Type Vacuum Research Articles

Effect of molten salt phase change layer on thermal performance of solar vacuum collector

A novel straight through vacuum solar energy collector with molten salt phase change thermal storage layer was proposed. Solar salt (60% NaNO3-40% KNO3) was used as phase change materials (PCMs), and the effect of phase change material layer on the thermal performance of straight-through type vacuum solar energy collector has been studied numerically. The results show that: A 13 mm thick phase change material layer was added to the collector tube with an outer diameter of 17 mm, and the heat storage was increased by 53.57%; when the solar radiation is stopped, a constant temperature of 4min-16min is maintained, and then the temperature drops more slowly than that without addition. Molten salt phase change layer can significantly reduce the influence of solar cycle and instability on the straight-through solar vacuum collector tube.

Heat transfer enhancement and field synergy analysis of vacuum collector tube with inserted rotor

Aiming at the large heat loss inside the traditional trough-type vacuum solar heat collecting tube, a new type of spiral three-blade rotor structure was designed and inserted into the inner tube side of the heat collecting tube. Based on the principle of fluid dynamics and field synergy, a mathematical model of the three governing equations of the fluid in the tube was established. Numerical simulations of the heat transfer and flow in the flow field in the two types of collector tubes with or without interpolated rotors were performed. Performance comparisons were made in terms of velocity field, pressure field, temperature field, and field synergy coupling ability. The results of the comprehensive evaluation index of heat transfer performance were finally given. The research shows that the PEC value continues to become larger with the increase in the inlet flow rate, from an initial value of 1.63 to a final value of 2.69. The heat transfer performance enhancement advantage of the new type vacuum heat collector tube is obviously greater than the disadvantage of flow resistance, and the comprehensive performance is better.

Goldstone bosons in different PT-regimes of non-Hermitian scalar quantum field theories

We study the interplay between spontaneously breaking global continuous and discrete antilinear symmetries in a newly proposed general class of non-Hermitian quantum field theories containing a mixture of complex and real scalar fields. We analyse the model for different types of global symmetry preserving and breaking vacua. In addition, the models are symmetric under various types of discrete antilinear symmetries composed out of nonstandard simultaneous charge conjugations, time-reversals and parity transformations; CPT. While the global symmetry governs the existence of massless Goldstone bosons, the discrete one controls the precise expression of the Goldstone bosons in terms of the original fields in the model and its physical regimes. We show that even when the CPT-symmetries are broken on the level of the action expanded around different types of vacua, the mass spectra might still be real when the symmetry is preserved at the tree approximation and the breaking only occurs at higher order. We discuss the parameter space of some of the models in the proposed class and identify physical regimes in which massless Goldstone bosons emerge when the vacuum spontaneously breaks the global symmetry or equivalently when the corresponding Noether currents are conserved. The physical regions are bounded by exceptional points in different ways. There exist special points in parameter space for which massless bosons may occur already before breaking the global symmetry. However, when the global symmetry is broken at these points they can no longer be distinguished from genuine Goldstone bosons.

Analysis of cycloid type vacuum compressors for water vapor compression systems at sub-atmospheric pressures

Current refrigerant regulations lead to a transition towards low GWP refrigerants and natural refrigerants. Water vapor (R718) has been introduced in different vapor compression chiller and heat pump systems. Current R718 systems are based on turbo type compressors due to the resulting sub-atmospheric operating pressure and the low volumetric cooling capacity. This leads to a rather limited application range due to the pressure ratio limitations of turbo compressors. The application range of R718 may be extended towards heat pump operation by using positive displacement compressors such as state of the art vacuum compressors. This paper analyses the application of an oil free cycloid type variable pitch screw vacuum compressor for a heat pump at 2…15 °C evaporation temperature and 25…85 °C condensing temperature. A chamber model was used for the compressor analysis. During the analysis the compressor geometry, its speed and leakage gap sizes were varied. The results include the compressor isentropic efficiency, its volumetric efficiency and the resulting discharge temperature.

Комплекс программ для численного анализа электровакуумных приборов клистронного типа.

Комплекс программ для численного анализа электровакуумных приборов клистронного типа.

Friction and wear behavior of Cu-La2O3 composite sliding against 52100 bearing steel in vacuum

Cu-La2O3 nanocomposite used as sliding electrical contact materials for satellites and spacecraft was fabricated via internal oxidation method followed by powder metallurgy. The Cu-La2O3 composites were subjected to the microstructure analysis, microhardness and tensile test. The tribological properties were performed using a pin-on-disk УТИ TB100 type vacuum tribometer in vacuum, rubbing against 52100 type bearing steel disk at different applied loads varied from 10 to 40 N. Results indicated that the La2O3 particles were uniformly dispersed in the copper matrix, and the size of La2O3 particles was below 50 nm. Besides, the La2O3 reinforcement was effective in improving tensile strength and microhardness. When the La2O3 content was 1.3 wt %, the tensile strength and microhardness of the Cu-La2O3 reached a maximum of 329 MPa and 118 Hv, respectively. The coefficient of friction slightly increased with the increasing La2O3 content. The wear rate of Cu-1.3 wt% La2O3 nanocomposite was 3.3 × 10−3 mg m −1 for 500 m in vacuum, which was reduced by 39% compared with that of pure Cu. When the normal load increased from 10 to 40 N, the wear mechanisms changed from abrasive wear to severe plastic deformation, delamination wear and fatigue wear.

Investigation into Window Insulation Retrofitting of Existing Buildings Using Thin and Translucent Frame-Structure Vacuum Insulation Panels

Insulation performance in older buildings is usually poor, so retrofitting the insulation in these buildings would reduce the energy required for heating, resulting in cost and energy savings. Windows account for a significant amount of the heat loss, therefore, we have developed vacuum layer type vacuum insulation panels (VIPs) with a frame structure that is also slim and lightweight. The developed VIPs are inexpensive and easy to install, as well as being slim and translucent, so retrofitting the window insulation of existing buildings can be easily performed. In this paper, we propose a frame covering with a low emissivity film and a gas barrier envelope coating, with a focus on a reasonable design method. Firstly, a structural model was created to evaluate the safety and specifications of the frame using element mechanical analysis. Next, a finite element model (FEM) was created to predict the insulation performance. Subsequently, experimental validation was completed and the insulation performance was evaluated with the measured thermal conductivity by a guarded hot plate (GHP) apparatus. Finally, case studies were used to evaluate the insulation performance under different conditions. The optimum design included a reasonable frame-structure to hold the vacuum layer with a high insulation thermal conductivity performance of approximately 0.0049 W/(m·K).

法布里-珀罗薄膜干涉的光纤温度传感器

In order to develop a miniature fiber-optic temperature sensor with simple structure, low cost and mass production, the principle of optical coating interference-based temperature sensor was analyzed. The coating formula of temperature sensing probe was designed by TFCalc formula designing software using ZrO2 and Al2O3 materials. The thin film was deposited on the tip of multimode fiber by using electron-beam evaporation in Nanguang ZZS1100-8/G box type vacuum coating machine. The measurement system of coating interference-based temperature sensor was interrogated. The experimental result shows that the wavelength shift of the fiber-optic temperature sensor is linear in the range of 200-600℃, and the correlation coefficient was calculated to be 99.7%, the sensitivity of temperature is 8.3710-6/℃. The temperature sensor based on Fabry-Perot interference is suitable for mass production with stable performance, accurate point measurement, narrow installation position or higher application requirements for integrated sensor.

Detailed modeling and simulation of an out-in configuration vacuum membrane distillation process.

In this study, a detailed rigorous theoretical model was developed to predict the transmembrane flux of a shell-and-tube type vacuum membrane distillation (VMD) module for seawater desalination. Two modes of operation are used for performing the VMD, namely lumen-side feed (in-out) configuration and shell-side feed (out-in) configuration. In this study, detailed mathematical formulations are derived for an out-in configuration that is commonly used in seawater desalination applications. Experimental results and model predictions for mean permeate flux are compared and shown to be in good agreement. The results indicate that although the simple VMD model that maintains a constant permeate pressure is easy to use, it is likely to significantly overestimate the mean permeate flux when compared to the detailed model that considers the pressure build-up in the fiber lumen. The pressure build-up of water vapor in the fiber lumen is identified as the crucial factor that significantly affects the VMD performance because it directly reduces the driving force for vapor permeation through the membrane pores. Additionally, its effect is more pronounced at longer fiber lengths and higher permeate fluxes, and this is achieved at higher feed temperatures and velocities and at lower feed salinities. In conclusion, the results of the study are extremely important in module design for the practical applications of VMD processes.

Enhanced product quality in lubricant type vacuum distillation unit by implementing dividing wall column

Lubricants are highly value-add petroleum refinery products fabricated from lube base oils, the side cuts from lube-type vacuum towers of crude distillation units. In such a popular lubricant type vacuum distillation unit (LTVDU), the 4th lube side cut, nearby the feeding stage, is normally designed to control the 3rd lube cut end boiling point and the bitumen residue flash point temperature. With useless wider boiling point range than the other lube side cuts, its fate is to discharge as fuel or circulate back to the vacuum furnace for limited higher yield at the cost of more energy. This situation triggered our work to reduce boiling point overlap between the 3rd and 4th lube cuts by implementing dividing wall column (DWC) into LTVDU. This novel design is verified to benefit through an industrial case study. Namely, the 4th lube cut boiling point range is so dramatically narrowed as to be a new lube product, without adding extra heat loads. This way the lube base oil product yield can be greatly improved. Industrially, this DWC designed at LTVDU washing zone can deliver excellent hydraulics and carbon residual controlling performance for larger specific liquid flow by section crossing off for DWC.

Non-geometric Calabi-Yau backgrounds and K3 automorphisms

We consider compactifications of type IIA superstring theory on mirror-folds obtained as K3 fibrations over two-tori with non-geometric monodromies involving mirror symmetries. At special points in the moduli space these are asymmetric Gepner models. The compactifications are constructed from non-geometric automorphisms that arise from the diagonal action of an automorphism of the K3 surface and of an automorphism of the mirror surface. We identify the corresponding gaugings of mathcal{N} = 4 supergravity in four dimensions, and show that the minima of the potential describe the same four-dimensional low-energy physics as the worldsheet formulation in terms of asymmetric Gepner models. In this way, we obtain a class of Minkowski vacua of type II string theory which preserve mathcal{N} = 2 supersymmetry. The massless sector consists of mathcal{N} = 2 supergravity coupled to 3 vector multiplets, giving the STU model. In some cases there are additional massless hypermultiplets.

Carbon nanotubes based vacuum gauge

We have created an ionization type Vacuum gauge with sensor element based on an array of vertically aligned carbon nanotubes. Obtained asymmetrical current-voltage characteristics at different voltage polarity on the electrode with the CNTs. It was found that when applying a negative potential on an electrode with the CNTs, the current in the gap is higher than at a positive potential. In the pressure range of 1 ÷ 103 Torr vacuum gauge sensitivity was 6 mV/Torr (at a current of 4.5·10-5 A) and in the range of 10-5 ÷ 1 Torr was 10 mV/Torr (at a current of 1.3·10-5 A). It is shown that the energy efficiency of vacuum gauge can be increased in the case where electrode with CNT operates as an emitter of electrons.

A-38 バキュームブレーカの歴史とHASS 211(大気圧式バキュームブレーカ)およびHASS 215(圧力式バキュームブレーカ)の改定

A-38 バキュームブレーカの歴史とHASS 211(大気圧式バキュームブレーカ)およびHASS 215(圧力式バキュームブレーカ)の改定

The effect of process variables on the properties of nanoporous silica aerogels: an approach to prepare silica aerogels from biosilica

Silica aerogel, a nanoporous material, was produced by using rice husk ash via sol–gel method. The aim of the study is to examine effects of the acid type (acetic, hydrochloric, nitric, oxalic and sulfuric acid), dryer type (air, freeze, oven and vacuum) and the addition of tetraethyl orthosilicate on the structural and physical properties of aerogels produced from rice husk ash. In addition, this is the first study investigating the effect of vacuum oven drying on the structure of rice husk based silica aerogel. Specific surface area and pore size of obtained silica aerogels have been analyzed by the N2 adsorption and desorption measurements at 77 K via Brunauer–Emmett–Teller (BET) and Barrett–Joiner–Halenda (BJH) methods, respectively. Surface functional groups were determined with fourier transform infrared spectroscopy (FTIR). Surface morphology was examined with scanning electron microscopy (SEM). Moreover, density was calculated by tapping method. The results showed that all of the variables had remarkable effects on the final properties of the silica aerogel. The BET specific surface area of the silica aerogels increased with the addition of tetraethyl orthosilicate, while the tapping density decreased. The BET specific surface area and pore size of silica aerogels varied between 140.7–322.5 m2 g−1, and 5.38–12.05 nm, respectively. Silica aerogel which was obtained by using oxalic acid, tetraethyl orthosilicate addition and air dryer had the highest BET specific surface area (322.5 m2 g−1).

Design Optimization of a Sorption Integrated Sydney Type Vacuum Tube Collector

In order to reach the targets on emissions set by the European Commission, both new and existing buildings must reduce their fossil fuel inputs. Solar thermal cooling supplying on-site renewable heating and cooling could potentially contribute toward this goal. In this paper, a novel concept for solar thermal cooling providing efficient coproduction of cooling and heating based on sorption integrated vacuum tube collectors is proposed. A prototype collector has been constructed and tested in a solar laboratory based on a method developed specifically for sorption integrated collectors. From the test results, the key performance parameters have been determined and used to calibrate a mathematical model for trnsys environment. System simulation has been conducted to optimize the collector and sorption module configuration by performing a parametric study where different vacuum tube center–center (C–C) distances and sorption module designs are tested for a generic hotel in Ankara, Turkey. The parametric study showed that the heating and cooling output per year can be as high as 1000 kWh/m2 for solar fractions above 50%, and that the output per sorption module compared to the prototype can more than double with an optimized design. Furthermore, cooling conversion efficiencies defined as total cooling output per total solar insolation can be as high as 26% while simultaneously converting 35–40% of the incident solar energy into useful hot water.

Heat Resistance of Human Pathogens in Sous-Vide Products Studied in Model Nutrition Media

Sous-vide (French for ʽunder vacuum’) is a professional cooking method, by which, under oxygen-free conditions and precise temperature control, not only cooking but preservation is achieved. During the process the food matrix is vacuum-packed and undergoes a mild heat treatment, thus achieving an enhanced nutrition value and a better organoleptic character. Due to the mild heat treatment (55 to 90 °C), the high water activity, and the slight acidity of raw materials, the microbial quality assurance is a great challenge even for professionals. The heat treatment does not assure the inactivation of pathogen spores. In our experiments we used Clostridium perfringens representing the spore-forming pathogens, and Salmonella Enteritidis as a the food-borne infection bacterium. Effects of various temperatures were measured in normal and sous-vide type vacuum packaging. Higher thermal death rate in vacuum packaging was demonstrated for Salmonella Enteritidis and Clostridium perfringens.

Optical characteristics of poly(tetrafluoroethylene) thin film prepared by a vacuum evaporation

Poly(tetrafluoroethylene) (PTFE) thin films were deposited onto a glass slide substrate by a heat-resistance type vacuum evaporation apparatus due to changing the evaporation conditions. Transparency of the PTFE thin films prepared by the vacuum evaporation depended on the deposition conditions, i.e., temperatures of the basket, and distance between the evaporation source and substrate. To elucidate relationship between the molecular structure and transparency of the PTFE thin film prepared by the vacuum evaporation, chemical structures, crystallinity and thermophysical property were investigated. The chemical bonding state of the PTFE thin film prepared by the vacuum evaporation was almost the same as that of the pristine PTFE, however, the crystalinity was different. Although the pristine PTFE was crystal structure, the transparent evaporated thin film was estimated to be microcrystal structure. In addition, endothermic peaks in a differential scanning calorimeter (DSC) spectrum of the PTFE thin film were different from that of the pristine PTFE. These endothermic peaks of the PTFE thin film prepared by the vacuum evaporation shifted lower temperature compared to the pristine PTFE, which suggests that molecular weight of the PTFE thin film prepared by the vacuum evaporation decreased compared with that of the pristine PTFE.

Thermal Design of a Thermoelectric Micro-Generator

In this study, we fabricated micro thermoelectric power generator using freestanding film substrate, and we evaluated the performance of the generator from the standpoint of thermoelectric performance and thermal design. We fabricated a SiNx free-standing film substrate about 5 μm thick on Si wafer, using MEMS processes. Then, we prepared for both p and n type of bismuth telluride thermoelectric thin films by using a coaxial type vacuum arc evaporation method, and annealed for one hour at 573 K. As an electrode, Cu was deposited using a vacuum deposition method. We fabricated the thermoelectric power generator of 5 mm × 5 mm using a shadow mask for the patterning. The fabricated generator can create temperature difference of 22.3 K due to its high thermal resistance of the structure when the heat source temperature is 373 K. The exergy of the thermoelectric device is up to 7%. Therefore, the generator can convert about 0.4% of thermal energy into electric energy, even though the material performance is low with ZT = 0.28. The conversion efficiency is much higher than that of the conventional Π type thermoelectric module. It was possible to get higher performance by the thermal design, which is a more simple way than an improvement of ZT.

Brans-Dicke-Maxwell solutions for higher dimensional static cylindrical symmetric spacetime

In this paper, Brans-Dicke-Maxwell type vacuum solutions are considered for a static cylindrically symmetric spacetime in arbitrary dimensions. Exact solutions are obtained by directly solving the field equations for the case where an azimuthal magnetic field is present. Other configurations such as axial magnetic field case can be obtained by suitably relabeling the coordinates. We have also considered conformally related “Einstein frame” to relate the solutions we have obtained with the dilaton-Maxwell type solutions that exist in the literature. We see that for a special case the general solution we present reduces to dilaton-Melvin spacetime. The general relativistic limit of these solutions is also discussed and we found that this limit is different from the four dimensional case.

Integration of Sorption Modules in Sydney Type Vacuum Tube Collector with Air as Heat Transfer Fluid

Abstract Reduced thermal losses and simplified system integration have previously been identified as main opportunities to improve the concept of collector integrated sorption modules for solar heating and cooling. A concept for a facade integrated sorption collector using Sydney type vacuum tube technology and air based heat transfer has been developed and tested in the laboratory. The results from the tests have been used to validate an existing TRNSYS model that has been modified for use with air as heat transfer fluid. The work has been conducted within the FP7 EU iNSPiRe project with the aim to develop a plug & play solar cooling and heating solution.