Heat and mass transfer phenomena

The heat and mass transfer phenomena associated with packed-bed reactors are described in... 

The understanding of heat and mass transfer phenomena occurring during... 

As can be seen, there are quite a few degrees of freedom for the heat and mass transfer phenomena within a fuel bed or a packed bed. Consequently, the phenomenology is extremely complex. [15]... 

Several parameters have been seen to influence the crystallization of ice crystals in subcooled aqueous solutions. The primary factor is the extent of subcooling of the solution. Other factors include the agitation rate, the types and levels of solutes in solution. Huige (6) has summarized past work on conditions under which dusk-shaped and spherical crystals can be found in suspension crystallizers. The effects of heat and mass transfer phenomena on the morphology of an ice crystal growing in a suspension have not been fully understood. 

Di Matteo, P, Donsi, G. and Ferrari, G., The role of heat and mass transfer phenomena in atmospheric freeze-drying of foods in a fluidised bed, /. Food. Eng., 59 (2003) 267-275. 

By definition, the turnover frequency is expressed per number of active sites. So, catalytic samples that differ only in the amount active sites must exhibit the same values of turnover frequency. If not, heat and mass transfer phenomena are present. Specifically, the correct measurement of intrinsic kinetic data in heterogeneous catalysis is difficult due to the effect of heat and mass transfer, especially inside the pores of high specific-area materials. The turnover frequency reveals these phenomena. In other words, in the case of supported... 

The catalyst and particulate filter models were developed individually with different university partners. They are described in the following sections. A key issue for all models is robustness and scalability as the applications range from passenger cars to heavy-duty commercial vehicles. The models are physical and chemically based, consisting of a transport model for heat and mass transfer phenomena in the monolith in gas and solid phases, cf. Fig. 6. The monolith reactor modeling is discussed in more detail in Section III. 

In this section the models employed for simulation of catalytic monolith reactor are discussed, focusing on effective description of heat and mass transfer phenomena in monolith channel. The number of different mathematical models developed for converters of automobile exhaust gases over the last decades is huge—cf., e.g. Heck et al. (1976), Young and Finlayson (1976), Oh and Cavendish (1982), Zygourakis and Aris (1983), Chen et al. (1988),... 

The current chapter shows the application of mainly thermodynamic calculations, which have their basis in Chapters 4 and 5. However, as indicated in Chapter 3, a fundamental kinetic model, separated from heat and mass transfer phenomena, has yet to be established, particularly at high concentrations to extend the measurements pioneered in the laboratory of Bishnoi during the last three decades. The generation of such a time-dependent growth model and its application is one of the major remaining hydrate challenges. 

Heat and Mass Transfer Phenomena in Fluidization Systems... 

An extensive analysis of the behaviour of different types of non-adiabatic fixed bed reactor models is carried out and the importance of the heterogeneous one and two-dimensional models III-0 and III-T is stressed. Although in these models the heat and mass transfer phenomena are correctly taken into account, they... 

Yet from these studies it follows that heat and mass transfer phenomena by no means can be ignored. Kung [b6] showed that among wood particles of 2, 0.2, 0.02 cm only the smallest ones showed a uniform temperature distribution. Hence in actual pyrolysis reactors the rate of conversion will usually be controlled by heat transfer. When the latter is very slow, as in the Destrugas process, plant operating capacity may be strongly affected by the moisture content of the refuse. 

Physical conditions greatly depend on the aggregate state of the continuous phase (vapor in spray and tray condensers, liquid in pool-type condensers, and liquid film on the solid surface in packed bed condensers). Design of the most frequently used spray condensers, featuring vapor condensation on the water droplets, depends on the heat and mass transfer phenomena involved with saturated vapor condensation in the presence of the subcooled liquid droplets of changing mass. The process is very complex. For further details on the problems involved, consult Refs. 116 and 118. Such designs involve a substantial input of empirical data. 

Slurry back-mixing in the enhanced SBCR is significantly reduced by the addition of the down-comer/dip-tube flow path consequently, the gas and liquid phases likely exhibited more plug-flow behavior. Thus, for a given space velocity, the enhanced SBCR should yield a higher conversion than that of a CSTR [4]. Differences in conversion between the enhanced SBCR and CSTR reactor types may also be caused by the dissimilarity of heat and mass transfer phenomena. In addition, the relatively large L/D ratio of the SBCR may also contribute to its plug-flow characteristics. 

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