Showing papers on "Heat exchanger published in 2004"

Review of passive heat transfer augmentation techniques

Abstract: Heat transfer augmentation techniques (passive, active or a combination of passive and active methods) are commonly used in areas such as process industries, heating and cooling in evaporators, thermal power plants, air-conditioning equipment, refrigerators, radiators for space vehicles, automobiles, etc Passive techniques, where inserts are used in the flow passage to augment the heat transfer rate, are advantageous compared with active techniques, because the insert manufacturing process is simple and these techniques can be easily employed in an existing heat exchanger In design of compact heat exchangers, passive techniques of heat transfer augmentation can play an important role if a proper passive insert configuration can be selected according to the heat exchanger working condition (both flow and heat transfer conditions) In the past decade, several studies on the passive techniques of heat transfer augmentation have been reported The present paper is a review on progress with the passi

Fuel-Cooled Thermal Management for Advanced Aeroengines

Abstract: Fuel-cooled thermal management, including endothermic cracking and reforming of hydrocarbon fuels, is an enabling technology for advanced aero engines and offers potential for cycle improvements and pollutant emissions control in gas turbine engine applications. The successful implementation of this technology is, however, predicated on the use of conventional multicomponent hydrocarbon fuels and an understanding of the combustion characteristics of the reformed fuel mixture. The objective of this research is to develop and demonstrate the technologies necessary for utilizing conventional multicomponent hydrocarbon fuels for fuel-cooled thermal management, including the development of the endothermic potential of JP-7 and JP-8 +100, a demonstration of the combustion of supercritical/endothermic fuel mixtures, and conceptual design of a fuel-air heat exchanger. The ability to achieve high heat sinks with existing jet fuels (e.g., JP-7 and JP-8 +100) was demonstrated with a bench-scale test rig operating under flow conditions and passage geometries simulative of practical heat exchangers for aircraft and missile applications. Key measurements included fuel heat sink, reaction products, and extent of conversion: Full-scale sector rig tests were conducted to characterize the combustion and emissions of supercritical jet fuel, and demonstrate the safety and operability of the fuel system, including a fuel-air heat exchanger.

Air-cooled heat exchangers and cooling towers : thermal-flow performance evaluation and design

Abstract: During the last 30 years I have been involved in the theory and practice of thermal engineering and in particular, in the areas of air-cooled heat exchangers and cooling towers for the power, refrigeration, process and petrochemical industries in South Africa and internationally. During this period, I have authored and co-authored more than 120 papers that were published in technical journals or presented at conferences nationally or internationally. Most of these papers are included in a manuscript entitled "Air-cooled Heat Exchangers and Cooling Towers", in which Ipresent a systematic approach to the thermal performance evaluation and design of industrial air-cooled heat exchangers and cooling towers. This original publication also includes the relevant practice applicable to the design of cooling systems, based on my experience as a consultant to industry. Design offices throughout the world presently follow our design methods, or at least employ many of our research results. Our work has furthermore contributed to the development of improved cooling system designs (e.g. new dephlegmator header designs), components (e.g. single-row flattened finned tubes) and product improvement and quality control (e.g. performance testing and measurement of thermal contact resistance between fin and tube during production). Many of our research findings have found application in the modification of existing cooling systems. The manuscript has also been used as reference work during the presentation of short courses to practising engineers and consultants in industry and to engineering graduates at the University of Stellenbosch. A two-volume edition of this manuscript was published by PennWell Corp., Tulsa, Oklahoma, USA in 2004. Stellenbosch University http://scholar.sun.ac.za

Thermal management systems and methods

Abstract: A thermal management system for a vehicle includes a heat exchanger having a thermal energy storage material provided therein, a first coolant loop thermally coupled to an electrochemical storage device located within the first coolant loop and to the heat exchanger, and a second coolant loop thermally coupled to the heat exchanger. The first and second coolant loops are configured to carry distinct thermal energy transfer media. The thermal management system also includes an interface configured to facilitate transfer of heat generated by an internal combustion engine to the heat exchanger via the second coolant loop in order to selectively deliver the heat to the electrochemical storage device. Thermal management methods are also provided.

Liquid cooling system

Abstract: Liquid cooling systems and apparatus are presented. A number of embodiments are presented. In each embodiment a heat transfer system (106) capable of engaging a processor (104) and adapted to transfer heat from the processor is implemented. A variety of embodiments of the heat transfer system (106, 304, 420, 502, 600, 1300) are presented. For example, several embodiments of a direct-exposure heat transfer system (700, 800, 1000) are presented. In addition, several embodiments of a multi-processor heat transfer systems (900, 110, 1200) are presented. Lastly, several embodiments of heat transfer systems (1400, 1500) deployed in circuit boards are shown. Each of the heat transfer systems is in liquid communication with a heat exchange system that receives heated liquid (124) from the heat transfer system and returns cooled liquid (128) to the heat transfer system.

Modeling wood gasification in a countercurrent fixed‐bed reactor

Abstract: A one-dimensional, unsteady mathematical model is presented of fixed-bed countercurrent wood gasifiers, which couples heat and mass transport with wood drying and devolatilization, char gasification, and combustion of both char and gas-phase species. The model is used to simulate the structure of the reaction fronts and the gasification behavior of a laboratory-scale plant as the reactor throughput and the air-to-wood (or char) weight ratio are varied. It is observed that a wide zone, acting essentially as a countercurrent heat exchanger, separates combustion/gasification from devolatilization/ drying. Moreover, the former zone presents interesting dynamic patterns driven by the highly variable solid/gas heat transfer rates. For a constant air-to-wood weight ratio, the gasification process is improved by increasing the reactor throughput as a result of higher temperatures, in spite of the simultaneous reduction in the amount of char generated from wood devolatilization. In fact, an increase in the air-to-wood (or char) ratio always lowers the efficiency of the gasification process. Finally, good agreement is obtained between predictions and experiments for the axial temperature profiles and the composition of the producer gas. © 2004 American Institute of Chemical Engineers AIChE J, 50: 2306 –2319, 2004

Mitigation of Crude Oil Refinery Heat Exchanger Fouling Through Retrofits Based on Thermo-Hydraulic Fouling Models

Abstract: Crude oil fouling in refinery preheat exchangers is a chronic operating problem that compromises energy recovery in these systems. Progress is hindered by the lack of quantitative knowledge of the dynamic effects of fouling on exchanger heat transfer and pressure drop. The concept of a thermal ‘fouling threshold’, first introduced by Ebert and Panchal, is revisited here alongside models of hydraulic effects of fouling to provide a graphical tool, the modified temperature field plot, for assessing chronic chemical reaction fouling effects in refinery heat exchangers. Fouling data of varying quality, collected from pilot plant and refinery operation, were compared with two previously published threshold fouling models and one based on the Epstein deposition model. The model by Epstein showed the best agreement, primarily because it can accommodate fouling that is mass transfer as well as reaction controlled. The hydraulic analysis indicated that the simple slab approximation for fouling layers gave a reasonably good mapping between heat transfer and pressure drop effects as long as roughness contributions are not significant. Where roughness effects (or tube blockage) are important, the relationship between thermal and hydraulic performance is not straightforward. A case study, based on the network described by Panchal and Huang-Fu, is used to illustrate the thermo-hydraulic effects of fouling and the application of the modified temperature field plot.

Entropy Generation Extrema and Their Relationship With Heat Exchanger Effectiveness—Number of Transfer Unit Behavior for Complex Flow Arrangements

Abstract: While the concept of minimum irreversibility is associated with the maximum energy efficiency for energy conversion processes in thermal systems, we have found that it is not quite applicable to the heat exchanger analysis. The heat exchanger effectiveness can be maximum, having an intermediate value or minimum at the maximum irreversibility operating point depending on the flow arrangement of the two fluids. Similarly, the heat exchanger effectiveness can be minimum or maximum at the minimum irreversibility operating point. Our objective is to illustrate and discuss such heat exchanger performance and irreversibility trends by combining the temperature difference irreversibility with the P-NTU results for complex flow arrangements