Opportunities for Fundamental Research in Drying
Physical phenomena at the molecular level, such as van der walls interactions, can be used effectively for understanding and modeling drying relationships. Drying can be modeled utilizing fundamental phenomena, in contrast to most of the previous work in which these phenomena were used to explain empirical relationships.
New instruments and techniques provide an opportunity for advancing the knowledge of fundamental research in drying. The computer provides an opportunity for obtaining, storing, and analyzing a large quantity of data. Previously rather limited amounts of data were available from which analyses were made. New statistical and mathematical modeling approaches, a basis of much new fundamental research, need to be developed.
The two major developments make possible representing the drying relationship utilizing molecular building blocks to construct the product: newly-developed or about to be available instruments to measure and “see” the water molecule for a substrate (advanced electron microscopes), and high-speed, high-capacity computers (supercomputers).
The water molecule hp a diameter of 2 Å and a bond length of 0.9 Å. Water molecules are on a substrate which has a wide range of dimensions but much larger than water. As an example, hemoglobin protein with a molecular weight of 68,000 daltons has dimensions of 38 Å by 150 Å. Spectroscopy has been used to determine the presence of elements or molecules, such as water. During drying we are interested not only in the presence of water molecules but also the amount and movement of water. Hopefully, the observations and measurements during drying can be done without destroying the relationships between water and the substrate. A challenge for researchers is to utilize these techniques for nondestructive evaluation (NDE). The implications of the water molecule as a dipole and drying have not been explored--possibly another opportunity for fundamental research.
The scanning electron microscope (SEM) has a resolution of 100 to 200 Å; the transmission electron microscope (TEM), as low as 1–5 Å. and a scanning transmission electron microscope (STEM), combining the above with additional features, is expected to have a resolution of 0.5 Å. The photoelectron microscope (PEM) is presently used to survey the walls of cells. Further, the possibility of looking in three dimensions, to observe and characterize the movement, change of state, vaporization and condensation of water, offers new opportunities for research. The flow of water (liquid and gas) will be modeled as it moves through the products (fats, sugars, cellulose, proteins, minerals, etc.) in much the same way that the flow of electrons or ions can be represented as they move through metals. Likewise, the effect on elemental units of the product by browning, checking, splitting, or as represented by destruction of vitamins or stabilization of enzymes, can be related. These relationships can be utilized further to develop systems and equipment for drying. Admittedly, these measurement techniques have not been extensively developed for drying of biological products but offer considerable opportunities.
The supercomputer can be used to represent and model the drying phenomena from the most elemental component (electron, chemical, radical, atom, molecule) for which information is available and applied to the entire drying system.
The interaction of the water and substrate, energy involved, flow of water either as gas or liquid, and escape and measurement of water moving from the product (transcutaneous) can be used as parameters for the design of drying equipment. The components of the system can be modeled and the system can be represented with many parameters on the computer. The results of this approach using fundamental relationships can be used for several products and applications, providing results of a generic nature, while minimizing but not eliminating many of the time-consuming repetitive laboratory tests and empirical results from field tests.
KeywordsWater Molecule Moisture Transport Scanning Transmission Electron Microscope Microscopy Scan Acoustic Free Molecular Flow
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