Showing papers on "Thermodynamic cycle published in 2001"

Hydrocarbons as refrigerants — an overview

Abstract: Possibilities and problems of using hydrocarbons as working fluids in refrigerating equipment are discussed. An overview of safety standards is given. Different hydrocarbon alternatives are listed and characteristics in terms of thermodynamic cycles as well as heat transfer are shown. The general conclusion is that hydrocarbons offer interesting refrigerant alternatives for energy efficient and environmentally friendly refrigerating equipment and heat pumps. However, safety precautions due to flammability must be seriously taken into account. For some applications this can be done without adding noticeably to the total installation cost, but not in the general case.

Electroactive polymer thermal electric generators

Abstract: This disclosed generators include one or more transducers that use electroactive polymer films to convert thermally generated mechanical energy to electrical energy. The generators may include one or more transmission mechanisms that convert a portion of thermal energy generated from a heat source such as internal combustion, external combustion, solar energy, geothermal energy or waste heat, to mechanical energy that is used to drive the one or more transducers located in the generator. The energy received by the transducers may be converted to electrical energy by the transducers in conjunction with conditioning electronics located within the generator. One embodiment of the present invention provides an energy conversion device with two chambers each chamber including a diaphragm transducer that may convert thermal energy to electricity using a thermodynamic cycle such as a Stirling gas cycle. The thermodynamic cycle of the energy conversion device may be reversed to provide cooling to an external device such as a semiconductor device.

Modeling the Air-Cooled Gas Turbine: Part 1—General Thermodynamics

Abstract: This paper is Part I of a study concerned with developing a formal framework for modelling air-cooled gas turbine cycles and deals with basic thermodynamic issues. Such cycles involve gas mixtures with varying composition which must be modelled realistically. A possible approach is to define just two components, air and gas, the latter being the products of stoichiometric combustion of the fuel with air. If these components can be represented as ideal gases, the entropy increase due to compositional mixing, although a true exergy loss, can be ignored for the purpose of performance prediction. This provides considerable simplification. Consideration of three idealised simple cycles shows that the introduction of cooling with an associated thermal mixing loss does not necessarily result in a loss of cycle efficiency. This is no longer true when real gas properties and turbomachinery losses are included. The analysis clarifies the role of the cooling losses and shows the importance of assessing performance in the context of the complete cycle. There is a strong case for representing the cooling losses in terms of irreversible entropy production as this provides a formalised framework, clarifies the modelling difficulties and aids physical interpretation. Results are presented which show the effects on performance of varying cooling flowrates and cooling losses. A comparison between simple and reheat cycles highlights the role of the thermal mixing loss. Detailed modelling of the heat transfer and cooling losses is discussed in Part II of this paper Copyright © 2001 by ASME.

Cooling and heating apparatus and process utilizing waste heat and method of control

Abstract: The present invention provides a process and apparatus for utilizing waste heat to power a reconfigurable thermodynamic cycle that can be used to selectively cool or heat an environmentally controlled space, such as a room or a building. The present invention also provides a method of controlling the system, while allowing large variations in the heat input energy rate. The system provides a design which reasonably balances the need to maximize efficiency, while also keeping the design cost effective.

Optimum distribution of heat exchanger inventory for power density optimization of an endoreversible closed Brayton cycle

Abstract: In this paper, the power density (defined as the ratio of the power output to the maximum specific volume in the cycle) is taken as the objective for performance optimizations of an endoreversible closed Brayton cycle coupled to constant-temperature heat reservoirs in the viewpoint of finite-time thermodynamics (FTT) or entropy generation minimization (EGM). The optimum heat conductance distribution corresponding to the optimum power density of the hot- and cold-side heat exchangers for the fixed heat exchanger inventory is analysed using numerical examples. The influence of some design parameters on the optimum heat conductance distribution and the maximum power density and the optimum pressure ratio corresponding to the maximum power density are provided. The power plant design with optimization leads to higher efficiency and smaller size.} \fnm{3}{Author to whom correspondence should be addressed.

Method for Kalina combined cycle power plant with district heating capability

Abstract: A method is provided for implementing a thermodynamic cycle with district water heating capabilities that combines a simplified Kalina bottoming cycle with a district water heating plant. The preferred method includes pressurizing, vaporizing and superheating a mixture working fluid (e.g., H2O/NH3) using gas turbine exhaust energy in a heat recovery vapor generator, expanding the working fluid in a turbine to produce power, and then transferring the working fluid thermal energy to the district water by condensing the working fluid in a single stage condenser. The method can also include systems that efficiently use excess thermal energy only when the district water heating demand is low, e.g., during summer months. The method according to the invention provides for economically significant increases in district water heating efficiency as compared to conventional Rankine cycles with district water heating, while decreasing the cost of both the Rankine and nominal Kalina cycles using multi-component working fluids.

A thermodynamic comparison of the oxy-fuel power cycles water-cycle, graz-cycle and matiant-cycle

Abstract: Olav Bolland, Norwegian University of Science and Technology, N-7491 Trondheim, Norway, Tel: +47 73591604 Fax: +47 73598390 – E-mail: Olav.Bolland@tev.ntnu.no Hanne M. Kvamsdal, SINTEF Energy Research, N-7465 Trondheim, Norway, Tel: +47 73550465 Fax: +47 73593580 – E-mail: Hanne.Kvamsdal@energy.sintef.no John C. Boden, (CO2 Capture Project), BP Oil International, Sunbury-on-Thames, TW16 7LN, UK, Tel: +44 1932 771929 – Fax: +44 1932 763439– E-mail: bodenjc@bp.com

Thermodynamic Cycle Analysis of Magnetohydrodynamic-Bypass Hypersonic Airbreathing Engines

Abstract: The prospects for realizing a magnetohydrodynamic (MHD) bypass hypersonic airbreathing engine are examined from the standpoint of fundamental thermodynamic feasibility. The MHD-bypass engine, first proposed as part of the Russian AJAX vehicle concept, is based on the idea of redistributing energy between various stages of the propulsion system flow train. The system uses an MHD generator to extract a portion of the aerodynamic heating energy from the inlet and an MHD accelerator to reintroduce this power as kinetic energy in the exhaust stream. In this way, the combustor entrance Mach number can be limited to a specified value even as the flight Mach number increases. Thus, the fuel and air can be efficiently mixed and burned within a practical combustor length, and the flight Mach number operating envelope can be extended. In this paper, we quantitatively assess the performance potential and scientific feasibility of MHD-bypass engines using a simplified thermodynamic analysis. This cycle analysis, based on a thermally and calorically perfect gas, incorporates a coupled MHD generator-accelerator system and accounts for aerodynamic losses and thermodynamic process efficiencies in the various engin components. It is found that the flight Mach number range can be significantly extended; however, overall performance is hampered by non-isentropic losses in the MHD devices.

Thermodynamic Optimization of the HAT Cycle Plant Structure—Part I: Optimization of the “Basic Plant Configuration”

Abstract: A method for the thermodynamic optimization of the humid air turbine cycle plant structure is presented here. The method is based on the optimization of a basic configuration of the plant including basic components (compressor, turbine, combustion chamber, regenerator, and saturator), always present and connected in the same way in the plant structure and a heat exchange section which is viewed as a black-box where the heat transfer between hot and cold thermal flows occurs regardless of how many heat exchangers there are and of how they are interconnected. The optimal boundary conditions between the basic components and black-box are determined by calculating the conditions of maximum heat transfer in the black-box independently of the structure of the heat exchanger network. This is done by defining optimal composite curves in a Fortran routine at each step in the main optimization procedure. Once the structure of the heat exchanger networks that fulfill the optimal boundary conditions have been found, the optimal structure of the whole plant is obtained (see Section 2). The method is useful in a general sense as it can be applied to highly integrated energy systems in which it is difficult to define the optimal structure of the heat exchanger network in advance.

Power Density Optimization for an Irreversible Regenerated Closed Brayton Cycle

Abstract: In this paper, the power density, defined as the ratio of power output to the maximum specific volume in the cycle, is taken as objective for performance optimization of an irreversible regenerated closed Brayton cycle coupled to constant-temperature heat reservoirs in the viewpoint of finite time thermodynamics (FTT) or entropy generation minimization (EGM). The analytical formulae about the relations between power density and pressure ratio are derived with the heat resistance losses in the hot- and cold-side heat exchangers and the regenerator, the irreversible compression and expansion losses in the compressor and turbine, and the pressure drop loss in the piping. The maximum power density optimization is performed by searching the optimum heat conductance distribution corresponding to the optimum power density among the hot- and cold-side heat exchangers and the regenerator for the fixed total heat exchanger inventory. The influence of some design parameters, including the temperature ratio of the heat reservoirs, the total heat exchanger inventory, the efficiencies of the compressor and the turbine, and the pressure recovery coefficient, on the optimum heat conductance distribution and the maximum power density are provided. When the heat transfers between the working fluid and the heat reservoirs are carried out ideally, the analytical results of this paper become those obtained in recent literature. The power plant design with optimization leads to smaller size including the compressor, turbine, and the hot- and cold-side heat exchangers and the regenerator.

A Performance Map for Ideal Air Breathing Pulse Detonation Engines

Abstract: The performance of an ideal, air breathing Pulse Detonation Engine is described in a manner that is useful for application studies (e.g., as a stand-alone, propulsion system, in combined cycles, or in hybrid turbomachinery cycles). It is shown that the Pulse Detonation Engine may be characterized by an averaged total pressure ratio, which is a unique function of the inlet temperature, the fraction of the inlet flow containing a reacting mixture, and the stoichiometry of the mixture. The inlet temperature and stoichiometry (equivalence ratio) may in turn be combined to form a nondimensional heat addition parameter. For each value of this parameter, the average total enthalpy ratio and total pressure ratio across the device are functions of only the reactant fill fraction. Performance over the entire operating envelope can thus be presented on a single plot of total pressure ratio versus total enthalpy ratio for families of the heat addition parameter. Total pressure ratios are derived from thrust calculations obtained from an experimentally validated, reactive Euler code capable of computing complete Pulse Detonation Engine limit cycles. Results are presented which demonstrate the utility of the described method for assessing performance of the Pulse Detonation Engine in several potential applications. Limitations and assumptions of the analysis are discussed. Details of the particular detonative cycle used for the computations are described.

Thermodynamic optimization of the HAT cycle plant structure. Part II : Structure of the heat exchanger network

Abstract: In Part 1 of the paper a thermodynamic optimization methodology was presented for the basic configuration of a humid air turbine cycle plant in which the heat exchange section is viewed as a black-box separated from the rest of the plant (basic components), having a fixed structure. The results of the optimization apply to all the heat exchanger networks that fulfill the optimal boundary conditions between the black-box and the rest of the plant. The aim of this part is to define these heat exchanger networks using a combination of Pinch Technology and Second Law insights. The possibility of a further reduction in the number of heat exchangers is then investigated in order to achieve the best compromise between high performances and structural simplicity.

Impact of Dissociation and Sensible Heat Release on Pulse Detonation and Gas Turbine Engine Performance

Abstract: A thermodynamic cycle analysis of the effect of sensible heat release on the relative performance of pulse detonation and gas turbine engines is presented. Dissociation losses in the PDE (Pulse Detonation Engine) are found to cause a substantial decrease in engine performance parameters.

Performance improvements of the intercooled reheat regenerative gas turbine cycles using indirect evaporative cooling of the inlet air and evaporative cooling of the compressor discharge

Abstract: Inlet air cooling and cooling of the compressor discharge using water injection boost both efficiency and power of gas turbine cycles. An innovative method of cooling the inlet air (indirect evaporative cooling) is introduced. Six different layouts of the intercooled reheat regenerative gas turbine cycle are presented. Those layouts include the effect of different methods of inlet cooling and evaporative cooling of the compressor discharge (evaporative aftercooling). A parametric study of the effect of turbine inlet temperature, ambient temperature and relative humidity on the performance of all six layouts is carried out. The results indicate that as the turbine inlet temperature increases the optimum pressure ratio increases by 1.5 per 100 K for the regular intercooled reheat regenerative cycle and by 4.2 per 100 K for the intercooled reheat regenerative cycle with evaporative aftercooling. The cycles with evaporative aftercooling have distinctive patterns of performance curves and higher values...

Performance research of self regenerated absorption heat transformer cycle using TFE-NMP as working fluids

Abstract: A heat transformer is proposed in order to upgrade low-temperature-level energy to a higher level and to recover more energy in low-temperature-level waste heat. It is difficult to achieve both purposes at the same time using a conventional heat transformer cycle and classical working pairs, such as H 2 O–LiBr and HN 3 –H 2 O. The new organic working pair, 2,2,2-trifluoroethanol (TFE)- N -methylpyrolidone (NMP), has some advantages compared with H 2 O–LiBr and NH 3 –H 2 O. One of the most important features is the wide working range as a result of the absence of crystallization, the low working pressure, the low freezing temperature of the refrigerant and the good thermal stability of the mixtures at high temperatures. Meanwhile, it has some negative features like NH 3 –H 2 O. For example, there is a lower boiling temperature difference between TFE and NMP, so a rectifier is needed in refrigeration and heat pump systems. Because TFE–NMP has a wide working range and does not cause crystallization, it can be used as the working pair in the self regenerated absorption heat transformer (SRAHT) cycle. In fact, the SRAHT cycle is the generator–absorber heat exchanger (GAX) cycle applied in a heat transformer cycle. In this paper, the SRAHT cycle and its flow diagram are shown and the computing models of the SRAHT cycle are presented. Thermal calculations of the SRAHT cycle under summer and winter season conditions have been worked out. From the results of the thermal calculations, it can be found that there is a larger temperature drop when the waste hot water flows through the generator and the evaporator in the SRAHT cycle but the heating temperature can be kept the same. That means more energy in the waste heat source can be recovered by the SRAHT cycle.

Fundamental Study on a Novel Gas Turbine Cycle

Abstract: It is important and necessary to develop a new technology for CO 2 capture with less or even no energy penalty to make a breakthrough in greenhouse gas abatement. Towards this objective, we have proposed a novel gas turbine power plant, which is not only to capture CO 2 in the stage of combustion, but also to increase thermal efficiency of the power plant. The chemical-looping combustor in the proposed system consists of a fuel reactor (fuel reacts with metal oxide) and an air reactor (the resulting metal reacts with oxygen in air). This new system requires no additional energy consumption for CO 2 separation (i.e., no energy penalty) and no CO 2 separation equipment. Here, we have identified several breakthrough points in the proposed system and summarized promising results from experimental investigation on the chemical-looping combustion.

Ecological optimisation of an irreversible Stirling heat engine

Abstract: SYNOPSIS A general cycle model of an irreversible Stirling heat engine using an ideal or Van der Waals gas as the working substance is established. It includes three main sources of the irreversibility such as the heat transfer across finite-temperature differences in the isothermal processes, the regenerative loss resulting from the non-perfect regeneration in the regenerator, and the heat leak loss between the external heat reservoirs. The ecological function is taken as an objective function for optimisation. The performance characteristics of the Stirling heat engine at maximum ecological function are revealed. They are compared with other performance characteristics of the Stirling heat engine at maximum power output and efficiency in order to expound the significance of the ecological objective function. The results obtained here are of importance in the optimal design and operation of real Stirling heat engines. Finally, it is pointed out that the results obtained in this paper are very general, fr...

Thermodynamic and thermoeconomic analyses of an irreversible combined Carnot heat engine system

Abstract: A combined cycle model which includes the irreversibilities of finite-rate heat transfer in heat-exchange processes and heat leak loss of the heat source is used to analyse the performance of a multi-stage Carnot heat engine system. The efficiency, power output, ecological function and profit of operating the combined system are optimized. The optimally operating region of the combined system is determined. The optimal combined conditions between two adjacent cycles in the combined system are obtained. Moreover, the cycle model is generalized to include the internal irreversibilities of the working fluids so that the results obtained here become more general. Copyright © 2001 John Wiley & Sons, Ltd.

Analysis of a 115MW, 3-Shaft, Helium Brayton Cycle Using Nuclear Heat Source

Abstract: This paper describes the steady state performance analysis of a 3-shaft closed cycle helium turbine using nuclear heat source The analysis is carried out using a computer program, which is specifically made for this cycle The computer model was tested for various Turbine Entry Temperatures (TET) and absolute pressures The analysis of the change was focused on the compressors, as these are relatively more critical than the rest of the equipmentsThe change in TET triggered changes in shaft speed, mass flow rate, power output, absolute pressure etc Adjustable guide vanes were used to study the operation with constant surge margin The closed cycle was tested for various absolute pressures and it was established that the efficiency will not be affected in using the inventory control for the load variationCopyright © 2001 by ASME

Heat dissipating structure of electronic component, and heat dissipating sheet used for the same

Abstract: PROBLEM TO BE SOLVED: To conduct heat generated from the electronic component efficiently to the heat dispersion member, such as a heat sink, and at the same time to remove the electronic component and heat dissipation dispersion member, without damaging the structure of the heat dissipation sheet and electronic components, even after burn-in and heat cycle tests are executed to check the quality. SOLUTION: The heat dissipation structure body of electronic component is to be provided. In the heat dissipation structure body; a heat dissipation sheet, where a metal sheet and a heat-conducting member having viscosity are laminated between a heat generation electronic component and a heat dispersion member are to be contained; a metal sheet should be connected to the heat generation electronic component; and the heat-conducting member having viscosity should be connected to the heat dispersion member.

A multiple-use super-efficient heating and cooling system

Abstract: The present invention relates generally to a Multiple-Use Super-Efficient heating and cooling (10) together with a vapour-compression system (20) each including a respective continuous fluid path (44) and a continuous vapour-compression cycle (24). In this example both the fluid path (44) and the vapour-compression cycle (24) are adapted to carry water and refrigerant fluid, respectively. The continuous fluid path or Multiple-Use Super-Efficient heating and cooling system (44) of this example includes one or more external heating loads (40), latent heat accumulator (42) containing one or more phase change substances, circulating pump (46), and one or more heat exchangers (22) of the vapour-compression cycle (20) being in heat transfer means adapted to be in heat conductive communication with each other. The vapour-compression cycle (20) of this example is a standard vapour-compression heat pump cycle. The cycle (20) includes a condenser (22), a compressor (30), an evaporator (28), and an expansion valve (26) connected in a conventional manner. The compressor (30) may be driven by an electrical motor (32). The vapour-compression cycle (20) of another example is a standard vapour-absorption refrigeration cycle.