The energy and exergy analysis of counter-flow regenerative evaporative cooler

© 2018 Serbian Society of Heat Transfer Engineers. Recently the regenerative evaporative cooler (REC) has drawn great attention from researchers because it can cool the intake air below the wet-bulb temperature and approaching its dew point temperature. For further understanding of the heat and mass transfer occurred in a counter-flow REC, a novel mathematical model is developed based on the law of energy conservation and the principle of the thermodynamic theory. The proposed mathematical model is validated against experimental data from literature. The parametric study is performed to investigate the performance of the REC under different operating and geometrical conditions. It is found that the exergy destruction and exergy efficiency ratio of the REC are strongly influenced by the intake air velocity, the working to intake air ratio and channel gap, followed by the channel length. The working to intake air ratio choosing from 0.3 to 0.4 is appropriate in order to achieve better thermal performance with permissible level of thermodynamic cost. Moreover, the results obtained in this paper reveal that the best thermal performance does not correspond to the best thermodynamic performance. Thus, both the first and second law of thermodynamics should be considered for a comprehensive analysis

The energy and exergy analysis on the performance of counter-flow heat and mass exchanger for M-Cycle indirect evaporative cooling

© 2018 Serbian Society of Heat Transfer Engineers. The dew point Indirect Evaporative Cooling (IEC) achieved through Maisotsenko cycle (M-Cycle) is a complicated thermodynamic process. For further understanding of the heat and mass transfer occurred in a dew point indirect evaporative air cooler with M-Cycle counter-flow configuration, the paper presents a novel mathematical model that combined the law of energy conservation and the principle of the thermodynamic theory. The model was used to carry out the parametric study of the dew point air cooler under various inlet air temperature and relative humidity. Through the combined analysis of energy and exergy of the target IEC system, it is found that both the inlet air temperature and relative humidity have an important effect on the thermal performance and thermodynamic performance of the heat and mass exchanger. The high temperature environment helps to get better thermal performance and thermodynamic performance. It has been showed in this paper that the best thermal performance does not correspond to the best thermodynamic performance. Thus, the energy and exergy analysis should be implemented simultaneously for the optimization of the process to get the best thermal performance at permissible level of thermodynamic cost

Molecular epidemiology and antimicrobial resistance profiles of Klebsiella pneumoniae isolates from hospitalized patients in different regions of China

IntroductionThe increasing incidence of Klebsiella pneumoniae and carbapenem-resistant Klebsiella pneumoniae (CRKP) has posed great challenges for the clinical anti-infective treatment. Here, we describe the molecular epidemiology and antimicrobial resistance profiles of K. pneumoniae and CRKP isolates from hospitalized patients in different regions of China.MethodsA total of 219 K. pneumoniae isolates from 26 hospitals in 19 provinces of China were collected during 2019–2020. Antimicrobial susceptibility tests, multilocus sequence typing were performed, antimicrobial resistance genes were detected by polymerase chain reaction (PCR). Antimicrobial resistance profiles were compared between different groups.ResultsThe resistance rates of K. pneumoniae isolates to imipenem, meropenem, and ertapenem were 20.1%, 20.1%, and 22.4%, respectively. A total of 45 CRKP isolates were identified. There was a significant difference in antimicrobial resistance between 45 CRKP and 174 carbapenem-sensitive Klebsiella pneumoniae (CSKP) strains, and the CRKP isolates were characterized by the multiple-drug resistance phenotype.There were regional differences among antimicrobial resistance rates of K. pneumoniae to cefazolin, chloramphenicol, and sulfamethoxazole,which were lower in the northwest than those in north and south of China.The mostcommon sequence type (ST) was ST11 (66.7% of the strains). In addition, we detected 13 other STs. There were differences between ST11 and non-ST11 isolates in the resistance rate to amikacin, gentamicin, latamoxef, ciprofloxacin, levofloxacin, aztreonam, nitrofurantoin, fosfomycin, and ceftazidime/avibactam. In terms of molecular resistance mechanisms, the majority of the CRKP strains (71.1%, 32/45) harbored blaKPC-2, followed by blaNDM (22.2%, 10/45). Strains harboring blaKPC or blaNDM genes showed different sensitivities to some antibiotics.ConclusionOur analysis emphasizes the importance of surveilling carbapenem-resistant determinants and analyzing their molecular characteristics for better management of antimicrobial agents in clinical use

Correlation between Metabolite of Prostaglandin E2 and the incidence of colorectal adenomas

Colorectal cancer is a common malignancy, and the incidence and mortality rates continue to rise. An important factor in the emergence of inflammation-induced colorectal carcinogenesis is elevated cyclooxygenase-2. Prostaglandin E2 (PGE2) over-production is frequently equated with cyclooxygenase-2 gene over-expression. PGE2 can be assessed by measuring the level of prostaglandin’s main metabolite, PGE-M, in urine. Colorectal adenoma is a precancerous lesion that can lead to colorectal cancer. We conducted research to evaluate the association between urinary levels of the PGE-M and the risk of colorectal adenomas. In a western Chinese population, we identified 152 cases of adenoma and 152 controls patients without polyps. Adenoma cases were categorized into control, low-risk and high-risk groups. There was no significant change in PGE-M levels, between the control group and the low-risk adenoma group. In the high-risk group, the PGE-M levels were 23% higher than the control group. When compared to people with the lowest urine PGE-M levels (first quartile), people with greater urinary PGE-M levels had a higher chance of developing high-risk colorectal adenomas, with an adjusted odds ratio (95% CI) of 1.65 (0.76-3.57) in the fourth quartile group, (p= 0.013). We conclude urinary PGE-M is associated with the risk of developing high-risk adenomas. Urinary PGE-M level may be used as a non-invasive indicator for estimating cancer risk

Inconsistent nanoindentation test hardness using different Berkovich indenters

When testing the nanoindentation hardness of the same sample with different Berkovich indenters, inconsistencies arise even when the frame stiffness and indenter tip area functions are regularly calibrated. This phenomenon has not been fully understood, making it challenging to accurately test and compare material hardness data from different laboratories. To address this issue, incremental test hardness caused by indenter tip defects and indentation size effects (ISE) is quantified. The ISE correction method proposed in this study is based on the Nix-Gao model for nanoindentation load-indentation depth (P-h) curves, and an area function equivalent modeling method is used to reproduce the geometry of Berkovich indenters in finite element (FE) analysis. Although the test hardness using different Berkovich indenters is inconsistent, their intrinsic hardness remains consistent. The proposed ISE correction method is validated by FE simulation results for A508-3 and 316 L steel that match perfectly with the ISE-corrected experimental P-h curves. The analysis of load increments shows that tip defects affect the test result through statistically stored dislocation (SSD) and geometrically necessary dislocation (GND). Indenter tip defects mainly affect the nanoindentation test results through GND. The smaller the indenter tip radius, the higher the GNDs, and the higher the test hardness. The different effects of indenter tip defects on GND lead to inconsistent hardness measurements using different Berkovich indenters

Helium-induced damage in MAB phase MoAlB and Fe2AlB2: first-principles simulation

Similar to M _n+1 AX _n (MAX, M: transition metal, A: A group element, X: C or N, n = 1 ∼ 3) phase materials, MAB (M: transition metal, A: A group element, B: B) phases also exhibit excellent comprehensive mechanical and thermal properties that are applicable to future nuclear reactors. The origination and growth conditions of He bubbles under irradiation in MAB phase MoAlB and Fe _2 AlB _2 have been calculated through first-principles theory in this work. In general, Fe _2 AlB _2 may present lower single/di-vacancy formation energies and a consequent higher He bubble number density. The final He bubble shape and comparative average size of MoAlB and Fe _2 AlB _2 have been predicted as well. In MoAlB there will form large platelet-like He bubbles and small spherical ones. In Fe _2 AlB _2 there will form spherical He bubbles with different sizes. These He bubbles can all further link via interlayer vacancies into string-like shape. Fe _2 AlB _2 also possesses higher He-induced embrittlement tendency than MoAlB

Raman Spectra and Microstructure of Zinc Oxide irradiated with Swift Heavy Ion

Zinc oxide (ZnO) materials irradiated with 350 MeV 56Fe21+ ions were studied by Raman spectroscopy, Photoluminescence spectra (PL) and Transmission electron microscope (TEM). After 56Fe21+ ion irradiation, a strong oxygen vacancy (Vo) related defect absorption peak at 576 cm−1 and an interstitial zinc (Zni) -related defect at 80 cm−1~200 cm−1 formed, and with the increase of dose, the absorption peak was obviously enhanced. Through theoretical calculation, different Raman incident light test methods wereused to determine the oxygen vacancy defect (Vo). There were no significant variation tendencies in the other Raman characteristic lines. Our results demonstrate an energy loss process contributing to the defect structure during irradiation. TEM images showed a lot of fundamental defects. But we see no distinct amorphization in the samples in the electron diffraction images, indicating that the higher energy and irradiation dose hardly affected the structure and performance of zinc oxide

The Formation of Calcium–Magnesium Carbonate Minerals Induced by <i>Curvibacter</i> sp. HJ-1 under Different Mg/Ca Molar Ratios

Microbial mineralization of calcium–magnesium carbonate has been a hot research topic in the fields of geomicrobiology and engineering geology in the past decades. However, the formation and phase transition mechanism of calcium–magnesium carbonate polymorphs at different Mg/Ca ratios still need to be explored. In this study, microbial induced carbonate mineralization experiments were carried out for 50 days in culture medium with Mg/Ca molar ratios of 0, 1.5, and 3 under the action of Curvibacter sp. HJ-1. The roles of bacteria and the Mg/Ca ratio on the mineral formation and phase transition were investigated. Experimental results show that (1) strain HJ-1 could induce vaterite, aragonite, and magnesium calcite formation in culture media with different Mg/Ca molar ratios. The increased stability of the metastable phase suggests that bacterial extracellular secretions and Mg2+ ions inhibit the carbonate phase-transition process. (2) The morphology of bacteriological carbonate minerals and the formation mechanism of spherical minerals were different in Mg-free and Mg-containing media. (3) The increased Mg/Ca ratio in the culture medium has an influence on the formation and transformation of calcium–magnesium carbonate by controlling the metabolism of Curvibacter sp. HJ-1 and the activity of bacterial secretion

Deep Electronic State Regulation through Unidirectional Cascade Electron Transfer Induced by Dual Junction Boosting Electrocatalysis Performance

Abstract Unidirectional cascade electron transfer induced by multi‐junctions is essential for deep electronic state regulation of the catalytic active sites, while this advanced concept has rarely been investigated in the field of electrocatalysis. In the present work, a dual junction heterostructure (FePc/L‐R/CN) is designed by anchoring iron phthalocyanine (FePc)/MXene (L‐Ti3C2‐R, R═OH or F) heterojunction on g‐C3N4 nanosheet substrates for electrocatalysis. The unidirectional cascade electron transfer (g‐C3N4 → L‐Ti3C2‐R → FePc) induced by the dual junction of FePc/L‐Ti3C2‐R and L‐Ti3C2‐R/g‐C3N4 makes the Fe center electron‐rich and therefore facilitates the adsorption of O2 in the oxygen reduction reaction (ORR). Moreover, the electron transfer between FePc and MXene is facilitated by the axial Fe─O coordination interaction of Fe with the OH in alkalized MXene nanosheets (L‐Ti3C2‐OH). As a result, FePc/L‐OH/CN exhibits an impressive ORR activity with a half‐wave potential (E1/2) of 0.92 V, which is superior over the catalysts with a single junction and the state‐of‐the‐art Pt/C (E1/2 = 0.85 V). This work provides a broad idea for deep regulation of electronic state by the unidirectional cascade multi‐step charge transfer and can be extended to other proton‐coupled electron transfer processes