Heterogeneous overheating

The existence of the so-called microwave effect has not been proved. It does, however, seem to have been demonstrated that overheating of polar liquids [17] occurs and that hot spots are present in heterogeneous systems, especially at the interface [38]. Similarly, microwave irradiation results in an increase in the molecular mobility in solids [5 b]. 

Eventually, the sample size, penetration depth as well as heating rate are strongly coupled during microwave irradiation and may finally result in more homogeneous or heterogeneous heating of the material, which in turn can result in overheating of the material and creation of so called hot spots in the latter case. 

With the rotating-drum fermentor, the oxygen mass transfer is enhanced and overheating is prevented. The heterogeneity of the system is also reduced to a large extent as compared with static trays or a packed-bed fermentor [29]. It is possible to operate a rotating-drum fermentor continuously which enhances... 

Stretching the water, one can obtain negative pressure,The experimental limit for water around room temperature is around -1400 bar, this is close to the homogeneous nucleation limit (R) the heterogeneous one (Q) has to be between 0.025 bar and -100 bar, depending on the purity of the sample as well as on the rate of the overheating or the depressurization. Finally somewhere between -2000 and -4000 bar one will see the spinodal (S). The exact location of the spinodal of water is still debated. 

The only problem is that spinodals are not known. Experimental determination is not possible, becaus e heterogeneous nucleation always interfere. However one can use the experimental data to extrapolate the spinodal as the vaporisation limit of a very pure liquid with infinite overheating or depressurization level. The related experiments are very difficult up to know we have only a few data for water and a very few for other liquids. Equation of states (EoS) can describe the behaviour of stable liquids and vapours but may not necessarily reliable for their metastable counterparts. Obviously one can estimate the spinodal from an EoS by calculating the pressures and temperatures where the compressibility turns negative, but depending on the equation of state the results may even be qualitatively incorrect, for example if there are discontinuities in the two phase region. Therefore every method which can give us a fair estimate about the location of the spinodal would be important. 

Overheating of polar substances and the presence of hot spots has also been demonstrated the latter is particularly important in heterogeneous systems. All of these effects can be used to significantly improve reactions and even to perform reactions that do not occur under the action of conventional heating. 

This line subdivides the state areas of homogeneous, subsaturated, overheated wet gas and the state area of the heterogeneous, oversaturated wet gas, the mist area . On the saturation line, with isotherms change their inclination. Additionally, lines of equal relative humidity, so called (p lines, are also calculated by Eq. (5-12). 

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