Begell House Inc.
Multiphase Science and Technology
MST
0276-1459
27
2-4
2015
CHARACTERISTICS OF GAS AND NON-NEWTONIAN LIQUID TWO-PHASE FLOWS THROUGH A CIRCULAR MICROCHANNEL
99-115
10.1615/MultScienTechn.v27.i2-4.10
Akimaro
Kawahara
Advanced Thermal and Fluid Energy System
Division of Industrial Fundamentals
Faculty of Advanced Science and Technology, Graduate School of Science and Technology, Kumamoto University, Chuo-ku,
Kurokami 2-39-1, Kumamoto, Japan
Michio
Sadatomi
Department or Advanced Mechanical System, Graduate School of Science and Technology, Kumamoto University, Kurokami 2-39-1, Chuo-Ku, Kumamoto City, 860-8555, Japan
Wen Zhe
Law
Department or Advanced Mechanical System, Graduate School of Science and Technology, Kumamoto University, Kurokami 2-39-1, Chuo-Ku, Kumamoto City, 860-8555, Japan
Mohamed H.
Mansour
Department or Mechanical Power Engineering, Mansoura University, El-Goumhoria Street, EL-Mansoura 35516, Egypt
two-phase flow
microchannel
non-Newtonian fluid
bubble length
bubble velocity
void fraction
In this study, gas and non-Newtonian liquid two-phase flows in a horizontal circular microchannel have been investigated. The microchannel was a fused silica capillary tube with 0.25 mm inside diameter. Polyacrylamide aqueous solutions with different mass concentrations, which exhibit pseudo-plastic behavior with viscoelasticity, were used as non-Newtonian liquids, while nitrogen gas was used as the test gas. The flow pattern, the bubble length, the liquid slug length, the bubble velocity, and the void fraction were measured. The experimental data are compared to those for nitrogen gas and water two-phase flow. From the comparison, rheological properties of polyacrylamide solutions are found to significantly affect the flow parameter measured. Both bubble length and liquid slug length are much longer for the polyacrylamide solution than the water. Bubble velocity increases with concentration of polyacrylamide, especially for higher total volumetric flux. The bubble velocity for both the water and the polyacrylamide solution could be correlated with a drift flux model by using a newly developed distribution parameter equation, which is a function of capillary number and Laplace number. Void fraction decreases with increasing of polyacrylamide at fixed homogeneous void fraction. Void fraction for both Newtonian and non-Newtonian liquids could be correlated by the Kawahara et al. equation (Kawahara, A., Sadatomi, M., Kawaji, M., Okayama, K., and Chung, P. M.-Y., Assessment of Void Fraction Correlations for Adiabatic Two-Phase Flows in Microchannels, Proceedings of 3rd International Conference on Microchannels and Minichannels, Paper No. ICMM2005-75031, 2005) with the Lockhart-Martinelli parameter.
STUDY OF WATER TRANSPORT PHENOMENA IN POLYMER ELECTROLYTE FUEL CELLS IN THE THROUGH-PLANE DIRECTION
117-132
10.1615/MultScienTechn.v27.i2-4.20
Hideki
Murakawa
Department of Mechanical Engineering, Kobe University, 1-1 Rokkodai, Nada, Kobe 657-8501, Japan
Katsumi
Sugimoto
Department of Mechanical Engineering, Kobe University, 1-1 Rokkodai, Nada, Kobe 657-8501, Japan
Masataka
Sawada
Department of Mechanical Engineering, Kobe University, 1-1 Rokkodai, Nada, Kobe 657-8501, Japan
Masataka
Nishizaki
Department of Mechanical Engineering, Kobe University, 1-1 Rokkodai, Nada, Kobe 657-8501, Japan
Hitoshi
Asano
Department of Mechanical Engineering, Kobe University, 1-1 Rokkodai-cho, Nada-ku, Kobe 657-8501, Japan
Nobuyuki
Takenaka
Department of Mechanical Engineering, Kobe University, 1-1 Rokkodai, Nada, Kobe 657-8501, Japan
Yasushi
Saito
Institute for Integrated Radiation and Nuclear Science, Kyoto University, 2,
Asashiro-Nishi, Kumatori-cho, Osaka 590-0494, Japan
PEFC
neutron radiography
gas diffusion layer
water distribution
water transport analysis
A polymer electrolyte fuel cell (PEFC) generates electricity from an electrochemical reaction. However, water accumulation in the gas diffusion layer (GDL) reduces the cell performance. Therefore, the membrane must be kept at the appropriate humidity level for proton conduction. Hence, water management in a PEFC is essential for operation, and it is important to understand the liquid water transport phenomenon in a PEFC. In this study, to clarify the water accumulation phenomenon in the GDL under PEFC operating conditions, neutron radiography was used to visualize and measure the water distribution in the through-plane direction of a small fuel cell. The experimentally and numerically determined 2D water distributions in the through-plane direction of the membrane in the PEFC were compared. The experimental results showed that water accumulation in the GDL under the land was greater than that under the channel during early PEFC operation. Water evacuation from the GDL to the channel occurred mainly around the land corners. The water saturation distributions predicted numerically were similar to the experimental results. The water accumulation rate of the experimental results was lower than that of the numerical results at the beginning of PEFC operation. This was more apparent at a lower current density of 158 mA/cm2. The mole fraction of the vapor in the GDL under the land was higher than that under the channel, and it influenced the water accumulation in the GDL significantly.
EFFECT OF HEAT TRANSFER SURFACE STRUCTURE ON WALL TEMPERATURE AND VOID FRACTION CHARACTERISTICS IN BOILING TRANSITION
133-146
10.1615/MultScienTechn.v27.i2-4.30
Hitoshi
Asano
Department of Mechanical Engineering, Kobe University, 1-1 Rokkodai-cho, Nada-ku, Kobe 657-8501, Japan
Junpei
Yoshidome
Department of Mechanical Engineering, Graduate School of Engineering, Kobe University, 1-1, Rokkodai, Nada, Kobe 657-8501, Japan
Tomohiko
Nakamura
Department of Mechanical Engineering, Graduate School of Engineering, Kobe University, 1-1, Rokkodai, Nada, Kobe 657-8501, Japan; DENSO CORPORATION, Kariya, Aichi, 448-8661 Japan
Taisaku
Gomyo
Department of Mechanical Engineering, Graduate School of Engineering, Kobe University, 1-1, Rokkodai, Nada, Kobe 657-8501, Japan
subcooled flow boiling
boiling heat transfer
boiling transition
heat transfer enhancement
void fraction
This study deals with the departure from nucleate boiling (DNB) of subcooled flow boiling in a horizontal rectangular narrow channel. The effect of the structure of the heating surface, smooth and rough surface produced by thermal spray coating, on heat transfer and flow characteristics in boiling transition from nucleate to film boiling was examined. FC72 was used as the working fluid. The one side of the wall at the center of the narrow channel was replaced with the copper heating surface. The channel height was 4 mm, the channel width was 20 mm, and the heating length was 50 mm. The top wall was replaced with a transparent acrylic resin plate to observe the boiling flow behavior. Average void fraction was measured at the center of the channel by a capacitance probe in the boiling transition from nucleate to film boiling. As the results, the coating produced higher critical heat flux than the smooth surface. A large fluctuation of pressure in synchronization with void fraction fluctuation was observed just before the boiling transition. The fluctuation was caused by periodic change in boiling behavior of nucleate and film boiling. During the pressure fluctuation, the wall temperature gradually increased, and then a stable vapor film was formed. While the wall temperature at the start of the fluctuation for the coated surface was lower than the smooth surface, the effect of the surface structure on the wall temperature at the stable vapor film formation was little.
CONTACT ANGLE VARIATION IN WATER DROPLETS ON LOW-SURFACE-ENERGY SOLIDS
147-158
10.1615/MultScienTechn.v27.i2-4.40
Yukihiro
Yonemoto
Graduate School of Science and Technology, Kumamoto University, Chuo-ku,
Kurokami 2-39-1, Kumamoto, Japan
Tomoaki
Kunugi
Department of Nuclear Engineering, Kyoto University, Kyoto Daigaku-Katsura, Nishikyo-ku, Kyoto, Japan
wettability
line tension
size dependence of contact angle
evaporation
condensation
After deposition on solid surfaces, evaporating droplets affect the cooling of heat sources, ink-jet printing, and painting. During evaporation, the behavior of interfaces is very important because heat transfers occur through interfaces. As a droplet on a surface decreases its volume, its contact angle is not constant; a variation is generally observed, implying that the Young equation cannot explain this phenomenon. Moreover, the contact line recedes as the contact angle changes. This is referred to as the size dependence of the contact angle. This behavior is mainly explained based on the concept of line tension. From long-established research, line tension was found to depend on the contact line radius and contact angle, and takes negative, positive, or zero values. However, their relationship remains an unexplained problem to the present day. In this study, water droplet behavior under natural evaporation is experimentally observed and analyzed. The observed behavior, specifically the size dependence of the contact angle, is modeled based not on the line tension concept but on the concept of work of adhesion and the free energy of the contact area. Our model shows good agreement with the experimental data in regard to the size dependence of the contact angle during natural evaporation of water droplets. In addition, the size and contact angle dependences of the line tension are elaborated based on our model.
NUMERICAL SIMULATION OF CONVECTIVE TRANSPORT OF FLY ASH-WATER SLURRY IN HORIZONTAL PIPE BENDS
159-186
10.1615/MultScienTechn.v27.i2-4.50
Bibhuti Bhusan
Nayak
Department of Mechanical Engineering, National Institute of Technology, Durgapur, Durgapur-713209, India
Dipankar
Chatterjee
Academy of Scientific and Innovative Research (AcSIR), CSIR-Central Mechanical
Engineering Research Institute, Durgapur-713209, India; Advanced Design and Analysis Group, CSIR-Central Mechanical Engineering Research
Institute Durgapur-713209, India
Amar Nath
Mullick
Department of Mechanical Engineering, National Institute of Technology, Durgapur, Durgapur-713209, India
slurry transport
heat transfer
numerical simulation
Eulerian model
pipe bends
secondary flow
A 3D numerical study is conducted to analyze the thermo-fluidic transport associated with the flow
of water–fly ash slurry in 90 deg curved horizontal pipes having different radius ratios (ratio between
radius of curvature and radius of pipe) of 2.98 and 5.6. The above phenomena in bends is also compared
with straight pipe of the same length and diameter for the flow of spherical fly ash particle of
sizes 13 and 34 μ;m at velocities ranging between 1 and 5 m/s and particle concentrations within 10−50% by volume for each velocity. The simulation is carried out by deploying a Eulerian multiphase
model available in the commercial computational fluid dynamics code Ansys Fluent. The pipe wall is
kept at an isothermal condition of 400 K, whereas the slurry enters the pipeline at a temperature of
300 K. The results indicate that the pipes having bends enhance the heat transfer performance at the
expense of the increased pressure drop compared to the straight pipes and also the pressure drop and
heat transfer increase with decreasing radius of curvature due to the increase of the secondary flow in
the pipe bends. It is also observed that the pressure drop is always greater when the slurry contains
larger size particles. On the contrary, the heat transfer coefficient of the slurry having a smaller size
of particles is found more in comparison to the larger-size particle slurry.
EFFECT OF AN ACOUSTIC FIELD ON HYDRODYNAMICS OF A BINARY MIXTURE OF POWDERS
187-202
10.1615/MultScienTechn.v27.i2-4.60
Akash
Langde
Anjuman College of Engineering and Technology, Nagpur, Maharashtra, India
R. L.
Sonolikar
Laxminarayan Institute of Technology, Nagpur, Maharashtra, India
D. J.
Tidke
G.H. Raisoni College of Engineering, Nagpur, Maharashtra, India
binary mixture
cohesive force
acoustic field
frequency
minimum fluidization velocity
Multiple particulate phase hydrodynamics is important in many industrial applications that involve segregation or mixing processes. Conventional fluidization is often impossible because the interparticle attraction is large and use of acoustic field is considered as the best option to overcome the problem specifically in mineral classification, elutriation, sedimentation, crystallization, and fluid bed leaching, just to name a few. This paper presents findings of an investigation to increase the flowability of extremely cohesive powders and study the effect of acoustic intensity and frequency on the behavior of the mixture of binary material. It also presents the effect of sound waves on the minimum fluidization velocity, bed expansion, and minimum bubbling velocity. Experiments revealed that the minimum
fluidization velocity (Umfs) and minimum bubbling velocity (Umbs) with sound force first decrease and then increase with increase in bed mass fractions, which were varied from 20 to 80%. It is also
seen that bed height increases with an increase in mass fraction in the presence of acoustic field.
RADIAL AND AXIAL DEVELOPMENT OF BOILING TWO-PHASE FLOW IN A 5 × 5 HEATED ROD BUNDLE UNDER ATMOSPHERIC PRESSURE CONDITION
203-213
10.1615/MultScienTechn.v27.i2-4.70
Takahiro
Arai
City College of New York, 160 Convent Avenue, New York, NY 10031, USA; Central Research Institute of Electric Power Industry (CRIEPI) 2-6-1 Nagasaka, Yokosuka, Kanagawa 240-0196, JAPAN; Waseda University, 3-4-1, Okubo, Shinjuku-Ku, Tokyo, 169-8555, Japan
Masahiro
Furuya
Central Research Institute of Electric Power Industry (CRIEPI) 2-6-1 Nagasaka, Yokosuka, Kanagawa 240-0196, JAPAN; Waseda University, 3-4-1, Okubo, Shinjuku-Ku, Tokyo, 169-8555, Japan
Taizo
Kanai
Central Research Institute of Electric Power Industry, 2-11-1 Iwadokita, Komae-shi, Tokyo 201-8511, Japan
Kenetsu
Shirakawa
Central Research Institute of Electric Power Industry, 2-11-1 Iwadokita, Komae-shi, Tokyo 201-8511, Japan
Yoshihisa
Nishi
Nuclear Energy System Department Central Research Institute of Electric Power Industry, 2-11-1 Iwadokita, Komae-shi, Tokyo 201-8511, Japan
boiling two-phase flow
void fraction
rod bundle
subchannel void sensor
power profile
atmospheric pressure
The boiling two-phase flow in the fuel rod bundle of a boiling water reactor exhibits multidimensional and transient flow dynamics. Coolability of the fuel is the key to ensuring safety, particularly in the event of any accident that involves the coolant injection malfunctioning and the core becoming uncovered. This paper addresses boiling two-phase flow dynamics in a 5 × 5 heated rod bundle under atmospheric pressure. The diameter of the heated rod is 10 mm, the rod pitch is 13 mm, and the heated length is 3.71 m. The radial power profile is the key experimental parameter: (i) uniform, (ii) center peak, (iii) side peak, and (iv) corner peak. The cross-sectional void-fraction distribution of a total of 132 points was acquired at more than 800 frames (cross sections) per second with a SubChannel Void Sensor (SCVS). The axial void-fraction distribution was also acquired with eight pairs of SCVS, which explain the radial and axial development of boiling two-phase flow in the rod bundle.
LINEAR STABILITY ANALYSIS OF THE DISCRETIZED ONE-DIMENSIONAL TWO-FLUID MODEL EQUATIONS FOR SLUG CAPTURING IN VERTICAL FLOW
215-227
10.1615/MultScienTechn.v27.i2-4.80
Francesco
Galleni
Department of Mechanical Engineering, Imperial College London, South Kensington SW7 2AZ, United Kingdom
Raad I.
Issa
Department of Mechanical Engineering, Imperial College London, South Kensington SW7 2AZ, United Kingdom
two-fluid model
stability analysis
Von Neumann analysis
ill- posedness
vertical slug flow
slug capturing
In this paper, a Von Neumann analysis of the discretized form of the 1D two-fluid model is presented for slug flow in vertical pipes in order to study the effect of the discretization scheme on the ill-posedness of the system. The resulting growth rate is compared to that obtained from a stability analysis of the parent system of differential equations. It is shown that the discretization of the equations introduces a cutoff limit for short wavelengths, below which all the perturbations are damped. This is equivalent to rendering the system numerically well posed. It is suggested here that this effect, for practical sizes of the mesh, is sufficient to stabilize the system and to yield valid solutions that lead to the prediction of the initiation of slugs in vertical configurations, and hence the computations for intermittent vertical flow using the two-fluid model. Those computations have been validated in a companion paper against experimental data.
MECHANISTIC SIMULATION OF SLUG FLOW IN VERTICAL PIPES USING THE ONE-DIMENSIONAL TWO-FLUID MODEL
229-245
10.1615/MultScienTechn.v27.i2-4.90
Raad I.
Issa
Department of Mechanical Engineering, Imperial College London, South Kensington SW7 2AZ, United Kingdom
Francesco
Galleni
Department of Mechanical Engineering, Imperial College London, South Kensington SW7 2AZ, United Kingdom
vertical slug flow
intermittent flow
numerical simulation
two- fluid model
slug capturing
In this paper, an extension of the "slug capturing" technique to vertical slug flow is presented. In this method, the initiation and development of the slugs are obtained by solving the 1D transient two-fluid model equations. This approach has the advantage of being almost entirely mechanistic: the flow develops naturally as part of the transient calculation, thus minimizing the necessity of empirical correlations typically required to model the slug dynamics. The slug capturing technique had in the past been successfully applied in horizontal slug flow configurations, but the application to vertical flow is new. In the present work, the method was found to be able to capture the formation of slugs automatically in vertical pipes. Numerous simulations were performed for a large number of flow conditions and the results are compared with experimental data. It is shown that the computed flow and slug characteristics−such as the average liquid holdup in the pipe, and the velocity and frequency of the slugs−compare fairly well with the experimental data. A mesh sensitivity study is also presented to ensure that the predicted slug characteristics do not depend on the cell length for the practical sizes of the mesh used.
BEHAVIOR OF VAPOR BUBBLES GENERATED ON A SINGLE HEATER ROD PARTLY CONFINED BY METALLIC WALLS IN SUBCOOLED WATER
247-265
10.1615/MultScienTechn.v27.i2-4.100
Kenji
Takano
Department of Nuclear Engineering, Kyoto University, Katsura, Nishikyo-Ku, Kyoto, 615-8540, JAPAN
Yusuke
Hashimoto
Department of Nuclear Engineering, Kyoto University, Katsura, Nishikyo-Ku, Kyoto, 615-8540, JAPAN
Tomoaki
Kunugi
Department of Nuclear Engineering, Kyoto University, Kyoto Daigaku-Katsura, Nishikyo-ku, Kyoto, Japan
Takehiko
Yokomine
Advanced Energy Engineering Science, Interdisciplinary Graduate School of Engineering Science, Kyushu University, Kasuga-kouen 6-1, Kasuga, Fukuoka 816-8580, JAPAN; Department of Nuclear Engineering, Kyoto University, Kyoto-Daigaku Kastura, Nishikyo-Ku, Kyoto, 615-8540 Japan
Zensaku
Kawara
Department of Nuclear Engineering, Kyoto University, Kyoto-Daigaku katsura, Nishikyo-ku, Kyoto, 615-8540, Japan
subcooled boiling
rod vibration
bubble behavior
subcooled boiling-induced vibration (SBIV)
structural constraint
Vibration of a structure should be avoided to prevent any damage, such as fretting wear occurring between its components, leading to critical failure of the structure. As an industrial example, a fuel assembly in the reactor core of a pressurized water reactor (PWR) is considered as such a structure. A fuel assembly for a PWR, consisting of hundreds of 4-m-long fuel rods, is utilized in the vertical upflow of the coolant water in a reactor core under high-pressure and high-temperature conditions. Abnormal situations, such as system pressure drop or loss of coolant flow in the core may lead to unexpected subcooled boiling at the fuel rods, which generate heat due to the nuclear reaction. The behavior of vapor bubbles generated in subcooled boiling can be a cause of fuel rod vibration, i.e., subcooled boiling-induced vibration (SBIV). This paper describes some experiments studying SBIV of a single heater rod in distilled water under atmospheric pressure in order to understand the fundamental phenomena of the SBIV. These experiments focused on the effects of the structural constraints formed by metallic walls around the heater rod on the SBIV of the rod. Three configurations of structural constraints were provided in the experiments−single, parallel, and corner walls−under the thermal conditions of constant heat flux and in a certain range of subcooling degrees. The behavior of the generated vapor bubbles was observed to depend, in each case, on the structural constraints by the walls, which influenced the measured acceleration of the SBIV of the heater rod.
INDEX
267-269
10.1615/MultScienTechn.v27.i2-4.110