Poorly adiabatic

Figure 6.8 Temperature-time function of a poorly adiabatic (isoperibol) calorimeter after < short exothermic heat pulse.

On the other hand, RPBs suffer from poor heat transfer possibilities. Heat input could theoretically be achieved by use of eddy currents, microwaves, or sonic energy, and thus endothermic reactions are, in principle, possible. The heat removal is more problematic and exothermic reactions must be conducted adiabatically within the rotor. Alternating packing and heat transfer plates could perhaps be an option, although it would greatly increase the complexity and the price of the reactor. 

A survey of the literature shows that although very different calorimeters or microcalorimeters have been used for measuring heats of adsorption, most of them were of the adiabatic type, only a few were isothermal, and until recently (14, 15), none were typical heat-flow calorimeters. This results probably from the fact that heat-flow calorimetry was developed more recently than isothermal or adiabatic calorimetry (16, 17). We believe, however, from our experience, that heat-flow calorimeters present, for the measurement of heats of adsorption, qualities and advantages which are not met by other calorimeters. Without entering, at this point, upon a discussion of the respective merits of different adsorption calorimeters, let us indicate briefly that heat-flow calorimeters are particularly adapted to the investigation (1) of slow adsorption or reaction processes, (2) at moderate or high temperatures, and (3) on solids which present a poor thermal diffusivity. Heat-flow calorimetry appears thus to allow the study of adsorption or reaction processes which cannot be studied conveniently with the usual adiabatic or pseudoadiabatic, adsorption calorimeters. In this respect, heat-flow calorimetry should be considered, actually, as a new tool in adsorption and heterogeneous catalysis research. 

Adiabatic Screening A UNDESIRED onsef A aDIAB P, 1, t, dP/dt, dT/dt Simple kinetics EA, A Sample — a few grams Reasonably quick to test (— /> day) Poor/moderate sample agitation Not reliable for scale-up (high cefaclor)... 

V,/V-dimethylaniline, especially when those strong donors are paired with the relatively electron-poor MES derivative of the bis(arene)iron(ll) acceptor. As such, the dark reactions arise via essentially the same multistep mechanism as that for charge-transfer de-ligation, the difference arising from an adiabatic electron transfer (10) as the initial step that is thermally allowed when the driving force -AGET is sufficient to surmount... 

Although an optimum temperature profile may be specified from theoretical calculations, it may not be possible to achieve in practice. The maximum temperature which can be used is usually determined by the materials of reactor construction or the durability of a catalyst. Also, steep axial temperature gradients cannot be realised unless heat transfer rates are high. If heat transfer is poor and the overall process is exothermic, temperature programming of a single reactor may be impossible the reactor becomes virtually adiabatic. In cases such as these, staged reactors (discussed elsewhere in this volume) with intercoolers may be used as a compromise. 

When the exponential term dominates, the adiabatic exponent is y kv which means that it decreases with decreasing volume. The behavior is therefore poor at high pressures... 

At higher pressures, the composition limit appears to be experimentally independent of the dimensions of the equipment and has been widely considered to be a property of an adiabatically propagating mixture (Bl). This type of limit has been referred to as a fundamental limit. The demonstration of the existence of such a limit is an exceedingly difficult task. Since all flames radiate some of their thermal energy, it is impossible to stabilize a flame without losses to the surroundings. However, most flame gases are very poor radiators, and, since the residence time of the gases in the reaction zone of a flame is quite small, flames have been observed which come quite close to the adiabatic flame temperature (F14). 

Heat transfer in the radial direction is poor, so large reactors are best suited to adiabatic operation. If the temperature rise is significant, it may be controlled in some processes by recycling the liquid product or introducing a quench stream at an intermediate point. 

At such a scale and without stirring, the heat transfer with the surroundings, that is the jacket with hot water at 90 °C is very poor. Thus, adiabatic conditions should be assumed as a worst case approach. Under these circumstances, the heat released in the reaction mass serves to increase its temperature. Thus, we have to calculate the heat release rate. For a conversion of 1% per day, the heat release rate is... 

The manner of heat transfer is unusual, as this reaction cyclone is solar-heated. In any other cases, the carrier gas (e.g., nitrogen or product gas from the fast pyrolysis) must be preheated, because the heat transfer by direct contact of the particles to the cyclone wall is poor and only sufficient to keep the reactor at adiabatic conditions. Lede built two different cyclone reactors for experiments on the fast pyrolysis of... 

Figure 8 An example for which the classical dynamics is a poor approximation to the quantum dissociation at off-normal incidence on W(1 00) [65]. For high initial parallel momentum, K, the wavepacket propagates in an set of adiabatic librational states which have strong couplings between rotational and translational components. These show large, non-classical avoided crossings.

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