Low-pressure Generator Research Articles

Application of Grey Prediction in a Solar Energy-Assisted Photocatalytic Low-Pressure Drying Process

An experimental solar energy-assisted photocatalytic low-pressure dryer (SEPLD) for batch food dehydration was developed and tested in an attempt to completely utilize green energy and contribute to reducing greenhouse gas emissions. The dryer consists of high-transmittance glass used to absorb heat from solar radiation, by which means the water content of food products was vaporized and removed using a low-pressure generation system. The performance test, sensory evaluation, and compound analysis showed that the SEPLD had a faster dehydration rate than other drying processes, and samples retained better color and higher amounts of nutrients. Due to the photocatalyst's (TiO2) action, samples dried using the SEPLD had lower bacterial counts. During the food-drying process, the weight of materials is usually calculated with the drying time to obtain dehydration equations that can be used to further assess the efficiency of the drying equipment and drying performance, such as the drying characteristic curves, drying rate, diffusion coefficient, and so on. However, some information was not easy to obtain during the drying process. We spent a lot of time measuring the water content of a large number of raw materials, especially for those raw materials that were difficult to dry. In this study, some seasonal fruits (pineapple [Ananas comosus L. Merrill], tomato [Lycopersicon esculentum], and star fruit [Averhoa carambola L.]) were selected for the drying tests at 40, 50, and 60°C in the SEPLD. The grey prediction methodology (GPM) was used with water content data to establish the SEPLD drying model, and this was applied to simulate the drying process at different temperatures. The results showed that the accuracy of 60°C drying by GM(1,1) of the GPM was better than the other prediction models. It also indicated that the GPM was a feasible way to simulate the drying process. A patent for the SEPLD was granted and issued in Taiwan.

Second law analysis of double effect vapour absorption cooler system

In this paper, exergy analysis of double effect lithium bromide/water absorption refrigeration system is presented. The system consists of a second effect generator between the generator and condenser of the single effect absorption refrigeration system, including two solution heat exchangers between the absorber and the two generators. In order to simulate the refrigeration system by using a computer, a new set of computationally efficient formulations of thermodynamic properties of lithium bromide/water solution developed is used. The exergy analysis is carried out for each component of the system. All exergy losses that exist in double effect lithium bromide/water absorption system are calculated. In addition to the coefficient of performance and the exergetic efficiency of the system, the number of exergy of each component of the system is also estimated. This study suggests the component of the absorption refrigeration system that should be developed. The results show that the performance of the system increases with increasing low pressure generator (LPG) temperature, but decreases with increasing high pressure generator (HPG) temperature. The highest exergy loss occurs in the absorber and in the HPG, which therefore makes the absorber and HPG the most important components of the double effect refrigeration system.

Plasma-ion nitriding of alloy steel with the use of a low-pressure arc plasma generator

The microhardness and structure of coatings deposited by ion nitriding in low-pressure (on the order of 10−1 Pa) arc discharge plasma on steels with different alloying systems (37G2S, 25Kh5M, and R6M5) are considered. The characteristics of steels nitrided in arc discharge and by the traditional method (in a furnace) are compared.

Treatment of Meniere’s disease with the low-pressure pulse generator (Meniett device)

Until recently, surgery was the only treatment option for people with disabling Meniere’s disease that did not respond to adequate medical therapy. A new intermediate level treatment modality, the Meniett device, which applies low-pressure micropulses to the inner ear, has now been shown to be safe and effective. The device is portable and self-administered, requiring a 5-min three-times daily application for an indefinite period. Placement of a tympanostomy tube in the ear drum of the affected ear is necessary. Patient acceptance has been high. Long-term success in control of vertigo is over 80%. Although hearing loss is not improved, Meniett device usage does not adversely affect balance, as do most forms of surgical therapy. Use of the device does not preclude later surgical therapy.

Performance prediction of a solar/gas driving double effect LiBr–H2O absorption system

This paper presents the performance prediction of a solar/gas driving double effect LiBr–H2O absorption system. In order to use auxiliary energy more effectively and be less dependent on solar irradiation, a new kind of solar/gas driving double effect LiBr–H2O absorption system is designed. In this system, the high-pressure generator is driven by conventional energy, natural gas, and solar energy together with water vapor generated in the high-pressure generator, which supplies energy to the low-pressure generator for a double effect absorption system. The temperature of hot water supplied to the low-pressure generator is close to 90 °C. Apart from refrigeration in summer, this system also supplies space heating in winter and hot water throughout the year for family daily use. Simulation results illustrate that this kind of system is feasible and economical. Economic evaluation of several systems is also given in this paper in order to get a clear knowledge of the energy consumption of the system.

Invited commentary

Invited commentary

Performance comparison of double-effect parallel-flow and series flow water–lithium bromide absorption systems

The double-effect parallel flow absorption refrigeration cycle with water–lithium bromide as working fluid is analysed based on the concept of equilibrium temperature at the low pressure generator. Coefficient of performance (COP) and its sensitivity to operating conditions are compared with those for series flow cycle. Maximum attainable COP for parallel flow cycle is greater than that for series flow cycle throughout the range of operating conditions considered here. Performance of parallel flow system is more sensitive to the effectiveness of low pressure heat exchanger than that of series flow system.

Equilibrium low pressure generator temperatures for double-effect series flow absorption refrigeration systems

The equilibrium temperatures at the low pressure (LP) generator for double-effect series flow lithium bromide–water vapour absorption chiller are evaluated and the system performance is estimated at these temperatures. Influence of temperatures at high pressure (HP) generator, evaporator, condenser and absorber, and the effectiveness of heat exchangers on equilibrium temperature and internal heat transfer at LP generator, circulation ratio, and coefficient of performance are studied. Dual-heat mode of operation of the system is also investigated utilising low grade waste heat at the LP generator. Correlations are presented for equilibrium LP generator temperature, internal heat transfer at the low pressure generator, circulation ratio, coefficient of performance, optimum HP generator temperature and optimum circulation ratio for maximum coefficient of performance in terms of operating temperatures, which are useful in the design and control of absorption system even at the off-design conditions.

A novel absorption–recompression refrigeration cycle

This paper reports on a novel ejector boosted single–effect absorption-recompression refrigeration cycle. In this cycle, a steam generator, ejector and a concentrator replace the high and low pressure generators (concentrators) used in conventional double-effect absorption cycle machines, to re-concentrate the absorbent solution. The ejector here acts like a heat-pump to enhance the concentration process by increasing the flow of leaving vapour and by increasing the quantity of heat input at the concentrator. The paper provides a qualitative and quantitative description of the novel cycle and discusses design choices that lead to optimum matching of the absorbent concentrator and ejector. The important role the ejector plays in this novel refrigeration cycle is discussed and some experimental data are presented. An experimental lithium bromide refrigerator based on this cycle is described.

Optimal performance of double-effect series flow vapour absorption refrigeration systems with new working fluids

In a double-effect series flow vapour absorption refrigeration system (VARS), an optimum value of the low-pressure generator temperature exists at which all the vapour generated at the high-pressure generator is condensed. At these conditions, a comparative study of the performance of VARS using environment friendly refrigerants such as, R32, R134a, and R124 with N,N′-dimethyl acetamide (DMAC) as the absorbent is made. It is found that the system with R32-DMAC gives the best performance at high evaporator temperatures. R124-DMAC may be preferred at extreme operating conditions like low evaporator and high heat rejection temperatures. Influence of operating temperatures (high-pressure generator, evaporator, condenser and absorber) and the effectiveness of heat exchangers on the optimum low-pressure generator temperature, cut-off temperature, circulation ratio and coefficient of performance are studied. © 1998 John Wiley & Sons, Ltd.

Theoretical analysis of low-temperature hot source driven two-stage LiBr/H 2O absorption refrigeration system

A detailed theoretical analysis is presented for a two-stage LiBr/H 2O absorption refrigeration system, which consists of an evaporator, a low-pressure absorber, a low-pressure generator, a high-pressure absorber, a high-pressure generator, a condenser, a low-pressure heat exchanger and a high-pressure heat exchanger, driven by a low-temperature hot source. A comparison of results from the theoretical analysis and preliminary experiment indicates that the theoretical analysis developed can represent a real system with a reasonable accuracy, and is useful for future development.

Reduced Transplant Lung Volumes after Single Lung Transplantation for Chronic Obstructive Pulmonary Disease

Single lung transplantation is now an extremely successful option for the treatment of end-stage chronic obstructive pulmonary disease (COPD). This procedure involves placing a normal sized lung in a hyperinflated hemithorax. Preliminary observations of these patients suggest that the transplanted lung volume is smaller than expected and often the native (COPD) lung increases in volume. The purpose of this investigation was to quantify the volume contributions of the transplant and native lung to the total lung capacity. In seven patients who underwent single lung transplant for end-stage COPD the transplant and native lung volumes were measured by computer-analyzed planimetry immediately after transplant and the following 6 mo post-transplant. The transplant lung volume was smaller than predicted immediately after transplant at only 33 ± 5% (mean ± SD) of predicted TLC. This did not change significantly over the next 6 mo. Native lung volume increased following transplant to 74 ± 19% predicted TLC at 1 mo and 80 ± 16% at 6 mo. Five of the seven patients subsequently underwent measurement of pleural pressures at TLC. The mean static pleural pressure at TLC was low at −16 ± 5.1 cm H2O. In summary, following single lung transplantation for COPD the transplanted lung is significantly restricted. We conclude that the likely mechanism of this restriction is due to low transpulmonary pressure generation.

Reduced transplant lung volumes after single lung transplantation for chronic obstructive pulmonary disease.

Single lung transplantation is now an extremely successful option for the treatment of end-stage chronic obstructive pulmonary disease (COPD). This procedure involves placing a normal sized lung in a hyperinflated hemithorax. Preliminary observations of these patients suggest that the transplanted lung volume is smaller than expected and often the native (COPD) lung increases in volume. The purpose of this investigation was to quantify the volume contributions of the transplant and native lung to the total lung capacity. In seven patients who underwent single lung transplant for end-stage COPD the transplant and native lung volumes were measured by computer-analyzed planimetry immediately after transplant and the following 6 mo post-transplant. The transplant lung volume was smaller than predicted immediately after transplant at only 33 +/- 5% (mean +/- SD) of predicted TLC. This did not change significantly over the next 6 mo. Native lung volume increased following transplant to 74 +/- 19% predicted TLC at 1 mo and 80 +/- 16% at 6 mo. Five of the seven patients subsequently underwent measurement of pleural pressures at TLC. The mean static pleural pressure at TLC was low at -16 +/- 5.1 cm H2O. In summary, following single lung transplantation for COPD the transplanted lung is significantly restricted. We conclude that the likely mechanism of this restriction is due to low transpulmonary pressure generation.

Theoretical study of a new energy extraction scheme of a chemically pumped pulsed iodine laser amplifier

A new energy extraction scheme of a chemically pumped pulsed large-scale iodine laser based on a high-pressure pulsed singlet oxygen generator is proposed. In previous investigations only low-pressure oxygen generators have been considered. Since they require a high iodine density for an efficient amplifier operation, the lifetime of the stored energy is correspondingly small and thus only small-sized iodine amplifiers appear to be technically feasible. We found, however, that when the singlet oxygen is generated at high-pressure, the iodine density required can be considerably reduced so that the lifetime of the stored energy becomes sufficiently long to fill up large amplifier cells. A numerical model is developed and the extractable energy is theoretically estimated. It is shown that 0.2J/1·pass can be extracted when an input pulse of 20 ns duration (FWHM) and 1 J/cm2 fluence is fed into the amplifying medium.

Experience with a New Multifunctional Lithotripter, the Dornier MFL 5000: Results of 415 Treatments

The Dornier MFL 5000 is a new multifunctional work station for urologic diagnosis, endourology, and extracorporeal shock wave lithotripsy (ESWL). Features of this bathfree device include a tiltable U-arm with an under-table x-ray tube for stone localization, a low-pressure generator with twin-pulse technique, a modified semiellipsoid reflector, and an ultrasound unit for stone localization and monitoring. From April 1988 until January 31, 1989, 415 ESWL treatments were performed on this machine. The stones were 45.6% (189) caliceal, 25% (108) renal pelvic, 26% (108) ureteral, and 2.4% (10) branched. The majority of stones had a diameter between 8 and 20 mm. Stone disintegration required a mean of 2450 impulses. Mean treatment time was 33 minutes. Mean final generator voltage was 20 kV (range 17 to 24 kV). Post-ESWL ancillary procedures proved to be necessary in 24 patients (5.8%). The retreatment rate was 19.5% (81) including 4.8% (20) with planned multiple treatments. In 86.6% (359) of patients, a noninvasive oral analgesia technique was used successfully. Follow-up at 3 months could be obtained in 59.5% (247). The overall stone-free rate was 77.5% (191). ESWL was unsuccessful in 2.4% (10). The results of this study are comparable to those achieved with the modified Dornier HM3. The MFL 5000 has advantages, especially in the treatment of lumbar ureteral stones in situ, less radiopaque stones, and in obese patients. The under-table x-ray tube considerably reduces radiation exposure to room personnel and the treating urologist. Excellent imaging qualities are provided by the 14-inch image intensifier. The MFL 5000 proved to be satisfactory for a variety of endourologic procedures.

New Generator for Low Pressure Lithotripsy with the Dornier HM3: Preliminary Experience of 2 Centers

The technical innovation of a low pressure generator with a standard ellipsoid installed into the Dornier HM3 lithotriptor leads to a decrease in pressure at the second focus by 30 per cent. The preliminary experience with 273 patients treated at 2 centers is presented. The success rate in terms of stone disintegration was similar compared to the old generator (96 versus 97 per cent). However, the rate of secondary treatments increased from 8 to 15.5 per cent, respectively. Owing to the lower peak pressures at the second focus, an additional 700 impulses per session were necessary. The method of anesthesia was changed to a combination of an anxiolytic and analgesic drug in the majority of the patients. Treatment was judged as free of pain or with easily tolerable pain in 93 and 88 per cent of the patients, respectively.

Technical modifications of the Dornier HM-3 lithotriptor with an improved anesthesia technique

Three technical modifications have been introduced into the Dornier HM-3 lithotriptor at the Marienhospital Herne: a low-pressure generator, which reduces the energy at the second focus by 30%, a modified semi-ellipsoid with an increased aperture and altered geometric dimensions, and the twin-pulse technique, releasing two impulses synchronized with a single R-wave. The treatment standard achieved with the conventional HM-3 device could be maintained, with a radiological success rate for stone disintegration of 95%. Procedural time could be reduced. The mean number of impulses and rate of second treatments increased, mainly due to the increasing proportion of ureteral and branched calculi. Cutaneous petechiae were rarely observed, suggesting less tissue damage with the lower pressures used. The profound reduction in pain perception with these technical modifications led to a new anesthesia technique. A combination of an oral anxiolytic and oral analgesic was effective in 94%. The results suggest that patient comfort and safety during ESWL treatment have been considerably improved.

A two stage intermittent solar refrigeration system—Evaluation of salient parameters

A two stage intermittent solar refrigeration system is described briefly. In such a system, when flat-plate collectors are used for generation, it is very likely that the two generation temperatures are around the same value. The successful operation of the cycle under such conditions depends upon the proper selection of the initial solution concentrations in the high and low pressure generators and the volume ratio of the generators. These parameters have been evaluated with the help of the thermodynamic analysis of the refrigeration cycle operating with ammonia as the refrigerant and water as the absorbent.

低圧タービンロータ材の両振引圧疲労における塑性ひずみ繰返しの影響

The rotor axes in low pressure turbines and generators in service are occasionally subjected to such a loading that a few overloads happen to be overlapped to the steady state repetition of low level stresses. Unless understanding the influence of overloads, therefore, the fatigue design of turbine rotors will not be completed. Such loadings supposedly give rise to an extreme acceleration of fatigue crack growth. In this paper, by employing the same material as usual low pressure turbine rotors', heat-treated 3.5Ni-Cr-Mo-V steel, the influence of overloads on the fatigue damage in the crack initiation and growth stages was investigated in alternating two-load level fatigue tests. The base block consisted of axial reversed strain cycling Δep=0.5% as overloads and constant stress cycling σa=421MPa (above the fatigue strength) or 372MPa (below the fatigue strength) as a baseline loading.Contrasting to the previous investigation on an annealed S40C steel, the material exhibited cyclic softening in the low cycle fatigue test whereas the induced plastic strain during the low cycle fatigue stage disappeared gradually in the course of the following base line loading; the application of overloads always reduced the crack initiation life. The failure life was also reduced shorter than the predicted from Manson's double linear damage rule with using the fatigue properties of virgin material. The crack growth retardation, which may be induced by the application of overloads in the crack growth stage, was not observed on this material unlike on the previous carbon steel.

A Low-Pressure Hydrogen Generator for Use in Filling Radiosonde Balloons

At weather stations outside of the United States meteorological balloons are usually inflated with hydrogen. At stations remote from large industrial centers it is usually cheaper to generate the hydrogen at the station than to ship it in cylinders from the industrial center. Probably the most common hydrogen generator for station use is of the high pressure chemical style where pressures in excess of 2000 p.s.i. are not uncommon. To reduce the number of serious accidents occurring through the use of these high pressure generators, a low pressure generator with a maximum pressure of 4 p.s.i. has been developed.