Lower Critical Point Research Articles

Analyzing the Failure of a Truck's Rear Axle Shaft Requires a Thorough Investigation to Pinpoint the Root Cause of the Issue

The analysis of a failed rear axle shaft from a dumper truck involved a comprehensive investigation to ascertain the underlying cause of the failure. Visual inspection, material analysis, mechanical testing, and fracture analysis were conducted to assess the condition of the axle shaft. The axle shaft exhibited signs of fatigue failure, with the fracture surface showing fatigue striations. Microstructural analysis revealed a coarse grain structure with inclusions, indicating potential material defects. Tensile testing showed that the axle shaft had lower-than-expected mechanical properties, suggesting a possible issue with material quality or heat treatment. Based on the analysis, the root cause of the failure was determined to be a combination of material defects and fatigue loading. Types of investigation like as visual examination, chemical analysis, hardness test, tensile test, fractography and ultrasonic test, and microstructure examination. Microstructure observation of the sample indicates a normal ferrite–pearlite (lower critical point) sorbite-type structure with some spheronization seen on some portions Results indicate that the failure occurred due to a sudden load on the axle shaft, specifically at its weakest point. The shear stresses on the axle shaft were insufficient to withstand the stresses caused by the sudden loading. Based on the analysis, make recommendations for corrective actions to prevent similar failures in the future. This may include design improvements, material changes, maintenance procedures, or operational changes. This may include design improvement, material changes, maintenance procedures, and operational changes. Implement the recommended corrective actions to prevent similar failures in other axle shafts or similar components.

The exploration of indigenous plant-based coagulant for sumbawanese cheese production as probiotic source

Sumbawa cow's milk processing is still limited even though it has the potential to be developed. Therefore, a diversification product like cheese as a source of probiotic is required. Cheese derived from milk that is coagulated using rennet which is expensive and has high halal critical point. Thus, an alternative coagulant that is affordable with low halal critical point such as local plant-based material is needed. This study used Sumbawa local cow’s milk to produce cheese which coagulated using pineapple and gooseberry and the addition of Lactobacillus lactis as the lactic acid bacteria. Observed parameters were clotting time, yield, hardness, protein, total fat, total lactic acid bacteria, and sensory quality. This experiment showed that the cheese yielded using pineapple was higher than that of gooseberry, while the cheese coagulated using gooseberry (26714 N/m2) was having firmer texture. Meanwhile, clotting time, protein content and total fat content of the cheese coagulated using both coagulants were the same. The total lactic acid bacteria of the cheese coagulated using pineapple and gooseberry was similar 10.80 Log CFU/mg and 10.84 Log CFU/mg, respectively. Sensory evaluation using quantitative descriptive analysis showed that the cheese coagulated using pineapple extract has higher aftertaste and bitter taste. Meanwhile, the cheese coagulated using gooseberry extract was dry, grainy, yellowish, and its overall acceptance was higher than that of pineapple.

Pure hydrogen gas production in a coal supercritical water gasification system with CO2 as transporting medium

Supercritical water gasification (SCWG) technology was a clean coal conversion and utilization technology, which could decompose low-grade coal into gaseous products and make efficient and clean use of them. However, system with H2O transporting had much energy consumption on heating transporting medium and side reactions at heating process would weaken the gasification effect. Considering the advantages of low critical point and low specific heat capacity of CO2, and the precedent of CO2 as a transport medium in non-supercritical systems, CO2 was expected to become a transport medium in supercritical water gasification systems and to achieve the goal of improving the gasification effect of heating process and reducing energy consumption. A supercritical water coal gasification system of was established with lignite as raw material in this paper. Production yields of gasification with CO2 as the transporting medium at different working conditions were investigated. CO2 and H2O were used as the transporting medium of the system, contrastively. Compared with H2O-transporting system, production of H2 and CO2 in CO2-transporting system decreased while that of CH4 and CO increased as well. Furthermore, both energy and exergy efficiency of CO2-transporting system were higher than that of H2O-transporting system. The result proved the superiority of CO2 as the transport medium of supercritical water gasification system.

Controllable selection of martensitic variant enables concurrent enhancement of strength and ductility in a low-carbon steel

A novel strategy through controlling the selection of martensitic variant in metallic materials is proposed to break through the trade-off between strength and ductility. Here we prepared a high-strength low-carbon steel by applying the two-stage mechanical processing combined with high-temperature large-reduction compression and the subsequent compression above the low critical point of austenitization. The steel has the lowest degree of static recrystallization and dynamic recrystallization after the two-stage mechanical processing, leading to the smallest prior austenite grains with an average diameter of 16.4 μm and the highest dislocation density of 10.21 × 1014 m−2. With the refinement of the prior austenite grains caused by the adjustment of the two-stage deformation process, the driving force required for martensitic transformation increases and variants selectivity becomes stronger, leading to a large number of fine martensitic laths and nanoscale twins after martensitic transformation. Consequently, the best combination of strength and ductility is obtained, with the yield strength of 871 MPa, tensile strength of 1054 MPa and the total elongation of 25%. The use of variant selection exploits the strengthening of both grain boundaries and dislocations, resulting in simultaneous enhancement of strength and ductility. These findings demonstrate how multiple deformation mechanisms can be deliberately activated via the controllable selection of martensitic variants.

Resurrection of carbon dioxide as refrigerant in solar thermal absorption cooling systems

The existing air conditioning and cold storage systems use conventional compressor based systems, compelling more electricity and greenhouse gasses (GHG) emissions. The incumbent cooling system uses synthetic refrigerants (CFCs, HCFC, and HFCs) that outperform natural refrigerants but are banned or under time bared permission due to their harmful effects. The global community of (196 parties till 2017) has ratified Paris Accord to limit GHG emissions and use low Global Warming Potential (GWP) refrigerants, and after the ban on existing synthetic refrigerants, quested for suitable natural working fluids and retrofitting in the existing system. Among ASHRAE envisaged natural refrigerants, CO2 has resurrected as an emerging refrigerant after the availability of high pressure technologies. The proposed design of solar assisted absorption chiller employing CO2 as a heat transfer fluid for a commercial dwelling is simulated for a dwelling in the hot and humid, moderate and sun adverse region (Lahore, 31.5204° N, 74.3587° E) to assess the thermal properties of the proposed design. A thermal storage tank with immersed heat exchangers augmented to meet the intermittency of solar energy. A solar evacuated glass tube collector (EGTC) with U-shaped copper tubes is used to collect solar heat energy. Integration of renewable energy (RE) systems is inevitable due to the persistent energy crisis and climate change situations. Solar energy is a promising source of energy abundantly available in hot areas. CO2 is a natural refrigerant that outperforms ASHRAE envisaged natural refrigerants due to the low critical point. A solar thermal cooling system employing a 35.2 kW absorption chiller driven via heat energy harnessed with EGTC using R-744 supported by an auxiliary furnace is simulated in a TRNSYS® Simulation environment. The simulated system covers the cooling requirements of a large three-room dwelling in Lahore, Pakistan. The proposed design comprises an R-744-based solar heating system combined with a hot water-fired absorption chiller. The results were dynamically simulated for the hot climate of Lahore, Pakistan, with average yearly maintained temperatures of 23 °C, 26 °C, and 21 °C for the three rooms and 0.21 solar fraction for the whole year.

Evaluation of ionic liquids as absorbents for absorption refrigeration systems using hydrofluoro-olefin refrigerant

In this study, we evaluate the use of ILs as absorbents in a double effect absorption refrigeration system using HFO refrigerant. By examining the properties of various refrigerant/absorbent mixtures, we identify the most efficient refrigerant/absorbent pair for the aforementioned absorption refrigeration system. First, we identify a suitable HFO refrigerant for the system. Among the candidates in this study, R1336mzz(Z) and R1234ze(Z) can be used in the absorption refrigeration system because both have low flammability and high critical points. Then, we analyze the characteristics of ILs as absorbents in the absorption refrigeration system. Imidazolium ILs have relatively low viscosities of approximately 20 mPa s at temperatures exceeding 50 °C and high stability. Next, we analyze the characteristics of refrigerant/absorbent pairs. When R1336mzz(Z) and R1234ze(Z) are used as the refrigerant, [OMIM][BF4] have the highest solubilities in oprating conditions. The solubility value of R1234ze(Z) with [OMIM][BF4] is 0.256 at 289.89 kPa and 80 °C, while the solubility value of R1336mzz(Z) with [OMIM][BF4] is 0.154 at 128.02 kPa and 80 °C. Finally, we analyze the performance of the refrigeration system. When the R1234ze(Z)/[OMIM][BF4] is used in the absorption refrigeration system, the COP and cooling capacity of the system exhibit the values of 0.516 and 0.549 kW, respectively.

Оценка степени влияния фактора подвижности стенок щели при расчёте величины протечек в рабочей части спирального компрессора. Часть 1

The scroll type compressor is widely used in the medium capacity segment of refrigeration and air conditioning technology including heat pumps. Today there is an active process of changing from hydrofluorocarbons to natural refrigerants with low global warming potential. CO2, with its low critical point and correspondingly high operating pressures, is gaining in importance. For operation with new refrigerants, the scroll compressor has to be adapted to take account of all its design features, the most important of which are the clearances in the machine's flow area. It has to be considered that the thermodynamic properties of carbon dioxide, different from hydrofluorocarbons, have a significant influence on the volume and energy values of the compressor. In this case relevance consists in increase of accuracy of compressor losses calculation and prediction of refrigeration machine characteristics. As the basic volumetric losses in the scroll compressor are leakages of working substance in its working part, and the process of flow of medium is unsteady, their quantitative component causes interest. The purpose of this work is to clarify the physical basis of the leakage process in the radial clearance and the degree of influence of various factors on it. Such analysis gives further opportunity to refine the methodology of calculation of leakages of compressed medium, taking into account the mobility factor of gap walls. It will raise accuracy of the received results which can serve as a base to prognosis of optimum characteristics of the compressor, due to their approximation and will allow to optimize designing of refrigerating machines at the chosen modes of work.

Transcriptomic Profiling Revealed Signaling Pathways Associated with the Spawning of Female Zebrafish under Cold Stress

As one of the critical abiotic factors, temperature controls fish development and reproduction. However, the effects of low temperature on the transcriptional regulation of zebrafish reproduction remain largely unclear. In this study, the fecundity of zebrafish was examined after exposure to cold temperatures at 19.5 °C, 19 °C, 18.5 °C, or 18 °C. The temperature at 19 °C showed no significant influence on the fecundity of zebrafish, but temperature at 18.5 °C or 18 °C significantly blocked the spawning of females, suggesting the existence of a low temperature critical point for the spawning of zebrafish females. Based on these observations, the brains of anesthetized fish under cold stress at different cold temperatures were collected for high-throughput RNA-seq assays. Key genes, hub pathways and important biological processes responding to cold temperatures during the spawning of zebrafish were identified through bioinformatic analysis. The number of down-regulated and up-regulated genes during the temperature reduction from egg-spawning temperatures at 19.5 °C and 19 °C to non-spawning temperatures at 18.5 °C and 18 °C were 2588 and 2527 (fold change ≥ 1.5 and p-value ≤ 0.01), respectively. Venn analysis was performed to identify up- and down-regulated key genes. KEGG enrichment analysis indicated that the hub pathways overrepresented among down-regulated key genes included the GnRH signaling pathway, vascular smooth muscle contraction, C-type lectin receptor signaling pathway, phosphatidylinositol signaling system and insulin signaling pathway. GO enrichment analysis of down-regulated key genes revealed the most important biological processes inhibited under non-spawning temperatures at 18.5 °C and 18 °C were photoreceptor cell outer segment organization, circadian regulation of gene expression and photoreceptor cell maintenance. Furthermore, 99 hormone-related genes were found in the brain tissues of non-spawning and spawning groups, and GnRH signaling pathway and insulin signaling pathway were enriched from down-regulated genes related to hormones at 18.5 °C and 18 °C. Thus, these findings uncovered crucial hormone-related genes and signaling pathways controlling the spawning of female zebrafish under cold stress.

Hydrogen-Free Deoxygenation of Bio-Oil Model Compounds over Sulfur-Free Polymer Supported Catalysts

AbstractHydrotreatment of bio-oil oxygen compounds allows the final product to be effectively used as a liquid transportation fuel from biomass. Deoxygenation is considered to be one of the most promising ways for bio-oil upgrading. In the current work, we describe a novel approach for the deoxygenation of bio-oil model compounds (anisole, guaiacol) using supercritical fluids as both the solvent and hydrogen-donors. We estimated the possibility of the use of complex solvent consisting of non-polar n-hexane with low critical points (Tc = 234.5 ºC, Pc = 3.02 MPa) and propanol-2 used as H-donor. The experiments were performed without catalysts and in the presence of noble and transition metals hydrothermally deposited on the polymeric matrix of hypercrosslinked polystyrene (HPS). The experiments showed that the presence of 20 vol. % of propanol-2 in n-hexane results in the highest (up to 99%) conversion of model compounds. When the process was carried out without a catalyst, phenols were found to be a major product yielding up to 95 %. The use of Pd- and Co-containing catalyst yielded 90 % of aromatic compounds (benzene and toluene) while in the presence of Ru and Ni cyclohexane and methylcyclohexane (up to 98 %) were the main products.

Insight into structural features of soluble portions from cellulose, cellobiose and monosaccharide methanolysis by GC/MS and ESI FTICRMS

Methanolysis of biomass has attracted increasing attention due to it has some advantages, such as low critical points and strong hydrogen donation ability. In this paper, methanolysis of cellulose, cellobiose (sucrose), and monosaccharide (glucose) were performed to obtain methanol-soluble portions (MSPs). The relatively volatile or less polar species in the MSPs were analyzed with a gas chromatograph/mass spectrometer (GC/MS), and the polar species were identified with a negative-ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometer (FTICRMS). According to analysis with GC/MS, the MSPs include ethers, esters, ketones, acids, sugars, phenols, and furans. The analysis with FTICRMS shows that the polar compounds in the MSPs are O1–O15 class species with 1–14 double bond equivalent (DBE) and 5–35 carbon atom number (CAN). The most abundant class species in MSPs from cellulose, sucrose, and glucose methanolysis are O5, O7, and O7, respectively. The species in MSPs from sucrose and glucose methanolysis center at higher DBE value and more CAN than those in MSP from cellulose methanolysis. Meanwhile, the oxygen atom number of O4–O10 class species in the MSPs were negatively correlated with the average DBE value. The results indicate that condensation intensively proceeded with the specific regularity during sucrose and glucose methanolysis.

In-situ extraction and impregnation of black walnut husk into polyethylene film using supercritical carbon dioxide with an ethanol modifier.

Walnuts are commonly cultivated for their kernel, which is a rich source of antioxidant phenolic compounds. The husk likewise contains antioxidant and antimicrobial compounds, but is typically discarded without further processing. Antioxidant compounds are useful in creating active packaging films, but typically decompose at melt extrusion temperatures in polymer processing. Due to carbon dioxide's low critical point and ability to swell polymer films, supercritical carbon dioxide may be used to impregnate phenolic compounds into polymers. For this study, a novel technique is used to simultaneously produce walnut husk extracts and impregnate the extract into polymer films in the same batch extractor using supercritical carbon dioxide with a 15 wt‐% ethanol modifier at 60°C at 19.4 MPa. The effect of varying the loading of walnut husk in the extractor upon impregnation mass was evaluated with the impregnation mass of the film increasing with walnut husk loading. It was determined by FTIR, as well as the reduction of the protein cytochrome c, that antioxidant compounds may be extracted from walnut husks and impregnated into low‐density polyethylene film (LDPE) by this technique.

Влияние состава сверхкритического растворителя на деоксигенирование модельных соединений био-нефти

Hydrofining of oxygen-containing compounds of bio-oil allows efficient use of the final product as a liquid fuel from biomass. Deoxygenation is considered to be one of the most perspective ways to modernize bio-oil. Generally, deoxygenation is carried out under fairly strict conditions in the presence of hydrogen in a medium of high-boiling hydrocarbons. This paper describes a new approach to deoxygenation of model compounds of bio-oil using supercritical liquids as a solvent and hydrogen donor. The possibility of using a complex solvent consisting of non-polar n-hexane with a low critical point (Tc = 234.5 °C, Pc = 3.02 MPa) and propanol-2 used as a hydrogen donor is evaluated. Experiments have shown that in the presence of 20 vol. % propanol-2 in n-hexane a maximum (99%) conversion of model bio-oil compounds with the formation of phenols with a yield of up to 95% is observed.

Liquid–Gas Equilibrium in Nanoparticle Network-Forming Systems

Mechanisms of phase formation in solutions of nano- and microparticles with anisotropic effective interactions have actively been discussed in the last years. Possible types of miscibility gaps for colloidal suspensions with anisotropic interaction have been analyzed within a statistical model including the variation of the reactivity of particles without a priori assumptions on the structure of clusters. It has been shown that the variation of model parameters allows the description of all observed miscibility gaps within a unified formalism. In particular, diagrams with the homogeneity region at zero temperature, closed loops, a lower critical point, and infinite immiscibility corridors have been obtained. Some types of diagrams have been described for the first time. It has been shown that a variable reactivity of particles is a key factor determining the type of phase diagram.

Discussion on the fluid-to-fluid scaling of heat transfer at supercritical pressures

Supercritical carbon dioxide (SCO2) has been extensively adopted in heat-transfer experiments due to its low critical point compared to supercritical water (SCW). While it helps to largely reduce the technical difficulty and cost, the experimental results need to be extrapolated to SCW using a set of reliable and well-validated fluid-to-fluid scaling criteria. In the present paper, a criterion for scaling the mass flux in normal and enhanced heat transfer regimes was achieved by using Computational Fluid Dynamic (CFD) approaches. This criterion as well as the available scaling laws were assessed based on a wide range of the experimental data. It was found that Prandtl number shows a significant and nonmonotone effect on the scaling of mass flux (and consequently Nusselt number). Similar exponents of the Prandtl number were obtained using different approaches, but a constant exponent failed to capture the nonmonotone effect, especially when the bulk temperature surpasses the pseudo-critical temperature where large variations in the thermophysical properties appear. A modified scaling criterion, which is applicable to the heat transfer deterioration occurred at low mass fluxes, was proposed for the Nusselt number. The deviation from the experimental data was significantly reduced after Grashof number was incorporated into the criterion.

Impregnation of mesoporous silica with mangiferin using supercritical CO2

The solvating power and diffusivity of supercritical carbon dioxide (scCO2) have attracted attention in recent years for the impregnation of polymers and porous matrices. This technique provides a final impregnated matrix that is free of solvents and it allows the use of thermosensitive drugs due to the relative low critical point of scCO2.The work reported here concerned the influence of parameters such as pressure, temperature, percentage of co-solvent, depressurization rate and time on the impregnation of mangiferin (MNG) into silica as a porous matrix. Increases in the values of the studied parameters led to an enhanced impregnation of MNG in all cases. Delivery profiles in simulated fluids were obtained. The profile for the gastric fluid shows a gradual release of MNG. The release of MNG in the intestinal fluid was faster than in the gastric fluid. The MNG was more soluble in the intestinal than in the gastric fluid.

Inactivation of Salmonella , Listeria monocytogenes and Escherichia coli O157:H7 inoculated on coriander by freeze-drying and supercritical CO 2 drying

Abstract Coriander, either fresh or inoculated with three strains of Escherichia coli O157:H7, Salmonella or Listeria monocytogenes, was treated with supercritical CO2 (scCO2, with and without drying) or freeze-dried. After drying in scCO2 for 150 min at 80 bar and 35 °C, the aerobic plate count, yeasts and molds, and the Enterobacteriaceae were reduced by 2.80, 5.03, and 4.61 log CFU/g, respectively. The total count of mesophilic aerobic spores was not significantly reduced by the treatment. Freeze-drying induced lower reductions with 1.23, 0.87, and 0.97 log CFU/g, respectively. After treatment at 100 bar and 40 °C without drying, inoculated strains of E. coli O157:H7, Salmonella, and L. monocytogenes were inactivated by >7.37, >4.73 and 4.99 log CFU/g, respectively. After drying in scCO2 for 150 min at 80 bar and 35 °C, the strains were reduced by >5.18 log CFU/g. Freeze-drying resulted in lower reduction with maximum 1.53, 2.03, and 0.71 log CFU/g, respectively. This study indicated that scCO2 can be used for drying while offering a good inactivation of E. coli O157:H7, Salmonella, and L. monocytogenes as well as most of the bacteria in the vegetative form naturally occurring on coriander. Industrial relevance Although dried foods are considered microbiological stable foods and show adverse conditions to microbial growth, they may still host pathogenic microorganisms, which may proliferate upon sufficient rehydration. Highly contaminated commodities such as herbs and spices can pose a threat to consumer health if not processed carefully. There is therefore a need to develop or improve drying techniques which can provide dried foods while reducing the initial contamination to acceptable levels in a single process. CO2 is a cheap, accessible solvent, with a low critical point (31 °C, 73.8 bar). Moreover, in the supercritical region, CO2 exhibits potent microbicidal properties. Therefore, supercritical CO2 drying could be a valuable alternative non-thermal technique for conventional drying methods, such as air-drying or freeze-drying, when medium to high value-added food products with high initial contamination are involved.

Prediction Technology of Reverse Setting Block Shape with Inherent Strain Method and Re-meshing Technology

In order to reduce the cost of corrections and time needed for the block assembly process, the reverse setting method is applied for a back-heated block to neutralize deck deformation. The proper reverse setting shape for a back-heated block to correct deformation improved the deck flatness, but an excessive amount of reverse setting could inversely affect the flatness of the block. A prediction method was developed for the proper reverse setting shape using a back-heated block, considering the complex geometry of blocks, thickness of the deck plate, and thermal loading conditions such as welding and back-heating. The prediction method was developed by combining the re-meshing technique and inherent strain-based deformation analysis using the finite element method. Because the flatness deviation was decreased until the lower critical point and thereafter it tended to increase again, the optimum value for which the flatness was the best case was selected by repeatedly calculating the predefined reverse setting values. Based on this analysis and the study of the back-heating deformation of large assembly blocks, including the reverse setting shape, the mechanism for selecting the optimum reverse setting value was identified. The developed method was applied to the actual blocks of a ship, and it was confirmed that the flatness of the block was improved. It is concluded that the developed prediction method can be used to predict the optimum reverse setting shape value of a ship’s block, which will reduce the cost of corrections in the construction stage.

Thermal Cycling Influence on the Transformation Characteristics of a Ni50Ti48Nb2 Shape Memory Alloy

The alloy was chosen in order to obtain a shape memory alloy having a wider hysteresis than equiatomic NiTi, that involves a better thermo-mechanical stability. Two samples investigated by differential scanning calorimetry (DSC) were previously annealed at 800oC/12 h and, respectively, 900 �C/12 h followed by furnace cooling. These were afterwards submitted to thermal cycling. The thermal cycling of a Ni50Ti48Nb2 alloy sample previously annealed at 900 �C/12 h results in lower critical points and higher hysteresis values as compared to those of the sample annealed at 800�C/12h, also submitted to thermal cycling. Thus, annealing a metallic part made of such an alloy at 900� C/12 h followed by thermal cycling prior to putting it into service enhances its reliability.

Erratum to: “Stochastic approach to the theory of stratification of water and aqueous solutions: A model of twinkling hydrogen bonds”

The equations of state for liquids and liquid solutions with intermolecular hydrogen bonds were derived in the dichotomous noise model for these bonds. The analytically obtained PT and TC phase diagrams show that finite-lifetime bonds can be responsible for new experimentally found phase transitions. These are (i) stratification of solutions in a closed TC region (i.e., a region with upper and lower critical points) and in a low-concentration TC region and (ii) low-temperature stratification of monomolecular liquids into heavy and light phases.

Risk assessment for the mercury polluted site near a pesticide plant in Changsha, Hunan, China

The distribution characteristics of mercury fractions at the site near a pesticide plant was investigated, with the total mercury concentrations ranging from 0.0250 to 44.3 mg kg−1. The mercury bound to organic matter and residual mercury were the main fractions, and the most mobile fractions accounted for only 5.9%–9.7%, indicating a relatively low degree of potential risk. The relationships between mercury fractions and soil physicochemical properties were analysed. The results demonstrated that organic matter was one of the most important factors in soil fraction distribution, and both OM and soil pH appeared to have a significant influence on the Fe/Mn oxides of mercury. Together with the methodology of partial correlation analysis, the concept and model of delayed geochemical hazard (DGH) was introduced to reveal the potential transformation paths and chain reactions among different mercury fractions and therefore to have a better understanding of risk development. The results showed that the site may be classified as a low-risk site of mercury DGH with a probability of 10.5%, but it had an easy trend in mercury DGH development due to low critical points of DGH burst. In summary, this study provides a methodology for site risk assessment in terms of static risk and risk development.