Hasil untuk "Low temperature engineering. Cryogenic engineering. Refrigeration"

Nurzhan Zhuldassov, Eby G. Friedman

Çağlar Yalçınkaya, O. Çopuroğlu

Abstract Ultra-high performance concrete (UHPC) is an innovative cement-based composite with high mechanical performance under tensile and compressive loads, extremely low permeability, and excellent durability. Because of these features, UHPC has the potential to contribute to the development of new architectural perspectives and structural systems with prolonged service life; therefore, it is anticipated that the use of UHPC in cast-in-situ applications will increase in the near future. As a result of its high Portland cement dosage, the hydration heat of UHPC can be relatively high compared to that of conventional concrete. Thus, ground granulated blast furnace slag (GGBS) can be used in UHPC formulation for reducing Portland cement dosage thereby limiting hydration heat while also addressing ecological and engineering concerns. In the scope of this study, the effects of GGBS replacement (0%, 30%, and 60%) on the hydration heat, strength, and microstructural characteristics of UHPC were studied. Results showed that GGBS-bearing UHPCs are more sensitive to ambient temperature in respect to cumulative heat. 60% GGBS replacement reduced cumulative heat release by 36% and 28% at 20 °C and 35 °C respectively. So, the benefit of GGBS on reducing hydration heat is less pronounced in hot weather. Performance differences in strength depending on the replacement ratio were only noticeable on the first day of curing. Prolonged curing time and fiber inclusion eliminated strength differences. Microstructural investigations indicated that Ca(OH)2 can be lowered up to 0.5%, and the Ca/Si ratio of the C–S–H phase was reduced below the value of 1.0 after 90 days of curing as a result of GGBS replacement.

Miguel Ávila-Gutiérrez, Manuel Delgado Mejías, Bernardo Peris Pérez et al.

Min Sang, Guanghui Liu, Shuai Liu et al.

Abstract In recent years, soft electrothermal actuators (ETAs) have attracted great concern because of their potential applications in biomimetic intelligent devices, soft robotics and aerospace engineering. However, achieving the simultaneous optimization of low-voltage actuation, ultrafast preparation and highly integrated functionality are main challenges to the development of ETAs. Herein, a flexible, hydrophobic, mechanically robust and electromagnetic-interference (EMI) shielding PTFE/MXene/PI soft ETA is constructed through a very simple and fast “cutting and sticking” method by taping PTFE and PI tapes onto the surface of MXene film. The commercially available PTFE and PI tapes endow PTFE/MXene/PI sandwich structure with ideal mechanically robustness and hydrophobic self-cleaning function, thus it can work in different environments. Remarkably, PTFE/MXene/PI sandwich structure shows an outstanding EMI shielding ability with the maximum SET value of 44 dB owing to the high electrical conductivity of MXene film. More importantly, the PTFE/MXene/PI sandwich actuator can bend from PTFE side toward PI side under the electrical stimulus, because the excellent electrothermal MXene layer is sandwiched between the two tapes with large difference in thermal expansion coefficients. Under a 6 V low voltage, the actuator can generate heat energy with the maximum saturation temperature of 110 °C and large bending deformation with the maximum bending angle of 122° within 40 s. Interestingly, the PTFE/MXene/PI structure can be designed and manufactured in different shapes and configurations upon actuation, such as the “S” shape and four-finger gripper. At last, a smart shielding curtain with the combination of actuation properties and EMI shielding performance is finally developed as a principle of concept, which further indicates the multifunctional PTFE/MXene/PI ETA can be widely applied in smart EMI shielding system and soft robotic devices.

Jin Lulu, Sheng Jian, Zhang Hua

The regulation of the throttling device has an important impact on the performance of constant-temperature and humidity cabinets. Based on a constant-frequency refrigeration system, the effects of EEV (electronic expansion valve) opening from 10% to 30% on the evaporator superheat, compressor discharge temperature, evaporator fin temperature, and temperature and humidity in the cabinet under different target conditions were experimentally studied. When the opening of the electronic expansion valve is 15%-30%, the superheat (8-15 ℃) and discharge temperature can be guaranteed in safe and reasonable ranges. When the opening of the electronic expansion valve is below 20%, a bypass capillary tube is set for a safe compressor operation with liquid cooling in suction. Under the conditions of low temperature and humidity and high temperature and humidity, the larger opening reduces the temperature and humidity adjustment time by 10-20 min. Under the conditions of a low temperature and high humidity and a high temperature and low humidity, the larger opening causes energy consumption for additional humidity compensation or thermal compensation and prolongs the temperature and humidity adjustment time. Under different target conditions, the relative humidity and dry bulb temperature in the small opening (15%) cabinet are closer to the target temperature and humidity than those for the large opening (25%, 30%), and the temperature and humidity control accuracy is higher.

R. Kumar, Adarsh Kumar

Md. Niamul Bari, Farzana Yasmin Muna, Mumtahina Rahnuma et al.

With the increasing population, the pollution of the environmental elements is increasing day by day. Activated Carbon (AC) is solid, carbonaceous, non-hazardous, and highly porous complex compound and due to its adsorption property, this is widely used in the purification of various elements of the environment such as air, water, chemical, metal, etc. So, the enthusiasm in the production of activated carbon by the utilization of cheap agricultural and industrial wastes is growing rapidly. This study has been carried out to demonstrate the attempt of utilizing Rice Husk (RH) as it is abundantly available, environmentally friendly, low cost and a kind of renewable precursor material for the production of activated carbon. The muffle furnace assisted alkaline activation with potassium hydroxide (KOH) at different ratios was performed. The effects carbonization temperature of 500°C and 700°C and impregnation ratios were evaluated on the basis of yield, volatile matter, carbon content, and activation burn-off. All in all, lower carbonization temperature 500°C gives better results with higher yield of 13.24% and 7.3% activation bunroff at 1:1 carbon to KOH ratio. The increasing ratio also decreased the volatile substances and comparatively better results obtained at less burning temperature. Journal of Engineering Science 13(1), 2022, 105-112

V. Savel, P. Rakluea, Thinnawat Jangjing et al.

This paper proposed IoT based water quality monitoring system using solar power and LoRaWAN. The objective is to study and develop water quality monitoring systems to make it easier for users or those who want to check water quality to see pH, temperature, turbidity, conductivity, and GPS viewpoint in the Cayenne LPP cloud, The water in front of the department of electronics and telecommunication engineering at the Rajamangala University of Technology Thanyaburi will be decided to be a test field. The various water quality data will be wirelessly transferred to the database on the Cayenne LPP cloud. It's also essential to use the greatest wireless connection method. To transport data in the field, the Low-Power Wide-Area Network and the Long-Range WideArea Network will be employed. Moreover, the system can be extended for 36 hours by charging the battery with a solar panel, and the water quality monitoring system error is less than 5%, according to the formula for determining the percentage mistake.

Zhang Tong, Yu Kezhi, Zhang Dezheng

To accurately forecast freeze-drying time, COMSOL software was used to simulate the sublimation drying process of pitaya slices based on the theory of heat and mass transfer in this study. The thickness of the red pitaya slices was 12 mm, and the radius was 4 cm. By simulating the water vapor flow coupled with the heat and mass transfer of the sublimation drying stage, the temperature distribution characteristics of pitaya slices, the movement of the sublimation interface, and the condition of ice sublimation, the sublimation cycle was forecast. Experiments were conducted to validate the model. The results show that the errors are low: the absolute error between the simulated and measured pitaya center temperatures is 0.9 ℃, the comparative error between the forecast and measured moisture ratios is only 1.2%, and the relative error between the simulated and measured dehydration rates is 6.63%. It can be concluded that the model can accurately simulate the dynamic changes in heat and mass transfer during the sublimation drying process. By comparing the simulated sublimation cycle of pitaya slices with different thicknesses, and considering the quality and production of freeze-drying products, it is concluded that 12 mm is the best thickness of red pitaya slices for freeze-drying.

L. Mesrar, A. Benamar, B. Duchemin et al.

Yifan Zhang, Xiaojie Li, Wei Wei et al.

Isocyanate is an efficient tissue anchor for engineering of strong bioadhesives. However, isocyanate-containing adhesives were seldom manufactured due to their requirement of water-free administration and time-consuming moisture-induced solidification. To address this issue, here, a solventless dual-component bioadhesive based on thiol-isocyanate cross-linking chemistry is reported. This dual-component bioadhesive consists of a hyperbranched polymer with thiol groups (HBPTE) and an isocyanate-modified polyethylene glycol (PEGNCO). HBPTE and PEGNCO are low-viscosity fluids at room temperature and hence could be used directly as adhesive components, in the absence of a catalyst and a solvent. The thiol-isocyanate click chemistry of components provides the HBPTE-PEGNCO mixture with a gelation time of 1.8-3 min, which makes it acceptable for practical applications. The abundance of isocyanate groups in the adhesive molecule provides strong bonding strength through formation of chemical linkages with reactive groups on the tissue. Moreover, in vitro and in vivo evaluations showed excellent biocompatibility of the HBPTE-PEGNCO adhesive. This dual-component bioadhesive based on solventless thiol-isocyanate click chemistry displayed a fast gelation time and excellent bonding performance, providing a pioneering idea for engineering isocyanate-containing bioadhesives.

R. S. Revuru, Nageswara Rao Posinasetti, Venkataramana Vsn et al.

Bingxu Lu, Qijie Jin, L. Chu et al.

Abstract The ceria-based catalyst exhibited excellent storage/release characteristics of ammonia, ensuring stable deNOx efficiency under fluctuating engineering conditions, while greatly reducing ammonia slip. In this work, characteristics of ammonia storage/release of CeSnWBaOx/TiO2 catalyst were investigated. Results showed that the catalyst exhibited much higher catalytic activity than the theoretical maximum under low NH3/NO ratios. Especially, the amount of effective ammonia release reached maximum at 250 °C with increase of excess NO. Low temperature was conducive to storage and the stable storage amount was 22.97 μmol·m−2 at 50 °C, effective release of ammonia occurred mainly at the active temperature window. Ammonia storage of the CeSnWBaOx/TiO2 catalyst was affected by the activation of active sites and thermal vibration at the same time. Ammonia storage under low temperature was mainly in physical form and at weak acid sites, while high temperature enhanced activation of ammonia, resulting in an increase of ammonia storage at 350 °C. The catalyst had both weak and strong stored-ammonia, strong stored-ammonia could be effectively released only in the induction of NO. Ammonia storage of catalyst was the key to ensure stable deNOx efficiency under fluctuating engineering condition. The characteristics are of great guiding significance for dealing with ammonia slip.

Gui-Fang Hua, Xiao-Jing Xie, Weigang Lu et al.

C2 separation is of great importance in the petrochemical industry. Traditionally, it is performed by distillation at cryogenic temperatures, which necessitates the consumption of a huge amount of energy to operate the refrigeration system in the production process. In this regard, it is imperative to seek alternative separation methods with high efficiency and low energy cost. Although of recent origin, metal-organic frameworks (MOFs) have already been extensively studied as advanced adsorbents in many applications, and significant progress has been made particularly in gas separation owing to their unprecedented porosity and tunable structures. In this review, we extrapolated three most frequently invoked design strategies for efficient C2 separation hinged upon supramolecular interactions, including molecular sieving, gate opening, and surface engineering. Recent progress of MOF materials in C2 separation was highlighted within each of these strategies, and their advantages and limitations are compared and discussed. Accordingly, we provide perspectives on current challenges and future emphases in designing MOF materials for hydrocarbon separation. With our continued efforts in this area, we expect that integrating supramolecular interactions in a single MOF system is a viable approach to achieve a balance between adsorption capacity and selectivity for different hydrocarbon separation scenarios.

Liu Liyao, Mao Jinfeng, Yun Changjiang et al.

A cold storage air-conditioning system based on separated heat pipe heat exchanger was designed, and the effect of influencing factors on the discharge performance and their response surfaces were experimentally investigated. The results show that the discharging performance of the cold storage air-conditioning system with separated heat pipe was stable; the maximum refrigeration capacity could reach 5.09 kW under experimental conditions. Cooling capacity increases with an increase in the circulating air volume while there is an optimum circulating air volume for dehumidification. The optimum circulating air volume for dehumidification is about 620 m3/h and the dehumidification capacity is about 4.32 kg/h, and the cooling capacity increases with the increase in temperature and humidity of the environment. The regression equation of the cooling capacity under different working conditions was obtained, and the effect of different influence factors on the cooling capacity was analyzed. Under the conditions with low circulating air volume, the influence of the heat pipe valve on refrigeration capacity is weak; however, with an increase in circulating air volume, its influence on refrigeration capacity increases.

王金, 李俊明

A theoretical model for annular flow of R1234ze(E) flow boiling in micro-tubes was proposed in this paper. The surface coefficient of heat transfer and pressure drop were calculated using the model. The variation in the liquid film thickness profile due to the gravitational effect, surface tension, and liquid-vapor interfacial stress was considered. The effect of the variation in the liquid film thickness profile on the heat transfer was analyzed. Furthermore, certain existing surface coefficients of heat transfer and empirical correlations of two-phase friction pressure drop were compared with the numerical results, and the comparison revealed deviations within 30%. The numerical results indicated that the variation in the liquid film thickness profile is evidently affected by gravity in the initial flow area, and the gravitational effect starts to weaken with the flow boiling process. The surface coefficient of heat transfer of annular flow with gravity was higher than that without gravity. Hence, the mean surface coefficient of heat transfer increased with gravitational acceleration. Furthermore, surface coefficient of heat transfer and pressure drop increased as the mass flux increased. Conversely, surface coefficient of heat transfer and pressure drop decreased as the diameters increased.

Zhuang Kunyu, Liu Xi, Yao Wei et al.

Dynamic ice-making technologies with super-cooled water can produce ice slurry efficiently; however, the prominent problem in the stability of this method is that ice blocking easily takes place in the super-cooling heat exchanger. This study developed a dynamic ice-making system based on a modular super-cooling releasing device which was set inside a super-cooled heat exchanger. Its main structure are dismountable spiral blades that can release super-cooled state of solutions and scrape the ice on the heat transfer surface. The performance test of the ice making system under different working conditions shows that the ice making system can stably produce ice slurry and effectively improve the ice-blocking problem. The highest ice packing fraction reached 9.1%, the maximum continuous ice making time was up to 521 s. The ice packing fraction increases with the continuous ice-making time. When the mass fraction of sodium chloride solution was 6%, the ice packing fraction and continuous ice-making time were significantly improved. The experiment obtained the optimal operating parameters of the ice making system: the flow rate of the ice making solution is 0.50 m3/h, the secondary refrigerant temperature is ﹣15 ℃, and the rotating speed of the spiral blades is between 175~225 r/min.

M. Nakabayashi, S. Kamachi, D. Malle et al.

Fungus-derived GH-7 family cellobiohydrolase I (CBHI, EC 3.2.1.91) is one of the most important industrial enzymes for cellulosic biomass saccharification. Talaromyces cellulolyticus is well known as a mesophilic fungus producing a high amount of CBHI. Thermostability enhances the economic value of enzymes by making them more robust. However, CBHI has proven difficult to engineer, a fact that stems in part from its low expression in heterozygous hosts and its complex structure. Here, we report the successful improvement of the thermostability of CBHI from T. cellulolyticus using our homologous expression system and protein engineering method. We examined the key structures that seem to contribute to its thermostability using the 3D structural information of CBHI. Some parts of the structure of the Talaromyces emersonii CBHI were grafted into T. cellulolyticus CBHI and thermostable mutant CBHIs were constructed. The thermostability was primarily because of the improvement in the loop structures, and the positive effects of the mutations for thermostability were additive. By combing the mutations, the constructed thermophilic CBHI exhibits high hydrolytic activity toward crystalline cellulose with an optimum temperature at over 70°C. In addition, the strategy can be applied to the construction of the other thermostable CBHIs.

Chenchen Weng, Jin-Tao Ren, Zhongpan Hu et al.

Low-cost and high-performance electrocatalysts for electrochemical reactions are of crucial importance for renewable and sustainable energy technologies including rechargeable metal-air batteries and fuel cells. Nanocarbon materials, as a promising alternative to replace the state-of-the-art noble metal electrocatalysts, have attracted much interest, whereas the balance of the defect engineering and electric conductivity for them is still challenging. This work reports a discrete CoOx nanoparticles (CoOx NPs) situated in N-doped graphitic carbon nanorings (CoOx@NGCR), featuring graphitic but defect-rich characteristics, through a facile process of hydrothermal synthesis and subsequent high-temperature pyrolysis with in situ catalytic graphitization. The synergy arising from defect engineering and enhanced electric conductivity as well as hollow ring-shaped nanostructure of the fabricated CoOx@NGCR significantly boost the electrocatalytic activity for oxygen reduction reaction (ORR) and oxygen evolution re...