Research Papers: Nuclear Power

Dynamic Heat-Exchanger Model for Any Combination of Water and Steam States

[+] Author and Article Information
Eunkyeong Kim

e-mail: eunkyeong.kim.mn@hitachi.com

Takuya Yoshida

e-mail: takuya.yoshida.ru@hitachi.com

Tatsurou Yashiki

e-mail: tatsuro.yashiki.zn@hitachi.com
Hitachi Research Laboratory,
Hitachi Ltd.,
7-2-1 Omikacho,
Hitachi, Ibaraki 319-1221, Japan

Contributed by the Nuclear Division of ASME for publication in the Journal of Engineering for Gas Turbines and Power. Manuscript received September 28, 2012; final manuscript received October 2, 2012; published online April 23, 2013. Editor: Dilip R. Ballal.

J. Eng. Gas Turbines Power 135(5), 052901 (Apr 23, 2013) (7 pages) Paper No: GTP-12-1381; doi: 10.1115/1.4007875 History: Received September 28, 2012; Revised October 02, 2012

The purpose of this study is to propose a dynamic heat transfer model for predicting transient heat recovery steam generator (HRSG) behaviors involving phase changes in heat exchanger tubes. The model deals with any combination of phase states by switching the equations for heat transfer coefficient, specific volume, and friction factor corresponding to their physical characteristics. The model also constrains the change of mass flow calculated by momentum balance to satisfy thermodynamic relationships which are neglected by conventional models. The simulation results show that the proposed model predicts the transient pressure drop, outlet mass flow changes, and the reduction in heat transfer coefficient caused by dryout during heating or evaporating processes. In addition, the model improves the accuracy of mass flow transients compared to those obtained by conventional models.

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Fig. 1

Steady-state relationships between partial derivative (∂P/∂h)v and quality xs. The dashed curve shows the density 1/v¯s.

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Fig. 2

Regions and weighting factors for calculating heat transfer coefficient, specific volume, and friction factor

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Fig. 3

Variables for the proposed heat transfer model

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Fig. 4

The heat transfer model divided into submodels

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Fig. 5

The configuration of heat exchangers for evaluating the proposed heat transfer model. Gas flowed though HEX 1 and HEX 2 and the water/steam flowed in the opposite direction.

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Fig. 6

Boundary condition

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Fig. 7

Simulation results (enthalpy, pressure, and mass flow)

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Fig. 8

Distribution of heat transfer coefficient along tube height (HEX 2, at 5000 s). The heat transfer coefficient was almost constant over the liquid region; it increased throughout the two-phase region and then decreased at the height where dryout occurred, and again was almost constant for the mist and vapor regions.

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Fig. 9

Simulation results (phase states)

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Fig. 10

The dryout quality along mass flow for different pressures. Calculated by the equation in JSME [12].

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Fig. 11

Simulation results (thermodynamic and dynamic densities)




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