Showing papers on "Thermal energy published in 1977"

Simultaneous Heat, Mass, and Momentum Transfer in Porous Media: A Theory of Drying

Abstract: Publisher Summary The well-known transport equations for continuous media are used to construct a rational theory of simultaneous heat, mass, and momentum transfer in porous media. Several important assumptions regarding the structure of the gas–liquid system in a drying process are made that require theoretical or experimental confirmation. This chapter presents a general theory that provides a starting point for the construction of special theories so that various drying processes can be studied analytically without recourse to an enormous computational effort. It analyzes the motion of a liquid and its vapor through a rigid porous media. The development of the relevant volume averaged transport equations, which describe the drying process, is also focused. The transport of momentum in the gas phase and the laws of mechanics are applied to the drying process. The thermal energy equations are considered by forming the total thermal energy equation, and the problem of determining the mass average velocities in the gas and liquid phases are also discussed.

Solar Energy Conversion with Fluorescent Collectors

Abstract: A new principle for solar energy conversion is proposed and evaluated theoretically. Collection and concentration of direct and diffuse radiation is possible by the use of a stack of transparent sheets of material doped with fluorescent dyes. High efficiency of light collection can be achieved by light guiding and special design of collectors. The optical path length in a triangular collector is computed. In combination with solar cells this type of collector offers the advantage of separating the various fractions of light and converting them with solar cells with different bandgaps. Theoretical conversion efficiency under optimum conditions is 32% for a system with four semiconductors. Thermal energy conversion offers several advantages over conventional collectors: High temperature and efficiency even under weak illumination, separation of heat transport and radiation collection, low thermal mass. Thermal efficiency is computed to be between 42% and 60%. Very attractive appear hybrid systems for generation of thermal and electric energy. An estimate of the economics of electricity generation shows that due to the concentration costs can be much lower than possible today. With the use of only silicon cells the breakeven point of $0.5/W is almost reached. Practical difficulties to be solved are: Synthesis of dyes with stringent requirements, identification of plastic materials with high transparency and development of solar cells with higher bandgaps.

Experimental considerations on a new automatic cooling device using temperature-sensitive magnetic fluid

Abstract: An automatic cooling device to eliminate the waste heat of machinery has been made by utilizing a temperature-sensitive magnetic fluid. This cooler requires no pump for flowing the fluid, since a part of the thermal energy is converted to the kinetic energy. If a permanent magnet is used, power supply is unnecessary. The cooler is expected to be maintenance-free and simple in shape.

Multimode solar energy collector and process

Abstract: A solar energy collector providing both concentrating-tracking functions and non-concentrating diffuse absorption functions in a single unit. The solar energy collector and process may provide both a higher temperature heat transfer fluid and a lower temperature heat transfer fluid for utilization in various processes, such as environmental conditioning, which may advantageously utilize thermal energy of two different temperatures. The solar energy thermal collector and process of this invention provides a high temperature thermal output in combination with a simplified tracking capability.

Geothermal energy conversion system

Abstract: A geothermal energy recovery system of improved efficiency makes use of thermal energy stored in hot, solute-bearing well water as it is pumped upward to the earth's surface through an extended heat exchange element for continuously heating a downward flowing organic fluid to a supercritical state. Some of the energy of the latter fluid is used within the well for operating a turbine-driven pump for pumping the hot, solute-bearing well water at high pressure and always in liquid state to the earth's surface, where it is reinjected into the earth in another well. The temperature difference between the upward flowing brine and the downward flowing organic fluid is maintained finite in a predetermined manner along the subterranean extended heat exchange element. After driving the deep-well turbine-driven pump, the organic fluid arises to the earth's surface in a thermally insulated conduit; at the earth's surface, vapor turbine electrical power generation equipment is driven by the heated organic fluid which is then returned into the well for reheating in the extended heat exchanger.

Properties of some salt hydrates for latent heat storage

Abstract: For the utilization of low-grade heat the latent storage of thermal energy is of great advantage because the heat can be preserved at a constant temperature perfectly matched to the special purpose of application. Investigations on the heat capacities, enthalpies of fusion, densities, crystallization behaviour and other chemical and physical properties have shown that the following salt hydrates are especially suitable media for storing low-grade heat. The eutectic mixture of water and 3.92% by weight of sodium fluoride, melting point (MP) = - 3.5°C, is extremely convenient and cheap for refrigerating or other cooling purposes. Lithium chlorate trihydrate, LiClO3. 3H2O, MP = +8.1°C has an extremely high storage capacity and other advantageous properties as a storage medium in cooling systems, but a very high price will limit its application. Calcium chloride hexahydrate, CaCl2. 6H2O, MP = + 29.2°C, is a suitable and cheap storage medium for heating purposes. For the same application disodium hydrogen phosphate dodecahydrate, Na2HPO4. 12H2O, MP = + 35.2°C, is even better because of the larger storage capacity per unit volume and other advantages which largely compensate the higher material cost. the unique properties of potassium fluoride tetrahydrate, KF. 4H2O, MP = +18.5°C, make it especially suitable for storing low-grade heat. It can directly function as an energy sink and as an energy reservoir in heat collecting and consuming systems. Examples of the practical applicability for residential heating, temperature levelling and cooling are described.

Combined solar radiation collector and thermal energy storage device

Abstract: A solar energy device for collecting solar radiation, converting the radiation to thermal energy and storing the thermal energy, and a process for manufacturing of same.

Survey of technology for storage of thermal energy in heat transfer salt

Abstract: The widespread use of nitrate-based fused salt mixtures as heat transport media in the petroleum and chemical process industries and in metallurgical heat-treatment operations has led to the development of satisfactory equipment for handling and containing these materials. A mixture known as heat transfer salt (HTS), which is composed of 40 percent NaNO/sub 2/, 7 percent NaNO/sub 3/, and 53 percent KNO/sub 3/ by weight, has been used commercially in large quantities as a heat transfer fluid. It has been suggested that this salt be used for storing energy as sensible heat in the temperature range 200 to 540/sup 0/C (400 to 1000/sup 0/F). The eutectic 54 percent KNO/sub 3/--46 percent NaNO/sub 3/ by weight known as ''draw salt,'' which has undergone less testing but is more stable thermally and more attractive economically than HTS and has similar physical properties, may be a desirable alternative. Several specific energy storage applications, such as intermediate-load and peaking electric power, solar energy, and energy from fluidized-bed coal burners, are discussed. Long-term stability and corrosion data on these salts are presently available only to approximately 480/sup 0/C. However, for the design and construction of energy storage facilities to operate over many years at temperaturesmore » up to approximately 540/sup 0/C, long-term tests of thermal stability and corrosion are needed. Means for obtaining such information are proposed.« less

Focusing solar energy apparatus

Abstract: An apparatus employing cylindrical focusing parabolic mirrors (parabolic troughs) of an optimized configuration capable of being manufactured by techniques of mass production to focus sunlight onto a specifically designed heat pipe which is to carry water or other heat transfer fluid. Focused sunlight energy is absorbed by the pipe, converted to thermal energy and transferred to heat the fluid in the pipe. Groups of mirrors are sequentially arranged so that the fluid in the pipes progressively absorbs more heat as it travels through the heat pipe. At some point in the fluid movement, depending upon the intensity of the specular sunlight the fluid, if liquid, may be converted to vapor. Transfer liquids other than water with higher boiling points may be used within the heat pipe and exit from the heat pipe in the liquid state. In either case, the steam, hot gas or superheated liquid is transmitted to a collector system which is then transported by standard steam pipes enclosed within a silvered glass envelope to a central thermal/electrical generating station. Collector mirror arrays are mounted to permit a single tracking motor to steer a large number of mirrors. All components are optimized for low maintenance and low cost to manufacture.

Thermal energy storage and utilization system

Abstract: A thermal energy storage and utilization system including at least a pair of especially configured liquid containing tanks interconnected by a heat exchanger for transferring thermal energy therebetween so that one of the tanks becomes a cold storage tank and the other becomes a heat storage tank. Various types of thermal energy input and output devices are connected to the liquid containing tanks for selectively supplying and/or utilizing the thermal energy stored therein.

Alternative electrical energy sources for Maine

Abstract: Prepared for the Central Maine Power Company Summary report.--Appendix A. Glaser, C. and Ruane, M. Conversion of biomass.--Appendix B. Jones, W. J. [et al.]. Conservation.--Appendix C. Waterflow, A. Geothermal energy conversion.--Appendix D. Ruane, M. Ocean thermal energy conversion.--Appendix E. Jones, W. J. Fuel cells.--Appendix F. Geary, J. and Jones, W. J. Solar energy conversion.--Appendix G. Ruane, M. Conversion of solid wastes.--Appendix H. Ruane, M. Storage of energy.--Appendix I. Mays, J. Wave energy conversion.--Appendix J. Mays, J. Ocean and riverine current energy conversion.--Appendix K. Labuszewski, T. Wind energy conversion.--Appendix L. Gruhl, J. Environmental impacts.

Temperature control of chill water and steam in heating, ventilation, air conditioning (HVAC) systems

Abstract: Apparatus for controlling the discharge temperature of thermal fluid presented from a common thermal source to one or more HVAC systems in a network, each HVAC controlling the volume of thermal fluid circulating therethrough by regulating the valve position of HVAC valve apparatus over a valve position range from a full closed position to a full open position in dependence on the thermal energy level required by one or more temperature regulated living spaces associated with each HVAC, the apparatus including electronic processing means in combination with dedicated temperature and valve position sensing apparatus for providing actual position signals for each fluid valve apparatus and an actual source discharge temperature signal, the electronic processing means determining the magnitude of the greatest thermal energy demand within a short term interval in dependence on the most open of the actual valve position signals and providing modulation of the source discharge temperature over the short term interval in dependence on the magnitude of the greatest thermal energy demand.

Thermal buffer system

Abstract: A quantity of aluminum is in heat exchange contact with a potassium loop and a steam/water loop. The potassium loop includes a solar energy collector and the solar-heated potassium melts the aluminum to store thermal energy as latent heat of fusion. The steam/water loop extracts steam at 1,000° F. as long as at least some of the aluminum is in the molten state. The steam/water loop includes a steam power turbogenerator unit as user; the quantity of aluminum should suffice to yield, upon resolidification, sufficient heat to satisfy the energy demand of the unit during night time.

Thermal control canister

Abstract: A heat dissipating instrument package of a spacecraft, located in a canister having walls in heat transfer relationship with the package, is maintained at a substantially constant temperature. Fixed conductance heat pipes on the canister walls are connected to variable conductance heat pipes, mounted on a radiator structure separated from the canister walls by a thermal blanket. The effective radiating area of the radiator structure is controlled by the variable conductance heat pipes in response to a comparison of a sensed temperature of the instrument package or the canister wall with a seat point value. The comparison controls a heater in a gas reservoir containing a non-condensable gas of the variable conductance heat pipe. To enable the set point to be varied over a relatively wide range, such a 0°-30° C., a thermal radiation shield for the gas reservoir prevents radiant energy from the exterior environment and thermal energy reflected from the spacecraft from overheating the non-condensable gas. In one embodiment, variable conductance heat pipe headers are provided between the canister and radiators, with isothermalizer feeder pipes on the radiators and canister walls; in further embodiments, variable conductance heat pipe feeder pipes are coupled directly between the canister walls and one or more radiators.

Environmentally assisted heating and cooling system

Abstract: A heating and cooling system comprises a first reservoir containing liquid at an elevated temperature, solar collecting means exposed to solar radiation for collecting solar energy and means disposed in thermal exchange relationship with said first reservoir for transmitting heat energy from said solar collecting means to said first reservoir, a second reservoir containing a liquid disposed in thermal exchange relationship with a portion of the earth, means for blending liquids derived respectively from thermal exchange relationship with said first and second reservoirs, a heat engine having first and second refrigerant coils, one of said refrigerant coils disposed in thermal exchange relationship with an atmosphere to be heated or cooled, and valve means responsive to the refrigerant pressure in said other coil for delivering blended liquid from said blending valve to thermal exchange relationship with said other refrigerant coil, whereby heat energy to be extracted from or delivered to said other refrigerant coil is exchanged with a blend of liquids, one of which derives its thermal energy from the sun and the other of which exchanges energy with the earth

Mass transport heat exchanger method and apparatus for use in ocean thermal energy exchange power plants

Abstract: Ocean thermal energy conversion (OTEC) uses a fluid, such as ammonia, hea by high-temperature surface water to provide a turbine-driving working gas. To condense the gas for re-use, a slurry of phase-transformation particles and cold ambient sea water is mixed in a deeply-submerged tank and delivered to a surface tank essentially at the cold sub-surface temperature. Condensing of the working gas is performed at the ocean surface level by exposure to the cold slurry temperature. Particle phase-transformation, which occurs at a temperature between that of the cold sub-surface water and the reject temperature of the heat-exchanger, maintains a surface tank temperature at about that of the sub-surface water.

Chemical storage of energy

Abstract: A method of storing energy at ambient temperature and recovering same at an elevated temperature which comprises decomposition of a chemical compound at high temperature with a decomposition product being used to form another compound at low temperature. Upon regeneration of the decomposition product from the other compound there is a release of the originally absorbed high temperature thermal energy.

Experimental Evaluation of a Cylindrical Parabolic Solar Collector

Abstract: Results are presented for a series of solar collector experiments in which the incident solar flux was concentrated by a single-axis tracking parabolic trough mirror. The concentrated solar flux was directed onto an absorber tube whose axis coincided with the focal axis of the concentrator. The performance of the collector was evaluated using three different absorbers; a black painted tube designed to operate near ambient temperature, a heat pipe which had a selective solar absorber coating applied to its surface, and a heat pipe which had its surface coated with a nonselective black paint. The peak efficiency for the collector in the absence of heat losses is approximately 62 percent when the incoming solar energy is normal to the collector aperature. The heat losses which occurred at elevated temperatures (300degreeC) decreased the peak efficiencies to 50 and 30 percent, respectively, for the selectively coated and black painted tubes. The experimental results establish the technical feasibility of using parabolic trough collectors for applications requiring thermal energy at temperatures up to 300degreeC.

Chemical reaction cycles for the recovery of low-level thermal energy

Abstract: At present, much thermal energy exhausted from industrial processes has been unrecoverably lost. In this paper a new method, a chemical heat pump is proposed for recovering such low-level energy by use of chemical reaction cycles. Through this method the low-level energy can be converted to higher and more useful energy. Thermodynamical study of this method and the practical example, Triangle Process 1, 2 and 3 are described.

Optically driven solar engine

Abstract: A solar engine having a plurality of elements which convert solar energy to usable mechanical motion, such as a piston and a thermally expandable fluid in a cylinder. The sun's rays are focused on a movable mirror which is provided to selectively direct the thermal energy to each of the piston and cylinder thermal energy converting elements. The thermal energy causes expansion of the fluid in the selected cylinder, thus moving the piston to provide mechanical motion. The thermodynamic cycle employed can be selected by the proper choice of the movable mirror timing and by the construction of the piston driven elements of the engine. The result is an efficient, flexible solar engine in which intermediate storage of thermal energy from the sun is not necessary.

Thermal energy flowmeter

Abstract: A method and apparatus for measuring the rate of flow and the totalized quantity of thermal energy flowing through a conduit. A small proportion of the thermal energy flowing through a conduit is by-passed to a heat exchanger, which is otherwise isolated from the thermal energy in the conduit, and shunted to a heat sink maintained at a reference temperature. The temperature differential along the heat shunt is measured as an indication of the total heat flow through the conduit.

Thermal loading of natural streams

Abstract: The impact of thermal loading on the temperature regime of natural streams is investigated by mathematical models, which describe both transport (convection-diffusion) and decay (surface dissipation) of waste heat over 1-hour or shorter time intervals. The models are derived from the principle of conservation of thermal energy for application to one- and two-dimensional spaces. The basic concept in these models is to separate water temperature into two parts: (1) excess temperature due to thermal loading and (2) natural (ambient) temperature. In order to formulate a linear decay model for excess temperature, the equations for back radiation, evaporation, and conduction, derived from the Lake Hefner study of U.S. Geological Survey, are linearized with reference to an arbitrary base temperature. It is shown that the resulting surface dissipation coefficient is predominantly influenced by wind speed and the mass-transfer coefficient of evaporation. Longitudinal dispersion is neglected in both transport models. Comparison of observed and calculated temperatures in seven natural streams shows that the models are capable of predicting transient temperature regimes satisfactorily in most cases. Mass-transfer coefficients of evaporation in streams are much higher than those commonly used for long-term calculations in a lake. Factors such as ground-water accretion, abrupt changes in thermalmore » loading, and unstable atmospheric conditions are found to have significant impacts on water temperature regimes. The dissipation of excess heat in natural streams is a gradual process frequently extending over a long downstream distance. For five out of the seven study reaches, the remaining excess heat at a point nearly 30 kilometers downstream was more than 50% of the initial thermal load.« less

Thermal energy storage and release utilizing combined sensible heat and latent heat of fusion

Abstract: A method for the storage and retrieval of thermal energy is disclosed, which in a two phase, two component system is able to utilize both the sensible heat of water (always one of the components) and the heat of fusion of the second component (a salt which forms a hydrate). The system to be employed must be graphically definable in a phase diagram including a liquidus, the compositional range of the system being selected so as to lie within the compositional range of the liquidus along which the system is to operate during both the heating and cooling cycles.

Thermal energy transformer

Abstract: For use in combination with a heat engine, a thermal energy transformer comprising a flux receiver having a first wall defining therein a radiation absorption cavity for converting solar flux to thermal energy characterized by a first wall defining a radiation absorption cavity having a solar flux entry aperture, and a second wall defining an energy transfer wall for the heat engine, and a heat pipe chamber interposed between the first and second walls having a working fluid disposed within the chamber and a wick lining the chamber for conducting the working fluid from the second wall to the first wall, whereby thermal energy is transferred from the radiation absorption cavity to the heat engine.

Temperature control in solar-to-thermal energy converters

Abstract: Solar-to-thermal energy converter comprising an insulated frame, a solar energy absorber mounted in the frame, a fluid flow heat exchange means thermally coupled to the absorber to carry away as thermal energy the absorbed solar energy, and a window transmissive to solar energy mounted in the frame above the absorber, featuring a temperature actuated heat loss enhancer comprising a fluid flow heat pickup means thermally coupled to the absorber, an exterior heat rejector element, a fluid flow heat rejector means thermally coupled to the heat rejector element, and a thermally actuated valve connected between said fluid flow pickup and rejector means to form a fluid flow circuit separate from the fluid flow heat exchange means and powered by the heat-produced differential buoyancy forces of the fluid therein when the valve is open.

Heat transfer system

Abstract: In a positive or negative heat transfer system with an intermittent source of positive or negative thermal energy, utilization means and a reservoir of heat transfer fluid flowing between the reservoir, the source and the utilization means, the reservoir is divided into two compartments of complimentarily variable volume and excess positive or negative thermal energy not required by the utilization means is used primarily to maintain the enthalpy of the fluid in one of the compartments of the reservoir at a maximum (for positive heat transfer) or mininum (for negative heat transfer) level, the volume of that one compartment being maintained at or reduced to a minimum until the required level of enthalpy is attained.