Thermodynamics Calculation

In summary, the problem is that the chillers all fail and there is no air circulation, leading to a gradual increase in temperature over time.
  • #1
skpmobile
6
0
Base temperature 68F
BTU - 8000
Cubic Feet of Air -10000

Coolign mechanism fails.
No air circulation.
Closed air space.

Starting at 68F what is the formula to calculate the temperature curve over time?
 
Engineering news on Phys.org
  • #2
Welcome to PF, Skpmobile, but please don't double-post. You've already asked this in General Physics. It will be dealt with when someone with the answer gets around to it. I don't know it myself.
 
  • #3
F? BTU? cubic feet?

Sounds like Newton's law of cooling here but you're going to need to flesh it out a bit and convert all units to SI first
 
  • #4
skpmobile said:
Base temperature 68F
BTU - 8000
Cubic Feet of Air -10000

Coolign mechanism fails.
No air circulation.
Closed air space.

Starting at 68F what is the formula to calculate the temperature curve over time?
I'm afraid I cannot make sense of the problem as posed. What is supposed to happen with 8000 BTU?

Cooling mechanism fails? If there is no heat transfer, there is no temperature change.

No air circulation would imply no convection.

Radiative heat transfer would occur, but that is very slow, and it depends on the temperature differential or rather Thot4-Tcold4

Without radiation and convection, one is left with conduction, but the problem states no cooling.

Does the problem infer putting 8000 BTU into 10000 cu ft of air with adiabtic boundary conditions?
 
  • #5
That's the way I am reading it. A 10,000 ft^3 volume at an initial 68°F with a Q = 8000 BTU input.

First Law stuff.
 
  • #6
Clarification

Astronuc said:
I'm afraid I cannot make sense of the problem as posed. What is supposed to happen with 8000 BTU?

Cooling mechanism fails? If there is no heat transfer, there is no temperature change.

No air circulation would imply no convection.

Radiative heat transfer would occur, but that is very slow, and it depends on the temperature differential or rather Thot4-Tcold4

Without radiation and convection, one is left with conduction, but the problem states no cooling.

Does the problem infer putting 8000 BTU into 10000 cu ft of air with adiabtic boundary conditions?

For Example:
I have a room with 8000 cubic feet of air in the room
There is equipment in the room that is generating 100BTUs
I currently have chillers in that room to cool it to 68F
If those chillers fail starting at 68F what would be the temperature increase over time?
 
  • #7
OK - that is a better description of the problem. It can be handled by a 'lump parameter' model, i.e. time dependent heat transfer in basically zero dimensions.

One is looking at heat source and loss of heat transfer from the system, so the internal energy, and therefore temperature, increases with time.
 
  • #8
Great, so what equation would i plug those paraketers into to calculate points on the curve?
 
  • #9
Last edited:
  • #10
Points of clarification:
- fixed volume of air (closed room)
-starting air temperature is 68F
-cubic feet is the measurement of the air
-standard air
-no air movement generated with the exception of thermally generated
movement
-chillers all fail at once (instant loss of cooling ability)
- Thermal factor (BTU) derived from equipment documentation
-maximum for that equipment (looking at a worst case scenario)

So if I understand your statement I would have a constant level of heat being generated (the BTUs) and no heat loss from that environment. So I am looking at generating a curve of heat increase, so my x-axis is time ( 1 minute increments ) and my y-axis is temperature ( 1 degree increments ) where do I go from here?
 
  • #11
The equipment rating should be in btu/hr rather than btu. Use the formula Q = 1.1xcfmxdT. As you have no air circulation, after adding up all the heatloads in the room and getting the total heat input in btu/hr, divide the room volume by 60. This gives you the temperature rise per minute.
 
  • #12
Gentlemen, I am a total laymen relative to physics would you be so kind as to plug my original numbers into the appropriate places in the equation so I have a clearer picture. Your assistance is greatly appreciated.
 
  • #13
Astronuc, I finally think I am getting it I just don't know how to determine time by the equation.

284064031.4... 21851079.33... 1.3... 10
Q...... C......Mass of...Temperature
.........Air at SL...Delta
 
  • #14
skpmobile said:
Great, so what equation would i plug those paraketers into to calculate points on the curve?

Once you start plugging things into parakeets, you're out of the realm of physics and getting into abnormal psychology. There are people here who can help you with that as well.
 

What is thermodynamics calculation?

Thermodynamics calculation is a branch of science that deals with the study of energy and its transformations in physical systems. It involves the use of mathematical equations and principles to analyze and predict the behavior of systems in relation to heat, work, and energy.

What are the laws of thermodynamics?

The four laws of thermodynamics are fundamental principles that govern the behavior and interactions of energy and matter. These laws state that energy cannot be created or destroyed, but only transferred or converted between different forms. They also establish the concept of entropy, which is the measure of a system's disorder or randomness.

What are some common applications of thermodynamics calculation?

Thermodynamics calculation has a wide range of applications in various fields, including engineering, physics, chemistry, and biology. Some common applications include designing efficient engines and power plants, analyzing heat transfer in buildings and industrial processes, and predicting chemical reactions and phase transitions.

What is the difference between thermodynamics calculation and heat transfer?

Thermodynamics calculation and heat transfer are closely related concepts, but they are not the same. Thermodynamics calculation is a broader field that deals with the overall behavior of energy and matter in a system, while heat transfer specifically focuses on the transfer of thermal energy between different objects or systems.

What are the units of measurement used in thermodynamics calculation?

The most commonly used units in thermodynamics calculation are the SI units, which include joules for energy, kelvins for temperature, and pascals for pressure. Other units such as calories and BTUs may also be used in specific applications.

Similar threads

Replies
25
Views
2K
  • General Engineering
Replies
11
Views
2K
Replies
14
Views
2K
Replies
10
Views
2K
Replies
40
Views
3K
  • General Engineering
Replies
1
Views
1K
  • General Engineering
Replies
5
Views
1K
  • Engineering and Comp Sci Homework Help
Replies
14
Views
1K
  • General Engineering
Replies
7
Views
3K
Replies
2
Views
1K
Back
Top