Author: Mohan Singh YadavPublisher:
ISBN:
Category :
Languages : en
Pages : 474
Book Description
Interfacial Area Transport Across Vertical Elbows in Air-water Two-phase Flow
Author: Mohan Singh YadavCharacterization of Geometric Effects Induced by 90 Vertical Elbows in Air-water Two-phase Flow
Author: Shouxu QiaoPublisher:
ISBN:
Category :
Languages : en
Pages :
Book Description
Conventional modeling of two-phase flows is typically based on experimental data acquired in straight flow channels of different flow orientations with no flow restrictions. No model is currently available to dynamically predict the transition between different flow orientations. To bridge this gap, it is important to characterize and model the geometric effects induced by flow restrictions or junctions in air-water two-phase flows. The present work investigates the effects of a 90 vertical-upward to horizontal and a 90 horizontal to vertical-downward elbow on two-phase flow and establishes the interfacial area transport equation (IATE) applicable to air-water two-phase flow influenced by the 90 elbows. A detailed database for the local and global two-phase flow parameters in different flow orientations and across vertical elbows is established with state-of-the-art four-sensor conductivity probes, a pressure transducer, and a high-speed video camera. The elbow effects are characterized by investigating the evolution of void fraction, interfacial area concentration, bubble velocity and two-phase pressure drop across and downstream of elbows. The degree of influence made by the elbow is characterized by the variance of void fraction. The axial development of the flow downstream of the elbow is modeled by an exponential function of the axial length based on the experimental data. Then, the dissipation length of the elbow is determined by characterizing the evolution of the elbow strength parameter. The elbow strength parameter is also used to correlate the void-weighted bubble velocity and covariance terms in the IATE. The two-phase pressure drop across the vertical elbows is modeled with a modified Lockhart-Martinelli correlation that considers the minor loss induced by these elbows. The developed models and correlations are implemented into the IATE to establish a model that is applicable to the region influenced by the elbow. The established IATE is evaluated by the data obtained in different flow orientations and across elbows in bubbly flow. The newly developed IATE can predict the interfacial area concentration with an average percent difference of 6% compared with the experimental data, demonstrating that the models and correlations developed in this work for the two-phase flow parameters in elbow influenced regions are reliable.
Inlet-induced Effects on Vertical Co-current Downward Air-water Two-phase Flow
Author: Daniel MenaPublisher:
ISBN:
Category :
Languages : en
Pages :
Book Description
To accurately design safe and efficient energy systems, such as nuclear reactors, the understanding of two-phase flow transport across ducts of varying orientations and inlet configurations is of critical importance. With this in mind, this study investigated the effects of inlets on interfacial structures of vertical-downward co-current air-water two-phase flow. Experiments were performed in a test facility that allows for the investigation of three different types of vertical downward inlets, namely: two-phase mixture injector without flow straightener (Type A), two-phase mixture injector with flow straightener (Type B), and 90° horizontal-to-vertical downward elbow (Type C). The effects of each inlet on global and local two-phase flow parameters are investigated in detail. Experiment results showed that the Type A inlet induces high rotation and turbulence in the mixture flow that leads to significant coalescence of the bubbles near the centerline of the pipe cross-section. The implementation of the flow straightener in the Type B inlet reduces the rotation and promotes the formation of uniform profiles of local two-phase flow parameters. For the Type C inlet, the creation of secondary flow in the elbow causes the bubbles to migrate to the inner curvature of the elbow resulting in the formation of asymmetrical distributions of void fraction and interfacial area concentration immediately downstream of the elbow inlet. An assessment of the available pressure loss models was performed. It was found that the Lockhart-Martinelli correlation can predict the pressure drop for the Type A, B, and C inlets with an average percent difference of 4.5%, 1%, and 3.4%, respectively, of the experimental data. Furthermore, the Minor Loss model evaluated for the Type C inlet predicts the pressure drop across the elbow with an average percent difference of 1.6%. In view of the one-dimensional transport of two-phase flow parameters, a model is proposed to characterize the dissipation region of the effects induced by the vertical-downward elbow inlet.
Interfacial Area Transport Equation for Bubbly to Cap-bubbly Transition Flows
Author: Theodore WoroszPublisher:
ISBN:
Category :
Languages : en
Pages :
Book Description
To fully realize the benefit of the two-group interfacial area transport equation (IATE) as a constitutive model for the interfacial area concentration in the two-fluid model, it is imperative that models be developed to dynamically transition from one-group to two-group flows. With this in mind, the two-group IATE is derived in detail to establish new expansion source terms that correctly account for the effects of intergroup bubble transport. In addition to this theoretical effort, the state-of-the-art four-sensor conductivity probe is used to establish a reliable experimental database of local two-phase flow parameters to characterize one-group to two-group transition flows and to support model development. The experiments are performed in vertical-upward air-water two-phase flow in a 5.08cm pipe. Additionally, the local conductivity probe is improved through systematic studies into: 1) signal "ghosting" electrical interference among probe sensors, 2) sampling frequency sensitivity, 3) measurement duration sensitivity, and 4) probe sensor orientation. Wake-dominated bubble transport characterizes the transition from one-group to two-group flows. Therefore, the necessary intergroup and intragroup wake entrainment source terms that are required for two-group interfacial area transport in transition flows are developed. Furthermore, an approach is developed to initiate the shearing-off source and reduce the one-group interaction mechanisms as an established two-group flow develops. The new interfacial area transport model for one-group to two-group transition flows is evaluated against the experimental database. The model accurately captures the exchange of void fraction and interfacial area concentration between group-I and group-II in transition flows. Overall, the group-I void fraction and interfacial area concentration are predicted within ±6% and ±4%, respectively, of the experimental data. The group-II void fraction and interfacial area concentration are predicted within ±9% and ±11%, respectively, of the experimental data.
Energy Research Abstracts
Author: NBS Special Publication
Author: Publisher:
ISBN:
Category : Weights and measures
Languages : en
Pages : 360
Book Description
Applied Mechanics Reviews
Author: Report
Author: United States. National Bureau of StandardsPublisher:
ISBN:
Category : Hydraulic engineering
Languages : en
Pages : 696
Book Description
Current Hydraulic Laboratory Research in the United States
Author: Publisher:
ISBN:
Category : Hydraulic engineering
Languages : en
Pages : 360
Book Description
Hydraulic Research in the United States 1970
Author: United States. National Bureau of StandardsPublisher:
ISBN:
Category : Hydraulic engineering
Languages : en
Pages : 360
Book Description