Molecular dynamics study of the influence of supercooling temperature and orientation of the crystallization front on its velocity in silver

The molecular dynamics method was used to study the influence of the supercooling temperature and the orientation of the crystallization front relative to the growing crystal on the front velocity in silver. According to the data obtained, the crystallization velocity with an increase in the supercooling temperature does not increase monotonically, but has a maximum at about 0.7-Tm (Tm is melting temperature), after which it gradually decreases, which is explained by a decrease in the diffusion mobility of atoms in the amorphous phase. Crystallization proceeds faster with the orientation of the front plane (100), slower - with the (110) and (111) orientations.

Moisture crystallization in bricks

To solve the problems concerning moisture behaviour in the material of construction’s enclosure, especially at alternating temperatures, is very important for the correct calculations of resistance to heat conduction of construction’s enclosure and, ultimately, for comfortable living conditions. However, there are still no methods for building enclosure’s materials that could determine the temperature of moisture crystallization in the material in solid phase. The premise of the research is that water incoming to the material of construction’s enclosure, presenting in the construction’s material in the form of oxides and salts, as a result of hydrolysis process of some elements, is an eutectic solution with unstable composition and concentration. Thus, the research of moisture crystallization process transfers from micro- area (when determining the temperature of crystallization by the size of material’s pores) to the nano- area when researching the eutectic solution at the possible condition of hydrates formation. The experimental technique was developed to perform laboratory research of the process of moisture freezing. The technique takes into account that freeze-thaw process of moisture in solid body is studied at significant difference between mass of liquid phase and mass of solid phase. The method was simplified for the broad use at working conditions. The simplicity of the method aimed at obtaining experimental resultsis compensated by the developed mathematical method of processing the results of the research. Mathematical solution of the problem based on the comparison of freezing curves behaviour of the samples in dry and humidified samples. Apart from the temperature of moisture freezing, the developed method allowed obtaining additional characteristics of moisture states, such as amount of unfrozen moisture in construction’s material, supercooling temperature, heat capacity of moisture in liquid and solid states, concentration of dissolved agents. Knowing the concentration of dissolved agents in the material, even without knowing the exact composition of these agents, allows manipulating the temperature of moisture freezing at the nanotechnology level.

Energy analysis of cyclic parameters of organic Rankine cycle system

Geothermal energy is a kind of green and non-polluting renewable energy. Medium and low-temperature geothermal energy below 150 °C is usually used directly for heating, industrial and agricultural heating, bathing, etc., and the utilization rate is low. Organic Rankine cycle (ORC) system can be used in a low-temperature geothermal power generation systems. Thermodynamic analysis of the thermal cycle system is carried out in this paper. Based on the principle of exergy analysis, the cycle parameters such as evaporation temperature, condensation temperature, superheating temperature, and supercooling temperature are analyzed. The results show that the exergy efficiency and system output power can improve by increasing evaporation temperature and the exergy loss can decrease in the evaporator. Increasing superheating temperature enhances the output power of the expander and the exergy loss in the condenser, decreases the exergy efficiency simultaneously. Increasing condensation temperature decreases the exergy efficiency of the system and the output power of the expander, and increases the exergy loss of the system. Although the output power of the expander will not be affected by supercooling temperature, the rise of supercooling temperature will reduce the exergy efficiency of the system and increase the exergy loss of the evaporator.

The Inhibition of Icing and Frosting on Glass Surfaces by the Coating of Polyethylene Glycol and Polypeptide Mimicking Antifreeze Protein

The development of anti-icing, anti-frosting transparent plates is important for many reasons, such as poor visibility through the ice-covered windshields of vehicles. We have fabricated new glass surfaces coated with polypeptides which mimic a part of winter flounder antifreeze protein. We adopted glutaraldehyde and polyethylene glycol as linkers between these polypeptides and silane coupling agents applied to the glass surfaces. We have measured the contact angle, the temperature of water droplets on the cooling surfaces, and the frost weight. In addition, we have conducted surface roughness observation and surface elemental analysis. It was found that peaks in the height profile, obtained with the atomic force microscope for the polypeptide-coated surface with polyethylene glycol, were much higher than those for the surface without the polypeptide. This shows the adhesion of many polypeptide aggregates to the polyethylene glycol locally. The average supercooling temperature of the droplet for the polypeptide-coated surface with the polyethylene glycol was lower than for the polypeptide-coated surface with glutaraldehyde and the polyethylene-glycol-coated surface without the polypeptide. In addition, the average weight of frost cover on the specimen was lowest for the polypeptide-coated surface with the polyethylene glycol. These results argue for the effects of combined polyethylene glycol and polypeptide aggregates on the locations of ice nuclei and condensation droplets. Thus, this polypeptide-coating with the polyethylene glycol is a potential contender to improve the anti-icing and anti-frosting of glasses.

Thermal Properties of Beef Tallow/Coconut Oil Bio PCM Using T-History Method for Wall Building Applications

Thermal energy storage using Phase Change Materials (PCM) is now widely applied to wall buildings. In general, PCM which is used for applications on building walls is organic PCM and has temperature range from 0℃ to 65oC. Beef tallow and coconut oil is a type of organic PCM known as Bio PCM needs to characterize by using the T-History Method. The T-History method is more accurate than Differential Scanning Calorimetry (DSC) and Differential Thermal Analysis (DTA). This study aimed to determine the thermal properties of beef tallow/coconut oil PCM using the T-History method. The beef tallow and coconut oil as bio PCM material was used in this study with the variation are respectively: 100%, 70+30%, 60+40%, and 50+50%. Tests are carried out using the T-History method. From the results of testing and analysis obtained supercooling temperature, melting temperature, specific heat, and latent heat for bio PCM beef tallow/coconut oil. The effect of adding coconut oil mixture to beef tallow caused a decrease in melting temperature and supercooling temperature, while the specific heat and latent heat of bio PCM of beef tallow/coconut oil ranged from 2.96-2.19 kJ/kg.℃ and 101.05-72.32 kJ/kg. The result obtained that this bio PCM material of cow beef tallow/coconut oil can apply, as additional material in wall building applications.

Assessing thermal tolerance of vulnerable alpine stream insects as part of a long-term monitoring project in the Teton Range, Wyoming

Alpine streams are predicted to decline as air temperatures warm and their water sources dry. Stream temperatures are expected to increase as glaciers and permanent snowfields decrease in size. For aquatic insects that are cold-adapted and restricted to small, high elevation streams fed by glaciers or snowfields, warmer water temperatures could be lethal. Conversely, less water in streams may increase the likelihood of insects freezing during winter months. We measured the critical thermal maximum (CTMAX) – the highest non-lethal temperature an insect can survive, and supercooling temperature – the temperature at which an insect freezes, of three alpine stoneflies, Zapada sp., Lednia tetonica and Lednia tumana, collected in Grant Teton and Glacier National Parks. CTMAX and supercooling point varied among species and with stream source (glacier-fed, snowmelt-fed and icy seep) and population (seven populations). Supercooling temperature was lowest in an alpine tarn and highest in glacier- and snowmelt-fed streams. Zapada sp. had the lowest CTMAX of the three species. Stoneflies from icy seeps had lower CTMAX than individuals from glacier- or snowmelt-fed streams. Individuals that likely experience the coldest winter temperatures had the lowest supercooling temperature. Similarly, stoneflies that experienced warmer water temperatures also had higher CTMAX values. Investigating the thermal tolerances of alpine stoneflies allows us to predict how these insects may respond to future climate change scenarios. Featured photo by Nicole Y-C on Unsplash. https://unsplash.com/photos/9XixVlnUCbk

Crystallization Behavior of Polypropylene/Syndiotactic1,2-Polybutadiene Blends

The melting and crystallization behaviors of Polypropylene/Syndiotactic1,2-polybutadiene (PP/s-PB) blends and neat PP were studied by using DSC, the results showed that the presence of s-PB in PP would have a strong impact on the crystallization capacity of PP. The presence of s-PB in PP could increase the crystallization temperature(Tc) of PP, and the s-PB could obviously lower supercooling temperature(Tm-Tc) of PP, but the s-PB in PP have a Slightly influence on the melting temperature(Tm) of PP. The proposed reason for those are that the crosslinking s-PB in high temperature is a nucleator for PP’s crystallization and increases PP’s crystalline rate. However, the s-PB lowers PP’s crystallinity. At the same time, the presence of PP in blends lowers s-PB’s crystallinity, but the PP in blends have a Slightly influence on the melting temperature(Tm) and crystallization temperature(Tc) of s-PB.

Crystal Orientation Rotation of Ice During Growth in a Bended Capillary

A control technique of crystal orientation of ice can presumably help to improve freezing processes of various industries. However, the technique without seed ice has not been established yet. The author had found that crystal orientation of ice rotated gradually during high-rate growth along a cooling wall. The purpose of this paper is to examine the crystal orientation rotation of ice during growth in several types of bended capillaries at supercooling temperature. We show that, after growing through the capillaries, c-axis of ice crystal is within a certain angle range. On the basis of the measurement the rotation of crystal orientation before and after the growth through some sections of the capillaries, we constructed an empirical model of c-axis rotating gradually during ice growth in the capillary. The calculation of the model can explain the approach process of c-axis of ice crystal growing in the bended capillary to the specified direction.