Transient behaviour of shell and tube heat exchangers

Based on the dispersion model rather than on the conventional pluf-flow model, a method of predicting the transient behaviour of parallel and counterflow heat exchangers is developed, whereby the effects of shell-side flow maldistribution and the finite heat capacities of both fluids, tube bundle and shell are considered. The final solution has been obtained by numerical inversion of the Laplace transform, to determine the transient responses to arbitrary inlet temperature variations. The experiment was carried out in a one pass tube heat exchanger. The comparison between therotical and experimental results is presented and the feasibility of this method is discussed.     

银的抗菌整理

Dohmen公司开发的Docair银整理体系,是一种安全且易于处理的抗菌整理体系,已成功应用于工业生产中.该体系可用于各类纤维的连续与间歇工艺中.即便经过剧烈洗涤之后也可达到良好的抗菌效果.该体系与其他纺织品助剂有很好的相容性,并且通常对抗菌性能没有负面影响.     

Steady-State and Transient Behavior of Two Heat Exchangers Coupled by a Circulating Flowstream

Systems consisting of two heat exchangers coupled by a circulating flowstream are studied. The systems differ in the flow configurations of the single heat exchangers. For steady-state operation, there exists a heat capacity rate of the circulating flowstream that maximizes the temperature changes of the external flowstreams. Until now, this optimum has been calculated assuming that the overall heat transfer coefficients of the heat exchangers do not depend on the mass flow rate of the circulating flowstream. In this paper, the dependence of the overall heat transfer coefficient on the mass flow rate of the circulating flowstream is taken into account. For transient operating conditions, the system response to perturbations of inlet temperatures and mass flow rates is calculated by the method of Laplace Transforms and an explicit finite difference method. The most significant features of the coupled system become apparent by considering outlet temperature transients induced by perturbations of the mass flow rate of the circulating flowstream.     

Mean Overall Heat Transfer Coefficient in Heat Exchangers Allowing for Temperature-Dependent Fluid Properties

For temperature-dependent heat transfer coefficients and heat capacities, fast approximation methods are presented for the estimation of the effective overall heat transfer coefficient. The heat transfer coefficients are calculated for two, three, or four reference temperatures. For the parallel and countercurrent flow a known method is described that uses a hypothetical fluid temperature for the iteration-free consideration of variable heat capacities. For the mixed–unmixed cross flow a previous method for temperature-dependent heat transfer coefficients is refined to allow also for variable heat capacities. For the mixed–mixed cross flow a new iterative fast design and rating method is developed that is a suitable model for special multipass shell-and-tube heat exchangers. The accuracy of the methods is tested against numerical calculations with good results.     

Gas evolution during pyrolysis of various Colorado oil shales

Rates of evolution of C0₂, CO, H₂, CH₄ and the C₂ and C₃ hydrocarbons during the pyrolysis of seven Colorado oil shales have been measured. These shales, which are from various depths at two different sites, yield 34–255 ¦ of oil per tonne raw shale (9–61 US gal of oil per short ton raw shale) and linear heating at a rate of 2°C min⁻¹ was used for the retorting of all samples. The objective of the study is to monitor variations in gas evolution from shales of different organic content and from various stratigraphic and areal locations. Comparisons between shales from each site are made together with correlations with data from Fischer assays. A kerogen concentrate (mineral fraction removed by HCl-HF treatment) and retorted shale from a Fischer assay are also included. The ability of a kinetic model due to Campbell et al. to predict gas evolution is tested and it is found necessary to modify slightly some of the stoichiometric coefficients to obtain good agreement. The resultant kinetic model should adequately describe the gas and oil evolution behaviour of shale from the upper portion of the Green River formation.