Experimental Investigation and Empirical Correlations of Heat Transfer in Different Regimes of Air–Water Two-Phase Flow in a Horizontal Tube

2016 ◽  
Vol 9 (2) ◽  
Author(s):  
S. A. Nada
Keyword(s):  
Heat Transfer ◽  
Experimental Investigation ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Flow Rate ◽  
Two Phase Flow ◽  
Horizontal Tube ◽  
Flow Regimes ◽  
Phase Flow ◽  
Two Phase

This article reports on the experimental investigation of heat transfer to cocurrent air–water two-phase flow in a horizontal tube. The idea is to enhance heat transfer to the coolant liquid by air injection. Experiments were conducted for different air water ratios in constant temperature heated tube. Visual identification of flow regimes was supplemented. The effects of the liquid and gas superficial velocities and the flow regimes on the heat transfer coefficients were investigated. The results showed that the heat transfer coefficient generally increases with the increase of the injected air flow rate, and the enhancement is more significant at low water flow rates. A maximum value of the two-phase heat transfer coefficient was observed at the transition to wavy-annular flow as the air superficial Reynolds number increases for a fixed water flow rate. It was noticed that the Nusselt number increased about three times due to the injection of air at low water Reynolds number. Correlations for heat transfer by air–water two-phase flow were deduced in dimensionless form for different flow regimes.

A Natural Circulation Model of the Closed Loop, Two-Phase Thermosyphon for Electronics Cooling

2001 ◽  
Author(s):  
S. I. Haider ◽  
Yogendra K. Joshi ◽  
Wataru Nakayama
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Closed Loop ◽  
Two Phase Flow ◽  
Natural Circulation ◽  
Saturation Temperature ◽  
Electronics Cooling ◽  
Phase Flow ◽  
Two Phase

Abstract The study presents a model for the two-phase flow and heat transfer in the closed loop, two-phase thermosyphon (CLTPT) involving co-current natural circulation. Most available models deal with two-phase thermosyphons with counter-current circulation within a closed, vertical, wickless heat pipe. The present research focuses on CLTPTs for electronics cooling that face more complex two-phase flow patterns than the vertical heat pipes, due to closed loop geometry and smaller tube size. The present model is based on mass, momentum, and energy balances in the evaporator, rising tube, condenser, and the falling tube. The homogeneous two-phase flow model is used to evaluate the friction pressure drop of the two-phase flow imposed by the available gravitational head through the loop. The saturation temperature dictates both the chip temperature and the condenser heat rejection capacity. Thermodynamic constraints are applied to model the saturation temperature, which also depends upon the local heat transfer coefficient and the two-phase flow patterns inside the condenser. The boiling characteristics of the enhanced structure are used to predict the chip temperature. The model is compared with experimental data for dielectric working fluid PF-5060 and is in general agreement with the observed trends. The degradation of condensation heat transfer coefficient due to diminished vapor convective effects, and the presence of subcooled liquid in the condenser are expected to cause higher thermal resistance at low heat fluxes. The local condensation heat transfer coefficient is a major area of uncertainty.

scholarly journals Experimental investigation of air–water, two-phase flow regimes in vertical mini pipe

2011 ◽  
Vol 18 (4) ◽  
pp. 923-929 ◽  
Author(s):  
P. Hanafizadeh ◽  
M.H. Saidi ◽  
A. Nouri Gheimasi ◽  
S. Ghanbarzadeh
Keyword(s):  
Experimental Investigation ◽  
Two Phase Flow ◽  
Flow Regimes ◽  
Phase Flow ◽  
Two Phase

Two-Phase Wakes in Adiabatic Liquid-Gas Flow Around a Cylinder

2020 ◽  
Author(s):  
Dohwan Kim ◽  
Matthew J. Rau
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
High Speed ◽  
Gas Flow ◽  
Two Phase Flow ◽  
Water Channel ◽  
Phase Flow ◽  
Two Phase ◽  
Flow Around A Cylinder ◽  
High Heat Transfer

Abstract Small tubes and fins have long been used as methods to increase surface area for convective heat transfer in single-phase flow applications. As demands for high heat transfer effectiveness has increased, implementing evaporative phase-change heat transfer in conjunction with small fins, tubes, and surface structures in advanced heat exchanger and heat sink designs has become increasingly attractive. The complex two-phase flow that results from these configurations is poorly understood, particularly in how the gas phase interacts with the flow structure of the wake created by these bluff bodies. An experimental study of liquid-gas bubbly flow around a cylinder was performed to understand these complex flow physics. A 9.5 mm diameter cylinder was installed horizontally within a vertical water channel facility. A high-speed camera captured the movement of the liquid-gas mixture around the cylinder for a range of bubble sizes. Liquid Reynolds number, calculated based on the cylinder diameter, was varied approximately from 100 to 3000. Time-averaged probability of bubble presence was calculated to characterize the cylinder wake and its effects on the bubble motion. The influence of the liquid Reynolds number, superficial air velocity, and bubble size is discussed in the context of the observed two-phase flow patterns.

Power Rising and Descending Transient for the OTSG of a Small PWR

2020 ◽  
Author(s):  
Baihui Jiang ◽  
Zhiwei Zhou ◽  
Zhaoyang Xia ◽  
Qian Sun
Keyword(s):  
Heat Transfer ◽  
Flow Rate ◽  
Two Phase Flow ◽  
Flow Instability ◽  
Flow Stability ◽  
Phase Flow ◽  
Steam Generators ◽  
Two Phase ◽  
Water Reactors ◽  
Secondary Side

Abstract As key heat transfer system in small and medium size pressurized water reactors, once-through steam generators are important parts of energy exchange between primary and secondary circuits, and are very important for the design and operation of reactors. However, two-phase flow and heat transfer in once-through steam generators are very complicated. When a reactor experience power rising and descending transient, the heat removal of once-through steam generator, the flow rate, the inlet fluid temperature and outlet steam temperature will all change accordingly. Especially when a reactor is running at a low power, the flow rate of the secondary side of OTSG is extremely small and the single-phase region of the secondary side of OTSGs is also too small. The two-phase flow instability may occur, which has a serious impact on reactor operation and safety. So, a reasonable power-up and power-down transient scheme is required to ensure operational stability when starting up and shutting down a reactor. RELAP5/MOD4.0 is a commercial software developed by Innovative System Software, LCC for transient analysis of light water reactors (LWR). After years of development and improvement, RELAP5 has been a basic tool for analysis and calculation of various simulators of nuclear power plants. Scholars all over the world have carried out a large number of analysis of two-phase flow stability using RELAP5, and the results are reliable. This paper takes once through steam generators with given structural parameters as the research object, and uses RELAP5 as the calculation tool. The influencing factors of flow instability are discussed in this paper, and the operating parameters of the fluid on the primary and secondary sides are designed to satisfy the flow stability under different powers. And a set of power-up and power-down schemes for stable operation is proposed.

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