Investigation of Pre-and Post-Dryout Heat Transfer in Upward Steam-Water Two-Phase Flow at Low Flow Rate with Improved Surface Temperature Measurement

In order to improve the flow measurement accuracy of oil-water two-phase flow at low flow rate, this paper presents a plug-in conductance sensor array (PICSA) for the measurement of water holdup and cross-correlation velocity. Due to the existence of the insert body in PICSA, the effect of slippage and the non-uniform distribution of dispersed phase on the measurement of oil-water two-phase flow at low flow rate can be reduced. The finite element method is used to analyze the electric field distribution characteristics of the plug-in conductance sensor, and the sensor geometry is optimized. The dynamic experiment of oil-water two-phase flow is carried out where water cut Kw and mixture velocity Um are set in the range of 10–98% and 0.0184–0.2580 m/s respectively. Experimental results show that the PICSA has good resolution in water holdup measurement for dispersed oil-in-water slug flow (D OS/W), transition flow (TF), dispersed oil-in-water bubble flow (D O/W) and very fine dispersed oil-in-water bubble flow (VFD O/W). In addition, the cross-correlation velocity of the oil-water two-phase flow is obtained by using the plug-in upstream and downstream conductance sensor arrays. The relationship between the cross-correlation velocity and mixture velocity is found to be sensitive to the change of flow pattern, but it has a good linear relationship under the same flow pattern. Based on the flow pattern identification, a good prediction result of the mixture velocity is obtained using kinematic wave theory. Finally, a high precision prediction of the individual phase volume fraction of oil-water two-phase flow at low flow rate is achieved by using the drift flux model.

Download Full-text

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

Volume 3: Student Paper Competition; Thermal-Hydraulics; Verification and Validation ◽

10.1115/icone2020-16294 ◽

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.

Download Full-text

E111 Validation of Detailed Two-Phase Flow Simulation Code TPFIT for Water Jet (I) : Comparison of Experimental and Analytical Results of Jet Behavior at Low Flow Rate

The Proceedings of the National Symposium on Power and Energy Systems ◽

10.1299/jsmepes.2011.16.101 ◽

2011 ◽

Vol 2011.16 (0) ◽

pp. 101-102

Author(s):

Ryuhei IKUTA ◽

Yasuo KOIZUMI ◽

Kazuyuki TAKASE ◽

Hiroyuki YOSHIDA

Keyword(s):

Flow Rate ◽

Two Phase Flow ◽

Flow Simulation ◽

Water Jet ◽

Low Flow ◽

Phase Flow ◽

Two Phase ◽

Simulation Code ◽

Analytical Results ◽

Jet Behavior

Download Full-text

Experimental Study of Flow Boiling in Microchannel

ASME 5th International Conference on Nanochannels, Microchannels, and Minichannels ◽

10.1115/icnmm2007-30130 ◽

2007 ◽

Author(s):

S. G. Singh ◽

S. P. Duttagupta ◽

A. M. Kulkarni ◽

B. P. Puranik ◽

A. Agrawal

Keyword(s):

Heat Transfer ◽

Heat Flux ◽

Pressure Drop ◽

Flow Rate ◽

Heat Input ◽

Boiling Heat Transfer ◽

Two Phase Flow ◽

Phase Region ◽

Phase Flow ◽

Two Phase

With the reduction in size of electronic devices, the problem of efficient cooling is becoming more and more severe. Boiling heat transfer in microchannels is fast emerging as a promising solution to the problem. In the present work, microchannels were fabricated on a silicon wafer. A chrome-gold micro-heater was integrated and characterized on the other side of the wafer. The change in resistance of the micro-heater in the temperature range of 20 °C – 120 °C was found to be within 10%. Deionized water was used as working fluid in microchannel. The single-phase pressure drop across the microchannel was found to increase linearly with increasing flow rate in confirmation with conventional laminar flow theory. Also, the pressure drop decreases with an increase in heat input due to a reduction in viscosity. The study was extended to two phase flow with flow rate and heat flux as the control parameters. The onset of two phase flow, at a given heat flux, with a decrease in flow rate, can be identified by the departure of linear pressure drop to non-linearity; this point was also confirmed through visual observation. In two-phase region of flow, pressure drop was found to increase initially, passes through a maximum and then decreases, with a decrease in flow rate. The experiments are performed for several heat fluxes. Both the onset of two phase and maximum pressure drop in the two phase region shifts to higher flow rates with an increase in heat input. Such detailed experimental results seem to be missing from the literature and are expected to be useful for modeling of boiling heat transfer in microchannels. Another pertinent observation is presence of instability in two-phase flow. It was found that at higher flow rate and heat flux instability in two-phase flow was more. An attempt to record these instabilities was made and preliminary data on their frequency will be presented. This study may help to choose suitable operating conditions for a microchannel heat sink for use in electronics cooling.

Download Full-text

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

Journal of Thermal Science and Engineering Applications ◽

10.1115/1.4034903 ◽

2016 ◽

Vol 9 (2) ◽

Cited By ~ 5

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.

Download Full-text