## 2 Experiment Instrumentation  
The steam ejector refrigeration system is mainly composed of four components: a generator, a steam ejector, an evaporator, and a condenser. Other experimental components include a storage tank, a water ring vacuum pump, an evaporative condenser, pressure regulating valves, vacuum gauge and pipes, as displayed in Figure 1. The steam generator generates saturated steam with a certain pressure and temperature, then the saturated steam passes through a steam-pressure regulating valve and reaches the steam storage tank. The high-speed primary fluid from the steam storage tank entrained the vapour from the evaporator through the ejector to achieve the purpose of refrigeration and then discharges into the condenser for the next cooling cycle. A water ring pump is installed at the outlet of the water-cooled condenser and supplies a stable back pressure for the steam ejector as the back-pressure pump. It is used to cool the high-temperature steam in the condenser to prevent the pump body from being corroded and stabilize the gas pressure in the condenser. The purpose of installing evaporative condenser is to make the condensed water from the condenser cool down rapidly so that it can enter the next cooking cycle quickly and improve the cycling efficiency of the refrigeration system. The steam ejector outlet is equipped with a back pressure regulating valve to regulate the back pressure at different levels. The secondary fluid is evaporated from the evaporator, and its mass flow rate is measured by the vortex shedding mass flow meter. The measurement and control of the primary fluid pressure are mainly achieved by means of a pressure transmitter, a PID controller and a pressure regulating valve. The pressure transmitter not only measures and displays the pressure, as a pressure gauge but also converts the pressure in the steam storage tank into an electrical signal sent to the PID controller. The PID operator automatically acquires a given signal from the system and valve position feedback signal and adjust the output of the corresponding control according to the difference between the pressure and the electrical signal. Then the pressure regulating valve will change the mass flow of primary fluid after accepting the DC signal from the PID controller. Therefore, the experimental primary fluid pressure can maintain at a given value.  
A T-type thermocouple temperature control meter measures the temperature of the water in the evaporator which constantly adjusts to the temperature to reach the preset temperature, making sure the experiment can work under set conditions. 15 small holes are evenly opened on the ejector wall to measure the static wall pressure. The vacuum valve is connected to each hole through the vacuum silicon tubes. The pressure is carried through the valve and measured by the film vacuum gauge in turn. The error of the pressure transmitter of the full-scale is 0.5%. The instrument used to test the wall pressure is a film vacuum gauge with an error of 0.25% of the full scale. The mass flow rate of the secondary fluid is measured by a vortex flowmeter with the uncertainty of less than 0.33% and with the accuracy of 1%. The T-type thermocouple temperature control meter is used to measure the temperature with an error of \(\pm\) 1 \({}^{\circ}\)C and an error of 0.5% of full scale. Besides, energy balance analysis was performed on the evaporator, generator and condenser during equipment commissioning to ensure measurement accuracy.  
The cooling capacity of the experimental system is 12.5 kW. The maximum pressure and the saturated temperature of steam provided by the generator are 0.44 MPa and 148 \({}^{\circ}\)C, respectively. The cooling water circulating flow rate is 0.34-0.9 m\({}^{3}\)/h. The geometric parameters of the steam ejector are shown in Table 1. The operating conditions of the steam ejector are shown in Table 2.