# Homework Help: Average heat power

1. May 1, 2007

### NW8800

Hey I have 2 questions (q2 follows on from q1), both on average heat power:

1. The problem statement, all variables and given/known data

1) In an experiment to determine the rate at which heat is extracted from a hot material, 302 g of the material at 90 °C is put into a 50 mm diameter copper vessel to a depth of 90 mm as shown below. The hot material and calorimeter are placed in a container holding 196 g of cold water at 22.7 °C. The temperature of the water is then measured every 30 seconds for 3minutes. The results are plotted as in the previous question and the average temperature rise per second is calculated as 0.0065 ± 0.0005 °C/sec.
From the data provided and the graph below, determine the average heat power ( in kW ) transferred to the water

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2) When tested with hot material packed to a depth of 91 mm from the 50 mm diameter copper pipe used in the previous experiment the average heat power transferred to the water was found to be 5.9kW. What is the average heat power (in kW) transferred into the water PER METRE of copper container when packed with the same hot material and placed in a water cooled situation as shown.

2. Relevant equations

Not to sure

3. The attempt at a solution

I tried to use the P cond = kA (T h - T c)/L, but im not sure what k would be...

Cheers,

NW

2. May 2, 2007

### chaoseverlasting

You're given a graph right? So from that, you can find the value of kA/L ( as its a constant), and you know A(pi r^2) and L. So from there you have your heat current. Average heat would be total heat divided by 3 mins 30 secs in seconds.

3. Aug 20, 2008

### m42

Im also having problems with this. can someone help? thanks