Transient heat and mass transfer in laminar flow forced convection in ducts

The modelling of heat and mass regenerators often assumes the heat and mass transfer coefficients to be uniform and constant with time and position within the flow passages of the regenerator. This paper presents a study to examine the validity of this assumption. Experimental breakthrough curves of a single-blow test facility with a desiccant regenerator matrix are examined using a separation technique. The response curves are input to a model which computes the temporal and spatial distributions of the air-side heat and mass transfer coefficients. It is found that the variation of the Nusselt and Sherwood numbers is small for the slower mass transfer waves which determines the performance of regenerative dehumidifiers. The separation technique proves to be a powerful procedure for analysing experimental breakthrough curves.status: publishe

The nonlinear increase of nusselt number with friction factor in fully developed laminar duct flow

This paper deals with heat transfer in fully developed laminar flow in cylindrical ducts. For this type of flow, the product of friction factor with Reynolds number f Re and the Nusselt number are both constants. It is known that the Nusselt number increases with the shift of boundary condition from constant wall temperature to constant heat flux. Also, the ratio of the Nusselt number to f Re increases when the convexity of the duct is reduced, e.g.,a cylinder visavis parallel plates. This paper gives a simple physical explanation for these two phenomenona.status: publishe

Analyis of Eco-Driving Using Polynomial Fuel Consumption Models

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Minimum-fuel control of combustion engine powertrains

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Flow structure of lifted swirling jet flames

Swirling combustion is widely applied in various applications such as gas turbines, utility boilersor waste incinerators. This article contributes to the ongoing research by providing experimentaldata that are gathered in the mixing zone of a lifted swirling premixed natural gas flame. Theobjective of this paper is fivefold: (1) to introduce the lifted swirling flame featuring lowNO x emissions (2) to provide experimental data such as major species distributions, temperature and streamlines of the flow pattern, (3) to report on velocity bias in probability density function (PDF) distributions and to present PDF sequences of velocities in medium scale swirling flows, (4) to make an assessment on the local small-scale turbulence that is present in the swirling mixinglayer and (5) to provide new experimental data for model verification and development. The PDFs are corrected in order to compensate for the velocity bias phenomenon, which is typicalfor randomly sampled LDA data. Sequences of axial PDF data are presented and measurement locationsof interest are selected to look at the PDF characteristics of the internal and externalrecirculation zones, the mixing layer and the onset of the reacting flow into detail. The mixinglayer PDFs covered a wide velocity range and revealed bimodality; even the concept ofmulti-modality is suggested and explored. Analysis showed that a sum of two Gaussian distributionscan accurately envelop the experimental PDFs. The reason for this broadband turbulence behavior isto be found in combination of precessing and flapping motion of the flow structures, and also incombustion generated instabilities of the lifted flame. As a result, the flame brush is wide (largescale motion) and the mixing (small-scale turbulence) flattens any high temperatures in thecombustion process. The multi-scale turbulence concept is subsequently used to make anassessment of the local turbulence characteristics in the mixing layer.The idea is that the PDFs capture both contributions of the flow-inherent fine grain turbulence (u′ l ) which is superposed on slowlarge scale fluctuating structures. It is this u′ l that will be of interest in continued research on the classification of the lifted flame into acombustion regime diagram (e.g. Borghi diagram). Finally, the bimodalitycharacter in reacting flows and the prediction of large-scale structuresmay be a challenge for LES researchers.status: publishe

Optimization of overfire air systems of cylindrical combustion chambers

The optimization of overfire air injection in cylindrical combustion systems with respect to the combustion performance is studied. Relevant integral performance parameters regarding residence time and overall mixing are discussed. Finally, different design concepts are screened and the influence of some geometrical parameters is investigated. The results are translated in terms of a maximum penetration length. The findings show good agreement with experiments carried out before.status: publishe

Review of disposal technologies for chromated copper arsenate (CCA) treated wood waste, with detailed analyses of thermochemical conversion processes

Several alternative methods for the disposal of chromated copper arsenate (CCA) treated wood waste have been studied in the literature, and these methods are reviewed and compared in this paper. Alternative disposal methods include: recycling and recovery, chemical extraction, bioremediation, electrodialytic remediation and thermal destruction. Thermochemical conversion processes are evaluated in detail based on experiments with model compounds as well as experimental and modelling work with CCA treated wood. The latter category includes: determination of the percentage of arsenic volatilised during thermal conversion of CCA treated wood, identification of the mechanisms responsible for arsenic release, modelling of high temperature equilibrium chemistry involved when CCA treated wood is burned, overview of options available for arsenic capture, characterisation of ash resulting from (co-)combustion of CCA treated wood, concerns about polychlorinated dibenzo-p-dioxins/furans (PCDD/F) formation. Finally, the most appropriate thermochemical disposal technology is identified on short term (co-incineration) and on long term (low-temperature pyrolysis or high-temperature gasification.status: publishe