Testing : Thermal Management

MIRA is one of the world's leading consultancies for vehicle thermal management.  In developing this service MIRA has built up one of the most comprehensive suites of thermal management development facilities to be found on one site.  Our expertise in testing powertrain cooling and climate control systems on vehicles ranges from motorcycles, through passenger cars and commercial vehicles up to the unique challenges presented by a main battle tank.

MIRA has a unique combination of expertise in thermodynamics, computational simulation techniques including CFD, test facilities and supporting services.  Our approach is covered in more detail in our Thermal Management Consultancy pages.

Our thermal management testing services include:

Powertrain Cooling

The under-bonnet (underhood) environment presents a considerable thermal management challenge.  Under-bonnet packaging constraints are extremely tight, engines are increasingly powerful and there is the need to locate more heat sensitive components, such as electronic control units.  Meeting this challenge requires an accurate understanding of the temperatures and airflows.  This knowledge enables MIRA's engineers to identify areas of risk, target resources to raise the vehicle's limiting ambient operating temperature.  In turn this leads to:

• Improved reliability
• Access to new markets
• Reduced warranty claims

Instrumentation is used to determine:

• Temperature control of coolants, fluids and lubricants
• Underbonnet temperature control

Typical workscope:

• Determination of heat exchanger flow/pressure drop characteristic
• Evaluation of installed coolant pump flow performance
• Measurement of underbonnet airflow rates
• Powertrain cooling tests in Climatic Wind Tunnel (CWT)
  • Gradient test - Gross Vehicle Weight
  • Gradient test - Gross Towing Weight
  • Maximum speed test? Idle test
  • Key-off hot soak test

HVAC / Climate Control System Evaluation and Development Activities

Now standard fit on most vehicles the climate control system is unusual in that drivers and passengers only tend to notice it if it is malfunctioning; causing discomfort due to obtrusive airflow, temperature or noise.

MIRA has experience of evaluating the performance of climate control systems on a wide range of vehicles.  A typical system evaluation includes:

Air conditioning system test bench testing

The air-conditioning system test bench enables prototype AC systems to be fully engineered before installation, reducing vehicle development times. The system under development is installed in to the rig with the various components mounted in the same manner and orientation as intended in the vehicle. The chambers of the rig act as the vehicle under-bonnet and cabin environments with metered and conditioned air-flows supplied to the relevant heat exchangers. A variable speed electric motor drives the A/C compressor allowing the system to be operated as it would be on the vehicle. The ability to develop the A/C system in isolation from the vehicle enables work to be started much earlier in the programme and reduces the need for full vehicle prototypes.

Cabin mock up

In some instances MIRA’s engineers build a representation of the vehicle’s cabin to evaluate the system’s IP performance in the laboratory. This cabin mock up enables evaluation of characteristics such as the defrost / demist airflow pattern without a prototype vehicle.

Full Evaluation of Body Leakage

In order to account for ram airflow, these tests are usually conducted at five vehicle speeds in our Full Scale Aerodynamic Wind Tunnel.  As an alternative, where ram air effects are deemed to be negligible, static body leakage tests can be conducted in the thermofluids laboratory.  Both techniques provide a measure of vehicle body leakage and calibration of leakage flow rate against pressure drop across vehicle boundary.  To quantify body leakage an equivalent hole size is calculated which is a measure of body sealing, build quality and control of extract flow.

Interior Airflow Test

Determination of vehicle interior airflow with the climate control system controls at various settings. This evaluation is again conducted at five air speeds in the Wind Tunnel, and uses the body leakage calibration curves to derive absolute volumetric flow rates of air through the passenger compartment.

Individual Air Vent Flow Analysis

The air flow rate from each individual vent outlet is measured using non-restrictive flow metering apparatus. This leads to a full description of air flow distribution within the vehicle interior.

Defrost / demist Test

In addition to ensuring customer satisfaction, passing a defrost test is a legislative requirement.  The defrost and demist performance of the vehicle is evaluated by subjecting the vehicle to controlled freezing conditions and then monitoring screen and side window clearance patterns against time following heater turn-on. This work would be conducted in the MIRA Environmental Chamber or the Climatic Wind Tunnel (CWT).

Heater Core Evaluation

Determination of coolant pressure drop across the heater core over a range of flow rates at three different inlet temperatures. The calibration data derived from this exercise is then used to determine installed flow rates throughout CWT testing.

Air-Conditioning Performance Evaluation

Temperature pull-down tests carried out at various vehicle speeds in the CWT. A wide range of underbonnet and interior temperatures are derived from this study, and plotted against time. This evaluation is usually conducted at two elevated ambient temperatures, typically around 35°C and 48°C. The maximum temperature for testing in the CWT is 55°C.

Heater Performance Evaluation

A similar test schedule to the A/C test is conducted for the heater performance, with ambient conditions now set at sub-zero temperature levels - typically around -20°C. Minimum ambient temperature achievable in the CWT is -40°C.

Heater Controllability

The controllability of the interior temperature is assessed by monitoring temperature at specific locations and at incremental settings of the heater controls. Results of this study are presented in terms of heater controllability vs time, and temperature control curves.

Air-Conditioning Controllability

The controllability of the interior temperature is assessed by monitoring temperature at specific locations and at incremental settings of the air conditioning controls. Results of this study are presented in terms of A/C controllability vs time, and temperature control curves.

Statistical subjective appraisals

Being representative of the real-world conditions in which a vehicle’s climate control system is expected to perform makes MIRA’s CWTs ideal for subjective appraisal of the system performance.  The controlled and repeatable environment enables control strategies and potential failure modes to be replicated and experienced by members of the development team. Statistical subjective appraisals involve the recording of a range of individuals’ opinions of their comfort against a subjective scale. As well as being a usual requirement for final system sign-off, this can be useful at the target setting phase particularly when developing systems for new markets.

Condensate drain tests

These tests are conducted subjectively in various vehicle orientations on MIRA’s proving ground.

Thermal imaging

Non-intrusive analytical techniques such as this thermal imaging camera give repeatable and accurate results. It is a versatile technique that enables quick appraisal with minimal instrumentation. It is useful for:

• Heat exchanger studies
• Defrost/Demist distribution evaluation and guide-vane development
• Heated seat performance
• Areas where conventional techniques are intrusive or inaccessible

Complementary Services and Facilities

Thermal management testing is part of MIRA's comprehensive capabilities for thermal management, aerodynamics and fluid dynamic .  Further details of which can be found using the following links:

Thermal Management Consultancy

Aerodynamic Consultancy

Climatic Wind Tunnel – CWTone
Climatic Wind Tunnel – CWTtwo
Fluid Systems Engineering Centre
Full Scale Aerodynamic Wind Tunnel
Model Scale Aerodynamic Wind Tunnel
Computational Fluid Dynamics (CFD) suite
Extensive Proving Ground test circuits