Modeling of Automotive A/C Evaporators 2002-01-1287

In this paper a model for Automotive Air Conditioning evaporators is presented, including a comparison between calculated and measured results for two different types of evaporator: tube and fins and plate and fins.

The development of the model has been carried out by the Universidad Politécnica de Valencia in co-operation with the Universidad Politécnica de Catalunya and two companies: FASA-RENAULT and FRAPE-BEHR, under a research project supported by the Spanish Agency for R&D: CICYT.

The input data for the model are the HEX geometry and the inlet conditions and mass flow rate of both flows. Then the model calculates the outlet conditions and all the performance parameters.

The developed model is able to take into account the following aspects of the HE:

• Tube or plate evaporators as well as any flow configuration: parallel, counter-flow, cross-flow and multi-pass.
• Any distribution of fluid speed and temperature at the HE inlets
• Any refrigerant, with water or air as secondary fluid
• Local evaluation of the thermodynamic properties of the fluid, providing a detailed knowledge of the distribution of these properties along the HE
• Local evaluation of the heat transfer and friction coefficients
• Longitudinal conduction through the evaporator walls

The flow through the HE is considered to be steady. The refrigerant flow inside the tubes or channels is considered to be one-dimensional. The refrigerant flow is divided into the different circuits, and each circuit is divided in small pieces, i.e. refrigerant cells. The air flow through the HEX is divided in 1D air cells including the exterior part of the piece of the tube of a refrigerant cell and a number of fin plates.

The experimental data measured in the test bench of the company for two different evaporator models working with refrigerant R134a have been compared with those predicted by the model for a wide range of operating conditions.

The performed comparison shows that the model is able to predict evaporator's performance (refrigeration capacity, outlet temperatures and pressures) within a ± 5%. This proves the model to be a helpful tool for evaporator design and optimization.