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A non-steady-state method has been used for determining the effective diffusion coefficient, D(e), and a distribution constant, K(i), of small molecules in alginate gel beads. A mathematical model based on Pick's law and includingexternal film diffusion resistance describe the diffusion process. Criticalexperimental parameters for the estimation of D(e) and K(i), for both one- and two-parameter methods were the initial solute concentration in the bulk liquid, the void fraction inthe reactor, and the experimental starting point. In our analysis, the two-parameter method is preferable. Incorporation of an estimate of the film resistance into the overall model increased the estimated values of D(e) significantly and improved the stability of the term over a range of reactor agitation rates. (c) 1995 John Wiley & Sons Inc.

In the present study, local flow properties are investigated in pilot plant scale fluidized bed reactors using both fibre optic and capacitances probes. Measurements are conducted at ambient as well as at 150°C. The system used is air and spent FCC particles (mean particle diameter: 65~m), The static bed height is I.6m. Bubbling and turbulent regimes (V=O.40 and 0.70 m/s) are investigated in two 0.3 and 0.5 m 10 columns.Bubble fraction under the bubbling regime and at room 'temperature, measured using fibre optic and capacitance probes, are in good agreement However,in the turbulent regime, fibre optic probes are prone to underestimate the bubble fraction while capacitance sensors tend to overestimate it. These discrepancies between fibre optic and capacitance measurements increase with temperature.Using capacitance probes, a prevalent flat bubble rise velocity profile is measured. This is assigned to the relatively slow response, to the size and to the geometry of the capacitance probes. Overall this gives an underestimation of the bubble frequency and an overestimation of the bubble contact time and the bubble contact length.Due to the high fibre optic probe sensitivity, care should be taken in the interpretation of signals. Overestimation of bubble frequency leads to underestimation of both bubble contact times and bubble contact lengths.

In recent years, it has become essential to consider the total carbon footprint of a construction project. Commonly, the question has been: ’What is the best material to be used in this context?’ In this paper we argue that this question is incomplete, not taking the complexity of design choices into consideration. This paper intends to share light on how to analyse some factors that influence the construction of buildings in order to contribute to climate change mitigation, taking this complexity into consideration. Calculation of fossil greenhouse gas (GHG) emissions for two load-bearing structures for office buildings in 4, 8 and 16 storeys with equal functional requirements; e.g. load bearing capacity, acoustic performance, fire resistance and adaptability are addressed. The main materials for the load-bearing structures are cross laminated timber (CLT) elements and precast concrete elements respectively. The result show that one cannot on a general basis conclude that either type of load-bearing structure cause less fossil GHG emissions. It is always important to consider the building design, functionality as well as external conditions such as location when considering different load-bearing structure materials.