Auto-cascade refrigeration (ACR) systems can reach ultra-low temperatures but often suffer from two major drawbacks: high compressor exit (discharge) temperatures and low system performance. Many previous studies have focused on performance enhancement while neglecting the critical issue of compressor discharge temperature. Although techniques such as vapor injection, two-stage compression, and additional heat exchangers can enhance system efficiency, they also introduce structural complexity and higher costs. To address these challenges, this study proposes a novel hybrid refrigeration cycle that integrates a cascade cycle with an ACR system. The objective is to lower the compressor discharge temperature and improve the overall performance while maintaining simplicity through the use of environmentally friendly refrigerant mixtures. Four different configurations were studied: three modified cascade refrigeration cycles and one ejector-enhanced cascade refrigeration (MECR) cycle. The MECR system achieved the best results, with a coefficient of performance of 0.894 and an exergy efficiency of 30.1% at evaporator exit and condensation temperatures of −60 °C and 30 °C, respectively. The compressor discharge temperature was reduced by 36.9%, improving safety when using low-global warming potential refrigerants. Relative to comparable systems reported in the literature, the proposed design improved exergy efficiency by up to 58.2% without compromising structural simplicity. These findings demonstrate that the MECR configuration provides a practical balance between performance improvement, safety, and system simplicity, offering meaningful advantages for ultra-low-temperature applications without increasing the system complexity.
To address the common problems associated with traditional chemisorption sorbents， including their loose structure， lack of effective heat- and mass-transfer pathways， and poor cycling stability， this study proposes and synthesizes a novel graphene-based composite sorbent. By embedding strontium chloride （SrCl<sub>2</sub>） into a three-dimensionally interconnected graphene network， continuous and efficient channels for heat conduction and mass transfer were constructed， significantly enhancing the sorbent's cycling stability and thermophysical transfer performance. The composite sorbent achieves a high ammonia uptake， of 0.577 g/g， at an evaporation temperature of -10 ℃， reaching 84.1% of the theoretical value. The specific cold storage capacity reaches 639.89 kJ/kg， which is 1.9 times that of ice storage. Under a desorption condition driven by a 90 ℃ heat source， the ammonia desorption capacity reaches 0.572 g/g. In constant-pressure desorption experiments simulating hot water supplied by a non-concentrated solar collector， over 90% of the cold storage process was completed within 4 h of stable sunlight. The proposed graphene-based composite sorbent demonstrated excellent performance in terms of both energy storage density and cyclic stability， thus providing solid technical support for engineering applications of solar-driven adsorption cold storage systems.
Heating and ventilation. Air conditioning, Low temperature engineering. Cryogenic engineering. Refrigeration
Abstract In this paper, the system performance of R744 and R744/R170 mixed refrigerants used in a single-stage compression transcritical cycle at low evaporation temperature was studied by simulation method, and the effect of evaporation temperature, outlet temperature of gas cooler, R170 ratio on coefficient of performance (COP), discharge temperature, optimal pressure, and compression ratio were analyzed. The results show that Popt increases and decreases with the increase of outlet temperature and evaporation temperature of gas cooler and increases first and then decreases with the increase of R170 proportion. In the heating system, the maximum and minimum Popt of R744/R170 (25/75) were 1.35 MPa, 3.6 MPa, and 2.6 MPa and 1.23 MPa, 2.93 MPa, and 1.87 MPa lower than that of R170 (0%, 22.4%, and 50%); compared to pure R744, the system pressure of the mixed R744/R170 is lower. The COPe and COPh increase with the increase of evaporation temperature and decrease with the increase of outlet temperature of the gas cooler. With the increase of R170 proportion, they first decrease and then increase; the maximum COPe and COPh of R744 were 22.4%, 29.6%, and 21.2% and 10.3%, 13.8%, and 10.8% higher than those of R170 at 22.4%, 50% and 75%, respectively.
Sub-Kelvin refrigeration technology (<1 K) is a critical supporting technology for cutting-edge physics research and quantum technology. Currently, it mainly includes adsorption refrigeration, dilution refrigeration, and adiabatic demagnetization refrigeration. Adsorption refrigeration is limited by its evaporative cooling principle, with the lowest temperature higher than 200 mK. Dilution refrigeration and adiabatic demagnetization refrigeration can achieve temperatures below 10 mK. The former can provide a larger continuous cooling capacity between 20 mK and 100 mK, while the latter, based on solid-state refrigeration, can operate efficiently under a microgravity environment. This article briefly introduces the principles, development history, and technical prospects of these three technologies.
Heating and ventilation. Air conditioning, Low temperature engineering. Cryogenic engineering. Refrigeration
Refrigerated tank containers are currently the primary method of transporting cryogenic liquids. The air outlet of the refrigeration system is blocked by the liquid tank, resulting in low energy efficiency of the refrigeration system. This study aims to improve the energy efficiency of the refrigeration system for a tank container with a limited installation space. The resistance loss of the air duct is reduced and the air volume of the condenser is increased by optimizing the condenser air duct structure and pipeline arrangement, thereby improving energy efficiency. By optimizing the structure of the air outlet, sufficient air volumetric flow rate can be achieved under blocked conditions. By optimizing the pipeline arrangement, the resistance loss of the condenser is reduced, and the air volumetric flow rate is increased. The test results of the above system show that air duct structure optimization and condenser flow path optimization can improve the energy efficiency of the refrigeration system by 25.0%, indicating that the proposed optimization scheme can effectively improve the energy efficiency of the refrigeration system for tank containers.
Heating and ventilation. Air conditioning, Low temperature engineering. Cryogenic engineering. Refrigeration
Abstract Binding two separate elastomeric substrates is of great importance for the fabrication of next generation stretchable devices including epidermal electronics and soft robotics. However, it is still extremely challenging to find an adhesive to bind arbitrary elastomers with excellent adhesion strength and reliability without compromising the stretchability of the laminated elastomeric substrates. In this study, a sub-micron-thick (∼500 nm) stretchable adhesive was synthesized by using a vapor-phase deposition method. The stretchable adhesive consists of a copolymer film containing curable epoxy and hydroxyl functionalities with sufficiently low glass transition temperature (Tg) in order to render the adhesive elastomeric. Moreover, depositing the adhesive layer in vapor phase induced an interpenetrating polymer network (IPN) at the interface between the elastomeric substrate and stretchable adhesive layer, which enabled strong binding between arbitrary elastomeric substrates such as polydimethylsiloxane (PDMS), Silbione™, 3M VHB™, and Ecoflex™, with substantially enhanced adhesion stability and high transparency. The adhesion strength was fully retained even after more than 105 times of repeated stretch-release cycles of 50% strain. The IPN-induced stretchable but ultrathin adhesive layer developed in this study will serve as a platform bonding technology for the wide range of soft matter engineering applications.
Abstract As an environmentally friendly, green, and low-carbon construction material, cemented sand and gravel (CSG) dam is widely used in civil engineering and water conservation projects in China. This study describes the progress of research on CSG dams (materials) in recent years, including the progress of engineering related to cemented gravel dams, the static, dynamic, and thermodynamic properties and intrinsic structure models of dam building materials, the static, dynamic, and temperature field analysis of dam structures, and the design of dam profiles; and on this basis, it proposes the direction of further research and development of cemented gravel structures, which will provide research for new cemented gravel structures in China. Structure design, old and diseased engineering structure removal and reinforcement, and safety assessment to provide research status and new ideas.
Abstract Based on the requirements of low hydration heat and temperature rise of cement slurry used in deep-water gas hydrate formation, the thermal control effects of slag and fly ash on heat development of cement slurry were quantitatively and qualitatively investigated. The results show that the temperature rise, hydration heat and heat release rate of cement slurry were successfully reduced by slag and fly ash, which is beneficial to the cementing of gas hydrate formation, the engineering accidents, such as enlarged diameter, were avoided. Compared with pure cement slurry, the temperature rise of sample PCF37.5% and PCS37.5% was reduced by 16.5 and 12.1 °C, respectively. The hydration heat of sample PCF37.5% and PCS37.5% at 48 h was reduced by 35.3 and 16.3%, respectively. Secondly, the thermal control mechanisms of slag and fly ash on heat development of cement slurry were studied by X-ray Diffraction, Scanning Electron Microscope and Low Field Nuclear Magnetic Resonance Testing. As a result, the quantitative analysis shows that the heat development of cement slurry was controlled firstly by the lower hydration heat characteristics of slag and fly ash. The hydration heat of slag and fly ash at 48 h is 28.153 ∼ 47.067 J/g and 2.0549 ∼ 4.765 J/g, respectively. Besides, the qualitative analysis of hydration process and products shows that the heat development was also controlled by delay effect of slag and fly ash. Compared with pure cement slurry, the hydration products of sample PCF50.0% and PCS50.0% were obviously reduced. The innovation of this study is that the fly ash and slag were used to control the heat development of cement slurry used in hydrate formation. Especially, the control mechanisms were obtained quantitative calculation and qualitative analysis. Furthermore, the research results could provide technical reference for the design of cement slurry for hydrate formation cementing.
Abstract Thermocouples are one of the most widespread used sensors for temperature measurements in several applications, thanks to their robustness, low cost and ease of installation. However, when used in high temperature environments or in the presence of flames or elevated hot sources, the measurement can be affected, for example, by radiative exchanges to and from the ambient. The focus of the present study is to experimentally assess the thermal radiation effect on the thermocouple measurements in a controlled environment. To do so, K-type thermocouples having different diameters (1 mm and 0.2 mm) and radiated homogeneously from all sides are used to measure the air temperature between 40 ° C and 145 ° C inside a black-body calibrator cavity. The experimental data are then used to implement and discuss an existing radiation correction framework, the reduced radiative error method (RRE). The results suggest to use smaller size thermocouples to reduce the errors associated with thermal radiation and improve the accuracy of the measurement. Additionally, the results show that the effect of thermal radiation is higher for larger size thermocouples, i.e. thermocouples with 1 mm diameter show an error of 1 % in the range considered here. This error reduces by a factor of three when using thermocouples with 0.2 mm diameter. This benefit needs to be ultimately balanced with engineering considerations – smaller sized thermocouples are more likely to break during positioning or experiments.
Dielectric materials with ultralow dielectric constant, excellent mechanical properties, and good thermal stability have a broader application prospect in microelectronic devices with the rapid growth of 5G communication systems. On this basis, a series of lightweight polyarylene ether nitrile (PEN)/PSS‐octamethyl substituted (POSS) foams have been prepared by supercritical carbon dioxide foaming technique combining the strategy of low dielectric constant POSS doping and the introduction of bubbles. The effects of the introduction of POSS and foaming temperature on the foaming behavior of PEN/POSS composites are studied. The density of PEN/POSS foam with 5 wt% POSS is as low as 0.208 g cm−3 and the homologous porosity is up to 82.1%, which realizes the lightweight preparation of engineering plastics. Due to the introduction of POSS and pores, the PEN/POSS foam exhibits an ultralow dielectric constant of 1.83 at 1 kHz, while the dielectric loss is as low as 0.0036 and high thermal stability (Td5 > 453 °C). In addition, the specific modulus of PEN/POSS foam is up to 1.07 GPa cm−3 g−1 due to the high performance of the PEN. These excellent properties make PEN/POSS foams have great potential in the application of microelectronic devices.
In order to understand the behavior and to determine the effective operational parameters of a solar-driven ejector air conditioning system at low or medium temperature, a dynamic model depends on the principles of conservation, the momentum mass and energy is developed. For this purpose, the thermodynamic characteristics of the liquid and vapor refrigerant were identified using the Engineering Equation Solver (EES) software. Linear Fresnel solar reflector has been used as a tool to convert solar energy into thermal energy. Water (R718) was used as a refrigerant. The operational conditions for the studied solar-driven ejector air conditioning system are as follows: evaporator temperature “Te =283.15 K”, condenser temperature “Tc =305.15 K”, and generator temperature “Tg = 373.15 K”. The performance of the ejector air conditioning system was compared as a function of the operating parameters of the subsystem. The average value of thermal efficiency of the Fresnel linear concentrator has reached 31.60 %, the drive ratio “ω” is 0.4934, the performance value of the ejector air conditioning subsystem “COPejc” is 60.664 % and the average value of the thermal performance of the machine “STR” has touched 19.17 %. The results obtained through this scientific subject are stimulating and encouraging, where this technique can be used for air conditioning in desert areas in southern Algeria, where fossil energy (petroleum, gas, etc.) is extracted and produced in various types.
Quench protection is a major issue for high temperature superconductor (HTS) magnets that operate at high current densities with high stored magnetic energy. Quenches do not propagate rapidly in HTS coils and these coils heat up quickly because there isn’t enough copper in the conductor. In addition, the conductor critical current and the engineering critical temperature will vary depending on the field orientation within the conductor. This paper points out the difference between current re-distribution within a magnet to keep a magnet from quenching and true quench protection where a portion of a coil has turned normal and the magnet stored energy is being deposited into the growing coil normal region. This paper discusses some magnet quench protection methods for both low temperature superconductor (LTS) and HTS magnets that are in the literature. A number of quench methods that work very well for LTS magnets may not work at all for an HTS magnet. The anisotropy of HTS conductors can be a limiting factor on whether a quench protection method works.
Abstract Scaffolds consisting of cylindrical struts are one of the high-potential tissue engineering materials because the highly porous structure can easily induce cell infiltration/migration and efficiently deliver nutrients to the cells. In addition, cryopreservable scaffolds have attracted much interest in tissue engineering because they can be prospective ready-to-use “living” biomaterials consisting of a patient’s own cells. In this study, we investigated a cryopreservable cell-printed scaffold consisting of microscale cylindrical struts. To fabricate the scaffold, we developed a 3D cell-printing system supplemented with microfluidic channels, a core-shell nozzle, UV treatment system, and low-temperature working plate. The scaffold consisted of a cell-laden collagen/dimethyl sulfoxide (DMSO) mixture in the core region and a methacrylate gelatin (GelMA)/DMSO mixture in the shell region. After cryopreservation, the preosteoblasts (MC3T3-E1) loaded in the scaffold showed reasonable cell viability (∼85%). Moreover, no significant difference was observed in the cell proliferations and ALP activities of the cryopreserved scaffold and non-cryopreserved scaffold. Based on these results, we believe that the fabrication process can be one of the potential techniques for fabricating cryopreservable scaffolds consisting of cylindrical struts.
Abstract In this investigation, we have studied the problem of peristaltic flow with heat transfer through the gap between coaxial inclined tubes where the inner tube is rigid and the outer tube has sinusoidal wave travelling down its wall. The problem has been formulated in cylindrical coordinate system. The equations governing the flow have been simplified under the long wavelength and low Reynolds number assumptions. The exact solution is obtained for the temperature profile. The perturbation solutions for the velocity and pressure gradient are obtained for small couple stress parameter. Pressure difference per wavelength and frictional forces on the tube walls have been computed numerically. Results are demonstrated for various flow parameters. The better pumping results occur in vertical tube, while less pumping is seen in horizontal tube. The size of trapped bolus is small in triangular wave as compared to other waves. The present study has a wide range of applications in bio-medical engineering like the transport phenomenon in peristaltic micro pumps.
Despite its small volume and quick refrigeration, semiconductor refrigeration plates have good application potential in refrigerated transportation. To examine the cooling capacity of the storage box with a semiconductor, an experimental bench was established to investigate the working performance of a storage box with two semiconductors types, namely, TEC1-12706 and TEC1-12712. The twice experiments started with 2 000 mL ice cubes and the combination with 1 500 mL ice cubes, 3 kg foodstuffs , and 3 bottles of mineral water with a volume of 500 mL respectively in the storage box. Meanwhile, different heat dissipation method of the hot side and fan arrangement of the cold side were both considered during the test. The results show that the TEC1-12712 with water-cooling has a larger cooling capacity than the TEC1-12706 with air-cooling. Comparing the performance of same type of refrigeration chip using water and air-cooling, it was inferred that the water-cooling has a better cooling effect and a shorter resistance time. Moreover, a better airflow distribution appears when the fan is arranged below the cold side of the refrigeration chip rather than beside it. With the cold storage demand for a volume of 0.1 m3, two chips of the TEC1-12706 type with air-cooling on the hot side are preferred. Over 10 hours, the center temperature of the box was maintained at 6 ℃ and the minimum value in the box was approximately 0 ℃. With the freezing demand, two chips of type TEC1-12712 with water-cooling on the hot side and the fan below the cold side are preferred. With this application method, the center temperature is controlled below 0 ℃ within 3 hours.
Heating and ventilation. Air conditioning, Low temperature engineering. Cryogenic engineering. Refrigeration
The European Union brings some restrictions to the use of some refrigerants, which has been higher than 150 global warming potential (GWP) value, in mobile air conditioning (MAC) systems as in directive no 2006/40/EC [1]. Then these GWP limits were extended air conditioning and refrigeration systems with regulation the Regulation (EU) No, 517/2014 [2]. Presently, most of the MAC systems use R134a as the refrigerant; however, the GWP value of the R134a is 1300 [3] and [4]. The refrigerants such as R1234yf, R1234ze(E), R152a and R444A, can be considered as alternative refrigerants having low GWP for automotive air conditioning systems. Table 1 shows the thermophysical properties of the above-mentioned refrigerants. Among them, R1234ze(E) can be used instead of R134a due to the their similar properties [5]. However, the cooling performance of R1234ze(E) is 30 % lower in average than that of R134a when used in a similar medium capacity vapor compression system [6] to [8]. Furthermore, the performance of R1234ze(E) can be improved when the mixture of some refrigerants used to obtain required properties. The R444A consists of 83 % R1234ze(E), 12 % R32 and 5 % R152a, (by mass) and its GWP value is 93 [4] and [9] which meets the European regulations. Devecioğlu and Oruç [10] calculated the performance parameters of R1234yf, R444A and R445A for a MAC system. It was found that the R444A and R445A have lower cooling capacity, but higher coefficient of performance (COP) than that of R1234yf. Lee et al. [11] investigated the performance of R444A, R445A, R152a, and R1234yf in an automotive air conditioning (AAC) system as an alternative to R134a. The highest COP was obtained when the system was working with R152a. Cheng et al. [9] tested an air source heat pump (HP) system using the different concentrations of R32/R1234ze(E) mixture numerically. It was determined that the heating and cooling capacities were improved compared to the R134a baseline system. Meng et al. [12] determined the performance of a refrigeration system using the mixture of R152a and R1234ze(E) refrigerants as an alternative to R134a. The mixture of 50 % R1234ze(E) and 50 % R152a was found to be the best alternative for R134a. It was demonstrated that the cooling capacity of R1234ze(E)/R152a mixture was very similar to R134a and can be used without any change in the compressor. Li et al. [13] reported that R134a Experimental Investigation of an Automotive Air Conditioning System Using R444A and R152a Refrigerants as Alternatives of R134a Direk, M. – Mert, M.S. – Soylu, E. – Yüksel, F. Mehmet Direk* – Mehmet Selçuk Mert – Eren Soylu – Fikret Yüksel Yalova University, Faculty of Engineering, Turkey