# Calculating R value

1. Mar 28, 2016

### Jway

1. The problem statement, all variables and given/known data
Determine the R value of the unknown specimen using a conventional hot box.

Surface area of the specimen is 0.009 m2.
Initial Hot Room Temperature = T Hot Initial = 30 ° C = 303.15 K
Initial Cold Room Temperature = T Cold Initial = 20 °C = 293.15 K

Time for both rooms reach to equilibrium = 2 hours = 7200 seconds
Temperature after 2 hours in hot room = T Hot final = 22 °C = 295.15 K
Temperature after 2 hours in cold room = T Cold Final = 22 °C = 295.15 K
The gas in Hot room is Specific heat capacities = 1 J/(kg K) and masses = 1 kg
The gas in Cold room is Specific heat capacity = 1 J/(kg K) and masses = 1 kg

2. Relevant equations

R Value = dT x A / Q
Q = m x c dt / time

3. The attempt at a solution

Determine rate of heat flow.

Q = m x c x (T Cold Final - T Cold Initial ) / Time difference

= 1 kg x 1 J/(kg K) x (295.15 K – 293.15 K) / 7200 sec

= 2.78e-4 J per Sec

Determine R value

R Value = dT x A / Q

= ((T Hot Initial - T Cold Final) x A) / Q

= ((303.15 K – 293.15 K) x 0.009 m2 ) / 2.78e-4 J per Sec

= 324

2. Apr 2, 2016