Showing papers on "Thermal efficiency published in 2004"

Thermodynamic cycles using thermal diluent

Abstract: A thermodynamic system that produces mechanical, electrical power, and/or fluid streams for heating or cooling. The cycle contains a combustion system that produces an energetic fluid by combustion of a fuel with an oxidant. A thermal diluent may be used in the cycle to improve performance, including but not limited to power, efficiency, economics, emissions, dynamic and off-peak load performance, and/or turbine inlet temperature (TIT) regulation and cooling heated components. The cycle preferably includes a heat recovery system and a condenser or other means to recover and recycle heat and the thermal diluent from the energetic fluid to improve the cycle thermodynamic efficiency and reduce energy conversion costs. The cycle may also include controls for temperatures, pressures, and flow rates throughout the cycle, and controls power output, efficiency, and energetic fluid composition.

Recent Studies in Turbine Blade Cooling

Abstract: Gas turbines are used extensively for aircraft propulsion, land-based power generation, and industrial applications. Developments in turbine cooling technology play a critical role in increasing the thermal efficiency and power output of advanced gas turbines. Gas turbine blades are cooled internally by passing the coolant through several rib-enhanced serpentine passages to remove heat conducted from the outside surface. External cooling of turbine blades by film cooling is achieved by injecting relatively cooler air from the internal coolant passages out of the blade surface in order to form a protective layer between the blade surface and hot gas-path flow. For internal cooling, this presentation focuses on the effect of rotation on rotor blade coolant passage heat transfer with rib turbulators and impinging jets. The computational flow and heat transfer results are also presented and compared to experimental data using the RANS method with various turbulence models such as k-e, and second-moment closure models. This presentation includes unsteady high free-stream turbulence effects on film cooling performance with a discussion of detailed heat transfer coef- ficient and film-cooling effectiveness distributions for standard and shaped film-hole geometry using the newly developed transient liquid crystal image method.

PV Thermal systems: PV panels supplying renewable electricity and heat

Abstract: With PV Thermal panels sunlight is converted into electricity and heat simultaneously. Per unit area the total efficiency of a PVT panel is higher than the sum of the efficiencies of separate PV panels and solar thermal collectors. During the last 20 years research into PVT techniques and concepts has been widespread, but rather scattered. This reflects the number of possible PVT concepts and the accompanying research and development problems, for which it is the general goal to optimise both electrical and thermal efficiency of a device simultaneously. The aspects that can be optimised are, amongst others, the spectral characteristics of the PV cell, its solar absorption and the internal heat transfer between cells and heat-collecting system. Another important level of optimisation is for the PVT device geometry and the integration into a system. The electricity and heat demand and the temperature level of the heat determine the choice for a certain system set-up. With an optimal design, PVT systems can supply buildings with 100% renewable electricity and heat in a more cost-effective manner than separate PV and solar thermal systems and thus contribute to the long-term international targets on implementation of renewable energy in the built environment.

Boosting for High Load HCCI

Abstract: Homogeneous Charge Compression Ignition (HCCI) holds great promises for good fuel economy and low emissions of NOdx and soot. The concept of HCCI is premixed combustion of a highly diluted mixture. The dilution limits the combustion temperature and thus prevents extensive NOdx production. Load is controlled by altering the quality of the charge, rather than the quantity. No throttling together with a high compression ratio to facilitate autoignition and lean mixtures results in good brake thermal efficiency. However, HCCI also presents challenges like how to control the combustion and how to achieve an acceptable load range. This work is focused on solutions to the latter problem. The high dilution required to avoid NOdx production limits the mass of fuel relative to the mass of air or EGR. For a given size of the engine the only way to recover the loss of power due to dilution is to force more mass through the engine. This paper shows that this can be done by the use of turbocharging or a mechanically driven compressor. The cost of forcing more air through the engine and the higher peak pressure requirements are discussed and quantified by simple engine modelling supported by experimental data. (Less)

Thermal management using synthetic jet ejectors

Abstract: The utility of a synthetic jet ejector for thermal management at low flow rates is discussed. A synthetic jet ejector typically consists of a primary "zero-mass-flux" unsteady jet driving a secondary airflow through a low profile, high aspect ratio channel. A simple configuration of a nominally two-dimensional jet ejector in a rectangular channel is used to investigate the effects of channel width on the induced flow rate, power dissipated, heat transfer coefficient and thermal efficiency. An active heat sink for high power microprocessors is developed using the jet ejector concept and its performance is discussed.

Method and system for recovering carbon dioxide

Abstract: To provide a method for recovering carbon dioxide, in which thermal energy for regenerating a CO2 absorbing solution and power for compressing the recovered CO2 are supplied, and high thermal efficiency is achieved, and a system therefor. A system for recovering carbon dioxide including a high pressure turbine 3, an intermediate pressure turbine 7, and a low pressure turbine 8; a boiler 1 for generating steam for driving the turbines; an absorption tower 18 filled with a CO2 absorbing solution for absorbing and removing CO2 from combustion exhaust gas of the boiler; a regeneration tower 24 for regenerating the absorbing solution having absorbed CO2; a compressor 42 for compressing the removed CO2; a turbine 41 for a compressor, which is driven by some of the exhaust steam of the high pressure turbine; turbines 51 and 52 for auxiliary machinery, which are driven by some of the exhaust steam of the intermediate pressure turbine; and supply pipes 45 and 55 for supplying exhaust steam of the compressor turbine and the auxiliary machinery turbines to a reboiler 30 of the regeneration tower as a heating source.

System and method for thermal management

Abstract: A system (10) for the management of thermal transfer in a gas turbine engine (14) includes a heat generating sub-system disposed in operable communication with the engine (14), a fuel source (18) configured to supply a fuel, a fuel stabilization unit (16) configured to receive the fuel from the fuel source (18) and to provide the fuel to the engine (14), and a heat exchanger disposed in thermal communication with the fuel to effect the transfer of heat from the heat generating sub-system to the fuel. A method of managing such thermal transfer includes removing oxygen from the fuel in the fuel atabilization unit (16), transferring heat from the heat generating sub-system to the fuel, and combusting the fuel in gas turbine engine (14). System (10) can be used for the thermal management of an aircraft.

Flue gas desulfurization at high temperatures : A review

Abstract: The energy demand of the world, which increases in accordance with the rise in economic development, will have to be met by the prevalent energy sources, such as coal, new sources, as well as improvement of the efficiency of energy production technologies. However, the growth in energy production need not take place to the detriment of the environment, so that strict regulations on pollutant emissions have been imposed around the world. Combined cycle power generation systems are being advanced t oday, due to their higher thermal efficiency and superior environmental performance and economics, compared to conventional plants. Hot gas cleaning techniques to remove sulfur and other impurities in the flue gas streams offer the key advantages to such systems. This paper reviews briefly the Hot Gas Desulfurization (HGD) techniques and the processes' development and performance estimates, some test programs using HGD, and market potential and economic issues.

Advanced high efficiency, ultra-low emission, thermochemically recuperated reciprocating internal combustion engine

Abstract: An apparatus including a reciprocating internal combustion engine and a thermochemical recuperator in which a fuel is reformed. The thermochemical recuperator is heated by exhaust gases from the reciprocating internal combustion engine and steam for the reforming process is produced by passing feed water through an engine lubricating oil heat exchanger, an engine cooling system heat recovery system and an exhaust gas heat recovery system arranged in series.

Current, maximum power and optimized efficiency of a Brownian heat engine

Abstract: A microscopic heat engine is modeled as a Brownian particle in a sawtooth potential (with load) moving through a highly viscous medium driven by the thermal kick it gets from alternately placed hot and cold heat reservoirs. We found closed form expression for the current as a function of the parameters characterizing the model. Depending on the values these model parameters take, the engine is also found to function as a refrigerator. Expressions for the efficiency as well as for the refrigerator performance are also reported. Study of how these quantities depend on the model parameters enabled us in identifying the points in the parameter space where the engine performs with maximum power and with optimized efficiency. The corresponding efficiencies of the engine are then compared with those of the endoreversible and Carnot engines.

Energy recovery system

Abstract: An energy recovery system for hybrid automobile. The energy recovery system generates electricity by utilizing the temperature difference between a high temperature thermal medium and a low temperature thermal medium. As the high temperature thermal medium, engine coolant for cooling an engine is used. As the low temperature thermal medium, pump refrigerant for cooling by a heat pump is used. The heat pump maintains the pump refrigerant at a low temperature by using heat from the engine coolant. Therefore, while electricity is reliably generated at a thermoelectric converter, energy is efficiently used for cooling the pump refrigerant.

Hydrogen as Homogeneous Charge Compression Ignition Engine Fuel

Abstract: Hydrogen has been proposed as a possible fuel for automotive applications This paper reports an experimental investigation of hydrogen as HCCI engine fuel The aim of the experimental study is to investigate the possibility to run an HCCI engine on an extremely fast burning fuel such as hydrogen as well as to study the efficiency, the combustion phasing and the formation of emissions The experiments were conducted on a single-cylinder research engine with a displacement volume of 16 litres and pancake combustion chamber geometry Variation of lambda, engine speed, compression ratio and intake temperature were parts of the experimental setting The engine was operated in Homogenous Charge Compression Ignition (HCCI) mode and as comparison also in Spark Ignition (Sl) mode Hydrogen was found to be a possible fuel for an HCCI engine The heat release rate was extremely high and the interval of possible start of combustion crank angles was found to be narrow The high rate of heat release limited the operating range to lean (λ>3) conditions On the other hand operation on extremely lean mixtures (X=6) was found possible The possible operating range was investigated when intake gas temperature was used for control and also this control interval was found to be narrow, especially when richer cases were run The maximum load in HCCI mode was an IMEPn of 35 bar which is about half of the load possible in Sl mode and about half the maximum load in HCCI mode with other fuels For the loads where HCCI operation could be conducted indicated thermal efficiency for HCCI was superior to that of SI NOx emissions were, as expected, found to decrease when lambda was increased and the levels were very low in HCCI mode High levels of hydrogen were found in the exhaust with HCCI When the engine was operated on low lambdas (ie λ=3) emissions of carbon monoxide and hydrocarbons were detected, probably originating from evaporated and partially oxidized lubrication oil