New data on two-phase two-component heat transfer and hydrodynamics in a vertical tube

1987 ◽  
Author(s):  
K. REZKALLAH ◽  
G. SIMS
Keyword(s):  
Heat Transfer ◽  
Vertical Tube ◽  
Two Phase ◽  
Two Component

Experimental Investigation on Natural Circulation in a Thermosyphon Reboiler

2010 ◽  
Author(s):  
Xing Luo ◽  
Yanming Gao ◽  
Stephan Kabelac
Keyword(s):  
Heat Transfer ◽  
Tube Bundle ◽  
Flow Boiling ◽  
Natural Circulation ◽  
Liquid Product ◽  
Pilot Scale ◽  
Vertical Tube ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Set Up

Thermosyphon reboilers are widely used in refineries, petrochemical industries and other chemical processes. The liquid product stream coming from the bottom of the vapor-liquid separator is heated in an evaporator consisting of a vertical tube or tube bundle. When the evaporation occurs, the specific volume of the two-phase fluid increases. The upward buoyancy force caused by the density difference between the evaporator and down-flow pipe drives the fluid flowing through the evaporator in to the separator and forms a natural circulation. The experiments were conducted in a pilot scale thermosyphon system in which the evaporator consists of 7 steel tubes (outside diameter 30 mm, wall thickness 2 mm, length 4 m). A mathematical model was set up to simulate the heat transfer and pressure drop, in which empirical equations from literature were used. With the help of the simulation, the flow boiling heat transfer coefficients inside the tubes can be evaluated from a few measured local wall temperatures.

Numerical Investigation on Pool Boiling Over a Vertical Tube Coupled With In-Tube Condensation

2019 ◽  
Author(s):  
Shuai Ren ◽  
Wenzhong Zhou
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
Boiling Heat Transfer ◽  
Power Plants ◽  
Pool Boiling ◽  
Heat Removal ◽  
Vertical Tube ◽  
Two Phase ◽  
Maximum Heat ◽  
Maximum Heat Transfer

Abstract Pool boiling and in-tube condensation phenomena have been investigated intensively during the past decades, due to the superior heat transfer capacity of the phase change process. In passive heat removal heat exchangers of nuclear power plants, the two phase-change phenomena usually occur simultaneously on both sides of the tube wall to achieve the maximum heat transfer efficiency. However, the studies on the effects of in-tube condensation on external pool boiling heat transfer are very limited, especially in numerical computation aspect. In the present study, the saturated pooling boiling over a vertical tube under the influences of in-tube steam condensation is investigated numerically. The Volume of Fluid (VOF) interface tracking method is employed based on the 2D axisymmetric Euler-Euler multiphase frame. The phase change model combining with a mathematical smoothing algorithm and a temporal relaxation procedure has been implemented into CFD platform by user defined functions (UDFs). The two-phase flow pattern and bubble behavior have been analyzed. The effects of inlet steam mass flow rate on boiling heat transfer are discussed.

Passive Control of Two-Phase Flow Thermal Instabilities in a Vertical Tube Evaporator

2016 ◽  
Vol 8 (4) ◽  
Author(s):  
Ghazali Mebarki ◽  
Samir Rahal
Keyword(s):  
Heat Transfer ◽  
Void Fraction ◽  
Passive Control ◽  
Two Phase Flow ◽  
Tube Wall ◽  
Vertical Tube ◽  
Control Technique ◽  
Control Element ◽  
Phase Flow ◽  
Two Phase

Passive heat transfer techniques are considered to be one of the most important means to enhance heat transfer in heat exchangers that allow also reducing their size and manufacturing cost. Moreover, this passive technique can also be used to control the thermal instabilities caused by the two-phase flow in the evaporators. The thermal instabilities are undesirable because they can lead to a tube failure. For this purpose, a numerical study of the two-phase flow with evaporation in a vertical tube has been performed in this work. The volume of fluid (VOF) multiphase flow method has been used to model the water vapor–liquid two-phase flow in the tube. A phase-change model, for which source terms have been added in the continuity and energy equation, has been used to model the vaporization. The numerical simulation procedure was validated by comparing the obtained results with those given in the literature. The passive control technique used here is a ring element with square cross section, acting as a vortex generator, which is attached to the tube wall at various positions along the tube. Instabilities of temperature and void fraction at the tube wall have been analyzed using fast Fourier transforms (FFTs). The results show that the attachment of the control element has a significant influence on the value and distribution of the void fraction. Higher positions of the control element along the tube allow reducing the magnitude of void fraction oscillations.

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