Abstract
KEYWORDS – Aluminium, exchanger, microbial contamination, inoculation, corrosion
ABSTRACT –
Research and/or Engineering Questions/Objective
The context of this study is the microbial proliferation on aluminium heat exchangers. Different studies have been carried out on this topic but only on steel and stainless steel alloys. These studies revealed an important impact of some bacteria on steel material corrosion resistance. We know that microbial contamination of parts leads to vehicle odour problem and we demonstrated that the contamination at high concentration can be harmful to aluminium corrosion resistance in a short time [F2014-LWS-075]. The objective of the study is to develop a specific test for microbial proliferation control and evaluation.
Methodology
The objective of the study was to establish a test method to evaluate the heat exchanger microbial development. For that, we implemented a protocol to establish an accurate and repeatable procedure to ensure the test of aluminium heat exchangers. The first step of the test consists in the cleaning of the heat exchanger by de-ionized water and sampling. Aluminium samples are place inside Petri dishes containing growth media. The test is based on inoculation of the aluminium samples by microbial solutions containing a mix of several strains of interest. Then, the preparation is put inside climatic chamber under temperature and humidity control to insure optimal microbial development. After the incubation phase, the observation of samples is performed by macroscopic views to conclude on the microbial contamination proliferation and then by microscopic views to check the growth impact on the aluminium materials.
Results
This protocol has been applied on aluminium evaporators. These products are integrated in climatic cooling loop. These exchangers have the particularity to condensate a high quantity of water leading to microbial contamination proliferation. During the tests, we observed a microbial growth on the aluminium samples. That allows us to confirm the efficiency of the protocol. Then, we were able to quantify the proliferation and surface concentration by analyzing macroscopic views of the samples. Finally, an investigation of the test impact on corrosion resistance of the aluminium has been done by microscopic analyses.
Limitations of this study
Limitation of this study is the automotive field of application because the microbial contamination is specific to the Aluminium exchangers present inside vehicle architecture.
What does the paper offer that is new in the field including in comparison to other work by the authors?
The first investigations revealed aluminium microbial contamination impacts on corrosion and odour issues. That the reason why we had to develop a new specific test to control the microbial proliferation on heat exchangers.
Conclusions
This study permits to develop a new test for heat exchanger microbial seeding impact evaluation. We are now able to rank our technologies thank to the reliability of the test and so evaluate the impact of our process steps (thermal treatment, surface treatment, materials used…).