Free Flow Area Research Articles

Steady-flow Cf-Nre Correlation for the Wire Gauze Regenerator Inferred from Linear Wave Analysis

Linear wave analysis of unsteady flow in the wire mesh regenerator is extended to account for viscous losses (shear at the wall and abrupt change in the free-flow area). As a test of relevance to the Stirling gas circuit, the standard, unsteady-flow momentum equation is re-expressed in terms of the algebra [admittance ratios, pressure ratios) of the linear wave approach. This permits the steady-flow friction factor, Cf, to be extracted and plotted as a function of Reynolds number, Ntc. The resulting correlation is found to correspond closely to the experimentally determined counterpart. An explanation is found for the discrepancy noted between computed and observed pressure drops in the Stirling cycle machine.

Leaf litter decomposition in three Louisiana freshwater forested wetland areas with different flooding regimes

Litter decomposition was studied for one year in three Louisiana forested wetland sites with different flooding regimes. Decomposition was significantly higher in a crayfish pond where flooding was manipulated by pumping. Only 20% of the original dry mass remained after 46 weeks versus over 40% in the natural and impounded wetland forests. Nitrogen was immobilized in the natural and impounded areas but was mineralized during the spring and summer in the managed area. Phosphorus was not immobilized in the natural and impounded areas like nitrogen but was mineralized much more slowly in these areas than it was in the managed area. Because of the slower decomposition in the natural and impounded areas, falling leaf litter buries the old, partially decomposed material. Thus, there tends to be a net accumulation of organic matter, nitrogen, and phosphorus in stagnant, more flooded areas and mineralization and/or export from free-flowing areas.

Analysis of RO flux decline due to membrane surface blockage

Recent work has shown that, flux decline due to precipitation of a scaling salt such as CaSO 4 on RO membranes, is governed by a surface blockage rather than a cake filtration mechanism. Crystal growth sites, scattered on the membrane, spread out laterally, increasingly blocking the membrane free flow area. Flux decline, resulting from gradual blockage of the membrane flow area, is analyzed for both laminar and turbulent flow conditions. Predicted results are shown to conform to experimental observations.

Asymmetrically corrugated plate heat exchanger plates

Design flexibility for plate heat exchangers is a measure of the ability to adjust the characteristics of individual channels (semi-)independently to suit a particular application. Conventional plate heat exchangers with approximately sinusoidal corrugations have limited design flexibility since the channels for the two heat- exchanging streams are generally geometrically identical. Corrugations that are assymetrical in profile make it possible to construct physically different configurations from a set of identical plates: channels of different cross-sectional free flow area are feasible. Such plates used in various orientations with respect to each other were found to be less efficient than plates with sinusoidal corrugations because a lower heat transfer rate is obtained per unit of pumping power. However, when the flow rates or allowable pressure drops of the two streams exchanging heat differ greatly, such plates may be advantageous.

Optimal heat pipe heat exchanger design

A typical heat pipe heat exchanger with continuous planar fins and a staggered equilateral triangular pitch of the tubes is subject to optimization from the point of view of the ratio heat flow/weight and heat transfer effectiveness. Different optimization procedures are explained in detail and numerical results are given in the application. The procedures are as follows. 1. A. If hot and cold fluid mass flow velocities in the minimum free flow areas are given, one obtains the maximum of the ratio heat flow, Q /mass, M for optimal values of fin density and equilateral triangular pitch. The ratio of evaporator to condenser lengths observes a relation which allows Q/M to be permanently at its peak with respect to the dimensionless saturation temperature. 2. B.1. One obtains the maximum of the ratio heat flow/evaporator mass for optimal fin and triangular pitches. 2. One selects the cold fluid mass flow velocity G 2 so as to obtain equality between evaporator and condenser fin side heat transfer coefficients. The optimal pitches found at the evaporator also lead to the maximum of heat flow/condenser mass. 3. There is an optimal value of the ratio of evaporator to condenser lengths which ensures Q/M to be a maximum with respect to the dimensionless saturation temperature. 3. C.1. As B.1.2. G 2 remains variable. A condenser with maximal heat exchanger heat transfer effectiveness is “linked” to the optimized evaporator. One obtains the ratio of evaporator to condenser lengths and the ratio of hot and cold fluid heat capacities as optimal functions of G 2 . 4. D.1. As B.1.2. G 2 remains variable. The ratio of evaporator to condenser lengths is selected from the condition: Q/M maximum with respect to the dimensionless saturation temperature. It follows that this ratio becomes an optimal function of G 2 . The ratio of the heat capacities is derived as an optimal function of G 2 too. The heat flow value, the number of tubes in a row and the number of rows do not affect optimization results. The optimization procedures presented in this paper may be used, with adequate transformations, for other heat pipe heat exchanger configurations.

Northern Squawfish (Ptychocheilus oregonensis) Predation on Juvenile Salmonids in Sections of the Willamette River Basin, Oregon

Predation by northern squawfish (Ptychocheilus oregonensis) on salmonids was studied in spring months in several lower, free-flowing areas of the Willamette River drainage, Oregon. During 1976 and 1977, 1127 northern squawfish were collected by electrofishing and seining, and examined for food contents. Almost 59% of the squawfish stomachs contained food items, but only 2% contained salmonids. Principal foods were insects, crayfish, and sculpins (Cottidae), and the majority (over 90%) of squawfish had not consumed more than one principal food type. We suggest that previous reports of squawfish predation in flowing rivers were misleading because they were often based on artificial situations (below dams or in waters following hatchery releases) which could have inflated salmonid predation values. Further, the true predatory nature of squawfish is clouded because of their rapid digestion of food and the long lag time in examination of gut contents by previous researchers. Our sampling techniques avoided these shortcomings by sampling in free-flowing areas and by examining squawfish stomach contents immediately after capture.Key words: squawfish, Ptychocheilus oregonensis; predation, food habits, Oregon

Seasonal Movements of White Sturgeon (Acipenser transmontanus) in the Mid-Columbia River

Twenty-nine white sturgeon (Acipenser transmontanus) were instrumented in 1975 and 1976 with separately identifiable radio transmitters to study seasonal movements in the mid-Columbia River, southeastern Washington. Tagged fish remained in free-flowing areas of the river and were inactive in winter. Movements occurred in summer and early fall. Activity appeared related to water temperature and sturgeon size.

Exploration for Artesian Water in the Sokoto Basin, Nigeriaa

AbstractThe Sokoto basin in semiarid northwestern Nigeria contains Cretaceous and Tertiary semiconsolidated deposits that dip gently northwest off an oldland of pre‐Cretaceous crystalline rocks. Until recent years the dug well has been the chief source of ground water for the Hausa cultivators and the pastoral Fulani inhabitants of the region. Borehole exploration sponsored by US AID and the Geological Survey of Nigeria with technical guidance from the writers of the U. S. Geological Survey has revealed that the basal section of the Gwandu Formation contains a productive artesian sand aquifer throughout a 5,700 square mile area. Transmissibilities of the aquifer proved to be as high as 180,000 Imperial gallons a day per foot but generally decrease towards the west. The free flow areas total about 1,000 square miles with pressure heads in boreholes up to + 83 feet above land surface and individual flows as great as 12,000 gallons per hour. Beneath the Gwandu, pressure aquifers in the Rima Group and the Gundumi Formation also produce flowing water in the lowland (fadama) of the Sokoto River. In the southern part of the basin, however, only one aquifer is present in the Cretaceous sequence, because the Gundumi aquifer is absent and the Rima aquifer apparently grades into the upper permeable section of the Illo Group. The quality of the water from all the pressure aquifers is generally quite good, although the iron content is high in places and salinity increases in the very deep aquifers.In Sokoto Province more than 2 million people and their livestock use less than 5 mgd of water drawn from dug wells and about 1 mgd from boreholes. The newly discovered flowing artesian water can do much to improve the water supplies of remote villages in the province and even supplement river irrigation during the dry season in the fertile fadama.