An Investigation of Compressor Slugging Problems
Mathematical models have been popularly applied to study the compression processes of superheated refrigerant vapor in compressors. As to the case when refrigerant enters a compressor cylinder in the state of liquid and vapor mixture, however, the availability of fundamental studies is very limited. -A mathematical model is presented to simulate the compression processes of two-phase saturated refrigerant mixture. Factors leading to slugging are analyzed. It is explained why certain types of compressors are less prone to slug. Introduction Under nonnal operation of compressors, refrigerant is drawn into compressor cylinders in the state of super heated vapor. However, liquid refrigerant, or a portion of liquid refrigerant, can enter compressor cylinders under certain circumstances, such as during the cold start of a compressor. In some of the scroll compressor applications [13], refrigerant liquid is even deliberately injected into the gas pockets to decrease the discharge gas temperature under high compression ratios and thereby to extend the operating range of such compressors. Liquid refrigerant entering compressor cylinders has been a concern for a long time. However, not enough has been achieved from the view point of mathematical modeling. An extensive literature review was done in this area, but no satisfactory thennodynamic model, which could be used to simulate the compressor cylinder processes, was found. Simpson and Lis [4] measured cylinder pressures during compressor liquid ingestion in reciprocating compressors and presented an empirical relation for predicting the maximum cylinder pressure in terms of compressor power, bore size, and stroke length. Singh, Nieter, and Prater [5-6] applied the polytropic equation to simulate compressor cylinder pressure, but the polytropic index in their model is considered as a variable and can be chosen arbitrarily. It is necessary to develop a mathematical model to predict the cylinder refrigerant thermodynamic properties instantaneously and to study the effects of liquid entering the cylinder on the compressor performance by simulating the thermodynamic process of compressing the liquid and vapor mixture. Slugging problems are detrimental to compressors. Under extreme conditions, the compressor cylinder pressures could be as high as ten times the peak pressures under normal operations [5], due to the incompressibility of liquid, consequently damaging the compressor valves and reducing the reliability and lifetime of compressors. These effects should always be avoided, if possible. Does the liquid and vapor mixture entering compressor cylinders necessarily lead w a slugging problem? It depends on the quality (the ratio of vapor mass to the total mass of the liquid and vapor mixture) of the refrigerant entering the compressor cylinders, the kinematics of the compressor, and whether the compressor is a high side design or a low side design. For compressors with low side design, since the compressor shell is filled with cool suction gas and the cylinder temperature is not very hot, a slugging problem is likely to happen because of the lack of heat transfer from the cylinder to the liquid-vapor mixture, especially during the cold start. On the other hand, the cylinder of the compressor in a high side design is heated by the relatively high temperature discharge gas, therefore the possibility of liquid slugging is reduced. Common sense tells us that slugging is more likely to occur in compressors when refrigerant of low quality flows into the cylinders. However, the influence of the kinematics of a compressor on the possibility of slugging is not so obvious, and has to be studied through mathematical modeling. Thermodynamic Model
Experimental investigation of the heating performance of refrigerant injection heat pump with a single-cylinder inverter-driven rotary compressor
Applying the refrigerant injection technology to air-source heat pump had been proved to be an effective access to acquire a better performance in the cold regions. In this paper, the test-bed of R410A single-cylinder rotary compressor vapor injection (SCRCVI) system with flash tank was built and measured by changing the compressor frequency f and injection pressure Pinj under various ambient temperatures. The experimental results indicated that the effect of refrigerant injection became stronger as the ambient temperature decreased. So the SCRCVI showed a superior heating performance at lower ambient temperature, and the conventional single-stage vapor compression (CSVC) system would exhibit higher COPh, while the ambient temperature was beyond the critical value. Compared with the CSVC system, the Qh and COPh were improved by 9.1 ~ 29.5 and 5.35 ~ 7.89%, respectively, under the ambient temperature Tod = − 10 °C. The injection pressure ratio Rp under different operating conditions was varied in the range between 0.2 and 0.22. Specifically, the trend in variation of Rp was reliably used to optimize the refrigerant injection system design and the control strategy.
Legal Process and the Discovery of Better Policies for Fostering Innovation and Growth
Our chapter concerns how legal process can lead to efficient policies for fostering innovation and growth. Future innovation will depend at least as much on how laws are made as on a priori analyses of the optimal content of those laws. Of particular importance is whether U.S. choice of law and choice of forum rules promote an efficient market for law. Our analysis supports three suggestions for improving the law to support growth. First, the rules governing the selection of the jurisdiction whose law governs productive activity can significantly affect growth and innovation. Second, any proposal aimed at increasing growth through a change in law or legal institutions should take account of the existence of multiple jurisdictions and parties’ ability to choose the jurisdiction whose law controls their transactions. Third, we suggest harnessing the power of jurisdictional competition among the states through a federal law enforcing contracting parties’ choice of law except to the extent states legislatively override the choice of law and regulate local transactions. We apply this analysis to several areas of the law that are critical to growth and innovation: non-competition clauses, business associations, the legal profession, internet law, insurance, property law, products liability, and franchise regulation.