Vapor Gas Research Articles

Integrated CO2 systems for supermarkets: Field measurements and assessment for alternative solutions in hot climate

In Europe CO2 transcritical booster systems have become a trusted solution in the field of commercial refrigeration. The main challenge for these systems is to become appealing in warm climates. Beside the various technological solutions that can be introduced, an interesting possibility is to fulfill all the thermal needs (refrigeration, heating and air-conditioning) with one single and compact unit.The present paper focuses on the monitoring of an integrated CO2 transcritical booster system, serving a 1500 m2 supermarket located in Italy, able to satisfy both cooling and heating demands using one single unit. The analysis of the monitoring data shows that the unit performance is strongly influenced by the high gas cooler discharge temperature in the summer and by the implemented control strategy for heat recovery. While the parallel compression can increase the system capacity and also entirely satisfy the air-conditioning demand, the system efficiency is still strongly penalized at high external temperatures. In wintertime, the system is forced to work in transcritical condition and the use of the external evaporator allows to entirely meet the space heating and sanitary hot water demands of the supermarket.A steady-state model of the considered refrigeration system is developed and validated against the collected field measurements. The model is then used to assess some solutions to improve the performance of the integrated CO2 booster unit. The simulated configurations considered overfed evaporators, vapour ejectors and evaporative gas cooler. To face the challenge of improving the performance of CO2 system in warm climates, simulations have been run for the cities of Milan and Tunis. The results of the simulations show that vapour ejectors and evaporative gas cooler offer a good potential to reduce the electrical power consumption during the warmest periods, while overfed evaporators increase the performance almost independently from the external temperature. The combined adoption of overfed evaporators along with ejectors and evaporative gas cooler can increase up to 18% the yearly average COP in both locations compared to the original booster system configuration. For existing systems the adoption of overfed freezers and evaporative gas cooler along with the increase of the evaporating pressure at the external evaporator are considered as possible solutions to increase the performance with limited changes.

Gas-Induced Phase Transition of Dipeptide Supramolecular Assembly

Gas-Induced Phase Transition of Dipeptide Supramolecular Assembly

Directional Water Transfer Janus Nanofibrous Porous Membranes for Particulate Matter Filtration and Volatile Organic Compound Adsorption.

In order to reduce the possible harm caused by air pollution, excellent personal protective materials are attracting more and more attention. Therefore, the research of multifunctional materials that can filter particulate matter (PM) and volatile organic compounds (VOCs) simultaneously is of great significance. In addition, in cold weather, water vapor in the exhaled gas condenses into small droplets inside the respirator causing uncomfortable feeling of dampness. Herein, we prepared several types of cyclodextrin-containing Janus nanofibrous porous membranes by electrospinning, which can efficiently filter PM of different sizes in the air, effectively adsorb VOCs, and orientate moisture from exhaled gas to the outside of the membranes to provide a dry and comfortable environment. These advantageous features, combined with the cheap price and easy availability of component materials and low respiratory resistance, highlight the great potential of these Janus nanofibrous porous membranes in the development of personal wearable air purifiers.

Characterization and Source Apportionment of Atmospheric VOCs in Tianjin in 2019

The characterization and source apportionment of atmospheric volatile organic compounds (VOCs) in Tianjin in 2019 were investigated based on high-resolution online monitoring data observed at an urban site in Tianjin. The results showed that the average annual concentration of VOCs was 48.9 μg·m-3, and seasonal concentrations followed with winter (66.9 μg·m-3) > autumn (47.9 μg·m-3) > summer (42.0 μg·m-3) > spring (34.6 μg·m-3). The chemical compositions of the VOCs were alkanes, aromatics, alkenes, and alkynes, which accounted for 65.0%, 17.4%, 14.6%, and 3.0% of the VOCs concentrations on average, respectively. The proportion of alkanes, aromatics, and alkynes was the highest in autumn, summer, and winter, respectively, while a higher alkenes proportion was observed in summer and winter. The ozone formation potential contribution of alkanes, alkenes, aromatics, and alkynes in spring and summer was 16.9%, 48.6%, 33.5%, and 1.0%, respectively, and the species with higher contributions were ethene, propylene, m,p-xylene, 1,2,3-trimethylbenzene, toluene, isoprene, trans-2-butene, cis-2-pentene, o-xylene, and m-ethyltoluene. During autumn and winter, the aromatics contributed as much as 91.5% to the secondary organic aerosol (SOA) formation potential, and o-xylene, toluene, m,p-xylene, ethylbenzene, o-ethyltoluene, and benzene were the main contributing species. Positive matrix factorization was applied to estimate VOCs source contributions, and automobile exhaust, liquefied petroleum gas/natural gas (LPG/NG) and gasoline evaporation, solvent usage, petrochemical industrial emissions, combustion, and natural sources were identified as major sources of VOCs in spring and summer, accounting for 29.2%, 19.9%, 16.4%, 10.3%, 7.3%, and 6.6%, respectively. While in autumn and winter, the contributions of LPG/NG and gasoline evaporation, automobile exhaust, combustion, solvent usage, and petrochemical industrial emissions were 32.4%, 21.9%, 18.5%, 13.3%, and 8.4%, respectively. Compared to the source contributions in spring and summer, a significant increase was observed for LPG/NG and combustion emission of 62.8% and 153.4%, respectively, and other sources decreased by 18.4%-25.0% in autumn and winter. Source composition spectrums showed that the petrochemical industry and solvent usage were the main emission sources of alkenes and aromatics in spring and summer, and combustion and solvent usage were the main emission sources of aromatics in autumn and winter. Thus, focus should be played on the petrochemical industry and solvent usage in spring and summer and on combustion and solvent usage in autumn and winter to further prevent and control ozone and SOA in Tianjin.

Ultralow-detection limit ammonia gas sensors at room temperature based on MWCNT/WO3 nanocomposite and effect of humidity

Nanocomposite-based NH3 gas sensors working at room temperature were systematically fabricated by compositing multi-walled carbon nanotubes (MWCNTs) and tungsten oxide (WO3) nanobricks at different mass ratios. The response of the nanocomposite-based sensors increases with increasing WO3 content from 0 to 95 wt% then decreases as the WO3 content continuously increases to 100 wt%. The sensor with 95 wt% of WO3 shows a significant enhancement in NH3 gas sensing characteristics, namely, high response (~350% with 60 ppm NH3), ultralow limit of detection (6 ppb), and selectivity to NH3. The enhancement of gas sensing characteristics was attributed to the synergistic effect of the p-p junction between MWCNT and the inversion layer on the WO3 surface caused by the adsorbed oxygen gas and water vapor in ambient air. The response increases while the sensor's resistance decreases with increasing relative humidity from 25% to 65%. Hence, MWCNT/WO3 nanocomposite is a promising material for selective sub-ppm NH3 gas sensor at room temperature.

Spin-exchange collisions in hot vapors creating and sustaining bipartite entanglement

Spin-exchange collisions in alkali or alkali/noble gas vapors are at the basis of quantum sensing, nucleon structure studies, tests of fundamental symmetries, and medical imaging. We here show that spin-exchange collisions in hot alkali vapors naturally produce strong bipartite entanglement, which we explicitly quantify using the tools of quantum information science. This entanglement is shown to have a lifetime at least as long as the spin-exchange relaxation time, and to directly affect measurable spin noise observables. This is a formal theoretical demonstration that a hot and dense atomic vapor can support longlived bipartite and possibly higher-order entanglement.

Electrospinning Superassembled Mesoporous AIEgen-Organosilica Frameworks Featuring Diversified Forms and Superstability for Wearable and Washable Solid-State Fluorescence Smart Sensors.

Flexible optical sensors are widely studied and applied in many fields. However, developing highly stable and washable wearable sensors in optics is still facing significant challenges. Here, we demonstrate an AIEgen-organosilica framework (TPEPMO) hybrid nanostructure-based flexible optical sensor, which is prepared by a two-step co-condensation and electrospinning superassembly process. Organosilica precursors with aggregation-induced emission (AIE) features are covalently linked into periodic mesoporous organosilica (PMO) frameworks with high fluorescent efficiency due to the restriction of intramolecular motion. The three-dimensional space of ordered porous materials provides abundant reaction sites, allowing rapid and sensitive monitoring of analytes. TPEPMOs exhibit good properties as acidic pH fluorescent sensors with a pKa of 4.3. A flexible film is obtained by dispersing TPEPMO nanospheres in a poly(lactic-co-glycolic acid) (PLGA) and polyacrylonitrile (PAN) hybrid fibrous matrix (TPEPMO-CFs) using the electrospinning superassembly technique and is successfully served as an efficient fluorescent probe for the naked eye detection of ammonia gas and HCl vapor by emission changes. The fluorescence of TPEPMO-CFs can be reversed in the presence of volatile acidic/alkaline gas for more than five cycles, exhibiting excellent recyclability. In addition, TPEPMO-CF sensors show excellent washability and long-term photostability (fluorescence was maintained above 94% after washing 10 times). These stimuli-responsive AIEgen-organosilica frameworks featuring diversified forms and superstability for wearable and washable solid-state fluorescence exhibit great potential for smart gas sensors, wearable devices, and solid-state lighting applications.

Hydrogen storage properties of Mg–Nb@C nanocomposite: Effects of Nb nanocatalyst and carbon nanoconfinement

The Mg–Nb@C nanocomposite has been synthesized by a reactive gas evaporation method to simultaneously achieve carbon nanoconfinement and add Nb nanocatalyst. The size of Mg particles is range from 14 to 26 nm with average size of 20 nm. The small Nb catalyst about 5 nm are decorated in Mg particles, and the proportion of Nb is about 8 wt%. The amorphous carbon layer with thickness of 2 nm is coated on the surface of Mg–Nb nanocomposite. The nanocomposite can absorb 6.4 wt% H2 and desorb 6.3 wt% H2 in 5 min at 673 K. At 573 K, it can also uptake 5.8 wt% H2 in 10 min and release 4.8 wt% H2 in 60 min. The Ea for hydrogenation and dehydrogenation are reduced to 60.2 and 59.7 kJ mol−1, respectively. Carbon nanoconfinement and Nb nanocatalyst effectively improve the hydrogen sorption kinetic of Mg.

Energy, environmental and economic analysis of electric vapour compression and gas driven absorption heat pumps for single-family houses

The aim of this paper is to compare energy consumptions, CO2 emissions, and operative costs of condensing boilers, electric vapour compression heat pumps and gas driven absorption heat pumps to provide space heating and domestic hot water. The analysis is performed for 140 m2 single-family houses in five different Italian cities whose envelope features depend on the location. For each location, two different envelope conditions are considered. The first one is a non-insulated building, while the second one is the same building, but an external thermal insulation is added on vertical walls and roof. To avoid internal renovation, radiators are maintained as emission system. Combined dynamic simulations are performed to appreciate building and system interactions. A 6 second time step is set to evaluate properly interactions and the DHW profile demand. In addition, the GHP dynamic model is a grey box model experimentally validated. The results show that electric vapour compression heat pumps reach the highest non-renewable primary energy savings (>32%) compared to condensing boilers, but their operative costs are higher due to the higher specific cost of electricity in Italy. Gas driven absorption heat pumps achieve a lower consumption reduction than electric heat pumps (>22%), but they have also the minimum operative cost among the three technologies.

Development of measurement method for non-condensable gas in water vapor

Development of measurement method for non-condensable gas in water vapor

Low global warming potential (GWP) refrigerant supermarket refrigeration system modeling and its application

• A high fidelity model for a low -GWP refrigerant supermarket refrigeration system was developed. • The model was validated by manufacture and lab testing data with accuracy within ±4%. • A near-optimal high side pressure was obtained through extensive simulation running of the model. • The model was also used to generate battery equivalent model for using in grid interactive controls. As an environmentally friendly low global warming potential (GWP) refrigerant, Carbon dioxide (CO 2 ) has continuously gained popularity and research attention as alternative refrigerant for supermarket refrigeration system. In this paper, to fulfill the increasing need of accurate Low-GWP supermarket refrigeration models for development of supervisory level control and optimization strategies, a high fidelity model is developed for CO 2 transcritical supermarket refrigeration system which includes compressor rack of low temperature (LT) compressors and medium temperature (MT) compressors, air-cooled gas cooler, evaporator, expansion valves and other auxiliary equipment. A resistance-capacity model structure is proposed to simulate the display cases. Semi-thermodynamic models are proposed to estimate reciprocating compressors volumetric efficiency and power consumption. The zone modeling approach is used for evaporator simulation, and air-cooled gas cooler is modeled with distributed modeling method. The expansion valve simulation is based on orifice flow model. To calibrate these models, both manufacture performance data and experimental data are used. The experiments are conducted with a full instrumental CO 2 supermarket refrigeration system installed in Oak Ridge National Lab Flexible Research Platform (FRP). The simulation model can predict the system performance, including power consumption, cooling capacity, mass flow rate, temperature, and pressure, with high accuracy (within ±4%) compared to experimental data. In addition, this developed model has been used to create the system optimum high side pressure for high side expansion valve control, and to generate wide operating range simulation data for developing the batter-equivalent commercial refrigeration system model which can be used in grid interactive control development.

РАЗРАБОТКА КЕРАМИЧЕСКИХ ТЕПЛОГЕНЕРИРУЮЩИХ СОЛНЕЧНЫХ КОЛЛЕКТОРОВ-ПЛИТ

An urgent problem of the modern world is the global warming of the Earth, fraught with a climatic catastrophe. In addition, an important strategic task for Armenia is the issue of reducing the costly imported risky supplies of hydrocarbon and nuclear fuel and increasing the country's energy security. The Union of Armenian Ceramics Manufacturers has developed a new generation of ceramic heat-generating solar collector- plates, which allow converting solar energy into thermal energy of hot water in a more efficient, easily accessible and cheap way. Water heated in such an environmentally friendly and widely available way can be used for hot water supply (DHW) and additional auxiliary heating of premises. In Armenia, to obtain hot water for domestic and technical needs, electricity is used and hydrocarbon fuel is burned in an amount equivalent to USD 200...300 million per year. At the same time, tens of thousands of tons of carbon dioxide, water vapor and other greenhouse gases are emitted into the atmosphere. With the massive introduction of ceramic solar collector plates, for example, in the form of roof tiles or other facade elements, it is possible to obtain very cheap hot water for hot water supply and warm air for additional auxiliary heating of premises in the spring - autumn seasons of the year. The mass introduction of collector tiles (the so-called "heliofication" of buildings, countries) will save a significant amount of electricity, natural gas and other types of fuel for heating water, and significantly reduce the emission of greenhouse gases into the atmosphere. The large-scale introduction of solar roof tiles in several countries in the region is likely to help mitigate the global warming. The solarization of Armenia will also make it possible to reduce the expenditure of financial resources for the purchase of energy carriers and direct the saved funds to the development of the country's economy.

Experimental investigation of waste heat recovery from the disposal of ammonium perchlorate

Every production process will inevitably generate waste. Sustainability can be achieved by utilising these waste products for adding value to the cycle. The intensity of the waste depends upon the level of harm it causes to the human and the environment. Among that, the hazardous waste is prioritized because of the toxicity and the diversity of its type. Chemical wastes can be classified hazardous by the toxicity characteristic leaching procedure or soluble threshold limit concentration. Ammonium perchlorate wastes are classified as hazardous due to the irreversible ailments it has caused to humans due to its contamination. Ammonium perchlorate is a powerful oxidizer used in the production of solid rocket propellant. Waste generated during the production of ammonium perchlorate in the form of mother liquor is a threat to environment. Complete and efficient disposal of ammonium perchlorate is a need of time. In this paper a novel method has been identified and experimented for the disposal of ammonium perchlorate. To make the process cost effective a methanol based solvent which is an effluent from HTPB production plant is used as a fuel to compliment the disposal of ammonium perchlorate. In addition to the disposal of ammonium perchlorate, the energy contained in this powerful oxidizer can be retrieved using a heat recovery unit. Theoretical calculations are done and the heat capacity of the flue gases from incineration is found to be 17.28 kW with this novel method approximately 28 Kg of ammonium perchlorate can be disposed per day. The exhaust gases from the incinerator was analysed as contain hydrochloric acid acidic gas and water vapour. Wet scrubbing of exhaust with sodium hydroxide is suggested to ensure an environment friendly disposal. The ash generation during the process is nullified by the usage of methanol based solvent.

СТРУКТУРА ФИЛЬТРАЦИОННОЙ КРИВОЙ И СПОСОБЫ ЕЕ АППРОКСИМАЦИИ. ЧАСТЬ 1. ЗАКОН ДАРСИ И НИЖНИЙ ПРЕДЕЛ ЕГО ПРИМЕНЕНИЯ. ФИЛЬТРАЦИЯ ЖИДКОСТЕЙ В МИКРОПОРИСТЫХ СРЕДАХ

The description of the lower limit of the application of Darcy’s law is given, which is due to the influence of a number of anomalous factors that arise during the filtration flow of liquids through low-permeability finely dispersed media. The influence of such factors as the action of the forces of intermolecular interaction is considered; boundary layers and surface wettability; concentration and electric potential gradients; the presence of impurities in the liquid; gas saturation and vaporization; changes in the structure of the porous medium, separately or in the aggregate, leading to a violation of Darcy’s law.

Temperature parameters in the combustion chambers of CUMMINS KTA-50 engines operating on various fuels under different fuel consumption rates

The issue of a comparative study of fuel consumption and temperature characteristics of gas-diesel BelAZ 75131 mining dump trucks equipped with an on-board cryogenic fuel system and hauling rock mass at the Kuzbass open-pit coal mine is considered in the article. A brief analysis of the efficiency of using liquefied natural gas (LNG) - methane - as a motor fuel for mining dump trucks is carried out. It is noted that the use of LNG fuel for heavy-duty dump trucks is one of the most promising ways to improve the environmental and economic performance during the operation of this type of mining equipment. The technique and instrumental base for conducting research are presented. The relationship between natural ratios of diesel fuel replacement with natural gas and the energy charge of these replacement is studied. The following data are presented: data on the consumption of vaporous (gaseous superheated) natural gas (hereinafter gaseous natural gas) during field operation of gas-diesel BelAZ 75131 mining dump trucks; flow rate of gaseous natural gas in pipelines; consumption of antifreeze at the inlet to the liquefied natural gas evaporator, as well as antifreeze temperature at the inlet and outlet of the evaporator; temperature of gaseous natural gas at the outlet of the reducer after the evaporator; data on the comparison of temperature profiles in the cylinders of CUMMINS KTA 50 internal combustion engine under diesel and gas-diesel operation.

On Distribution of Velocities Inside a Vapor–Gas Bubble Occurring in an Acoustic Field

On Distribution of Velocities Inside a Vapor–Gas Bubble Occurring in an Acoustic Field

Designing of screen-printed stannous oxide (SnO2) thick film sensors modified by cobalt and nitrogen elements for sensing some toxic gases and volatile organic compounds

The present research deals with fabrication of undoped SnO2, Co2+ doped SnO2 and nitrogen doped SnO2 nanostructures. These three materials were prepared by cost effective co-precipitation method. While the thick film sensors of the prepared materials was design by screen printing photolithography technique. The fabricated materials were characterized by several techniques. The structural properties of the screen-printed thick films measured by X-ray diffractometer (XRD), which confirms the formation of tetragonal SnO2 nanoparticles with average particle size between 15 and 17 ​nm. The morphological properties of fabricated thick of SnO2 were studied by scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HR-TEM) to get surface and lattice characteristics of prepared material. The EDS technique was utilized to get the elemental composition of the prepared thick film sensors. While the UV-DRS technique was used to get the band gap energy of undoped SnO2 and modified SnO2 sensors. Additionally, the materials were investigated by means of Brunauer-Emmett-Teller (BET) study, and from BET results the cobalt modified SnO2 has found to be higher surface area. These all-prepared sensors were applied for gas sensing results of NO2, LPG, CO and volatile organic compounds (VOC’S). The modified sensors found to be very effective at NO2 and VOC gas vapors with 80.23% and 69.13% gas response for cobalt modified SnO2 was observed. The tested gases NO2 and VOC found to be very selective modified sensors. Reusability and recycling results demonstrate that Co2+ doped SnO2 is very efficient, long time stable and reproducible sensor at NO2 and VOC gases at minimum gas concentration and moderate temperature.

Numerical optimization of evaporative cooling in artificial gas diffusion layers

The utilization of evaporative cooling in the gas diffusion layers (GDLs) of fuel cells or electrolyzers can effectively dissipate the heat produced by high power density operation, thus leading to economically more competitive electrochemical cells. The highly porous GDLs offer a large surface area, allowing to cope with larger heat fluxes and leading to larger evaporation rates. The understanding of the best GDL structure and cell operating conditions for optimized cooling is difficult to determine, given the complexity of the multi-physical processes involved. A direct pore-level numerical modeling framework was developed to analyze the heat and mass transport phenomena occurring within GDLs with integrated evaporative cooling. A three-dimensional model was developed that solves the Navier-Stokes equations, species transport and energy conservation equations in the gas domain, and energy conservation equations in the stagnant fluid phase and solid phase. Evaporation at the liquid-vapor interface was modeled using kinetic theory. The GDL geometry was approximated by an artificial lattice so as to enable the analysis of the effect of a systematic change in the geometry on the transport and evaporation characteristics. A parametric study indicated that increasing the GDL’s porosity from 0.8 to 0.9 and the operating temperature from 60°C to 80°C led to an increase of the evaporation rate of 19.9% and 197%, respectively. Changing the thermophysical properties of the carrier gas (air to hydrogen) enhanced the evaporation rate, and therefore the cooling of the GDL, by a factor 2.7. The decrease of the amount of vapor in the carrier gas at the water-gas interface impacted positively the evaporative cooling in the GDL.

Combination of imine bond and samarium emitter enables turn-off fluorescence detection of hydrazine in vapor and water samples

The development of convenient and efficient fluorescence techniques is of great significance for selective detection and precise determination of biotoxic N2H4 in human health and environmental sciences. By the pre-organization-assisted template synthesis, disclosed here is a luminescent Sm(III) macrocycle-based probe Sm-2m bearing dynamic imine bonds as recognition moieties which provides the selective and ratiometric turn-off fluorescence sensing for N2H4 over various amine species based on the N2H4-induced structure transformation. This fluorescent sensing process finished within 20 min shows the low limit of detection (0.18 μM, 7.2 ppb) and wide linear sensing range (0–60.0 μM). Furthermore, probe Sm-2m is also be used to quantitatively determine N2H4 in vapor gas and water samples through fluorescence color changes, which are evaluated by the Sm-2m-impregnated test paper strips and RGB value outputs. Finally, our proposed smartphone-based analytical method gives satisfactory N2H4 detection results. It is thus believed that this work can shed some lights on development of optical probes and detection techniques for N2H4, even other hazardous chemicals.

Enhanced mechanical and antioxidant properties of biodegradable poly (lactic) acid‐poly(3‐hydroxybutyrate‐co‐4‐hydroxybutyrate) film utilizing α‐tocopherol for peach storage

Poly (lactic) acid‐poly(3‐hydroxybutyrate‐co‐4‐hydroxybutyrate) (PLA‐PHB) blends were prepared through melting method and incorporated with α‐tocopherol. The structural, thermal, mechanical and antioxidant properties of resulting active films were characterized, and its preservation effect on peaches (Prunus persica L.) was investigated. Results revealed that the glass transition temperature (Tg) of PLA film was reduced from 53.2°C to 39.7°C after addition of plasticizer but increased again to 43.3°C after supplementation with α‐tocopherol. PLA‐PHB are polyesters with carboxylic groups that interacted with the hydroxide groups of α‐tocopherol. Furthermore water vapour permeability, gas permeability and elongation at break were significantly improved, and 72.1% 2,2‐diphenyl‐1‐picrylhydrazyl free radical scavenging activity was observed. PLA‐PHB‐α‐tocopherol group revealed higher combined water and less oxidative spoilage through low‐field nuclear magnetic resonance (LF‐NMR) and effectively extended the shelf life of peach. Thus, the plasticized PLA‐PHB‐α‐tocopherol film can be used as an active biodegradable packaging for fruits and vegetables.