Thermodynamic Rankine cycles

In apphcation to electric utihty power generation, MHD is combined with steam (qv) power generation, as shown in Figure 2. The MHD generator is used as a topping unit to the steam bottoming plant. From a thermodynamic point of view, the system is a combined cycle. The MHD generator operates in a Brayton cycle, similar to a gas turbine the steam plant operates in a conventional Rankine cycle (11). 

Power plants based on the Rankine thermodynamic cycle have served the majority of the world s electric power generation needs in the twentieth century. The most common heat sources employed by Rankine cycle power plants are either fossil fuel-fired or nuclear steam generators. The former are the most widely used. 

Rankine Cycle Thermodynamics. Carnot cycles provide the highest theoretical efficiency possible, but these are entirely gas phase. A drawback to a Carnot cycle is the need for gas compression. Producing efficient, large-volume compressors has been such a problem that combustion turbines and jet engines were not practical until the late 1940s. 

A concept of the cycle of thermodynamic processes, introduced later than the Carnot cycle. Modifications of the Rankine cycle are of practical importance in boiler design, in relating the successive thermodynamic changes as water is converted to steam, expands and converted to mechanical energy in a turbine, then condenses and returns to the boiler. 

Rankine cycle, 23 231—234 Thermodynamic stability, of MgB2 superconductors, 23 833 Thermodynamic state variables,... 

Figure 9-15. Combined Brayton-Rankine Cycle Thermodynamics...

The Rankine cycle diagram placed adjacent the Brayton cycle in Figure 9-15 is indicated as a simple steam cycle with superheat, but no reheat and no multi-pressure steam generation. The thermodynamic advantage of the Rankine bottoming cycle is the lowered temperature of heat rejection, in the steam condenser, from the overall combined cycles. 

Applying the first and second laws of thermodynamics of the open system to each of the four processes of the Rankine cycle yields ... 

Incident solar energy is absorbed by the surface water of the oceans. Ocean surface temperatures in excess of 26°C occur near the equator. Pure water has a maximum density at a temperature of 4°C. The chilled water tends to settle to the depths of the ocean. The combination of the warmed ocean surface water and cold deep ocean water provides the thermodynamic condition needed to operate a heat engine called ocean thermal energy conversion (OTEC). A typical closed-cycle OTEC Rankine cycle using a working fluid such as ammonia or a freon is suggested. 

Why may the thermodynamic performance of a vapor Rankine cycle be improved potentially by using a nonazeotropic mixture working fluid ... 

The thermodynamic power cycles most commonly used today are the vapor Rankine cycle and the gas Brayton cycle (see Chapter 4). Both are characterized by two isobaric and two isentropic processes. The vapor... 

THERMODYNAMIC EFFICIENCY THE CARNOT, OTTO, DIESEL, AND RANKINE CYCLES... 

Rankine cycle - A thermodynamic cycle which can be used to calculate the ideal performance of a heat engine that uses a condensable vapor as the working fluid (e.g., a steam engine or a heat pump). 

Rankine Cycle - The thermodynamic cycle that Is an Ideal standard for comparing performance of heat-engines, steam power plants, steam turbines, and heat pump systems that use a condensable vapor as the working fluid efficiency is measured as work done divided by sensible heat supplied. 

Microturbines, pumps, and compressors are key components used to implement thermodynamic cycles for power generation, propulsion, or cooling. Thermodynamic power cycles use a working fluid that changes state (pressure and temperature) in order to convert heat into mechanical work. To achieve high power density, the pressures and temperatures of the fluid in the cycle should be kept to the high levels common at large scale. Common cycles are the Brayton gas power cycle and the Rankine vapor power cycle, described next. 

The phenomenon of spontaneous condensation in a supersaturated vapour is of interest in different fields of natural science and in various technical applications, e.g. wind tunnels and steam turbines. Expecially with respect to Organic Rankine Cycles for heat recovery there exists some interest in the conditions for the onset of spontaneous condensation in the so-called Wilson point and in the influence of the released heat of condensation on the flow field for different working fluids. From this point of view, we started systematic investigations on spontaneous condensation of pure vapours in stationary supersonic nozzle flow with the intention to cover a wide range of thermodynamic state for substances of different molecular structure. In this paper we present experimental results for carbon dioxide and compare them in a first step with results... 

In summary, to obtain similar thermod5mamic efficiency, it appears that nitrogen-based systems will have somewhere around 40% larger volume than helium-based systems. Their capital cost will be higher because of the less optimal thermodynamic properties of nitrogen compared with helium. However, the nitrogen-based Brayton cycle is expected to be less expensive than the equivalent Rankine steam cycle because of the low-pressure steam components and the moisture separator components required for the Rankine cycle. 

Thermodynamic cycle type Direct Rankine cycle with steam turbine... 

The SPINNOR and VSPINNOR are designed to operate within an indirect cycle without intermediate heat exchanger. Rankine cycle with superheated steam at about 7MPa is used. The thermodynamic efficiency is 35-37.5%. 

---