Showing papers on "Thermodynamic cycle published in 2009"

Carbon-ammonia pairs for adsorption refrigeration applications: ice making, air conditioning and heat pumping

Abstract: A thermodynamic cycle model is used to select an optimum adsorbent-refrigerant pair in respect of a chosen figure of merit that could be the cooling production (MJ m(-3)), the heating production (MJ m(-3)) or the coefficient of performance (COP). This model is based mainly on the adsorption equilibrium equations of the adsorbent-refrigerant pair and heat flows. The simulation results of 26 various activated carbon-ammonia pairs for three cycles (single bed, two-bed and infinite number of beds) are presented at typical conditions for ice making, air conditioning and heat pumping applications. The driving temperature varies from 80 degrees C to 200 degrees C. The carbon absorbents investigated are mainly coconut shell and coal based types in multiple forms: monolithic, granular, compacted granular, fibre, compacted fibre, cloth, compacted cloth and powder. Considering a two-bed cycle, the best thermal performances based on power density are obtained with the monolithic carbon KOH-AC, with a driving temperature of 100 degrees C; the cooling production is about 66 MJ m(-3) (COP = 0.45) and 151 MJ m(-3) (COP = 0.61) for ice making and air conditioning respectively; the heating production is about 236 MJ m(-3) (COP = 1.50).

A theoretical study on a novel combined power and ejector refrigeration cycle

Abstract: A new combined power and refrigeration cycle is proposed for the cogeneration, which combines the Rankine cycle and the ejector refrigeration cycle by adding an extraction turbine between heat recovery vapor generator (HRVG) and ejector. This combined cycle could produce both power output and refrigeration output simultaneously, and could be driven by the flue gas from gas turbine or engine, solar energy, geothermal energy and industrial waste heats. Parametric analysis and exergy analysis are conducted to examine the effects of thermodynamic parameters on the performance and exergy destruction in each component for the combined cycle. The results show that the condenser temperature, the evaporator temperature, the turbine inlet pressure, the turbine extraction pressure and extraction ratio have significant effects on the turbine power output, refrigeration output, exergy efficiency and exergy destruction in each component in the combined cycle. It is also shown that the biggest exergy destruction occurs in the heat recovery vapor generator, followed by the ejector and turbine.

Exergy analysis of gas turbine trigeneration system for combined production of power heat and refrigeration

Abstract: A conceptual trigeneration system is proposed based on the conventional gas turbine cycle for the high temperature heat addition while adopting the heat recovery steam generator for process heat and vapor absorption refrigeration for the cold production. Combined first and second law approach is applied and computational analysis is performed to investigate the effects of overall pressure ratio, turbine inlet temperature, pressure drop in combustor and heat recovery steam generator, and evaporator temperature on the exergy destruction in each component, first law efficiency, electrical to thermal energy ratio, and second law efficiency of the system. Thermodynamic analysis indicates that exergy destruction in combustion chamber and HRSG is significantly affected by the pressure ratio and turbine inlet temperature, and not at all affected by pressure drop and evaporator temperature. The process heat pressure and evaporator temperature causes significant exergy destruction in various components of vapor absorption refrigeration cycle and HRSG. It also indicates that maximum exergy is destroyed during the combustion and steam generation process; which represents over 80% of the total exergy destruction in the overall system. The first law efficiency, electrical to thermal energy ratio and second law efficiency of the trigeneration, cogeneration, and gas turbine cycle significantly varies with the change in overall pressure ratio and turbine inlet temperature, but the change in pressure drop, process heat pressure, and evaporator temperature shows small variations in these parameters. Decision makers should find the methodology contained in this paper useful in the comparison and selection of advanced heat recovery systems.

Nonlinear pyroelectric energy harvesting from relaxor single crystals

Abstract: Energy harvesting from temperature variations in a Pb(Zn1/3Nb2/3)0.955Ti0.045O3 single crystal was studied and evaluated using the Ericsson thermodynamic cycle. The efficiency of this cycle related to Carnot cycle is 100 times higher than direct pyroelectric energy harvesting, and it can be as high as 5.5% for a 10degC temperature variation and 2 kV/mm electric field. The amount of harvested energy for a 60degC temperature variation and 2 kV/mm electric field is 242.7 mJmiddotcm-3. The influence of ferroelectric phase transitions on the energy harvesting performance is discussed and illustrated with experimental results.

Thermodynamic analysis of different two-stage transcritical carbon dioxide cycles

Abstract: The aim of this paper is the thermodynamic evaluation and optimisation of different two-stage transcritical carbon dioxide cycles. Five different cycles are studied: basic single-stage cycle, single-throttling with two-stage compression cycle, split cycle, phase separation cycle and single-stage cycle coupled with a gas cooling circuit. Each basic cycle is analysed for the effect of internal heat transfer between different streams of refrigerants. In the case of two-stage compression, intermediate cooling between the compressor stages is present. An analysis on the Plank cycle for intermediate pressure higher than critical one is performed. Each cycle is optimised with regards to energy performance, calculating the optimal values of both the upper and the intermediate pressures. In the case of split cycle, the ratio of the mass flow rate in the main stream to the one in the auxiliary stream is also optimised.

Toward Heat Energy Harvesting using Pyroelectric Material

Abstract: This study investigates the feasibility of heat energy harvesting using pyroelectric effect. In order to improve the effectiveness of the energy conversion from heat to electricity, the synchronized switch harvesting on inductor (SSHI) (Guyomar et al., 2005) technique is experimentally tested, which has already proved its quality in electromechanical conversion. For several amplitude variations of temperature from 0.5 to 8.0 K, the conversion efficiency is found about 0.02% of Carnot thermodynamic cycle with a standard interface. Under the same heating conditions, experimental results show that the SSHI technique increases the converted energy by a factor which is about 2.5 times of the standard interface, with which the efficiency practically becomes 0.05% of Carnot thermodynamic cycle. In this case, the produced electrical power for temperature amplitude 7 K is more than 0.3 mW for an energy harvesting device composed of 8 g of active material. The main power limitation is due to temperature frequency. ...

Theoretical and experimental investigation of an organic Rankine cycle for a waste heat recovery system

Abstract: This article describes and evaluates an organic Rankine cycle (ORC) for a waste heat recovery system by both theoretical and experimental studies. Theoretical analysis of several working fluids shows that cycle efficiency is very sensitive to evaporating pressure, but insensitive to expander inlet temperature. Second law analysis was carried out using R600a as a working fluid and a flow of hot air as a heat source, which is not isothermal, along the evaporator. The result discloses that the evaporator's internal and external entropy generation is the main source of total entropy generation. The effect of the heat source temperature, evaporating pressure, and evaporator size on the entropy generation rate is also presented. The obtained useful power is directly linked to the total entropy generation rate according to the Gouy—Stodola theorem. The ORC testing system was established and operated using R600a as a working fluid and hot water as a heat source. The maximum cycle efficiency of the testing...

How much exergy one can obtain from incident solar radiation

Abstract: A thermodynamic model is proposed to study the exergetic content of incident solar radiation reaching on the Earth’s surface which can be used to produce work through a dually cascaded thermodynamic cycle. The “topping” cycle is an ad hoc engine created by nature that connects the outer shell of the terrestrial atmosphere (which is in equilibrium with the extraterrestrial solar radiation) to the collector of a solar heat engine operating on the Earth’s surface. The work produced by the topping cycle is dissipated in form of scattering, absorption, heat, movement of air masses (wind), etc. The “bottoming” cycle is a heat engine operating between the collector and surrounding temperatures, and delivers useful work. It is shown that the maximum work extractable from this system as exergy is obtained when both cycles operate reversibly. An expression for this maximum work, which represents the exergy of incident solar radiation on the Earth’s surface, is proposed. The application of the present model is illustrated and validated by calculating the exergy of solar radiation based on some measurements. The results obtained by the present model are compared to the ones obtained through other models available in the open literature.

High efficiency positive displacement thermodynamic system

Abstract: Devices and methods for moving a working fluid through a controlled thermodynamic cycle in a positive displacement fluid-handling device (20, 20′, 20″) with minimal energy input include continuously varying the relative compression and expansion ratios of the working fluid in respective compressor and expander sections without diminishing volumetric efficiency. In one embodiment, a rotating valve plate arrangement (40, 42, 44, 46) is provided with moveable apertures or windows (48, 50, 56, 58) for conducting the passage of the working fluid in a manner which enables on-the-fly management of the thermodynamic efficiency of the device (20) under varying conditions in order to maximize the amount of mechanical work needed to move the target quantity of heat absorbed and released by the working fluid. When operated in refrigeration modes, the work required to move the heat is minimized. In power modes, the work extracted for the given input heat is maximized.

Energy recovery system using an organic rankine cycle

Abstract: A thermodynamic system for waste heat recovery, using an organic rankine cycle is provided which employs a single organic heat transferring fluid to recover heat energy from two waste heat streams having differing waste heat temperatures. Separate high and low temperature boilers provide high and low pressure vapor streams that are routed into an integrated turbine assembly having dual turbines mounted on a common shaft. Each turbine is appropriately sized for the pressure ratio of each stream.

Impact of EGR fraction on diesel engine performance considering heat loss and temperature‐dependent properties of the working fluid

Abstract: Exhaust gas recirculation (EGR) to reduce feed gas NOx emission is common practice in modern diesel engines. Dilution of the intake air with cooled recirculated exhaust gas limits the production of in-cylinder NOx due to a lowering of the adiabatic flame temperature and a reduction in oxygen content of the intake mixture. EGR also reduces the mixture-averaged ratio of specific heats (γ) of the combustion charge leading to a reduction in the thermodynamic cycle efficiency. This trade-off between minimizing NOx production and maximizing cycle efficiency is of critical importance when calibrating EGR control schemes. Modeling tools that allow a quantitative analysis of this trade-off can be very beneficial in tuning EGR systems over a range of operating conditions. In this study, the systematic development of a model that allows an assessment of the impact of EGR on three parameters, namely (a) the thermodynamic cycle efficiency, (b) the mixture temperatures during the cycle and (c) the mixture-averaged γ, is presented. This is accomplished through a numerical solution of the energy equation while considering the effects of heat loss and temporally varying mixture-averaged values of γ. Results for a simple phenomenological model relating fuel-burn rate with EGR fraction and the impact of EGR fraction on NOx reduction are also included. Copyright © 2008 John Wiley & Sons, Ltd.

Combined heat and power cycle system

Abstract: A combined heat and power cycle system includes a heat generation system having at least two separate heat sources having different temperatures. The combined heat and power cycle system includes a first rankine cycle system coupled to a first heat source among the at least two separate heat sources and configured to circulate a first working fluid. A second rankine cycle system is coupled to at least one second heat source among the at least two separate heat sources and configured to circulate a second working fluid. The first and second working fluids are circulatable in heat exchange relationship through a cascaded heat exchange unit for condensation of the first working fluid in the first rankine cycle system and evaporation of the second working fluid in the second rankine cycle system. At least one heat exchanger is disposed at one or more locations in the first rankine cycle system, second rankine cycle system, or combinations thereof.

A novel CO2 refrigeration system achieved by CO2 solid-gas two-phase fluid and its basic study on system performance

Abstract: In this report, a new CO2 refrigeration system is introduced, which can achieve a refrigeration capability below the CO2 triple point of −56.6 °C. The proposed CO2 refrigeration system consists of two thermodynamic cycles arranged in cascade, where one is a CO2 trans-critical cycle and another is a trans-triple-point cycle. An experimental set-up is constructed and tested in order to obtain a basic knowledge about this CO2 system. Based on the measured data, it is concluded that the built CO2 refrigeration system can operate continuously and stably, although dry ice particles exist in the closed CO2 loops. An average COP (a ratio of cooling energy to the compressor power consumption) is measured at 2.45 in the present experiment range for the low-pressure system of the experimental set-up. In addition, the influence of the condensation temperature on the refrigeration cycle is investigated and more studies are needed for the future optimization work.

A combined double-way chemisorption refrigeration cycle based on adsorption and resorption processes

Abstract: An innovative combined double-way chemisorption refrigeration cycle based on adsorption and resorption processes is presented Two different reactive salts were used as sorbents and ammonia was utilized as the refrigerant in the proposed cycle The useful cold was obtained from the evaporation heat of the refrigerant during the adsorption process and from the reaction heat of the low-temperature salt during the resorption process The proposed combined double-way cycle has a distinct advantage of higher coefficient of performance (COP) in comparison with conventional adsorption cycle or resorption cycle Experimental verification indicated that the advanced combined double-way cycle is feasible for refrigeration application, and the ideal COP of the basic cycle was about 124 Theoretical results showed that the proposed combined double-way cycle could improve COP by 167% and 60% when compared with conventional adsorption cycle and resorption cycle, respectively