First law of thermodynamics rate problem

  • Thread starter tron_2.0
  • Start date
  • #1
29
0

Homework Statement


consider a room that is initially at the outdoor temperature of 20 degrees C. The room contains a 100-W lightbulb, a 110-W TV set, a 200-W refrigerator, and a 1000-W iron. Assuming no heat transfer through the walls, determine the rate of increase of the energy content of the room when all of these electric devices are on.


Homework Equations


dE/dt (of the control mass)= -Q(convection)+W(electrical)-Q(conduction)
W(electrical)=Q(convection)?

The Attempt at a Solution


I tried to take into account that the electrical work is given, but im unsure on how this correlates to the rate of increase of energy. am i solving the first equation i wrote for dE/dt? and if thats the case, how would i find the average heat transfer coefficiant for Q(conv) since i can cancel out Q(conduction)?

thanks a lot
 

Answers and Replies

  • #2
Borek
Mentor
28,806
3,301
You are told to assume no heat is lost.

Honestly, I have no idea what to make out of your analysis of the problem, it seems to be completely off.
 

Related Threads on First law of thermodynamics rate problem

  • Last Post
Replies
11
Views
2K
Replies
8
Views
2K
  • Last Post
Replies
3
Views
12K
  • Last Post
Replies
2
Views
1K
  • Last Post
Replies
0
Views
6K
  • Last Post
Replies
4
Views
1K
  • Last Post
Replies
4
Views
900
  • Last Post
Replies
2
Views
12K
  • Last Post
Replies
1
Views
5K
Replies
4
Views
1K
Top