Performance of Compact Heat Exchanger in Non-Perpendicular Cooling Airflows
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During recent years the main focus in the vehicle industry has been on cutting
the fuel consumption and emissions as well as improving the vehicle performance.
To be able to meet these demands additional systems are being introduced
into the vehicle. These implementations do not only affect the engine
power and the emission levels, they also tend to increase the operating temperature
in the engine bay, which in turn increases the cooling demand. Therefore,
a trend toward increased cooling performance for vehicles is also seen. There are
a number of solutions to solve this demand and for heavy vehicles the most suitable
way is to install additional heat exchangers positioned at other locations in
the vehicle, due to the limited underhood space. These extra heat exchangers
may not be located in the most appropriate position and it is not unusual that
the airflow is not perpendicular to the heat exchanger core. For some vehicles
today these types of installations can already be seen. Therefore, it is important
to evaluate the effects on cooling airflows. Since both heat transfer and pressure
drop over the heat exchanger will be affected by the angled airflow these parameters
as well as the flow field characteristics, have to be analysed and evaluated.
This thesis presents a performance evaluation of standard automotive compact
heat exchangers and their performance in non-perpendicular airflows. Four angles
have been tested to predict variances in pressure drop, heat transfer rates
and airflow characteristics. Laboratory experiments and 3D Computational
Fluid Dynamics (CFD) simulations have been conducted to study the effects.
Methods have been developed to simulate heat exchangers in angled conditions
as well as internal parts of the core. The results have been correlated with the
experiments to find similarities and deviations.
The results showed that the additional loss due to the angling of the heat exchanger,
is due to the forced re-direction of the airflow into the core. This loss
is increased with the magnitude of the angling. Neither the static pressure drop
nor the heat transfer rate was significantly affected by the inclination angle of
the heat exchanger relative to the airflow. To reduce the pressure drop within
the installation the surrounding geometries had to be considered to prevent areas
of losses. If a specific installation is going to be evaluated the information
presented in this thesis is of great importance and could be used to find an
optimal design for the system.

Thursday, January 1, 2015
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