The two recent global emergencies (stratospheric ozone depletion and global warming) force refrigerating engineers and operators to face a new revolution on the choice of the working fluids for the ...different applications of refrigeration technology. Chemistry by now runs short of new synthetic products meeting within acceptable limits all the requirements asked for by the different refrigeration applications, and compromise solutions are more and more necessary, involving a limited use of few old-generation fluids, the new family of products HFO and an increased consideration for natural refrigerants. While dealing with these topics, this paper will show how basic thermodynamics can highlight important characteristics of a refrigerant.
Endovenous laser treatment (EVLT) is an efficient method to treat incompetent saphenous veins with high occlusion rates. Major side effects reported with 810 nm and 980 nm diode laser are ...postoperative pain and bruising. Recently laser systems with higher wavelengths (WSLWs), associated with new energy delivery devices, seem to reduce some side effects previously reported. Aim of this study is to verify if there are real clinical advantages in the use of WSLWs, reviewing the comparison studies present in the literature. After a search on MEDLINE database, a review of all papers concerning WSLWs, was made. Five studies of comparison between different wavelength, 810 vs.. 980 nm, 940 vs.. 1320 nm, 810 vs.. 1320 nm, 980 vs.. 1500 nm and 980 vs.. 1470 nm were found. These studies report similar results: the WSLWs produce fewer side effects. New optical fibers have also been developed; WSLWs with the use of these new fibers dramatically changed the postoperative period, with a reduction of pain and bruising. There is no scientific evidence that WSLWs have any effect on long-term outcome, although short-term differences have been found for some side effects. Other parameters are also important: in particular, LEED and cold tumescent anesthesia are critical points. Laser fiber design probably has a significant effect on treatment success in the performance of EVLT and also how the energy is delivered (pulsing or continuous mode) and the pull-back rate of the laser fiber are possible factors affecting complication ratios and pain scores, regardless of the type of wavelength used.
In this paper, the PD properties of an ester oil/PB and a mineral oil/PB system undergoing a moisture transient are investigated using a needle-plane electrode under natural cooling. The temperature, ...moisture concentration and water activity of the oil are continuously monitored. Moreover, an improved moisture diffusion model is developed by using COMSOL Multiphysics to verify the experimental results. The measurement results show that there is a sharp reduction of partial discharge inception voltage (PDIV) or a sudden increase of PD intensity in the process of natural cooling for both ester oil and mineral oil system. However, the PDs extinguish gradually after the occurrence of the minimum of PDIV. For the cooling mode selected in this study, the minimum of PDIV for the ester oil system appears in the third hour after cooling begins, while it is about in the second hour for the mineral oil system. In addition, the simulation results are consistent with the experimental data.
This paper focuses on the influence of repetitive square wave voltage rise time on partial discharge pulse characteristics in the ultra-high frequency range. Paerial Discharge (PD) tests on ...single-point contact crossed pairs were carried out using repetitive square wave voltages with a wide range of rise times, from 200 ns to 400 μs, including also 50 Hz sinusoidal voltage waveforms. Experimental results show that rise time has a significant influence on magnitude and frequency spectrum of PD pulses. Voltages of shorter rise times generate larger PD pulses with a predominance of high frequency components in the energy spectrum. Interpretations are presented for this phenomenon.
Nowadays, plain and microfin tubes are largely used in refrigeration and air conditioning industries for condensation inside macroscale tubes. The mechanisms of condensation heat transfer and ...pressure drop are tightly linked with the prevailing two-phase flow regime, but not much evidence about the effect of microfins on the condensation flow patterns is still available in the open literature. A deep overview about the relevant literature on two phase flow pattern visualization inside tube considering experimental techniques, suggested flow regime maps and models for heat transfer coefficient is presented. Furthermore, this paper presents the extensive experimental contribution of the Authors with smooth and microfin tubes. The collected data for plain tube are compared against different flow pattern maps. The flow visualizations obtained for microfin tube are compared with those of plain tube; moreover, two flow regime maps proposed by present Authors for smooth and enhanced tubes are validated.
► A comprehensive review on two phase flow patterns visualization inside tubes. ► Flow pattern maps for condensation inside smooth and microfin tubes are validated. ► Flow pattern comparison between plain and enhanced tubes.
The present paper reports local heat transfer coefficients measured during condensation of R1234yf within a single circular 0.96 mm diameter minichannel and compares them to the ones of R134a.
This ...experimental work is carried out in a unique test apparatus which allows to determine the local heat flux extracted from the condensing fluid from the temperature profile of the coolant. For this purpose, the temperatures of the coolant and of the wall are measured along the test section. The saturation temperature is determined from the saturation pressure which is measured at inlet and outlet of the test channel.
Condensation tests are carried out at mass fluxes ranging between 200 and 1000 kg m
−2 s
−1 and the heat transfer coefficients result to be lower as compared to the ones of R134a. Since the saturation temperature drop directly affects the heat transfer rate, the pressure drop during adiabatic two-phase flow of R1234yf is also measured and compared to R134a.
Acute amnestic syndrome is an uncommon clinical presentation of neurological disease. Differential diagnosis encompasses several syndromes including Wernicke-Korsakoff and transient global amnesia ...(TGA). Structural lesions of the fornix account for a minority of cases of acute amnestic syndromes. Etiology varies from iatrogenic injury to ischemic, inflammatory, or neoplastic lesions. A prompt diagnosis of the underlying pathology is essential but challenging. The aim of this review is to systematically review the existing literature regarding cases of acute amnestic syndrome associated with non-iatrogenic lesions of the fornix.
We performed a systematic literature search on PubMed, Scopus, and Web of Science up to September 2023 to identify case reports and case series of patients with amnestic syndrome due to fornix lesions. The systematic review was conducted according to PRISMA guidelines. The research was limited to articles written in English. Cases of fornix damage directly ascribable to a surgical procedure were excluded.
A total of 52 publications reporting 55 cases were included in the review. Focusing on acute/subacute onset, vascular etiology was highly prevalent, being responsible for 78% of cases, 40/55 (74%) of which were due to acute ischemic stroke. The amnestic syndrome was characterized by anterograde amnesia in all patients, associated with retrograde amnesia in 27% of cases. Amnesia was an isolated presentation in most cases. Up to two thirds of patients had persistent memory deficits of any severity at follow-up.
Acute amnestic syndrome can be rarely caused by fornix lesions. In most cases of acute/subacute presentation, the etiology is ischemic stroke, mainly caused by strokes involving the subcallosal artery territory. The differential diagnosis is challenging and a distinction from common mimics is often difficult on a clinical basis. A high index of suspicion should be maintained to avoid misdiagnosis and provide adequate acute treatment to patients with time-dependent disease, also employing advanced neuroimaging. More research is needed to better understand the outcome and identify prognostic factors in patients with amnestic syndrome due to fornix lesions.
A new general flow pattern/flow structure based heat transfer model for condensation inside horizontal, plain tubes is proposed based on simplified flow structures of the flow regimes, and also ...includes the effect of liquid–vapor interfacial roughness on heat transfer. The model predicts local condensation heat transfer coefficients for the following flow regimes: annular, intermittent, stratified-wavy, fully stratified and mist flow. The new model has been compared to test data for 15 fluids (R-11, R-12, R-22, R-32, R-113, R-125, R-134a, R-236ea, a R-32/R-125 near-azeotrope, R-404A, R-410A, propane,
n-butane, iso-butane and propylene) obtained in nine independent research laboratories. The new model has been tested over the following range of conditions: mass velocities from 24 to 1022 kg/(m
2
s), vapor qualities from 0.03 to 0.97, reduced pressures from 0.02 to 0.80 and tube internal diameters from 3.1 to 21.4 mm. Overall, the model predicts 85% of the heat transfer coefficients in the non-hydrocarbon database (1850 points) to within ±20% with nearly uniform accuracy for each flow regime and predicts 75% of the entire database to within ±20% when including the hydrocarbons (2771 points), the latter all from a single laboratory whose data had some unusual experimental trends over part of their test range.
A new flow pattern map and flow pattern based heat transfer model for condensation inside horizontal plain tubes are proposed in this two-part paper. In Part I, a new version of a two-phase flow ...pattern map, originally developed by Kattan et al. J. Heat Transfer 120 (1998) 140 for flow boiling, is presented for condensation inside horizontal tubes while a new heat transfer model is presented in Part II. The new flow pattern map incorporates a newly defined logarithmic mean void fraction (LM
ε) method for calculation of vapor void fractions spanning from low pressures up to pressures near the critical point. Several other modifications are also made that are appropriate for condensation as opposed to evaporation. In the absence of void fraction data at high reduced pressures for these conditions, the new LM
ε method has been indirectly validated using the convective condensation model for annular flow and corresponding heat transfer test data at reduced pressures up to 0.8. The new map has also been successfully compared to some recent flow pattern observations for condensation and other existing flow transition criteria and maps.
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