•Fouling and heat transfer characteristics of a typical heat exchanger are investigated.•A critical row number is obtained, after which the per-tube fouling will reach stable.•The effects of ...geometric parameters and operating conditions are investigated.•Optimum parameters are obtained according to orthogonal array design method.•A correlation of the Nusselt number after fouling reaches stable is obtained.
In this paper, numerical simulations were performed for the fouling characteristics and heat transfer performance after fouling on the H-type finned tube heat exchangers, and the optimum parameters studies were also conducted according to the orthogonal array design method. Firstly, the effect of row number on the fouling results were discussed. It was found that there was a critical row number Ncr=6, and the fouling results will reach a constant value when the row number is larger than the critical row number. Then, the orthogonal array design method was employed to design the test arrangements, and the effects of six geometric parameters and two operating conditions on the fouling results as well as heat transfer performance after fouling were investigated. The order of the effects of each factor and the optimum parameters corresponding to the least fouling and best heat transfer performance after fouling were also determined. At last, a correlation of the Nusselt number after fouling Nuf∗ with the geometric parameters and the operating conditions was obtained. The results showed that the optimum conditions we determined using the orthogonal array design method do have less fouling or have better heat transfer performance after fouling than the reference cases in the test arrangements. The correlation of Nuf∗ has good prediction accuracy, and it can be useful in the design and evaluation of heat exchanger in dusty environment.
•Honeycomb finned tube heat exchangers is proposed for waste heat utilization.•Heat transfer coefficients at the fouling state are monitored in real time.•Fouling thermal resistance is selected as ...the evaluation index of fouling degree.•Fouling characteristics are numerical investigated to reveal the fouling mechanism.•Honeycomb H-type finned tube bundle has the lowest fouling thermal resistance.
A large number of fly ash particles in flue gas easily cause the fouling problem of heat exchangers, which seriously affects the efficient utilization of flue gas waste heat. In this study, experimental and numerical investigations on fouling and heat transfer characteristics in cross flow heat exchangers were carried out. The on-site experimental system was established, and the heat transfer coefficients for different heat-transfer surfaces at the fouling state were monitored in real time. The weakened degree of heat transfer coefficient and fouling thermal resistance are adopted to assess the effect of fouling on the heat transfer performance and compare the practicality of four different heat-transfer surfaces under dusty conditions. Numerical investigation was performed with the fouling model established in previous work to model the thermal-hydraulic and fouling processes. Numerical results are compared with experimental measurements and a good agreement is achieved. Results showed that compared with the aligned circular tube bundle, using H-type fins or honeycomb tube bundle both improve the anti-fouling performance, especially for the honeycomb H-type finned tube bundle, which has the lowest fouling thermal resistance. Therefore, due to the characteristics of easily soot-blowing and lower fouling thermal resistance, honeycomb heat exchangers are suitable for waste heat utilization of dusty flue gas.
Introduction
Our previous study has confirmed that a novel curcumin derivate nicotinate‐curcumin (NC) can facilitate autophagic flux in THP‐1 cells induced by oxidized low‐density lipoprotein.
Aims
...Given that autophagy plays critical roles in neurodegenerative diseases, the present study was carried out to investigate whether NC can improve cognitive function of rats with diabetes mellitus (DM) via restoring autophagic flux in CA1 hippocampus.
Results
Our results showed that NC treatment improved cognitive deficit and attenuated neuronal loss as well as cellular ultrastructure impairment in the CA1 region of DM rats induced by streptozotocin. Moreover, NC lowered the expressions of the apoptosis‐related proteins Bcl‐2, Bax, Cyt‐c, and cleaved Caspase‐3. Notably, NC treatment reversed autophagic flux impairment as evidenced by the deceases in LC3‐II and p62 protein levels, and autophagosome accumulation in the hippocampal CA1 region of DM rats. However, these protective effects of NC were abolished by cotreatment with 3‐methyladenine (an autophagy inhibitor) and chloroquine (an autophagic flux inhibitor), respectively. Furthermore, NC treatment decreased the expressions of phosphorylated mammalian target of rapamycin (mTOR) and p70 ribosomal protein S6 kinase (p70S6k) proteins in the CA1 region of DM rats.
Conclusions
These results indicate that NC ameliorates DM‐induced cognitive function impairment via restoring autophagic flux might by inhibiting mTOR/p70S6k activation in the CA1 region, and NC may be a promising agent for diabetic cognitive dysfunction prevention and treatment.
Melatonin, a pivotal photoperiodic signal transducer, may work as a brown-fat inducer that regulates energy balance. Our study aimed to investigate the effects of melatonin treatment on the body fat ...accumulation, lipid profiles, and circulating irisin of rats with high-fat diet-induced obesity (DIO). Methods: 30 male Sprague-Dawley rats were divided into five groups and treated for 8 weeks: vehicle control (VC), positive control (PC), MEL10 (10 mg melatonin/kg body weight (BW)), MEL20 (20 mg/kg BW), and MEL50 (50 mg/kg BW). The vehicle control group was fed a control diet, and the other groups were fed a high-fat and high-calorie diet for 8 weeks to induce obesity before the melatonin treatment began. Melatonin reduced weight gain without affecting the food intake, reduced the serum total cholesterol level, enhanced the fecal cholesterol excretion, and increased the circulating irisin level. Melatonin downregulated the fibronectin type III domain containing 5 (FNDC5) and lipoprotein lipase (LPL) mRNA expressions of inguinal white adipose tissue (iWAT) and induced the browning of iWAT in both the MEL10 and MEL20 groups. Conclusion: Chronic continuous melatonin administration in drinking water reduced weight gain and the serum total cholesterol levels. Additionally, it enhanced the circulating irisin, which promoted brite/beige adipocyte recruitment together with cholesterol excretion and contributed to an anti-obesity effect.
•An on line fouling experimental system is set up in a boiler system.•Experimental studies on heat transfer and fouling performance for different heat exchangers are performed.•Effect of tube types ...and arrangements on heat transfer and fouling are investigated.•Comparison between experimental and numerical results are conducted.•Anti-fouling measures and structures are discussed.
An on line experimental system was set up in a heating boiler so as to reproduce dusty working environments in heat recovery systems and to investigate heat transfer and fouling performance of different kinds of finned tube heat exchangers. Measurements are reported for the heat transfer coefficients, fouling and the effect of fouling on heat transfer performance of five different H-type finned tube heat exchangers. Fouling resistance and the weakened degree of heat transfer coefficient are employed to evaluate the effect of fouling on the heat transfer performance. Numerical simulations are also conducted on the fouling performance of each heat exchanger bundle and compared to the measurements. Double H-type fins can slightly reduce the heat transfer performance but also reduce fouling. Elliptical finned tubes with the same tube pitch decrease heat transfer performance and increase fouling, and with the same relative tube pitch, significantly increase the heat transfer performance before fouling, and can effectively reduce fouling.
•Fouling and heat transfer characteristics of a typical heat exchanger are investigated.•A multiple mean cycle method is proposed based on a comprehensive fouling model.•The effects of geometric ...parameters are discussed.•The staggered elliptical tube is proposed to reduce the fly-ash fouling.
Particulate fouling on flue gas heat exchanger surfaces reduces heat transfer efficiency and increases the instability of equipment operation. It is necessary to develop a better understanding of how fouling occurs, aiming to find strategies to predict and reduce it. In this paper, a multiple mean cycle method is proposed based on a comprehensive fouling model considering the deposition and removal mechanisms, combined with the discrete phase model and dynamic mesh method, to predict the fouling morphology. Then the effects of transverse pitch, longitudinal pitch, tube shape and arrangement on fly-ash fouling and heat transfer characteristics are examined. It is found that, for aligned arrangement, the fly-ash particles are mainly deposited at the upwind stagnation region at the first row and whole windward side of the rest rows; for staggered arrangement, the fly-ash particles are deposited at the upwind stagnation region. The multiple mean cycle method can predict the fouling morphology efficiently and keep the characteristic of non-uniform fouling distribution. The fouling mass increases with the increase of relative transverse and longitudinal pitches. The elliptical tube bundle with small relative transverse and longitudinal pitches can obviously reduce the fouling mass especially for the staggered elliptical tube. Compared with the aligned circular tube arrangement, the fouling mass mf is decreased by 81.1% at 10min. In addition, the weaken degree of Nusselt number after fouling ΔNu for the staggered elliptical tube is only about 49.8% of the aligned circular tube arrangement. Consequently, using the staggered elliptical tube contributes to reduce the fly-ash fouling, decrease the soot-blowing frequency and ensure the efficiency, economy and safety of flue gas heat exchangers.
•Review on MSR catalytic system construction from perspective of energy-mass transfer.•Classification of catalyst types for MSR reaction was presented.•Improving catalytic performance by using ...additives and supports was reported.•Porous structures of catalytic systems and their impacts were discussed.•The construction of photo-thermal coupling catalytic system for MSR was reviewed.
Methanol is regarded to be a promising hydrogen carrier owing to the virtues of high hydrogen content and liquid-state at room temperature. Methanol can be converted into hydrogen-rich gas through methanol steam reforming (MSR) process at mild reaction conditions, making it a high-quality onsite hydrogen source. The key problem of MSR technology for hydrogen production is to develop suitable and highly efficient catalytic system. Different from previously published reviews on MSR reaction, the main idea of this article is to shed light on the setting up process of MSR catalytic system from the perspective of energy-mass conversion. In this work, the researches on improving the durability, carbon deposition resistance and sintering resistance of MSR catalyst by material modification, additives utilization, and structure optimization are reviewed. Studies on revealing MSR reaction path under different catalytic conditions are discussed. Researches on heat/mass transport and distribution behaviors in MSR reactor under different catalyst structures are also displayed. This review detailedly summarizes the methodologies to optimize the catalytic system for reducing energy barrier of MSR, improving methanol conversion efficiency and rate, which can lay the foundation for engineering application of MSR technology.
Background
CKLF-like MARVEL transmembrane domain-containing 6
(
CMTM6
) is a critical regulator of tumor immunology among various cancers. However, the role and underlying molecular mechanism of
...CMTM6
in oral squamous cell carcinoma (OSCC) progression remains unclear.
Methods
The expression of
CMTM6
,
PD-L1
and
CD163
in OSCC tissues were detected by immunohistochemistry on tissue microarray. The effect of
CMTM6
knockdown on OSCC cells and macrophage polarization were analyzed by CCK-8 assay, apoptotic assay, would-healing assay, transwell assay and qPCR. OSCC cell derived exosomes were obtained by ultracentrifugation and the mechanistic studies were conducted by qPCR and Western Blot. 4-Nitroquinoline N-oxide (4NQO) induced OSCC mice were used for verifying the effect of
CMTM6
downregulation on M2 macrophage infiltration and tumor growth.
Results
In OSCC samples, higher
CMTM6
expression has been obviously associated with higher pathological stage of OSCC patients,
CD163
+ macrophages infiltration and
PD-L1
expression.
CMTM6
knockdown of OSCC cells inhibited proliferative, migrative and invasive abilities of OSCC cells, as well as inhibited M2 macrophage polarization in vitro with downregulating
PD-L1
expression. Importantly, exosomes from OSCC cells shuttled
CMTM6
to macrophages and promoted M2-like macrophage polarization through activating ERK1/2 signaling. In addition, in 4NQO-induced OSCC mice,
CMTM6
level was positively associated with
CD163
,
CD206
and
PD-L1
as well as M2-like macrophage infiltration.
Conclusion
OSCC cell-secreted exosomal
CMTM6
induces M2-like macrophages polarization to promote malignant progression via ERK1/2 signaling pathway, revealing a novel crosstalk between cancer cells and immune cells in OSCC microenvironment.
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