Glass Vacuum Research Articles

An experimental investigation of the heat losses of a U-type solar heat pipe receiver of a parabolic trough collector-based natural circulation steam generation system

The performance of a parabolic trough collector (PTC)-based steam generation system depends significantly on the heat losses of the solar receiver. This paper presents an experimental study of the heat losses of a double glazing vacuum U-type solar receiver mounted in a PTC natural circulation system for generating medium-temperature steam. Field experiments were performed to determine the overall heat losses of the receiver. Effects of wind, vacuum glass tube, radiation, and structural characteristics on the heat losses were analyzed. The thermal efficiency of the receiver was found to be 0.791 and 0.472 in calm and windy days, respectively, at a test temperature of about 100°C, whereas the thermal efficiencies became 0.792 and 0.663, respectively, while taking the receiver element into consideration. The heat losses were increased from 0.183 to 0.255kW per receiver for the two cases tested. It was shown that neither convection nor radiation heat losses may be negligible in the analysis of such U-type solar receivers.

Model to predict design parameters and performance curves of vacuum glass heat pipe solar collectors

Glass heat pipe solar collectors are becoming very popular for heating/sanitary water production. The use of a double glass system, with vacuum in between (Dewar scheme), allows to minimize heat dispersion to the environment, and to reach potentially temperature levels in competition with much more expensive parabolic trough concentrating solar collectors (stagnation temperatures in excess of 200°C are reported). It opens their use to solar energy conversion (i.e. low-temperature ORC technology). However, in the technical literature there is not much information on the design criteria of these collectors, and of models for evaluating absorbed solar radiation and thermo-fluid-dynamics performance.Starting from the collector’s location weather data and tilt angle, a model to evaluate the absorbed solar radiation is developed. It is based on (I) calculation of the actual angle between solar radiation and the absorbing cylindrical pipe surface; and (II) calculation of the actual absorbed radiation by the heat pipe surface, also including the mutual shading between the different heat pipes, allowing the estimate of the performance in design conditions. Sensitivity to the main design variables is examined. The model includes heat transfer (radiation, forced/natural convection, phase transition) in the different sections of the heat pipe.

Analysis of Heat Losses of Absorber Tubes of Parabolic through Collector of Shiraz (Iran) Solar Power Plant

In this article heat losses of absorber tubes of parabolic trough collectors for the collector field of 250 kW Shiraz (Iran) solar thermal power plant is evaluated for various conditions. For analysis, both experimental measurements and numerical modeling are made to find the impact of failure of heat collecting tubes. The amount of heat losses are compared numerically for 3 different types of tubes; vacuum, lost vacuum (air) and broken glass (bare) tube. The experimental measured data are used to validate the numerical simulation. For temperature measurements around the glass tube and absorber tube an infrared thermograph (IR) camera is used. Thermal images are calibrated with measuring some local temperatures. For theoretical simulation a commercial code for thermal analysis of parabolic collectors are used. An absorber tube with vacuum reduces significantly the heat losses in comparison with broken tube or tube without vacuum. During power plant operation poor isolation or any glass tube failure should be avoided for any solar thermal power plants.

Performance Study of the Glass Vacuum Tube Photovoltaic/Thermal Heat Pump System

Many studies found that the decrease in photovoltaic (PV) cell temperature by 10 o C can improve the efficiency by 0.5-0.7% based on the reference efficiency of 15%. In this paper, the refrigerant R134a is used to cool down the PVs and thus improve the efficiency. The novel glass vacuum tube PV/thermal (PV/T) panel, made of 6 glass vacuum tube – PV module – aluminium sheet – cooper tube sandwiches connected in series, is coupled with a heat pump system acting as the evaporator. Numerical models are established for the performance study. The simulation results indicate that the electrical efficiency is mainly affected by the solar radiation, while the thermal efficiency is mainly affected by the ambient temperature. The annual mean thermal efficiency, electrical efficiency and COP are 0.659, 0.136 and 3.8, respectively.

VSiPMT for underwater neutrino telescopes

Underwater neutrino telescopes are nowadays considered among the most important aims in the field of astroparticle physics. Their structure consists of a cubic-kilometer three-dimensional array of photosensitive devices aimed at the detection of the Cherenkov light emitted by charged particles produced by high energy neutrino interactions with the Earth.To date, a crucial role in this kind of experiments has been played by PhotoMultiplier Tubes (PMTs), however they suffer from many drawbacks such as linearity-to-gain relationship and difficulty in single photon counting. The next generation of experiments will require further improvements in photon detectors performances, therefore alternatives to PMTs are currently under study.In particular the most promising development in this field is represented by the rapidly emerging CMOS p-n Geiger-mode avalanche photodiode technology (G-APD or SiPM), that will allow the detection of high-speed single photons with high gain and linearity. In order to overcome the limit of small sensitive surfaces we suggest an innovative design for a modern hybrid, high gain, silicon based Vacuum Silicon Photomultiplier Tube (VSiPMT) based on the combination of a SiPM with a hemispherical vacuum glass PMT standard envelope. In this work we describe the full SiPM characterization realized by our group and we present the results of our Geant4-based simulations of electron backscattering over the SiPM surface.

Vacuum silicon photomultipliers: Recent developments

VSiPMT (Vacuum Silicon PhotoMultiplier Tube) is an innovative design for a modern hybrid, high gain, silicon based photodetector based on the combination of a SiPM with a hemispherical vacuum glass PMT standard envelope. In such a device photoelectrons emitted by the photocathode are accelerated and focused by an electric field towards a small focal area covered by the SiPM which therefore acts as an amplifier, thus substituting the classical dynode chain of a PMT.With a view to the realization of a first prototype of VSiPMT our group is carrying out a preliminary work aimed at the study of SiPM performances as an electron detector, including an accurate Geant4-based simulation of the interaction between SiPM and electron beams. In order to perform a full characterization of the SiPM we developed an experimental setup for the extraction and the acceleration of a beam of backward secondary electrons emitted after the bombardment of a carbon foil by a proton beam extracted in a TTT-3 accelerator.

Analysis of Conduction Heat Loss From a Parabolic Trough Solar Receiver with Active Vacuum by Direct Simulation Monte Carlo

Results are reported of a numerical analysis of conduction heat loss from a parabolic trough solar receiver with controlled pressure within the annular gap between the tubular absorber and the glass vacuum jacket. A direct simulation Monte Carlo (DSMC)model of rarefied gas within the annular gap is coupled to radiation heat transfer for directional- and spectral-dependent concentrated incident solar radiation. This modeling approach is valid for high Knudsen numbers, and consistently predicts slightly higher heat loss than a continuum model using slip boundary conditions in the range of pressures of interest around 1 Pa. 3-D simulations of axial flow through the annular gap predict higher gas conductance by the DSMC method than by slip flow models, with values converging as pressure increases.

A Glass Dielectric Paste for Preparation Transparent Spacers of Vacuum Glass by Screen Printing

Vacuum glass is a new building material with excellent energy conservation and sound insulation properties. Usually, the spacers between two pieces of flat glass substrates are mini-rings of metal. In the present research, the spacers were prepared with a glass dielectric paste by screen printing, and then sintered till them transparent. The glass dielectric paste for the preparation of transparent spacers of vacuum glass was prepared by using low melting glass powder and terpineol ethyl cellulose solution. The composition of the paste with preferable properties was evaluated as in mass percent: organic vehicle 20-25, and low melting glass powder 73-80. The rheological behaviors of the typical paste were characterized by using an ARES (RFS-III) rheometer. It is found that a weak flocculated network structure is formed in the paste for the high solid filler. The spacers were prepared by screen printing the paste on the glass substrate and then sintered. The transparent, Vickers hardness of the spacers as well as the binder forces between the spacers and the substrate is reported. The reliability of the prepared transparent spacers for the vacuum glass was discussed.

Investigation of a Hybrid Photovoltaic Thermal Heat Pump System

The decrease of photovoltaic (PV) cell temperature by 10 °C is expected to improve the PV electrical efficiency by 0.6-0.7% based on the reference efficiency of 15%. Different cooling liquids like air and water have been introduced to pass across the PVs to reduce the cell temperature, and thus increase the electrical efficiency. In this paper, the refrigerant R134a was used as the cooling liquid and a PV/thermal (PV/T) collector was coupled with a heat pump system acting as the evaporator, which was expected to achieve a better cooling effect and energy performance due to its low boiling temperature. A hybrid PV/T collector, made of 6 glass vacuum tube – PV module – aluminum sheet – cooper tube sandwiches connected in series, worked as the evaporator of the heat pump system. Numerical steady models were established for each component of the heat pump system and part of the PV/T collector/evaporator for predicting their energy performance under the weather data of January 14th at Tibet, China. The results showed that the maximum COP could reach up to 7.6. The daily average thermal efficiency and electrical efficiency were 0.764 and 0.104, respectively.

다중회귀분석법을 이용한 진공유리패널 모서리 접합부와 공정변수간의 수학적 모델 개발

고유가 시대를 맞아 에너지 절약이 사회적으로 이슈화됨에 따라 진공유리에 대한 관심이 높아지고 있다. 진공유리 개발을 위한 핵심 공정 중 유리모서리 접합공정은 두 장의 유리 사이를 진공으로 유지하기 위해 높은 신뢰도를 요한다. 본 논문에서는 유리 모서리 접합 시 기존 프릿을 이용하여 접합하는 방법과 달리 고밀도열원인 수소혼합가스를 이용하여 모서리를 접합하는 공정을 제시하였다. 또한 유리의 파손 및 변형방지를 위해 전기로내의 분위기 온도를 설정하고 균일도를 측정하였다. 기초시험을 통해 모서리접합 공정변수를 설정하고 공정변수에 따른 유리 모서리 접합부 면적과의 수학적관계식을 다중회귀분석으로 도출하였다. The concern about vacuum glass is enhanced as society gets greener and becomes more concerned about energy savings due to the rising cost of oil. The glass edge sealing process needs the high reliability among the main process for the vacuum glass development in order to maintain between the two glass by the vacuum. In this paper, the process of the edge sealing was performed by using the hydrogen mixture gas which is the high density heat source unlike the traditional method glass edge sealing by using the frit as the soldering process. The ambient temperature in the electric furnace was set in the edge sealing to prevents the thermal impact and transformation of the glasses and the temperature distribution uniformity was measured. The parameter of the edge sealing was set through the basic test and the mathematical relation with the area of the glass edge parts according to the parameter was drawn using the multiple regression analysis method.

실험계획법을 이용한 진공유리 Pillar 재료의 혼합비율 최적화

The manufacturing method of the pillar is one of the main process where it is used in vacuum glazing and semi-conductor display field. Pillar can be arranged by screen printing method. However it may unable to spread all pattern of metal mask according to the ingredient of the mixture. In addition, spreaded mixture doesn't maintain the original shape according to the viscosity. In this research, the pillar tried to be arranged through the screen printing by using the inorganic compound of the alumina and silica base. This study suggested a method in which it can decrease the test frequency and design the composition of the vacuum glass pillar by using the mixture design.

Study and Optimization on graft polymerization under normal pressure and air atmospheric conditions, and its application to metal adsorbent

Radiation-induced graft polymerization of glycidyl methacrylate (GMA) onto non-woven polyethylene (NWPE) fabric was achieved under normal pressure and air atmospheric conditions, without using unique apparatus such as glass ampoules or vacuum lines. To attain graft polymerization under normal pressure and air atmospheric conditions, the effects of the pre-irradiation dose, pre-irradiation atmosphere, pre-irradiation temperature, de-aeration of GMA-emulsion, grafting atmosphere in a reactor, and dissolved oxygen (DO) concentration in GMA-emulsion on the degree of grafting (Dg) were investigated in detail. It was found that the DO concentration had the strongest influence, the pre-irradiation dose, de-aeration of emulsion and grafting atmosphere had a relatively strong impact, and the pre-irradiation atmosphere and pre-irradiation temperature had the least effect on Dg. The optimum DO concentration before grafting was 2.0mg/L or less. When a polyethylene bottle was used as a reactor instead of a glass ampoule, graft polymerization under normal pressure and air atmospheric conditions could be achieved under the following conditions; the pre-irradiation dose was more than 50kGy, the volume ratio of GMA-emulsion to air was 50:1 or less, and the DO concentration in GMA-emulsion during grafting was below 2.0mg/L. Under these grafting conditions, Dg was controlled within a range of up to 362%. The prepared GMA–grafted NWPE (GMA–g-NWPE) fabric was modified with a phosphoric acid to obtain an adsorbent for heavy metal ions. In the column-mode adsorption tests of Pb(II), the adsorption performance of the produced phosphorylated GMA–g-NWPE fabric (fibrous metal adsorbent) was not essentially dependent on the flow rate of the feed. The breakthrough points of 200, 500, and 1000h−1 in space velocity were 483, 477 and 462 bed volumes, and the breakthrough capacities of the three flow rates were 1.16, 1.15 and 1.16mmol-Pb(II)/g-adsorbent.

Comparative Study on Hybrid PV/T Heat Pump Systems Using Different PV Panels

Many studies have found that the photovoltaic (PV) cell temperature plays an important impact on the solar-to-electricity conversion efficiency. Different cooling liquids like air and water have been introduced to pass across the PVs to reduce the cell temperature, and thus increase the electrical efficiency. In this paper, the refrigerant R134a is used as the cooling liquid and the PV/thermal (PV/T) panel is coupled with a heat pump system acting as the evaporator, which is expected to achieve a better cooling effect and energy performance due to its low boiling temperature. Two different kinds of PV/T panels, glass vacuum tube (GVT) type and flat plate (FP) type, are proposed for the study on the energy performance comparison. The results show that the GVT PV/T panel has an average thermal efficiency of 0.775 and an average electrical efficiency of 0.089 (based on the reference efficiency of 0.12), which is 73.4% and 1.1% higher than that of the FP PV/T panel respectively, with the solar radiation varying from 200 W/m2to 1000 W/m2. The GVT PV/T heat pump system has an average COP of 5.6, 9.8% higher the FP PV/T heat pump system. The GVT PV/T heat pump system has a better energy performance than the FP PV/T heat pump system.

Exfoliation of graphite by pyrolysis of bromine–graphite intercalation compounds in a vacuum glass tube

Graphite intercalation compounds (GICs) of bromine were rapidly heat-treated and exfoliated at 500°C in vacuum to obtain oxygen-free exfoliated graphite materials. We developed a continuous process—from intercalation to exfoliation—that could be conducted in a single glass tube without exposure to air so as to obtain oxygen-free exfoliated graphite products. It was possible to repeat the process of intercalation and exfoliation several times using bromine, which enabled large-scale exfoliation of graphite at 500°C—comparable to that obtained from GICs produced from sulfuric acid.

Experimental study on a hybrid photovoltaic/heat pump system

Several studies have found that the decrease of photovoltaic (PV) cell temperature would increase the solar-to-electricity conversion efficiency. Different working fluids such as air and water have been used for the cooling of PV modules, but the improvement in energy performance has been found to be small. In this paper, R134a refrigerant was employed to cool the PV modules. With its low evaporating temperature, it was expected to achieve better cooling effect and electrical performance of the PV modules than using air and water working fluids. An experimental rig of a hybrid micro PV panel-based heat pump system was constructed for the performance testing in a laboratory at the University of Nottingham. A small PV panel was made of 6 glass vacuum tube – PV module – aluminium sheet – cooper tube (GPAC) sandwiches connected in series, acting as the evaporator. This was coupled with a small heat pump system. The glass vacuum tubes reduced the heat loss from the PV panel to the ambient, resulting in the improvement of thermal performance. Three testing modes were proposed to investigate the effect of solar radiation, condenser water flow rate and condenser water supply temperature on energy performance. The testing results showed that an averaged COP reached 3.8, 4.3 and 4.0 under the three testing modes with variable radiation, condenser water supply water temperature and water flow rate, respectively, but this could be much higher for a large capacity heat pump system using large PV panels on building roofs. The COP increased with the increasing solar radiation, but decreased with the increasing condenser water supply temperature and water flow rate. The electrical efficiency of PV panel was improved by up to 1.9% based on a reference PV efficiency of 3.9%, compared with that without cooling. The condenser water supply temperature and water flow rate had little effect on the electrical performance.

Numerical Analysis of Heat Loss From a Parabolic Trough Absorber Tube With Active Vacuum System

In current designs of parabolic trough collectors for concentrating solar power plants, the absorber tube is manufactured in segments that are individually insulated with glass vacuum jackets. During the lifetime of a power plant, some segments lose vacuum and thereafter suffer from significant convective heat loss. An alternative to this design is to use a vacuum pump to actively maintain low pressure in a long section of absorber with a continuous vacuum jacket. A detailed thermal model of such a configuration is needed to inform design efforts for such a receiver. This paper describes a combined conduction, convection, and radiation heat transfer model for a receiver that includes the effects of nonuniform solar flux on the absorber tube and vacuum jacket as well as detailed analysis of conduction through the rarefied gas in the annular gap inside the vacuum jacket. The model is implemented in commercial CFD software coupled to a Monte Carlo ray-tracing code. The results of simulations performed for a two-dimensional cross-section of a receiver are reported for various conditions. The parameters for the model are chosen to match the current generation of parabolic trough receivers, and the simulation results correspond well with experimental measurements.

Metal glass vacuum tube solar collectors are approaching lower-medium temperature heat application

Solar thermal collectors are widely used worldwide mainly for hot water preparation at a low temperature (less than 80?C). Applications including many industrial processes and central air conditioning with absorption chillers, instead require lower-medium temperature heat (between 90 degrees C and 150 degrees C) to be driven when using solar thermal energy. The metal absorber glass vacuum tube collectors (MGVT) are developed for this type of applications. Current state-of-art and possible future technology development of MGVT are presented.

Effect of Surface Finish of Braced Pillars on Stress Distribution of Vacuum Plate Glass

The braced pillars were machined by grinding and spark machining. 3-D topography and surface roughness of two kinds of braced pillars were measured. The effect of two kinds of braced pillars on stress distribution of vacuum plate glass was analyzed by electrometric method, and was in comparison. The stress distribution of their important sides was obtained such as sealing side, supporting side and braced pillar. The experimental result showed that maximal stress of braced pillar for vacuum glass occurred in the end side of each braced pillar. Controlling high precision of the brace height and good flatness of the glass sheet considerably improve vacuum plate glass quality, such as its strength, its dependability and service life.

The Electrical Insulation of the TF Coils of ITER

The Toroidal Field (TF) system of ITER consists of 18 coils in which the winding pack (WP) is formed by 7 stacked double pancakes (DP). The conductors in the TF coil are operated in steady state mode with a current of 68 kA providing a flux of 5.4 T at the plasma axis. The conductors are wrapped with turn insulation and embedded in grooves manufactured in so called radial plates. The grooves are closed with covers, wrapped with glass and polyimide tapes and vacuum impregnated. This layout of the TF WP prevents the accumulation of stresses in the turn insulation, making unlikely the occurrence of a turn-to-turn short circuit. The insulation of the WP will undergo during ITER design lifetime fast neutron fluencies up to 3.2x1021n/m2, which is equivalent to 10 MGy. Standard epoxies degrade if submitted to such doses, developing mechanical properties that would not withstand the estimated operation in-plane shear stress in the range of 45 MPa. The use of a radiation-hard thermoset for glass-fiber composites (cyanate ester) is considered and the on-going extensive qualification work will be presented. The technical solution of how to isolate critical High Voltage (HV) areas like the joint connections or voltage taps is also discussed.

Equipment and procedure for measuring physicochemical properties of hygroscopic crystals

The equipment and procedure for measuring different characteristics of hygroscopic crystals in a temperature interval from −100 to +100°C is described. A glass vacuum cuvette is placed into a massive metal vessel, the temperature of which may be varied over wide limits. The measured temperature dependence of permittivity ɛ in the phase transition area of strongly hygroscopic crystals of ammonium pyroselenite (NH4)2Se2O5 and (ND4)2Se2O5 at about room temperature is given.