A solar still is used to make fresh water from salt water by evaporation. Assume that during a summer day that 1000 BTU/ft sq of solar energy falls on the surface of the salt water. Determine how many inches of water are evaporated in 30 days. Assume that 1040 BTUs is needed to distill one pound of water.
To determine how many inches of water are evaporated in 30 days using a solar still, we need to calculate the total solar energy available and then divide it by the energy required to evaporate one pound of water.
Given:
- Solar energy falling on the surface of saltwater: 1000 BTU/ft sq
- Energy required to distill one pound of water: 1040 BTU
First, we need to convert the solar energy falling on the surface to total energy over the 30-day period. Assuming the energy input is constant throughout the day:
Total energy input = (energy per square foot) * (surface area of saltwater) * (number of days)
The surface area of saltwater is not provided, so we will make an assumption. Let's assume we have a solar still with a surface area of 10 ft sq.
Total energy input = 1000 BTU/ft sq * 10 ft sq * 30 days
Total energy input = 300,000 BTU
Now, we need to calculate the number of pounds of water that can be evaporated using this energy:
Number of pounds of water evaporated = (total energy input) / (energy required to distill one pound of water)
Number of pounds of water evaporated = 300,000 BTU / 1040 BTU
Number of pounds of water evaporated ≈ 288.46 pounds
Finally, we need to convert the pounds of water evaporated into inches. This conversion requires knowing the density of water, which is approximately 62.4 pounds/ft^3.
Number of inches of water evaporated = (number of pounds of water evaporated) / (density of water * surface area of saltwater)
Using the assumed surface area of 10 ft sq:
Number of inches of water evaporated = 288.46 pounds / (62.4 pounds/ft^3 * 10 ft sq)
Number of inches of water evaporated ≈ 0.462 inches
Therefore, it is estimated that approximately 0.462 inches of water will be evaporated in 30 days using a solar still with the given conditions.