temperature 100 C, and evaporator temperature 20 C.
R245fa is chosen as the working fluid and the estimated COP
of ECS is 0.63, not including pumping power. The ECS design
specification is shown in Table 2. The ejector design using 1-
D ejector model (Huang et al., 1999) for ECS of SACH-k2 is
shown in Table 3.
2.3.1. Control of generator liquid level
The generator of ECS is designed in shell-tube type as shown
schematically in Fig. 5. Liquid refrigerant (R245fa) is in the
shell side and the heating fluid (glycol water from solar collector)
is in the tube side. Refrigerant vapor is generated in the
shell side to drive the ejector. Instantaneous variation of solar
radiation intensity may result in large variation of liquid level
in the generator of ECS. Conventional high-low level control
(ON/OFF) will cause large variation in generator temperature/
pressure and unstable performance of ECS. A level control
system is thus developed in the present study. A refrigerant
gear pump with variable-speed motor (300e2000 rpm,
maximum power input 750 W, maximum pumping head
140 kg cm2) was used for liquid level control in generator. The
feedback control system uses a float-type magnetic liquid
level gage to measure the level and to vary the flowrate by
regulating motor speed of pump to control the level.
The liquid level should be controlled at certain level of
accuracy in order to provide stable pressure to the ejector. The
liquid level should be higher than the heating tubes to ensure
better heat exchanging. The level control system will accurately
control liquid level at 12 1 cm from the bottom of the
generator. Fig. 6 is the feedback control system to adjust the
inlet liquid flowrate to the generator. The proportionalintegral
control algorithm (PI) was implemented in the
controller.