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Research Papers: Evaporation, Boiling, and Condensation

Numerical Analysis of Heat Transfer Characteristics of a Falling Film Type Plate-Fin Condenser/Reboiler

[+] Author and Article Information
Yuanyuan Zhou

Department of Refrigeration and Cryogenic
Engineering,
School of Energy and Power Engineering,
Xi'an Jiaotong University,
Xi'an 710049, China
e-mail: zhouyy@stu.xjtu.edu.cn

Jianlin Yu

Department of Refrigeration and Cryogenic
Engineering,
School of Energy and Power Engineering,
Xi'an Jiaotong University,
Xi'an 710049, China
e-mail: yujl@mail.xjtu.edu.cn

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received January 17, 2015; final manuscript received April 5, 2016; published online April 26, 2016. Assoc. Editor: Amitabh Narain.

J. Heat Transfer 138(8), 081501 (Apr 26, 2016) (9 pages) Paper No: HT-15-1043; doi: 10.1115/1.4033347 History: Received January 17, 2015; Revised April 05, 2016

Falling film type condensers/reboilers applied to cryogenic air separation units (ASUs) have drawn more attentions in recent years. This paper presents and analyzes a mathematical model for the falling film plate-fin condensers/reboilers (FPCR). In the modeling, both the laminar falling film evaporation and condensation processes, incorporating with interference of mass transfer and interfacial shear stress, are considered, and related to a plate-fin heat exchanger (PHX). The liquid film flow and heat transfer characteristics of oxygen and nitrogen fluids in the PHX are analyzed under given conditions by solving the model with a numerical iteration method. The variations of liquid film thicknesses and local heat transfer coefficients of oxygen and nitrogen as well as the total local heat transfer coefficient have been obtained. Furthermore, the effects of the inlet mass flow rate allocation ratio (i.e., the ratio of inlet mass flow rate of oxygen liquid over the base plate to that over the fin surfaces) on the wetted length of the heat transfer surfaces, the heat transfer performance, and the oxygen liquid circulation ratio (i.e., the ratio of the inlet liquid mass flow rate to the generated vapor mass flow rate) are also discussed. A proper inlet mass flow rate allocation ratio of oxygen liquid is presented. The wave effects are further considered and analyzed through the inclusion of a model for the wave factor.

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Figures

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Fig. 1

A typical ASU flowsheet

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Fig. 2

Schematic diagram of a falling film type PHX: (a) A 2D schematic of computational elements; (b) a 3D schematic of a computational oxygen passage; and (c) oxygen and nitrogen liquid films over the base plate

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Fig. 3

Flowchart of the calculation procedure

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Fig. 4

Liquid film thicknesses and local heat transfer coefficients on base plate and fin surfaces versus the channel length: (a) oxygen side and (b) nitrogen side

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Fig. 5

Variation of the temperature distribution versus the channel length

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Fig. 6

(a) Local heat transfer coefficients versus the channel length. (b) Comparison of heat transfer coefficient values based on the proposed model with those evaluated by experimental correlations from literature.

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Fig. 7

(a) Liquid film thicknesses on base plate and fin surfaces versus channel length under different inlet mass flow rate allocation ratios of oxygen fluid and (b) variation of wetted length with the inlet mass flow rate allocation ratio

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Fig. 8

Oxygen circulation ratio versus the channel length under different inlet mass flow rate allocation ratios of oxygen fluid

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Fig. 9

Total local heat transfer coefficient versus the channel length under different inlet mass flow rate allocation ratios of oxygen fluid

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