Minimum Flow Area Research Articles

Effect of Pin Fin Arrangement on Endwall Heat Transfer.

Experiments were conducted to measure the local heat transfer on an endwall with pin fin array. Heat transfer behavior was examined for the cases of a single pin, a single row, in-line and staggered arrays having six streamwise rows. Thermosensitive liquid crystal film was used to measure the local heat transfer coefficient on the endwall. Neural network was applied for the color-to-temperature transformation of the thermosensitive liquid crystal. Local heat transfer on the endwall having a single row of pin fin was affected by flow acceleration between the pin fins rather than the horseshoe vortex around the pin fin. Therefore, the average Nusselt number exhibited a good correlation to the Reynolds number Renax, which was based on the average velocity of the minimum flow area, regardless of the pin fin spacing. For in-line and staggered arrays, the average Nusselt numbers correlated with the Reynolds number Remaxdecreased with the reduction of the pin fin spacing.

Local Convective Behavior and Fin Efficiency in Shallow Banks of In-Line and Staggered, Annularly Finned Tubes

Local mass transfer data for high-profile fins in the second row of in-line and staggered, circular-finned tubes are presented for Reynolds numbers from 5000 to 28,000 based on hydraulic diameter and velocity at the minimum flow area. The data, obtained using an optical adaptation of the naphthalene sublimation technique, show that local variations in heat transfer do not cause significant fin efficiency deviations from the analytical solution of Gardner (contrary to earlier reports). Average heat transfer and pressure drop data indicate that the thermal performance of the in-line arrangement is comparable to the staggered configuration.

Effect of Pin Fin Arrangement on Endwall Heat Transfer.

Experiments were conducted to measure the local heat transfer on an endwall with a pin fin array. Heat transfer behavior was examined for the cases of a single pin, a single row, in-line and staggered arrays having six streamwise rows. Thermosensitive liquid crystal film was used to measure the local heat transfer coefficient on the endwall. Neural network was applied for the color-to-temperature transformation of the thermosensitive liquid crystal. Local heat transfer on the endwall having a single row of pin fin was affected by flow acceleration between the pin fins rather than the horseshoe vortex around the pin fin. Therefore the average Nusselt number exhibited a good correlation with the Reynolds number Remax which was based on the average velocity of the minimum flow area, regardless of the pin fin spacing. For in-line and staggered arrays, the average Nusselt numbers associated with the Reynolds number Remax decreased with the reduction of the pin fin spacing.

Pressure Drop Measurements on the Shell Side of a Cylindrical Shell-and-Tube Heat Exchanger

Representatkie pressure distributions from an extensive survey of the shell-side pressure field within the tube bundle of an E-type segmented-baffle shell-and-tube heat exchanger are presented. Reynolds numbers based on minimum intertubc flow area were varied within the range 270-2,200. Strategically placed tubes forming part of the bundle were fitted with pressure tappings and were used to measure (1) axial distributions of cross-flow pressure drop, symmetric about the pass partition lane and in the central vertical plane of the bundle, and also at the edge of the bundle near the bypass lane; (2) flow pressure drops between adjacent baffle compartments; and (3) circumferential pressure distributions on selected tubes in the center and at the periphery of the bundle. Comparison of the results with those obtained in a previous study with no pass partition lane reveal the effect of the removal of the central row of tubes on the shell-side flow distribution.

A Hydrodynamic Analysis of Fluid Flow Between Meshing Spur Gear Teeth

A hydrodynamic analysis of the pumping action resulting from the meshing of spur gear teeth was performed. Both compressible (for air) and incompressible (for oil) flow cases were considered. The computed results included the velocity of the fluid at the minimum flow area between the meshing teeth. The pressure and temperature in the mesh region were also computed for the compressible flow case. The velocities were computed as a function of the mesh angle with the pitch line velocity as the normalizing parameter. The calculations required a detailed analysis of the involute geometry to compute the proper mesh region volumes and exit flow areas. For the incompressible calculations with wide face gears, it was found the peak fluid velocity could greatly exceed the pitch line velocity. For the compressible calculations, it was found that sonic conditions could be reached at the minimum flow area leading to the possibility of shock formation downstream of this region. Parametric results for both sets of calculations, including backlash, diametral pitch, and other factors, are presented.

Condensation of downward flowing R-113 vapor on bundles of horizontal smooth tubes.

Film condensation of downward flowing R-113 vapor at near atmospheric pressure on in-line and staggered bundles of smooth tubes was experimentally investigated. The inlet vapor velocity range (based on the minimum flow area) was varied from 2.1 to 20 m/s, while the condensation temperature difference range was varied from 3 to 30 K. Based on the momentum and heat transfer analogy for the condensing film flow, empirical equations for the heat transfer coefficient were derived for both the in-line and staggered tube bundles. These equations compared well with most of the available experimental data for both refrigerants and steam.

Drag forces and shedding-vortices of a circular cylinder transverse in a pipe.

In order to investigate flow fields in vortex flow meters, we used a circular cylinder transverse in a pipe instead of a vortex -shedding bluff body. Then, time-averaged pressure distributions on the surface of the cylinder are measured, and fluctuating streamwise velocities are analyzed statistically. The contraction ratio β of a cylinder diameter to a pipe diameter varies between 0.102 and 0.510. The wall blockage of a pipe strongly influences the flow fields. Brief results are as follows. Drag coefficients and Strouhal numbers defined by the mean flow velocity are rapidly increased with β. However, the modified drag coefficients and modified Strouhal numbers, which are defined by the mean velocity through the minimum flow area in a pipe, are nearly equal to those in a two-dimensional uniform flow. Further, vortices shedding from a cylinder are aligned along the axis of a pipe.

Initiation of sand transport over coarse beds in tidal entrances

A tidal entrance often acts as a source or a sink for sand in the littoral zone. At many entrances in biologically productive regions the bed in the vicinity of the throat section (minimum flow area) is composed of sediment containing coarse material including large shells, with sand occurring in the interstitial regions between the shell-defined roughness elements. A stochastic relationship giving the critical bed shear stress for the initiation of sand transport under these conditions is applied to hydraulic and sedimentary data obtained from two entrances in Florida. The results agree well with the critical bed shear stresses derived from data based on the observation of sand movement at the bed. The entrainment function based on observations is found to be approximately three times the value obtained from Shields' criterion. A practical implication is that the use of Shields' criterion in the computation of the rate of sand transport will in general overpredict the rate through the entrance.

Free radical propulsion concept

ANEW propulsion concept which may have particular usefulness for transfer of loads from low Earth orbit (LEO) to geosynchronou s Earth orbit (GEO) is presented. Electrical energy in the form of microwaves is used to heat a propellant gas, thus providing thrust. An outline of the concept and experimental results in support of it are presented. Contents A variety of possible future space missions involve the transfer of substantial masses from LEO to GEO. 1 A crucial factor in propulsion systems designed to meet this need is the ratio of total mass required in LEO to payload mass in GEO, due to the fact that Earth-to-orbit cost is a major fraction of total cost. Systems presently considered for such missions include chemical systems and electrostatic ion propulsion systems. Figure 1 presents payload mass ratio as a function of specific impulse for these systems. Chemical systems provide short trip times at the expense of mass ratios of 3 or greater. Electrostatic ion propulsion systems can achieve mass ratios of 1.25-2.5, but require trip times of 50 days or longer. There is an intermediate range of specific impulse not accessible to present systems which would allow moderate trip times while maintaining mass ratios similar to those of electrostatic systems. The free radical propulsion concept presented here may prove capable of operating in that regime. The concept is illustrated schematically in Fig. 2. Electric power from solar panels is used to operate a microwave generator, and microwave energy is coupled to a propellant gas by means of a resonant cavity. The gas is ionized partially by the microwave fields, and inelastic collisions of gas molecules with the resultant electrons serve to dissociate the gas. The gas is allowed to recombine downstream, with the recombination energy heating the gas. The hot gas is expanded through a nozzle to produce thrust. Molecular hydrogen, with a theoretical specific impulse of 2100 s (100% conversion), is the most attractive propellant. Sample calculations on a hydrogen thruster for a thrust of 1 N and a specific impulse of 1500 s yield the following results: mass flow rate, 6.8xlO~ 5 kg/s; minimum input power, 7.3 kW; minimum flow area (nozzle throat), 4x 10 ~2 to 4x 10 ~4 m2 for pressures of 13.3 to 1330 N/m2, respectively; and thrust densities of the order of 100 N/m2. Attractive features of the free radical propulsion concept in comparison to electrostatic ion propulsion or similar systems are increased thrust, thrust density, and thrust-to-power ratio.

Depth of Maximum Velocity and Minimum Flow Area of Tidal Entrances

ABSTRACTTidal entrances on sandy coasts change their size and configuration at all times with scouring by tidal current and silting by incoming littoral drift. The minimum flow area of a long time stable or so-called equilibrium tidal entrance, however, is known to be usually in a relatively narrow range of it. Thus, it may be a unique function of external forces and the other channel properties.The objective of this paper is to investigate the stability requirements on the basis of analyses together with existing field data.Firstly, an explicit solution of channel current and bay tide is derived with one dimentional linearized approach.Secondly, the depth at which the channel velocity reaches its maximum, is obtained analytically based on the exiplicit solution. A graphical method to find the depth for trapezoidal and parabolic sections is given with applying figures prepared.The relationship between the minimum flow area and the tidal prism is investigated in the light of the present analytical approach...

Equilibrium Flow Areas of Inlets on Sandy Coasts

The minimum flow area below mean sea level in the entrance channel of a tidal inlet on a sandy coast is a unique function of the tidal prism. Bottom material size, presence or absence of jetties, and magnitude of the littoral drift appear not to affect this relationship, within the accuracy of available data. The magnitude of the currents through the inlet channel are determined by the range of tide. The tendency for wave-induced littoral currents to transport sand towards an inlet and to reduce its flow area should vary with the intensity of wave action, but the data available do not show wide deviations from the equilibrium area, possibly because hydrographic surveys are made during calm weather. Reduction in the tidal prism of an inlet will reduce the equilibrium flow area at the minimum cross section of the inlet channel.

Frequency of the Karman Vortex Streets in Tube Banks

In the note “Aerodynamically induced vibration in coolers”, by D. G. Mabey (pp 876-7, December 1965 Journal), the results of Grotz and Arnold concerning the frequency of the Karman vortex streets in tube banks, such as in heat exchangers, are mentioned, as is also the law of the linear relation between f(T—d)/V and (2T-L)/d, as found by Putnam, where f frequency of vortex sheddingT transverse distanceL longitudinal distance between tubesd outer diameter of tubeV mean stream velocity based on minimum flow area between the tubesThis linear relation has no theoretical justification and cannot be accurate, as is admitted by the author cited. A further investigation on a theoretical basis seems to be necessary.