1 / 13

Lecture 8

Lecture 8. Grain Moisture: Importance and Measurement (continued). Moisture Transfer. Diffusion-particle to particle contact Leakage Exchange via surface Diffusion via intergranular spaces Convection currents. Pixton and Griffiths (1971).

rana-gamble
Download Presentation

Lecture 8

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Lecture 8 Grain Moisture: Importance and Measurement (continued)

  2. Moisture Transfer • Diffusion-particle to particle contact • Leakage • Exchange via surface • Diffusion via intergranular spaces • Convection currents

  3. Pixton and Griffiths (1971) • 120 g lots of 22.1% mc placed in 500 g lots at 13.7% mc. Temperatures 5 and 22.5oC. • Moisture transfer stopped after 65 d at 22.5oC, but continued for 140 d at 5oC. • Moistures of wet and dry grain were never equal (why??).

  4. Vapor diffusion • Diffusion coefficients: • 2.5 x 10-4 mm2/s at 5oC • 8 x 10 -4 mm2/s at 22.5oC • Normal air: 23.9 mm2/s at 8oC.

  5. Convection Currents • More important in bulk-stored grain. • Movement varies with the type of structure, temperature differentials, moisture differentials, selective heating (from sun) on portions of the facility.

  6. Moisture Measurement

  7. Direct Methods • Accurate • Karl Fischer method: reaction of iodine with water in the presence of sulfur dioxide and pyridine to form hydriodic acid and sulphuric acid. • Air oven: wt difference. Loss of volatile components. • Distillation with toluene. Boiling ground sample > 100C with toluene. • NIR, microwave methods: need calibration, vary from variety to variety, sample size is critical. • Single kernel testers.

  8. Indirect Methods • Electronic meters • Capacitance – more accurate than resistance meters over a range of mc. 150-1250 g sample. Temp. correction. Chart. • Resistance measures electrical resistance. • RH meter: meausres RH of intergranular air. • Hair hygrometer • Wet bulb, dry bulb thermometer • Need to measure RH after 1-2 h of sample collection.

  9. Reading • Chapter 2: Moisture and its measurement. In D. B. Sauer (ed.). In Storage of cereal grains and their products, AACC, St. Paul, MN.

More Related