| Abstract |
Low temperature vapor-turbine cycle can be used at different applications in a modern power generation technology. The cycle is a basic component in binary power stations, heat recovery systems and geothermal power engineering. Usually, a high temperature (THS) ñ heat source for these cycles is in a range of 363 K to 423 K. A low temperature (TLS) of sink varies depending on a climate in a field of application and optimal design of the station. In the geothermal engineering TLS could be as low as 283Ö288K. In the present analysis, comparative data obtained for flammable (Butane, Pentane) and nonflammable (R-134a, R-21, R-245fa) WF are related to a case of constant temperature for both a heat source and sink of the cycle. The high performance data obtained for the cycle model including only intrinsic losses. A thermal coefficient of performance (COPT) is in a range of 16.5 to 15.0 for THS / TLS = 373 / 303 K. Reducing TLS to 288 K provides COPT in a range 19.7 to 18.0. Mass flow rate GM = 80Ö50 kg/kW-h at TLS = 303 K and GM = 61Ö40 at TLS = 288 K. The analysis also shows influencing the WF properties on the optimal equipment design. Following parameters may be important. A volumetric flow rate GV at the turbine outlet parameters, which would influence on hydraulic pressure drop in pipelines and heat transfer in the condenser, and turbine efficiency and size. For the tested working fluids GV = 22Ö75 cm/kW-h at TLS = 303 K. However, GV increases up to GV = 28Ö96 cm/kW-h at TLS = 288 K. WF properties also influence on a structure of the condenser heat load. For the analyzed WE a heat transfer area related to cooling of vapor fraction could be as high as 5Ö10%. This case is especially important in designing of the air-cooled condensers. A turbine efficiency could be achieved a relatively high level above 0.85 in case of rather low pressure in the outlet. However, for R-134a with PL = 5Ö8 bar the efficiency should be lower, down to 0.75. Nowadays, in selecting of a working fluid (WF) both factors must be taken into account engineering aspects and environmental characteristics. A lot of experience has been accumulated in recent developments of working fluids in refrigeration and heat pumping industries during the latest decade. An attitude to ozone depleting potential (ODP) is identical in the great majority of the countries. At the same time the Kyoto Protocol on a global warming is still under discussion. Modern trend on applications of natural working fluids is reasonable. For any type of working fluid, an optimal design of hermetically sealed equipment is critical to resolve issues related to flammability, toxicity and environmental requierments. |