# Homework Help: Solar Dryer Drying Time Estimation

1. Oct 10, 2008

### JaWiB

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:

$$\frac{mR_{n}+{\rho}_{a}c_{p}({\delta}e)g_{a}}{{\lambda}_{v}(m+\gamma)}$$

Where, unfortunately, m, $$g_a$$, $$c_p$$, $$\rho$$, and $${\delta}e$$ 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.