What is the heating surface of a water tube with a diameter of 3 ½ inches and 20 feet long?

To calculate the heating surface area of a water tube, you can use the formula for the surface area of a cylinder, which is relevant here since water tubes are cylindrical in shape. The formula for the surface area (excluding the ends) of a cylinder is:

Surface Area = π × Diameter × Length.

In this case, you are given the diameter as 3 ½ inches and the length as 20 feet.

First, convert the diameter from inches to feet:

3 ½ inches = 3.5 inches. Since there are 12 inches in a foot, this converts to:

3.5 inches ÷ 12 = approximately 0.29167 feet.

Next, using the length in feet (20 feet) along with the converted diameter, the formula would look like this:

Surface Area = π × 0.29167 ft × 20 ft.

Using the value for π (approximately 3.14159), the calculation proceeds as follows:

= 3.14159 × 0.29167 × 20

= 3.14159 × 5.8334

≈ 18.32 ft².

This computed area of approximately 18.32 square feet matches one of the choices, confirming