An analysis of multiple superheated and saturated regions in a stagnant binary film

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A film model for heat and mass transfer with fog formation

An analysis is presented of a binary film with fog formation and a negligible induced velocity (traditionally referred to as “Stefan—Nusselt flow”). The governing equations of energy diffusion, coupled with the saturation condition, are solved and analytical correction factors are derived. Subsequently, the “negligible induced velocity” (NIV) fog film model is applied to channel flow, yielding analytical expressions for the variation of bulk vapour mass fraction, bulk temperature, and the possible creation of bulk fog. Multiplying the NIV correction factor for fog only by the classical film model correction factors for induced velocity, reveals that the product corresponds to the film model correction factors for the combined effects of fog and induced velocity. Furthermore, a thorough comparison with theoretical and experimental results of foregoing two-dimensional studies, concerning fog formation in the presence of free and forced convection, confirms the accuracy of the present fog film model

Leaching models for multiple immersed materials and for granular materials flushed in a column

The present paper addresses the leaching of hazardous contaminants from immersed and replenished materials and from granular materials flushed in a column. First, the leaching of an immersed material in contact with a limited volume of leachant is studied. The mass transfer from material to leachant is assumed to be inversely proportional to ¿t (i.e. following the semiinfinite medium diffusion model). The leaching model accounts for the concentration of the contaminant in the leachant, the (deviation from) equilibrium partition of the contaminant between material and leachant, and leachant replenishment. The governing equations are solved in closed form, yielding the contaminant concentration in leachant and monolith versus the elapsed time. For special cases this solution corresponds to the leaching expressions obtained by Godbee and Joy (1974). Subsequently, the unsteady leaching process from a granular material packed in a column, flushed by a leachant, is modeled. Here, the mass transfer from material to leachant is also assumed as inversely proportional to ¿t. The model leads to a moving boundary problem, the governing partial differential equations are transformed and solved using asymptotic techniques. Approximate expressions are obtained for the contaminant concentration of the material and in the leachant. Of special practical interest is the leachant concentration at the exit of the column as here the leachant can be collected in flasks and analyzed. Finally, the models are generalized to systems where the mass transfer is an arbitrary power function of time. The resulting equations can for instance be used for determining an effective diffusion coefficient and/or comparing immobilization yields

Particle-size distribution and packing fraction of geometric random packings

This paper addresses the geometric random packing and void fraction of polydisperse particles. It is demonstrated that the bimodal packing can be transformed into a continuous particle-size distribution of the power law type. It follows that a maximum packing fraction of particles is obtained when the exponent (distribution modulus) of the power law function is zero, which is to say, the cumulative finer fraction is a logarithmic function of the particle size. For maximum geometric packings composed of sieve fractions or of discretely sized particles, the distribution modulus is positive (typically 0<alpha<0.37). Furthermore, an original and exact expression is derived that predicts the packing fraction of the polydisperse power law packing, and which is governed by the distribution exponent, size width, mode of packing, and particle shape only. For a number of particle shapes and their packing modes (close, loose), these parameters are given. The analytical expression of the packing fraction is thoroughly compared with experiments reported in the literature, and good agreement is found

Topics in Cement and Concrete Research

In recent decades, the construction sector has faced many changes. One of these changes is the shift in the role of national government from one-sided practices in which the government was solely responsible for strategic and long-term spatial planning to a multi-actor and multi-level arena. One outcome was a rearrangement of the balance between public and private responsibilities. This has led to new procurement routes and contracts as Private Finance Initiative (PFI) and Public Private Partnerships (PPP), as well as to a more performance-oriented client (both public and private). At the same time, construction firms changed their strategic focus from cost efficiency to adding value for money for the client, resulting in new contract forms such as Design & Construct (D&C), Building, Operate & Transfer (BOT) and variants there from. So far, governments of most European countries have their own restrictive specifications for the use of building materials

Comments on "Transition from transpiration to film cooling"

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A film model for free convection over a vertical porous plate with blowing or suction

A film model is described for free convective heat transfer and friction in the presence of wall suction or injection. The analysis yields a thermal correction factor, which appears to be the classical (Ackermann) expression, and a novel friction correction factor, derived here for the first time. Both correction factors are applied to free convection along a vertical flat porous plate for values of the Prandtl number of 0.73, 1 and 7. Subsequently, the film theory predictions are compared with the numerical and asymptotic results of a boundary layer analysis, performed by previous investigators. On the basis of this comparison, a modified correction factor is proposed which correlates excellently with the results of the boundary layer analyses

Comments on "Effect of humid air flow rate on the filmwise condensation inside a vertical cooled pipe: numerical and experimental study"

No abstract