# Hose losing heat

1. Aug 24, 2006

### NotMrX

Hello,

This problem has been messing me up.

A person waters their yard. He has a rubber hose cylinder with an inner radius,$$R_i[\tex], of 1.5 cm and an outer radius, [tex]R_o$$, of 1.7 cm. The thermal conductivity of of rubber is 0.2 in SI units. The hose is 5 meters long, L. The hose is completely in the air with a temp of 30 Celsius while the water has a temp of 20 Celsius. Ignoring the heat loss from the end what is the power or heat loss per second.

Here is my attempt:
$$P=K*A\frac{\DeltaT}{r}$$
$$dA=L*2*\pi*dr$$
$$P=K\frac{\DeltaT}{r}L*2*\pi*dr$$
$$P=k*2*\pi*\DeltaT*L*Ln\frac{R_o}{R_i}$$

It seems like something is wrong though.

Last edited: Aug 24, 2006
2. Aug 24, 2006

### NotMrX

Here is the question; I coulnd't get latex to work this time.

A person waters their yard. He has a rubber hose cylinder with an inner radius of 1.5 cm and an outer radius of 1.7 cm. The thermal conductivity of of rubber is 0.2 in SI units. The hose is 5 meters long, L. The hose is completely in the air with a temp of 30 Celsius while the water has a temp of 20 Celsius. Ignoring the heat loss from the end what is the power or heat loss per second?

3. Aug 30, 2006

### NotMrX

Here is my attempt:
$$P=kA\frac{dT}{dr}[\tex] [tex]A=2L\pi(r_f-r_i)[\tex] [tex]dA=L\pidr$$
[tex]P=k*dA

4. Aug 30, 2006

### Hootenanny

Staff Emeritus