# Experimental Research on the Effects of Suction Ports on Twin Screw Expander Performance
## 1 Introduction  
Coal, oil and natural gas consumption have increased all over the world with economic development and improvements in the average standard of living. High levels of fossil fuel consumption have caused significant environmental pollution and negative effects on human health. The sustainable development of society requires cleaner and more efficient energy. New forms of energy, such as solar energy, ocean energy and nuclear energy, have gained much attention over the last decade. The usage of low-grade thermal sources has become a popular topic for researchers all over the world. Many studies have been carried out on the recovery and utilization of energy from low-grade thermal sources [1]. Advanced new thermoelectrics may be a key technology that can be used to transform heat directly into power. Recent advances in enhancing the performance of novel fiber /fabric-based flexible thermoelectrics demonstrate an exciting direction for the development of wearable electrocardiographic systems [2, 3]. However, this technology cannot meet the demand for heat recovery in high heat capacity situations. The organic Rankine cycle (ORC) is another technology used [4] for heat-power transformation.  
The ORC system uses organic working fluid, such as refrigerant, instead of water in a traditional steam Rankine cycle. It is suitable for various thermal sources and has a larger capacity. It is appropriate for recovering excess heat from many kinds of heat sources, such as geothermal energy, solar energy, and industrial waste heat. The thermodynamic cycle,working fluids, expander, and heat exchanger all affect the performance of the ORC system. The expander used in the ORC system is the most important piece of equipment, and there are many kinds of expanders. At present, single-screw, twin screw, scroll and turbine expanders are mainly used [5; 6; 7; 8]. Screw expanders are suitable for medium-scale ORC systems. The best expander performance is obtained with a rotation speed of 3000 rpm. In terms of fluids, R123 and R245 fa are frequently used for ideal operation pressure and system performance. The maximum power output is about 300 kW [9]. Twin screw expanders have advantages similar to twin screw compressors, such as high reliability, multi-phase transportation and good dynamic balance. The calculation of geometric characteristics can be performed according to the twin screw compressor method.  
An ORC's performance is affected by the temperature of the heat source and thermal power fluctuations. A fluctuating heat source results in a reduction in the isentropic efficiency of the expander and, consequently, a reduction in system efficiency [10]. [PERSON] et al. presented numerical investigations of a twin screw expander for low-grade (\(\leq\)100 \({}^{\circ}\)C) heat-to-power conversion applications based on the bottoming Trilateral Flash Cycle [11]. An analysis of the effects of different inlet qualities of the R245 fa working fluid and of the revolution speed on the expander's performance was carried out. Different aspects of the performance of the twin screw expander, such as rotational speed, torque and output power, are all influenced by the inlet pressure of the expander [12]. [PERSON] et al. designed a detailed contrast experiment on three expanders and investigated the effects of the suction port area and the rotor length on the expander's performance [13]. By analyzing the measured p-\(\theta\) diagrams of twin screw expander, the features of the working process were identified [14].  
Based on previous research, geometric construction has a significant effect on the performance of twin screw expanders. Among the various factors, suction ports play a significant role in the suction process. In this paper, an experimental investigation into the pressure loss caused by suction ports is carried out. The effects of suction ports on the pressure loss value, the suction process and performance are discussed.