scholarly journals Cooling of Large Area for Flow Boiling in Narrow Channels by Improved Liquid Supply

2008 ◽  
Vol 3 ◽  
pp. 75-82
Author(s):  
Shinichi MIURA ◽  
Yukihiro INADA ◽  
Yasuhisa SHINMOTO ◽  
Haruhiko OHTA
Keyword(s):  
Flow Boiling ◽  
Large Area ◽  
Narrow Channels

Heat Transfer and Bubble Movement of Double- and Single-Side Heating Subcooled Flow Boiling in Narrow Channels

2005 ◽  
Author(s):  
Liang-Ming Pan ◽  
Chuan He ◽  
Ming-Dao Xin ◽  
Tien-Chien Jen ◽  
Qinghua Chen
Keyword(s):  
Heat Transfer ◽  
Flow Boiling ◽  
Narrow Channel ◽  
Nucleate Boiling ◽  
Bubble Behavior ◽  
Subcooled Flow Boiling ◽  
Narrow Channels ◽  
Subcooled Flow ◽  
Single Side ◽  
Micro Channels

Compared with conventional channels, narrow and micro channels have significant heat transfer enhancement characteristic. With smooth internal surface, such channels can efficiently avoid encrustation at the washing of the high-speed liquid. Moreover, heat transfer elements can be easily assembled. These types of channels have been adopted extensively in many engineering applications, e.g. microelectronic cooling, advanced nuclear reactor, cryogenic, aviation and space technology and thermal engineering. Geometrical size of flow passage-away affects heat exchange of flow boiling, with the result that the bubble in narrow channel acts very different from those in non-narrow channel. This paper experimentally compared the bubble behavior with different heating methods of narrow rectangular channels, and the bubble behavior of subcooled flow boiling of R-12 in the narrow channels both with double side and single heating. Experimental settings are: the heating length of test-section is 400 mm, the cross-section is 35 mm in width and 2mm in gap size, mass flux is 700∼1500 kg.m−2.s−1, the heat flux is 25∼70kW.m−2 and the pressure is 1.3∼2.0 MPa. Comparisons were made on Onset of Nucleate Boiling (ONB) point and bubble characters with various flow patterns. Results revealed that the characteristics of double and single side heating shown good agreement with proper modifications.

scholarly journals Structure and Inter-Annual Variability of the Freshened Surface Layer in the Laptev and East-Siberian Seas During Ice-Free Periods

2021 ◽  
Vol 8 ◽  
Author(s):  
Alexander Osadchiev ◽  
Dmitry Frey ◽  
Eduard Spivak ◽  
Sergey Shchuka ◽  
Natalia Tilinina ◽  
...  
Keyword(s):  
Surface Layer ◽  
Sea Water ◽  
Warm Season ◽  
Kara Sea ◽  
Ekman Transport ◽  
Large Area ◽  
Narrow Channels ◽  
Lena River ◽  
Annual Variability ◽  
Ice Coverage

This work is focused on the structure and inter-annual variability of the freshened surface layer (FSL) in the Laptev and East-Siberian seas during ice-free periods. This layer is formed mainly by deltaic rivers among which the Lena River contributes about two thirds of the inflowing freshwater volume. Based on in situ measurements, we show that the area of this FSL during certain years is much greater than the area of FSL in the neighboring Kara Sea, while the total annual freshwater discharge to the Laptev and East-Siberian seas is 1.5 times less than to the Kara Sea (mainly from the estuaries of the Ob and Yenisei rivers). This feature is caused by differences in morphology of the estuaries and deltas. Shallow and narrow channels of the Lena Delta are limitedly affected by sea water. As a result, undiluted Lena discharge inflows to sea from multiple channels and forms relatively shallow plume, as compared to the Ob-Yenisei plume, which mixes with subjacent saline sea water in deep and wide estuaries. Due to small vertical extents of FSL in the Laptev and East-Siberian seas, wind conditions strongly affect its spreading and determine its significant inter-annual variability, as compared to relatively stable FSL in the Kara Sea. During years with prevailing western and northern winds, FSL is localized in the southern parts of the Laptev and East-Siberian seas due to southward Ekman transport, meridional extent (<250 km) and area (∼250,000 km2) of FSL are relatively small. During years with strong eastern winds FSL spreads northward over large area (up to 500,000 km2), its meridional extent increases up to 500–700 km. At the same time, area and position of FSL do not show any dependence on significant variability of the annual river discharge volume and ice coverage during warm season.

Boiling Incipience in Narrow Channels

2000 ◽  
Author(s):  
M. S. Lakshminarasimhan ◽  
D. K. Hollingsworth ◽  
Larry C. Witte
Keyword(s):  
Flow Boiling ◽  
Heated Surface ◽  
Transition Process ◽  
Nucleate Boiling ◽  
Nucleation Theory ◽  
Hysteresis Phenomenon ◽  
Transfer Coefficients ◽  
Narrow Channels ◽  
Liquid Crystal Thermography ◽  
Boiling Incipience

Abstract Experiments were performed to investigate nucleate flow boiling and incipience in a flow channel, 1 mm high × 20 mm wide × 357 mm long, vertical, with one wall heated uniformly and others approximately adiabatic. Subcooled R-11 flowed upward through the channel; the mass flux varied from 60 to 4586 kg/(m2s). The inlet subcooling varied from 3.0 to 15.3 °C, and the inlet pressure ranged up to 0.20 MPa. Liquid crystal thermography was used to measure distributions of surface temperature from which the heat transfer coefficients on the heated surface were calculated. Observations of the boiling incipience superheat excursion and the hysteresis phenomenon are presented and discussed. In laminar flow, a boiling front was observed that clearly separated the region cooled by single-phase convection from the region experiencing nucleate boiling. A prediction for the wall temperature and heat flux at boiling incipience based on nucleation theory compared favorably with the data. An incipience turning angle was defined to describe the transition process from the point of incipience to fully developed nucleate boiling. Fully developed saturated nucleate boiling was correlated well by Kandlikar’s technique.

Reconfigurable magnetic microrobot swarm: Multimode transformation, locomotion, and manipulation

2019 ◽  
Vol 4 (28) ◽  
pp. eaav8006 ◽  
Author(s):  
Hui Xie ◽  
Mengmeng Sun ◽  
Xinjian Fan ◽  
Zhihua Lin ◽  
Weinan Chen ◽  
...  
Keyword(s):  
Magnetic Fields ◽  
Colloidal Particles ◽  
Particle Simulation ◽  
Coherent Motion ◽  
Collective Modes ◽  
Colloidal System ◽  
Large Area ◽  
Collective Behaviors ◽  
Narrow Channels ◽  
Discrete Particle Simulation

Swimming microrobots that are energized by external magnetic fields exhibit a variety of intriguing collective behaviors, ranging from dynamic self-organization to coherent motion; however, achieving multiple, desired collective modes within one colloidal system to emulate high environmental adaptability and enhanced tasking capabilities of natural swarms is challenging. Here, we present a strategy that uses alternating magnetic fields to program hematite colloidal particles into liquid, chain, vortex, and ribbon-like microrobotic swarms and enables fast and reversible transformations between them. The chain is characterized by passing through confined narrow channels, and the herring school–like ribbon procession is capable of large-area synchronized manipulation, whereas the colony-like vortex can aggregate at a high density toward coordinated handling of heavy loads. Using the developed discrete particle simulation methods, we investigated generation mechanisms of these four swarms, as well as the “tank-treading” motion of the chain and vortex merging. In addition, the swarms can be programmed to steer in any direction with excellent maneuverability, and the vortex’s chirality can be rapidly switched with high pattern stability. This reconfigurable microrobot swarm can provide versatile collective modes to address environmental variations or multitasking requirements; it has potential to investigate fundamentals in living systems and to serve as a functional bio-microrobot system for biomedicine.

Minichannel Heat Transfer: An Overview on Activities in Europe

2003 ◽  
Author(s):  
Manfred Groll ◽  
Rainer Mertz
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Pressure Drop ◽  
Heat And Mass Transfer ◽  
Heat Exchangers ◽  
Flow Boiling ◽  
Pool Boiling ◽  
Current Status ◽  
Narrow Channels ◽  
Evaporation Heat

An overview will be given about investigations on heat and mass transfer in narrow channels and narrow cavities, from work carried out in the last years up to the current status of research of some relevant scientific groups in Europe. The major topics of this report are evaporation heat transfer and the flow boiling pressure drop in narrow channels; microscale heat and mass transfer phenomena in pool boiling from enhanced evaporator tubes with sub-surface channels are also addressed. In the last years a challenging topic has been the enhancement of the efficiency of heat exchangers by employing micro-structured heat transfer surfaces. The need for smaller heat exchangers with higher heat transfer rates and/or smaller thermal approaches is caused by the ongoing miniaturisation of mechanical and electronic components, leading to higher heat fluxes which can damage or even destroy the components. On the other hand, enhanced heat transfer in big equipment, e.g. heat exchangers for the petrochemical and chemical industries, can lead to significant materials and energy savings and thus reduce environmental pollution. Therefore the European Union, European industries and national organisations have supported various projects to develop and to investigate a new generation of heat transfer surfaces, to better understand the related heat transfer phenomena and to model the heat transfer from these micro heat exchanger elements. There is a very extensive research in this scientific field, comprising both flow boiling and pool boiling. The present paper deals with heat transfer in narrow channels and/or cavities and with the flow boiling pressure drop occurring during heat and mass transfer in narrow channels. Investigations of major European institutions, carried out in the past and at the moment will be presented as a contribution to the overview on the current state-of-the-art in Europe, without claim of completeness. Some recent results on microscale pool boiling and flow boiling obtained in our institute will also be presented (Shuai et al., 2002; Kulenovic et al., 2002; Chen et al., 2002a, b).

Heat Transfer and Bubble Movement of Two-Side and One-Side Heating Subcooled Flow Boiling in Vertical Narrow Channels

2006 ◽  
Vol 128 (8) ◽  
pp. 838 ◽  
Author(s):  
Liang-Ming Pan ◽  
Tien-Chien Jen ◽  
Chuan He ◽  
Ming-dao Xin ◽  
Qing-hua Chen
Keyword(s):  
Heat Transfer ◽  
Flow Boiling ◽  
Subcooled Flow Boiling ◽  
Narrow Channels ◽  
Subcooled Flow ◽  
Bubble Movement

Critical Heat Flux During Subcooled Flow Boiling of Alumina Nanofluids in a Narrow Channel

2010 ◽  
Author(s):  
Saeid Vafaei ◽  
Dongsheng Wen
Keyword(s):  
Heat Flux ◽  
Surface Temperature ◽  
Critical Heat Flux ◽  
Flow Boiling ◽  
Pure Water ◽  
Pressure Fluctuations ◽  
Narrow Channel ◽  
Inlet Temperature ◽  
Subcooled Flow Boiling ◽  
Narrow Channels

This work reported an experimental study of flow boiling of pure water and aqueous alumina nanofluids in a 0.5 millimetre narrow channel. An open-ended stainless steel microchannel system is constructed where liquids are supplied by a syringe pump and heated by a variable DC power source, with synchronized measurement of the surface temperature distribution along the channel and pressure fluctuations associated with bubbles. The effect of nanoparticle concentration, inlet subcooling and mass flow rate and on critical heat flux in a microchannel is investigated. A modest increase in CHF is observed for nanofluids, being higher at higher particle concentrations and higher inlet subcoolings. Regular fluctuations in temperature and pressure signals suggest a cyclic boiling events occurring in the narrow channel; the large pressure fluctuation, coupling with the surface temperature and inlet temperature fluctuations, would affect flow boiling mechanisms in narrow channels.

scholarly journals Study on Measure Approach of Void Fraction in Narrow Channel Based on Fully Convolutional Neural Network

2021 ◽  
Vol 9 ◽  
Author(s):  
Wenjun Chu ◽  
Yang Liu ◽  
Liqiang Pan ◽  
Hongye Zhu ◽  
Xingtuan Yang
Keyword(s):  
Neural Network ◽  
Convolutional Neural Network ◽  
Void Fraction ◽  
High Speed ◽  
Nuclear Power ◽  
Flow Boiling ◽  
Image Features ◽  
High Speed Photography ◽  
Flow State ◽  
Narrow Channels

Void fraction is one of the key parameters for gas-liquid study and detection of nuclear power system state. Based on fully convolutional neural network (FCN) and high-speed photography, an indirect void fraction measure approach for flow boiling condition in narrow channels is developed in this paper. Deep learning technique is applied to extract image features and can better realize the identification of gas and liquid phase in channels of complicated flow pattern and high void fraction, and can obtain the instantaneous value of void fraction for analyzing and monitoring. This paper verified the FCN method with visual boiling experiment data. Compared with the time-averaged experimental results calculated by the energy conservation method and the empirical formula, the relative deviations are within 11%, which verifies the reliability of this method. Moreover, the recognition results show that the FCN method has promising improvement in the scope of application compared with the traditional morphological method, and meanwhile saves the design cost. In the future, it can be applied to void fraction measurement and flow state monitoring of narrow channels under complex working conditions.

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