Desiccant-coated heat exchangers （DCHEs） play an important role in dehumidification. However， considering the ineffective structural optimization and selection of operating conditions， the efficiency of the current dehumidification technology needs improvement. Therefore， in this study， an efficient hydrogel composite material was developed， a dehumidification experimental platform was established， and a physical model of a hydrogel-based desiccant-coated heat exchanger was developed in COMSOL based on the material characteristics. Three structural parameters， including adsorbent coating thickness， fin spacing， and air channel length， were extracted. The dehumidification performance was optimized and experimentally verified. The study determined that the hydrogel-based desiccant heat exchanger had the best dehumidification performance when the coating thickness was 0.4 mm， fin spacing was 2.2 mm， and air passage length was 20 mm. Unlike other models， this model considers the coupling of multiple physical fields， including the humidity field， adsorbed water fraction field， and fluid temperature field in the heat exchanger. The moisture removal capacity increased by 10.35 g/kg （dry air）， and the moisture removal rate improved by 48.65% after structural optimization.
Heating and ventilation. Air conditioning, Low temperature engineering. Cryogenic engineering. Refrigeration
To investigate the low-temperature tolerance of <italic>Phoenix canariensis</italic> seeds and isolated seed embryos, along with the physiological changes that occur during cryopreservation, fresh seeds were dried to 25%, 20%, and 15% moisture content and then cryopreserved at -20 ℃ and -196 ℃ (LN<sub>2</sub>). The results showed that the survival rate of intact seeds gradually increased with decreasing water content. The survival rate of isolated seed embryo cultures increased with decreasing water content, and the growth rates of seeds and seed embryos dried to 11.6% moisture content were not significantly different from those of the unfrozen groups. The viability of LN<sub>2</sub>-preserved intact seeds and isolated seed embryos was higher than that of the -20 ℃ preservation group. After cryopreservation, the sucker part of the seed embryos was damaged more severely than the cotyledon after low-temperature preservation; however, this damage did not affect the subsequent growth of the seed embryos. After drying to an 8% moisture content, the superoxide dismutase (SOD) activity of the seeds was lower than that of fresh seeds, and the CAT activity and MDA content increased. After cryopreservation, the SOD activity and CAT activity of the seeds increased, and the MDA content decreased, whereas the MDA content of the seeds increased significantly after drying, indicating that excessive dehydration was not conducive to seed cryopreservation. <italic>Phoeni canariensis</italic> seeds are highly resistant to low temperatures and can be preserved in liquid nitrogen for long periods.
Heating and ventilation. Air conditioning, Low temperature engineering. Cryogenic engineering. Refrigeration
Winter heating of passenger compartments in electric vehicles relies on vehicle air-conditioning systems， in which the air outlet temperature must be rapidly increased to the set value. These systems typically adopt a reverse Carnot heat-pump cycle， which does not achieve sufficient heating capacity in low-temperature environments， thus preventing the air outlet temperature from rapidly reaching the set temperature during cold starts. To ensure that the system provides sufficient heating capacity under these conditions， a hot-gas bypass heat-pump cycle was used to replace the reverse Carnot heat-pump cycle. By bypassing the refrigerant from the high-pressure side to the low-pressure side， the suction pressure of the compressor was increased， ensuring stable operation of the compressor under low-temperature heating conditions. A staged hot-gas-bypass heat-control strategy， with an additional exhaust throttle valve to reduce the time required to establish high pressure， is proposed. A simulation model of a this proposed system， using R290 as the refrigerant， was established， and a test bench was built to calibrate the simulation model. Using this simulation， differences between the hot-gas-bypass heat-pump cycle and the reverse Carnot heat-pump cycle were examined， and the effects of the optimization strategy were verified. Under low-temperature conditions （-25 ℃ and -20 ℃）， the proposed system achieved better heating performance than the reverse Carnot heat pump cycle. Relative to the pre-optimization control strategy， the proposed optimized hot-gas-bypass heat-pump cycle control strategy reduces the time required for the air outlet temperature to reach the target temperature by 36%.
Heating and ventilation. Air conditioning, Low temperature engineering. Cryogenic engineering. Refrigeration
Mg-Zn-Ca alloy is a promising candidate for orthopaedic implants such as bone plates and screws, as it has a similar mechanical strength and elastic modulus to bone, and it degrades in the body without causing toxicity or inflammation. Drilling studies are necessary to optimize the drilling process parameters, to evaluate the machinability and surface integrity of Mg-Zn-Ca alloy, and to ensure the effective and efficient drilling for various applications in the medical and engineering fields. The present experimental study emphasizes the influence of Ca content, biofriendly coolants and their combined effect with standard drill bits on the surface quality and axial thrust force in the drilling operation of Mg-Zn-Ca alloy. The drilling parameters such as cutting speed, feed rate, standard tools, bio-compatible coolants were optimized with respect to the amount of Ca in the Mg-Zn alloy. The axial thrust force and average surface roughness of drilled holes were considered as response of the experiments. The drilled surfaces were measured for average surface roughness in the transverse direction along the centre path of the drilled hole and a qualitative analysis was also carried out using advanced confocal microscope. The results revealed that the cutting speed among continuous factors significantly influenced the axial thrust force and average surface roughness. The effect of categorical factors was assessed using a regression based ranking method. The results of statistical analysis revealed that high speed steel, and vegetable oil offered improved surface quality, whereas the coconut oil showed low axial thrust force. The liquid nitrogen showed high value of axial thrust force and average surface roughness due to the brittleness induced by cryogenic coolant before drilling operation.
To meet the need for energy efficiency improvement and substitution of traditional refrigerants in the field of supermarket refrigeration, a supermarket booster refrigeration system using the eco-friendly zeotropic refrigerant CO2/R1234yf is proposed in this study. A thermodynamic model is established and compared with that of a pure CO2 booster refrigeration system. The results show that the maximum COP (1.40) of the system using CO2/R1234yf was obtained under the optimal CO2 mass fraction (0.94) and discharge pressure (8.81 MPa). The COP of the CO2/R1234yf booster refrigeration system was significantly improved compared with the pure CO2 system, which increased by 7.25% when the ambient temperature was 35 ℃. The APF improvement of the CO2/R1234yf booster system was 2.68%–4.72%. The APF increased with an increase in the latitude of typical cities. The exergy efficiency of the CO2/R1234yf booster system first increased and then decreased with increasing CO2 mass fraction. The CO2/R1234yf booster refrigeration system exhibited the highest exergy efficiency (0.18) when the CO2 mass fraction was 0.95, which was 4.62% higher than that of the CO2 system.
Heating and ventilation. Air conditioning, Low temperature engineering. Cryogenic engineering. Refrigeration
Data center computer room air-conditioning equipment operates for prolonged periods, and its performance must be tested and evaluated annually to ensure safe and efficient operation. This study conducts field measurements on the server layout, blind plate structure, and working condition adaptability in the rack. The thermal environment of a data center using the closed cold aisle underfloor air distribution system is studied, and the thermal environment safety and energy efficiency throughout the year are evaluated through thermal performance indicators and energy efficiency indicators. The results show that it is recommended to install a rack with a power of more than 2 kW in the middle area of the cold aisle. Installing a blind plate in the gap between the racks can promote the circulation of cold air inside the server, reduce the backflow interference of hot air, and reduce the maximum outlet temperature by 3.32 °C. The average supply air speed was reduced by approximately 24%. Under summer operating conditions, the PUE, WUE, and CUE of the data center were approximately 1.2, 3.5, and 0.84, respectively, and the WUE exhibited strong seasonality. Under winter operating conditions, free cooling can effectively reduce the energy consumption of data centers. In addition, the overheating problem of the racks at the end of the cold aisle of the data center is significant. The cabinet cooling index of the 16 racks was less than 90%, and the heat loss was high.
Heating and ventilation. Air conditioning, Low temperature engineering. Cryogenic engineering. Refrigeration
Andreas Himmelsbach, T. Standau, J. Meuchelböck
et al.
Abstract Nowadays, numerous techniques are used to quantify the resistance of cellular polymers against a thermal load. These techniques differ in significance and reproducibility and are all dependent on foam density, structure (i.e., cell size and -distribution) and sample geometry. Very different behaviors are expected for extrusion- and bead foams, as well as for amorphous and semi-crystalline polymers. Moreover, established tests use temperature ramps which would lead to temperature gradients within the sample and thus to faulty results. In this study, we developed a new approach from an engineering perspective to minimize these influences. In this approach, the resistance against the thermal load is derived from a steady creep test with defined temperature steps under a mechanical load, which is specifically set for each foam sample depending on its static compression behavior at room temperature. The two-stage test therefore combines (i) a standard quasi-static compression test at room temperature and (ii) a creep test with stepwise increased thermal loading. For each foam type, a rather low mechanical load (stress) is determined from the quasi-static compression test at room temperature; low enough to remain below the collapse strength and avoid irreversible deformation (i.e., buckling and/or breaking of the cell walls). This load is then applied in a creep test where the temperature is increased in defined steps from room temperature to a temperature close to T g or T m . The stepwise increase and holding of the temperature for a defined time enables a homogeneous temperature in the test specimen. The approach was applied to (i) polystyrene extrusion and bead foams (i.e., XPS and EPS), which have different foam structure, (ii) amorphous and semi-crystalline bead foams of polystyrene (EPS) and polypropylene (EPP), (iii) bead foams with different densities (30, 60, 120, and 210 kg/m3) and (iv) to a new type of bead foam made of the engineering polymer polybutylene terephthalate (E-PBT). The termination criterion for the test is defined as the temperature at which a relative compression of 10% is reached in the creep test with temperature steps. We suggest calling it the heat stability temperature THS. For the studied foams, the procedure delivers characteristic THS values that allow a good comparison between different polymer matrices and densities. The heat stability temperature THS of amorphous PS foams (i.e., XPS and EPS) was determined to be 98 °C, which is close to the glass transition temperature T g . Using the same approach, values of 99–107 °C were determined for EPP and 186 °C for the semi-crystalline bead foam E-PBT.
Transparent materials with high strength and toughness are highly demanded as engineering materials for consumer electronic, structural, and optical applications. Inspired by the “brick‐and‐mortar” structure in nacre, transparent glass/polymer composites have demonstrated an exceptionally high toughness and impact resistance. However, these composites suffer from low strength and low working temperatures due to polymeric components. Herein, a simple bioinspired approach to achieve a combination of high fracture toughness (KIC = 2.0 MPa m1/2) and optical transparency in a lithium disilicate/apatite glass‐ceramic through the creation of an acicular crystalline phase and a weak glassy interface is reported. This bioinspired approach represents a new pathway to manufacturing transparent materials for a variety of applications where mechanical performance is a necessity.
Despite the success of multiscale modeling in science and engineering, embedding molecular-level information into nonlinear reactor design and control optimization problems remains challenging. In this work, we propose a computationally tractable scale-bridging approach that incorporates information from multi-product microkinetic (MK) models with thousands of rates and chemical species into nonlinear reactor design optimization problems. We demonstrate reduced-order kinetic (ROK) modeling approaches for catalytic oligomerization in shale gas processing. We assemble a library of six candidate ROK models based on literature and MK model structure. We find that three metrics—quality of fit (e.g., mean squared logarithmic error), thermodynamic consistency (e.g., low conversion of exothermic reactions at high temperatures), and model identifiability—are all necessary to train and select ROK models. The ROK models that closely mimic the structure of the MK model offer the best compromise to emulate the product distribution. Using the four best ROK models, we optimize the temperature profiles in staged reactors to maximize conversions to heavier oligomerization products. The optimal temperature starts at 630–900K and monotonically decreases to approximately 560 K in the final stage, depending on the choice of ROK model. For all models, staging increases heavier olefin production by 2.5% and there is minimal benefit to more than four stages. The choice of ROK model, i.e., model-form uncertainty, results in a 22% difference in the objective function, which is twice the impact of parametric uncertainty; we demonstrate sequential eigendecomposition of the Fisher information matrix to identify and fix sloppy model parameters, which allows for more reliable estimation of the covariance of the identifiable calibrated model parameters. First-order uncertainty propagation determines this parametric uncertainty induces less than a 10% variability in the reactor optimization objective function. This result highlights the importance of quantifying model-form uncertainty, in addition to parametric uncertainty, in multi-scale reactor and process design and optimization. Moreover, the fast dynamic optimization solution times suggest the ROK strategy is suitable for incorporating molecular information in sequential modular or equation-oriented process simulation and optimization frameworks.
Abstract Four-dimensional (4D) printing of stimuli-responsive materials with the ability to change their shapes or functions when subjected to external stimuli has garnered much interest due to their tremendous potential applications in various biomedical and engineering devices. Recently, 4D printing of electrically-conductive shape memory polymers (SMPs) have become increasingly attractive due to its prospects in the fields of biomedicine, soft robotics, flexible electronics etc. However, the translation of these research into practical applications is often hindered by low electrical conductivity, as well as complicated programming and design. In this work, we report a facile approach to achieve highly conductive SMP-based 4D-printed devices. The SMP-based devices can be printed on typical 3D digital light projection (DLP) or mask stereolithography (MSLA) printers from photopolymer resins with the ability to tune the shape memory transition temperatures ranging from 20 °C to 50 °C. High electrical conductivity of up to 2 × 104 S cm-1 was achieved through electroless deposition of copper with high adhesion strength of up to 1.5 MPa. The application of the technique to fabricate smart switches – with the ability to monitor temperature changes – for electrical safety devices was successfully demonstrated. The approach presented herein may be further explored and developed to capitalise on the stimuli-responsiveness and electrical conductivity of 4D-printed SMPs to find value in various engineering applications.
The development of biodegradable materials with high osteogenic bioactivity is important for achieving rapid bone regeneration. Although hydroxyapatite (HAp) has been applied as a biomaterial for bone engineering due to its good osteoconductivity, conventional synthetic HAp nanomaterials still lack sufficient osteogenesis, likely due to their high crystallinity and uncontrollable architecture. A design of HAp nanoparticles mimicking bone features may create good microenvironments that promote osteogenesis for rapid bone regeneration. In this study, HAp nanoparticles with a comparatively less crystalline structure and nanorod shapes mimicking biological HAp nanocrystals of natural bone were fabricated using a simple chemical precipitation approach with mild temperature control in the absence of any organic solvents. Transmission electron microscopy (TEM) indicated that HAp nanorods with aspect ratios from 2.0 to 4.4 were synthesized by adjusting the reaction time as well as the reaction temperature. Fourier transform infrared spectroscopy and X-ray diffraction experiments displayed that HAp nanorods prepared at 30 °C (HAp-30 with an aspect ratio of 2.9) had a low crystalline structure and B-type CO32- substitution similar to those of natural HAp originating from bone tissue. The energy-dispersive spectroscopy (EDS) results showed that the Ca/P ratio of HAp-30 was 1.66 ± 0.13. An in vitro biological evaluation against rat bone marrow-derived mesenchymal stem cells indicated that the resulting HAp nanorods had excellent biocompatibility (with an ∼80-fold increase in IC50 compared to that of conventional HAp nanoparticles). Interestingly, the alkaline phosphatase (ALP), alizarin red S, and immunofluorescence staining results all showed that stem cells display an obvious osteogenesis dependence on the HAp nanostructure. Specifically, HAp nanorods with a moderate aspect ratio had the optimal osteogenic capacity (e.g., HAp-30 offered a 2.8-fold increase in ALP expression and a 4-fold increase in OCN expression relative to that provided by irregular HAp at day 14). It is expected that HAp nanorods with controllable architectures and size have potential as a kind of new bioactive bone filler for bone defect repair.
Perfecting the existing technologies and developing new ones require to rethink the processes in order to obtain qualitatively new results. Widespread use of cryogenic engineering in the chemical industry and medicine calls for a thorough analysis of both the efficiency of thermodynamic cycles and the hardware design of appropriate equipment. The power necessary to obtain low working medium temperatures is distributed between the cooling of the object and the losses in the various elements of the cryogenic setup. One of the best ways to increase the efficiency of the setup is to use the cold energy recovery. This is done by using various designs of recuperative heat exchangers, such as twisted heat exchangers. Existing methods of calculating the parameters of power equipment are based on empirical dependencies, which require some justification and clarification in order to be used for calculating cryogenic equipment parameters. The article describes the experimental setup, presents the research methods applied and analyses the results of the study on convective heat transfer in external flow past the tubular surface of the twisted heat exchanger. The obtained results for the laminar gas flow mode at Re < 2300 allowed determining the length of the initial heat section depending on the regime parameters of the contact phases and the geometric specifications of the twisted heat exchanger. The obtained dependence will make it possible to refine the method of calculating the parameters of the twisted heat exchanger in the annular channel.
The physical and mechanical properties of rocks at high temperatures change considerably with geothermal exploitation, underground coal gasification, and nuclear engineering construction, posing a threat to the safety of underground engineering. To investigate the effect of temperature on micro‐ and macroscale damage of sandstone, a series of uniaxial compressive strength (UCS) tests were conducted using an MTS 815 mechanical testing system. Acoustic emission (AE) monitoring, scanning electron microscopy (SEM), and nuclear magnetic resonance (NMR) were also employed. Macroscopically, it was found that the physical and mechanical properties of sandstone change with treatment temperature, but these changes do not follow a monotonic trend. In addition, the brittle‐ductile transition occurs at approximately 600°C, which is further confirmed by AE monitoring. Regarding the microstructural evolution of sandstone, the percentage of micropores shows a monotonically decreasing trend with increasing treatment temperature. The change in mesopores decreases slightly first, then shows a gradual increase, and finally decreases. The macropores first decrease and subsequently increase with increasing temperature. The decreasing trend of the meso‐ and macropores is attributed to thermal expansion at a relatively low temperature. However, the decrease in mesopores is due to their coalescence into macropores at higher temperatures. Furthermore, the integral value of the NMR spectrum first decreases and then increases with increasing treatment temperature, corresponding to the decrease in porosity from 25°C to 200°C, and then increases with temperature to 900°C. Finally, a constitutive model for the deformation and fracture of sandstone is established based on the effective medium theory and AE energy. The present study is helpful for improving the understanding of the process of thermal damage sandstone from both micro‐ and macroscale perspectives.
Future universal quantum computers solving problems of practical relevance are expected to require at least 106 qubits, which is a massive scale-up from the present numbers of less than 50 qubits operated together. Out of the different types of qubits, solid state qubits are considered to be viable candidates for this scale-up, but interfacing to and controlling such a large number of qubits is a complex challenge that has not been solved yet. One possibility to address this challenge is to use qubit control circuits located close to the qubits at cryogenic temperatures. In this work we evaluate the feasibility of this idea, taking as a reference the physical requirements of a two-electron spin qubit and the specifications of a standard 65 nm complementary metal-oxide-semiconductor process. Using principles and flows from electrical systems engineering we provide realistic estimates of the footprint and of the power consumption of a complete control-circuit architecture. Our results show that with further research it is possible to provide scalable electrical control in the vicinity of the qubit, with our concept.