Thermal Management on the Test Stand

May 31, 2019

Media-carrying components are essential for electromobility. To validate them for their application, valves and hoses, tubes and housings as well as cooling and heating systems must be tested thoroughly under changing pressure and temperature conditions. For electrical appliances, the added analysis of performance and power consumption over the entire service life contributes to improving energy efficiency.

Author: Johannes Montag

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X-Ray car. computer generated image..

Mobility requires reliable thermal management so that man and machine can adapt to varying environmental conditions. Climate-control systems and all their components must permanently withstand extreme load changes. Instead of testing the load-bearing capacity with proprietary test setups or in real operation, manufacturers can now put their components to the test with the aid of pressure cycling and function test benches. From an early stage of development and during series production, the repeatable and precise tests enable products to be optimized flexibly and economically.

Pressure Cycling at -40°C to +140°C

In order to test the quality or to validate a new product within the scope of an audit, the component is inserted into the test chamber of the pressure cycling test bench. This can be a complete auxiliary heater for an electric car or individual valves, hoses and other hollow bodies that must be able to withstand several hundred thousand load changes over e.g. 15 years. The test medium is a water-glycol mixture or pure glycol (e.g. Glysantin G40, G44, G48). The cooling circuit is typically tested in a temperature range from -40°C to +20°C (-40°F to +68°F), the heating circuit from +20°C to +140°C (+68°F to +284°F). A specially developed closed test media circuit uses pressure to prevent the formation of vapors containing alcohol (risk of explosion). An environmental simulation can be generated in an optional climate chamber at temperatures ranging from -40°C to +150°C ( -40°F to +302°F).

The flow rate of the test medium can vary from 1 to 50 l/min at a pressure of 0.2 to 12 bar or higher. The load changes are freely programmable with sinusoidal or trapezoidal rise at a test frequency of 0.2 to 2 Hz or faster. Static and dynamic pressure tests, leak tests and vacuum tests can be performed. The testing system can be used to test complete systems, assemblies and components made of various plastics, metals and sealants. Products made of new materials can thus be reliably validated. With the aid of realistic simulation, the weak points in the material combination – for example around a weld seam – are precisely sounded out and can be optimized early in the development process as well as during production.

Energy Efficiency in Battery Operation

Situated in central Germany in the historic town of Nordhausen is a company at the forefront of R&D for testing systems. Poppe + Potthoff Maschinenbau  offers a function test bench for electrical appliances such as cooling and heating units, control valves, pumps, etc..

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The function test bench measures the consumption and performance data of heating and cooling units under changing temperature conditions so that their efficiency can be optimized.

At alternating temperatures, power consumption and performance are tested – optionally with low or high voltage power supply to simulate operation via on-board battery and generator or the traction accumulator. Heating and cooling still costs a lot of range on the way to electric mobility, since the required electricity must be diverted from the battery power. Realistic tests on the test bench help to precisely measure and improve the energy efficiency of the units. The comparison of test results before and after the load test on the pressure cycling test bench also shows how power consumption and performance change over the service life.

The test object is connected to the desired power supply (low voltage 0 to 20VDC / 5A) or high voltage (0 to 600VDC / 150A) and the test media circuit. The test medium (water-glycol mixture or pure glycol, e.g. Glysantin G40, G44, G48) circulates at a freely adjustable temperature of -35°C to +100°C (-31°F to +212°F) and a flow rate of 1 to 50 l/min. Optionally, the test can also be carried out in a climatic chamber at -40°C to +140°C (-40°F to +284°F) in order to simulate changing ambient temperatures, as they can also occur on the vehicle test tracks in the arctic cold or desert heat.

Time-Lapse for Lifetime Tests

A comprehensive long-term test usually takes 20 to 30 days – depending on the selected frequency of the load changes. The temperature and volume flow of the test medium as well as the ambient temperature vary around the clock according to the programmed test cycles, if the test takes place in the climatic chamber. The temperature at the inlet and outlet of the test object is measured continuously, as well as the flow rate, pressure and pressure drop, current and voltage in the high and low voltage range. The focus is on the thermal and electrical performance of the heating and cooling unit under varying environmental conditions. Optionally, thermal sensors can be mounted on the product to indicate during the test where energy is lost (thermal bridges) or where the component becomes very hot (fire hazard).

Safe and Easy to Operate

The test benches are very easy to operate and meet the highest safety standards. The test chamber consists of welded stainless steel, the safety window of high-strength polycarbonate. The test sequences created on the PC can simply be called up manually via coded recipe management or by hand-held scanner. Measurement data acquisition and visualization are realized with LabVIEW applications from National Instruments. All test procedures and data are automatically stored on the system and can be exported to the network for evaluation. The open software structure makes it possible to integrate additional sensors (e.g. thermal sensors) and data during testing. This means that the system can be extended at any time to map numerous customer-specifically relevant parameters. Testing services as well as prompt service via remote maintenance and on-site technicians are also part of the service package of the special machine manufacturer which is part of the German Poppe + Potthoff Group.

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