Condensation of NH3 within a plate heat exchanger of small diameter channel

Conference paper (2019)

Authors

X. Toa Engineering Thermodynamics - Mechanical, Maritime and Materials Engineering
J.A. Kirkenier Bluerise
C.A. Infante Ferreira Engineering Thermodynamics - Mechanical, Maritime and Materials Engineering
Research Group
Engineering Thermodynamics (Mechanical, Maritime and Materials Engineering) (TU Delft)
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Published Date

2019

Language

English

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Faculty

Mechanical, Maritime and Materials Engineering

Department

Process and Energy

Research Group

Engineering Thermodynamics

Abstract

Most plate heat exchangers (PHEs) have hydraulic diameters in the range of 2∼5 mm and show characteristics of both macro-channels and micro-channels. Both gravity and surface tension have non-negligible influences and determine the heat transfer and frictional pressure drop.

This paper investigates NH3 condensation in a PHE with a hydraulic diameter of 2.99 mm. The large surface tension of NH3 enhances the micro-channel characteristics. The heat transfer coefficients (HTCs) are compared with homogeneous and separated models, respectively. Both models have been previously compared with the experimental data of HFCs, hydrocarbons and HFOs. The prediction for NH3 is generally good since the deviations are small, while the sensitivity to mass fluxes and vapor qualities cannot be estimated properly. The data of frictional pressure drop are predicted by a correlation of two-phase Fanning friction factor, which is based on homogeneous flow and includes the influences of mass fluxes, vapor qualities, hydraulic diameters, chevron angles, etc. The fluid properties of NH3 are significantly different between liquid and vapor phases, and the averaged density derived from homogeneous flow is under-estimated. The prediction is improved by calculating the averaged density from the void fraction models of separated flow.