Typical Structure,Variety,and Multi-Scale Characteristics of Meiyu Front

Meiyu front plays an important role in summer rainfall in central China. Based on the GMS-5 satellite images, NCEP reanalyses （2.5°×2.5°） and final analyses （1°×1°） data, and meteorological conventional sounding observations, the horizontal and vertical structures of the Meiyu front were summarized using multiple diagnostic variables, including winds, temperature, jet stream, front, pseduo-equivalent potential temperature, divergence, vertical motion, static instability, etc. In this paper, four cases were selected and analyzed, two of which are in 26-28 June and 23 July 2002 during the Experiment on Heavy Rain in the Meiyu period in the lower reaches of the Yangtze River, and the others are in May and July 1998. The two cases in July 1998 and July 2002 are the secondary Meiyu front cases. The results show that the structures and characteristics of the Meiyu front are different for various cases, or at various places and time, or at various stages of one case, and the frontal characteristics can be converted from the polar front to the equatorial front. Because of the interaction of the different scale circulations in the high and low latitudes, the horizontal structure of the Meiyu front has various forms. The results in this paper also show that the typical Meiyu front consists of a narrow band with a high gradient of potential equivalent temperature below 500 hPa, south of which is warm and moist air mass, and north of which is the transformed air mass from the midlatitude ocean or polar continent. Below the mid troposphere, south of the front blows southwesterlies, while north blows easterlies. The ascending motion and precipitation usually occur ahead of the Meiyu front. In the upper troposphere, the subtropical front is above the Meiyu front, but two fronts are separated. In addition, the upper westerly jet stream and the easterlies to the south of the Meiyu front result in the upper divergent flow field. The multi-scale characteristics of the horizontal structure of the Meiyu front can be summarized as follows： in the upper troposphere, there exist the subtropical westerly jet, the easterlies to the south of the Meiyu front, and the South Asian high; at the mid troposphere, 500 hPa, the subtropical high over the West Pacific is the main weather system, to the northwest of which there are some short-wave troughs; in the lower troposphere, the planetary-scale southwesterly monsoon, the large-scale low-level southwesterly jet, and the mesoscale vortex or wave in the shear line are closely associated with the Meiyu front.

Heat Transfer and Friction Characteristics of Printed Circuit Heat Exchangers with Different Channel Structures for S-CO_(2) Power System

Printed circuit heat exchanger(PCHE)has been widely used in supercritical carbon dioxide(S-CO_(2))power systems because of its high heat transfer efficiency and good compactness.However,due to the large variety of PCHE configurations,channel selection in practical applications lacks a basis.Therefore,this paper discussed the heat transfer and friction characteristics and the synergy of three fields in the channel under the guidance of the field synergy principle for four typical PCHE channels.Additionally,the comprehensive performance of four channels was compared.Finally,the heat transfer and friction factor correlations for S-CO_(2)in four channels were established.The findings demonstrate that the synergy of velocity and pressure fields of the straight channel PCHE is better(β≈180°),so its resistance loss is relatively small.The zigzag and sinusoidal wavy channels and the airfoil fins can reduce the angle a between the temperature gradient and velocity,thus enhancing the heat transfer.The sinusoidal wavy channel can reduce flow resistance compared to the zigzag channel due to the rounded corners.The streamlined airfoil structure can guide the flow and reduce backflow,thus reducing resistance losses.In the range of Re studied in this paper,the maximum error of the proposed heat transfer and friction factor correlations of PCHE is 7.0%,which shows good fitting accuracy.The research in this paper can provide a reference for the selection and design of PCHE with different channel configurations.

Recent progress of flexible rechargeable batteries

The rapid popularization of wearable electronics,soft robots and implanted medical devices has stimulated extensive research in flexible batteries,which are bendable,foldable,knittable,wearable,and/or stretchable.Benefiting from these distinct characteristics,flexible batteries can be seamlessly integrated into various wearable/implantable devices,such as smart home systems,flexible displays,and implantable sensors.In contrast to conventional lithium-ion batteries necessitating the incorporation of stringent current collectors and packaging layers that are typically rigid,flexible batteries require the flexibility of each component to accommodate diverse shapes or sizes.Accordingly,significant advancements have been achieved in the development of flexible electrodes,current collectors,electrolytes,and flexible structures to uphold superior electrochemical performance and exceptional flexibility.In this review,typical structures of flexible batteries are firstly introduced and classified into mono-dimensional,twodimensional,and three-dimensional structures according to their configurations.Subsequently,five distinct types of flexible batteries,including flexible lithium-ion batteries,flexible sodium-ion batteries,flexible zinc-ion batteries,flexible lithium/sodium-air batteries,and flexible zinc/magnesium-air batteries,are discussed in detail according to their configurations,respectively.Meanwhile,related comprehensive analysis is introduced to delve into the fundamental design principles pertaining to electrodes,electrolytes,current collectors,and integrated structures for various flexible batteries.Finally,the developments and challenges of flexible batteries are summarized,offering viable guidelines to promote the practical applications in the future.