Showing papers on "Thermodynamic cycle published in 1988"

Fundamentals of Engineering Thermodynamics

Abstract: 1 Getting Started: Introductory Concepts and Definitions. 1.1 Using Thermodynamics. 1.2 Defining Systems. 1.3 Describing Systems and Their Behavior. 1.4 Measuring Mass, Length, Time, and Force. 1.5 Specific Volume. 1.6 Pressure. 1.7 Temperature. Chapter Summary and Study Guide. 2 Energy and the First Law of Thermodynamics. 2.1 Reviewing Mechanical Concepts of Energy. 2.2 Broadening Our Understanding of Work. 2.3 Broadening Our Understanding of Energy. 2.4 Energy Transfer by Heat. 2.5 Energy Accounting: Energy Balance for Closed Systems. 2.6 Energy Analysis of Cycles. Chapter Summary and Study Guide. 3 Evaluating Properties. 3.1 Getting Started. Evaluating Properties: General Considerations. 3.2 p-v-T Relation. 3.3 Studying Phase Change. 3.4 Retrieving Thermodynamic Properties. 3.5 Evaluating Pressure, Specific Volume, and Temperature. 3.6 Evaluating Specific Internal Energy and Enthalpy. 3.7 Evaluating Properties Using Computer Software. 3.8 Applying the Energy Balance Using Property Tables and Software. Chapter Summary and Study Guide. 4 Control Volume Analysis Using Energy. 4.1 Conservation of Mass for a Control Volume. 4.2 Forms of the Mass Rate Balance. 4.3 Applications of the Mass Rate Balance. 4.4 Conservation of Energy for a Control Volume. Chapter Summary and Study Guide. 5 The Second Law of Thermodynamics. 5.1 Introducing the Second Law. 5.2 Statements of the Second Law. 5.3 Identifying Irreversibilities. 5.4 Interpreting the Kelvin-Planck Statement. 5.5 Applying the Second Law to Thermodynamic Cycles. 5.6 Second Law Aspects of Power Cycles Interacting with Two Reservoirs. Chapter Summary and Study Guide. 6 Using Entropy. 6.1 Entropy-A System Property. 6.2 Retrieving Entropy Data. 6.3 Introducing the T dS Equations. 6.4 Entropy Change of an Incompressible Substance. 6.5 Entropy Change of an Ideal Gas. 6.6 Entropy Change in Internally Reversible Processes of Closed Systems. 6.7 Entropy Balance for Closed Systems. 6.8 Directionality of Processes. 6.9 Entropy Rate Balance for Control Volumes. Steady-State Flow Processes. Chapter Summary and Study Guide. 7 Exergy Analysis. 7.1 Introducing Exergy. 7.2 Conceptualizing Exergy. 7.3 Exergy of a System. 7.4 Closed System Exergy Balance. 7.5 Exergy Rate Balance for Control Volumes at Steady State. 7.6 Exergetic (Second Law) Efficiency. 7.7 Thermoeconomics. Chapter Summary and Study Guide. 8 Vapor Power Systems. 8.1 Modeling Vapor Power Systems. 8.2 Analyzing Vapor Power Systems-Rankine Cycle. 8.3 Improving Performance-Superheat and Reheat. 8.4 Improving Performance-Regenerative Vapor Power Cycle. 8.5 Other Vapor Cycle Aspects. 8.6 Case Study: Exergy Accounting of a Vapor Power Plant. Chapter Summary and Study Guide. 9 Gas Power Systems. Internal Combustion Engines. 9.1 Introducing Engine Terminology. 9.2 Air-Standard Otto Cycle. 9.3 Air-Standard Diesel Cycle. 9.4 Air-Standard Dual Cycle. Gas Turbine Power Plants. 9.5 Modeling Gas Turbine Power Plants. 9.6 Air-Standard Brayton Cycle. 9.7 Regenerative Gas Turbines. 9.8 Regenerative Gas Turbines with Reheat and Intercooling. 9.9 Gas Turbines for Aircraft Propulsion. 9.10 Combined Gas Turbine-Vapor Power Cycle. Chapter Summary and Study Guide. 10 Refrigeration and Heat Pump Systems. 10.1 Vapor Refrigeration Systems. 10.2 Analyzing Vapor-Compression Refrigeration Systems. 10.3 Refrigerant Properties. 10.4 Cascade and Multistage Vapor-Compression Systems. 10.5 Absorption Refrigeration. 10.6 Heat Pump Systems. 10.7 Gas Refrigeration Systems. Chapter Summary and Study Guide. 11 Thermodynamic Relations. 11.1 Using Equations of State. 11.2 Important Mathematical Relations. 11.3 Developing Property Relations. 11.4 Evaluating Changes in Entropy, Internal Energy, and Enthalpy. 11.5 Other Thermodynamic Relations. 11.6 Constructing Tables of Thermodynamic Properties. Charts for Enthalpy and Entropy. 11.8 p-v-T Relations for Gas Mixtures. 11.9 Analyzing Multicomponent Systems. Chapter Summary and Study Guide. 12 Ideal Gas Mixture and Psychrometric Applications. Ideal Gas Mixtures: General Considerations. 12.1 Describing Mixture Composition. 12.2 Relating p, V, and T for Ideal Gas Mixtures. 12.3 Evaluating U, H, S, and Specific Heats. 12.4 Analyzing Systems Involving Mixtures. Psychrometric Applications. 12.5 Introducing Psychrometric Principles. 12.6 Psychrometers: Measuring the Wet-Bulb and Dry-Bulb Temperatures. 12.7 Psychrometric Charts. 12.8 Analyzing Air-Conditioning Processes. 12.9 Cooling Towers. Chapter Summary and Study Guide. 13 Reacting Mixtures and Combustion. Combustion Fundamentals. 13.1 Introducing Combustion. 13.2 Conservation of Energy-Reacting Systems. 13.3 Determining the Adiabatic Flame Temperature. 13.4 Fuel Cells. 13.5 Absolute Entropy and the Third Law of Thermodynamics. Chemical Exergy. 13.6 Introducing Chemical Exergy. 13.7 Standard Chemical Exergy. 13.8 Exergy Summary. 13.9 Exergetic (Second Law) Efficiencies of Reacting Systems. Chapter Summary and Study Guide. 14 Chemical and Phase Equilibrium. Equilibrium Fundamentals. 14.1 Introducing Equilibrium Criteria. Chemical Equilibrium. 14.2 Equation of Reaction Equilibrium. 14.3 Calculating Equilibrium Compositions. 14.4 Further Examples of the Use of the Equilibrium Constant. Phase Equilibrium. 14.5 Equilibrium Between Two Phases of a Pure Substance. 14.6 Equilibrium of Multicomponent, Multiphase Systems. Chapter Summary and Study Guide. Appendix Tables, Figures, and Charts. Index to Tables in SI Units. Index to Tables in English Units. Index to Figures and Charts. Index. Answers to Selected Problems: Visit the student.

The Application of Availability and Energy Balances to a Diesel Engine

Abstract: The maximum power that can be extracted from an engine operating at a given condition was determined by means of analyses based on the first and second laws of thermodynamics. These analyses were applied to a heavy-duty single-cylinder open-chamber diesel engine operated at constant speed. Over the range of operating conditions investigated, the second-law efficiency (ratio of brake power to maximum extractable power) of the engine, which increased with engine load, was found to vary from 22 to 50 percent. It was concluded that besides heat transfer, the combustion process was the most important source of irreversibility and accounted for 25 to 43 percent of the lost power.

GASCAN—An Interactive Code for Thermal Analysis of Gas Turbine Systems

Abstract: A general, dimensionless formulation of the thermodynamic, heat transfer, and fluid-dynamic processes in a cooled gas turbine is used to construct a compact, flexible, interactive system-analysis program A variety of multishaft systems using surface or evaporative intercoolers, surface recuperators, or rotary regenerators, and incorporating gas turbine reheat combustors, can be analyzed Different types of turbine cooling methods at various levels of technology parameters, including thermal barrier coatings, may be represented The system configuration is flexible, allowing the number of turbine stages, shaft/spool arrangement, number and selection of coolant bleed points, and coolant routing scheme to be varied at will Interactive iterations between system thermodynamic performance and simplified quasi-three-dimensional models of the turbine stages allow exploration of realistic turbine-design opportunities within the system/thermodynamic parameter space The code performs exergy-balance analysis to break down and trace system inefficiencies to their source components and source processes within the components, thereby providing insight into the interactions between the components and the system optimization tradeoffs

Optimal Temperature -Entropy Curves for Magnetic Refrigeration

Abstract: Magnetic refrigeration utilizes the temperature dependent entropy change produced in a ferromagnetic or paramagnetic material when subjected to a change in magnetic field. By blending different materials together the temperature-entropy (T-S) behavior of the refrigerant may be tailored to maximize system performance. Optimal T-S diagrams for magnetic refrigerators using Carnot, Ericsson and Brayton cycles were determined and compared to results of thermodynamic numerical models.

Rotary recuperative magnetic heat pump

Abstract: A bench scale rotary magnetic heat pump now being built is described. The unique design feature of this heat pump is the method for achieving recuperator fluid flow, which relies simply on parallel flow paths; the primary flow leg allows heat transfer between external load and sink and magnetic working material, while parallel flow accomplishes recuperation. The bench scale test is intended to demonstrate feasibility of the concept and to verify that all significant loss mechanisms are identified and treated properly in performance models, but is not a scaled down version of a practical heat pump. Working material is gadolinium foil 76 µm thick with 127 µm spaces for fluid flow. Magnetic fields are created by neodymium-iron-boron permanent magnets with an air gap field of about 0.9 Tesla. Due to the low field (practical heat pumps will use superconducting magnets with field strength around 9 T), temperature lift is limited to 11 K.

An Analytical Model of Heat Transfer to the Suction Gas in a Low-Side Hermetic Refrigeration Compressor

Abstract: H Doyle Thompson Dept of Mechanical Engineering Purdue University W Lafayette, IN 47907 (317) 494-5624 Heat transfer to the suction gas in a hermetic compressor is known to have adverse effects on compressor performance This can be explained in an overall sense by thermodynamic cycle analysis The extent of suction gas heated inside the compressor and the areas in which this heating occurs requires a more detailed heat transfer analysis The analytical model for this study is a small (about 1/3 horsepower), low-side, reciprocating, hermetic compressor The heat transfer equations for this model are, derived from steady-state energy balances on the overall system and on various compressor components Where applicable, heat transfer coefficients are determined from correlations found in the literature A volumetric efficiency and a compression efficiency are determined from the experimental data Some of the heat transfer coefficients for the complex threedimensional geometries were also determined from experimental measurements The model is used to predict the compressor performance over a range of operating conditions Comparison with experimental measurements shows that the major trends are predicted by the model Model adequacy and potential improvements are discussed

Cogeneration by combining gas turbine engine with organic rankine cycle

Abstract: The gas turbine engine is known by its relatively low efficiency especially at part load. Therefore, to conserve energy and reduce the operating cost, waste heat is recovered by combining a heat-exchange gas turbine cycle with closed organic Rankine cycle. A computer programme was made to calculate parametrically the individual and combined cycle performances, namely the work and efficiency of each. The parameters considered were: gas turbine pressure ratio; maximum cycle temperature; fluid-air mass ratio; and type of working fluid. This analytical study shows that R113 is the optimum choice because it gives the smallest, hence the most economical, size of turbo-expander. Maximum cycle temperature and pressure ratio are relatively the most important parameters. Economic analysis indicates very good rate of return on investment, related with heat recovery by cogeneration.

Method of converting thermal energy to work

Abstract: A method is provided for converting sensible heat energy of a heating fluid supplied by a high-temperature heat source to work, by means of a thermodynamic cycle employing a multi-component working fluid, wherein a "rich solution" having a higher concentration of lower boiling component, or components, is heated in a vapor generator in counter-current heat exchange with the heating fluid to produce a vapor-liquid mixture which is introduced into a lower zone of a rectifier and separated therein into a "lean solution" having a higher concentration of said lower boiling component, or components, and a vapor mixture; the enthalpy of the vapor mixture is increased by passing it through a superheater in counter-current heat exchange with said heating fluid at its highest temperature; the vapor mixture is then expanded in a first turbine to an intermediate pressure level thereby to generate work and subsequently in a second turbine to a low pressure level to generate additional work; the spent vapor mixture is then recycled to an absorber wherein it is dissolved in said lean solution so as to regenerate said rich solution. The cycle is characterized mainly in that a portion of said lean solution emerging from the rectifier, is decompressed, by means of an expansion device, into a so-called flash drum wherein the lean solution separates into a yet leaner solution and a vapor mixture which is expanded in a turbine to produce additional work.

Thermodynamic cycles for refrigeration and heat transformer units H2O/LiBr

Abstract: The exact theoretical refrigeration and transformer thermodynamic cycles, of units working with H2O/LiBr, are presented on the enthalpy-temperature as well as on the temperature-entropy diagram. The heat quantities involved with, have been calculated for many such cycles. Afterwards the obtained results have been correlated by short relations allowing the fast computation of the related quantities. The fast algorithm obtained can be used to predict optimal operating conditions in a very short computer time even if personal computers are used to.

Methods for heat transfer and temperature field analysis of the insulated diesel, phase 3

Abstract: Work during Phase 3 of a program aimed at developing a comprehensive heat transfer and thermal analysis methodology for design analysis of insulated diesel engines is described. The overall program addresses all the key heat transfer issues: (1) spatially and time-resolved convective and radiative in-cylinder heat transfer, (2) steady-state conduction in the overall structure, and (3) cyclical and load/speed temperature transients in the engine structure. These are all accounted for in a coupled way together with cycle thermodynamics. This methodology was developed during Phases 1 and 2. During Phase 3, an experimental program was carried out to obtain data on heat transfer under cooled and insulated engine conditions and also to generate a database to validate the developed methodology. A single cylinder Cummins diesel engine was instrumented for instantaneous total heat flux and heat radiation measurements. Data were acquired over a wide range of operating conditions in two engine configurations. One was a cooled baseline. The other included ceramic coated components (0.050 inches plasma sprayed zirconia)-piston, head and valves. The experiments showed that the insulated engine has a smaller heat flux than the cooled one. The model predictions were found to be in very good agreement with the data.

The Kalina cycle and similar cycles for geothermal power production

Abstract: This report contains a brief discussion of the mechanics of the Kalina cycle and ideas to extend the concept to other somewhat different cycles. A modified cycle which has a potential heat rejection advantage but little or no performance improvement is discussed. Then, the results of the application of the Kalina cycle and the modified cycle to a geothermal application (360/degree/F resource) are discussed. The results are compared with published results for the Kalina cycle with high temperature sources and estimates about performance at the geothermal temperatures. Finally, the conclusions of this scoping work are given along with recommendations of the direction of future work in this area. 11 refs., 4 figs., 1 tab.

Compression Ratio Optimization in a Direct-Injection Diesel Engine: A Mathematical Model

Abstract: This paper describes the development and results of a mathematical model for a single cylinder, naturally-aspirated, direct-injection diesel engine, used to study the effect of compression ratio on the different performance parameters. The model simulates a full thermodynamic cycle and considers the intake and exhaust processes, instantaneous heat transfer, instantaneous friction, and instantaneous blowby

Thermally Regenerative Hydrogen/Oxygen Fuel Cell Power Cycles

Abstract: Two thermodynamic power cycles are analytically examined for future engineering feasibility. These power cycles use a hydrogen-oxygen fuel cell for electrical energy production and use the thermal dissociation of water for regeneration of the hydrogen and oxygen. The first cycle uses a thermal energy input at over 2000K to thermally dissociate the water. The second cycle dissociates the water using an electrolyzer operating at high temperature (1300K) which receives both thermal and electrical energy as inputs. The results show that while the processes and devices of the 2000K thermal system exceed current technology limits, the high temperature electrolyzer system appears to be a state-of-the-art technology development, with the requirements for very high electrolyzer and fuel cell efficiencies seen as determining the feasibility of this system.

Liquid-ring expansion engine with condensate return

Abstract: The invention concerns a method employing a liquid-ring expansion engine to convert the pressure energy of compressed vapours into motive energy. At the same time, the forces of the rotating liquid ring, which consists of gas condensate, are to be used to feed condensate continuously to the vapour generator in the sense of thermodynamic cycles. With such an expansion engine, two functions of the cycle, letting gas expand and pressing condensate into the vapour generator, can be performed by a unit that is simple to manufacture and long-lived. No pump is needed. High-grade mechanical energy can be obtained with the expansion engine and two heat exchangers (for vaporisation and condensation of the working medium) without disadvantages in the energy conversion, for example on the basis of the organic Rankine cycle. In this device, the functions of an expansion engine and a boiler feed pump overlap. The unit is simple to manufacture and long-lived.

Analysis of a pressure driven absorption refrigeration cycle

Abstract: This study presents an analysis of a pressure driven absorption refrigeration cycle which utilizes a membrane separation process to achieve refrigerant-absorbent (R/A) separation. Since the performance of such membranes cannot be predicted generally, the analysis is accomplished by computing cycle performance as a function of the effectiveness of the membrane separation process. The net refrigeration effect and work input are determined based on thermodynamic property data for several working fluid combinations, and desirable characteristics for refrigerant-absorbent pairs are identified. The solubility parameter is used to characterize the potential for separation by candidate membrane materials. The absorbent tetraethylene glycol dimethyl ether (E-181) is found to have good potential for separation from Refrigerants 21 and 22 by typical membranes such as cellulose acetate. The coefficient of performance of the proposed cycle is lower than that of a standard vapour compression cycle operating between the same temperature limits. Improved cycle performance may be achieved by development of a working fluid pair having a more nearly optimum combination of properties.

An Example of the Manipulation of Effective Vapor Pressure Curves by Thermodynamic Cycles

Abstract: The performance of a two-stage Rankine cycle employing a working fluid mixture and solution circuits has been computed with reference to heat pump applications. Its performance is compared to the single-stage version of this cycle and of operating with pure refrigerants. It is found that the two-stage cycle operates along an effective vapor pressure curve of very flat slope, resulting in pressure ratios that are reduced to about one third compared to conventional cycles. For large temperature differences between heat sink and source the Coefficient of Performance (COP) can be increased by up to 50 percent.

Temperature transformation for high-temperature heat pumps

Abstract: A heat pump cycle is introduced that allows heat pumping between two very high temperature levels, while the suction temperature of the working fluid vapor passing through the compressor is considerably lower. This effect of Temperature Transformation is achieved by using a working fluid mixture instead of a single pure component and by employing an unconventional cycle design. The proposed cycle allows the extension of heat pump applications to high temperature levels without encountering operating problems for conventional compressors. This cycle and its features are explained. Its performance has been calculated and the results are presented and discussed.

Evaluation of potential military applications of Stirling engines. Final report, January-June 1988

Abstract: This paper reports on the potential military applications of the Stirling engine. In the applications considered here, the major advantages cited for the Stirling engine are multifuel capability, efficiency, and low noise levels. These potential advantages are small compared to current diesels. Diesels are already able to burn broadcut fuels, have high efficiency, and can be adequately muffled. Their major disadvantages are size, weight, and cost. These disadvantages are only severe in vehicular and mobile-power applications where the competition is open-cycle internal combustion engines (diesel, spark-ignition, or turbine). In underwater and space-power applications where closed-cycle engines are a necessity, the use of Stirling engines shows more promise.

Aerobic heat engine, particularly for the propulsion of hypersonic aircraft

Abstract: Heat engine essentially characterised in that the turbine T precedes the compressor C and is separated from the latter by a cooling heat exchanger Ech supplied with cryogenic fluid This engine thus operates according to a thermodynamic cycle which, with respect to conventional heat engines, is reversed It is advantageous to take liquid hydrogen as the cryogenic fluid The hydrogen leaving the exchanger Ech may then supply a combustion centre F1 situated upstream of the turbine, and a combustion centre F2 situated downstream of the compressor C Application to hypersonic aircraft

Magnetic heat pump design

Abstract: Heat pumps utilizing the magnetocaloric effect offer a potentially attractive alternative to conventional heat pumps and refrigerators. Many physical configurations of magnetic heat pumps are possible. Major classes include those requiring electrical energy input and those with mechanical energy input. Mechanical energy is used to move magnets, working material, or magnetic shielding. Each type of mechanical magnetic heat pump can be built in a rotary (recuperative) or reciprocal (regenerative) configuration. Machines with electrical energy input utilize modulation of the magnetic field to cause working material to execute the desired thermodynamic cycle, and can also be recuperative or regenerative. Recuperative rotary heat pumps in which working material is moved past stationary magnets is the preferred configuration. Regenerative devices suffer performance degradation from temperature change of regenerator material and mixing and conduction in the regenerator. Field modulated cycles are not practical due to ac losses in superconducting magnets. Development of methods for recuperator fluid pumping is the major challenge in design of rotary recuperative devices. Several pumping options are presented, and the design of a bench scale heat pump described. 7 refs., 7 figs.

Testing of a Stirling cycle cooler

Abstract: Stirling cycle coolers have long been used as low temperature refrigeration devices. They are relatively compact, reliable, commercially available, and use helium as the working fluid. The Stirling cycle, in principle, can be used for household refrigeration and heat pumping applications as well. Currently, these applications are almost entirely provided by the vapor compression technology using chlorofluorocarbons (CFCs) as working fluids. It has been known that CFCs cause depletion of the ozone layer that protects the earth against harmful levels of ultraviolet radiation from the sun. A recent report of a ''hole'' in the ozone layer above Antarctica and of possible environmental and health consequences from ozone depletion aroused public attention. The urgent need to reduce the future used of CFCs should instigate investigation of non-CFC alternative technologies. The Stirling cooler technology, which does not use CFCs, could be a viable alternative. A laboratory test of the performance of a Stirling cooler is reported and its implications for household refrigeration are explored. 11 refs., 6 figs., 2 tabs.

Advanced sensible heat solar receiver for space power

Abstract: NASA Lewis, through in-house efforts, has begun a study to generate a conceptual design of a sensible heat solar receiver and to determine the feasibility of such a system for space power applications. The sensible heat solar receiver generated in this study uses pure lithium as the thermal storage medium and was designed for a 7 kWe Brayton (PCS) operating at 1100 K. The receiver consists of two stages interconnected via temperature sensing variable conductance sodium heat pipes. The lithium is contained within a niobium vessel and the outer shell of the receiver is constructed of third generation rigid, fibrous ceramic insulation material. Reradiation losses are controlled with niobium and aluminum shields. By nature of design, the sensible heat receiver generated in this study is comparable in both size and mass to a latent heat system of similar thermal capacitance. The heat receiver design and thermal analysis were conducted through the combined use of PATRAN, SINDA, TRASYS, and NASTRAN software packages.