Showing papers on "Heat exchanger published in 1990"

Compact Heat Exchangers

Abstract: This book is covered under the following headings: Basic {epsilon}-N{sub tu} analysis for complicated flow arrangements; Single-phase heat transfer and pressure drop measurements, correlations and predictions; and Applications of compact heat exchangers.

Simultaneous optimization models for heat integration.

Abstract: In this paper, a simple yet general superstructure for heat integration is presented. The superstructure is a stage-wise representation where within each stage exchanges of heat can occur between each hot and each cold stream. The proposed representation does not rely on any heuristics that are based on the concept of the pinch point, and its simplicity enables a simultaneous consideration for design factors without the limitations of a sequential analysis. In part one of this three part series of papers, an NLP model is first introduced for the targeting of heat exchanger networks. As will be shown, the model can simultaneously target for area and energy cost while properly accounting for the differences in heat transfer coefficients between the streams. Constraints on matches can also be easily handled. Furthermore, if a fixed utility consumption is specified, the model reduces to an area targeting model. In the last section of the paper, the proposed representation is also applied to the modeling of multi-stream exchangers. Examples for all the applications are presented to illustrate the efficiency and effectiveness of the proposed model. integration problems. Based on this representation, optimization models that require very reasonable solution times are proposed to simultaneously account for the different design factors. In part I of this series of papers, the model is introduced and first presented for the simultaneous targeting of energy and area for heat exchanger networks with fixed flows and fixed supply and target temperatures. As will be shown, if a particular level of energy recovery is specified by fixing the utility requirement for the network, the model reduces to an area targeting formulation. Finally, it is shown that the proposed model can be incorporated in the optimization of a HEN involving multi-stream heat exchangers. The capability for modeling multi-stream heat exchangers is an important one since they can offer significant advantages over conventional single-hot-single-cold exchangers in certain applications, especially in cryogenic plants. In part II (Yee and Grossmann, 1990), the model is formulated as a mixed integer nonlinear programming (MINLP) problem for the synthesis of heat exchanger networks. Annual cost, comprising of utility cost, area cost as well as fixed charges for exchanger units are optimized simultaneously. As will be shown, the model not only can account for design constraints such as forbidden, required or restricted matches, but also certain piping specifications (i.e. no stream splits). Finally, in Part III (Yee et al., 1990) of the series, the formulation is extended to the simultaneous synthesis of process and heat exchanger network where the flows and temperatures are treated as variables. The important features of this model are that it optimizes both area and energy in the embedded network, that it handles constraints effectively, and if desired, that it enables the simultaneous synthesis of the detailed network structures. PROBLEM STATEMENT In order to address the various heat integration problems in this series of three papers, it will be assumed that given are a set of hot process streams HP to be cooled and a set of cold process streams CP to be heated. Specified are also a set of hot utilities HU and a set of cold utilities CU and their corresponding temperatures. The various problems to be considered are as follows: L A r e a targeting: Given fixed flows, inlet and outlet temperatures, and fixed utility requirement, determine minimum area cost, allowing for the possibility of nonvertical heat transfer and specification of constraints. 2. Simultaneous area and energy targeting: Given fixed flows, inlet and outlet temperatures, determine area and energy consumption to minimize cost allowing for nonvertical heat transfer and specification of constraints. 3. Modeling of multi-stream exchangers: Given fixed or variable flows, inlet and outlet temperatures, determine area requirement for a multi-stream exchanger allowing for specification of design constraints. 4. Synthesis: Given fixed flows, fixed or variable inlet and outlet temperatures, determine the energy consumption, number of exchangers, area requirement, and network configuration which minimizes annual cost while allowing for specification of constraints on matches, heat loads, and stream splitting. 5. Simultaneous process and HEN synthesis: Given the superstructure of a process with streams that can be heat integrated with variable flows, inlet and outlet temperatures, determine the optimal process and heat exchanger network design which minimize the annual cost while allowing for specification of design constraints. Problems 1,2, and 3 will be addressed in this paper, problem 4 in Part II (Yee and Grossmann, 1990), and problem 5 in Part III (Yee et al., 1990). In these problems, the following assumptions will be made: • Constant heat capacities • Constant heat transfer coefficients • Countercurrent heat exchangers The next section will present a common superstructure representation that can be used to address all the problems cited above. In the proposed model, no heuristic assumptions are required, and all parameters need not be fixed but rather can be optimized. To simplify the problem, however, the type of stream splitting will be restricted. As will be discussed later, this restriction simplifies the model significantly and allows for efficient and very reasonable solution times. SUPERSTRUCTURE REPRESENTATION The proposed representation for heat integration is a stage-wise superstructure which allows for different possibilities and sequences for matching streams. This superstructure can be viewed as an extension of the one presented in Grossmann and Sargent (1977) where within each stage potential exchanges between any pair of hot and cold streams can occur. It also resembles that of the spaghetti design concept brought forth by Linnhoff and coworkers, where the composite curves are divided into sections or a series of stages. In the spaghetti design, the number of stages is equal to the number of energy intervals (e.g. see Figure 1). In each section of the composite curves, the corresponding cold streams are matched with the corresponding hot streams in order to obtain vertical heat transfer. As a result, spaghetti designs usually require a large number of exchangers. In the proposed superstructure, the number of stages does not have to be equal to the number of energy intervals since the temperatures corresponding to each stage will be treated as variables to be optimized. This in fact allows for opportunities for criss-cross heat exchange when streams have different heat transfer coefficients. In general, the number of stages required to model the heat integration will seldom be greater than either the number of hot streams NH or the number of cold streams Nc. This is due to the fact that an optimal design usually does not require a large number of exchangers, meaning that a particular stream does not exchange heat with many streams. The superstructure for the proposed model is then derived as follows (see Figure 2): 1. Fix the number of stages, typically at maxfA^, Nc) 2. For each stage, the corresponding stream is split and directed to an exchanger for each potential match between each hot stream and each cold stream. The outlets of the exchangers are mixed which then defines the stream for the next stage. 3. The outlet temperatures of each stage are treated as variables. Note that the derivation of the superstructure does not require the identification of the pinch point or the partitioning into subnetworks. An example of a superstructure involving two hot and two cold streams is shown in Figure 2. The two stages are represented by eight exchangers, with four possible matches in each stage and variable temperatures between each stage. Note that alternative parallel and series configurations are embedded as well as possible rematching of streams. Also, for simplicity in the presentation, it will be assumed that the utilities are placed at the outlet of the superstructure. An assumption on the type of stream splitting allowed in the proposed superstructure can significantly simplify the model formulation. This restriction is illustrated in Figure 3. The assumption specifies that the outlet temperature of a particular stream at each exchanger of a stage is the same as the outlet temperature of the stage. As shown in Figure 3, for stream H1, the outlet temperature of both exchanger H1-C1 and exchanger H1-C2 at each stage are assumed to be equal. The motivation behind this assumption is that by setting these temperatures to be the same, the nonlinear heat balance around each exchanger and the heat mixing equations can be eliminated. For each stream, only an overall heat balance must be performed within each stage. The simplification is especially relevant when the inlet heat capacity flow rates of the streams are fixed. For these cases, flow variables are no longer needed in the model. As a result, not only is the dimensionality of the problem reduced, but the feasible space of the problem can be defined by a set of linear constraints as will be shown later in the paper. The nonlinearities of the model, involving the calculation of areas using stage temperatures, are isolated in the objective function. The model therefore becomes very robust and can be solved with relative ease. Before presenting the detailed model for the targeting problems, it is worthwhile to have a brief review of previous work. REVIEW OF AREA AND ENERGY TARGETING In nearly all of the current HEN synthesis methods, the HEN problem is decomposed into subproblems which progressively determine the characteristics of the final design. Because of this decomposition, trade-offs between level of energy recovery and heat exchanger area required cannot be accounted for explicitly. Current methods rely heavily on area targeti

Heat Transfer Through Falling Film Evaporation and Boiling on Horizontal Tubes

Abstract: Evaporation and boiling heat transfer coefficients are presented for thin, distilled water films flowing over the outside of horizontal, electrically heated brass tubes. Tests were conducted with a thin-slot water distribution system for 2.54- and 5.08-cm-dia smooth tubes. Both local and average heat transfer data were obtained for nonboiling and boiling conditions corresponding to feedwater temperatures ranging from 49 to 127C and heat-flux values ranging from 30 to 80 kW/m{sup 2}. Feedwater flow rates ranged from 0.135 to 0.366 kg/s per meter length per side of the tube. Both nonboiling and boiling correlations of the average heat transfer coefficients were developed and compared.

Duplex heat exchanger

Abstract: A duplex heat exchanger comprises unit heat exchangers which have a plurality of tubes arranged parallel with each other and comprise fins each interposed between two adjacent ones of such tubes, opposite ends of each tube being connected to a pair of headers in fluid connection therewith. The unit heat exchangers are closely juxtaposed to each other fore and aft in a direction of air flow. Coolant circuits of said unit heat exchangers are connected either in series or in parallel with each other.

Precooling heat exchange arrangement integral with mounting structure fairing of gas turbine engine

Abstract: A precooling heat exchange arrangement includes a hollow fairing mounted on a forward side of an engine mounting structure extending radially across an annular fan duct of a gas turbine engine. The fairing has an aerodynamically-shaped external wall disposed in the main air flow through the fan duct, spaced upper and lower internal plenums and a middle internal plenum disposed therebetween and sealed therefrom. A conduit routes hot bleed air flow from the engine to and from the lower and upper plenums of the fairing and at least one heat exchanger is mounted in the fairing. The heat exchanger includes a heat transfer structure having an interior in communication with the upper and lower plenums and having an exterior in communication with the fan duct air flow and the middle plenum of the fairing such that a fractional portion of fan duct air flow can divert from the fan duct and pass across the exterior of the heat exchanger in heat transfer relationship with the hot bleed air passing through the interior of the heat exchanger for cooling the hot bleed air. An air flow control mechanism is provided in communication with the middle plenum of the fairing for routing cool fan duct air flow to the core engine compartment after passing over the exterior of the heat transfer structure.

Geothermal heat transfer system

Abstract: A geothermal system for conditioning air in an enclosed space by transferring heat between the air and a heat exchange liquid which is circulated through a line buried in the earth. The line transfers heat between the earth and the heat exchange liquid circulating through the line. The line is constructed to facilitate the expansion and contraction of the line with changes in temperature and to facilitate the transfer of heat between heat exchange liquid in the line and the earth without causing ice to form around the line.

Optimization of a closed-cycle otec system

Abstract: Optimization of an ocean thermal energy conversion (OTEC) system is carried out by the Powell method (the method of steepest descent). The parameters in the objective function consist of the velocities of cold sea water and warm sea water passing through the heat exchangers, the phase change temperature, and turbine configuration (specific speed, specific diameter, ratio of blade to diameter). Numerical results are shown for a 100 MW OTEC plant with plate-type heat exchangers using ammonia as working fluid, and are compared with calculation results for the case when the turbine efficiency is fixed.

Cold plate for cooling electronics

Abstract: A multi-layered cold plate is customized for cooling a plurality of electronic components to be arranged in thermal communication with the cold plate by dividing the cold plate into a plurality of hypothetical cooling zones, determining the cooling needed for the respective cooling zones for cooling the electronic components adjacent the zones, and tailoring a heat exchanger layer of the multi-layered cold plate with different heat exchanger structures in respective cooling zones to provide relatively high and relatively lower efficiency cooling where needed A coolant flow, jet impingement heat exchange structure formed of alternately stacked orifice plates and spacer plates provides the high efficiency cooling The heat exchanger layer is the only layer of the cold plate which must be customized for accommodating a particular arrangement of electronic components to be cooled

Pressure drop considerations in the retrofit of heat exchanger networks

Abstract: Analyse des relations entre la perte de charge, les coefficients de transfert de chaleur et les aires d'echangeurs de chaleur

Heating and cooling apparatus

Abstract: A heating and cooling method and apparatus for a single, closed loop configuration for directly exchanging thermal energy with the earth for both heating and cooling purposes. A refrigerant, which is pumped through the apparatus by a compressor, undergoes two phase transitions during each circuit through the loop. A subterranean heat exchanger has a pair of manifolds in flow communication with a plurality of substantially horizontally oriented tubes. Refrigerant flowing through the tubes has sufficient velocity to sweep lubricant oil, which has escaped from the compressor, along with it for return to the compressor. An expansion valving assembly automatically meters and regulates the flow rate and pressure of the refrigerant during both the heating mode and the cooling mode of the apparatus. A refrigerant storage device automatically supplies or accepts the change in quantity of the refrigerant required when the apparatus changes from either the heating or cooling mode to the reverse mode. A bypass mechanism anticipates the low pressure condition which arises at the compressor input during reversal or startup of the apparatus and provides multiple attempts to overcome inertial resistance corresponding thereto. A modified embodiment of the apparatus provides a non-phase-change heat exchanger flow communicating in tandem to remove a portion of the thermal energy for auxiliary thermodynamic purposes.

Treatment of heat exchangers to reduce corrosion and by-product reactions

Abstract: The invention provides a method of extending the useful life of high temperature heat exchangers, e.g., reactor feed/effluent heat exchangers, in installations where the heat exchanger is contacted by a process fluid stream, e.g., a feedstock comprising ethylbenzene, at a temperature where the process stream may cause deterioration of contacted metal surfaces of the heat exchanger and/or undergo catalytic reaction as a result of contact with the contacted metal surfaces. The new method comprises the step of mechanically removing material from those surfaces of the heat exchanger that are to be contacted by the process fluid stream, so as to render said surfaces less susceptible to attack from said high temperature process fluid stream.

Air to air recouperator

Abstract: heat recouperator having a rotary wheel heat exchanger uses a random matrix media comprising a plurality o~ small diameter heat-retentive fibrous material, which provides high thermal efficiency in exchanging heat between inlet and exhaust air streams.

Engine intake temperature control system

Abstract: A combustion air induction system for an internal combustion engine equipped with a turbocharger to provide charge air to the engine includes a pair of heat exchangers arranged in series in the conduit communicating the charge air outlet of the turbocharger to the induction manifold of the engine. Charge air from the turbocharger first travels through a charge air to engine coolant heat exchanger, and then travels through a charge air to ambient air heat exchanger. A bypass passage is controlled by a valve to bypass charge air around the charge air to ambient air heat exchanger under predetermined conditions.

Multiple serpentine tube heat exchanger

Abstract: A multiple serpentine tube heat exchanger having side-by-side arranged serpentine-shaped passageways each extending across the core and a mixing chamber connecting one such passageway to at least one other. The passageway constituting the back of the heat exchanger core has an enlarged internal surface area relative to the passageway constituting the face of the heat exchanger core. Microgrooving of the passageway can be used to further enhance heat transfer.

Active seat cooling system

Abstract: A cooling system for cooling units of furniture adapted for supporting the human body, and for car seats, steering wheels and arm rests, includes two main components. A closed loop air conditioning subsystem has a first motor which drives a compressor in which a refrigerant fluid is compressed. The compressed fluid is passed into a condenser where the compressed fluid is cooled by dissipating its heat into the environment, and from where the compressed fluid is released through an expansion valve into an evaporator. The evaporator becomes cool due to expansion of the refrigerant fluid into a gas and consequent absorption of heat from the evaporator's body and immediate environment. The refrigerant gas is returned from the evaporator into the compressor. The second main component of the invention is a subsystem where a working fluid is in heat exchange relationship with the evaporator of the first system whereby the working fluid is cooled in the evaporator and is thereafter sent by a pump or fan, driven by a suitable motor, into cooling members, such as cooling coils incorporated within the seat or other item of furniture (or related item) which is cooled directly.

Ground source air conditioning system comprising a conduit array for de-icing a nearby surface

Abstract: A ground source air conditioning system for a structure. The system comprises a de-icing conduit array for de-icing nearby surfaces, such as sidewalks, parking lots and driveways. The air conditioning system includes a refrigeration unit, and the heat from the refrigerant in the refrigeration unit is transferred to a heat transfer fluid. The heat transfer fluid is conducted to a heat exchanger, which preferably is located underground, such as an array of vertically or horizontally arranged conduits. Alternately, a water reservoir can be employed as the heat exchanger. When necessary, the heat transfer fluid is conducted through the de-icing conduit array positioned immediately beneath the surface to be de-iced. The amount of heat transfer fluid directed to the de-icing array can be regulated, and in warmer seasons it can be isolated altogether from the rest of the system. The air conditioning system may further include a system which heats or cools the inside of the structure, such as a heat pump, in addition to the refrigeration equipment.

Air cooled heat exchanger for multi-chip assemblies

Abstract: An air-cooled self-contained evaporator and condenser apparatus with no external power source, the apparatus including a cold plate having a first surface with recesses formed therein in a matrix or array corresponding to the matrix or array of chips on a multi-chip module or unit. The opposite surface of the cold plate includes a finned arrangement which, in conjunction with the cold plate, forms part of an isolated evaporation chamber of the cooling unit, with the chamber housing a boilable fluid which changes phase from liquid to vapor. Positioned above and contiguous with the isolated chamber is a condensing chamber, including a plurality of tubular passageways, the external portions of which are finned for ready removal of heat. For attachment of the cold plate portion of the unit to the chips, suitable heat transfer slugs, such as aluminum nitride slugs, are affixed in the recesses, with opposites surfaces thereof bonded to the exposed faces of the chips. Heat is transferred from the chips through the slugs, through the cold plate to cause boiling of the fluid within the chamber, the vapors of which are condensed in the upper part of the cooling unit to thus return as fluid to the chamber.

Mathematical modeling and analysis of heat pipe start-up from the frozen state

Abstract: The start-up process of a frozen heat pipe is described and a complete mathematical model for the start-up of the frozen heat pipe is developed based on the existing experimental data, which is simplified and solved numerically. The two-dimensional transient model for the wall and wick is coupled with the one-dimensional transient model for the vapor flow when vaporization and condensation occur at the interface. A parametric study is performed to examine the effect of the boundary specification at the surface of the outer wall on the successful start-up from the frozen state. For successful start-up, the boundary specification at the outer wall surface must melt the working substance in the condenser before dry-out takes place in the evaporator.

Hemisphere handbook of heat exchanger design

Abstract: Heat exchanger theory fluid mechanics and heat transfer thermal and hydraulic design of heat exchangers mechanical design of heat exchangers physical properties.

Submerged rotating heat exchanger-reactor

Abstract: An apparatus transfers heat for the purpose of purifying raw feed liquid, separating dissolved gases from liquids, vaporizing heat transfer fluids or containing and regulating biological/chemical reactions. The feed liquid is directed into an evaporator module submerged in a solar pond or other body of heated liquid. The evaporator module includes a rotating housing through which a plurality of spaced apart substantially horizontal open ended heat transfer tubes extend. A heating liquid is directed through the heat transfer tubes. The feedwater is distributed within the evaporator module so as to cause the feedwater to descend into heat transferring contact with the heat transfer tubes and thereby vaporize a portion of the feedwater. A preferred embodiment of the evaporator module is disclosed which includes cavitation fins for urging the heated liquid through the evaporator module.

Advanced survivable space solar power system

Abstract: A photovoltaic electric power system for use in space A self contained sun powered electric power generating system comprising a fresnel mirror array made up of a plurality of quadrilateral mirrors individually mounted on a generally flat supporting structure with the mirrors aimed at a common point above the structure, a photovoltaic array positioned at the common point by a movable strut mechanism, heat exchanger means at the PV array to draw excess heat therefrom, coolant lines from the heat exchanger means running through the struts to transfer heat to heat pipes configured as flat panels at the edges of and perpendicular to the supporting structure, and positioning means attached to a separate structure to enable the system to track the sun The system is designed to fold into itself in the form of an elongate box for launch, maneuvering and protection

Heating or air conditioning system for a motor vehicle

Abstract: Improved air-conditioning of the rear-seat area of a motor vehicle is achieved substantially independently from the front-seat area in a heating or air-conditioning system having means for controlling the temperature of the supply air via a front-seat control unit by employing a front air flap with a cool air passage at the inlet of a heat exchanger. A front-seat air-mix chamber is connected with a rear-seat air-mix chamber having a rear-seat area duct, a rear-seat foot duct, and a rear-seat air-mix flap with a cool air passage therethrough to control the proportion of cool and warm air entering the ducts. Cool air is provided from the inlet side of a heat exchanger flowing through the cool air passage in the front air flap and the cool air passage in the rear-seat air-mix flap while warm air is provided from the outlet of the heat exchanger. The rear-seat air-mix flap is actuated either jointly with a front-seat air-mix flap in a front-seat air-mix chamber by a temperature-setting element on the front-seat control unit or by a separate rear-seat control unit.

Air cycle air conditioner for heating and cooling

Abstract: A compact, air cycle air conditioning system including compressor, turbine, heat exchanger and high speed electric motor is thermostatically controlled to supply either hot or cold conditioned air to a load air space. In a second arrangement, compact, exhaust gas driven air cycle air conditioning system including a compressor, turbine, two heat exchangers and an exhaust turbine is controlled by means of an exhaust gas bypass arrangement and supplies either hot or cold conditioned air to a load air space. In a third arrangement compact, exhasut gas driven air cycle air conditioning system includes an expansion turbine, two compressors, two heat exchangers and an exhaust turbine which is preferably controlled by means of an exhaust gas bypass arrangement and supplies either hot or cold conditioning air to a load air space.

Performance analysis of a closed-loop climate control system using underground air tunnel

Abstract: A passive summer cooling technique that utilizes the underground soil temperature has application in climate control of residential as well as agricultural buildings. The soil temperature stays fairly constant at a depth of eight feet or more. Earlier studies have shown the usefulness of this technique for an open-loop system. However, the previous analyses in the literature did not evaluate the usefulness and limitations of this method for closed-loop air conditioning. In this study an analysis of the coefficient of performance (COP) of a closed-loop system, based on the above technique, in combination with a conventional air conditioner, has been done. In this system, the cooling needed to neutralize the heat gain of the conditioned space is provided by the air cooled in an underground air pipe in combination with an air conditioner. The underground air tunnel is used for hot parts of days and is off for cooler parts of days and nights. The analysis has been done by a computer model solution, using central finite difference method.

Cogeneration system with recuperated gas turbine engine

Abstract: A turbine engine is provided with a primary surface, counterflow heat exchanger for preheating the compressed air from the compressor prior to its entry into the combustor. The recuperator includes three concentric cylindrical shells which completely encircle the hottest components of the engine. The outermost shell includes a plurality of inlet openings for receiving air from the compressor, and a plurality of outlet openings for discharging the air into the combustor. The innermost shell includes a plurality of inlet openings for receiving gases from the turbine and a plurality of outlet openings communicating with an exhaust duct. The central shell is a corrugated tube which divides the space between the inner and outer shells into a plurality of concentric annular flow chambers, and allows heat transfer between adjacent chambers. Annular turbulators may be inserted in the chambers. The engine may be used in a cogeneration system in which the exhaust duct is coupled to a boiler, and a temperature-controlled valve is provided for controlling the proportion of exhaust gases entering the recuperator relative to those directly entering the boiler. The engine may also be used in a system using intercooling and reheating, or integrated with an air cycle in which it is used to cool water.