Showing papers on "Heat capacity rate published in 2003"

Method and apparatus for achieving temperature uniformity and hot spot cooling in a heat producing device

Abstract: A method of controlling temperature of a heat source in contact with a heat exchanging surface of a heat exchanger, wherein the heat exchanging surface is substantially aligned along a plane. The method comprises channeling a first temperature fluid to the heat exchanging surface, wherein the first temperature fluid undergoes thermal exchange with the heat source along the heat exchanging surface. The method comprises channeling a second temperature fluid from the heat exchange surface, wherein fluid is channeled to minimize temperature differences along the heat source. The temperature differences are minimized by optimizing and controlling the fluidic and thermal resistances in the heat exchanger. The resistances to the fluid are influenced by size, volume and surface area of heat transferring features, multiple pumps, fixed and variable valves and flow impedance elements in the fluid path, pressure and flow rate control of the fluid, and other factors.

Heat transfer system

Abstract: A thermodynamic system includes a cyclical heat exchange system and a heat transfer system coupled to the cyclical heat exchange system to cool a portion of the cyclical heat exchange system. The heat transfer system includes an evaporator including a wall configured to be coupled to a portion of the cyclical heat exchange system and a primary wick coupled to the wall and a condenser coupled to the evaporator to form a closed loop that houses a working fluid.

Exact solution for cooling of electronics using constructal theory

Abstract: This article deals with the constructal-theory based solution for conductive cooling of electronics. The problem falls in the category of a more general “area to point” flow problem. Heat generated in a fixed area is to be discharged to a heat sink located on the border of the heat generating area through relatively high conductive link(s). This will maintain a limited temperature difference between the hot spot inside the heat generating area and the heat sink. Constructal-theory based solution in this article is supported by and matched with an analytical and exact heat transfer analysis of the physical problem. The solution procedure starts with heat transfer analysis and geometric optimization of the smallest heat generating area. The assembly of optimized smallest areas in a fixed but larger heat generating area by introducing a high conductive link and geometric optimization of the area leads to achieve the goal of conductive cooling of a larger area. Sequence of assembly of optimized areas in a relatively larger area and geometric optimization of this area is continued until the required area size to be cooled is obtained. The process of assembly and optimization steps leads to the formation of a tree-network of high conductive links inside the heat generating area. Along with geometric optimization of a heat generating area in each step, the tree-network of high conductive links is optimized with respect to high conductive material allocation in the heat generating area as well.

System with an internal combustion engine, a fuel cell and a climate control unit for heating and/or cooling the interior of a motor vehicle and process for the operation thereof

Abstract: A system with an internal combustion engine which has a heat transfer circuit, a fuel cell and a climate control unit which is accommodated in the heat transfer circuit of the internal combustion engine. The system has a heat transfer arrangement for transferring the exhaust heat of the fuel cell to the heat transfer circuit and a bypass for bridging a segment of the heat transfer circuit which runs through the internal combustion engine so that, in the bypassed operating state, an isolated circuit is formed. In stationary operation, this enables an optimized operating mode since the internal combustion engine is no longer heated and the exhaust heat of the fuel cell is fully available for heating purposes. The climate control unit can have a fuel cell and an arrangement for transferring the heat produced by the fuel cell to the vehicle interior has a fan unit by which an air flow can be produced for cooling the fuel cell and a heating unit which is powered by the fuel cell and by which the air flow for heating the vehicle interior can be additionally heated. For cooling or heating the interior of a motor vehicle, the system can have a cooling circuit with a compressor, a condenser, an expansion element, and a first evaporator and an APU or a fuel cell to electrically power the compressor, and a second cooling circuit a second evaporator, the second cooling circuit being connected to the first cooling circuit.

Advanced heat recovery and energy conversion systems for power generation and pollution emissions reduction, and methods of using same

Abstract: Disclosed herein are various systems and methods for producing mechanical power from a heat source. In various illustrative examples, the system may include a heat recovery heat exchanger, a turbine, an economizer heat exchanger, a condenser heat exchanger, and a liquid circulating pump, etc. In other embodiments, a desuperheater may be employed. In one illustrative embodiment, the system comprises a first heat exchanger adapted to receive a fluid from a heat source and a working fluid, wherein, when the working fluid is passed through the first heat exchanger, the working fluid is converted to a vapor via heat transfer with the fluid from the heat source, at least one turbine adapted to receive the vapor, and an economizer heat exchanger adapted to receive exhaust vapor from the turbine and the working fluid, wherein a temperature of the working fluid is adapted to be increased via heat transfer with the exhaust vapor from the turbine prior to the introduction of the working fluid into the first heat exchanger. The system further comprises a condenser heat exchanger that is adapted to receive the exhaust vapor from the turbine after the exhaust vapor has passed through the economizer heat exchanger and a cooling fluid, wherein a temperature of the exhaust vapor is reduced via heat transfer with the cooling fluid, and a pump that is adapted to circulate the working fluid to the economizer heat exchanger.

Fan supplied heat exchanger fin performance under frosting conditions

Abstract: In this paper, a validated numerical model for frost growth on heat exchange fins is modified to simulate a fan-supplied finned heat exchanger under refrigeration frosting conditions. It is found that frost growth on refrigeration heat exchangers causes a dramatic drop in the fin heat rate, airflow rate, and fin efficiency while the pressure drop increases. A sensitivity study shows the effects of changing several design parameters including the type of fan.

Fluid circuit heat transfer device for plural heat sources

Abstract: A heat sink or heat transfer device particularly for integrated circuits, uses a phase change working fluid in a cyclic flow path having at least one evaporator that serves multiple heat sources. The evaporator can be an integral vessel made of thermally conductive material to which the multiple heat sources are coupled, preferably at evaporation points that are placed on opposite sides of a fluid reservoir for the liquid phase of the working fluid that feeds the evaporation points via capillary flow through a picking material.

Auxiliary cooling device

Abstract: An auxiliary cooling device is used in another main cooling device, such as a refrigerator. The auxiliary cooling device includes a thermoelectric element, such as a Peltier element, which includes a heat source and a heat sink. The heat sink is used to directly or indirectly cool an item, such as a bottle of liquid. The heat source, which is insulated from the heat sink, is in close thermal contact with a heat exchange fluid in a container. The heat exchange fluid is used as a thermal buffer for the waste heat generated by the cooling process. That waste heat may be transmitted into the main storage chamber of the main cooling device.

Transient Analysis of Flat Heat Pipes

Abstract: A stable numerical procedure is developed to analyze the transient performance of flat heat pipes for large input heat fluxes and high wick conductivity. Computation of flow and heat transfer in a heat pipe is complicated by the strong coupling among the velocity, pressure and temperature fields with phase change at the interface between the vapor and wick. A structured collocated finite volume scheme is used in conjunction with the SIMPLE algorithm to solve the continuity, energy and momentum equations. In addition, system pressurization is computed using overall mass balance. The stability of the standard sequential procedure is improved by accounting for the coupling between the evaporator/condenser mass flow rate and the interface temperature and pressure as well as the system pressure. The improved numerical scheme is applied to a flat two-dimensional heat pipe and shown to perform well. Parametric studies are performed by varying the vapor core thickness of the heat pipe and the heat input at the evaporator. The model predictions are validated by comparing the heat pipe wall temperatures against experimental values.Copyright © 2003 by ASME

Choosing Working Fluid for Two-Phase Thermosyphon Systems for Cooling of Electronics

Abstract: The heat fluxes from electronic components are steadily increasing and have now, in some applications, reached levels where air-cooling is no longer sufficient. One alternative solution, which has ...

Convective Drying with Time-Varying Heat Input: Simulation Results

Abstract: Intermittent drying aims to match the heat input rate to the drying kinetics of the material so as to avoid thermal degradation of heat-sensitive products in particular. This paper presents results of a liquid diffusion model to examine the effect of varying the rates of heat input by convection heat transfer. This is accomplished by varying the drying air velocity, varying the air temperature as well as its relative humidity over different periods of time in a sequential manner. One of the outcomes of this work is guidelines for use of a heat pump to dehumidify the drying air. While most heat pump dryers are designed to operate continuously, our results show that it is not necessary to use heat pump continuously over the entire drying period. This option saves running costs by reducing use of electrical power in the drying cycle. Furthermore, it is possible to save capital costs by utilizing a smaller heat pump for a given dry product output. Alternatively, a given heat pump system can be used t...

Ecological Optimization and Parametric Study of an Irreversible Regenerative Modified Brayton Cycle with Isothermal Heat Addition

Abstract: An ecological optimizationalong with detailed parametric study of ana irreversible regenerative Brayton heat engine with isothermal heat addition have been carried out with external as well as internal irreversibilities. The ecological function is defined as the power output minus the power loss (irreversibility) which is ambient temperature times the entropy generation rate. The external irreversibility is due to finite temperature difference between the heat engine and the external reservoirs while the internal irreversibilities are due to nonisentropic compression and expansion processes in the compressor and the turbine respectively and the regenerative heat loss. The ecological function is found to be an increasing function of the isothermal-, sink- and regenerative-side effectiveness, isothermal-side inlet temperature, component efficiencies and sink-side temperature while it is found to be a decreasing function of the isobaric-side temperature and effectiveness and the working fluid heat capacitance rate. The effects of the isobaric-side effectiveness are found to be more thanthose of the other parameters and the effects of turbine efficiency are found to be more than those of the compressor efficiency on all the performance parameters of the cycle.

Heat transfer in a MEMS for microfluidics

Abstract: Paper presents an 1D model for the heat transfer in a limited but significant region of an actuator?sensor structure for the determination of fluid and flow characteristics. As an essential step for the design of this structure, the usefulness of the model in the framework of the structure?s functionality is underlined. In the first part of the work, the main heat transfer mechanisms are detailed by qualitative and quantitative evaluations. The 1D model is derived from the heat rate balance of the region we are interested in. In the second part of the work, we compare the data obtained by simulating the 1D model with the experimental data. Also, some full 3D simulations of the fluid flow and heat transfer are made using a commercial software package. Part of these numerical results are compared with the corresponding experimental data. The modeling errors are discussed for both sets of comparisons. Finally, we comment the merits of the 1D model versus the 3D approach. The results obtained herein might be directly used for various thermally based actuators and sensors for flow control and measurement both in micro and macro world.

Method for detecting changes in a first flux of a heat or cold transport medium in a refrigeration system

Abstract: The invention concerns a method for detecting changes in a first flux of a heat or cold transport medium in a refrigeration system whereby the first flux is conveyed through a heat exchanger wherein occurs heat transfer form the first flux to a second flux of a coolant medium transporting heat or cold. The inventive method aims at enabling the fastest possible detection of said changes. Therefor, it consists in monitoring the first flux flowing through the heat exchanger by detecting the change in heat content of the second flux of the medium or a value derived therefrom.

Convective coolant heat transfer in internal combustion engines

Abstract: Simple heat transfer correlations are known to underpredict the single-phase convective heat transfer coefficient when applied to internal combustion (IC) engine cooling passages. The reasons for such underprediction were investigated using a specially designed test rig which was operated under a wide variety of test conditions relevant to IC engine operation. Data from this rig study identified that undeveloped flow (fluid dynamically and thermally), surface roughness and fluid viscosity variation with temperature were the physical reasons responsible for the mismatch. Simple empirical heat transfer models have subsequently been extended to take account of these factors and are shown to give much improved correlation with rig data, and data from an engine study. The implications of this work for predicting engine heat transfer in a three-dimensional computational fluid dynamics environment are discussed.

Method for detecting changes in a first media flow of a heat or cooling medium in a refrigeration system

Abstract: The invention concerns a method for detecting changes in a first flow of a heating or cooling medium in a refrigeration system whereby the first flow is conveyed through a heat exchanger wherein occurs heat transfer from the first flow to a second flow of a heating or cooling medium. The earliest possible detection of the changes is desired. For this it is provided that for the supervision of the first media flow moving through the heat exchanger a change in the enthalpy of the second media stream or a value derived therefrom is determined.

Optimization of a phase change heat sink for extreme environments

Abstract: Results of numerical optimization are reported for a phase change heat sink used to cool electronic equipment in extreme environments. The heat sink consists of a conventional, extruded aluminum sink embedded in a block of phase change material. This type of heat sink is used in infrared cameras carried by fire fighters into burning buildings. Optimization of the geometry of the heat sink assembly involves determination of the fin length, the fin thickness, and the base thickness that maximizes the time time before the base of the heat sink reaches a critical temperature. The numerical model is briefly described, and representative results of the simulation are presented. The optimum design for a given combination of heat load, conductance to ambient, and phase change material is discussed. The model can easily be applied to other geometries, heat loads, and material properties.