Measuring the h conv from velocity not the same as that he gave

In summary, the conversation discussed determining the heat loss per square meter of skin surface due to convection at a temperature of -40 degrees Celsius and moderate wind conditions. The calculated value was 660 kcal/hr*m^2, but there was a discrepancy in the convective heat transfer coefficient used. It was determined that the equation hcov= 10.45 - v + 10√v could be used for velocities between 2 to 20 m/s. This information can be applied to future questions and illustrates the importance of understanding the variables involved in calculations.
  • #1
Manaf12
2
0

Homework Statement


Determine the heat loss per square meter of skin surface due to convection at -40degreeC in moderate wind (0.5 m/s, Kc=10 Kcal/m2-hr-degreeC), assuming that the skin temperature is 26degreeC.

Homework Equations


hcov= 10.45 - v + 10√v
ΔQ/Δt = A hconv (Tskin - Tair)

The Attempt at a Solution


ΔQ/Δt/A= 10 x (26+40)
=660 kcal/hr*m^2

NOTE: i think it is wrong because when i measure hconv from the velocity =17≠10
 
Physics news on Phys.org
  • #2
Well, there are a couple of ways of looking at this. First, convective heat transfer coefficients are dependent on so many variables that in this complex situation you can't expect a simple calculation to be very good. His made up number is as likely to be right as yours. Second, made up problems often have made up numbers. You've undoubtedly calculated the acceleration of boxes sliding down ramps with completely made up coefficients of friction, and a hundred other similar examples. That didn't bother you then, why should this bother you now? Third, his number is in the ballpark and it is 10 which makes the calculation simple. Since he is just making this up and he can't say very accurately what the true number might be, give him credit for making a convenient choice. He could have made up a number with eighteen digits of precision. That wouldn't have illustrated the concept any better.
 
  • #3
hey, thank you for the response, I found after a long period of searching that if the velocity between 2 to 20 m/s we can calculate the hconv from this hcov= 10.45 - v + 10√v
and from this question I found when I can use the equation above that will help in other questions , always simple questions helps

Thank you very much
 

FAQ: Measuring the h conv from velocity not the same as that he gave

What is "Measuring the h conv from velocity"?

"Measuring the h conv from velocity" refers to the process of calculating the convective heat transfer coefficient (h conv) using the flow velocity of a fluid. This is done in order to determine the rate of heat transfer between a solid surface and the surrounding fluid.

Why is measuring h conv from velocity not the same as the value given?

The value of h conv given is typically an average or a theoretical value, while measuring h conv from velocity takes into account the specific conditions and properties of the fluid and surface being studied. This can result in a different value, as it is a more accurate representation of the actual heat transfer taking place.

What factors can affect the accuracy of measuring h conv from velocity?

The accuracy of measuring h conv from velocity can be affected by factors such as the geometry and surface roughness of the solid surface, the properties and behavior of the fluid, and the experimental setup and measurement techniques used.

How is h conv calculated from velocity?

The h conv value is calculated using the formula h conv = (q/AΔT), where q is the heat transfer rate, A is the surface area, and ΔT is the temperature difference between the solid surface and the fluid. The flow velocity is used to determine the heat transfer rate, which is then used in the formula to calculate h conv.

What are the advantages of measuring h conv from velocity?

Measuring h conv from velocity allows for a more accurate and specific determination of the convective heat transfer coefficient, as it takes into account the unique conditions of the experiment. This can provide valuable insights and data for further research and applications in various industries such as engineering and environmental science.

Similar threads

Heat transfer from body through layers, using h, T, d, A
Replies
1
Views
2K
Meteor impact - Heat vaporization and capacity
Replies
4
Views
2K
How calculate the Heat flux requiered to evaporate sub cool water
Replies
1
Views
2K
How Does Wind Speed Affect Perceived Temperature and Heat Transfer?
Replies
4
Views
2K
Velocity exiting Heat Exchanger
Replies
2
Views
1K
Heat transfer and Fluid Flow Struggling Problems
Replies
25
Views
4K
Heat transfer - Transient state involving a solid and a surface
Replies
1
Views
2K

Hot Threads

Recent Insights

Back
Top