Browsing by Subject "Laminar flow"
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Item A finite difference study of transient heat transfer involving hydrodynamic variation in the thermal entrance region of a circular tube(Texas Tech University, 1970-08) Kliewer, Raymond M.Not availableItem A study of thermal transients involving hydrodynamic variation in the thermal entrance region of a circular tube(Texas Tech University, 1968-06) Kliewer, Raymond M.A study of the induced hydrodynamic flow transient and the imposed thermal transient associated with step increases in wall temperature for laminar gas flow in a clrcular tube is presented. The basic governing equations are derived with property variations taken into account. The governing equations are put into an appropriate form for numerical solution. Problem data are specified using air as the gas, and solutions are obtained for three different step increases in the tube wall temperature. It is determined that the step increase in wall temperature produdes not only a thermal transient but also an induced hydrodynamic transient resulting in a corresponding friction factor transient.Item An apparatus for heat transfer and frictional studies of gas flow in a tube with large temperature differences(Texas Tech University, 1965-05) Chance, James LarryThe design of an apparatus for heat transfer and frictional studies of gas flow in a tube with large temperature gradients is presented. This experimental apparatus is unique in that it incorporates heat flux meters, temperature and velocity probes, and a means of varying the heat flux distribution. Temperature and velocity profiles, previously not available, can be obtained by traversing the air stream with the probes. Direct measurements of the heat flux can be made with the heat flux meters. With this apparatus more accurate values for heat transfer coefficients and friction factors should be obtained, as well as a far greater insight into the physical problem.Item An experimental investigation of heat transfer and friction in a circular tube for laminar flow of air under conditions of large transverse temperature gradients(Texas Tech University, 1969-05) Chance, James LarryNot availableItem Computations of strongly forced laminar cold-flow jet and methane-air diffusion flames(2006) Barve, Vinayak Vidyadhar; Ezekoye, Ofodike A.Previous work has shown that for sufficiently high periodic forcing amplitudes, laminar diffusion flames can burn in an effectively partially premixed mode. Experimental observations show that the luminosity and sooting properties of the forced flames are significantly modified by the presence of strong forcing. In this work, simulations are performed to study the effects of strong forcing on flow field development in strongly forced laminar isothermal jets and methane air diffusion flames. Unforced and strongly forced cold-flow jets are simulated using a higher order finite volume CFD code. The jet was forced by varying the jet exit velocity over a range of forcing amplitudes and frequencies and it was found that the jet Strouhal number (St) was the important parameter in characterizing flowfield development. Further, the forced jets showed increased entrainment and increased entrainment rates as compared to the non-forced jets. The computations are extended to laminar methane–air diffusion flames. The combustion reactions were modeled using detailed gas-phase chemistry and complex thermo-physical properties. The radiation heat transfer was modeled using the S-6 Discrete Ordinates Method. A 2 equation soot chemistry model for soot nucleation, surface growth and oxidation was used. First an unforced flickering methane–air diffusion flame was modeled and then the flame was forced by varying the amplitude and frequency of the fuel velocity in the nozzle. Cases where the peak velocity in the fuel stream reached 6 times the mean velocity are examined. The internal nozzle flow was also simulated since the near-nozzle region was of particular interest due to the strong mixing processes occurring there and the subsequent effect on the flame properties. Lifted forced flames were also examined, and it was found that the partial premixing in the near nozzle region and modified gas phase chemistry in the forced flames can explain the reduction in soot production for the strongly forced flames.Item Computer simulation of the laminar upflow of air in heated vertical tubes(Texas Tech University, 1970-08) Koski, Jorman AlbertA computer oriented numerical model based on integral equations is used to simulate the leuninar upflow of air in a heated vertical tube. The simulations are based on boundary conditions encountered by Gerald S. Kirby and James L. Chance of Texas Tech University while conducting an experimental, analysis of the problem. The computer results are compared to the experimental results both in the flow fields produced and in the friction factors and Nusselt numbers determined. In addition, the computer model is used to study the effect of free convection on the flow field. The data derived are then used to develop friction factor and Nusselt number correlations which account for the free convection effects present.Item Directing cell migration by dynamic control of laminar streams(2010-12) Moorjani, Samira Gian; Shear, Jason B.; Morrisett, Richard; Zhang, John X.; Aldrich, Richard W.; Zaman, MuhammadInteractions of cells with their chemical microenvironments are critical to many polarized processes, including differentiation, migration, and pathfinding. To investigate such cellular events, tools are required that can rapidly reshape the microscopic chemical landscapes presented to cultured cells. Existing chemical dosing technologies rely on use of pre-fabricated chemical gradients, thus offering static cell-reagent interactions. Such interactions are particularly limiting for studying migration and chemotaxis, during which cells undergo rapid changes in position, morphology, and intracellular signaling. This dissertation describes the use of laminar streams, containing cellular effector molecules, for precise delivery of effectors to selected subcellular regions. In this approach, cells are grown on an ultra-thin polymer membrane that serves as a barrier to an underlying reagent reservoir. By using a tightly-focused pulsed laser beam, micron-diameter pores can be ablated in the membrane upstream of desired subcellular dosing sites. Emerging through these pores are well-defined reagent streams, which dose the targeted regions. Multiple pores can be ablated to allow parallel delivery of effector molecules to an arbitrary number of targets. Importantly, both the directionality and the composition of the reagent streams can be changed on-the-fly under a second to present dynamically changing chemical signals to cells undergoing migration. These methods are applied to study the chemotactic responses of neutrophil precursor cells. The subcellular localization of the chemical signals emerging through pores is found to influence the morphological evolution of these motile cells as they polarize and migrate in response to rapidly altered effector gradients.Item Pressure gradient in the laminar non-isothermal flow of a gas through a vertical tube(Texas Tech University, 1969-12) Hitchcock, Woodrow WilsonNot availableItem The effect of transverse temperature gradients on the velocity and temperature profiles for laminar flow of air(Texas Tech University, 1969-05) Kirby, Gerald SimmonsNot availableItem The effects of boundary layer development and turbulence on the performance of a gas-blown spark gap switch(Texas Tech University, 1984-12) Glass, Bradley LyleThe effects of boundary layer development and turbulence on a gas-blown spark gap switch operated in the self breakdown mode are presented. The switch consisted of two electrodes mounted flush in the diverging walls of a wind tunnel. The electrode spacing was 2.54 mm at the minimum separation distance and the wind tunnel had an aspect ratio based on the minimum separation distance of 40:1 to insure two-dimensional flow. To obtain various stages of boundary layer development for laminar flow, entry lengths of 0, 6.19, 17.46, 22.78, and 57.3 cm were used. These were tested at divergence angles of 5.0 and 10.0 degrees. Turbulence was investigated by placing a coarse, plastic grid 7.62 mm" upstream of the minimum electrode spacing using the 22.78 cm entry length and a 10.0 degree divergence angle. The gas used was instrument grade dry air (< 10 ppm H2O), and the electrode material was 304 stainless steel. It was found that switch performance at low flow velocities was improved with entry lengths up to 17.46 cm and then deteriorated with increasing length. This suggests that there is a stage of boundary layer development that produces optimum switch operation at minimum flowrates. The results also suggest that there is an average gas density level that must be attained at the minimum separation point before the maximum voltage can again be applied to the switch. For the only turbulence test conducted, 10.0 degree divergence angle with an entry length of 27.78 cm, switch performance was improved as compared with the laminar case.Item The effects of mass flow rate and electrode divergence angle on the performance of gas-blown spark gap switches(Texas Tech University, 1984-05) Clarke, James RichardThe effects of mass flow rate and electrode divergence angle on the performance of a gas-blown spark gap switch operated in the self-breakdown repetitive mode are presented. The switch was flushed with a two-dimensional, laminar flow directed between a diverging pair of electrodes. Voltage versus t i a e data were obtained for two average flow velocities, based on the flow area at the point of minimum electrode separation, of 4.1 and 8.2 m/s. The two divergence angles used were 5 and 10 degrees, and the minimum electrode separation distance was 2.54 ma. High-speed interferograms showing density variations in the gas were obtained and linked with the voltage data in order to identify various types of breakdown events and to develop both qualitative and quantitative definitions for use in the reduction of the data. From the analysis of the data, it was determined that an increase in either the mass flow rate or the electrode divergence angle improved switch performance by reducing the percentage of switch closures which were considered failures.Item Unstable laminar flow through non-adiabatic, vertical, circular tubes(Texas Tech University, 1971-05) Carroll, Leland BusbyNot available