The Chinese Journal of Process Engineering

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Research progress and application of heat transfer enhancement of twisted oval tubes

Xiuzhen LI Yingying TAN Junfei YUAN Zhanwei WANG Lin WANG

The Chinese Journal of Process Engineering 2022, 22 (5): 561-572. DOI: 10.12034/j.issn.1009-606X.221153

Abstract （599）

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The twisted oval tube has simple structure, excellent heat transfer enhancement and anti-fouling performance, and has become one of the research hotspots in the field of passive heat transfer enhancement. In recent years, researchers have carried out a lot of research on the heat transfer performance of twisted elliptical tubes (bundles) through experiments and numerical simulations. The mechanism of heat transfer enhancement is explained.Although there are reviews on the technology of twisted oval tube exchangers, there are deficiencies in the induction of the heat transfer enhancement characteristics of twisted oval tubes and the analysis of the research clues of the engineering application. This review focuses on the internal and external heat transfer and flow resistance performance of the twisted oval tube, and summarizes the influence of the structure of the twisted oval tube (bundle), working fluid and flow state on the heat transfer performance and flow resistance characteristics. The review also reviews the engineering application cases of twisted oval tube heat exchangers, and outlines the contents to be perfected in the researches on twisted oval tubes, and prospects the development trend of the research on heat transfer intensification of twisted oval tubes. This review is expected to provide guidance and reference for deepening the theoretical research and engineering practice of twisted oval tubes.

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Progress on catalysts for hydrogen production by low temperature methanol water reforming

Zhan SHEN Zhidong JIANG Pengfei ZHANG Ziyu ZHANG Haiying CHE Zifeng MA

The Chinese Journal of Process Engineering 2022, 22 (5): 573-585. DOI: 10.12034/j.issn.1009-606X.221147

Abstract （1119）

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Methanol is a promising energy carrier owing to its simple structure, high hydrogen content and huge production capacity. Methanol steam reforming (MSR) is an energy-saving and efficient on-site hydrogen production method. Combined with fuel cells, MSR can be applied in many fields. However, due to the high reaction temperature (250~300℃), there are some problems such as slow start-up, high CO content and low thermal efficiency. Low temperature methanol water reforming (LT-MWR), including LT-MSR and aqueous-phase reforming of methanol (APRM), means that the reaction proceeds below 200℃, and maintains high reaction activity, which can reduce the preheating time and the side reactions, and achieve stronger thermal coupling with fuel cells. In this review, the performance and defects of commercial catalysts are firstly introduced based on characterization results. The research of LT-MWR catalysts for hydrogen production is reviewed, including Cu-based catalysts, noble metal catalysts and photo-synergistic catalysts. The modification strategies for low temperature Cu-based catalysts are summarized, including synthesis methods, structure design and element doping. The commercial CuZnAlOx catalyst at home and abroad has the characteristics of high methanol conversion and good stability, despite its relatively high price and low activity below 200℃. Because the activity of Cu-based catalysts is greatly affected by temperature, the catalytic activity decreases sharply at low temperature. By appropriate modification, Cu-based catalysts can perform high activity at low temperature. Noble metal catalysts have high activity at low temperature, but they are expensive and the synthesis process is complex. Photo-synergistic catalysts are functional under the condition of light, which is still in the research stage. The synthesis method can strengthen the micromixing degree and reproducibility. Appropriate structure design can increase the specific surface area and thermal stability of the catalyst. Element doping enables better dispersion of active components and modifies the surface structure. Three modification strategies can effectively improve the performance of Cu-based catalyst for LT-MSR, reducing the content of CO content while maintaining high activity. Finally, the prospect and challenges of LT-MSR catalysts for hydrogen production are prospected.

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Research progress on degradation of organic pollutants in water by catalytic ozonation

Shuhuan WANG Lilong ZHOU Zhengjie LI Jilong HAN Runjing LIU Jimmy YUN

The Chinese Journal of Process Engineering 2022, 22 (5): 586-600. DOI: 10.12034/j.issn.1009-606X.221094

Abstract （550）

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For the further development of industry and improvement of living resources for everyone, the pollution of water resources is one of the urgent problems to be solved nowadays. The organic pollutants can be removed effectively by the catalytic ozonation process and the method is easy to operate, so it has been used in industry widely. The selection of catalysts has an important influence on the catalytic oxidation process of organic pollutants. In this study, the mechanism of the homogeneous catalytic ozonation process and heterogeneous catalytic ozonation process were analyzed and summarized. The catalytic effects of noble metal catalysts, transition metal catalysts, alkaline earth metal catalysts, and non-metal catalysts that have been used in heterogeneous catalytic ozonation to remove organic pollutants were summarized. The methods that have been used to improve the catalytic activity of these catalysts were also reviewed. The effects of pH value, ozone concentration, catalyst dosage, and the concentration of organic matters on the process of catalytic ozonation were summarized. It is pointed out that the main problem in the process of degradation of organic pollutants by catalytic ozonation is the loss of active components and the reduction of catalytic activity in an aqueous solution. Therefore, for future research, the development and preparation of novel catalysts with high catalytic activity and stability remain the research focus of this process.We can take the measures of improving the adsorption capacity of the catalyst, improving the transfer capacity of ozone in water, and using the synergistic coupling of different active components to effectively inhibit the loss of active components, improve the service life of the catalyst and improve the stability of the catalyst at the same time, to achieve the purpose of effective degradation of organic pollutants.

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