Modeling Two Phase Flow Heat Exchangers for Next Generation Aircraft
Hayder H. Al-Sarraf †, Assaad Alsahlani ‡
‡Department of Aeronautical Technical Engineering- Engineering-Technical College / Najaf, ALFurat Al-Awsat Technical University, 31003 Al-Kufa, Iraq
ABSTRACT: This work presents modeling of two- phase flow heat exchangers to be used in modeling of NASA’s next-generation aircraft (N3- X). The heat exchanger model, which could be a condenser or an evaporator, currently accommodates two working fluids; kerosene (jet fuel) and a refrigerant (R134a). The primary goal is to obtain a dynamic, robust model by using numerical simulation tools (MATLAB/ SIMULINK) which can simulate the system efficiently and would be used in the conceptual aircraft (N3-X) model. The final goal is to investigate the influence of pressure and enthalpy perturbations on the system. In other words, how quickly this system responds to change to perturbations, therefore the model will be transient. Two examples are used for demonstration of the transient response of a two-phase heat exchanger to a perturbation in pressure and enthalpy. Initially, pressure perturbation variation effects on how the quality of R134a effects the magnitude of the two-phase flow heat transfer coefficient, therefore the two-phase heat transfer rate calculated. This changing pressure approach used to provide a rapid thermal response to a rapid thermal load variation. For this analysis, a sample time of 0.000001 seconds was used. In addition, an enthalpy perturbation was investigated. Since, changing pressure suddenly from the higher value (650 kPa) to the lower value (555 kPa) is not a real, physical scenario in life, the pressure change with transfer function would be employed to transform the system into a first-order system with two different time constants. Eventually, the time constant of the system plays a significant role in obtaining a quicker response.
Keywords : Two-phase flow; Heat exchanger; Pressure Perturbation; N3-X aircraft; Transient response