Numerical Study of Induced Condensation upon Mixing Flows of Water-stream Flow in a Tee-Junction Pipe (original) (raw)
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Journal of Engineering for Gas Turbines and Power, 2001
An analytical study is made of the perforated pipe distributor for the admission of high-energy fluids to a surface steam condenser. The results show that for all perforated pipes there is a general characteristic parameter M ͑kD/L f ͒, which depends on the pipe geometry and flow properties. Four cases are considered based on the value of the characteristic parameter M. (1) When M у1/4, momentum controls and the main channel static pressure will increase in the direction of the streamline. (2) When 1/6 рM Ͻ1/4, the momentum effect balances friction losses and the pressure will decrease to a minimum, and then increase in the direction of flow to a positive value. (3) When 0ϽM Ͻ1/6, friction controls and the pressure will decrease to a minimum, then increase slowly, but the total pipe static pressure difference will always be negative. (4) When M ϭ0, a limiting case when the ratio of the length to the diameter is infinite. This analysis is useful not only for the design of perforated pipe distributors for turbine condensers over a wide range of dimensions, fluid properties, and side hole pressure but also for many other technical systems requiring branching flow distribution.
Heat Transfer, Part B, 2005
The flow and heat transfer rates inside a condenser depend on the specification of inlet, wall, and exit conditions. For steady/quasi-steady internal condensing flows, the vapor's ability to sense exit condition and, for certain exit conditions, even change its density (despite low Mach numbers) allows the flow to have a rather significant dependence on conditions downstream of the condenser. The change in flows due to change in exit conditions is usually accompanied by significant changes in interfacial mass transfer rates and associated locations of the interface. Both experimental and direct computational simulation results presented here show that this is indeed the case for a large class of flows of pure vapor experiencing film condensation on the inside walls of a vertical tube. In applications, the totality of boundary conditions is determined not only by the condenser; but also by the flow-loop (or the system)-of which the condenser is only a part. Therefore, the results outlined here should contribute towards a better understanding of the behavior (particularly the extent to which flow "ellipticity" and vapor compressibility affect the flow regimes of operation-i.e. annular, plug/churn, etc.) and response of condensers (transients due to start-up, system instabilities, etc.) in different application systems (e.g. Rankine Cycle Power Plants, Capillary Pumped Loops, Looped Heat Pipes, Thermal Management Systems, etc.). In this connection, two experimental examples of relevant system instabilities are also presented here. In summary, the experimental results presented here, and the computational results summarized here but presented elsewhere, reinforce the fact that there exist multiple steady solutions (with different heat transfer rates) for different exit conditions. However under certain flow situations there exists a "natural" steady flow with a "natural" exit condition. This happens if the vapor flow is seeking a specific exit condition and the conditions downstream of the condenser allow the vapor the choice to select it.
The Canadian Journal of Chemical Engineering, 2012
The condensation of pure steam flowing inside a vertical tube has been extensively studied during the last nine decades. Considerable amount of experimental and analytical efforts can be found due to the significance of this subject in practice. In the present work (Part I), experimental investigations have been performed over a range of pressure (0.1 < P < 0.35 MPa) and internal tube diameter (D i = 10, 20 and 43 mm). A twodimensional computational fluid dynamic (CFD) simulations have been carried out commercial software Fluent 6.2 [Fluent 6.2, "User's Manual to FLUENT 6.2," Fluent Inc., Lebanon, USA, 2005]. CFD results were used to predict the temperature profiles, pressure drop and the heat transfer coefficient, which was in close agreement with the experimental values. The film characteristics predicted by the CFD simulations have been compared qualitatively with the photographic images. Further, the CFD model developed in Part I extended for the analysis of all the experimental data reported in the published literature.
Journal of Heat Transfer, 2007
Reported experimental and computational results confirm that both the flow features and heat-transfer rates inside a condenser depend on the specification of inlet, wall, and exit conditions. The results show that the commonly occurring condensing flows’ special sensitivity to changes in exit conditions (i.e., changes in exit pressure) arises from the ease with which these changes alter the vapor flow field in the interior. When, at a fixed steady mass flow rate, the exit pressure is changed from one steady value to another, the changes required of the interior vapor flow toward achieving a new steady duct flow are such that they do not demand a removal of the new exit pressure imposition back to the original steady value—as is the case for incompressible single phase duct flows with an original and “required” exit pressure. Instead, new steady flows may be achieved through appropriate changes in the vapor/liquid interfacial configurations and associated changes in interfacial mass,...
Energy, 2020
This paper deals with the intensification of water vapour condensation in vertical pipes. Two configurations of vertical condensers are compared. A standard configuration and a novel configuration with cooling water at the inner pipe wall in direct contact with the condensing vapour. For this configuration, a detailed mathematical model of heat transfer is made using empirical relationships to describe the behaviour of the liquid film and vapour. The focus is placed on a detailed description of the processes at the vapour-liquid interface. The results of the mathematical model are compared with an experimental study in which the real condensing power was assessed depending on the vapour mass flow rate, the cooling water temperature at the pipe inlet, and the volumetric flow rate of the cooling water. This paper presents specific mean heat transfer coefficients useable for design calculations. The results show that the heat transfer coefficient is proportional to the liquid film temperature as well as the vapour flow rate. The condensers are compared with the same vapour flow rate and cooling water temperature. The novel configuration rejects the same amount of condensation heat as the standard configuration, but only requires a third of the amount of cooling water.
A Heat Exchanger with Water Vapor Condensation on the External Surface of a Vertical Pipe
Energies
The paper is concerned with water vapor condensation on vertical pipes. The vertical position of pipes in a condenser is not discussed very often. Its application has a number of particularities in terms of the numerical determination of heat transfer. In the first stage of this paper, the authors focus on the experimental identification of heat transfer during vapor condensation on vertical pipes with a diameter of 14.0 × 1.0 mm. The pipes are placed in a narrow channel and the steam flows around them in a perpendicular direction. Two channel widths were tested, i.e., 20.0 and 24.0 mm. In the second stage, numerical modelling (CFD) is used for a detailed identification of the vapor velocity fields near the pipes. In the third stage, the results of the experimental measurements and numerical modelling are compared with data published by various authors. There are studies in the literature dealing with axial flow around vertical pipes; however, the associated results are based on con...
Poly-disperse simulation of condensing steam-water flow inside a large vertical pipe
International Journal of Thermal Sciences, 2016
The condensation of saturated steam bubbles in sub-cooled water inside a vertical pipe was studied by poly-disperse CFD simulations. Six test cases with varied pressure, liquid sub-cooling and diameter of the gas injection orifices were simulated. Baseline closures presented for non-drag forces in previous work were found to be reliable also in non-isothermal cases. The effect of bubble coalescence and breakup is over-weighting in the region close to steam injection in case of small orifice diameter. With the increase of orifice diameter, breakup becomes dominant in determining bubble size change. The effect of interphase heat transfer coefficient correlations was investigated. The widespread RanzeMarshall correlation was found to underestimate the condensation rate, especially at high pressure levels. In contrast, satisfying agreement with the experimental data was obtained by the Tomiyama correlation.
Models for water steam condensing flows
Archives of Thermodynamics, 2012
Models for water steam condensing flows The paper presents a description of selected models dedicated to steam condensing flow modelling. The models are implemented into an in-house computational fluid dynamics code that has been successfully applied to wet steam flow calculation for many years now. All models use the same condensation model that has been validated against the majority of available experimental data. The state equations for vapour and liquid water, the physical model as well as the numerical techniques of solution to flow governing equations have been presented. For the single-fluid model, the Reynolds-averaged Navier-Stokes equations for vapour/liquid mixture are solved, whereas the two-fluid model solves separate flow governing equations for the compressible, viscous and turbulent vapour phase and for the compressible and inviscid liquid phase. All described models have been compared with relation to the flow through the Laval nozzle.