Inflection Point Temperature Research Articles

The characteristics of steam chamber expanding and the EOR mechanisms of tridimensional steam flooding (TSF) in thick heavy oil reservoirs

Aiming at the shortcoming of conventional steam flooding (CSF), tridimensional steam flooding (TSF) was proposed to expand the limited steam chamber and to enhance the low oil recovery in thick heavy oil reservoirs. In this paper, based on mechanisms of thermal recovery, two 3D experimental models were designed to investigate the evolution of steam chambers and production performance. A new method was proposed to utilize inflection point temperature and remaining oil saturation to identify utilizable ranges, hot water zones, and steam chambers. Then, based on the parameters of the indoor experiments, three numerical models were built to further study advantages of TSF. The results show that: i) Compared to CSF, TSF possesses a plumper steam chamber, a higher steam quality and a more stable displacement front; ii) The oil recovery of TSF can reach 52.85%, while it is only 43.31% for CSF at the same time; iii) At the end of TSF, the volume of steam chamber, low oil saturation zone, low pressure zone, and low viscosity zone is 3.08 times, 3.31 times, 1.61 times, and 1.55 times, respectively, compared to CSF, which demonstrates that TSF is effective. As a result, TSF can effectively expand steam chamber and enhance oil recovery in thick heavy oil reservoirs.

Study on Mechanism and Effect of Different Viscosity Reducing Methods on Offshore Heavy Oil

Abstract Bohai is rich in heavy oil. And its efficient development is significant. In this essay, ordinary heavy oil and extra one were selected, and the viscosity characteristics was also investigated referring to its internal composition. And so as the reducing viscosity effects of steam, oil-soluble viscosity reducer, diesel, emulsifier, flue gas and carbon dioxide. The experimental results show that resin and asphaltene content have positive effect on the viscosity of heavy oil. Compared with ordinary heavy oil, the drop is significantly greater when the temperature increases by 10°C. For ordinary heavy oil, the inflection point temperature is from 50°C to 70°C, and for extra-heavy oil, it is above 100°C. For ordinary heavy oil, its flow effect can be better improved without too high temperature, while it’s totally different for super heavy oil. For which, higher temperature and other auxiliary viscosity reduction methods are needed to achieve better flow performance. Diesel oil reduce viscosity of heavy oil by similar solubility principle, but the demand for diesel oil is large. At 50°C, the viscosity of super heavy oil with 0.5% emulsion viscosity reducer added is 36 mPa·s, but the water content needs to reach above 30%.Oil-soluble viscosity reducer reduces viscosity by dissolving asphaltenes and resins and dismantling aggregate structure of heavy oil aromatic flakes.However, the dosage should reach about 20 %, so that the viscosity of super heavy oil can be reduced to the level of dilute oil. Overall, for developing super heavy oil, steam compound with oil soluble viscosity reducer can be taken into account at the early production stage, and the emulsion viscosity reducer can be used in the middle development stage and wellbore viscosity reduction and lifting process. Finally, for ordinary heavy oil, flue gas’s viscosity reduction effects, nitrogen and carbon dioxide are investigated. It is found that the viscosity reduction effect of carbon dioxide is the best, followed by flue gas and nitrogen. Considering the offshore gas source, cost and carbon emission requirements, it is recommended to use flue gas in the field. The research provides theoretical guidance and technical reference for development of different types of offshore heavy oil.

Comparative study of the composition and microstructural properties of semi-coke from microwave and conventional pyrolysis of low rank coal

Microwave pyrolysis technology can effectively realize the clean and quality improvement of coal. In order to study the changes of each component of coal in the process of microwave pyrolysis, the d002, La, Lc, combustion reactivity and conductivity of semi-coke after pyrolysis were analyzed by using XRD, TG, conductivity meter and other testing instruments, and the infrared spectra of semi-coke after pyrolysis were finely resolved by using Origin peak-splitting technique, and the composition of the coal gas in the process of pyrolysis and its percentage content were analyzed. The composition and percentage content of gas in the pyrolysis process were analyzed and compared with conventional pyrolysis. The results showed that compared with conventional pyrolysis, microwave pyrolysis can be completed at a lower temperature and microwave pyrolysis is more favorable to the release of volatile components, in which the content of CO and H2 in the gas fraction increased significantly compared with conventional pyrolysis. At the same pyrolysis temperature, the microwave semi-coke has a higher maximum combustion rate temperature than the conventional semi-coke, which is conducive to improving the thermal stability of semi-coke. The orderliness of the semi-coke increased with the increase of pyrolysis final temperature, resulting in the phenomenon of "similar graphitization". The increase in the number of carbon microcrystalline structures generates off-domain electrons, leading to a significant increase in conductivity. Meanwhile, FT-IR peak fitting analysis revealed that the R value inflection point temperature of microwave semi-coke was much lower than that of conventional semi-coke, which further proved that microwave pyrolysis could be accomplished at lower temperatures, and the C value showed a decreasing tendency with the increase of the final temperature of pyrolysis, which indicated that pyrolysis was an effective method to improve the quality of coal. The above analysis shows that compared with conventional pyrolysis, microwave can prepare high stability and high conductivity semi-coke at lower temperature.

Experimental Tests on In Situ Combustion Using Dynamic Ignition Simulation System in High-Temperature and High-Pressure Conditions

The study of crude oil oxidation characteristics is fundamental to the design of ignition in situ combustion. Experimentation is the most crucial method for studying the oxidation characteristics of crude oil. Aiming to address the challenges posed by high temperature, high pressure, and rapid temperature changes during the combustion of crude oil, a dynamic simulation system for high-temperature and high-pressure ignition is designed. In order to study the oxidation characteristics of the crude oil ignition process, we conducted experiments using a high-temperature and high-pressure dynamic ignition simulation device. The experiments focused on determining the ignition point of crude oil under different pressure conditions, oil–water ratios, heating rates, gas injection rates, and other relevant characteristics. The kinetic model for the oxidation process of crude oil ignition was established. The kinetic parameters were calculated for different ignition conditions and the apparent activation energy for each oxidation stage was determined. Additionally, the stability of in situ combustion was evaluated under various ignition parameters. The results show that the Arrhenius curves for crude oil exhibit noticeable differences in the HTO (high-temperature oxidation) and LTO (low-temperature oxidation) regions. The curves demonstrate good linearity in the HTO region, with correlation coefficients exceeding 0.9. Moreover, the apparent activation energies in the HTO region range from 8.01 to 26.7 kJ/mol. The apparent activation energies and finger front factors were calculated for the HTO stage under different pressure conditions. The results showed that, as the pressure increased, the autoignition point, inflection point temperature, and apparent activation energy of the crude oil decreased. This suggests that increasing the pressure can enhance the HTO of the crude oil. The spontaneous ignition point of the crude oil exhibited an upward trend as the heating rate increased. Additionally, the maximum temperature during the combustion process generally increased with the heating rate, reaching a maximum temperature of 453.1 °C. The tests demonstrated that the simulation system is capable of real-time monitoring and recording of oxidation parameters during the combustion process of crude oil. This system can provide essential data for project implementation and numerical simulation.

The influence of temperature rise on the friction torque of ball screw during low speed operation

This study used innovative testing methods to investigate the effect of physical temperature rise on low-speed friction torque of double nut ball screws. 72 experiments were conducted using two samples and three protocols. Found the inflection point temperature and inflection point velocity. Below the inflection point temperature, the frictional torque increases with the increase of speed; Above this temperature, the frictional torque first decreases and then increases. Below this inflection point speed, the frictional torque first decreases and then increases; Above the inflection point velocity, the friction torque decreases with increasing temperature. Based on the Strebeck theory, the variation of friction coefficient with temperature was studied; When it is below the inflection point speed, it fluctuates greatly with the increase of temperature, but when it is above the inflection point speed, the fluctuation is small and steadily decreases with the increase of temperature. In addition, based on the theoretical models of Coulomb friction torque and viscous friction torque, the results of this model are in good agreement with the measurement results above the inflection point speed, indicating the correctness of the theory and providing good theoretical guidance for engineering designers.

Statistical Study of the Characteristics of Coal Spontaneous Combustion Gases and Temperature

ABSTRACT The occurrence of coal spontaneous combustion has a significant impact on both the safety of personnel and mine recovery. In order to establish an early warning system for combustion, it is crucial to develop a mathematical model that characterizes indicator gases and coal temperature. In this study, we investigated the O2, CO, and CO2 characteristics of data collected from a goaf beam pipe in the Mengcun mine. Our findings demonstrate a linear decrease in O2 concentration with goaf depth and a strong negative correlation between CO and O2. We observed that CO/∆O2 and CO/CO2 increased to a maximum and then decreased as the goaf depth increased. Furthermore, we found that the peaks of these parameters at the same sampling point corresponded to the same goaf depth, and both occurred at the junction between the air-leakage and oxidation zones. By using a logistic model to fit the CO and C2H4 data, we developed a model that characterizes the relationships among CO, C2H4, and coal temperature based on statistical laws. The model provides direct information about the inflection point temperatures of C2H4 and CO, with the former being slightly lower within the same coal sample. The overall difference between the inflection point temperatures is relatively small, about 10°C. The initial temperature ratio of C2H4 and CO remains essentially constant at 3.8. C2H2 concentrations are low and irregular, and the presence of this gas can be used to assess when coal enters the accelerated oxidation stage. This research result provides a new research view for elucidating the distribution characteristics of coal spontaneous combustion index gas.

Aldosterone activates cerebrovascular smooth muscle BK channels in absence of β1 subunits, yet these potentiate steroid action and thus facilitate aldosterone-induced dilation of cerebral arteries.

Calcium/voltage-gated, big conductance K+ channels (BK α subunits or slo1 proteins) modulate smooth muscle (SM) tone and thus cerebral artery diameter. In cerebral arteries, the BK current phenotype is conditioned by regulatory β1 subunits which fine-tune channel activity to tissue-specific physiology. Several physiological steroids modify BK function and may modify cerebral artery function. Thus, cholesterol and pregnenolone inhibit SM BK and evoke middle cerebral artery (MCA) constriction through recognition by slo1 whereas estradiol and cholanes activate SM BK through recognition by β1. Aldosterone is a steroid with documented vasoactive properties, yet the involvement of BK in aldosterone's cerebrovascular action and the contribution of distinct channel subunits to this action remain unknown. Here, we first used nanoscale differential scanning fluorimetry to test whether aldosterone (0.3-100 μM) could directly bind BK α or β1 subunits. Changes in temperature of onset and inflection point (indicators of protein-steroid binding) were evident at 10 and 1 µM aldosterone for α and β1. Next, MCA SM cells were enzymatically isolated from mice, and cell-free recordings were conducted to determine changes in BK activity by aldosterone. Increased activity by aldosterone was concentration-dependent: EC50 = 3 μM; ECMAX = 10 μM, at which activity increased by 20%. Consistently with this small yet reproducible SM BK activation, 10 μM aldosterone dilated MCA by 2%, independently of circulating and endothelial factors. In SM cells and MCA segments from β1-/- mice, aldosterone activated BK with reduced potency and efficacy, and vasodilation by the steroid was evoked by very high concentrations (>>10 µM). Therefore, aldosterone is able to activate SM BK in absence of β1, yet this regulatory subunit potentiates aldosterone action and thus enables subµM-µM aldosterone to dilate MCA.

Inflection point temperature characteristics of carbon fiber composite core conductors

Carbon fiber composite core conductor is a new construction, which is new overhead transmission times the capacity of the conductor. Transmission line times the capacity of the transformation project has great potential for exploration, but due to the short time put into actual operation, the research is relatively weak, and cannot accurately assess its characteristics, therefor resulting in the further promotion of carbon fiber conductor application is limited. In this paper, based on the geographical characteristics of carbon fiber conductors in actual operation, a set of" inflection point temperature" model for carbon fiber conductors is built, measuring the stall distance L, height difference angle β and initial temperature t0 of carbon fiber composite core conductor. So based on the stall distance L, height difference angle β and initial temperature t0 to calculate the carbon fiber composite core conductors, the theoretical basis at the inflection point temperature, which is for the further study of the arc sag characteristics of the multi-capacity conductor can be made.

Bakteriyel selüloz ve boraks katkılı atık gazete kağıtlarının termal ve optik özelliklerinin incelenmesi

Bu çalışmada geri dönüştürülmüş atık gazete kağıtlarından üretilmiş kağıtlara katkı maddesi olarak bakteriyel selüloz (BS) ilavesinin ve kağıdın yanma özelliğini geciktirmek amacıyla boraks pentahidrat (Na2B4O7.5H2O) uygulamasının, üretilen kağıtların termal ve optik özellikleri üzerine etkileri araştırılmıştır. Boraks uygulaması için daldırma yöntemi seçilmiş olup karşılaştırma yapabilmek için üretim esnasında boraks ilavesi de çalışılmıştır. Kağıtların yanma karakteristikleri ve kinetiğini belirlemek için termal özellikleri belirlenmiştir. Optik özellikleri için parlaklık, sarılık ve renk değerleri (L*,a*,b*) belirlenmiştir. TGA verileri değerlendirildiğinde daldırma yöntemi ile boraks uygulaması sonucu dönüm noktası sıcaklığının 377,53 °C’den 335,55 °C’ye düştüğü, sadece BS katkısı ile 379,53 °C’ye bir miktar artış gösterdiği tespit edilmiştir. BS katkılı kağıtların daldırma yöntemi ile boraks uygulaması sonucunda dönüm noktası sıcaklığının 334,24 °C’ye düştüğü ve %44,03 oranı ile diğer örneklere göre en yüksek 590 °C deki kalıntı miktarı verdiği belirlenmiştir. Sonuç olarak daldırma yöntemi ile boraks uygulaması yapılan BS katkılı kağıtların termal dayanımlarının diğerlerine göre daha iyi olduğu, BS ve boraksın kağıdın yanması sırasında kalori oluşumunu azalttığı dolayısı ile yanmayı hızlı bir şekilde sonlandırdığı, optik özellikler açısından BS katkısının ve boraks uygulamasının kağıdın parlaklık değerini azalttığı, sarılık değerini arttırdığı belirlenmiştir.

Classification of Spontaneous Combustion Hazard Levels of Coal with Different Metamorphism Degrees

ABSTRACT Coal spontaneous combustion is the main disaster affecting the safety production of mines, and efficient early warning is the key to controlling coal spontaneous combustion disasters. In order to construct an early warning system for spontaneous combustion disasters of coal with different degrees of metamorphism, the programmed-temperature control experiment was conducted to obtain the change curve of the volume fraction of the index gases of the low, medium and high degrees of metamorphosis, and then the Logistic function is used to fit the volume fraction and temperature of the index gases, and the mathematical model of the index gas and temperature of the index gases with different degrees of metamorphism is obtained, and the inflection point temperature is determined, and finally the spontaneous combustion hazard level of the coal is divided in combination with the initial temperature of the index gases. The results show that the changes of coal sample index gases and characteristic temperatures with different degrees of metamorphism are different; the initial appearance temperature of CO is about 30°C, while the initial appearance temperature of C2H4 and C2H2 is positively correlated with the degree of metamorphism, and the initial appearance temperature is 117°C (low), 123°C (medium) and 137°C (high) for C2H4, 291°C (low), 297°C (medium) and 297°C (high) for C2H2; For the same marker gas, the inflection point temperature increases with the degree of metamorphism, indicating that the higher the degree of metamorphosis, the less likely it is to oxidize at the beginning; According to the variation characteristics of coal spontaneous combustion, based on the initial emergence temperature of CO and C2H4 and CO inflection point temperature, coal spontaneous combustion is divided into five states: safe, low risk, medium risk, high risk and catastrophic state, and the energy level transition map between each state indicates that the energy required to transition from safe state to low risk and high risk state is the largest. Once the high-risk state is crossed, it does not require higher energy to maintain the continuous development of spontaneous combustion of coal and evolve into a catastrophic state. The classification of coal spontaneous combustion hazard levels with different degrees of metamorphism can provide prior data and form effective support for intelligent early warning of coal spontaneous combustion.

Study of D-limonene as novel green hydraulic fracturing surfactant in shale gas reservoir

This study focuses on rock-fluid interaction during hydraulic fracturing in shale gas reservoir. Hydraulic fracturing is a well stimulation technique used to create fracture network in reservoirs by connecting the main planar hydraulic fracture with the pre-existing natural fracture. Hydraulic fracturing fluid additives such as surfactants are added into the hydraulic fracturing fluid system to enhance oil and gas productivity by assisting fluid recovery after fracturing. The main objective of this study is to evaluate the effectiveness and formation damage parameters of the proposed novel green surfactant as hydraulic fracturing fluid additive where commercial-chemical based surfactant was studied for comparison purpose. The green surfactant used was D-limonene whereas Sodium Alpha Olefin Sulfonate (AOS) was used as commercial-chemical based surfactant. Thermogravimetric analysis (TGA) was done to ensure the D-limonene can withstand the high reservoir temperature in which the D-limonene had inflection point and onset temperature of 410 °C and 380 °C respectively. Soaking test was then conducted where the shale samples were soaked in hydraulic fracturing fluid for seven days. The outcome of the soaking test was then studied in Scanning Electron Microscopy (SEM) and wettability analysis. The SEM test showed that the average pore size of the soaked shale samples were similar to the original shale sample which indicated minimal to no formation damage caused by the hydraulic fracturing fluid. Besides that, the contact angle test resulted in the distilled water and D-limonene forming a contact angle of 90° and 0° respectively on the shale samples. The AOS formed contact angles between 65° and 75° for the tested concentrations. From the results, the shale sample was found to be oil wet and showed a high affinity towards the D-limonene followed by AOS and distilled water. Higher affinity of the surfactants promoted the desorption of the hydraulic fracturing fluid from the shale surface.

Experimental Study of Dynamic Mechanics Characteristics of Saturated Marble under Low Temperature

The effect of low temperature on dynamic mechanical properties of low-temperature frozen marble at a high strain rate was studied by a dynamic impact test. The influence of temperature changes (25°C–40°C), especially negative temperature changes, on dynamic strength, peak strain, and failure mode of the marble was analyzed. Combined with the fracture morphology, the reasons for the deterioration of dynamic mechanical strength of water-saturated marble at lower negative temperatures were investigated. The experimental results show that the dynamic mechanical properties of marble are significantly affected by the change of freezing temperature. The dynamic strength firstly decreases and then increases with the decrease of temperature in the range of 25°C to −20°C, but the dynamic strength decreases sharply after −20°C. The peak strain increases first, then decreases, and then increases, and the inflection point temperature of the change is −5°C and −20°C, respectively, which is completely different from the static load test results of frozen rock at low temperature. According to fracture morphology analysis, water-ice phase transformation at −5°C leads to the nucleation and expansion of a large number of microcracks and micropores in marble, and the interaction between slip separation cracks and microstructures caused by shear deformation under impact separates the massive crystals inside the rock into microscopic crystals, thus reducing the bearing capacity and strength of marble. From −5°C to −20°C, the ice medium and marble matrix contract when cooled, and the microcracks and micropores caused by the phase transition gradually close during the contraction process, the integrity of the rock is restored, and the dynamic strength of the rock is increased. At −20°C, there is a great difference in the shrinkage rate of the marble matrix and the ice medium, and the internal microstructure increases. Meanwhile, the impact amplifies the brittleness of the rock at low temperatures, leading to a sharp decrease in the dynamic strength of the marble.

Effects of increasing air temperature on physiological and productive responses of dairy cows at different relative humidity and air velocity levels

This study determined the effects of increasing ambient temperature (T) at different relative humidity (RH) and air velocity (AV) levels on the physiological and productive responses of dairy cows. Twenty Holstein dairy cows were housed inside climate-controlled respiration chambers, in which the climate was programmed to follow a daily pattern of lower night and higher day T with a 9°C difference, excluding effects from sun radiation. Within our 8-d data collection period, T was gradually increased from 7 to 21°C during the night (12 h) and 16 to 30°C during the day (12 h), with an incremental change of 2°C per day for both nighttime and daytime T. During each research period, RH and AV were kept constant at 1 of 5 treatment levels. A diurnal pattern for RH was created, with lower levels during the day and higher levels during the night: low (RH_l: 30-50%), medium (RH_m: 45-70%), and high (RH_h: 60-90%). The effects of AV were studied during the day at 3 levels: no fan (AV_l: 0.1 m/s), fan at medium speed (AV_m: 1.0 m/s), and fan at high speed (AV_h: 1.5 m/s). Effects of short and long exposure time to increasing T were evaluated by collecting data 2 times a day: in the morning [short: 1 h (or less) - exposure time] and afternoon (long: 8 h - exposure time). The animals had free access to feed and water and both were ad libitum. Respiration rate (RR), rectal temperature (RT), skin temperature (ST), dry matter intake, water intake, milk yield, and composition were measured. The inflection point temperatures (IPt) at which a certain variable started to change were determined for the different RH and AV levels and different exposure times. Results showed that IPt under long exposure time for RR (first indicator) varied between 18.9 and 25.5°C but was between 20.1 and 25.9°C for RT (a delayed indicator). The IPt for both RR and RT decreased with higher RH levels, whereas IPt increased with higher AV for RR but gave a minor change for RT. The ST was positively correlated with ambient T and ST was not affected by RH but significantly affected by AV. For RR, all IPt was lower under long exposure time than under short exposure time. The combination of higher RH levels and low AV level negatively affected dry matter intake. Water intake increased under all treatments except RH_l-AV_l. Treatment RH_h-AV_l negatively affected milk protein and fat yield, whereas treatments RH_m-AV_m and RH_m-AV_h reduced milk fat yield. We concluded that RH and AV significantly affected the responses of RR, RT, ST, and productive performance of high-producing Holstein cows. These responses already occurred at moderate ambient T of 19 to 26°C.

A New Method for Calculating the Inflection Point Temperature of Heavy-Oil Rheology Transforming From Non-Newton Fluid into the Newton Fluid

Abstract The inflection point temperature of rheology (IPTR) of heavy oil transforming from a non-Newtonian fluid into a Newtonian fluid is a key parameter in the steam huff- and-puff process. It is particularly relevant in terms of optimizing injection parameters, calculating the heating radius, and determining well spaces. However, the current approach exhibits obvious shortcomings, such as the randomness of the selected tangent line and inadaptability for extra-heavy oil with high viscosity. For extra-heavy oil, the absolute error between the predicted and experimental values obtained using the tangent method has been reported to be between 15.6 °C and 16.9 °C with a relative error of between 17.4% and 18.8%. Therefore, this paper presents a novel method for calculating IPTR using viscosity–temperature data. The approach is based on the Arrhenius equation and quantitatively evaluates the IPTR according to the inflection point of the apparent activation energy. The IPTR values of four heavy-oil samples obtained from the Bohai Oilfield in China were quantitatively predicted according to viscosity–temperature data using the proposed method. The method's accuracy was verified by a series of rheological investigations on samples obtained from two heavy-oil wells. A regression of the rheological equations was performed in which 200 and 625 data points were tested, respectively, via regression to different temperatures, and the IPTR values of the different samples were obtained. The values of 75 °C and 100 °C obtained from a significant volume of experimental test data agreed well with the predicted values of 79 °C and 100 °C calculated by the proposed method. Additionally, the new method was used to predict IPTR according to the published viscosity–temperature data of ten heavy-oil samples from the Shengli Oilfield. Again, a good correspondence was found, and mean absolute and relative errors of 3 °C and 4.6%, respectively, were reported. Therefore, the proposed model was confirmed to improve the prediction accuracy of the existing method and provided a new method for calculating the IPTR of heavy oil.

Experimental study on supercritical heat transfer characteristics of CO2/R41 mixture in microchannel

• Supercritical convective heat transfer characteristics of CO 2 /R41 blends in square porous flat tube microchannel were studied. • The peak values of heat transfer coefficient were analyzed. • Experimental data were compared with the heat transfer correlations. Past researches have shown that CO 2 /HFC mixtures and microchannel heat exchanger could benefit solving the problems of high operating pressure and relatively low cycle efficiency. In this paper, the supercritical heat transfer characteristics of R41, CO 2 /R41 (20.5/79.5) and CO 2 /R41 (51.4/48.6) in square porous flat tube microchannel with the hydraulic diameter of 0.715 mm were experimentally studied. The experimental conditions were as follows: the operating pressure of 6.5–7.5 MPa, the mass flow rate of 150–300 kg/m 2 s, the heat flux of 3–9 kW/m 2 , the fluid temperature of 20–90 °C. The results show that, similar to pure CO 2 , heat transfer coefficient (HTC) of mixtures also appears a peak value near the pseudocritical region. At higher operating pressure, the peak value is less and the change of HTC is gentle. Meanwhile, the inflection point temperature is high. When the bulk temperature is less than the inflection point temperature, HTC is higher at low operating pressure. When the bulk temperature is greater than the inflection point temperature, HTC is higher at high operating pressure. Peak value of HTC decreases and the inflection point temperature of mixtures becomes higher when the CO 2 mass fraction is low. With the increase of R41 mass fraction, the change of HTC is gentle. The width of the peak distance in the pseudocritical region becomes wider. The model of Petrov and Popov is recommended as the prediction model for CO 2 /R41 mixtures. This research can serve as a database for the design of CO 2 /R41 mixtures microchannel heat exchangers.

Prediction of the effective thermal conductivity of an adsorption bed packed with 5A zeolite particles under working conditions

To predict effective thermal conductivity (ETC) of an adsorption bed during the adsorption process, a scale-up model is established that couples a macro-level comprehensive thermal conductivity model and a microlevel grand canonical Monte Carlo (GCMC) method. The effect of the adsorbed phase on the gas phase thermal conductivity is comprehensively considered. The proposed model is validated with experimental data for the thermal conductivities of the zeolite adsorbent particles and bed. Comprehensive sensitivity analyses regarding the effects of the pressure and temperature on the ETC of the adsorption bed are conducted. The results show that the thermal conductivities of the zeolite adsorbent particles and bed can be divided into three regions, namely, the weak adsorbed phase region (0–0.1 kPa), the adsorbed phase and gas phase competitive region (0.1–50 kPa), and the saturation adsorption region (50–1000 kPa). Inflection point temperatures of 350, 450, and 600 K are identified for the three regions. The gas adsorption effect can be ignored when the temperature is higher than these inflection point temperatures. The ETC of the adsorption bed will be underestimated when the adsorption phase is not considered, and it will be overestimated when the coupled effect of the adsorption phase and gas phase is ignored.

Influence of temperature dependent matrix properties on the high-rate impact performance of thin glass fiber reinforced composites

The influence of measurement temperature on the high velocity (>100 m/s) impact performance was investigated for three thermosetting epoxy resin S-2 glass composite systems. These three model resins were chemically similar but have different glass transition temperatures (Tg) and molecular weights between crosslinks (Mc) through the use of different diamine curing agents (Jeffamine® D230, D400, and D2000). Impact performance was quantified by the projectile kinetic energy absorbed (KE50) as calculated from the characteristic ballistic velocity (V50) of the composites during high velocity impact. Among the resin systems, the KE50 remained essentially constant over a broad range of temperatures for each composite set and modestly increased with decreasing Mc. The superficial damage area associated with delamination showed remarkable sigmoidal behavior as a function of the testing temperature relative to the Tg (T-Tg). Damage was high for low T-Tg values (glassy resin) and decreased as the resin traversed its Tg into the rubbery region. These damage area trends were found to depend on the resin Mc, with higher Mc values resulting in lower overall damage area and a lower inflection point temperature. High speed videography of the back surface of the samples showed that lower damage areas correlated with an increased back face deflection, which enabled energy absorption with relatively less delamination. Composite mechanical tests were performed to validate the impact performance and explain the deformation mechanisms observed during impact energy dissipation. Our results illustrate the critical importance of the resin architecture and temperature-dependent viscoelastic behavior on the impact properties of composites for impact-resistance applications.

Highly fluorescent and antimicrobial polyfuran based nanocomposites

In this study, the effects of p-type zirconium (IV) oxide (ZrO2) and n-type cobalt(II, III) oxide (Co3O4) nanoparticles on the structural, physical and antibacterial properties of polyfuran (PFU) were investigated. PFU synthesized via chemical oxidative polymerization method showed a semi-crystalline feature different from its characteristic amorphous nature. The nanometal-oxide filling process increased the degree of crystallinity of PFU from 34 % to 52 % and the inflection point temperature from 616 °C to 685 °C. Interaction between nanoparticles and polymer chains slightly reduced the particle size of PFU matrix. While diamagnetic ZrO2 nanoparticles increased the fluorescence quantum yield of PFU, paramagnetic Co3O4 nanoparticles reduced it. Alternating current (ac) conductivity measurements have shown that filling process increased the electrical conductivity of PFU. Nanoparticles increased the inhibition zone diameter of PFU against Escherichia coli (E. Coli) and Staphylococcus aureus (S. aureus) bacteria up to about 7 mm. The results showed that PFU/ZrO2 and PFU/Co3O4 nanocomposites are highly suitable materials for low-cost photoelectric and antimicrobial applications.

The temperature difference compensation effect of BCP-based OLEDs by variable temperature transient electroluminescence

The variable temperature transient electroluminescence characteristics in BCP-based organic light emitting diodes (OLEDs) are studied in this paper. The temperature difference compensation effect (TDCE) is found in the BCP-based OLEDs with different structures by transient electroluminescence response. The TDCE was affected by electron mobility and electron suppression traps, when the temperature is between 200 K and 300 K, the compensation temperature difference caused by electron mobility and electron suppression traps is 25 K and 20 K, respectively. Moreover, we calculate the derivative of the effective exciton numbers to temperature, and find that the inflection point temperature difference between different devices is consistent with the compensation temperature difference.

Shifts in temperature response of soil respiration between adjacent irrigated and non-irrigated grazed pastures

Land management practices that increase food production are needed to match demand from a growing global population. Adoption of these practices needs to be balanced by potential adverse consequences such as nutrient losses and production of greenhouse gases. We previously demonstrated that pasture soils irrigated during summer-dry conditions had significantly less soil carbon than adjacent unirrigated pastures, despite increased plant production. Precise reasons for lower carbon under irrigation were not clear but both inputs (photosynthesis) and losses (respiration) of carbon are regulated by soil moisture and temperature. Our objective was to determine whether the temperature and moisture response of soil respiration differed between 13 adjacent irrigated and unirrigated soils (0-0.1 m). Soil respiration rates were measured in the laboratory using a temperature block where rates of respiration were measured within 5 h at ˜3 °C increments between 6 and 60 °C (20 temperatures) and at 5 different moisture contents. Temperature response, sensitivity and key temperature parameters (temperature optimum (Topt) and inflection point temperature (Tinf)) were calculated using macromolecular rate theory (MMRT). Respiration rates increased with increasing moisture content similarly for both irrigated and unirrigated soils. However, soil respiration at the same temperature was significantly (P < 0.05) lower and Q10 higher in irrigated soils. Tinf and Topt were greater in irrigated soils. We attribute the lower respiration in irrigated soils to a disproportionate loss of available carbon, total soil carbon loss was ˜14% while the differences in respiration were between 58% at 10 °C and 41% at 20 °C. The lower carbon availability in irrigated soils was likely responsible for the increased Q10, Tinf and Topt as substrate decomposability and availability became more limiting so that ongoing decomposition became increasingly dependent on solubilisation and diffusion of remaining carbon substrates to micro-organisms. We postulate that as respiration becomes increasingly limited by substrate supply through physical chemistry processes (diffusion, and sorption/desorption) rather than substrate biodegradability, the temperature response curve will shift from a MMRT dominated response (with a temperature optimum) to an Arrhenius dominated response (exponential). Our data suggest that commencement of irrigation removed moisture limitation during normally dry summers and led to a loss of soil carbon due to an initially increased microbial activity that has now decreased as carbon availability declined.