Spreading coefficient Subject

The mode of action of immobilized PDMS-hydrophobed silica antifoam in porous defoamers does not appear to have been the subject of basic research. Of particular interest would be studies of the effectiveness of the use of a non-spreading oil in order to better understand the role of the initial spreading coefficient in determining delivery of the antifoam to foamed blood. The role of defoamer pore structure, antifoam properties, blood flow rates, and foam bubble sizes in determining drop sizes of released antifoam would be of interest in considering the design of filters suitable for removal of that material. 

A surface heat transfer coefficient h can be defined as the quantity of heat flowing per unit time normal to the surface across unit area of the interface with unit temperature difference across the interface. When there is no resistance to heat flow across the interface, h is infinite. The heat transfer coefficient can be compared with the conductivity the conductivity relates the heat flux to the temperature gradient the surface heat transfer coefficient relates the heat flux to a temperature difference across an unknowm distance. Some theoretical work has been done on this subject [8], but since it is rarely possible to achieve in practice the boundary conditions assumed in the mathematical formulation, it is better to regard it as an empirical factor to be determined experimentally. Some typical values are given in Table 2. Cuthbert [9] has suggested that values greater than about 6000 W/m K can be regarded as infinite. The spread of values in the Table is caused by mold pressure and by different fluid velocities. Heat loss by natural convection also depends on whether the sample is vertical or horizontal. Hall et al. [10] have discussed the effect of a finite heat transfer coefficient on thermal conductivity measurement. 

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