Detachment Frequency Research Articles

Studies on pool boiling heat transfer (modification of correlation of macrolayer thickness and measurements of macrolayer thickness at low heat fluxes)

The macrolayer thickness at critical heat flux has been determined based on the energy balance relation qCHF = ρlH fg δl. f, with measurements of the critical heat flux and the detachment frequency of vapor masses (coalesced bubbles) for various liquids at pressures from 0.05 MPa to 0.35 MPa for upward and vertical 20 mm diameter disk heaters. The macrolayer thickness correlation proposed in the fourth report of this series by Kumada and Sakashita was modified with the data obtained in the present report. Macrolayer thicknesses at low heat fluxes for water and ethanol under atmospheric pressure were also measured while changing the orientation of the heating surface from vertical to downward. The measured macrolayers at low heat fluxes were thinner than those by obtained from existing data measured by a probe method in the nucleate boiling region

Studies on Pool Boiling Heat Transfer. 7th Report. Modification of Correlation of Macrolayer Thickness and Measurement of Macrolayer Thickness at Low Heat Fluxes.

Macrolayer thickness at critical heat flux was measured for various liquids in the pressure range of 0.05MPa to 0.35MPa for upward and vertical disk heaters of 20mm diameter. Macrolayer thickness is determined based on the energy balance relation qCHF=ρlHfgδl·f, with measurements of the critical heat flux and the detachment frequency of vapor masses (coalesced bubbles) completely covering the heating surface. The correlation of macrolayer thickness proposed in the 4th report of this series by Kumada and Sakashita [Trans. JSME, 58-552 (1992), 2505] was modified with the data obtained in the present report. Macrolayer thickness in low heat fluxes for water and ethanol under atmospheric pressure was also measured by changing the orientation of the heating surface from a vertical direction to a downward direction. The data in low heat fluxes were thinner than the existing data measured by a probe method in the nucleate boiling region and agreed fairly well with the proposed correlation.

Pool boiling heat transfer—I. Measurement and semi-empirical relations of detachment frequencies of coalesced bubbles

Measurements were made of the detachment frequency of coalesced bubbles from circular, horizontal 2–30 mm diameter disks and thin, horizontal 0.2–3 mm diameter wires at high heat fluxes and atmospheric pressure. The disks area heated copper cylinder and a sintered brass plate through which nitrogen gas is blown. Detachment frequencies from disks and thin wires were measured with water, ethanol and Freon-113. The bubble frequency was determined with high speed video. Semi-empirical correlations of bubble frequencies are proposed for both disks and thin wires. The correlations were derived by the dimensional analysis of force balance equations relevant to the behavior of bubbles.

Pool boiling heat transfer—II. Thickness of liquid macrolayer formed beneath vapor masses

The macrolayer thickness was determined on the basis of the energy balance relation q CHF = δ 1 ϱ 1 H fg f, which was derived from the dryout model for liquids, proposed by Katto and co-workers. The critical heat flux (CHF) and the detachment frequency were measured on 20 mm diameter horizontal and vertical heated disks at pressures of 0.03–0.4 MPa with water, ethanol, methanol and acetone. Two semi-empirical correlations for the macrolayer thickness were derived by dimensional analysis of a model in which primary or coalesced bubbles form a macrolayer. The proposed correlations arrange the data of macrolayer thickness obtained from CHF measurements well.

A model of biofilm detachment

A general mathematical framework for modeling biofilm detachment is presented. The approach is founded on a material balance on biomass that equates the detachment rate to the product of a detachment frequency and a detaching particle mass. The model provides a theoretical basis for deriving many of the empirical detachment rate expressions in common use and can thus lend some insight into their physical and biological significance. By allowing for variation in the detachment frequency with depth in the biofilm, the model permits derivation of detachment expressions that reflect a dependence on chemical or physiological gradients in the biofilm. Analysis of literature data sets from two different biofilm systems suggests, in both cases, that detachment is a growth-associated phenomenon.

The influence of surface conditions and subcooling on film-transition boiling

The influence of surface oxidation, liquid subcooling and surface roughness on pool boiling from a 1.27-cm copper sphere is reported in the present study. The sphere was specially designed to minimize support interference with vapor formation and removal; the surface was carefully prepared so that surface roughness and oxidation could be controlled. Experiments were conducted for four different surface roughness levels and subcooling up to 22°C for Freon-113 and up to 50°C for water. Experiments were also conducted with oxidized spheres in Freon-113. In general, the data and observations show that increased subcooling, roughness, and oxidation increase the heat flux during the stage of film boiling near the minimum heat flux where liquid-solid contact is possible. Such increases carry over into transition boiling as well. Vapor bubble detachment frequencies and diameters are reported. A curious “parent-son” detachment mode was observed. Such behavior is explained by a recirculating liquid flow pattern behind the parent bubble that entrains the son bubble. Oscillation amplitudes and frequencies of the vapor envelope during transition boiling are also reported. The heat flux data for subcooled water exhibit the dual maxima reported by other investigators. An explanation is given that relies on the idea of Witte and Lienhard that a quenching system can choose either a “film-transition” or a “nucleate-transition” curve.

On the flexibility of municipal boundaries

In models of systems of communities, the assumptions concerning the ease with which boundaries, once drawn, can be adjusted play a central role. Even in a system with many jurisdictions, flexibility of boundaries is a key factor in determing how land rents get allocated within and across communities. We argue that, of the variety of observed types of boundary change, only landowner-initiated detachments (removal of land from existing jurisdictions) are likely to correspond to the type of flexibility needed for Tiebout-like outcomes. We show that detachments are empirically rare in the United States and that institutional rules governing boundary change tend to make detachment difficult. Thus, neither the evidence on the frequency of detachments nor the evidence on institutional rules governing boundary change supports the flexible-boundaries hypotheses.

The role of breakdown of the blood-retinal barrier in cell-injection models of proliferative vitreoretinopathy.

Rabbits were given an intravitreous injection of 5.0 x 10(5) rabbit retinal pigment epithelial (RPE) cells, human RPE cells, or human dermal fibroblasts in one eye and an injection of vehicle alone in the other eye. Some rabbits were treated with retinal cryopexy or intravenous sodium iodate on the day before injection. Vitreous fluorophotometry (VFP) and fundus examinations were performed before and at various times after cell injections. Retinal detachments were graded by premortem ophthalmoscopic examinations and postmortem gross pathologic examinations. Eyes injected with cells had higher VFP readings than eyes injected with vehicle at all time points. Eyes injected with fibroblasts or rabbit RPE had significantly higher mean VFP values before the onset of retinal detachment than those injected with human RPE cells. Within each group, high levels of fluorescein leakage in the first week correlated well with severity of subsequent traction retinal detachment and the fibroblast and rabbit RPE groups had more severe detachments than the human RPE group. Treatment with cryopexy or sodium iodate resulted in higher VFP readings, a higher frequency of retinal detachments, and detachments that occurred earlier and that were more severe. These data demonstrate that intravitreous cells cause blood-retinal barrier breakdown in rabbits and that the amount and duration of this breakdown are important variables in retinal detachment formation.

Netzhautablösung nach Implantation einer Hinterkammerlinse

In a series of 6000 cases of pseudophakia following extracapsular cataract extraction and implantation of Simcoe-type posterior chamber lenses, observed for a minimum of 20 months, the incidence of retinal detachment was 21 cases (0.33%). Significant risk factors include male sex (18/21, 82%), high myopia (axial length, over 25 mm in men), intraoperative rupture and late discussion of the posterior capsule. The frequency of retinal detachment following intracapsular cataract extraction without lens implantation was four times greater than that after extracapsular cataract extraction with implantation of a posterior chamber lens. After intracapsular cataract extraction and implantation of an iris-fixation lens it was eight times greater. Horseshoe tears, most of which were located in the peripheral superior quadrants, were seen in 14 eyes (76%). In three eyes no holes were detected. Reattachment was less successful in eyes with posterior chamber implants than in phakic eyes with retinal detachments.

Retinal Detachment Following Endophthalmitis

Fifty-five consecutive patients with a clinical diagnosis of bacterial endophthalmitis were reviewed. All patients were treated with systemic, periocular, topical, and intravitreal antibiotics. In addition, 33 of the patients underwent a pars plana vitrectomy. Nine retinal detachments occurred within six months of initial diagnosis. The higher frequency of retinal detachment in the vitrectomy group (21%) as compared to those patients managed without vitrectomy (9%) may be explained by a combination of surgical complications and the increased severity of endophthalmitis in the vitrectomy group. The two patients who developed retinal detachment during vitrectomy surgery rapidly progressed to no light perception. Conversely, the repair of retinal detachments diagnosed postoperatively had a good prognosis.

Metal transfer in arc welding as a varicose instability. II. Development of model for arc welding

For pt.I see ibid., vol.18, p.1431 (1985). A model of metal transfer in open arc welding is developed which provides a framework for predicting the influence of welding parameters in steady and pulsed current welding. It is found possible to present results in terms of simple expressions which are in broad agreement with available observations. Considered here are aspects such as droplet evolution, detachment frequency and size, selection of pulse parameters, influence of electrostatic stress on transfer, drop dynamics and the relationship between balance of force approaches to transfer and the present instability model.

Effects of 2-Hydroxyethylmethacrylate on the plasma membrane of mouse and human fibroblasts and on beating heart cells, as measured by cell detachment, lactate-dehydrogenase release and contraction frequency: A comparison of three test systems

Effects of 2-Hydroxyethylmethacrylate on the plasma membrane of mouse and human fibroblasts and on beating heart cells, as measured by cell detachment, lactate-dehydrogenase release and contraction frequency: A comparison of three test systems

Complete and core vitrectomies in the treatment of experimental posterior penetrating eye injury in the rhesus monkey. II. Histologic features.

A controlled trial of pars plana vitrectomy for posterior penetrating eye injury was done in a group of rhesus monkeys to compare the results of limited (core) and complete vitrectomies performed one day and two weeks after injury. Although core vitrectomy was technically easier and led to fewer operative complications, the frequency of traction retinal detachment was significantly higher than after a complete vitrectomy. There was no significant difference between eyes operated on one day or two weeks after injury.

Complete and core vitrectomies in the treatment of experimental posterior penetrating eye injury in the rhesus monkey. I. Clinical features.

A controlled trial of pars plana vitrectomy for posterior penetrating eye injury was done in a group of rhesus monkeys to compare the results of limited (core) and complete vitrectomies performed one day and two weeks after injury. Although core vitrectomy was technically easier and led to fewer operative complications, the frequency of traction retinal detachment was significantly higher than after a complete vitrectomy. There was no significant difference between eyes operated on one day or two weeks after injury.

Importance of zinc for human sperm head-tail connection.

Head-tail detachment of ejaculated human spermatozoa was studied with phase contrast microscopy. The frequency of head-tail detachment was assessed after sperm exposure to the anionic detergent sodium dodecyl sulfate (SDS) for 60 min at 22 degrees C. Decapitation was enhanced by EDTA. Zinc reversibly inhibited native as well as EDTA induced head-tail disconnection. Still a certain proportion of spermatozoa were resistant to EDTA-treatment and this proportion significantly increased upon 24 h of saline storage. The development of EDTA resistance was enhanced by EDTA treatment before storage. A physiological role for zinc as a preserver of an inherent mechanism for head-tail detachment is suggested.

The Incidence of Retinal Detachment Following Phacoemulsification

THE frequency and characteristics of aphakic retinal detachments have long been of interest. Historically, aphakic retinal detachments have been reported to comprise 5-33% of retinal detachment series.1 Retinal referral centers in the United States report an incidence of aphakic retinal detachments of about 25% in several large series.2•4 The incidence of retinal detachment in the general population is reported as 0.01%.5•6 This small incidence gives emphasis to the importance of this complication following cataract surgery.

Dripping characteristics in a horizontal tube film evaporator

The knowledge of the mode of liquid flow between neighboring consecutive tubes in a horizontal tube bundle is important to the understanding of transport rate characteristics. Drop size, drop detachment frequency and the distance between drop-producing sites at the bottom of the tube were studied as a function of surface tension, tube size and spatial location of the tube in the vertical column in the bundle. Comparison between smooth and grooved tubes is reported. The effect of dripping on the (mass) transfer rates is demonstrated. The study also reveals a hysteresis-type phenomenon which is associated with the direction of flow rate increments.

Peripheral retinal lesions in aphakia

The peripheral retina of 150 aphakic eyes with uncomplicated extraction was studied with the Goldmann three-mirror contact lens. The patients were examined 1 month to more than 2 years after cataract extraction. In addition to degenerations which are descirbed everywhere and are seen both in phakic and aphakic eyes, the authoris have emphasized lesions which they consider to be specific of aphakia. These lesions are retinal haemorrhages of wich four types are described; pigmentary anomalies and retinal tears and holes. Taking into consideration the great frequency of aphakic retinal detachment in comparison with phakic detachment, it is evident that such lesions must be held liable in aphakic retinal detachment.

The vitreous in aphakia

The authors have studied the vitreous in 150 aphakic eyes after uneventful operations. They were examined by the slit-lamp and the Goldmann three-mirror glass. Two types of lesions were revealed: (1) 42% showed rupture of the anterior hyaloid membrane; this is not considered dangerous. (2) 69.3% showed posterior detachment of the vitreous, a more serious lesion. It is often associated with retinal lesions such as haemorrhage, pigmentary anomalies, and retinal tears. In view of such lesions, one cannot consider the aphakic patient as a normal subject and aphakia as a physiological condition. The frequency of retinal detachment in the aphakic bears witness to it.

Effect of heater vibration on the boiling process

The effect of harmonic oscillations on bubble detachment frequency and its dispersion is considered. The experiments were performed at frequencies from 20 to 100 Hz, at oscillation amplitudes of 0 to 0.4·10−4 m. It was established that vibration leads to a decrease in detachment frequency and dispersion.