Heat transfer of bubbly flow on inner wall of annular channel

The results of heat transfer to supercritical water flowing upward in a vertical annular channel (1-rod channel) and tight 3-rod bundle consisting of the tubes of 5.2-mm outside diameter and 485-mm heated length are presented. The heat-transfer data were obtained at pressures of 22.5, 24.5, and 27.5 MPa, mass flux within the range from 800 to 3000 kg/m2·s, inlet temperature from 125 to 352°C, outlet temperature up to 372°C and heat flux up to 4.6 MW/m2 (heat flux rate up to 2.5 kJ/kg). Temperature regimes of the annular channel and 3-rod bundle were stable and easily reproducible within the whole range of the mass and heat fluxes, even when a deteriorated heat transfer took place. The data resulted from the study could be applicable for a reference estimation of heat transfer in future designs of fuel bundles.

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Boiling Heat Transfer From an Oscillated Water Column Through a Porous Domain: A Simplified Thermodynamic Analysis

Volume 8: Heat Transfer and Thermal Engineering ◽

10.1115/imece2016-66901 ◽

2016 ◽

Author(s):

Ersin Sayar

Keyword(s):

Heat Transfer ◽

Boundary Layer ◽

Water Column ◽

Thermodynamic Analysis ◽

Bubbly Flow ◽

Pool Boiling ◽

Oscillating Flow ◽

Transition Regime ◽

Core Flow ◽

The Core

Heat transfer in an oscillating water column in the transition regime of pool boiling to bubbly flow is investigated experimentally and theoretically. Forced oscillations are applied to water via a frequency controlled dc motor and a piston-cylinder device. Heat transfer is from the electrically heated inner surface to the reciprocating flow. The heat transfer in the oscillating fluid column is altered by using stainless steel scrap metal layers (made off open-cell discrete cells) which produces a porous medium within the system. The effective heat transfer mechanism is enhanced and it is due to the hydrodynamic mixing of the boundary layer and the core flow. In oscillating flow, the hydrodynamic lag between the core flow and the boundary layer flow is somehow significant. At low actuation frequencies and at low heat fluxes, heat transfer is restricted in the single phase flows. The transition regime of pool boiling to bubbly flow is proposed to be a remedy to the stated limitation. The contribution by the pool boiling on heat transfer appears to be the dominant mechanism for the selected low oscillation amplitudes and frequencies. Accordingly the regime is a transition from pool boiling to bubbly flow. Nucleate-bubbly flow boiling in oscillating flow is also investigated using a simplified thermodynamic analysis. According to the experimental results, bubbles induce highly efficient heat transfer mechanisms. Experimental study proved that the heater surface temperature is the dominant parameter affecting heat transfer. At greater actuation frequencies saturated nucleate pool boiling ceases to exist. Actuation frequency becomes important in that circumstances. The present investigation has possible applications in moderate sized wicked heat pipes, boilers, compact heat exchangers and steam generators.

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Investigation into aerodynamic and heat transfer of annular channel with inner and outer surface of the shape truncated cone and swirling fluid flow

Journal of Physics Conference Series ◽

10.1088/1742-6596/891/1/012143 ◽

2017 ◽

Vol 891 ◽

pp. 012143

Author(s):

Yu L Leukhin ◽

E V Pankratov ◽

S V Karpov

Keyword(s):

Heat Transfer ◽

Fluid Flow ◽

Outer Surface ◽

Annular Channel ◽

Truncated Cone

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Experimental Study on Heat Transfer of Single-Phase Flow and Boiling Two-Phase Flow in Vertical Narrow Annuli

10th International Conference on Nuclear Engineering, Volume 3 ◽

10.1115/icone10-22212 ◽

2002 ◽

Cited By ~ 3

Author(s):

Suizheng Qiu ◽

Minoru Takahashi ◽

Guanghui Su ◽

Dounan Jia

Keyword(s):

Heat Transfer ◽

Single Phase ◽

Two Phase Flow ◽

Annular Channel ◽

Phase Flow ◽

Single Phase Flow ◽

Transfer Coefficients ◽

Two Phase ◽

Narrow Annuli ◽

Narrow Gaps

Water single-phase and nucleate boiling heat transfer were experimentally investigated in vertical annuli with narrow gaps. The experimental data about water single-phase flow and boiling two-phase flow heat transfer in narrow annular channel were accumulated by two test sections with the narrow gaps of 1.0mm and 1.5mm. Empirical correlations to predict the heat transfer of the single-phase flow and boiling two-phase flow in the narrow annular channel were obtained, which were arranged in the forms of the Dittus-Boelter for heat transfer coefficients in a single-phase flow and the Jens-Lottes formula for a boiling two-phase flow in normal tubes, respectively. The mechanism of the difference between the normal channel and narrow annular channel were also explored. From experimental results, it was found that the turbulent heat transfer coefficients in narrow gaps are nearly the same to the normal channel in the experimental range, and the transition Reynolds number from a laminar flow to a turbulent flow in narrow annuli was much lower than that in normal channel, whereas the boiling heat transfer in narrow annular gap was greatly enhanced compared with the normal channel.

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Investigation of aerodynamics and heat transfer of the modular jet recuperator

Journal of Physics Conference Series ◽

10.1088/1742-6596/2039/1/012001 ◽

2021 ◽

Vol 2039 (1) ◽

pp. 012001

Author(s):

P D Alekseev ◽

Yu L Leukhin

Keyword(s):

Heat Transfer ◽

Gas Flow ◽

Annular Channel ◽

Secondary Flows ◽

Cocurrent Flow ◽

Outlet Section ◽

Entire Cross Section ◽

Staggered Arrangement ◽

Perforated Pipe ◽

The Impact

Abstract A study of the aerodynamics and heat transfer of a jet modular recuperator with a change in its geometric characteristics has been carried out. The influence of the in-line and staggered arrangement of the blowing holes, as well as the diameter of the perforated pipe is considered. In all considered variants, the number of holes, their diameter and gas flow rate through the recuperator remained unchanged. Numerical modeling of the problem was carried out in a three-dimensional setting using the ANSYS Fluent 15.0 software package. It was found that with the in-line arrangement of the blowing holes, secondary flows are formed between their longitudinal rows in the form of swirling jets of opposite rotation directed towards the outlet section of the recuperative device, through which the main part of the heated air flows out. With the staggered arrangement of the blowing holes, the formation of spiral vortices is disturbed, the air flow is carried out along the entire cross section of the annular channel, increasing the drift effect of the flow on the impact jets, which leads to a decrease in the intensity of heat transfer and its uniformity along the length of the working surface. An increase in the diameter of the inner perforated pipe leads to a decrease in the drift effect of the cocurrent flow on the jets, an increase in the distribution uniformity of the heat flux along the length of the heat transfer surface, and an increase in the heat transfer coefficient.

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Heat transfer and flow region characteristics study in a non-annular channel between rotor and stator

Thermal Science ◽

10.2298/tsci110702138m ◽

2012 ◽

Vol 16 (2) ◽

pp. 593-603 ◽

Cited By ~ 1

Author(s):

M. Nili-Ahmadabadi ◽

H. Karrabi

Keyword(s):

Heat Transfer ◽

Reynolds Number ◽

Flow Characteristics ◽

Annular Channel ◽

Flow Region ◽

Air Gap ◽

Heat Transfer Characteristics ◽

Transfer Characteristics ◽

Flow And Heat Transfer ◽

Slip Ring

This paper will present the results of the experimental investigation of heat transfer in a non-annular channel between rotor and stator similar to a real generator. Numerous experiments and numerical studies have examined flow and heat transfer characteristics of a fluid in an annulus with a rotating inner cylinder. In the current study, turbulent flow region and heat transfer characteristics have been studied in the air gap between the rotor and stator of a generator. The test rig has been built in a way which shows a very good agreement with the geometry of a real generator. The boundary condition supplies a non-homogenous heat flux through the passing air channel. The experimental devices and data acquisition method are carefully described in the paper. Surface-mounted thermocouples are located on the both stator and rotor surfaces and one slip ring transfers the collected temperature from rotor to the instrument display. The rotational speed of rotor is fixed at three under: 300rpm, 900 rpm and 1500 rpm. Based on these speeds and hydraulic diameter of the air gap, the Reynolds number has been considered in the range: 4000<Rez<30000. Heat transfer and pressure drop coefficients are deduced from the obtained data based on a theoretical investigation and are expressed as a formula containing effective Reynolds number. To confirm the results, a comparison is presented with Gazley?s (1985) data report. The presented method and established correlations can be applied to other electric machines having similar heat flow characteristics.

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Heat Transfer and Pressure Drop for Flow Boiling of Water in Narrow Vertical Rectangular Channels

1st International Conference on Microchannels and Minichannels ◽

10.1115/icmm2003-1084 ◽

2003 ◽

Cited By ~ 11

Author(s):

Jianyun Shuai ◽

Rudi Kulenovic ◽

Manfred Groll

Keyword(s):

Heat Transfer ◽

Pressure Drop ◽

Flow Boiling ◽

Bubbly Flow ◽

High Heat ◽

Flow Patterns ◽

Industrial Applications ◽

Heat Fluxes ◽

Experimental Conditions ◽

Rectangular Channels

Flow boiling in small-sized channels attracted extensive investigations in the past two decades due to special requirements for transfer of high heat fluxes from narrow spaces in various industrial applications. Experiments on various aspects of flow boiling in narrow channels were carried out and theoretical attempts were undertaken. But these investigations showed large differences, e.g. up till now the knowledge on the development of flow patterns in small non-circular flow passages is very limited. This paper deals with investigations on flow boiling of water in two rectangular channels with dimensions (width×depth) 2.0×4.0 mm2 and 0.5×2.0 mm2 (corresponding hydraulic diameters are 2.67 mm and 0.8 mm). The pressure at the test section exit is atmospheric. For steady-state experimental conditions the effects of heat flux, mass flux and inlet subcooling on the boiling heat transfer coefficient and the pressure drop are investigated. Flow patterns and the transition of flow patterns along the channel axis are visualized and documented with a video-camera. Bubbly flow, slug flow and annular flow are distinguished in both channels. Preliminary flow pattern maps are generated.

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