Showing papers on "Heat exchanger published in 1999"

A short time step response factor model for vertical ground loop heat exchangers

Abstract: The short-term behavior of ground-coupled heat pump systems is important for design of ground loop heat exchangers, energy analysis of ground source heat pump systems, and design of hybrid ground source systems. This paper describes the development of short time-step temperature response factors for vertical ground loop heat exchangers as used in ground-coupled heat pump systems. The short time-step response factors allow for a direct evaluation of system energy consumption and electrical demand in hourly or shorter time intervals. The development of the temperature response factors is based on an analytically validated, transient two-dimensional implicit finite volume model designed for the simulation of heat transfer over a vertical U-tube ground heat exchanger. The short time-step response factors are implemented as part of a component model for TRNSYS and an example application is provided based on an actual building.

A transient two-dimensional finite volume model for the simulation of vertical U-tube ground heat exchangers

Abstract: The ability to predict both the long-term and short-term behavior of ground loop heat exchangers is critical to the design and energy analysis of ground source heat pump systems. A numerical model for the simulation of transient heat transfer in vertical ground loop heat exchangers is presented. The model is based on a two-dimensional fully implicit finite volume formulation. Numerical grids have been generated for different pipe sizes, shank spacing and borehole sizes using an automated parametric grid generation algorithm. The numerical method and grid generation techniques have been validated against an analytical model. The model has been developed with two main purposes in mind. The first application is used in a parameter estimation technique used to find the borehole thermal properties from short time scale test data. The second application is the calculation of nondimensional temperature response factors for short time scales that can be used in annual energy simulation.

Thermoelectric heat exchanger

Abstract: Disclosed is a system for thermally conditioning and pumping a fluid. The system includes a thermoelectric heat exchanger having a thermoelectric device configured to pump heat. Heat exchangers are provided for transferring heat to and from the thermoelectric device and for generating a fluid flow across the thermoelectric device. The conditioned fluid may be placed in thermal communication with a variety of objects, such as a vehicle seat, or anywhere localized heating and cooling are desired. Thermal isolation may also be provided in the direction of flow to enhance efficiency.

Ventilator system and method

Abstract: The ventilator system and method use a isolating heat exchanger to selectively transfer heat between exhaust air leaving an enclosed space and outside air entering the enclosed space. The system operates in three basic modes, under the control of a microprocessor-based controller which is responsive to the temperatures inside and outside of the enclosed space. In the heating mode, heat is transferred from the exhaust air to the outside air when the enclosed space requires heating. In the cooling mode, heat is transferred from the outside air to the exhaust air when the outside air temperature is higher than that in the enclosed space. In the supplemental cooling mode, heat transfer between the exhaust and outside air is reduced or eliminated when the outside air temperature is below the desired temperature in the enclosed space and cooling is required. In the heating mode, the heat exchanger is selectively heated when necessary to defrost it. A by-pass is provided for the introduction of outside air in order to avoid heating of the outside air by the exhaust air during the supplemental cooling mode of operation, and/or provide fresh air to the enclosed space without cooling the heat exchanger while it is being defrosted.

Door mounted heat exchanger for outdoor equipment enclosure

Abstract: A modular door mounted heat exchanger (10) for use with an outdoor equipment enclosure (12) of the type having a sealed equipment compartment (22) used to house heat generating electronics and telecommunications equipment (29) therein is disclosed. The heat exchanger includes a door panel (33) sized and shaped to be received on, and to close an access opening (20) defined as a part of the equipment enclosure. The door panel has an interior surface (34) for facing inwardly of the enclosure, and an exterior surface (36) for facing outwardly of the enclosure. A heat exchanger cover (37) constructed and arranged to be mounted to the exterior surface of the door panel is provided. The heat exchanger cover defines a plenum (38) between the exterior surface of the door panel and the heat exchanger cover. At least a first opening (40) and at least a spaced second opening (41) are defined within the plenum for defining an air flow path (44, 45) passing within and at least partially along the plenum. At least one fan (42, 48, 79) is provided for drawing air into and exhausting air out of the plenum through the at least first and second openings, respectively. The fan is constructed and arranged to draw outside air through the plenum for cooling the exterior surface of the door panel, so that the air within the enclosure that comes into contact with the interior surface of the door panel is in turn cooled.

Integrated devices and systems for performing temperature controlled reactions and analyses

Abstract: Reactor systems that include a reaction receptacle that includes a plurality of reservoirs disposed in the surface of a substrate. The reactor system also typically includes a temperature control element having at least a first heat exchanger thermally coupled to it. The heat exchanger is, in turn, disposed within the at least one of the reservoirs whereby the heat exchanger transfers heat to or from a fluid disposed within the reservoir, which heat is conducted to or from the temperature control element.

Simulation of heat exchanger performance by artificial neural networks

Abstract: The artificial neural network technique was applied to heat transfer through a series of problems of increasing complexity. For the simplest problem of one-dimensional heat conduction with linear activation function, it is possible to give physical meaning to the synaptic weights of the network. A network with sigmoid activation function was used for non-linear representation of convection problems where identification of the weights with physical variables was not possible. Two cases of convective heat transfer with one and two heat transfer coefficients and artificially generated data were examined. Finally, the method was applied to the analysis of data obtained in the laboratory for a single-row, fin-tube heat exchanger. It is shown that a better prediction with smaller scatter is obtained in comparison to a conventional power-law correlation for the heat transfer coefficients.

Influence of the adhesion force crystal/heat exchanger surface on fouling mitigation

Abstract: The accumulation of unwanted crystalline deposits (fouling) reduces the efficiency of heat exchangers considerably. In order to decrease the cost of fouling two strategies have been developed. The first fouling mitigation strategy is based on the modification of energy and geometry related characteristics of the heat transfer surface to realize an increased duration of the induction period. By means of a DSA (drop shape analysis) measurement device the interaction at the interface crystal/heat transfer surface is determined. The deployment of the fracture energy model and the interfacial defect model relates wetting characteristics to the adhesion phenomenon. Hence, a first estimation of the optimal choice of surface material is realized. Furthermore, the influence of surface topography on interfacial interactions has been analyzed. The second fouling mitigation strategy is based on the adjustment of the hydrodynamic flow conditions using a pulsation technique. Here, single strokes of higher velocity are superimposed on the stationary flow. These strokes shift the equilibrium of forces to an improved removal process. Fouling experiments have proved that pulsation is a powerful tool to mitigate the built-up of fouling layers on heat transfer surfaces.

Cooling apparatus for electronic devices

Abstract: An apparatus for cooling an electronic device that includes a fluid heat exchanger, a chiller, and a pump. The fluid heat exchanger transfers heat from a hot portion of the surface of the electronic device to a fluid and has a body through which the fluid may be circulated. The body has a protrusion having a first surface that may be thermally coupled to the hot portion such that the surface of the body is sufficiently distant from the surface of the electronic device that sufficient ambient air may circulate therebetween so as to substantially prevent condensation from forming on the surface of the electronic device and from forming on and dripping from the heat exchanger when the fluid is cooled to at least the dew point of the ambient air and circulated through the body. A heat-conducting path is provided from the first surface to a region of the body that is thermally coupled to the fluid when the fluid is circulated through the body. The chiller circulates the fluid through a chiller and the fluid heat exchanger.

Precooling system for joule-thomson probe

Abstract: A miniature refrigeration system and method of operation. A primary refrigerant is pressurized by a compressor (130) to a relatively low pressure, for safety reasons. The compressed primary refrigerant is passed through a primary-to-secondary heat exchanger (240), to precool the gas mixture. The secondary side of the primary-to-secondary heat exchanger (240) is cooled by a secondary refrigeration system. The primary refrigerant exiting the primary outlet of the primary-to-secondary heat exchanger passes to a primary Joule-Thomson expansion element (150) where the high pressure gas is expanded to a lower temperature. This low temperature gas cools a heat transfer element mounted in the outer wall of the catheter of cryoprobe, to cool surrounding tissue. Return gas can flow back through a distal primary-to-primary heat exchanger (160) to further cool the incoming high pressure gas mixture. A proximal primary-to-primary heat exchanger (140) can be added between the primary-to-secondary heat exchanger (240) and the primary compressor (130).

Fuel-cell engine stream conditioning system

Abstract: A stream conditioning system for a fuel cell gas management system or fuel cell engine. The stream conditioning system manages species potential in at least one fuel cell reactant stream. A species transfer device is located in the path of at least one reactant stream of a fuel cell's inlet or outlet, which transfer device conditions that stream to improve the efficiency of the fuel cell. The species transfer device incorporates an exchange media and a sorbent. The fuel cell gas management system can include a cathode loop with the stream conditioning system transferring latent and sensible heat from an exhaust stream to the cathode inlet stream of the fuel cell; an anode humidity retention system for maintaining the total enthalpy of the anode stream exiting the fuel cell related to the total enthalpy of the anode inlet stream; and a cooling water management system having segregated deionized water and cooling water loops interconnected by means of a brazed plate heat exchanger.

Air-Side Heat Transfer and Friction Correlations for Plain Fin-and-Tube Heat Exchangers With Staggered Tube Arrangements

Abstract: This paper deals with heat exchangers having plain fins on a staggered array of circular tubes. Correlations are developed to predict the air-side heat transfer coefficient and friction factor as a function of the Reynolds number and geometric variables of the heat exchanger such as tube diameter, tube pitch, fin spacing, etc. A multiple regression technique was used to correlate 47 sets of heat exchanger data to develop the heat transfer and friction correlation. The correlations are applicable to heat exchangers having small diameter tubes (or large tube pitch to tube diameter ratio), whose performance previous correlations failed to predict adequately. The heat transfer correlation applicable to three or more row configuration predicts 94% of the data within {+-}20%, and the heat transfer correlation applicable to one- or two-row configuration predicts 94% of the data within {+-}20%. The friction correlation predicts 90% of the data within {+-}20%.

Modular low pressure delivery vehicle air conditioning system

Abstract: A modular air conditioning system comprises a self--contained refrigeration power cell, a heat exchanger, and a low pressure refrigerant communication circuit operably coupling the refrigeration power cell to the heat exchanger. The refrigeration power cell comprises a compressor, a condenser, an expansion device, and an evaporator which are serially coupled to form a high pressure closed refrigeration circuit. The low pressure refrigerant communication circuit thermally interfaces with the condenser to remove heat from the high pressure closed refrigerant circuit. Alternatively, a first circuit thermally interfaces with the evaporator to remove heat from the low pressure refrigerant. A first heat exchanger is adapted to mount in the cabin of an over-the-road or off-road vehicle. Preferably, a second heat exchanger and a second low pressure refrigerant communication circuit is included.

Integrated fuel processor, furnace, and fuel cell system for providing heat and electrical power to a building

Abstract: An integrated system (10) includes a fuel cell assembly (40) for supplying electrical power to a building, a furnace (20) having a heating chamber (22) and a heat exchanger (24) for supplying heat to the building, and a reformer (50) for providing a supply of reformate directly to the furnace (20) and the fuel cell assembly (40). The system may include a controller (80) for apportioning the supply of reformate to the fuel cell assembly (40) and the furnace (20) in response to heating and electrical power needs of the building. In another embodiment, an integrated system (100) includes a fuel cell assembly (140) for providing electrical power to a building, a reformer/furnace unit (130) comprising a chamber (132) and a heat exchanger (134) for providing heat to a building, and wherein fuel is reformed/oxidized in a fuel-rich environment in said chamber to produce a supply of reformate for said fuel cell assembly (140), and in a fuel-lean environment in said chamber for releasing heat. The system (100) may also include a controller (180) for operating the chamber (132) between a fuel-rich and a fuel-lean environment in response to heating and electrical power needs of the building.

Temperature control of electronic devices using power following feedback

Abstract: A method for controlling a device temperature measures a parameter related to device power consumption and utilizes the parameter to control the device temperature. This can be achieved with a system including a heat exchanger, a power monitor, and a circuit which controls the temperature setting of the heat exchanger. The circuit uses as inputs the power level, heat exchanger temperature, and set point. The system thus eliminates the need for temperature sensing devices in or connected to a chip, responds to the temperature of the device and not the package, can be used for high volume chip manufacturing, does not require significant surface area of a device for temperature sensing, and eliminates the need for chip power profiles. Significantly, the system allows a set point to be maintained with minimal overshoot or undershoot.

Heat exchanger, heat pump, dehumidifier, and dehumidifying method

Abstract: A heat exchanger which is relatively small in size for an exchangeable heat quantity and high in heat exchange efficiency, comprising a first compartment (310) allowing a first fluid (A) to flow and a second compartment (320) allowing a second fluid (B) to flow, and a first fluid path (251) allowing a third fluid which exchanges heat with the first fluid (A) to flow and a second fluid path (252) allowing a third fluid which exchanges heat with the second fluid to flow, these fluid paths passing through these compartments, wherein the first flow path (251) and second flow path (252) are formed integrally with each other, the third fluid flows from the first flow path (251) through the second flow path (252), the third fluid evaporates at a specified pressure in the first flow path (251), and the third fluid condenses at approximately the specified pressure in the second fluid path (252), whereby heat can be transferred from the first compartment to the second compartment because the third fluid flows from the first fluid path through the second flow path, and heat transfer coefficient is high because heat transfer is made by evaporation or condensation.

The effect of variable viscosity on the entropy generation and pumping power in a laminar fluid flow through a duct subjected to constant heat flux

Abstract: Entropy generation and pumping power required for a laminar viscous flow in a duct subjected to constant heat flux has been investigated. The temperature dependence of the viscosity is taken into consideration. The ratio of pumping power to total heat flux decreases considerably and entropy generation increases along the duct length for viscous fluids. Therefore, it is shown that an optimum duct length may be obtained which minimizes total energy losses due to both entropy generation and pumping power. For low heat-flux conditions, entropy generation due to viscous friction becomes dominant and the dependence of viscosity on temperature must be considered in order to determine entropy generation accurately.

Integrated bleed air and engine starting system

Abstract: An integrated bleed air and engine starting system for an engine utilizes an innovative flow multiplier air turbine starter to provide bleed air supply to an ECS as well as starting an engine The technique reduces bleed air consumption by mixing fan stage air and high stage air for ECS fresh air usage It also can eliminate or reduce the size of the precooler heat exchanger The system includes an air turbine starter subsystem and an air flow subsystem The air turbine starter subsystem includes a compressor, a turbine, and a common shaft fixed between the compressor and turbine Also provided is a gear coupled to a gearbox which links the engine with a shaft, as well as a variable nozzle valve intermediate the turbine and engine The air flow subsystem comprises a diverter valve downstream of the turbine, an isolation valve intermediate the turbine and an auxiliary power unit, and a check valve downstream of the compressor and turbine A fan is in air flow communication with the compressor and engine

Numerical Investigations of Optimal Heat Conductivity in Micro Heat Exchangers

Abstract: The aim of this work is to determine the order of magnitude of the optimal heat conductivity by simulation. Furthermore, the question of whether and, if so, how operational and geometrical parameters influence the optimal heat conductivity is addressed. Finally, an assessment is made of the need for similar investigations, i.e. taking into account axial heat conductivity processes within the wall materail, for the design of conventional heat exchangers