I have studied following domains in details

PET Blow Molding As part of the project, I was supposed to understand details of the PET blow molding process. This was required to understand the various faults that occur during the process and generate relevant reports based on the collected machine data.
De-Mineralization Learned the complete process of demineralization. That included understanding the chemistry involved. This information was to define relations between the various process parameters. Idea was to run performance analysis on the acquired data and optimize utilization of the reagents.
HVAC Learned the fundamental thermodynamics behind HVAC. Also learned in details the various control strategies that are used for climate control. Used this knowledge to do performance analysis of the acquired data and found ways to minimize energy consumption.
Wind turbines Studied in detail about grid based and grid less AC generators that are used by various wind turbines. Used the knowledge on relation between AOA with power generated to detect whether the control system are operating at optimal AOA. Also did analysis of relation between change in wind direction with respect to power generated.
Mass Spectrometry This subject was part of the product development that I was involved in. Studied this domain to very detailed level. This knowledge was used in developing very fast magnet control for the high resolution MS. Also the study helped in doing Application level RnD.