Assessment of the background oriented schlieren application in testing the temperature limit of an axisymmetric ventilation jet

Authors:

• Jacek Hendiger,
• Marta Chludzińska,
• Piotr Ziętek

Abstract

The aim of this study was to assess the potential of applying the Background Oriented Schlieren (BOS) technique to test the temperature limit of a non-isothermal ventilation jet used in ventilation. The BOS technique is potentially simple when used under real conditions with no optical sets and the presence of architectural or logistic obstacles. So far, optical methods with higher sensitivity have been used for qualitative tests. This study examined whether this method could be used for qualitative tests in heating and air-conditioning, where low temperature differences pose a challenge. Analyses were performed using a nozzle with a diameter of 100 mm. Measurements were carried out in air at 28 L/s. Temperature differences of −5 K and +10 K were applied between the supply air and environment. The tests were carried out in two stages: empirical measurements using thermal anemometry probes, followed by visualisations using the BOS technique. The test results demonstrated the effectiveness of the BOS application in testing the temperature limit of a ventilation jet. This made it possible to determine a temperature limit corresponding to a total temperature difference in the jet of 2 K. Analyses showed good agreement between empirically and theoretically obtained values for the temperature distribution in the jet. The application of the BOS technique in this kind of test may be limited by a minimum temperature difference, which will ensure that the results obtained will be accurate. However, this can be improved by fine-tuning the image analysis and enhancing the test equipment parameters.