.085 ≤ TsubTi ≤ 0.107 and H ≥ 30 mm. Good agreement was found between the experimental results and the correlation predictions with a maximum deviation of 25%. At high Reynolds number, the wetting front propagation was faster due to the high velocity and flow inertia. As the ratio ΔTsubTi increased, the wetting front propagation was accelerated. The effect of the nozzle-to-surface height on the propagation speed was negligible for H ≥ 30 mm. The effect of the increased liquid head on the terminal velocity was weakened by the drag forces on the jet as well as the jet instabilities associated with the large spacing. Keywords: Jet impingement, Quenching, Wetting front propagatio

Performance improvement of power plants using absorption cooling system

In the present paper, an integration of a (Lithium Bromide–Water) absorption inlet air cooling scheme to a cooled gas turbine-based combined cycle was analyzed. The waste heat energy of the exhaust gas prior to the exit of the waste heat recovery steam generator was chosen to power the cooling system. Nubaria Power Station, 120 km South East of Alexandria has been selected as a reference plant for the present study. It includes 3 generation modules, each including 2 * 250 MW gas turbine and 250 MW Steam turbine. A thermodynamic model of the overall integrated scheme of the cooling and power cycles is introduced. A parametric study of the effect of different operational conditions, namely; ambient temperature, relative humidity, compressor inlet air temperature, and part load on performance parameters was carried out. The model shows an increase of 11% in the produced electricity when the inlet air was cooled from 30 °C to 10 °C, Also, harvesting of condensed fresh water at a rate of 3.5 gm per kg of inlet air at ambient relative humidity of 60%. The model results have been verified by observing the real performance of the plant at various ambient conditions to ensure the accuracy of the model predictions. Keywords: Absorption, Inlet air cooling, Combined cycle modeling, Waste heat recover