Premature dryout due to flow oscillation is a very important factor in designing boiling systems. The flow oscillation depends, in general, on system size and/or configuration, and therefore the relationship between t...
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Premature dryout due to flow oscillation is a very important factor in designing boiling systems. The flow oscillation depends, in general, on system size and/or configuration, and therefore the relationship between the premature dryout and the flow oscillation has not been fully understood so far. In this investigation, a CHF experiment in a forced flow boiling channel under the oscillatory flow condition has been conducted. Numerical simulation has also been conducted based on the lumped-parameter model of the boiling channel. The simulation well represents the transient behavior of the dryout under the oscillatory flow condition.
The dynamics of a lumped-parameter model for describing the behavior of airborne dust in animal housing are used in the development of controllers for an airborne dust control system. Proportional (P) and Proportional...
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The dynamics of a lumped-parameter model for describing the behavior of airborne dust in animal housing are used in the development of controllers for an airborne dust control system. Proportional (P) and Proportional-integral (PI) feedback controllers designed from the viewpoint of modern state-variable control theory are used as an airborne dust control system in ventilated animal housing. Linear quadratic regulators (LQRs) with output feedback control of a linear-invariant system are chosen for this study. The *** represented by a linear dynamic equation that describes the dynamic behavior of airborne dusts undergoing turbulent diffusive deposition and gravitational settling in a ventilated airspace. To illustrate this procedure, the design was applied to control the dust concentration in typical animal housing.
The present work considers a theoretical analysis of the heat transfer augmentation of in-tube flows due to the addition of an array of fins at the outer surface of the tube. The fins having annular shape and constant...
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The present work considers a theoretical analysis of the heat transfer augmentation of in-tube flows due to the addition of an array of fins at the outer surface of the tube. The fins having annular shape and constant thickness are uniformly spaced in the heat-exchange region. The aim of the article is to examine the thermal response of various spatial-weighted mean values of the axially varying external convective coefficient within the framework of statistical analysis. It was found that the arithmetic spatial mean and the geometrical spatial mean of the external convective coefficient provide accurate estimates of the upper and lower bounds, respectively, for the exact heat transfer rates. This finding, in conjunction with the use of an approximate lumped-parameter model for the energy conservation equation, permits a simplistic algebraic evaluation of the thermal performance of this kind of externally finned tube with different geometrical and thermal arrangements. A complete set of results is presented in graphical form and can be used for optimization of cooling processes.
Mathematical analysis of a model for describing the dynamic behavior of airborne dust undergoing turbulent diffusive and gravitational deposition in any location of a ventilated airspace is presented from the standpoi...
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Mathematical analysis of a model for describing the dynamic behavior of airborne dust undergoing turbulent diffusive and gravitational deposition in any location of a ventilated airspace is presented from the standpoint of a lumped-parameter approximation. The governing equation can be represented by a first-order vector-matrix differential equation. The key point of the model structure is the transport matrix [B] in terms of transport mechanisms of airborne dust. A matrix [D] is the product of the inverse matrix of [B] and the inverse diagonal matrix of lump volumes. This product can be used to evaluate the local transport phenomena of airborne dust. From the physical and mathematical properties of the model the overall mixing factor of the ventilation system can be estimated. The model is capable of predicting the air exchange rate required to maintain acceptable levels of airborne dust based on dust production rates. An analysis of the stability properties of the system equation is presented. The practical use of the model is also illustrated.
A lumped, in time and space, model of stream-aquifer interactions is developed. The model is based upon mass balance and ancillary phenomenological equations that can evaluate changes in streamflow and groundwater qua...
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A lumped, in time and space, model of stream-aquifer interactions is developed. The model is based upon mass balance and ancillary phenomenological equations that can evaluate changes in streamflow and groundwater quantity and quality. The model is applied to the Santa Margarita River, San Diego County, California to assess the impacts of proposed discharges of reclaimed wastewater on streamflows and underlying groundwaters. The model is relatively simple and economical to apply, thus minimizing analysis costs.
A lumped-parameter model was used for stimulating the dynamics of an irrigation canal using the concepts of optimal control theory. Using the state-space approach presented by Corriga , the problem was formulated as a...
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A lumped-parameter model was used for stimulating the dynamics of an irrigation canal using the concepts of optimal control theory. Using the state-space approach presented by Corriga , the problem was formulated as a discrete optimal control problem, and the solutions for gate opening in the presence of known variations in water withdrawal rates were obtained by solving the algebraic Riccati equation. An example problem was considered, and the variations in the depth of flow obtained by using the optimal control theory were compared with the results obtained from an unsteady open-channel flow model. For small and slow changes in the flow rates, the difference between the two models in predicting the changes in water surface elevation was not significant. However, as the variations in withdrawal rates increased, the accuracy of the optimal control model (which is based upon small perturbations around the uniform flow) in predicting the water surface elevations decreased.
A simple lumped-parameter model for the frequency-dependent transmission line is presented in this paper. The transients due to sequential energisation of a 345 kV transmission system have been computed with the propo...
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A simple lumped-parameter model for the frequency-dependent transmission line is presented in this paper. The transients due to sequential energisation of a 345 kV transmission system have been computed with the proposed line model. The computed results show satisfactory agreement with field measurements.
The paper examines the problem of controlling domestic electric stored-energy heating systems and describes the development of a self-tuning control scheme which can adjust the off-peak charging of the store to minimi...
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The paper examines the problem of controlling domestic electric stored-energy heating systems and describes the development of a self-tuning control scheme which can adjust the off-peak charging of the store to minimise electrical energy consumption. The charging time is controlled by a store temperature-regulator which is designed by application of the well known self-tuning minimum-variance control technique. The regulator uses a statistical estimator, based on a lumped-parameter model of the thermal behaviour of the building and heating system, to predict the next day's heating energy demand before the start of the off-peak charging period. The control scheme assumes no prior knowledge of the thermal characteristics of the building or heating plant and is suitable for low-cost microprocessor implementation. The long-term performance of the self-tuning charge controller is assessed by digital simulation of a building heated by one of two widely different types of commercial storage heating systems (a fan-assisted block storage heater and a water-storage central heating system). Results are presented which show that the control scheme behaves well and achieves substantial energy savings without the need for manual commissioning. Modification of the basic self-tuning control scheme to compensate for the peculiarities observed in the operation of high-leakage or low-capacity stores is also investigated.
A theoretical study is made on stochastic fluctuations in power reactors. The theory is demonstrated by treating a specific but widely existing example of liquid-cooled and -moderated reactor operated with either natu...
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A theoretical study is made on stochastic fluctuations in power reactors. The theory is demonstrated by treating a specific but widely existing example of liquid-cooled and -moderated reactor operated with either natural convection or forced circulation. Attention is first directed to the thermodynamical analysis of the elementary transport processes of the energy released by fissions through the fuel and coolant. A set of equations for the lumped reactor system are derived for the state variables, i. e. coolant flow-rate, coolant temperature and fuel temperature. In the present paper, a noise source bringing about fluctuations of the coolant flow-rate is assumed to be the most influential among all the noise sources. This idea is taken into the stochastic model by using the Langevin method. As a result of the above treatment, a stochastic description is given for the transport processes of nuclear, thermal and hydraulic quantities by deriving the Markoffian master equation and subsequently the moment equations. The theory is examined by reference to the neutron noise spectrum for the two kinds of the coolant flow pattern. It is shown that the theory can describe quantitatively, at least in part, the actual observed noises, in particular the anomalous growth of neutron noise spectra at lower frequencies.
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