7/24/2009. CFD study of a passenger car HVAC system. Marcelo Kruger Victor Arume de Souza Regis Ataides Martin Kessler Cesareo de La Rosa Siqueira

Transcription

1 CFD study of a passenger car HVAC system CFD study of a passenger car HVAC system Marcelo Kruger Victor Arume de Souza Regis Ataides Martin Kessler Cesareo de La Rosa Siqueira Gustavo Maia Vinicius Leal 1 1

2 Agenda Introduction Goals Computational model Geometry Mesh Boundary condition Results Remarks Introduction Following Hucho et al ( Aerodynamics of Road Vehicles ), every consideration of air conditioning of cars must be focused on its occupants. In this sense, thermal comfort inside a vehicle is a major concern in automotive industry. In tropical countries, such as Brazil, car HVAC system should guarantee a comfortable environment for the passengers, and specially for the driver, his/her alertness and ability to concentrate on traffic depends on this level of comfort

3 Goals Develop and implement a computational model to evaluate the main flow characteristics on the interior of a passenger car HVAC system; Based on the model, study the temperature rise that air experiments when passing through the duct system, influenced by the heat that stems from the engine, for different mass flow rates; Determine how much the mass flow rate influence the temperature at the outlet. 5 Computational Model - Geometry Air Inlet 1 st Region 2 nd Region 3 rd Region 6 3 3

4 Computational Model - Geometry Inlet grid 7 Computational Model - Mesh Hybrid Mesh: tetrahedral + prisms About 4,8 millions of elements 8 4 4

5 Computational Model - Hypotheses Steady state flow; Incompressible; Turbulent; Fluid properties: Air Density: 1,225 [kg/m 3 ] Viscosity: 1,7894e-05 [kg/m s] 9 Computational Model Boundary Conditions Inlet mass flow: Model Inlet mass flow (m³/h) Case Case Case Case Inlet temperature: C (300 K) Outlet with atmospheric pressure

6 Computational Model Boundary Conditions Prescribed temperature (experimental) on the walls 2nd Region Position Temperature [ºC] Point 31 50,9 Point 32 46,5 Point 33 48,5 Point 34 45,3 Point 35 49,3 Point 36 48,8 1st Region Point 37 - Point 38 53,5 Point 39 47,2 Point 40 42,4 Point 41 50,6 11 Computational Model Boundary Conditions Prescribed temperature (experimental) on the walls 3rd Region Position Temperature [ºC] Point 01 44,6 Point 02 46,7 Point 03 48,5 Point 04 45,8 Point 05 46,4 Point 06 49,8 Point 07 51,8 Point 08 49,3 Point 09 47,0 Point 10 49,3 Point 11 49,6 Point 12 50,4 Point 13 51,0 Point 14 49,6 Point 15 48,1 Point 16 46,9 Point 17 47,

7 Results Fluid flow features evaluated: Velocity field to identify recirculation areas, zones of death (low velocities) volume, where the fluid could be for a long time, increasing the temperature; Streamlines; Temperature field; 13 Results Velocity field 228m 3 /h 260m 3 /h 290m 3 /h 320m 3 /h m/s 7 7

8 Results Velocity Vectors at outlet 4 228m 3 /h 260m 3 /h 290m 3 /h 320m 3 /h 15 Results Temperature field 228m 3 /h 260m 3 /h 290m 3 /h 320m 3 /h

9 Results Heat Transfer Mass flow [m 3 /h] Outlet Average Temperature [ C] Heat transfer in the walls [W] Inlet Temperature = C (300K) Results Streamlines 4 228m 3 /h 260m 3 /h 290m 3 /h 320m 3 /h

10 Results Mass flow [m 3 /h] Mass flow variation % Heat Transfer [W] Heat transfer variation % The flux of 228 m 3 /h has been used as the reference. Remarks The development of the numerical model allowed to better understand the flow behavior inside the HVAC system; The influence of mass flow on heat transfer inside the HVAC system has been evaluated; The streamlines and temperature field at outlet have shown very similar behaviour for all configurations; The velocity vectors and streamlines indicated some recirculation areas, thatt could be responsible for increasingi of temperature;

11 Remarks The outlet average temperature indicated an increasing of 11 C comparing with the inlet temperature; The temperature variation at the outlet suffered little influence due to variation on mass flow rate. For all four mass flow rates considered (40% change between the smaller and the larger mass flow rates) the average temperature at the outlet stayed within one degree Celsius range. The heat transfer, on the other hand, changed significantly due to mass flow rate: the heat transfer suffered an increase of around 31% between the smaller and the larger mass flow rate. 21 Thanks! Contact: Marcelo Kruger kruger@esss.com.br 11 11