Nominal Mean Research Articles

Local heat transfer and flow distribution in a three-pass industrial heat exchanger

Local heat transfer from single tubes in an industrial-sized, three-pass heat exchanger of the inline tube bundle type was measured. The transversal and longitudinal pitches were 1.8 D and 1.5 D, respectively, the height of each pass was 30 D and the Reynolds number was 20 000. The measurements were made using an electrically heated cylindrical probe of the metallic film type, an instrument normally used in small-scale laboratory setups to gain detailed information about local heat transfer. The probe was positioned at various tube locations and rotated to yield the circumferential variation of the local heat transfer. Depending on location, local mean heat transfer was less than half or more than twice the nominal mean value. These variations were related to the non-uniform flow distributions present inside the heat exchanger, evidenced by computational fluid dynamics calculations. Also, the calculated velocities were used with an empirical correlation for the Nusselt number, and the results agreed very well with the measured values.

Simulations and physical measurements of glass spheres flowing down a bumpy incline

An inclined chute facility and its associated diagnostics has been developed and utilized to study the flow of granular materials. A variety of flow regimes and flow phenomena were observed. Fully developed flows were observed over a bumpy base for a range of slopes. Under some conditions, these flows were dominated by friction and under other conditions, collisions played a dominant role. A variety of unsteady flows were also observed. These include decelerating flows, accelerating flows, and wavy (periodic) flows. The characteristics of the base strongly influenced the flow regime and flow dynamics. Discrete particle simulation model parameters were determined from individual particle tests and particle impact experiments. Simulations of nominally steady flows at two fixed angles showed relatively good agreement with experimental values for particle velocities near the side-walls and on the top surface. The mass flow rate and the flow depth were also consistent with the experiments; however, both experiments and simulations exhibited significant fluctuations about the nominal mean values. The simulations were utilized to interpret flow parameters interior to the flow (i.e., in regions that cannot easily be measured non-intrusively). Far from the side-walls, the granular temperature was found to have a maximum near the bumpy base and to decrease toward the top surface — consistent with granular kinetic theory predictions for flows on bumpy inclines, without side-walls. Near the side-walls the behavior was substantially different with granular temperature decreasing from the top to a minimum at the lower `corners' of the chute. This behavior is consistent with experimental measurements of fluctuation velocities near the side-walls. The simulations confirm that the previous discrepancy in the variation of the granular temperature with depth between kinetic theory and near-side-wall measurements was a result of the side-walls, which cause strong three-dimensional structure in the flow.

Toxicity of crude oil and dispersed crude oil to ghost shrimpPalaemon serenus and larvae of Australian bassMacquaria novemaculeata

Acute 96-h LC50 values of the water-accommodated fraction (WAF) of crude oil, dispersants (Corexit 9500 and Corexit 9527) and dispersed oil combinations were determined in semistatic bioassays with seawater, using the ghost shrimp Palaemon serenus and larval Australian bass (fish) Macquaria novemaculeata. Sodium dodecyl sulphate (SDS) and zinc sulphate were used as reference toxicants and identical bioassays were conducted using these compounds. Total petroleum hydrocarbon (TPH) uptake of shrimp was also measured on the samples taken from the bioassays. The nominal mean (n=4) 96-h LC50 standard error (SE) values for WAF of crude oil, Corexit 9527, Corexit 9500, dispersed oil (9527) and dispersed oil (9500) were 258,000 ppm (13,000), 49.4 ppm (6.4), 83.1 ppm (5.8), 8.1 ppm (0.3), and 3.6 ppm (0.3) in the shrimp bioassays, respectively. The nominal mean (n=4) 96-h LC50 (SE) values calculated from the fish larval bioassays were 465,000 ppm (16,000), 14.3 ppm (0.9), 19.8 ppm (1.6), 28.5 ppm (1.4), and 14.1 ppm (2.6) for WAF of crude oil, Corexit 9527, Corexit 9500, dispersed oil (9527), and dispersed oil (9500), respectively. These LC50 values indicate that dispersed oil combinations were significantly more toxic to these organisms than WAF of crude oil. TPH uptake of shrimp increased in correlation to exposure concentrations, and the presence of dispersant made oil more available for shrimp. © 2000 John Wiley & Sons, Inc. Environ Toxicol 15: 91–98, 2000

Semantic differences of suffixal alternates in Hungary

Some of the inflectional paradigms of the Hungarian lexicon containsuffixal alternates which do not vary freely with each other, but certaininflected forms are connected to specific senses of the lexical item. Amongverbal suffxes the -ik suffix marking the third personsingular form of the present tense indicative behaves in this way, which oncertain verbs can simultaneously signal intransitivity, while the alternatefor with the zero suffix is transitive. On other verbs, the choice betweenthe bare -t and -Vtt forms of thepast tense suffix (in 3rd person singular) can indicate sense differences.The inflectional paradigm of some verbs can even contain more than oneinstance of semantic distinction among alternates. A peculiar differencebetween the multiple plural forms of nouns derived from adjectives is basedon whether the nominal meaning is an occasional one or the nominal lexemehas become completely independent. The same difference is reflected in theaccusative form of these nouns, too. Different personal possessive suffixalforms of nouns can signal differences between the types of the possessiverelation (real possession or part-whole relation), instead of differentiatingsenses of the basic form. The adverbial forms of adjectives with lAg, -An and -Ul suffixescan also indicate sense distinctions.

General disequilibrium analysis with inside debt

This paper incorporates inside nominal debt into a Keynesian general disequilibrium model. It shows how nominal wage adjustment may be insufficient to restore Walrasian equilibrium. Nominal wage reductions lower aggregate demand by increasing debt service burdens. This aggravates Keynesian deficient demand unemployment. When there is classical unemployment, falling nominal wages mean that the economy may hit a Keynesian constraint before it attains Walrasian full employment. In situations of repressed inflation, rising nominal wages reduce debt service burdens and increase aggregate demand, thereby worsening the extent of excess demand.

Capillary electrophoretic behaviour of humic substances from Sphagnum peats of various geographical origin: relation with the degree of decomposition

SummaryHumic substances (HS) extracted from 14 Sphagnum peats of various geographical origin were submitted tocapillary electrophoresis (CE) in free solution and in entangled polymer solutions (25 gl‐1 and 50 gl−1) of polyethylene glycol (PEG). Electrophoretic runs were made in uncoated capillaries (75 μm internal diameter) using a tris‐hydroxymethylaminomethane (TRIS)‐phosphate buffer (pH 8.3) eventually containing PEG and applying a voltage of 10 kV. The HS extract of a Lithuanian peat was fractionated by ultrafiltration into five fractions with a nominal mean relative molecular mass (M) of 3000, 7500, 20 000, 75 000 and 200 000 Da. Without PEG, migration times were not correlated with the logarithm of M, but linear relations were obtained with 25gl−1 and 50gl−1 PEG solutions. Both solutions separated the different fractions by size; the best regression and the largest interval of linearity, M from 3000 to 200 000 Da, was obtained with the 25gl−1 PEG solution. At 10kV and without PEG, migration times ranged from 6.5 to 8.1 min and did not differentiate the peats, whereas at 25gl−1 PEG, migration times ranged from 3.3 to 6.5 min and, when plotted as a function of either the r value or the von Post index (H), which are used to evaluate the degree of decomposition of horticultural peats, they separated samples on the basis of their geographical origin and probable type of mire complex. At 25gl−1 PEG, migration times also showed a well‐defined linear decreasing trend with the increase of mean annual temperatures. These relations suggest the hypothesis that humification in mires goes along with an increase in the average size of humic molecules.

Evaluation of compulsory declaration of crude protein in feed mixtures for poultry

The analysed (Kjeldahl) content of crude protein (CP) in seven standardised formulated feed mixtures for poultry, sampled from 11 feed mills through 8 yrs in western Norway, was compared to the nominal guaranteed level. Samples with analysed CP outside the statutory range were designated as faulty. 3.2% of the samples from the grower mixture were faulty. For the other mixtures: hen1, cage, breeder, chicken, broiler and hen2, the figures were 10.9%, 6.5%, 2.8%, 20.6%, 10.1% and 24.0%, respectively. The nominal mean content of CP ranged from 140 g kg −1 in grower to 220 g kg −1 in hen2. The linear correlation between the percentage of faults and the nominal CP level in the mixtures was significant ( p<0.05). On average, 97% of the faulty samples were substandard. Only 3% had a higher CP content than declared. The mixtures produced in some regions were almost without faults; in other regions, the faults were more frequent. An apparent decrease in the overall frequency of faults during the period was recorded, though not at a statistical acceptable level of significance ( p>0.05).

Mix proportions for high strength concrete

This paper deals with the plain concretes used in a study of fibre-reinforced concretes which required nominal mean 28 day cube strengths of 40, 60, 80, 100 and 120 N mm 2 . A standard 42.5 N Portland cement (BS 12) was used, which had a C 3S C 2S ratio of about 6.1, with a marine dredged sand and either a crushed limestone or a gravel of 10 mm maximum particle size. For strengths of 80 N mm 2 and greater, 10% silica fume and a naphthalene-based superplasticizer were included, each being added in aqueous form. Mix proportions were chosen to produce fresh concrete of high workability and suitable for inclusion of a reasonable volume of fibres. Values of slump were typically 150 ± 50 mm but did not adequately reflect the workability and stability of the range of concretes used. Cement contents varied from about 340 to 510 kg m 3 , with water cement ratios of 0.24–0.56. There seemed to be a practical limit to the 28 day cube strength of about 115 N mm 2 with the limestone and 100 N mm 2 with the gravel with the materials used. Good correlations were found between cube strength and three forms of indirect tensile strength.

Assessment of the effect of molecular size on the electrophoretic mobility of humic substances

SummaryThe basic principles of the electrophoretic behaviour of humic substances (HS) still need to be systematically investigated. HS extracted from a Cryorthod (HS–1) and from an Haplumbrept (HS–2) were first fractionated by ultrafiltration to obtain two series of fractions of reduced polydispersity with a nominal mean relative molecular mass (M) of 7500, 20000, 40000, 75000 and 200 000 Da. Fractions extracted from the same soil behaved like an homologous series when tested by size exclusion chromatography, showing a linear relation of M with molecular size. When plotted against their mean M, the elution volumes of HS fractions extracted from the two different soils originated lines of different slope. Absolute electrophoretic mobilities of the fractions were determined in polyacrylamide gel slabs of increasing polyacrylamide concentration using a single buffer system; in all gels there was a close linear relation between the electrophoretic mobility and the logarithm of the mean M of HS fractions. Extrapolation of mobilities of HS–1 at zero gel concentration gave intercepts that did not differ significantly, showing that there was a constant mobility for all fractions in free solution. These results mean that charge differences have little effect on the electrophoretic mobilities of HS extracted from the same soil and imply the theoretical possibility of determining M distributions of HS by polyacrylamide gel electrophoresis in a single buffer system. Mobilities of HS–2 fractions were compared with those of HS–1: the latter fitted the regression equations of mobility against logarithm of the molecular weight obtained from HS–1 humic substances only in gels of small acrylamide concentration. Deviations were larger at small M, probably because of the increasing fulvic character of the fractions, and increased in gels of greater acrylamide concentration, indicating that charge differences may not be negligible when comparing humic substances extracted from different soils.

The Characteristics of Elastically Contacting Ideal Rough Surfaces

Abstract The analysis of the elastic contact of ideal rough surfaces is presented in this paper. The rough asperities are assumed to be spherical with the same vertical height and spatial distance. The mutual influence of asperities is considered. Numerical results show that for the same load, the contact area is less than the Hertzian prediction, while the pressure distribution is still of a Hertzian type, but is increased to some extent. We find that the asperity interaction is associated with a parameter, called the “loading level,” which combines the surface texture, mechanical properties, and the nominal mean pressure. Of significant importance is the discovery of the variation of the reference plane position with the contact load. In the classical theory of rough contact (Greenwood and Williamson, 1966), the reference plane was in fact assumed to be in the mean line position. We prove that the location of the reference plane is determined by the number of contacting asperities and the loading level, thus making the analysis of the contact of rough surfaces somewhat complex.

The Behaviour of Transverse Roughness in EHL Contacts

By assuming the contact geometry in elastohydrodynamic lubrication (EHL) to be that of an infinitely long contact with given nominal film thickness and mean pressure and considering the elastic displacements of the separate components of the initial roughness, it is possible to extend the Greenwood and Johnson analysis for sinusoidal pressure to any two-dimensional roughness. For typical EHL pressures the viscosity effects are negligible, so the Reynolds equation can be linearized and solved analytically; the solution provides a criterion to relate the amplitudes of the undeformed and deformed roughness to the wavelength, and shows that roughness with a short wavelength is likely to persist after deformation. The linearization of the Reynolds equation is extended to the transient case and it is found that the complete solution is made of two separate parts: the particular integral (steady state solution) and the complementary function (which depends on the entry of the partly deformed roughness into the Hertzian zone).

Data and Model for Progressive Fouling in Cross-Flow Microfiltration of Yeast on Three Industrial Mineral Membranes

The variation of permeation flow as a function of time was experimentally studied from the initial three fast transient to its final stabilization in the case of filtration of a yeast suspension using industrial microfiltration membranes from Tech-Sep S.A.(01703 Miribel, France), SCT S.A. (65460 Bazet, France), and Le Carbone-Lorraine S.A.(54530 Pagny sur Moselle, France) with the same nominal mean pore diameter (0.2 [mu]m). The influences of three operating conditions, concentration of yeast, transmembrane pressure, and velocity, were systematically obtained. The behaviors of the three membranes differ, as expected, because their structures as characterized by rugosity measurements and electron micrographs are very different. The correlation of the results is based on a two-term equation, adding a transient term to the steady flow J[sub 1] initially equal to the initial permeate flow rate J[sub 0] before any fouling minus J[sub 1]. The parameters in the correlation of J[sub 1] and the transient flow term were obtained by statistical analysis of experimental results and yield a representation of the experimental results with an error on the order of 10%.

Fatigue of wire ropes bent over small sheaves

The fatigue performance of heavily loaded wire ropes bent over rather small sheaves has been investigated. A selection of 28 and 35 mm diameter ropes of 6 x 36 construction was tested over sheaves with D/ d ratios between 12 and 20. Three different groove profiles with diameters 2.5% less than the nominal rope diameter and mean loads of up to 65% of the rated axial strength of the rope were used. Under the conditions examined, a 28 mm independent wire rope core bright wire rope had the best fatigue life and a 28 mm fibrecore galvanized rope the worst. One of the three grooves employed severely decreased fatigue life.

Migration and citizenship1

Abstract This article proposes a notion of citizenship which goes beyond its nominal meaning of ‘membership of a state’. Citizenship is seen as a normative as well as an analytical concept, which refers to the equality and universality of rights embedded in the institutions of political communities. Citizen rights of migrants have to be analysed within a framework which includes both the sending and receiving state. Different bundles of rights are identified, which determine positions of migrants within this frame of reference. The article categorises rights according to their dependence on nominal citizenship and on residence into universal human rights, internal and external citizenship, alien rights and special rights of long term resident alien citizens. The normative content of citizenship can be invoked to challenge the legitimation of inequalities and boundaries between the positions of citizenship, held by immigrants and native populations. Two different approaches to policy changes along these li...

The effect of transverse plate vibration on the mean laminar convective boundary layer heat transfer rate

Heat transfer experiments were conducted to ascertain the effects of transverse plate vibration on the local heat transfer rate, that is, the local Nusselt number. The nominal mean free-stream velocity for the main results presented in this paper is 4 m/s, giving a Reynolds number range up to 2.5 × 10 5. The plate vibration frequency is 60 Hz, and the typical plate vibration level at the excitation point of the heat transfer test plate ranges from 1.7 to 12 mm/s (peak). The effect of the plate vibration on the heat transfer is attributed to the stability characteristics of the induced boundary layer velocity oscillations. A detailed flow-field investigation indicates that the induced velocity oscillations in the laminar boundary layer are unstable. It is the nonlinear development of these unstable velocity oscillations and the resulting laminar-turbulent transition that produces an increase in the local heat transfer rate. The local heat transfer augmentation is in some cases as large as 290%. It is observed that at low levels of plate vibration the rate at which the local heat transfer increases with respect to the downstream direction is large and that the local heat transfer augmentation occurs mainly in the downstream region of the test plate. As the level of plate vibration is increased, the rate at which heat transfer increases with respect to the downstream direction is reduced, but the starting point at which heat transfer augmentation begins is moved upstream.

Effect of notch root radius on fatigue crack initiation

The initiation of a fatigue crack terminates the useful life of small components. The initiation process is intimately related to cyclic plastic deformation and thus occurs mostly at notches where stresses are elevated appreciably. The root radius of such notches dictates the severity of stress and strain concentration. Using notched specimens of varying root radii the initiation lives were determined experimentally. Both the fictitious elastic notch root stress and the local strain at the notch root have been used to correlate with the initiation life. The local strain approach, together with Neuber's rule, is observed to give less scatter. The design-oriented nominal mean stress method of Juvinall yields results comparable with the local strain approach.

切欠き深さおよび切欠き半径の異なるＵ形二重切欠き材の強度に及ぼす干渉効果の実験的検討

The interference effect of double symmetrical U-shaped notches of unequal notch depth and/or unequal notch radius on the strengths were investigated experimentally. The notch pitch range in which the general yield strength is reduced was able to be predicted by using the upper and lower bound theorems. The X-shape extension of plastic deformation occurred in the notch pitch range influenced by the interference effect. The notch tensile strength was also reduced by the interference effect. The magnitude of the reduction of notch strength ratio and the notch pitch range influenced by the interfarence effect were almost equal to thoes of the general yield stress ratio, or the ratio of the general yield stress at the net section of the notched bar to that of the smooth bar. The nominal mean stress at the net section at fracture was also reduced by the interference effect. The fracture along the inclined plane connecting two notches situated diagonally was caused by the X-shape extension of plastic deformation in the notch pitch range showing the strong interference effect. The fracture at the net section occurred in the notch potch range showing the weak interference effect. The difference in notch depth has much stronger influence on the interference effect than the difference in notch radius does.

Thermal ratchetting of a tube with non-uniform thickness

Two-dimensional (plane stress) finite-element analyses have been carried out to investigate the thermal ratchetting behaviour of a thin tube with an eccentric bore (eccentricity/mean wall thickness = 0.2). The tubes were subjected to steady internal pressure and cyclic, linear through-thickness temperature gradients. If the mechanical loading is characterized by the nominal mean stress ( σ m) at the thinnest section, the ratchetting boundary is accurately predicted by a simple, analytical, beam model. For high thermal loads ( σ t σ y > 2.5 ) the maximum mid-thickness ratchet strains are conservatively predicted. However, for lower thermal stresses the mid-thickness ratchet strains are underpredicted. The value of the creep stress exponent has no effect on the ratchet strains obtained under complete redistribution conditions. The first cycle ratchet strains under no-creep conditions are practically identical to the complete redistribution values.

Seston retention by Whatman GF/C glass-fiber filters

The efficiency of Whatman GF/C glass-fiber filters for the retention of seston (dry weight) from North Sea water was tested. Uni-Pore polycarbonate membranes with pore sizes of 0.4, 1 and 5 pm diameter were used as standard 'sieve' fllters, since they have well-defined pore sizes. Using means of the differences of paired filters, it was found that GF/C glass-fiber filters retain seston from North Sea samples as efficiently as 0.4 pm Uni-Pore filters at a seston concentration range of about 1.5 to 15 mg dm-3; this covers most of the German Bight water bodies in summer. Glass-fiber filters retained significantly (P < 0.001) more seston than 1 pm Uni-Pore filters and thus more as their nominal mean retention size of 1.2 p would suggest. Comparison of seston retention of GF/C and Uni-Pore filters by regression analysis revealed that GF/C filters tend to retain relatively more seston as the water becomes clearer and sample volumes greater; this is the case in the western German Bight (Secchi depth about 7 to 9 m, seston concentrations < 2 mg dm-3, sample volumes filtered: 600 to 1000 cm3). This higher retention of GF/C filters is significant (P = 0.05) when compared with 0.4 pm Uni-Pore filters but highly significant (P < 0.001) with 1 pm Uni-Pore filters. This indicates that particles < 1 pm contributes significantly to the seston weight in such open North Sea water It seemed unlikely. however, that adsorbed dissolved organic matter caused a 'seston' weight increase.

Design Nomographs of Compression Helical Springs for Predetermined Reliability Levels

This paper discusses a probabilistic approach for the design of Compression Closely Coiled Helical Springs subjected to periodic axial loading. The classical design procedure results in deterministic geometric parameters with tolerances normally chosen according to standards without due regard to their effects on the mission success as normally expressed by a reliability level. With the proposed design procedure, the engineer can specify nominal mean values for the geometric parameters and their tolerances according to a predetermined reliability level. Design nomographs are presented to help the engineer, in the early stages of design, to choose between many alternatives. Computer algorithms can easily be written to verify the final or optimum design.