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Homework Help: Solar Dryer Drying Time Estimation

  1. Oct 10, 2008 #1
    1. The problem statement, all variables and given/known data

    The problem is fairly simple (hah): estimate the time it will take for a solar dryer (which I have to design) to dry 50 pounds of fruit from 80% water to 10% water.

    2. Relevant equations

    It seems there are at least a few equations that give an approximation for evaporation rates. THe first one that comes up is the penman equation:


    Where, unfortunately, m, [tex]g_a[/tex], [tex]c_p[/tex], [tex]\rho[/tex], and [tex]{\delta}e[/tex] depend on temperature, wind speed, and relative humidity (Credit: wikipedia for all of the above)

    3. The attempt at a solution

    I could go on with all the other equations impacting those variables, but since I don't have a lot of data to work with (really we were just given solar radiation data for surrounding areas) I figure I must be able to make some approximations to boil this down to something more manageable.

    Any idea where to start here?

    I can probably fairly easily find an estimate for average temperature during the times/location that we're desiging this to be used. I can probably also estimate energy coming into the dryer and the energy leaving through the walls. But I don't know how that will affect the humidity, air flow, and temperature inside the dryer.
  2. jcsd
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