Calculating Exit Temperature of a Fan Given its CFM and Blade Size

Click For Summary

Discussion Overview

The discussion revolves around calculating the exit temperature of air from a fan given its CFM (Cubic Feet per Minute), blade size, and other conditions. Participants explore the factors influencing exit temperature, including environmental conditions and heat sources, while considering theoretical and practical implications.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant questions whether the given conditions (CFM, blade diameter, inlet temperature) are sufficient to determine exit temperature, suggesting that additional factors like atmospheric pressure may need to be considered.
  • Another participant notes that common understanding suggests a fan would lower exit temperature, but later clarifies that the cooling effect felt by a person is due to moisture evaporation rather than actual temperature reduction.
  • A participant presents a scenario involving an outside temperature of 15°C and an inside environment with a heater and fan, asking for the resulting inside temperature but is informed that heat transfer through walls must also be accounted for.
  • One reply indicates that the temperature difference through the fan is approximately 15°F, but does not provide a definitive calculation for the exit temperature.
  • A later post describes a specific setup involving a fan blowing over a finned tube heater and expresses concern about finding the exit temperature, framing it as a forced convection problem but indicating difficulty in finding relevant information to solve it.

Areas of Agreement / Disagreement

Participants do not reach a consensus on how to calculate the exit temperature, with multiple competing views on the factors that need to be considered and the complexity of the problem remaining unresolved.

Contextual Notes

Participants acknowledge the need to consider additional factors such as heat transfer through walls and the specifics of forced convection, but do not resolve these complexities or provide a unified approach to the calculations.

math111
Messages
42
Reaction score
0
If I have a typical Fan with a given CFM or even the outside diameter of the blade can I find the exIting temperature? Is there a formula out there to determine the exit temp.

Assumptions:
The fan is located in the middle of a room so we are not mixing in different temperatures.

Given:
CFM, Dia of the blade, Inlet Temp.

Finding:
Exit Temperature

My thoughts.
1. Are my given conditions enough or will more factors be involved like pressure(atmpoheric[14.696 psi], etc..
2. Common sense would think it would make the exit temp lower due to air being blow when a fan cools you down when standing next to it.

Thanks.
 
Last edited:
Engineering news on Phys.org
math111 said:
If I have a typical Fan with a given CFM or even the outside diameter of the blade can I find the exIting temperature? Is there a formula out there to determine the exit temp.

Assumptions:
The fan is located in the middle of a room so we are not mixing in different temperatures.

Given:
CFM, Dia of the blade, Inlet Temp.

Finding:
Exit Temperature

My thoughts.
1. Are my given conditions enough or will more factors be involved like pressure(atmpoheric[14.696 psi], etc..
2. Common sense would think it would make the exit temp lower due to air being blow when a fan cools you down when standing next to it.

Thanks.


By doing some more research I found out the Fan will not cool a person but cause a affect by only drying/evaporate moisture from the persons skin making it feel cooler called the brush temperature. Also it says it might raise the temp of the room because heat rises and if its a ceiling fan it will blow the heat downward.
 
My problem is..

1. If I have an outside environment of 15 C
2. Inside environment of 30 Ft Dia. Circle = 2826 SF
3. Heater 4Kw with a Fan 860 CFM

what is the inside temperature going to be with this heater running.
 
Last edited:
You can't calculate the inside temperature without the heat transfer through the walls. The delta-T through the fan is 15 F, though...
 
ok some updates:

I have a fan going a Fan at 750 CFM blowing straight at a Finned Tube with a S/S enclosure with Holes in it directly in front of it.

'FAN'(750CFM)---> blowing over 'Finned Tube'(Fins and Tube@4kW)-->Blowing out of a S/S Heater guard with holes in it. I nned to find the exit temperature is my concern..?

It seems like a forced convection problem but I am not finidng the right information to solve it.
 

Similar threads

Underground pump vault airflow considerations
  • · Replies 15 ·
Replies
15
Views
4K
How Can I Determine the Maximum Flow Rate for a Heat Exchanger Cooling Oil?
  • · Replies 1 ·
Replies
1
Views
2K
Estimating humidifier evaporative capacities
  • · Replies 1 ·
Replies
1
Views
3K
Undergrad Calculating Heat in Exhaust Pipes: Internal Temperature
  • · Replies 1 ·
Replies
1
Views
2K
Undergrad Atmospheric humidity for water production.
  • · Replies 3 ·
Replies
3
Views
3K
Graduate Thermo: Calculating the temperature drop from gas leaving a system
  • · Replies 11 ·
Replies
11
Views
10K
Calculating Pressure Loss in Compressible Fluid Flow: A Case Study
  • · Replies 9 ·
Replies
9
Views
4K
Undergrad I want to heat up my room, would a fan towards the radiator work?
  • · Replies 12 ·
Replies
12
Views
22K
High School Infrared Detectors & The 2nd Law of Thermodynamics
  • · Replies 152 ·
6
Replies
152
Views
12K
Problem set with air conditioners and thermodynamics
  • · Replies 5 ·
Replies
5
Views
3K