FDSC 310 Lecture Notes - Lecture 3: Hygrometer, Psychrometrics, Dynamic Equilibrium
10 Oct 2017
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Transpiration: evaporation of water from produce to air when air is not saturated with moisture. occurs through evaporation and vapor diffusion. Has cooling effect since energy required for evaporation, energy comes from produce in form of heat. Helps absorption of minerals when plant is alive. Degree of cooling ex: 1% moisture evaporates from 100kg of produce at 20celsius. water evaporated (m) 1kg for water to evaporate its latent heat l of vaporization needs to be absorbed (2260kj/kg) Because of high moisture heat capacity cp of produce can be assumed equal to water (4. 2kj/kgc) Disadvantage: results in water loss (weight loss) 3-4 % moisture loss represent quality loss. Happens in specialized tissues: stomatae (opening in epidermidis with guard cell that open and close continuously vary in density) lenticels, wax, cuticle, cuticular membrane, corky, tissue. Involves vapor diffusion process happens under influence of water vapor pressure gradient. Obeys basic law of gas diffusion, ficks law.
