Showing papers on "Heat capacity rate published in 1987"

Heat exchanger performance monitor

Abstract: A performance monitor generates a fouling factor which indicates the level of fouling of a heat exchanger having a heat exchange surface area and through which a heat exchange medium passes having a known specific heat. Temperature transmitters are utilized to obtain values for the input and output temperatures of the heat exchange medium as well as the temperature in the heat exchanger of a heat exchange fluid used to transfer heat to or from the heat exchange medium. Modules are used to generate a value for an actual heat transfer coefficient in the heat exchanger as a function of the temperatures, flow rate and constant parameters such as area and specific heat, for the heat exchanger. The actual heat transfer coefficient is compared with a nominal or original heat transfer coefficient to determine if any deterioration in the coefficients has occurred which reflects the fouling of the heat exchanger. A simple ratio of the nominal to actual heat transfer coefficient is taken as a measure of this fouling factor.

Second-law-based thermoeconomic optimization of two-phase heat exchangers

Abstract: This paper presents a closed-form analytical method for the second-law-based thermoeconomic optimization of two-phase heat exchangers used as condensers or evaporators. The concept of internal economy as a means of estimating the economic value of entropy generated (due to finite temperature difference heat transfer and pressure drops) has been proposed, thus permitting the engineer to trade the cost of entropy generation in the heat exchanger against its capital expenditure. Results are presented in terms of the optimum heat exchanger area as a function of the exit/inlet temperature ratio of the coolant, unit cost of energy dissipated, and the optimum overall heat transfer coefficient. The total heat transfer resistance represented by (1/U = C1 + C2 Re{sup {minus}n}) in the present analysis is patterned after Wilson (1915) which accommodates the complexities associated with the determination of the two-phase heat transfer coefficient and the buildup of surface scaling resistances. The analysis of a water-cooled condenser and an air-cooled evaporator is presented with supporting numerical examples which are based on the thermoeconomic optimization procedure of this paper.

The dynamics of a solid-adsorption heat pump connected with outside heat sources of finite capacity

Abstract: The problem of the response of a heat pump to the solicitations of the heat reservoirs is an important problem which has not been extensively studied up to now In this publication, a case study concerning a solid adsorption heat pump working with the zeolite water pair in a single state cycle is presented The equations needed to solve the problem are presented and are solved numerically in a particular case The numerical simulation is validated by experimental results A sensitivity study of the results of the numerical simulation is then presented vs the most important parameters The thermodynamic cycle is seen to be very sensitive to the values of the various heat exchange coefficients as well as to the heat rates exchanged between the heat pump and the heat reservoirs

Method of utilizing thermal energy

Abstract: A method is provided for utilizing sensible heat energy supplied by a high-temperature heating fluid, employing a multi-component working fluid thermodynamic cycle, wherein a solution rich in a lower boiling component is heated in a vapor generator in counter-current heat exchange with the heating fluid to produce a vapor-fluid mixture which is separated in a rectifier into a lean solution and a vapor mixture; the enthalpy of the vapor mixture is optionally increased in a superheater by counter-current heat exchange with said heating fluid at its highest temperature; the vapor mixture is then expanded thereby to perform the function of the cycle; and the spent vapor mixture is dissolved in said lean solution in an absorber so as to regenerate the rich solution; characterized in that the rich solution leaving the absorber is compressed and divided into a first and second parts; the first part is heated by counter-current heat exchange with said lean solution drawn from the rectifier, whereafter said first part of the rich solution is recycled to the vapor generator; whereas the second part of the rich solution extracts additional heat from the heating fluid leaving the vapor generator, by counter-current heat exchange, and is then fed into the rectifier for counter-current mass and heat exchange with the vapor-liquid mixture formed in the vapor generator.

Compound generating system

Abstract: PURPOSE: To improve utilization efficiency by alternately and reversibly operating a heat pump system which recovers the environmental heat quantity and an organic Rankine cycle generating system which converts the environmental heat quantity from a heat accumulating system into electric power energy. CONSTITUTION: The environmental heat from a first intake port 2 is recovered by a working fluid in an evaporator 5. A motor 8 is driven through surplus power at night, and the working fluid heated at high temperature is compressed through a compressor 7, heats a working fluid from a low temperature bath 14 through a condenser 9 consisting of a heat pump system 1, and is accumulated in a high temperature bath 13. On the other hand, the heat pump system 1 is stopped in the daytime, cooling water is introduced into the evaporator 5, the environmental heat is introduced into a preheater 22 in an organic Rankine cycle generating system 18 to operate a supplying pump 21, and the high temperature working fluid from the high temperature bath 13 is introduced into the condenser 9 to operate the condenser as a evaporator and to operate the compressor 8 as a turbine and to operate the motor (generator) 8 as a generator. The compound generating system can therefore be simplified and the utilization efficiency can also be improved. COPYRIGHT: (C)1988,JPO&Japio

Available work from a finite source and sink: How effective is a Maxwell’s demon?

Abstract: The maximum work obtainable from a finite heat source and finite heat sink, initially at respective temperatures T+ and T−, is determined as a function of the temperature ratio τ=T−/T+ and the heat capacities of the source and sink. The thermal efficiency with which this work is delivered is found to be well approximated by η*=1−τ1/2 for τ≥0.1, independent of the source and sink heat capacities. It is noted that η* occurs in other contexts for which work or power output is optimized, and is a surprisingly ‘‘universal’’ efficiency. A reversible polycycle that delivers the maximum work using an ideal gas working fluid is found to exist only if the heat capacity of the heat sink exceeds that of the working fluid. An example of a finite source/sink combination from which work can be generated is an enclosed gas, divided in half by a partition with a small, controllable trap door operated by a Maxwell’s demon. If the demon opens and closes the door selectively, so as to achieve a temperature difference across ...

Performance of ejector heat pumps

Abstract: An ejector-compression heat pump can use low-grade thermal energy in the neighbourhood of 93.3°C (200°F) to provide space cooling and heating. This paper applies the existing ejector theory to estimate the performance of an ejector heat pump system at various operating conditions. The study includes parametric, sensitivity and off-design analyses of the heat pump performance. The performance enhancement options and desired ejector geometry are also examined. Refrigerants 11, 113 and 114 are three of the halocarbons most suitable for the ejector heat pump system. The estimated coefficients of performance for a simple ejector heat pump are 0.3 for the cooling mode and 1.3 for the heating mode at a sample operating condition in which the refrigerant (R-11) boiling temperature is 93.3°C (200°F), condensing temperature 43.3°C (110°F) and evaporating temperature 10°C (50°F). A 24 per cent performance improvement is predicted for a heat pump with two-stage ejectors and regenerative heat exchangers. The off-design performance is relatively insensitive to the evaporator temperature variations.

Dual source external heating system for a heat pipe

Abstract: An external heating system for a heat engine such as a Stirling cycle engine which permits thermal energy to be provided by solar energy or fuel combustion sources. The system employs a complexly shaped heat pipe evaporator section having an enclosed cavity for receiving solar energy and another section forming hollow fins which is exposed to hot combustion gasses. Accordingly, either heat source may be used to evaporate working fluid within the heat pipe which is transferred to the associated heat engine.

Device for the cooling of an x-ray source

Abstract: A device is disclosed for the cooling of an X-ray tube contained in a casing, using a fluid put into forced circulation in a cooling circuit comprising a heat exchanger. The device of the invention can be used to obtain efficient cooling while, at the same time, using a small volume of fluid and a heat exchanger of smaller size than in the prior art. To this end, the cooling circuit comprises means to, firstly, store a quantity of heat accumulated by the fluid when the latter reaches a pre-determined temperature during an examination period and, secondly, to restore this quantity of heat during an idle period which follows the examination period.

A Comparison of the Predicted and Measured Thermodynamic Performance of a Gas Turbine Cogeneration System

Abstract: The thermodynamic performance of a gas turbine cogeneration system is predicted using a computer model The predicted performance is compared to the actual performance, determined by measurements, in terms of various thermodynamic performance parameters which are defined and discussed in this paper These parameters include the electric power output, fuel flow rate, steam production, electrical efficiency, steam efficiency, and total plant efficiency Other derived parameters are the net heat rate, the power-to-heat ratio, and the fuel savings rate This paper describes the cogeneration plant, the computer model, and the measurement techniques used to determine each of the necessary measurands The predicted and the measured electric power compare well The predicted fuel flow and steam production are less than measured The results demonstrate that this type of comparison is needed if computer models are to be used successfully in the design and selection of cogeneration systems

Chemical heat pump using heat of reversible catalytic reactions

Abstract: One of the most important objects of research in the field of energy conservation is development of a high temperature heat pump for the industrial sector. In this framework this paper introduces a new concept of heat pump, which is a hybrid between a compressor and chemical heat pump, where instead of the latent heat of liquids, the proposed system uses the heat of gaseous catalytic reversible reactions (type A → B + C). This paper proposes a simple scheme with a mathematical model for the calculation of the parameters necessary to qualify the behaviour of the Heat Reaction Chemical Heat Pump (HRCHP). The Coefficient of Performance (COP) is calculated as a function of the temperature of the heat source, the temperature to which the pump upgrades the heat and the conversion of the chemical reaction. A more optimized scheme is prospected.

The upgrading of waste heat by means of water-sulphuric acid absorption heat transformers

Abstract: The technical and economic feasibility of a single-stage water-sulphuric acid heat transformer, as evaluated through a simplified mathematical model, is discussed in this paper. Three different criteria of optimality are considered. The first two respectively account for the exergetic and the enthalpic value of the useful heat. The third criterion is based on an approximate evaluation of the fixed and operating costs, considered proportional to the inverse of the heat storage capacity. An analysis based on the values of the coefficient of performance and of the mass flow rates, expressed as a function of the gross temperature lift, points out the significance of the criterion based on the heat storage capacity. This result is also supported by considering the ability of the heat transformer to maintain its performance in different external conditions.

Outdoor unit for a heat pump

Abstract: An outdoor unit for a heat pump is usable under very cold weather conditions since the outdoor unit includes an auxiliary heating system which heats a heat exchanger in order to prevent the heat exchanger from forming frost and which also compensates for the decline in heating capacity. Further, the outdoor unit has an air flow preventing arrangement which prevents the flow of air through the heat exchanger when the absorption of the heat from the atmosphere is not efficient. The outdoor unit drives compressors by an internal combustion engine in order to reduce the consumption of electric power and the coolant for the engine is also utilized to provide auxiliary heat to the heat exchanger. The outdoor unit also includes a boiler to compensate for the lack of heating capacity in the engine waste heat. The boiler is operated when the atmospheric temperature is less than the predetermined value.

Aqua-ammonia heat transformers

Abstract: The theoretical performance characteristics of single-stage and double-stage heat transformers using aqua-ammonia as binary mixture have been discussed. The coefficients of performance, energy efficiencies, mass circulation ratio, pump work etc. have been analysed as a function of heat delivery temperature. Thus, heat transformers represent an attractive solution for upgrading low temperature waste heat to higher temperature useful heat with minimum consumption of external energy.

Process and apparatus to improve the power factor of compressor-operated (hybrid) refrigerators or heat pumps functioning with solution cycle

Abstract: A process for the operation of hybrid compression-absorption heat pumps or refrigerators with the use of fluid medium containing a mixture of differently volatile components (typically two) easily soluble in each other. During heat extraction, in a first counter current heat exchange, vapor of the more volatile component is partially dissolved in the liquid of the less volatile component. Simultaneously, an additional portion of the volatile component is condensed. Importantly, the medium is discharged from the first heat exchange in a stage of incomplete dissolution/condensation of the vapor phase. The combined medium is expanded and absorbs heat in a second counter current heat exchange phase, during which the more volatile component is both expelled from the solution and evaporated. A counter current heat exchanger is connected between the first and second heat exchangers, and uses low pressure medium exiting from the second heat exchange to effect cooling and thus further dissolution and condensation of the high pressure medium exiting from the first heat exchange.

Solar system for generating steam

Abstract: PURPOSE: To reduce the installation space and cost for equipment and installations by providing a first heat exchanger in which heat is exchanged between hot thermal medium heated by collected heat and transported feed water as well as a second heat exchanger which generates steam for processing by heating the feed water with the operating medium. CONSTITUTION: Thermal medium 15 heated to the set temperature by collecting heat in a solar collector 1 exchanges heat with feed water 16 in a heat exchanger 2 where the feed water 16 is heated by the thermal medium 15. As the quantity of heat that can be collected by the solar collector 1 exceeds the set value when the sunshine is abundant, only the set amount regulated by a control valve CV3 is introduced into a heat exchanger 12, and the excessive hot feed water 16 passes through a control valve 4 to be stored in a storage tank 3. The feed water 16 now regulated to the set temperature and set flow rate becomes saturated gas by receiving heat of waste heat source 14 in a heat exchanger 9, which is then compressed in a compressor 10 and exchanges heat with operating medium 17 in the heat exchanger 12. Consequently, the feed water 16 becomes usable steam at still higher temperature and pressure and is supplied to the process. COPYRIGHT: (C)1988,JPO&Japio

The development of engine evaporative cooling system

Abstract: A fundamental heat transfer study has been conducted on a new engine cooling system in which heat is removed from the engine through the boiling process in the water jacket and is radiated to the air through a condenser. By carrying out a basic experiment using a model boiler as a substitute for the cylinder heat water jacket and a real engine experiment, the following cooling system characteristics were found: First, a good heat transfer coefficient can be obtained up to an order of 10/sup 3/ kw/m/sup 2/ heat flow with only a small coolant flow. Second, it is possible to obtain a more uniform temperature distribution over the engine structure by making use of the cooling by boiling characteristics which remove more heat from hotter surfaces than from cooler ones. Third, the good response of this system's variable temperature control procedure greatly reduces knocking, which in turn increases power.

Influence of two-dimensionality of the front with heat losses on the limits of stationary gasless combustion

Abstract: The authors consider the mathematical consequences of a two-dimensional analysis of a combustion wave with heat losses on the limits of stationary gasless combustion within a cylindrical reaction zone. The computerized simulation incorporates the degree of transformation in the final combustion product, the thermal diffusivity coefficient, the specific heat, the heat transfer coefficient, the thermal effect of the reaction, a kinetic law of component interaction, and the rate constant dependent on the temperature according to the Arrhenius equation.

Binary electricity and heat generator

Abstract: PURPOSE: To supply heat and electricity simultaneously, effectively and stably even from moderate and low temperature waste heat by pressing working medium vapor from an evaporator, conducting generation on the one hand and heat supply on the other hand and bringing the rate to an adjustable state. CONSTITUTION: An evaporator E is supplied with a heat source fluid at 60°C, the temperature of the fluid is lowered up to 50°C at an outlet for the evaporator, working medium vapor at 47°C such as fluorocarbon is generated, the vapor is pressed by a compressor Co, and the temperature of the vapor is elevated at 100°C. The working medium vapor is divided into two in response to the openings of first and second flow control valves V 1 , V 2 . A generator G is driven by steam fed to a steam power plant T. Working medium vapor completing its work gives heat to cooling water in a first condenser C 1 and is changed into a condensate at 35°C. The condensate is forwarded to the evaporator E by a pump P. Vapor fed to a second condenser C 2 gives heat to a fluid to be heated at 80°C and the temperature of the fluid is elevated up to 95°C, and the pressure of the fluid is reduced through an expansion valve V e and the fluid is sent to the evaporator E. The rate of generation to heat supply is altered arbitrarily by the first and second flow control valves V 1 , V 2 . COPYRIGHT: (C)1989,JPO&Japio

Method of recuperating the condensation heat of a refrigeration system, and refrigeration system for carrying out the method

Abstract: In order, in a refrigeration system with recuperation of the condensation heat, to counteract a reduction of the refrigerating capacity on changing over from cold production operation alone to simultaneous cold production and heat recuperation operation, the refrigerant condensate which accumulates is supercooled before its supply to the pressure relief member (18). To this end, a second heat exchanger (16) is used, which is connected on the refrigerant side after a first heat exchanger (14) which serves as liquefier. The active heat exchange surface of the second heat exchanger (16) is in this connection adapted to the respective operating state by means of accumulation of refrigerant condensate depending on the temperature level of the recuperated condensation heat, as a result of which simple regulation of this temperature level is simultaneously brought about.

Method for increasing the coefficient of performance of hybrid refrigeration machines or heat pumps

Abstract: The method according to the invention is proposed for the operating of compression-absorption heat pumps or refrigeration machines (of hybrid heat pumps and refrigeration machines), using a working medium consisting of two media of different volatility but which dissolve well one in the other. In the method, when heat is extracted during a first heat exchange operation, on the one hand the vapour of the more volatile component (component with lower boiling point) is dissolved in the liquid of the less volatile component (component with higher boiling point) (absorption), on the other hand the vapour of the less volatile component is condensed (condensation), then, after expansion of the working medium, when heat is supplied during a second heat exchange operation, on the one hand the more volatile component is at least partially driven out of the solution (degassing), on the other hand the less volatile component is at least partially evaporated (evaporation), after which the working medium is compressed. … The novelty of the method according to the invention is that the working medium is derived from the first heat exchange operation as a mixture of two different phases (liquid and vapour) of different concentration. … The heat pump or refrigeration machine suitable for realising the method according to the invention includes, in series connection in the direction of flow of the working medium, a condenser-absorber (1), a liquid-cooling inner heat exchanger (5), a pressure reducer (2), an evaporator-degasser (3) and a pressure increaser (compressor) (4), the output of the latter being connected to the input of the condenser-absorber (1). … The novelty of the device is that a vapour-cooling inner heat exchanger (6) is interposed between the condenser-absorber (1) and the liquid-cooling inner heat exchanger (5). … …

Designing Animal Ventilation Schedules with Counterflow Heat Exchangers

Abstract: VENTILATION rates in environmentally controlled animal facilities are determined by minimum rates required to effect heat and moisture equilibrium and minimum air quality. The use of heat recovery systems modifies the net thermal exchange and thereby the ventilation rate required to maintain thermal equilibrium. A mathematical equation was developed to compute the air mass flow rate required for constant temperature when using a counterflow heat exchanger. The equation computes air mass flow rates as a function of the net sensible heat to be removed from the building, overall heat transfer coefficient of the heat exchanger, heat exchanger surface area, interior dry bulb temperature of the animal facility and ambient dry bulb temperature. Air mass flow rates were compared for systems with and without a counterflow heat recovery system. Condensation within the heat exchanger was shown to have a large effect upon the heat recovery rate. The relative magnitude of heat recovery with condensation was compared to sensible heat recovery for typical house and ambient conditions. The actual heat recovery rate with condensation could be more than double the sensible heat recovery rate at reasonable levels of sensible heat effectiveness ratio.

Optimum heat release for a reciprocating internal combustion engine

Abstract: The problem of finding the cylinder pressure trace which maximizes engine efficiency is formulated in terms of cylinder pressure-dependent frictional, heat, and mass losses. The governing equations are recast into a form to which optimal control theory can be applied, and the pressure trace together with the corresponding optimum heat release profile which yield maximum efficiency are found. Results for optimum heat release are compared to results for both conventional rates of heat release and for the theoretical Otto cycle, and show that significant gains in efficiency are possible if the optimum heat release is employed.

Heat exchanger having a variable volume flow, and variable dwell times of the medium

Abstract: The invention relates to heat exchangers for variable volume flows Qs and variable dwell times tv of the medium which is heated or cooled in the heat exchanger, with a constant outlet temperature (Ta). Such heat exchangers are of interest, particularly for use in continuous-flow sterilizers. The variable volume flow Qs is implemented in that the heat exchanger is composed of n partial heat exchangers, each having constant partial volume flows Qx. These are preferably designed in accordance with the function Qx = constant *23(x-1) where 1

Device for calculating the amount of recovered heat energy

Abstract: The invention relates to a device for calculating the amount of heat energy obtained in a heat-recovery device in an air-conditioning system in which a heat exchanger is arranged in an air channel. Hitherto, it has not been possible to determine the effective power of heat recovery devices but the theoretically calculated recovered heat has had to be accepted without conclusive information on the efficiency of the heat recovery device actually being obtained. According to the invention, a process is provided which supplies precise, conclusive information on the amount of heat energy actually recovered, and the said device is characterised in that a speed meter (9) for the air speed in the air channel, a temperature measuring device for the difference in air temperature between the two sides of the heat exchanger and an input component for the cross-section of the air channel are provided, and in that electronic switching elements are provided and are connected to a display device, with which switching elements the amount of heat energy recovered can be calculated and transmitted to the display device so that the amount of heat energy actually recovered can be monitored during operation of the heat recovery device.

Regenerative machine and heat engine with external heat supply

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.