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Heat Transfer Resistance (heat + transfer_resistance)

Distribution by Scientific Domains
Engineering83%

Selected Abstracts

Theoretical analysis on thermoelectric power generation with rectangular-fin elements and its applicability in micro systems

HEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 3 2006
Yutaka Oda
Abstract A thermoelectric module, which consists of rectangular-fin elements and has a simple structure suitable for micro fabrication, was newly proposed for a micro- to milli-scale thermoelectric power generator. A unit model was introduced to examine the basic characteristics of thermoelectric power generation with rectangular-fin elements. Theoretical descriptions of the power density and conversion efficiency were given by solving one-dimensional heat and current flows inside the elements. Then, it was found that there exist optimum aspect ratios of the elements to achieve maximum power density and conversion efficiency. Power density becomes larger if the module is downsized with a similarity in shape, while conversion efficiency remains constant, i.e., smaller devices show better performance. Finally, comparative analysis with a standard pi-type module was conducted to emphasize the superiority of the proposed module in micro systems, when convective heat transfer resistance is taken into account. © 2006 Wiley Periodicals, Inc. Heat Trans Asian Res, 35(3): 224,244, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20108 [source]

Studies on pyrolysis of vegetable market wastes in presence of heat transfer resistance and deactivation

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 9 2005
Ruby Ray
Abstract In the present investigation, the pyrolysis of predried vegetable market waste (dp=5.03 mm) has been studied using a cylindrical pyrolyser having diameter of 250 mm under both isothermal and non-isothermal conditions within the temperature range of 523,923 K with an intention to investigate the effective contribution of different heat transfer controlling regime namely intra-particle, external along with kinetically control regime on the overall global rate of pyrolysis. Thermogravimetric method of analysis was utilized to obtain experimental data for both isothermal and non-isothermal cases by coupling a digital balance with the pyrolyser. The pyrolysis of vegetable market waste has been observed to exhibit deactivated concentration independent pyrolysis kinetics, analogous to catalytic poisoning, throughout the entire range of study. The deactivation is of 1st order up to 723 K and follows the 3rd order in the temperature range of 723heat transfer resistance. While studying the pyrolysis process under non-isothermal conditions, a segregated ramp function of furnace temperature rise has been used. The transient profiles of the reactant and products have been simulated following the similar procedure followed under isothermal conditions. When experimental data and simulated values are compared, it is observed that unlike the case of isothermal condition, the global pyrolysis rate is controlled by intra-particle heat transfer resistance. Copyright © 2005 John Wiley & Sons, Ltd. [source]

An advanced model to assess fouling and slagging in coal fired boilers

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 14 2002
Minghou Xu
Abstract The assessment of the influence of fouling and slagging on the heat transfer in utility boilers has obtained significant interest both during boiler design and operation. This paper presents a strategy to investigate this influence by introducing heat resistance to represent fouling and slagging on furnace walls. The evaluation of this strategy was performed using the plant heat flux reading data together with a 3-D computational fluid dynamics code. The model considers the influence of the operating conditions to the incident heat fluxes and these are used to assess the heat transfer resistance from the measured absorbed heat fluxes. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Modell und Programm CLIMT zur einfachen Ermittlung der Raumlufttemperatur und Raumluftfeuchte bei freier Klimatisierung

BAUPHYSIK, Issue 3 2010
Peter Häupl Prof. Dr.-Ing. habil. i. R., bis 30.
Berechnungsverfahren; Feuchte; Wärme Abstract In der Planungspraxis besteht Bedarf nach einem vergleichsweise (siehe TRNSYS, ENERGY PLUS) einfachen und zuverlässigen Handwerkszeug zur Quantifizierung des Raumklimas. In diesem Beitrag wird ein praktikables Modell zur Ermittlung der Stundenwerte für die Raumlufttemperatur, die Empfindungstemperatur (Mitteltemperatur aus Raumluft- und Umschließungsflächentemperatur) und die Raumluftfeuchte in Abhängigkeit vom Außenklima (Außenlufttemperatur, Wärmestrahlung und relative Luftfeuchtigkeit der Außenluft), von den Gebäudeparametern (Geometrie, Wärmetransportwiderstände der Hüllkonstruktion, Wärme- und Feuchteabsorptionsvermögen der Bauteile), von der Lüftung und der Raumnutzung (innere Wärmequellen, innere Feuchtequellen und raumluftregulierte Heizung) bei freier Klimatisierung vorgestellt. Die Ergebnisse bilden den Quelltext für das nutzerfreundliche Windows-Programm CLIMT (CLimate-Indoor-Moisture-Temperature). Modell und Programm CLIMT werden durch einen Vergleich mit Rechenwerten nach TRNSYS und Messwerten in einem Testhaus validiert. Die Ergebnisse stimmen sehr gut überein. Das Programm CLIMT ist anwenderfreundlich und praxistauglich. Model and program CLIMT for a simplified determination of room temperature and relative humidity under arbitrary climate conditions. In planning practice there is a need for a comparably simple (cf. TRNSYS, ENERGY PLUS), reliable tool for quantifying an indoor climate. In this article a practicable model is put forward for determining the hourly values for natural conditioning of indoor air temperature, the perceived temperature (average of air and enclosing surface temperatures) and the interior air humidity in relation to the external climate (external air temperature, radiant heat and relative humidity of the outside air), the building parameters (geometry, heat transfer resistance of the shell structure, heat and moisture absorption properties of the components), the ventilation and the use of the space (interior heat sources, interior moisture sources and interior air-regulated heating). The results form the source text for the user-friendly Windows program CLIMT (CLimate-Indoor-Moisture-Temperature). The CLIMT model and program are validated in a test house by comparing values calculated using TRNSYS with measured values. The results agree very well. The CLIMT program is user-friendly and practically-oriented. [source]

Vapor Condensation Heat Transfer in a Thermoplate Heat Exchanger

CHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 7 2007
J. Mitrovic
Abstract The heat transfer and pressure drop in a thermoplate heat exchanger operating as a condenser have been investigated experimentally. In order to separate the heat transfer resistances in the condensation process, the single phase forced convection has been studied using distilled water and Marlotherm oil in the thermoplate and correlations developed for the Nusselt number and the friction factor. For the condensation experiments, an apparatus has been constructed comprising two identical condensers composed of the same thermoplate type as employed in the single phase experiments. Isopropanol is used as a test fluid at pressures below atmospheric pressure. The heat transfer resistances in the condensation experiments are separated and expressions for the condensation heat transfer and pressure drop are developed with the aid of the results obtained in the single phase studies. [source]