Showing papers on "Thermodynamic cycle published in 1998"
TL;DR: In this article, the authors provide a unique view into the physics behind the heat pipe operation, which was considered a thermal network of various components, by first-order, linear, ordinary differential equations.
186 citations
TL;DR: In this article, the authors review some recent developments in thermodynamic cycles as well as new and innovative thermal power cycles applicable to solar thermal power and present a new thermal power cycle for solar thermal energy.
Abstract: This article reviews some recent developments in thermodynamic cycles as well as new and innovative thermal power cycles applicable to solar thermal power
164 citations
TL;DR: In this article, the Kalina cycle has been analyzed thermodynamically for which a general code has been developed for the calculation of thermodynamic properties of the mixture of NH3-H2O mixture.
139 citations
TL;DR: In this article, the authors used a packed bed of inert material to store heat between the adsorption and desorption phases of the cycle and used it to construct a 10 kW water chiller.
96 citations
TL;DR: In this paper, a solar-driven Stirling engine is modelled as a combined system which consists of a solar collector and a stirling engine, and the performance of the system is investigated, based on the linearized heat loss model of the solar collector.
Abstract: A solar-driven Stirling engine is modelled as a combined system which consists of a solar collector and a Stirling engine. The performance of the system is investigated, based on the linearized heat loss model of the solar collector and the irreverisible cycle model of the Stirling engine affected by finite-rate heat transfer and regenerative losses. The maximum efficiency of the system and the optimal operating temperature of the solar collector are determined. Moreover, it is pointed out that the investigation method in the present paper is valid for other heat loss models of the solar collector as well, and the results obtained are also valid for a solar-driven Ericsson engine system using an ideal gas as its engine work substance. © 1998 John Wiley & Sons, Ltd.
76 citations
TL;DR: In this paper, a performance analysis based on the maximum power density criterion has been carried out for an irreversible regenerative reheating Joule-Brayton engine, and the obtained results were compared with those obtained using the conventional maximum power performance criterion.
Abstract: A performance analysis based on the maximum power density criterion has been carried out for an irreversible regenerative reheating Joule-Brayton engine. The obtained results were compared with those obtained using the maximum power performance criterion. The design parameters under the optimal conditions have been derived analytically and their effects on the engine's performance have been discussed. The overall effects of reheating, regeneration and internal irreversibilities are investigated. The obtained results may provide a general theoretical tool for the optimal design and operation of real non-regenerative and regenerative reheating gas turbines.
67 citations
TL;DR: In this paper, the effect of heat resistance on the performance of an air refrigeration cycle is analyzed with a finite time heat transfer analysis with nonisentropic compression and expansion.
66 citations
TL;DR: In this paper, a new cycle model, which includes the heat leak from the heat sink to the cooled space and irreversibilities due to the internal dissipation of the working fluid besides the finite-rate heat transfer between the working liquid and the external heat reservoirs, is established and used to calculate the maximum coefficient of performance and cooling rate of the absorption refrigeration system for a given total heat-transfer area of the heat exchangers.
64 citations
Dissertation•
01 Aug 1998
TL;DR: In this article, thermodynamic and mixture property models of the Einstein cycle were created to gain insight into the cycle's operating characteristics and to calculate its performance, and a conceptual demonstration model was built and successfully operated, showing for the first time the viability of the cycle.
Abstract: After developing the theory of relativity, Albert Einstein spent several years working with Leo Szilard on absorption refrigeration cycles. In 1930, they obtained a US patent for a unique single pressure absorption cycle. The single pressure eliminates the need for a solution pump. Their cycle has only recently been rediscovered. The cycle utilizes butane as its refrigerant, ammonia as a pressure equalizing fluid, and water as an absorbing fluid. This cycle is dramatically different in both concept and detail than the better-known ammonia-water-hydrogen cycle. In this study, thermodynamic and mixture property models of the Einstein cycle were created to gain insight into the cycle's operating characteristics and to calculate its performance. A conceptual demonstration model was built and successfully operated, showing for the first time the viability of the cycle. The model results found that the system pressure is an important design parameter, with the COP having an optimum when the system pressure is equal to the saturation pressure of the butane refrigerant. It was also found that for a given system pressure, there is a maximum condenser-absorber temperature and a minimum evaporator temperature.
62 citations
TL;DR: In this paper, the transcritical CO 2 process fits well to the air dehumidification process observed in a heat pump dryer, resulting in an equivalent or even better coefficient of performance than the comparative R134a process.
Abstract: The transcritical CO 2 process fits well to the air dehumidification process observed in a heat pump dryer. Gains (respectively avoided losses) in connection with heat transfer during the air heating phase and superior compressor performance make up for the higher throttling losses of the process, resulting in an equivalent or even better coefficient of performance than the comparative R134a process.
58 citations
TL;DR: Olsson et al. as mentioned in this paper investigated whether there are any thermodynamic advantages of using ammonia-water mixture cycles in small direct-fired biomass-fueled cogeneration plants, and the main interest is to achieve a higher net power output.
TL;DR: In this paper, the authors explored the lower size limit placed on regenerative heat engines by thermodynamics and heat transfer and showed that a small-scale heat engine fabricated from a low-thermal-conductivity material can be made with a length scale approaching 1 mm.
Abstract: This article explores the lower size limit placed on regenerative heat engines by thermodynamics and heat transfer. Information derived in this work has direct relevance to the development of mesoscopic heat engines that are based on standard gas cycles employing regeneration. A model is developed for the Stirling cycle that incorporates a regenerator effectiveness term and an axial conduction term, both of which are dependent on the length scale of the device. The thermal efficiency for the engine is determined in terms of the cycle temperature ratio, the expansion ratio, regenerator effectiveness, and a nondimensional term called the conduction parameter. Results from this study show that a small-scale heat engine fabricated from a low-thermal-conductivity material can be made with a length scale approaching 1 mm. Such a device would undoubtedly be composed of numerous microscale components. Below the 1-mm limit, efficiency suffers to such a degree that solid-state thermoelectric devices would become a ...
TL;DR: In this article, the authors derived the relation between optimal profit and COP of an endoreversible Carnot heat pump based on a relatively general heat transfer law: q∞Δ(Tn).
TL;DR: In this paper, the effect of irreversibilities due to thermal resistances and regenerative losses on the performance of a magnetic Ericsson refrigeration cycle is investigated, based on the Curie law and Newtonian heat-transfer law.
Abstract: The effect of the irreversibilities due to thermal resistances and regenerative losses on the performance of a magnetic Ericsson refrigeration cycle is investigated, based on the Curie law and Newtonian heat-transfer law. Some fundamental optimum relations and general performance characteristics of the cycle are obtained. The maximum cooling rate and some important performance parameters are calculated. The optimal operating regions of the cycle are determined. The results obtained will be helpful for the optimal design and operation of real magnetic Ericsson refrigerators.
TL;DR: In this article, an ejector was placed between a generator and a condenser of a conventional single-effect absorption refrigerator, which entrained low-pressure refrigerant vapour from the evaporator and discharged it to the condenser.
Abstract: This paper describes an experimental study of a novel heat-operated refrigeration cycle, ‘combined ejector-absorption refrigeration cycle’. In this novel cycle, an ejector was placed between a generator and a condenser of a conventional single-effect absorption refrigerator. The high-pressure vapour refrigerant produced in the generator section was used as the motive fluid for the ejector which entrained low-pressure refrigerant vapour from the evaporator and discharged it to the condenser. This was shown to significantly increase the cooling capacity and COP of the novel refrigerator above that of a conventional absorption unit with little increase in system complexity. © 1998 John Wiley & Sons, Ltd.
Patent•
07 Apr 1998
TL;DR: In this paper, a waste-heat boiler adapted to a Rankine cycle provided with turbines for driving an electric generator was used for generating an electric power generating system and using exhaust combustion products from a fuel-fired device as a thermal heat source.
Abstract: An electric power generating system and method of operation is comprised of a waste-heat boiler adapted to a Rankine cycle provided with turbines for driving an electric generator. The waste-heat boiler uses exhaust combustion products from a fuel-fired device as a thermal heat source for vapor regeneration of an organic heat exchange fluid mixture used in the Rankine cycle.
Patent•
23 Jan 1998
TL;DR: A combined cycle power plant which has a backup function at startup and even during operation, and surely maintains steam cooling in the event of occurrence of an accident is discussed in this article.
Abstract: A combined cycle power plant which has a backup function at startup and even during operation, and surely maintains steam cooling in the event of occurrence of an accident. The combined cycle power plant serves to surely maintain steam cooling by conducting to a steam cooling system (400), which causes a high pressure portion being cooled, of a gas turbine to be cooled by steam, a high pressure steam or a medium pressure steam from an exhaust heat recovery boiler (200), when an exhaust steam, which is a cooling steam for the steam cooling system (400), from a high pressure turbine (301) suddenly decreases, to use the same as a cooling steam.
TL;DR: In this paper, the power output and thermal efficiency of a finite-time optimized solar-radiant Ericsson heat engine is studied. And the results of this theoretical work provide a base line criteria for use in the performance evaluation and design of such engines as well as for using in performance comparisons with existing extra-terrestrial solar power plants.
Patent•
03 Sep 1998
TL;DR: In this article, a comparison study between the regular reheat regenerative cycle and the invented cycle is done and the results indicate that a gain in efficiency of up to 25% is obtained when applying invented cycle at the same conditions of pressure, temperatures, number of reheating stages, and feed water heaters.
Abstract: Reheat of reheat regenerative steam power cycle increases its efficiency by increasing the average temperature of heat reception In spite of such an increase in efficiency, reheating increases the irreversibility of feed water heaters by using superheated steam of a greater temperature difference in the regenerative cycle This invention introduces some modifications to the regular reheat regenerative steam power cycle that reduces the irreversibility of the regenerative process The invention applies reversible reheating in addition to the regular reheating and uses smaller temperature differences across feed water heaters than the regular cycle A comparison study between the regular reheat regenerative cycle and the invented cycle is done The results indicate that a gain in efficiency of up to 25% is obtained when applying invented cycle at the same conditions of pressure, temperatures, number of reheating stages, and feed water heaters In addition, the invented cycle has some practical advantages associated with up to 50% reduction in the mass flow rate that is regularly reheated for the same output power Such advantages such as less pressure drop and heat transfer loss Such advantages allow us to use a greater number of reheating stages of the invented cycle for the same pressure drop and heat transfer losses of the reheater pipes of the regular cycle Another practical advantage of the invented cycle over the regular cycle is higher heat transfer coefficients for the heat exchangers of the feed water heaters because they are mainly operated in the two-phase region Such practical advantage results in smaller sizes for the heat exchangers of the invented cycle compared with the ones for the regular cycle
01 Nov 1998
TL;DR: In this article, an ejector boosted single-effect absorption-recompression refrigeration cycle is described. And the ejector is used as a heat-pump to enhance the concentration process by increasing the flow of leaving vapour and increasing the quantity of heat input at the concentrator.
Abstract: This paper reports on a novel ejector boosted single–effect absorption-recompression refrigeration cycle. In this cycle, a steam generator, ejector and a concentrator replace the high and low pressure generators (concentrators) used in conventional double-effect absorption cycle machines, to re-concentrate the absorbent solution. The ejector here acts like a heat-pump to enhance the concentration process by increasing the flow of leaving vapour and by increasing the quantity of heat input at the concentrator. The paper provides a qualitative and quantitative description of the novel cycle and discusses design choices that lead to optimum matching of the absorbent concentrator and ejector. The important role the ejector plays in this novel refrigeration cycle is discussed and some experimental data are presented. An experimental lithium bromide refrigerator based on this cycle is described.
TL;DR: In this article, a Moisture Air Turbine (MAT) cycle is proposed for improving the characteristics of land-based gas turbines by injecting atomized water through an inlet into a compressor.
TL;DR: In this article, a solar-driven ejection absorption refrigeration (EAR) cycle with reabsorption of the strong solution and pressure boost of the weak solution is considered and the physical model is described and the corresponding thermodynamic calculation is performed with the working pair NH3-LiNO3.
Abstract: This paper deals with a solar-driven ejection absorption refrigeration (EAR) cycle with reabsorption of the strong solution and pressure boost of the weak solution. The physical model is described and the corresponding thermodynamic calculation is performed with the working pair NH3–LiNO3. It is demonstrated that the EAR cycle has obvious advantages as compared with the conventional absorption refrigeration cycle: (1) the controllable high absorption pressure allows for substantially high coefficients of performance by the action of a liquid–gas ejector in which the low-pressure refrigerant vapour is injected and pressurized as a result of the ejection of high-pressure solution; (2) internal steady operation can be realized for refrigeration cycles driven by unsteady heat sources, especially for solar energy, by adjusting the power input consumed by solution pumps under the condition of economical and reasonable utilization of electric energy. © 1998 John Wiley & Sons, Ltd.
Patent•
23 Sep 1998
TL;DR: In this article, the authors proposed a new type of regenerative working and thermal processes, where the drive energy of which is supplied by external combustion of the fuel is obtained only in exceptional cases, since the flue gases usually have low specific thermal capacity.
Abstract: The invention relates to regenerative working and thermal processes, the drive energy of which is supplied by external combustion of the fuel. The heat supply for this, almost always assumed to be isothermic, is achieved only in exceptional cases, since the flue gases usually have a low specific thermal capacity. The invention explains new types of processes in order to obtain the optimum thermodynamic efficiency even for these less efficient heating cases. The heating heat exchangers and thermal regenerators used in regenerative processes are replaced by regenerative heat exchangers, which comprise a plurality of short regenerators, which are connected by tubular heat exchangers for the heating medium. It is thereby possible to supply the heat to the process not at a fixed but at a sliding temperature. In the same way, regenerative coolers are used for the dissipation of heat from Stirling engines and regenerative heat pumps or refrigeration machines, if, for example, only air is available as heat transfer medium.
TL;DR: In this paper, the authors derived the optimal cooling load and the COP of two-heat-reservoir refrigeration cycles with and without heat leakage and showed that the existence of heat leakage does not affect the optimal configuration of a cycle with an infinite low-temperature source.
TL;DR: In this article, the maximum cooling density of a Stirling refrigerator operating in a closed regenerative thermodynamic cycle is presented, where the cooling density is defined as the cooling load per unit volume of the refrigerator.
Abstract: The maximum cooling density of a Stirling refrigerator operating in a closed regenerative thermodynamic cycle is presented in this paper. The cooling density is the cooling load per unit volume of the refrigerator. Since the size of the refrigerator is involved in the cooling density, the maximization of the cooling density has given a critical compression ratio. The maximum cooling density serves as a better comparison criterion for thermoeconomic considerations.
TL;DR: In this article, the optimization problem of a combined heat pump cycle made of two endoreversible Carnot heat pump cycles in series without intermediate reservoirs is investigated using finite-time thermodynamics.
TL;DR: In this article, the authors used temperature-entropy diagrams to describe three sorption refrigeration technologies (liquid absorption, solid adsorption, chemical reaction) for basic and simple advanced cycles.
Abstract: Temperature–entropy diagrams are usually used to describe heat-driven engines as well as vapour compressor refrigerators, but they have not yet been used for sorption refrigeration. Such Carnot cycles are introduced here to describe three sorption refrigeration technologies (liquid absorption, solid adsorption, chemical reaction). This is performed for basic cycles (without heat recovery) and for simple advanced cycles. Equivalent four-temperature Carnot cycles are obtained for basic cycles, whereas equivalent six-temperature Carnot cycles are obtained for advanced cycles. This approach shows that the quantity ΔH-TΔS (where ΔH and ΔS are the enthalpy and entropy variations associated with mass transfer during a cycle in/out of the sorbers) plays the same role as the mechanical energy in vapour compression cycles.
TL;DR: In this article, the specific network and efficiency of an open-cycle-twin-shaft gas turbine with precooled exhaust gases were investigated and compared to conventional systems, and it was concluded that the precooling has a marked effect on the specific networks and efficiency at low temperature ratios.
TL;DR: In this article, a universal model of an n-stage combined Carnot cycle system is established, and several major irreversibilities which often exist in real thermodynamic cycles, such as finite-rate heat transfer in the heat exchange processes, heat leak losses of the heat source, and internal dissipation of the working fluid, are included in the model so that many models of irreversible and endoreversible Carnot cycles which appear in the literature can be regarded as special cases of the universal cycle model.
Abstract: A universal model of an n-stage combined Carnot cycle system is established. Several major irreversibilities which often exist in real thermodynamic cycles, such as finite-rate heat transfer in the heat-exchange processes, heat leak losses of the heat source, and internal dissipation of the working fluid, are included in the model so that many models of irreversible and endoreversible Carnot cycles which appear in the literature can be regarded as special cases of the universal cycle model. The efficiency, power output and rate of heat input are optimized. Some characteristic curves of the cycle system are presented. Some important performance bounds are given. The optimal combined conditions between two adjacent cycles in the combined cycle system are determined. The optimal performance of an arbitrary-stage irreversible, endoreversible, and reversible combined Carnot cycle system can be directly derived for specific choices of some parameters. The results obtained here are of general significance for both physics and engineering.