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A mass flow based generalized microchannel heat exchanger model.

Number: pap. n. 128

Author(s) : HUANG L., AUTE V., RADERMACHER R.

Summary

Microchannel heat exchangers (MCHXs) are widely used in the automotive industry and are gaining popularity in the stationary HVAC&R industry due to their compact size and lower weight. One of the practical phenomena that significantly affect the performance of a microchannel heat exchanger is refrigerant flow maldistribution. This maldistribution can occur due to header geometry or due to uneven heat transfer and pressure drop in the different microchannel tubes. The latter can happen due to air flow maldistribution on the heat exchanger face. This paper presents the development and validation of a finite volume based microchannel heat exchanger simulation model that can account for refrigerant and air flow maldistribution. A segment by segment approach accounting for flow regime change is employed in the calculation. The model is based on the epsilon-NTU method, can account for 2-dimensional air maldistribution and uses empirical correlations for the calculation of local heat transfer coefficient, pressure drop and void fraction. In the model, the various mass flow rate unknowns and corresponding residual equations are generated dynamically with the help of a junction-tube adjacency matrix. A nonlinear equation solver alongside an approximation technique is used to solve the flow distribution problem in a stable manner. The approximation technique also helps in reducing the thermo physical property calculations required, thereby speeding up the simulation. The model is validated against experimental data for a CO2 gas cooler. Furthermore, the effect on refrigerant flow due to uneven air flow on heat exchanger face is investigated.

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Pages: 9 p.

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Details

  • Original title: A mass flow based generalized microchannel heat exchanger model.
  • Record ID : 30004271
  • Languages: English
  • Source: 10th IIR-Gustav Lorentzen Conference on Natural Working Fluids (GL2012). Proceedings. Delft, The Netherlands, June 25-27, 2012.
  • Publication date: 2012/06/25

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