Investigating the conjugate heat transfer phenomena on various ducts for aircraft environmental control system

Abstract

All commercial aircraft employ a system called Environmental control system (ECS) to ensure an environment that accomplishes the physiological and comfort demands by passengers and aircrew. This task requires functionalities like temperature control, humidity regulation apart from the governing of cabin pressure. The energy source for ECS is a pressurized hot air bleed (180 °C-250 °C, 2.75 bar) from the engine or Auxiliary Power Unit (APU) along with the ram air. During the functional operation, the unit of Heating, Ventilation, and Air Conditioning (HVAC) duct experiences repetitive temperature fluctuations in addition to the cyclic pressurization leading to thermal fatigue and cyclic stress over the duct material, promoting crack propagation at weld zones in the duct. Therefore, a comparative investigation on conjugate heat transfer analysis is done at welded joints annexed to the bypass valve and trim air valve using airflow bench set up and validated by computational fluid dynamics. During this investigation, the circular duct with spherical junction (D/d = 3.84 & L/d = 6) was the most efficient and economical design that could fit in for designing air conditioning duct undergoing high thermo-cyclic stress.