Nikolai Kolev

On the evaluation of the interfacial turbulence (the Marangoni effect) in gas (vapour)—liquid mass transfer: Part I. A method for estimating the interfacial turbulence effect

Two widespread approaches for evaluation of the influence, upon gas (vapour)—liquid mass transfer in the case of ‘positive mixtures’ (dσ/dx < 0), of the interfacial turbulence caused by the surface tension gradients (Marangoni effect) have been surveyed and analysed critically. It is shown that the assumption of direct proportionality of mass transfer enhancement and Marangoni number has not been well justified. Evidence is given which supports the concept of defining the enhancement factor by the ratio R = Ma/Mac)n. Some problems concerning the enhancement dynamics of mass transfer, the initiation threshold of the Marangoni instabilities, as well as the limits of saturation have been discussed thoroughly. By correlating a large amount of experimental data from the literature, equations have been derived concerning the critical Marangoni number Mac and the exponent n. These equations are proposed for use when accounting for the Marangoni effect in gas (vapour)—liquid systems regardless of contactor type and solutions employed, the enhancement effect being obtained in relation to local mass transfer efficiency.

A NEW COLUMN PACKING FOR OPERATION AT EXTREMELY LOW LIQUID LOADS

Abstract It has been demonstrated that the ‘honeycomb packing’ made of sintered PVC sheets is well wetted even at extremely low liquid velocities. For example, at a liquid superficial velocity of 0.00008 m3/(m2 s) the effective surface is between 114 and 178 m2/m3 depending on the particular packing design. Having high effective surface at extremely low superficial velocities, the packing operates at full counter-current flow, while other packings demand a re-circulation of the absorbent. It is shown that compared to some of the highly efficient packings, the use of the new packing leads to considerable pressure drop reduction and to an increase of the volumetric mass-transfer coefficient.

Performance characteristics of a packing with boundary layer turbulizers: Part 1. Pressure drop and loading point

Abstract A novel design of a honeycomb packing with turbulizers in the region of the boundary layer (Turbo-Pack) has been designed and investigated. The presence of turbulizers is shown to decrease the pressure drop per mass transfer unit in cases of both gas-film and liquid-film controlled mass transfer. A comparison of the best packings known so far from the literature shows that, regarding such an important parameter as pressure drop per mass transfer unit, the novel packing has significant advantages. On the basis of experimental data obtained by studying 11 different packing designs in liquids of various viscosity, equations for determining the performance characteristics of the novel packing are obtained. In the first part of this work, the data on packing design, pressure drop and loading point are presented.

A new type of a gas-steam turbine cycle with increased efficiency

Abstract A new system with a gas–steam turbine particularly effective for district heating systems is proposed. Compared to the existing combined installations, including a gas turbine, a waste heat utilization and a steam turbine, it shows significantly lower capital cost and an increase of the thermodynamic efficiency. The simultaneous expansion of gas and steam in one turbine, as well as the utilization of the heat of condensation of the waste gases at the installation outlet allows the overall thermodynamic efficiency, calculated on the basis of the lower calorific value, to reach 108.7%.

On the evaluation of the interfacial turbulence (the Marangoni Effect) in gas (vapour)—liquid mass transfer: Part II. Modelling of packed columns accounting for axial mixing and Marangoni effects

Abstract By considering axial mixing and Marangoni effects as the most important side-effects accompanying heat and mass transfer in packed columns, a unified approach has been developed for gas (vapour)—liquid column design. Based on the diffusion model, all necessary equations have been defined by also including estimates for the Marangoni instabilities. The dimensionless equations needed to evaluate the model parameters were derived by ‘cold’ experiments and proved to be valid for absorption, desorption and distillation. Numerical experiments for two packing types (Raschig rings and HOLPACK) have been performed, and the data concerning the contribution of HOLPACK in ethanol—water distillation correlated. Evidence is presented that the influence of Marangoni instabilities upon column efficiency depends to a great extent on the performance concentrations, thus reaching 29% for Raschig rings and 49% for HOLPACK packing. The adequacy of the model is proved in terms of the results obtained.

Pressure drop of arranged packings with vertical walls

Abstract Among the known types of packings, arranged packings with vertical walls have the lowest pressure drop for one transfer unit at comparable free volume as well as the highest efficiency at a given pressure drop. Reliable equations are derived for pressure drop determination in industrial apparatuses filled with this kind of packing. The pressure drop is presented as a sum of two terms-pressure drop (in the vertical channels) of the packing rows themselves and local pressure drop of the boundary sections between the rows. The experimental data for dry packing pressure drop, available in the literature and newly obtained, are described by new equation with mean deviation of 9.3%. Equations for determination of wetted packings pressure drop up to the loading point and above it are obtained, too. The proposed equations can also be used to determine the loading point.

Über den Einfluss der Axialvermischung bei Rektifikationskolonnen mit ungeordneten Füllkörperschüttungen

Zusammenfassung Es wird die Moglichkeit zur Berechnung der Rektifikationskolonnen mit ungeordneten Fullkorpern unter der Berucksichtigung der Axialvermischung mit Hilfe des Diffusionsmodells auf der Grundlage der allgemeinen Zusammenhange der Prozesse Absorption, Desorption und Rektifikation gezeigt. Die verwendeten experimentellen Daten werden bei der Rektifikation von zwei Systemen unter den Bedingungen, bei denen keine wesentliche oberflachliche und thermische Erscheinungen auftreten, erhalten.

Discrete distributions related to success runs of lengthk in aulti-state markov chain

We consider the time-homogeneous multi-state Markov chain {X , n ≥0} with states labeled as “0” (success) and “f” (failure), f = 1,2,… Let k be a fixed positive integer and SK be the event of a success run of length k in the sequence X0: X ,… In this article, joint probability generating functions for various statistics, related to the event SK0 are derived. In particular cases the exact distribution of the total number of successes S, the total number of failures F and the total number of trials N are deduced. The distribution of N is called the geometric distribution of order k for time-homogeneous {0,1,2,…}-valued Markov chain.

Performance characteristics of a packing with boundary layer turbulizers. III. Liquid film controlled mass transfer

Abstract The gas-film controlled mass-transfer rate in a honeycomb packing, with stamped groove turbulizers (Turbo-Pack) which affect the region of the boundary layer, has been studied. An equation for determining the mass-transfer coefficient as a function of gas velocity and the geometrical dimensions of the packing has been derived. It is found that the effect of the height of packing blocks is far less than that forecast by Zhavoronkovs equation which was derived for packings with a much higher wall thickness. Comparison of experimental data relevant to the novel design with reference packings cited in the literature shows that as far as its low values of pressure drop per mass transfer unit are concerned the Turbo-Pack packing is superior to all other known packings.

Systems Containing Contact Economizers for Flue Gas Heat Utilization

A reference is made to the fact that a significant part of the heat generated by combustion, is lost in the atmosphere with exhausted flue gases. Contact economizer systems are considered which help to utilize this heat by heating up the water before entering the boiler or by heating up urban heat supply water of the central heat supply network, as recycled back to the heating plant. Attention is drawn to some features of the new contact economizers which allow pressure drop values as low as 10–20 mm water head at high gas superficial velocities, i.e. up to 3 m/s. New process flow charts with contact economizers which helping to utilize heat at higher temperature levelsby simultaneous reduction of nitric oxides emissions down to 3 3 %, are given. The method developed for designing such systems is described, and data obtained in experiments with such industrial systems developed by the authors, are presented.