Study on Critical Heat Flux in Narrow Rectangular Channel With Longitudinal Vortex

2010 ◽  
Author(s):  
Yan-Ping Huang ◽  
Jun Huang ◽  
Jian Ma ◽  
Qiu-Wang Wang
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Test Section ◽  
Rectangular Channel ◽  
Longitudinal Vortex ◽  
Water Medium ◽  
Test Channel ◽  
High Heat Transfer ◽  
System Pressure

Longitudinal Vortex (LV) is produced by Longitudinal Vortex Generators (LVGs) with high heat transfer efficiency and acceptable pressure loss. Due to the relative long influence distance and simple structure, LVGs may be used in narrow channels with flat surface under high temperature and high pressure water medium, in this paper, the critical heat flux (CHF) is one of most important focus. The test channel has the size of 600 mm (length) × 40 mm (width) × 3 mm (height), was used to research the CHF characteristic of CHF affected by LVGs. The test channel is visual in three sides and remains one side for power supply. The LVGs used in the experiments are 14 mm (length) × 2.2 mm (width) × 1.8 mm (height) in dimensions, and periodically mounted on the inner wall of the steel plate. The parameters that are varied during the experiments as follows, system pressure from 0.43 to 0.85 MPa, inlet mass flow flux from 40.2 to 745.7 kg·m−2·s−1, inlet subcooling from 46.8 to 104.2 °C, exit quality from 0.183 to 0.997, surface heat flux from 0.294 to 2.316 MW·m−2. The experiments show that the CHF is improved by 24.3% while the total pressure drop through the test section is improved by 62.9%. The bubble growth and its evolutionary process in narrow rectangular channel with LVGs have been obtained during a short term when the CHF occurs, and it is found that the bubbles have been affected intensely by LV. Based on these experiment data, the growth and aggregation of bubbles have been depressed by LV, the mass, momentum and energy exchange between cold and hot areas in the test section have been strengthened. As a result, the heat transfer enhancement by LV can be explained by the destruction of thermal boundary layer.

Critical Heat Flux by High Velocity Liquid Flow in Narrow Rectangular Channel

2008 ◽  
Author(s):  
Hisashi Sakurai ◽  
Yasuo Koizumi ◽  
Hiroyasu Ohtake
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
High Speed ◽  
Rectangular Channel ◽  
Video Camera ◽  
Jet Flow ◽  
Heat Transfer Surface ◽  
Bubble Behavior ◽  
Film Type

Experiments of critical heat flux of extremely thin-fast plate jet film sub-cooled flow were conducted. The extremely thin-fast film-type jet of sub-cooled water was erupted into a stagnant pool. The heat transfer is augmented by the fast jet flow on the heat transfer surface. Vapor generated on the surface is easily taken away from the surface by the fast jet flow and leaves upward from the surface. The static head of water in the pool depress down the fast film-type jet flow on to the heat transfer surface and may collapse the vapor film that is formed between the heat transfer surface and the fast film flow. All these combine to have the possibility to improve the critical heat flux. In the experiments, the liquid sub-cooling was in the range of 30 ∼ 70 K. The thickness of the jet film was 0.2 mm and 0.5 mm. The width of the jet film was 2 mm. The velocity of the erupting jet film was 5.0 ∼ 32 m/s. The heat transfer surface was 2.0 × 2.0 mm heated electrically. The heat transfer surface was placed on the bottom of the pool. The fast-thin film jet was erupted on the bottom of the pool parallel to the heat transfer surface. Bubble behavior generated on the heat transfer surface was recorded by a high speed video camera at 10,000 frames/s. The highest critical heat flux obtained up to now is 3.2 × 107 W/m2. The analytical model of the critical heat flux for the present flow system will be presented.

An Experimental Study on Critical Heat Flux in Rectangular Channel With Different Angle of Inclination

2017 ◽  
Author(s):  
Ming Zhang ◽  
Yufeng Zhao ◽  
Tianfang Gao ◽  
Fangxin Hou ◽  
Peipei Chen
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Test Section ◽  
Boiling Heat Transfer ◽  
Natural Circulation ◽  
Rectangular Channel ◽  
Heating Surface ◽  
Test Facility ◽  
Test Surface ◽  
Forced Circulation

It is a hot research field to study the Critical Heat Flux (CHF) occurrence mechanism in boiling heat transfer. Although lots of researchers have studied on it, no unified conclusion has been achieved up to now. The proposed CHF occurrence mechanism is also not widely accepted. Because the void fraction close to the heating surface is larger when the heat flux approaches CHF, it is difficult to make visual observations of the boiling heat transfer on the heating surface. Usually the CHF mechanism is based on certain assumptions, and then confirmed by testing. Therefore, it is meaningful to study the occurrence of CHF by experimental methods. Based on the system design of the test system for CHF in a rectangular channel, an experimental facility was set up. The main test section consists of a rectangular flow channel with the copper heating surface downwards mounted into one of the channel walls. The fluid is deionized water. Fluid subcooling is 15 K. The entire test section is mounted on a rotating arm which can be set at different inclination angles from 0° (horizontal) to 90° (vertical). By adjusting the loop, the natural circulation and forced circulation test conditions can be achieved from the experimental facility. Through test research, visual observations are acquired about the bubble growth characteristics in the rectangular channel in the range of 0 ° to 90 °, and the test data about the CHF is also attained. It is found that under the condition of forced circulation and natural circulation, the CHF values is increased effectively with the improved mass flow rate and the increased inclination angles of the test section. Through visual observation, it is found that in forced circulation conditions, CHF occurs first at the entrance location of the test surface, rather than the maximal heat flux location of the test surface (test surface center) or the maximal local void fraction of the test facility (exit location of the test facility). In the natural circulation conditions, CHF occurs first at the exit location of the test facility. This phenomenon may imply that the mechanisms of CHF are different in forced circulation and natural circulation. In forced circulation, the flow plays a main role. In natural circulation, the local void fraction plays a main role. There are some differences in the experimental phenomena compared with the traditional CHF theory, like the bubble crowding theory and the micro fluid layer theory. Through the experiment research, the complexity of the flow boiling heat transfer was found. The flow and boiling heat transfer affect each other. It is can help us to research the CHF theory in flow boiling heat transfer.

The Preliminary Experimental Study Based on Failure Mechanism of the RPV Lower Head

2016 ◽  
Author(s):  
XianKe Meng ◽  
LiKai Fei ◽  
Aijing Zhang ◽  
SiJiang Xiong ◽  
Lei Cui ◽  
...  
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Test Section ◽  
Failure Modes ◽  
Rectangular Channel ◽  
Model Development ◽  
Severe Accident ◽  
Mitigation Measures ◽  
Containment Vessel ◽  
Lower Head

In-Vessel Retention is a key severe accident management strategy for reactors such as AP/CAP series reactors. The IVR success evaluation criterion is whether the RPV is melted through or not at the final RPV state. Once the RPV lower head melt through, the liquid corium will flow into the reactor cavity and will lead to complex phenomena, such us steam explosion and the reaction between the corium and concrete. These will make temperature and pressure of the containment vessel rise quickly and is a threat to the integrity of the containment vessel. When the wall surface of RPV lower head heating condition exceed the critical heat flux, the temperature rises rapidly, it is generally assumed that the RPV lower head in this state will inevitably melt through. This is the so-called IVR failure. In order to study the possible failure modes and mechanism of RPV lower head under the IVR measures, an experimental facility called TRECT is built. By measuring the parameters such as temperature, flow of the test section to study the influence to CHF by the parameters such as flow velocity and angle. All of these can provide reliable basis to the effectiveness appraisal and model development on the area of severe accident mitigation measures (IVR). To be specific, the test section is rectangular channel whose section is 50 × 20 mm. The upper surface is the heat surface and using a direct current heating mode to supply heat power. The heat flux can reach 1.5MW/m2. We use this upper surface heated rectangular channel to simulate RPV ERVC channel. By adjust the angle of test section to simulate the different circum ferential location of RPV lower head. And the Adjusting range can be 0° to 90°. The experimental results show that flow rate was reduced by 11% in the experiments, the critical heat flux density increased by 4.5%. Inclined angle increased from 16° to 29°, CHF increased by 7.9%.

Study on Boiling Heat Transfer in Narrow Channel and Horizontal-Narrow-Flat Space

2009 ◽  
Author(s):  
Yasuo Koizumi ◽  
Hiroyasu Ohtake ◽  
Takaaki Oshikawa
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Boiling Heat Transfer ◽  
Rectangular Channel ◽  
Pool Boiling ◽  
Flow Channel ◽  
Test Fluid ◽  
Large Bubble ◽  
Circulation Flow

Boiling heat transfer experiments were preformed for narrow-horizontal-channels at 0.1 MPa. Test fluid was ethanol. The height and the width of the test channels were in a range of 1.0 mm ∼ 4.0 mm and 1.0 mm ∼ 3.0 mm, respectively. The channel length was 30 mm and 60 mm. The boiling surface was at the center of the bottom wall of the flow channel. Both ends of the channel were opened to wide space filled with liquid. Pool boiling experiments for the small heat transfer surfaces of the diameter of 1.0 mm ∼ 20.0 mm were also performed. Following conclusions were obtained. As the diameter of the boiling surface became small in pool boiling, boiling heat transfer was enhanced and the critical heat flux increased. The relation between the boiling heat flux and the wall superheat in the narrow rectangular channel was the same as that of the pool boiling for the same heat transfer surface size. As the channel height became narrow, the critical heat flux became low. In the case of the narrow-rectangular channel, large-coalescent bubbles occupied the top part of the flow channel. When the large bubble reached one outlet of the channel, almost all coalescent bubbles in the channel left from the outlet. After the selective departure of bubble from a specific outlet had established, the small reverse-inclination of the flow channel had no effect to alter the bubble departure outlet. It was suggested that the considerable steady-circulation flow had established. The CHF condition was not given only by the mass balance that the liquid supply to the channel was equal to the vapor generation rate. It was suggested that other effects such as the circulation flow should be included into the consideration for the CHF condition.

Critical Heat Flux of Graphene Coated Copper Surface at High Pressures

2015 ◽  
Author(s):  
Nanxi Li ◽  
Amy Rachel Betz
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
High Pressures ◽  
Pool Boiling ◽  
Copper Surface ◽  
Test Fluid ◽  
System Pressure ◽  
Wall Superheat ◽  
Copper Cylinder

Boiling is an efficient way to transfer heat due to the latent heat of vaporization. Many variables, such as surface properties, fluid properties, and system pressure, will affect the performance of pool boiling. Enhanced pool boiling has extensive applications in chemical, microelectronics, and power industries. Previous research has shown that micro- or nanostructured surfaces and coated surfaces will increase heat transfer coefficients up to one order of magnitude at atmospheric pressure. Graphene as a very good material with superb mechanical and electrical properties also has potential to enhance pool boiling performance. The purpose of this research is to investigate heat transfer enhancement on a graphene coated surface compared to a plane copper surface at atmospheric pressure and increased pressures with deionized water. The effect of the graphene coating on the critical heat flux is also investigated. To carry out the experiments, we designed and fabricated a special experimental facility that will withstand the high pressures (up to 20 bar) and high temperatures. Graphene is coated on a 1 cm2 copper surface using spray coating. The boiling vessel is pressurized with nitrogen and the system pressure is controlled by a back pressure regulator. The test fluid is preheated to saturation temperature by two 500 W cartridge heaters. Multiple 150 W cartridge heaters are inserted in a copper cylinder to provide wall superheat for bubbles to nucleate on the studied surface. When the system reaches steady state, a process controller controls these cartridge heaters to increase the heat flux gradually from 0 kW/m2 to the critical heat flux. The copper cylinder is insulated with PTFE to minimize heat loss from the side. The gap between the copper cylinder and the insulation surface is carefully sealed with high temperature epoxy to reduce undesired nucleation sites. The wall superheat corresponding to each heat flux is extrapolated using Fourier’s law from three thermocouple readings. The heat transfer coefficient can thus be calculated at each heat flux for the every test fluid at its corresponding pressure. A camera with 3.2 cm field of view at a working distance of 12 cm to 15 cm is used to visualize the bubble formation on the heated surface.

scholarly journals Flow Boiling of Water on Titanium and Diamond-Like Carbon Coated Surfaces in a Microchannel

2010 ◽  
Author(s):  
Hai Trieu Phan ◽  
Nadia Caney ◽  
Philippe Marty ◽  
Ste´phane Colasson ◽  
Je´roˆme Gavillet
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Contact Angle ◽  
Atmospheric Pressure ◽  
Flow Boiling ◽  
Rectangular Channel ◽  
Diamond Like Carbon ◽  
Test Channel ◽  
Carbon Coated ◽  
Coated Surfaces

Experiments were performed to study the effects of surface wettability on flow boiling of water at atmospheric pressure. The test channel is a single rectangular channel 0.5 mm high, 5 mm wide and 180 mm long. The mass flux was set at 100 and 120 kg/m2 s and the base heat flux was varied from 30 to 80 kW/m2. Water enters the test channel under subcooled conditions. The sample surfaces are titanium (Ti) and diamond-like carbon (DLC) surfaces having a contact angle of 49° and 63°, respectively. The experimental results show different flow patterns that impact the heat transfer significantly. Compared to the Ti surface, the DLC surface shows a deterioration of 10% in heat transfer.

scholarly journals Predicting Critical Heat Flux With Multiphase CFD: 4 Years in the Making

2017 ◽  
Author(s):  
Emilio Baglietto ◽  
Etienne Demarly ◽  
Ravikishore Kommajosyula
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Bubble Dynamics ◽  
Flow Boiling ◽  
Heated Surface ◽  
Force Balance ◽  
Modeling Framework ◽  
Lift Off ◽  
Limiting Condition

Advancement in the experimental techniques have brought new insights into the microscale boiling phenomena, and provide the base for a new physical interpretation of flow boiling heat transfer. A new modeling framework in Computational Fluid Dynamics has been assembled at MIT, and aims at introducing all necessary mechanisms, and explicitly tracks: (1) the size and dynamics of the bubbles on the surface; (2) the amount of microlayer and dry area under each bubble; (3) the amount of surface area influenced by sliding bubbles; (4) the quenching of the boiling surface following a bubble departure and (5) the statistical bubble interaction on the surface. The preliminary assessment of the new framework is used to further extend the portability of the model through an improved formulation of the force balance models for bubble departure and lift-off. Starting from this improved representation at the wall, the work concentrates on the bubble dynamics and dry spot quantification on the heated surface, which governs the Critical Heat Flux (CHF) limit. A new proposition is brought forward, where Critical Heat Flux is a natural limiting condition for the heat flux partitioning on the boiling surface. The first principle based CHF is qualitatively demonstrated, and has the potential to deliver a radically new simulation technique to support the design of advanced heat transfer systems.

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