Quantifying Tree Hydration Using Electromagnetic Sensors

An automated method of determining tree water status would enable tree fruit growers, foresters and arborists to reduce water consumption, reduce orchard maintenance costs and improve fruit quality. Automated measurements could also be used to irrigate based on need rather than on fixed schedules. Numerous automated approaches have been studied; all are difficult to implement. Electromagnetic sensors that measure volumetric water content can be inserted in tree trunks to determine relative changes in tree water status. We performed automated measurements of dielectric permittivity using four commercially available electromagnetic sensors in fruit tree trunks over the 2016 growing season. These sensors accurately measure the ratio of air and water in soils, but tree trunks have minimal air-filled porosity. The sensors do respond, however, to bound and unbound water and the relative change in the output of the sensors thus provides an indication of this ratio. Sapwood is the hydro-dynamically responsive component of trunk anatomy and is nearest the bark. Sensor response improved when the waveguides were exposed to a greater percentage of sapwood. Irrigation-induced increases of approximately 0.5 MPa in stem water potential were associated with 0.5 unit increases in dielectric permittivity. Electromagnetic sensors respond to bound water in trees and thus have the potential to indicate tree water status, especially when the sensor rods are in contact with sapwood. Sensor modifications and/or innovative installation techniques could enable automated measurements of tree water status that could be used to precision irrigate trees.

Drying

The last step in the separation process for a biological product is usually drying, which is the process of thermally removing volatile substances (often water) to yield a solid. In the step preceding drying, the desired product is generally in an aqueous solution and at the desired final level of purity. The most common reason for drying a biological product is that it is susceptible to chemical (e.g., deamidation or oxidation) and/or physical (e.g., aggregation and precipitation) degradation during storage in a liquid formulation. Another common reason for drying is for convenience in the final use of the product. For example, it is often desirable that pharmaceutical drugs be in tablet form. Additionally, drying may be necessary to remove undesirable volatile substances. Also, although many bioproducts are stable when frozen, it is more economical and convenient to store them in dry form rather than frozen. Drying is now an established unit operation in the process industries. However, because most biological products are thermally labile, only those drying processes that minimize or eliminate thermal product degradation are actually used to dry biological products. This chapter focuses on the types of dryer that have generally found the greatest use in the drying of biological products: vacuum-shelf dryers, batch vacuum rotary dryers, freeze dryers, and spray dryers [1]. The principles discussed, however, will apply to other types of dryers as well. We begin with the fundamental principles of drying, followed by a description of the types of dryer most used for biological products. Then we present scale-up and design methods for these dryers. After completing this chapter, the reader should be able to do the following: • Do drying calculations involving relative humidity using the psychrometric moisture chart and the equilibrium moisture curve for the material being dried. • Calculate the relative amounts of bound and unbound water in wet solids before drying. • Model heat transfer in conductive drying and calculate conductive drying times. • Interpret drying rate curves. • Calculate convective drying times of nonporous solids based on mass transfer.