scholarly journals Favourably regulating two-phase flow regime of flow boiling HFE-7100 in microchannels using silicon nanowires

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Tamanna Alam ◽  
Wenming Li ◽  
Wei Chang ◽  
Fanghao Yang ◽  
Jamil Khan ◽  
...  
Keyword(s):  
Flow Regime ◽  
Thermal Management ◽  
Silicon Nanowires ◽  
Management System ◽  
High Speed ◽  
Flow Boiling ◽  
Flow Regimes ◽  
Phase Flow ◽  
Two Phase ◽  
Thermal Management System

AbstractHigh performance miniaturized electronic devices require enhanced, compact and reliable thermal management system. As an efficient compact space cooling technique, flow boiling in microchannels has recently gained wide acceptance. However, weak buoyancy effects and microgravity in avionics and numerous space systems operations hinder the performance of flow boiling microchannel thermal management system due to poor bubble departure capacity and unfavorable development of flow regimes. Here we report the flow boiling silicon nanowires (SiNWs) microchannels which can favorably regulate two-phase flow regimes by enhancing explosive boiling, minimizing bubble departure diameter, and smoothing flow regime transition. Extensive experimental investigations along with high speed visualizations are performed. The experiments are performed with the dielectric fluid HFE-7100 in a forced convection loop for wide range of heat and mass fluxes. High speed flow visualizations have been employed at up to 70 k frames per second (fps) to understand the boiling mechanism in terms of bubble dynamics, flow patterns, and flow regime developments for SiNWs microchannels. These studies show that SiNWs reduce intermittent flow regimes (slug/churn), improve rewetting and maintain thin liquid film at wall. Therefore, flow boiling in SiNW microchannels is promising to thermal management owing to its high heat transfer rate with low pressure drop and negligible microgravity sensitivity.

Measurement of Void Fraction and Pressure Drop of Air-Oil Two-Phase Flow in Horizontal Pipes

2004 ◽  
Vol 126 (1) ◽  
pp. 107-118 ◽  
Author(s):  
J. L. Pawloski ◽  
C. Y. Ching ◽  
M. Shoukri
Keyword(s):  
Pressure Drop ◽  
Flow Regime ◽  
Void Fraction ◽  
High Speed ◽  
Two Phase Flow ◽  
Flow Regimes ◽  
Phase Flow ◽  
Two Phase ◽  
Wide Range ◽  
Flow Regime Maps

The void fractions, flow regimes, and pressure drop of air-oil two-phase flow in a half-inch diameter pipe over a wide range of test conditions have been investigated. The flow regimes were identified with the aid of a 1000 frames per second high-speed camera. A capacitance sensor for instantaneous void fraction measurements was developed. The mean and probability density function of the instantaneous void fraction signal can be used to effectively identify the different flow regimes. The current flow regime data show significant differences in the transitional boundaries of the existing flow regime maps. Property correction factors for the flow regime maps are recommended. The pressure drop measurements were compared to the predictions from four existing two-phase flow pressure drop models. Though some of the models performed better for certain flow regimes, none of the models were found to give accurate results over the entire range of flow regimes.

Horizontal Two Phase Flow Regime Identification: Comparison of Pressure Signature, Electrical Capacitance Tomography (ECT) and High Speed Visualization

2012 ◽  
Author(s):  
Paul J. Kreitzer ◽  
Michael Hanchak ◽  
Larry Byrd
Keyword(s):  
Flow Regime ◽  
High Speed ◽  
Two Phase Flow ◽  
Flow Regimes ◽  
Electrical Capacitance Tomography ◽  
Phase Flow ◽  
Electrical Capacitance ◽  
Flow Conditions ◽  
Two Phase ◽  
Capacitance Tomography

Understanding the behavior of transient two phase refrigerant flow is an important aspect of implementing vapor compression systems in future aerospace applications. Pressure drop and heat transfer coefficient are important parameters that guide the design process, and are influenced by flow regime. Published two phase flow models rely heavily on a priori knowledge of the current two phase flow conditions including flow regime. Additional complications arise when applying published correlations to a range of systems because each correlation is based on a specific set of experimental conditions, including working fluid, flow orientation, channel size, and channel shape. Non-intrusive measurement techniques provide important advantages while measuring the behavior of two phase flow systems. A two phase flow experimental test rig has been developed at the Air Force Research Laboratory, providing a closed loop refrigeration system capable of producing flow regimes from bubbly through annular flow. Two phase flow is produced by pumping subcooled R134a through a heat exchanger with 40 minichannels into an adiabatic transparent fused quartz observation channel with a hydraulic diameter of 7 mm. Refrigerant mass flux is varied from 100–400 kg/m2s with a heat flux from 0–15.5 W/cm2. Temperatures ranged from 18–25 °C and pressures between 550–750 kPa. The data from high speed pressure transducers were analyzed using standard signal processing techniques to identify the different flow regimes. Initial results indicate that different flow regimes can be identified from their pressure signature. In addition, real-time void fraction measurements were taken using Electrical Capacitance Tomography (ECT). This paper describes the process behind ECT systems used to measure two phase flow conditions. Comparisons with high speed video assess the accuracy of ECT measurements in identifying various two phase flow conditions. Results indicate variations between ECT and high speed images, however, enough information is provided to create flow pattern maps and regime identification for different superficial vapor and liquid velocities.

Measurement of Void Fraction and Pressure Drop of Air-Oil Two-Phase Flow in Horizontal Pipes

2002 ◽  
Author(s):  
J. Pawloski ◽  
C. Ching ◽  
M. Shoukri
Keyword(s):  
Pressure Drop ◽  
Flow Regime ◽  
Void Fraction ◽  
High Speed ◽  
Two Phase Flow ◽  
Flow Regimes ◽  
Average Error ◽  
Phase Flow ◽  
Two Phase ◽  
Wide Range

The flow regimes and pressure drop of air-oil two-phase flow in a half-inch diameter pipe over a wide range of test conditions have been investigated. The flow regimes were identified with the aid of a 1000 frames per second high-speed camera. The current flow regime data show significant differences in the transitional boundaries from the flow regime maps of Mandhane et al. (1974), Taitel and Dukler (1974) and Spedding and Nguyen (1980). The pressure drop measurements were compared to the predictions from four existing pressure drop models: Homogeneous, Martinelli (1948), Chisolm (1973) and Olujic (1985). The Chisolm and Martinelli models were found to be the most accurate, with an average error of about 35 percent. A capacitance sensor for instantaneous void fraction measurement was developed. Results indicate the data from the sensor could be used to identify the different flow regimes.

High Speed Imaging and Two-Phase Flow Patterns During Flow Boiling in a Single Microchannel

2008 ◽  
Author(s):  
Jacqueline Barber ◽  
Khellil Sefiane ◽  
David Brutin ◽  
Lounes Tadrist
Keyword(s):  
High Speed ◽  
Two Phase Flow ◽  
Flow Boiling ◽  
Pressure Sensors ◽  
Flow Patterns ◽  
Bubble Nucleation ◽  
Phase Flow ◽  
Vapour Bubble ◽  
Two Phase ◽  
Over Time

Boiling in microchannels remains elusive due to the lack of full understanding of the mechanisms involved. A powerful tool in achieving better comprehension of the mechanisms is detailed imaging and analysis of the two phase flow at a fundamental level. We induced boiling in a single microchannel geometry (hydraulic diameter 727 μm), using a refrigerant FC-72, to investigate several flow patterns. A transparent, metallic, conductive deposit has been developed on the exterior of rectangular microchannels, allowing simultaneous uniform heating and visualisation to be conducted. The data presented in this paper is for a particular case with a uniform heat flux of 4.26 kW/m2 applied to the microchannel and inlet liquid mass flowrate, held constant at 1.33×10−5 kg/s. In conjunction with obtaining high-speed images and videos, sensitive pressure sensors are used to record the pressure drop profiles across the microchannel over time. Bubble nucleation, growth and coalescence, as well as periodic slug flow, are observed in the test section. Phenomena are noted, such as the aspect ratio and Reynolds number of a vapour bubble, which are in turn correlated to the associated pressure drops over time. From analysis of our results, images and video sequences with the corresponding physical data obtained, it is possible to follow visually the nucleation and subsequent both ‘free’ and ‘confined’ growth of a vapour bubble over time.

scholarly journals Thermal Performance of a Cylindrical Lithium-Ion Battery Module Cooled by Two-Phase Refrigerant Circulation

Energies ◽  
2021 ◽  
Vol 14 (23) ◽  
pp. 8094
Author(s):  
Bichao Lin ◽  
Jiwen Cen ◽  
Fangming Jiang
Keyword(s):  
Thermal Management ◽  
Management System ◽  
Cooling System ◽  
Maximum Temperature ◽  
Two Phase ◽  
Battery Thermal Management ◽  
Thermal Management System ◽  
Battery Thermal Management System ◽  
Li Ion ◽  
Battery Module

It is important for the safety and good performance of a Li-ion battery module/pack to have an efficient thermal management system. In this paper, a battery thermal management system with a two-phase refrigerant circulated by a pump was developed. A battery module consisting of 240 18650-type Li-ion batteries was fabricated based on a finned-tube heat-exchanger structure. This structural design offers the potential to reduce the weight of the battery thermal management system. The cooling performance of the battery module was experimentally studied under different charge/discharge C-rates and with different refrigerant circulation pump operation frequencies. The results demonstrated the effectiveness of the cooling system. It was found that the refrigerant-based battery thermal management system could maintain the battery module maximum temperature under 38 °C and the temperature non-uniformity within 2.5 °C for the various operation conditions considered. The experimental results with 0.5 C charging and a US06 drive cycle showed that the thermal management system could reduce the maximum temperature difference in the battery module from an initial value of 4.5 °C to 2.6 °C, and from the initial 1.3 °C to 1.1 °C, respectively. In addition, the variable pump frequency mode was found to be effective at controlling the battery module, functioning at a desirable constant temperature and at the same time minimizing the pump work consumption.

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