Abstract
Mixed refrigerant cycles (MRCs) offer a cost- and energy-efficient cooling method for the temperature range between 80 and 200 K. The performance of MRCs is strongly influenced by entropy production in the main heat exchanger. High efficiencies thus require small temperature gradients among the fluid streams, as well as limited pressure drop and axial conduction. As temperature gradients scale with heat flux, large heat transfer areas are necessary. This is best achieved with micro-structured heat exchangers, where high volumetric heat transfer areas can be realized. The reliable design of MRC heat exchangers is challenging, since two-phase heat transfer and pressure drop in both fluid streams have to be considered simultaneously. Furthermore, only few data on the convective boiling and condensation kinetics of zeotropic mixtures is available in literature. This paper presents a micro-structured heat exchanger designed with a newly developed numerical model, followed by experimental results on the single-phase pressure drop and their implications on the hydraulic diameter.
Highlights
In recent years, the application of Mixed refrigerant cycles (MRCs) as a reliable and ecient refrigeration method for hightemperature superconductors in cables, fault current limiters, etc. has been reviewed [13]
This paper presents a micro-structured heat exchanger designed with a newly developed numerical model, followed by experimental results on the single-phase pressure drop and their implications on the hydraulic diameter
The uncertainty of the hydraulic diameter estimated in section 2.2, accounts for over 99 % of the error bars of the calculated pressure drop
Summary
The application of MRCs as a reliable and ecient refrigeration method for hightemperature superconductors in cables, fault current limiters, etc. has been reviewed [13]. A correlation-based, numerical heat exchanger model has been presented, capable of calculating heat transfer and pressure drop of zeotropic uid mixtures simultaneously along the length of the heat exchanger [5]. Utilising this model, a micro-structured heat exchanger was designed for future use in MRCs. The counter-ow heat exchanger was produced by diusion welding of 60 micro-structured sheets (stainless steel grade 1.4571). Av ρv where A depicts the cross-section area and ρ the uid density Both isotropic wet-chemical etching and face-to-face stacking typically do not yield exact channel geometries.
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