An experimental study of starting plumes over area sources

Experiments have been performed to study the dynamics of plumes which develop, if buoyant fluid enters a homogeneous, unstratified environment through a source of finite width. The experiments were conducted in a cubic tank of salt water with 0.8m side length into which dyed fresh water was released at a constant volume-flow rate through a circular felt at the bottom. The governing non-dimensional parameter of the flow, namely the ratio of inflow velocity to buoyancy velocity, was varied over more than two orders of magnitude in the experiments. The flow is shown to pass through two distinct phases, and a new integral model is presented which describes the flow in the early stage. For later times and at larger distances from the source, the flow is found to be well described by Turner’s model for starting plumes from point sources

EXPERIMENTS WITH RELEASE AND IGNITION OF HYDROGEN GAS IN A 3 M LONG CHANNEL

ABSTRACT This paper presents results from laboratory experiments with hydrogen dispersions and explosions in a 3 m long channel. Our objective is to get a better understanding of the phenomena and to develop tools that can analyse hydrogen dispersions and explosions. A total of 5 test series were performed with flow rates of hydrogen from 1.8 dm³/min to 75 dm³/min. The propagation of the combustible hydrogen-air cloud in the channel was observed from high-speed video recordings. The hydrogen-air cloud in the channel behaves as a gravity current and the flow appears to be well described by Froude scaling with a length scale corresponding to the height of a layer of 100 % hydrogen. The Froude numbers observed in the experiments are in good agreement with the theory of "light-fluid intrusion" for gravity currents found in the literature. Numerical simulations with the Flacs code correlate well with the experimental results. The flame propagation indicated that approximately half the height of the channel was filled with combustible mixture. We believe that this Froude scaling can be useful as a tool to analyse the consequences of hydrogen release in buildings, channels and tunnels. NOMENCLATURE Fr Froude number, [-

EXPERIMENTS WITH RELEASE AND IGNITION OF HYDROGEN GAS IN A 3 M LONG CHANNEL

ABSTRACT This paper presents results from laboratory experiments with hydrogen dispersions and explosions in a 3 m long channel. Our objective is to get a better understanding of the phenomena and to develop tools that can analyse hydrogen dispersions and explosions. A total of 5 test series were performed with flow rates of hydrogen from 1.8 dm³/min to 75 dm³/min. The propagation of the combustible hydrogen-air cloud in the channel was observed from high-speed video recordings. The hydrogen-air cloud in the channel behaves as a gravity current and the flow appears to be well described by Froude scaling with a length scale corresponding to the height of a layer of 100 % hydrogen. The Froude numbers observed in the experiments are in good agreement with the theory of "light-fluid intrusion" for gravity currents found in the literature. Numerical simulations with the Flacs code correlate well with the experimental results. The flame propagation indicated that approximately half the height of the channel was filled with combustible mixture. We believe that this Froude scaling can be useful as a tool to analyse the consequences of hydrogen release in buildings, channels and tunnels. NOMENCLATURE Fr Froude number, [-

Effect of short-acting beta blocker on the cardiac recovery after cardiopulmonary bypass

The objective of this study was to investigate the effect of beta blocker on cardiac recovery and rhythm during cardiac surgeries. Sixty surgical rheumatic heart disease patients were received esmolol 1 mg/kg or the same volume of saline prior to removal of the aortic clamp. The incidence of cardiac automatic re-beat, ventricular fibrillation after reperfusion, the heart rate after steady re-beat, vasoactive drug use during weaning from bypass, the posterior parallel time and total bypass time were decreased by esmolol treatment. In conclusion: Esmolol has a positive effect on the cardiac recovery in cardiopulmonary bypass surgeries

Sediment deposition from turbidity currents in simulated aquatic vegetation canopies

A laboratory flume experiment was carried out in which the hydrodynamic and sedimentary behaviour of a turbidity current was measured as it passed through an array of rigid obstacles. The obstacles were intended primarily to simulate aquatic vegetation canopies, but could equally be taken to represent other things, for example forests or offshore wind turbines. The turbidity currents were generated by mixing naturally-sourced, poly-dispersed sediment into a reservoir of water at concentrations from 1 to 10 gL-1, which was then released in the experimental section of the flume by removing a lock gate. For each initial sediment concentration, runs with obstacle arrays with solid plant fractions of 1% and 2.5%, and control cases with no obstacles, were carried out. The progress of the current along the flume was characterized by the array drag term, CDaxtoe (where CD is the array drag coefficient, a the frontal area of cylinders per unit volume and xtoe the current toe position along the flume). The depositional flux of sediment from the current as it proceeded was measured at thirteen traps positioned along the flume. Analysis of these deposits divided them into fine (2.2–6.2 μm) and coarse (6.2-104 m) fractions. At the beginning of the development, the gravity current proceeded in an inertia dominated regime until CDaxtoe =5. And for CDaxtoe > 5, the current transitioned into a drag-dominated regime. For both fine and coarse sediment fractions, the rate of sediment deposition tended to decrease gradually with distance from the source in the inertial regime, remained approximately constant at the early drag-dominated regime, and then rose and peaked at the end of the drag-dominated stage. This implies that, when passing through arrays of obstacles, the turbidity currents were able to retain sufficient sediment in suspension to maintain their flow until they became significantly influenced by the drag exerted by the obstacles