Showing papers on "Thermal energy published in 2001"

Cosmological SPH simulations: The entropy equation

Abstract: We discuss differences in simulation results that arise between the use of either the thermal energy or the entropy as an independent variable in smoothed particle hydrodynamics (SPH). In this context, we derive a new version of SPH that manifestly conserves both energy and entropy if smoothing lengths are allowed to adapt freely to the local mass resolution. To test various formu- lations of SPH, we consider point-like energy injection and find that powerful explosions are well represented by SPH even when the energy is deposited into a single particle, provided that the entropy equation is integrated. If the thermal energy is instead used as an independent variable, unphysical solutions can be obtained for this problem. We also examine the radiative cooling of gas spheres that collapse and virialize in isolation and of halos that form in cosmological simulations of structure formation. When applied to these problems, the thermal energy version of SPH leads to substantial overcooling in halos that are resolved with up to a few thousand particles, while the entropy formulation is biased only moderately low for these halos. For objects resolved with much larger particle numbers, the two approaches yield consistent results. We trace the origin of the differences to systematic resolution effects in the outer parts of cooling flows. The cumulative effect of this overcooling can be significant. In cosmological simulations of moderate size, we find that the fraction of baryons which cool and condense can be reduced by up to a factor ~2 if the entropy equation is employed rather than the thermal energy equation. We also demonstrate that the entropy method leads to a greatly reduced scatter in the density-temperature relation of the low-density Ly-alpha forest relative to the thermal energy approach, in accord with theoretical expectations.(abridged)

A fundamental approach to transformer thermal modeling. I. Theory and equivalent circuit

Abstract: A simple equivalent circuit to represent the thermal heat flow equations for power transformers is presented. Key features are the use of a current source analogy to represent heat input due to losses, and a nonlinear resistor analogy to represent the effect of air or oil cooling convection currents. The effect was first quantified in 1817. It is shown that the idea of "exponential response" is not the best way to think of the dynamics of the situation. It is also shown that one can consider ambient temperature to be a variable input to the system, and that it is properly represented as an ideal voltage source.

Principles of Heat Transfer

Abstract: Preface. Guide to Instructors and Students. Acknowledgments. 1. Introduction and Preliminaries. 1.1. Applications and History. 1.2. Units and Normalization (Scaling). 1.3. Thermal Systems. 1.4. Heat Flux Vector q. 1.5. Heat Transfer Medium. 1.6. Conservation of Energy. 1.7. Conservation of Mass, Species, and Momentum. 1.8. Scope. 1.9. Summary. 1.10. References. 1.11. Problems. 2. Energy Equation. 2.1. Nonuniform Temperature Distribution: Differential--Volume Energy Equation. 2.2. Uniform Temperature in One or More Directions: Energy Equation for Volumes with One or More Finite Lengths. 2.3. Energy Conversion Mechanisms. 2.4. Bounding--Surface and Far--Field Thermal Conditions. 2.5. Heat Transfer Analysis. 2.6. Summary. 2.7. References. 2.8. Problems. 3. Conduction. 3.1. Microscale Heat Storage and Specific Heat Capacity c p . 3.2. Microscale Conduction Heat Carriers and Thermal Conductivity k. 3.3. Steady--State Conduction. 3.4 Transient Conduction. 3.5 Distributed--Capacitance (Nonuniform Temperature) Transient: T = T(x, t). 3.6. Lumped--Capacitance (Uniform Temperature) Transient: Internal--External Conduction Number N k 0.1, T = T(t). 3.7. Discretization of Medium into Finite--Small Volumes. 3.8. Conduction and Solid--Liquid Phase Change: Stefan Number Ste l . 3.9. Thermal Expansion and Thermal Stress. 3.10. Summary. 3.11. References. 3.12. Problems. 4. Radiation. 4.1. Microscale Heat Emission: Photon and Surface Thermal Radiation Emission. 4.2. Interaction of Irradiation and Surface. 4.3. Thermal Radiometry. 4.4. Enclosure Surface Radiation Heat Transfer Q r,I Among Gray, Diffuse, and Opaque Surfaces. 4.5. Prescribed Irradiation and Nongray Surfaces. 4.6. Inclusion of Substrate. 4.7. Summary. 4.8. References. 4.9. Problems. 5. Convection: Unbounded Fluid Streams. 5.1. One--Dimensional Conduction--Convection Energy Equation. 5.2. Parallel Conduction--Convection Resistance R k,u and Conduction--Convection Number N u = Pe L . 5.3. Evaporation Cooling of Gaseous Streams. 5.4. Combustion Heating of Gaseous Streams. 5.5. Joule Heating of Gaseous Streams. 5.6. Gas--Stream Volumetric Radiation. 5.7. Summary. 5.8. References. 5.9. Problems. 6. Convection: Semi--Bounded Fluid Streams. 6.1. Flow and Surface Characteristics. 6.2. Semi--In.nite Plate as a Simple Geometry. 6.3. Parallel, Turbulent Flow: Transition Reynolds Number Re L,t 6.4. Perpendicular Flows: Impinging Jets. 6.5. Thermobuoyant Flows. 6.6. Liquid--Gas Phase Change. 6.7. Summary of Nusselt Number Correlations. 6.8. Inclusion of Substrate. 6.9. Surface--Convection Evaporation Cooling. 6.10. Summary. 6.11. References. 6.12. Problems. 7. Convection: Bounded Fluid Streams. 7.1. Flow and Surface Characteristics. 7.2. Tube Flow and Heat Transfer. 7.3. Laminar and Turbulent Flows, Entrance Effect, Thermobuoyant Flows, and Phase Change. 7.4. Summary of Nusselt Number Correlations. 7.5. Inclusion of Bounding Solid. 7.6. Heat Exchange Between Two Bounded Streams. 7.7. Summary. 7.8. References. 7.9. Problems. 8. Heat Transfer in Thermal Systems. 8.1. Primary Thermal Functions. 8.2. Thermal Engineering Analysis. 8.3. Examples. 8.4. Summary. 8.5. References. 8.6. Problems. Nomenclature. Glossary. Answers to Problems. A. Some Thermodynamic Relations. A.1. Simple, Compressible Substance. A.2. Phase Change and Heat of Phase Change. A.3. Chemical Reaction and Heat of Reaction. A.4. References. B. Derivation of Differential--Volume Energy Equation. B.1. Total Energy Equation. B.2. Mechanical Energy Equation. B.3. Thermal Energy Equation. B.4. Thermal Energy Equation: Enthalpy Formulation. B.5. Thermal Energy Equation: Temperature Formulation. B.6. Conservation Equations in Cartesian and Cylindrical Coordinates. B.7. Bounding Surface Energy Equation with Phase Change. B.8. References. C. Tables of Thermochemical and Thermophysical Properties 899 C.1. Tables. Unit Conversion, Universal Constants, Dimensionless Numbers, Energy Conversion Relations, and Geometrical Relations. Periodic Table and Phase Transitions. Atmospheric Thermophysical Properties. Electrical and Acoustic Properties. Thermal Conductivity. Thermophysical Properties of Solids. Surface--Radiation Properties. Mass Transfer and Thermochemical Properties of Gaseous Fuels. Thermophysical Properties of Fluids. Liquid--Gas Surface Tension. Saturated Liquid--Vapor Properties. C.2. References. D. SOlver for Principles of Heat Transfer (SOPHT). D.1. Objective. D.2. SOPHT. List of Key Charts, Figures, and Tables. Subject Index.

Heat transfer apparatus

Abstract: The present invention relates generally to apparatus and methods for the spreading and dissipation of thermal energy from heat-producing components. More particularly, it relates to a heat transfer apparatus and methods particularly useful in the electrical arts. One embodiment of a heat transfer apparatus include but not limited to, a spring-biased member comprising a first side member, a second side member, and a connecting member adapted for spring-biased removable attachment to a heat-producing device. Another embodiment of a heat transfer apparatus is a spring-biased carrier that attaches to a heat-producing device and which carries a member, such as a finned plate. Another embodiment of a heat transfer apparatus is a spring-biased member comprising fingers for conducting thermal energy to a structure. Another embodiment of a heat transfer apparatus is a spring-biased clip used to attach separate heat-spreading/dissipating members, such as a finned plate, against a heat-producing member.

Energy management system and methods for the optimization of distributed generation

Abstract: An energy management system and method is provided for managing the generation and distribution of energy from an energy source to a building. The building has a desired building environment and a total energy profile including a thermal energy requirement and an electrical energy requirement. The energy management system comprises an energy generator arranged to convert energy from the energy source to thermal energy and electrical energy, a heat recovery unit arranged to recover byproduct heat from the energy generator, a cooling unit arranged to use a first portion of the thermal energy to drive a refrigeration unit, a heating unit arranged to use a second portion of the thermal energy to drive a heating unit, a heat storage unit arranged to store excess heat, and an energy optimizing controller.

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.

Piezoelectric micro-transducers, methods of use and manufacturing methods for same

Abstract: Various micro-transducers incorporating piezoelectric materials for converting energy in one form to useful energy in another form are disclosed. In one embodiment, a piezoelectric micro-transducer can be operated either as a micro-heat engine, converting thermal energy into electrical energy, or as a micro-heat pump, consuming electrical energy to transfer thermal energy from a low-temperature heat source to a high-temperature heat sink. In another embodiment, a piezoelectric micro-transducer is used to convert the kinetic energy of an oscillating or vibrating body on which the micro-transducer is placed into useful electrical energy. A piezoelectric micro-transducer also is used to extract work from a pressurized stream of fluid. Also disclosed are a micro-internal combustion engine and a micro-heat engine based on the Rankine cycle in which a single fluid serves as a working fluid and a fuel.

Membrane desiccation heat pump

Abstract: There is provided a system for pumping thermal energy. The system includes (a) a membrane permeator for removing vapor from a process gas and for providing a vapor-depleted process gas, and (b) a gas-liquid contactor for adding vapor from a liquid to a vapor-depleted gas to produce a vapor-added process gas. The system transfers a quantity of thermal energy from the liquid to the vapor-added process gas, and is also capable of upgrading the thermal energy to a higher temperature. The system may be used for various heat pump applications including chilling and waste heat or low level heat recovery.

Heat sink/heat spreader structures and methods of manufacture

Abstract: A heat sink/heat spreader structure utilizing thermoelectric effects to efficiently transport thermal energy from a variety of heat sources including integrated circuits and other electronic components. A method for manufacturing the heat sink/spreader is also disclosed.

Thermal diode for energy conversion

Abstract: Solid state thermionic energy converter semiconductor diode implementation and method for conversion of thermal energy to electric energy, and electric energy to refrigeration. In embodiments of this invention a highly doped n region (14) can serve as an emitter region, from which carriers can be injected into a gap region. The gap region (16) can be p-type, intrinsic, or moderately doped n-type (14). A hot ohmic contact (12) is connected to the n-type region. A cold ohmic contact (20) serves as a collector and is connected to the other side of the gap region. The cold ohmic contact has a recombination region formed between the cold ohmic contact and the gap region and a blocking compensation layer that reduces the thermoelectric back flow component. The heated emitter relative to the collector generates an emf which drives current through a series load. The inventive principle works for hole conductivity, as well as for electrons.

High-pressure high-temperature polycrystalline diamond heat spreader

Abstract: This invention presents a polycrystalline diamond heat spreader useful in electronic devices for transmitting thermal energy from a high-energy thermal source, such as an IC die, into a means for dissipating thermal energy, such as a heat sink. The heat spreader comprises a bondable material that forms in situ at high pressure and high temperature a low-impedance contact surface layer on at least one its major surfaces. The contact surface layer provides a means for chemically or metallurgically bonding the heat spreader to the IC die and or to the heat sink.

Thermal barrier enclosure system

Abstract: A thermal barrier enclosure system (10), comprising one or more thermal barriers. The thermal barrier enclosure system (10) is used to control the temperature in a shipping container or a refrigerator. Thermal control is achieved with one or more thermal control barriers comprised of an insulation barrier (20), a temperature sensitive device (22, 60), and a thermal conduit through which energy flows. The combination of the temperature sensitive device and thermal conduit forms a thermal regulator (22) that varies the thermal energy flow as the regulator is operated from its open to its closed position, and vise versa. A thermal control barrier with a reverse acting thermal regulator (60) can also be used to cool an energy storage material (58) and then to thermally insulate that material when the cooling source (23) is removed.

Investigation of a Fuel Cell Based Total Energy System for Residential Applications

Abstract: Residences require electricity for lights, appliances, and space cooling and thermal energy for space and domestic water heating. Total energy systems (TES) which provide both electricity and thermal energy can meet these needs more effectively than conventional systems because thermal energy rejected during the on-site production of electricity can be recovered to meet the heating loads. TESs based on fuel cell systems are particularly attractive because of their high efficiencies, quiet operation, and small size. This research evaluates a TES consisting of a fuel cell sub-system (FCS), an electric heat pump (HP), and a thermal storage tank (TS). A model of a grid-independent, electric load following TES is developed to determine the energy required to meet the hourly average electric and thermal loads of the residence. The TES uses a heat pump to provide space cooling. Electricity for air conditioning, lights, and appliances is provided by the FCS. Space heating and water heating of the residence are provided by the thermal energy available from the FCS. The TES is designed so that, heating requirements that exceed the heat available from the FCS can be satisfied by the HP and an electric water heater. A thermal storage tank is used to store and transfer thermal energy from the FCS to the residence. The results of the research include a comparison of the energy use by the TES to the energy use by conventional residential energy systems; an evaluation of the effects of climatic conditions on system performance and energy use; and a comparison of the life-cycle cost of the TES and conventional residential energy systems. The results indicate that total energy systems can reduce primary energy use by as much as 40 percent, but that to be economically attractive, the FCS cost must be reduced to approximately $500/kWe.

The effect of particle size and morphology on the in-flight behavior of particles during high-velocity oxyfuel thermal spraying

Abstract: A one-way coupled mathematical model is formulated to simulate the effects of particle size and morphology on the momentum and thermal energy transfer of particles during high-velocity oxyfuel (HVOF) thermal spraying. First, computational fluid dynamic techniques are implemented to solve the Favre-averaged mass, momentum, and energy conservation equations in the gas phase. The gas dynamic data are then used to model the behavior of particles in the gas field. The concept of sphericity is used to incorporate the effect of particle morphology into the model. The calculated results show that the particle velocity and temperature, before impinging onto the substrate, are strongly affected by particle size, morphology, and spray distance. Smaller particles are accelerated to a higher velocity but slowed down rapidly due to their smaller momentum inertia, while the larger particles are accelerated with some difficulty. The same tendency is observed regarding the effect of particle size on its thermal history.

Method for changing the temperature of a selected body region

Abstract: Heat transfer catheter apparatus and methods of making and using same are disclosed wherein fluid connection means is provided between the distal portions of two adjacent, thin-walled, high strength fluid lumens to define a closed loop fluid circulation system capable of controlled delivery of thermal energy to or withdrawal of thermal energy from remote internal body locations.

Temperature difference drive unit, and electric device, timepiece and light electrical appliance having the same

Abstract: Thermal energy is converted into a mechanical energy by a thermal converter that includes a phase change material whose phase changes between solid and liquid as a result of temperature changes in the operating environment. Because the phase change material does not change to the gas state during operation, good thermal conductivity can be achieved within a normal operating temperature range and sufficient mechanical energy can be obtained, thereby enhancing the conversion efficiency of the thermal converter. Also, because the case in which the phase material is contained is not required to be at a high pressure, the case can be easily manufactured and a compressing means such as a strong spring is not required, thus reducing a size of whole device.

Thermoelectric generator for a vehicle

Abstract: A thermoelectric generator includes a thermal generator to which thermal energy is provided from a heat source. In order to keep the output voltage of the thermal generator in a range suitable for charging a battery or for directly feeding into the vehicle's electrical system, the rate of heat production of the heat source and/or the cooling power of a cooling device for the thermal generator is controlled by a regulator. For this purpose, the regulator is connected to a temperature sensor which is mounted on the thermal generator. The regulator can be more cost-effectively configured than a D.C. converter between the output side of the thermal generator and the battery so that this converter can be dispensed with.

Estimation of the In-Cylinder Air/Fuel Ratio of an Internal Combustion Engine by the Use of Pressure Sensors

Abstract: This thesis investigates the use of cylinder pressure measurements for estimation of the in-cylinder air/fuel ratio in a spark ignited internal combustion engine. An estimation model which uses the net heat release profile for estimating the cylinder air/fuel ratio of a spark ignition engine is developed. The net heat release profile is computed from the cylinder pressure trace and quantifies the conversion of chemical energy of the reactants in the charge into thermal energy. The net heat release profile does not take heat- or mass transfer into account. Cycle-averaged air/fuel ratio estimates over a range of engine speeds and loads show an RMS error of 4.1% compared to measurements in the exhaust. A thermochemical model of the combustion process in an internal combustion engine is developed. It uses a simple chemical combustion reaction, polynomial fits of internal energy as function of temperature, and the first law of thermodynamics to derive a relationship between measured cylinder pressure and the progress of the combustion process. Simplifying assumptions are made to arrive at an equation which relates the net heat release to the cylinder pressure. Two methods for estimating the sensor offset of a cylinder pressure transducer are developed. Both methods fit the pressure data during the pre-combustion phase of the compression stroke to a polytropic curve. The first method assumes a known polytropic exponent, and the other estimates the polytropic exponent. The first method results in a linear least-squares problem, and the second method results in a nonlinear least-squares problem. The nonlinear least-squares problem is solved by separating out the nonlinear dependence and solving the single-variable minimization problem. For this, a finite difference Newton method is derived. Using this method, the cost of solving the nonlinear least-squares problem is only slightly higher than solving the linear least-squares problem. Both methods show good statistical behavior. Estimation error variances are inversely proportional to the number of pressure samples used for the estimation as predicted by the central limit theorem.

Heat dissipating silicon-on-insulator structures

Abstract: Heat dissipating Silicon-on-Insulator (SOI) structures which utilize thermoelectric effects to more effectively dissipate thermal energy from SOI-based electronic circuits.

Method and system for power production and assemblies for retroactive mounting in a system for power production

Abstract: In a method which, owing to improved environmental properties, allows production of power, power and thermal energy, power and cold, or power, thermal energy and cold, a system comprising a compression unit (C1, C2) is used for pressurizing a working fluid containing oxygen, preferably air. The system further comprises a combustion unit (CC) which downstream of the compressing unit (C1, C2) as seen in the direction of flow the working fluid, is arranged to supply a first amount of heat to the working fluid by substantially complete combustion of a fuel in the working fluid. An expansion unit (T1) is arranged to produce mechanical work during expansion of the working fluid. A heat recovery unit (HR) is arranged downstream of the expansion unit (T1) to divert a second amount of heat from the working fluid at a pressure above atmospheric pressure. The production of cold is made possible by further expansion unit (T2), by means of which the temperature of the working fluid can be made to be significantly below the ambient temperature. Assemblies are also provided for retroactive mounting in existing systems for power production comprising a gas turbine or an internal combustion engine.

Hybrid heat pump

Abstract: There is provided a hybrid heat pump system. The system includes (i) a membrane permeator having a permselective membrane capable of selectively removing vapor from a vapor-containing gas to yield a dry gas, (ii) a heat pump having (a) an internal side for exchanging thermal energy with a process fluid, (b) an external side for exchanging thermal energy with an external environment, and (c) a thermodynamic mechanism for pumping thermal energy between the internal side and the external side in either direction, (iii) means for conveying the vapor-containing gas into the membrane permeator, and (iv) means for routing the dry gas to either of the internal side or the external side.

Generation of electrical energy from thermal energy by the Seebeck effect e.g. for use with a vehicle combustion engine, involves using a Peltier module consisting of a number of Peltier

Abstract: Generation of electrical energy from thermal energy by utilizing the thermoelectric effect (Seebeck effect) requires using a Peltier module as a power module or a Seebeck module for utilizing the natural (air) temperature, the wind - and climate-difference in the environment and/or the waste heat of technical plant for the purposes of current (power) generation.

Apparatus and method for passive phase change thermal management

Abstract: A heat sink includes a heat sink body including a number of fins and a cavity for holding a phase change material and a number of particles to enhance the mixing of the phase change material during the operation of the heat sink. In operation, the body of the heat sink conducts thermal energy to the phase change material. The energy is absorbed during the phase change of the phase change material. After absorbing energy and changing to a liquid state, the phase change material continues to dissipate energy by convection. The convention currents in the cavity are directed by the shape of the cavity surfaces an enhanced by the particles intermixed with the phase change material.

Micro heat flux sensor using copper electroplating in SU-8 microstructures

Abstract: A micro heat flux sensor which can measure the thermal energy transfer per unit area has been designed, fabricated, and calibrated in a convective environment. The sensor which is based on a circular foil gage is composed of thermal paths and a thermopile. The thermal path is made in a LIGA-like process of SU-8 high aspect ratio microstructures and electroplated copper layers. The thermopile, a series of thermocouples, is used to amplify the output signal as a thermometer. When the sensor is placed on a high-temperature wall, heat flux from the wall flows through thermal paths and drains out to the environment, producing a temperature difference along its paths. Heat flux is obtained by calibrating this temperature difference in the thermopile of Ni-Cr or Al-Chromel pairs. The sensitivity of the heat flux sensor of Ni-Cr and Al-Chromel pairs is in the range of 0.1-2.0 and 0.4-2.0 µV mW-1 cm-2, respectively, in the heat flux range of 0-180 mW cm-2.

Method for converting thermal energy into mechanical work

Abstract: The invention relates to a method for converting thermal energy into mechanical work, whereby a first (4) and a second means (9) for storing thermal energy are alternately connected into a turbine branch (T). In order to increase the efficiency of this method, the invention provides that a compressed oxidizing gas (11) is cooled to a second temperature T2 before passing through the first means (4) for storing thermal energy, and the oxidizing gas is then increased, in one step, to a third temperature T3 when passing through the first means (4) for storing thermal energy.