Showing papers on "Thermodynamic cycle published in 2002"

Thermodynamic Cycle Analysis of Pulse Detonation Engines

Abstract: Pulse detonation engines (PDEs) are currently attracting considerable research and development attention because they promise performance improvements over existing airbreathing propulsion devices. Because of their inherently unsteady behavior, it has been difficult to conveniently classify and evaluate them relative to their steady-state counterparts. Consequently, most PDE studies employ unsteady gasdynamic calculations to determine the instantaneous pressures and forces acting on the surfaces of the device and integrate them over a cycle to determine thrust performance. A classical, closed thermodynamic cycle analysis of the PDE that is independent of time is presented. The most important result is the thermal efficiency of the PDE cycle, or the fraction of the heating value of the fuel that is converted to work that can be used to produce thrust. The cycle thermal efficiency is then used to find all of the traditional propulsion performance measures. The benefits of this approach are 1) that the fundamental processes incorporated in PDEs are clarified; 2) that direct, quantitative comparisons with other cycles (e.g., Brayton or Humphrey) are easily made; 3) that the influence of the entire ranges of the main parameters that influence PDE performance are easily explored; 4) that the ideal or upper limit of PDE performance capability is quantitatively established; and 5) that this analysis provides a basic building block for more complex PDE cycles. A comparison of cycle performance is made for ideal and real PDE, Brayton, and Humphrey cycles, utilizing realistic component loss models. The results show that the real PDE cycle has better performance than the real Brayton cycle only for flight Mach numbers less than about 3, or cycle static temperature ratios less than about 3. For flight Mach numbers greater than 3, the real Brayton cycle has better performance, and the real Humphrey cycle is an overoptimistic (and unnecessary) surrogate for the real PDE cycle.

State of the art in sorption heat pumping and cooling technologies

Abstract: Heat transformation with sorption systems has received increased attention in recent years. In this review it is intended to discuss current trends as well as forthcoming applications with the respective appropriate technology as it is deduced from activities in the field. Especially, we report about the papers and discussions of the International Sorption Heat Pump Conference (ISHPC'99) which was held in March 1999 in Munich, Germany. The review is grouped into a fundamentals part, a part about thermodynamic cycles, and an applications part. In the fundamentals part the discussion about working pairs and heat and mass transfer is reflected. Thermodynamic cycles which are being discussed are special solid sorption cycles, cycles fit for low-temperature driving heat, compression-sorption hybrids, and open cycles. In the applications part the classical cooling business is the main issue. The review comprises chillers and refrigerators which may be direct fired or waste heat driven. Interest is given to the improvement of efficiency on the one hand as well as to adaptation to low temperature waste heat use on the other hand — two very different developments. The use of solar energy as a heat source belongs to that area also. An additional important role — for decades — is played by automotive application. The area of heat pumping for heating purposes is less prominent but not negligible. Systems with a large capacity are being installed every once in a while, but the small scale domestic market still is not really covered with appropriate technology. Finally, industrial heat pumping involves the reverse cycle (heat transformer) also. Activity in this field is rather small. In summary, no unexpected developments can be reported on, but progress is steady and the market increases continuously, especially in the far east.

A thermodynamic analysis of a novel absorption power/cooling combined cycle

Abstract: In this paper a novel cycle, absorption power/cooling combined cycle, is proposed and thermodynamic analysis of this cycle is carried out in the logp - T graph. Based on the total heat efficiency ηand exergy efficiency ψ, the two evaluation index, and by simulation the thermodynamic theory and energy property of the novel cycle can be developed fully. And we can see the ηof the novel cycle and Kalina cycle are 19.50% and 14.54% respectively, and the ηof novel cycle is 34.10% higher than that of Kalina; the ψof the two cycles is 31.60% and 31.19% respectively. We also study the effect of feed concentration of rectifier, out pressure of turbine on the two evaluation index.

Simple and compact low-temperature power cycle

Abstract: A simple, compact, and relatively efficient thermodynamic power cycle system and process for extracting heat from a heat source stream and converting a portion of the heat to mechanical power. The system and process are composed of the same series of four processing units or steps found in the most basic form of a Rankine power cycle: (1) heating (means) of a pressurized working fluid to produce a superheated gas, (2) expansion (means) to a lower pressure to produce power, (3) condensation (means) of the low pressure gas to a liquid, and (4) pumping (means) of the liquid to high pressure to complete the cycle. The working fluid is heated under pressures above critical. The working fluid must have a critical temperature more than 40° F. lower than the temperature of the heat source stream and a normal boiling point less than 32° F.

LNG regassification process and system

Abstract: A system for vaporizing liquefied natural gas (LNG) utilizes the residual cooling capacity of LNG to condense the working fluid of a power producing work producing cycle and chills liquids that are used in a direct-contact heat transfer system to cool air. The cold air is used to supply air to a combustion gas turbine operating in conjunction with a combined cycle power plant. Power is produced from both the work producing cycle and the combined cycle power plant and the chilling of the intake air to the gas turbine increases the output capacity of the combined cycle power plant.

Novel Combined Power and Cooling Thermodynamic Cycle for Low Temperature Heat Sources, Part I: Theoretical Investigation

Abstract: A combined thermal power and cooling cycle proposed by Goswami is under intensive investigation, both theoretically and experimentally. The proposed cycle combines the Rankine and absorption refrigeration cycles, producing refrigeration while power is the primary goal. A binary ammonia-water mixture is used as the working fluid. This cycle can be used as a bottoming cycle using waste heat from a conventional power cycle or an independent cycle using low temperature sources such as geothermal and solar energy. An experimental system was constructed to demonstrate the feasibility of the cycle and to compare the experimental results with the theoretical simulation. Results showed that the vapor generation and absorption condensation processes work experimentally, exhibiting expected trends, but with deviations from ideal and equilibrium modeling. The potential for combined turbine work and refrigeration output was evidenced in operating the system. Analysis of losses showed where improvements could be made, in preparation for further testing over a broader range of operating parameters.Copyright © 2002 by ASME

Optimization of a novel combined power/refrigeration thermodynamic cycle

Abstract: A novel combined power/refrigeration thermodynamic cycle is optimized for thermal performance in this paper. The cycle uses ammonia-water binary mixture as a working fluid and can be driven by various heat sources, such as solar, geothermal and low temperature waste heat. It could produce power as well as refrigeration with power output as a primary goal. The optimization program, which is based on the Generalized Reduced Gradient (GRG) algorithm, can be used to optimize for different objective functions. Examples that maximize second law efficiency, work output and refrigeration output are presented, showing the cycle may be optimized for any desired performance parameter. In addition, cycle performance over a range of ambient temperatures was investigated. It was found that for a source temperature of 360K, which is in the range of flat plate solar collectors, both power and refrigeration outputs are achieved under optimum conditions. All performance parameters, including first and second law efficiencies, power and refrigeration output decrease as the ambient temperature goes up. On the other hand, for a source of 440K, optimum conditions do not provide any refrigeration. However, refrigeration can be obtained even for this temperature under non-optimum performance conditions.Copyright © 2002 by ASME

Loop heat pipe (LHP) development by utilizing coherent porous silicon (CPS) wicks

Abstract: This paper introduces a theoretical model for a Loop Heat Pipe (LHP) utilizing a coherent porous silicon (CPS) wick. The paper investigates the effects of different parameters on the performance of the LHP such as evaporator temperature, condenser temperature, total mass charge, wick thickness, porosity, and pore size. A LHP is a two-phase device with extremely high effective thermal conductivity that uses capillary forces developed inside its wicked evaporator to pump a working fluid through a closed loop. The loop heat pipe is developed to efficiently transport heat that is generated by a highly localized concentrated heat source and then to discharge this heat to a convenient sink. This device is urgently needed to cool electronic components, especially in space applications. The LHP has been modeled utilizing the conservation equations and thermodynamic cycle. The loop heat pipe cycle is presented on a T-s diagram. A direct relation is developed between the ratio of heat going for evaporation as well as heat leaking to the compensation chamber.

Thermodynamics of Airbreathing Pulse-Detonation Engines

Abstract: An analytical investigation was conducted of the idealized performance potential, from a thermodynamic cycle viewpoint, of airbreathing pulse-detonation engines (PDEs) primarily intended for air-vehicle propulsion. The investigation was restricted to the static operation of PDEs. The detonation-wave model used was of the classical Zel'dovich-von Neumann-Doering type, in which an initiating shock wave is followed by a Rayleigh-type combustion process in a duct, the detonation tube, of uniform cross-sectional area. The results of the analysis indicated that the idealized PDE performance was only slightly better than that of a simple, easily analyzed, constant-volume combustion, Lenoir-type surrogate cycle. The PDE also had the potential of being slightly more efficient, under idealized flight conditions, with induction ramming occurring, than the corresponding surrogate cycle. The corresponding surrogate cycle will advance thermodynamically, due to intake ramming, from a relatively inefficient Lenoir cycle to a more efficient Humphrey, or Atkinson, cycle.

Inherent CO2 Capture Using Chemical Looping Combustion in a Natural Gas Fired Power Cycle

Abstract: In this paper an alternative to the so-called “oxy-fuel” combustion for CO2 capture is evaluated. “Chemical looping combustion” (CLC), is closely related to oxy-fuel combustion as the chemically bound oxygen reacts in a stoichiometric ratio with the fuel. In the CLC process the overall combustion reaction takes place in two reaction steps in two separate reactors. In the reduction reactor, the fuel is oxidised by the oxygen carrier, i.e. the metal oxide MeO. The metal oxide is reduced to a metal oxide with a lower oxidation number, Me, in the reaction with the fuel. In this manner, pure oxygen is supplied to the reaction with the fuel without using a traditional air separation plant, like cryogenic distillation of air. The paper presents a thermodynamic cycle analysis, where CLC is applied in a Humid Air Turbine concept. Main parameters are identified, and these are varied to examine the influence on cycle efficiency. Results on cycle efficiency are presented and compared to other CO2 capture options. Further, an evaluation of the oxygen carrier, metals/oxides, is presented. An exergy analysis is carried out in order to understand where losses occur, and to explain the difference between CLC and conventional combustion. The oxidation reactor air inlet temperature and the oxidation reactor exhaust temperature have a significant impact on the overall efficiency. This can be attributed to the controlling effect of these parameters on the required airflow rate. An optimum efficiency of 55.9% has been found for a given set of input parameters. Crucial issues of oxygen carrier durability, chemical performance and mechanical properties have been idealized, and further research on the feasibility of CLC is needed. Whether or not the assumption 100% gas conversion holds, is a crucial issue and remains to be determined experimentally. Successful long-term operation of chemical looping systems of this particular type has not yet been demonstrated. The simulation points out a very promising potential of CLC as a power/heat generating method with inherent capture of CO2 . Exergy analysis show reduced irreversibilities for CLC compared to conventional combustion. Simulations of this type will prove useful in designing CLC systems in the future when promising oxygen carriers have been investigated in more detail.© 2002 ASME

Method and system for a thermodynamic process for producing usable energy

Abstract: The present invention comprises, in one embodiment, a process for producing energy through a thermodynamic cycle comprising transforming a first working fluid having at least two components into usable energy and a first exhaust stream; diverting at least a portion of the first exhaust stream to form a diverted first exhaust stream; transferring heat from the diverted first exhaust stream to the first working fluid, thereby partially condensing the diverted first exhaust stream to form a partially condensed diverted first exhaust stream; separating the partially condensed diverted first exhaust stream into a vapor stream and a liquid stream; and transforming the vapor stream into usable energy. The present invention also comprises a system for producing energy through novel implementation of a thermodynamic cycle.

The thermodynamic basis of pulsed detonation engine thrust production

Abstract: In recent years, several papers have been published comparing the detonative engine thermodynamic cycle with the classical Brayton cycle. While these papers appear to be converging on an industry-accepted thermodynamic model for the Pulsed Detonation Engine, PDE, total convergence has not yet occurred. This paper attempts to assist in the convergence by applying analysis to representative trajectories, fuel-to-air ratios, and component efficiencies. It is found that global conservation of energy for the post-detonative state provides a representative condition from which to compute nozzle expansion losses.

Finite time thermodynamic analysis of an irreversible regenerative closed cycle brayton heat engine

Abstract: This communication presents the parametric study of an irreversible regenerative Brayton cycle with nonisentropic compression and expansion processes for finite heat capacitance rates of external reservoirs The power output of the cycle is maximized with respect to the working fluid temperatures and the expressions for maximum power output and the corresponding thermal efficiency are obtained The effect of the effectiveness of the various heat exchangers and the efficiencies of the turbine and compressor, the reservoir temperature ratio and the heat capacitance rate of heating and cooling fluids and the cycle working fluid on the power output and the corresponding thermal efficiency has been studied It is seen the effect of cold side effectiveness is more pronounced for the power output while the effect of regenerative effectiveness is more pronounced for the thermal efficiency It is found that the effect of turbine efficiency is more than the compressor efficiency on the performance of these cycles

Miniature reciprocating heat pumps and engines

Abstract: The present invention discloses a miniature thermodynamic device that can be constructed using standard micro-fabrication techniques. The device can be used to provide cooling, generate power, compress gases, pump fluids and reduce pressure below ambient (operate as a vacuum pump). Embodiments of the invention relating to the production of a cooling effect and the generation of electrical power, change the thermodynamic state of the system by extracting energy from a pressurized fluid. Energy extraction is attained using an expansion process, which is as nearly isentropic as possible for the appropriately chosen fluid. An isentropic expansion occurs when a compressed gas does work to expand, and in the disclosed embodiments, the gas does work by overcoming either an electrostatic or a magnetic force.

Reciprocating hot air bottom cycle engine

Abstract: The invention is a reciprocating bottom cycle engine whose principal is heat addition by recovering heat from a top cycle engine through a counterflow heat exchange recuperator. The engine operation approximates the ideal bottom cycle for recovering heat from a top cycle: isothermal compression, recuperative heating, and constant entropy expansion. Such a cycle is capable of utilizing all the work potential between the hot top cycle exhaust and cool ambient temperature. Practical engines operating on this cycle do not achieve the ideal performance but are superior to Stirling or Ericsson Cycle engines in the amount of exhaust heat that can be converted to mechanical work and have been shown to be capable of enabling a typical natural gas fired engine to produce 17% more power from the same amount of fuel. All moving parts are lightly loaded and are only exposed to clean air, thus assuring long engine life with minimal maintenance. Furthermore, many of the bottom cycle parts can be obtained from existing reciprocating engines and it is even possible to integrate the top and bottom cycle engines on the same engine block. The invention provides a simple “bolt on” means of increasing fuel efficiency by increasing power without increasing fuel consumption.

Optimal Configuration and Performance of Heat Engines with Heat Leak and Finite Heat Capacity

Abstract: The optimal configuration of a class of two-heat-reservoir heat engine cycles in which the maximum work output can be obtained under a given cycle time is determined with the considerations of heat leak, finite heat capacity high-temperature source and infinite heat capacity low-temperature heat sink. The heat engine cycles considered in this paper include: (1) infinite low- and high-temperature reservoirs without heat leak, (2) infinite low- and high-temperature reservoirs with heat leak, (3) finite high-temperature source and infinite low-temperature sink without heat leak, and (4) finite high-temperature source and infinite low-temperature sink with heat leak. It is assumed that the heat transfer between the working fluid and the reservoirs obeys Newton's law. It is shown that the existence of heat leak doesn't affect the configuration of a cycle with an infinite high-temperature source. The finite heat capacity of a high temperature source without heat leak makes the cycle a generalized Carnot heat engine cycle. There exists a great difference of the cycle configurations for the finite high-temperature source with heat leak and the former three cases. Moreover, the relations between the optimal power output and the efficiency of the former three configurations are derived, and they show that the heat leak affects the power versus efficiency characteristics of the heat engine cycles.

Liquid phase diffusion bonding to a superalloy component

Abstract: A method for the manufacturing or repair of a superalloy gas turbine component including a liquid phase diffusion bonding process wherein the brazing heat treatment used for the diffusion bonding of a powder material to the component is accomplished by a heat cycle that is performed on the component for another purpose. A manufacturing solution heat treatment, a pre-weld heat treatment, a post-weld heat treatment, or a rejuvenating heat treatment may be used as the brazing heat treatment. The composition of the powder material is selected so that a desired set of material properties is achieved when the powder material is subjected to the dual-purpose heat cycle. In one embodiment, a 50/50 mixture of AM775 and IN939 powder is diffusion brazed to an IN939 superalloy component using a heat treatment which also functions as the post-casting solution heat treatment for the IN939 component.

Thermodynamic cycle and cfd analyses for hydrogen fueled air-breathing pulse detonation engines

Abstract: This paper presents the results of a thermodynamic cycle analysis of a pulse detonation engine (PDE) using a hydrogen-air mixture at static conditions. The cycle performance results, namely the specific thrust, fuel consumption and impulse are compared to a single cycle CFD analysis for a detonation tube which considers finite rate chemistry. The differences in the impulse values were indicative of the additional performance potential attainable in a PDE.

Triple Cycle: A Conceptual Arrangement of Multiple Cycle Toward Optimal Energy Conversion

Abstract: The purpose of this study is to find a maximum work output from various combinations of thermodynamic cycles from a viewpoint of the cycle systems. Three systems were discussed in this study: a fundamental combined cycle and two other cycles evolved from the fundamental dual combined cycle: series-type and parallel-type triple cycles. In each system, parametric studies were carried out in order to find optimal configurations of the cycle combinations based on the influences of tested parameters on the systems. The study shows that the series-type triple cycle exhibits no significant difference as compared with the combined cycle. On the other hand, the efficiency of the parallel-type triple cycle can be raised, especially in the application of recovering low-enthalpy-content waste heat. Therefore, by properly combining with a steam Rankine cycle, the organic Rankine cycle is expected to efficiently utilize residual yet available energy to an optimal extent. The present study has pointed out a conceptual design in multiple-cycle energy conversion systems.

Detailed Results for Nitric Oxide Emissions as Determined From a Multiple-Zone Cycle Simulation for a Spark-Ignition Engine

Abstract: A thermodynamic cycle simulation was developed for spark-ignition engines which included a formulation using multiple zones for the combustion process and the capability to compute the net nitric oxide (NO) change due to the “thermal” formation mechanism. This simulation was used to complete analyses for a commercial, 5.7 l spark-ignition V-8 engine operating at a part load operating condition at 1400 rpm with an equivalence ratio of 1.0. The engine possessed a compression ratio of 8.1:1, and had a bore and stroke of 101.6 and 88.4 mm, respectively. At the base case conditions, the nitric oxide emissions were 15.7 g/bhp-hr (2903 ppm). The effects of equivalence ratio, combustion duration, spark timing, exhaust gas recirculation, compression ratio, speed and load on nitric oxide changes were examined. Results for instantaneous nitric oxide as a function of crank angle are presented. The use of an adiabatic zone was shown to dramatically increase the nitric oxide levels relative to using the burned gas temperature. For the base case, almost 50% more nitric oxide was computed using the adiabatic temperature relative to the burned gas temperature. The importance of gas temperature, cylinder gas pressure, and composition is illustrated.Copyright © 2002 by ASME