Effects Of Low Temperature Conditions Research Articles

Simulation Study of the Swirl Spray Atomization of a Bipropellant Thruster under Low Temperature Conditions

The spray atomization of an injector significantly influences the performance and working life span of a bipropellant thruster of a spacecraft. Deep space exploration requires the thruster to be able to operate reliably at a low temperature range from −40 °C to 0 °C, so the effect of low temperature conditions on the atomization characteristics of injector spray is motivated to be comprehensively investigated. To study the swirl atomization characteristics of MMH (methylhydrazine), which is more difficult to atomize than NTO (nitrogen tetroxide), numerical simulations were conducted, employing the methods of VOF (volume of fluid) and LES (large eddy simulation) under low temperature conditions. The physical model with a nozzle size of 0.5 mm and boundary conditions with a velocity inlet of 3.89 m/s both follow the actual operation of thrusters. The development of spray atomization at low temperatures was observed through parametric comparisons, such as spray velocity, liquid total surface area, droplet particle size distribution, spray cone angle and breakup distance. When the temperature decreased from 20 °C to −40 °C at the same condition of flowrate inlet, those atomization characteristics of MMH propellant vary following these rules: the spray ejection velocity of MMH is significantly reduced by 7.7%, and gas-liquid disturbance sequentially decreases; the liquid film development is more stable, with a negative influence on atomization quality, causing difficulties for primary and secondary breakup, so the total surface area of droplets also decreases by 6.4%; the spatial distribution characteristics, spray cone angle and breakup distance vary less than 5%. Therefore, the low temperature condition can directly lower the combustion efficiency of thrusters with obvious performance degradation, but there are no significant changes in the propellant mixing and liquid film cooling. It is concluded that the bipropellant thruster can reliably work at low temperatures around −40 °C for deep space probe operation.

Spreading and shrinking behaviors of oil films with different viscosities on a cold immiscible liquid substrate

The spreading behavior of an oil film on an immiscible liquid substrate plays an important role in practical phenomena such as oil spills and thermal spraying. Especially in extremely cold regions such as the Arctic regions, the spreading behavior and balanced state of the spilled oil may be significantly affected due to the varying oil physical properties caused by the low temperature. The effect of low-temperature conditions on the spreading behavior remains poorly understood. The spreading experiments of silicone oils with viscosities of 50, 100, 350, and 1000 cs were carried out on cold substrates by controlling the liquid substrate temperature in the range of − 20 °C to 20 °C through a circulating bath. The effects of substrate temperature on the spreading morphology, equilibrium thickness, spreading rate and other parameters of the oil film were investigated. When the temperature was greater than 10 °C, silicone oils spread continuously, whereas when the temperature was less than 0 °C, some of them first exhibited a short period of shrinking behavior before spreading. The surface tensions at three interfaces, namely oil–air, oil–substrate, and substrate–air, were analyzed comprehensively. A novel equilibrium equation of the gravity-surface tension based on Neumann’s triangle rule was derived to calculate the stable thickness of the oil film, in which the contact angle at the three-phase junction was measured experimentally, and the quantitative relationship between the surface tension and temperature was considered. The calculated results were in excellent agreement with the experimental results. A modified prediction model was fitted to accurately describe the spreading velocity of the silicone oil by considering the effect of temperature on the viscosity and density. Finally, the variations in the temperature inside the oil film were discussed to explain the shrinking phenomenon. The study provides theoretical support for the creation of oil spill clean-up methods for low-temperature waters.

The effect of low temperature conditions on vibration durability of SAC105 interconnects

Electronic assemblies are often utilised in environments in which they are exposed to significant combinations of simultaneous vibration and thermal loads. In this study, vibration durability tests and results under isothermal conditions are presented for SAC105 solder joints of CR0805 chip resistor components. The tests are performed using a specially designed multi-cantilever printed wiring assembly (PWA) containing CR0805 components. Harmonic vibration durability tests were conducted at both room and low temperatures, for multiple deflection levels. The resistance of the resistor assemblies was continuously monitored to detect fatigue degradation of the interconnects during the vibration testing. A detailed 3D transient FE analysis is conducted to examine effective solder joint strains as a result of the applied deflections at various temperatures. The measured cycles to failure and calculated strains were used to derive S-N-plots. A comparison of fatigue behaviour at room and low temperature condition is drawn. Failure analysis results are presented to elucidate the failure modes. In addition, the development of Flip Chip specimens is shown including the custom manufacturing of Flip Chip components and first test results.

Effect of low temperature conditioning on flavor precursors of ‘Coreano’ garlic (Allium sativum L.) “seed” cloves

ISHS XXX International Horticultural Congress IHC2018: II International Symposium on Root and Tuber Crops: Value Added Crops for the Next Generation Effect of low temperature conditioning on flavor precursors of ‘Coreano’ garlic (Allium sativum L.) "seed" cloves

Spray, Combustion and Soot of Water-in-Fuel (n-Dodecane) Emulsions in a Constant Volume Combustion Chamber; Part II: Effects of Low Temperature Conditions and Oxygen Concentrations

The application of water-in-fuel (n-dodecane) emulsions (WFE) with a fixed water mass fraction of 10 wt% has been investigated in an optically accessible constant volume combustion chamber (CVCC) at varying low ambient temperatures conditions (Tgas=760–800K/ρgas=22.8kg/m3) such as found in direct-injection (DI) Diesel engine operations with (extreme) “Miller”-timing. Furthermore, oxygen concentrations have been decreased to 18 vol% and 15 vol% in order to emulate exhausRd in DI engines.As in Part I two injection strategies have been employed: first, a constant injection pressure case as for neat fuel and prolonged injection duration (strategy (A)), second, the injection pressure has been increased to keep a constant energy input flow, therefore, with constant injection duration (strategy (B)).Spray parameters and combustion characteristics have been assessed by Schlieren imaging, Mie-scattering, diffused back-illumination extinction imaging (DBIEI) and OH∗-chemiluminescence, respectively. Furthermore, the spray flame’s soot formation has been investigated through the detection of soot incandescence signals.For the WFE liquid lengths (LL) penetrate farther downstream the respective LOL at all ambient conditions, whereas, utilizing neat n-dodecane LLs remain upstream the LOL. The interaction between LL and the high-temperature reaction zone dominates the soot behaviour of WFE resulting in decreased dwell times between ignition and first soot occurrence. Decreasing gas temperatures at atmospheric oxygen concentrations generally decrease dwell times, even though, ignition delays and LOLs increase by the utilization of neat n-dodecane.Soot incandescence signal amplitudes decrease strongly employing WFE (150–270 times lower maximum signal values) compared to neat n-dodecane injections. During mixing-controlled combustion phase apparent heat-release rate (aHRR) amplitudes increase for WFE with injection strategy (B) compared to the neat fuel sprays. At the gas temperature of 760 K non-sooting lifted flames have been detected for both fuels. Calculated fuel-to-air ratios Φ evaluated at the respective LOL agree well with soot occurrences for both fuels. Utilizing WFE, the additional latent heat introduced by the water increases LOLs and to a further extent the liquid fuel core which is found within the spray flame and therefore, a fuel rich combustion zone is suggested to surround the liquid-phase WFE. Hence, soot formation persists for calculated fuel-to-air ratios Φ<2 at the LOL, although, detected soot incandescence signals were on very low amplitude levels injecting the WFE.

Low temperature conditioning combined with methyl jasmonate can reduce chilling injury in bell pepper

Bell pepper is a highly perishable vegetable and chilling injury is a principal physiological factor that negatively impacts the postharvest quality of peppers during transportation and storage. This study parsed the effects of low temperature conditioning (LTC) combined with methyl jasmonate (MeJA) on chilling injury during the storage of bell pepper fruit. The results showed that treatments of LTC combined with MeJA effectively maintained quality of bell pepper, suppressed the development of chilling injury index, delayed increase of malondialdehyde (MDA) content, inhibited the decline of chlorophyll and Vitamin C content, enhanced the activities and relative gene expressions of Peroxidase (POD), Catalase (CAT) and Ascorbate Peroxidase (APX). The results obtained point to treatments LTC combined with MeJA can be used as a useful technology for enhancing tolerance of postharvest chilling injury in bell pepper fruit.

Low-temperature conditioning enhances chilling tolerance and reduces damage in cold-stored eggplant (Solanum melongena L.) fruit

Eggplant fruit are vulnerable to chilling injury (CI) after prolonged storage at temperatures below 12 °C. Here, we tested the effect of low-temperature conditioning (LTC) on chilling tolerance in eggplant fruit, in which fruit were stored at 13 °C for 2 d, and then held at 4 °C. Our results indicated that LTC maintained the appearance of eggplant fruit, and retarded the development of CI; the effect of LTC was characterized by inhibited sepal browning, and reduced loss of anthocyanins, and total phenolic compounds. The activity and relative gene expression of peroxidase (POD) and catalase (CAT) were increased by LTC, whereas the activity and relative gene expression of polyphenol oxidase (PPO) was reduced. In addition, the level of malondialdehyde (MDA) was significantly reduced. Our results suggest that LTC induces a range of physiological and molecular responses that enhance chilling tolerance in eggplant fruit.

Effects of low temperature conditioning on fruit quality and peel browning spot in ‘Huangguan’ pears during cold storage

‘Huangguan’ pears are susceptible to peel browning spots (PBS) during cold storage. In this study, the effects of low temperature conditioning (LTC) on fruit firmness, soluble solids content (SSC) and PBS incidence in ‘Huangguan’ pears were investigated. Fruit were directly stored at 0°C (control) and conditioned at 10°C for 3 d (LTC), respectively. Afterwards, all fruit were stored at 0°C. Fruit firmness was unaffected by the LTC treatment. However, SSC was higher in the LTC-treated fruit than in control fruit on days 30 and 60. Compared with the control, LTC treatment effectively inhibited the development of PBS, reduced the activities of lipoxygenase (LOX) and polyphenol oxidase (PPO), reduced malondialdehyde (MDA) content in peel tissue, the decline in the phenolic content, and it showed higher proline content before the appearance of PBS. In addition, LTC treatment decreased the expression levels of LOX1, PPO1 and PPO5 genes, while it up-regulated the expression of the PPO4 gene in peel tissue. These results indicate that the alleviation effect of LTC on the development of PBS was closely related to reduced membrane lipid peroxidation, activities of LOX and PPO, and the expression of LOX1, PPO1 and PPO5 genes in peel tissue in ‘Huangguan’ pears.

Sclerotial formation of Polyporus umbellatus by low temperature treatment under artificial conditions.

Background Polyporus umbellatus sclerotia have been used as a diuretic agent in China for over two thousand years. A shortage of the natural P. umbellatus has prompted researchers to induce sclerotial formation in the laboratory.Methodology/Principal Finding P. umbellatus cultivation in a sawdust-based substrate was investigated to evaluate the effect of low temperature conditions on sclerotial formation. A phenol-sulfuric acid method was employed to determine the polysaccharide content of wild P. umbellatus sclerotia and mycelia and sclerotia grown in low-temperature treatments. In addition, reactive oxygen species (ROS) content, expressed as the fluorescence intensity of mycelia during sclerotial differentiation was determined. Analysis of ROS generation and sclerotial formation in mycelia after treatment with the antioxidants such as diphenyleneiodonium chloride (DPI), apocynin (Apo), or vitamin C were studied. Furthermore, macroscopic and microscopic characteristics of sclerotial differentiation were observed. Sclerotia were not induced by continuous cultivation at 25°C. The polysaccharide content of the artificial sclerotia is 78% of that of wild sclerotia. In the low-temperature treatment group, the fluorescent intensity of ROS was higher than that of the room temperature (25°C) group which did not induce sclerotial formation all through the cultivation. The antioxidants DPI and Apo reduced ROS levels and did not induce sclerotial formation. Although the concentration-dependent effects of vitamin C (5–15 mg mL−1) also reduced ROS generation and inhibited sclerotial formation, using a low concentration of vitamin C (1 mg mL−1) successfully induced sclerotial differentiation and increased ROS production.Conclusions/SignificanceExposure to low temperatures induced P. umbellatus sclerotial morphogenesis during cultivation. Low temperature treatment enhanced ROS in mycelia, which may be important in triggering sclerotial differentiation in P. umbellatus. Moreover, the application of antioxidants impaired ROS generation and inhibited sclerotial formation. Our findings may help to provide new insights into the biological mechanisms underlying sclerotial morphogenesis in P. umbellatus.

Effects of low temperature conditioning on chilling injury and quality of cold-stored juicy peach fruit.

Effects of low temperature conditioning on chilling injury and quality of cold-stored juicy peach fruit.

Low temperature conditioning reduces postharvest chilling injury in loquat fruit

Chilling injury occurs in loquat ( Eriobotrya japonica Lindl. cv. Luoyangqing) fruit when they are stored at temperatures lower than 5 °C. In attempts to reduce this chilling injury, the effect of low temperature conditioning (LTC) was examined. Loquat fruit were conditioned at 5 °C for 6 days before 0 °C storage for up to 54 days. Control fruit stored at 0 °C exhibited severe symptoms of lignification and tissue browning, and a decrease in percentage juice. LTC treatment significantly reduced these chilling injury symptoms, and doubled storage life. In terms of acceptability (tissue browning, internal browning (IB) index <0.4; fruit decay, <10%; flesh firmness, <6.0 N; percentage juice, >60%), fruit could only be stored for 40 days at 0 °C with a 3 days shelf life at 20 °C, while LTC fruit could be stored for 60 days at 0 °C with a similar shelf life. Similarly, LTC fruit could be stored for 40 days with a 5 days shelf life at 20 °C, while fruit could be only stored for 20 days at 0 °C with a 5 days shelf life. Our results confirm that LTC can effectively alleviate postharvest chilling injury of loquat fruit and may provide longer storage life with acceptable external and internal quality.

The effect of low-temperature conditions on the electrochemical polymerization of polypyrrole films with high density, high electrical conductivity and high stability

High-quality polypyrrole-hexafluorophosphate (PPy-PF 6) films with high density (∼1.4 g/cm 3), high conductivity (>300 S/cm for unstretched film) and high electrochemical stability are obtained reproducibly by galvanostatic polymerization at low-temperature conditions. The optimal polymerization current density of J p=0.02–0.05 mA/cm 2 was obtained at the polymerization temperature of T p=−40°C. The surface morphology of the film sensitively varies depending upon the properties of electrode and its surface conditions. The transport measurements characterize the high-density PPy-PF 6 film as a disordered metal close to the boundary of disorder induced metal–insulator (M–I) transition. The X-ray diffraction measurements suggest that partially crystalline structure of PPy-PF 6 film is related to the transport properties. The uniaxial stretching induces an increase of the conductivity up to ∼930 S/cm in a direction parallel to stretching as well as the anisotropy of conductivity. The comparative studies of thermogravimetric analysis (TGA), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) for PPy-PF 6 films prepared at room-temperature and low-temperature conditions show that the latter exhibit better thermal stability as well as electrochemical stability under long oxidative polarization.

Pollen selection for low temperature adaptation in tomato

Pollen selection experiments were conducted in tomato to determine the effects of low temperature conditions during pollination on the rate of root elongation of the progeny. Pollen was harvested from an F1 interspecific hybrid between a high altitude Lycopersicon hirsutum accession and the cultivated tomato L. esculentum. The pollen was applied to stigmas of malesterile L. esculentum plants maintained in growth chambers set at either 12°C/7°C or 24°C/18°C. BC1 seeds from the low and normal temperature crosses were germinated and root elongation rate was measured at either 9°C or 24°C. At 9°C, the rate of root elongation for progeny of the low temperature crosses was higher than for progeny of crosses at normal temperatures; at 24°C the rate of root elongation was similar for the two crossing treatments. To compare the temperature responses of the two backcross populations we also calculated the relative inhibitory effect of low temperature on the rate of root elongation: the ratio between the rate of root elongation at 9°C to that at 24°C. Root elongation of seedlings from the low temperature crosses was less inhibited by the cold than root elongation for progeny of the normal temperature crosses. These results suggest a relationship between pollen selection at low temperatures and the expression of a sporophytic trait under the same environmental stress.