The Cooling Power of Wind: Reducing Car Hood Temps at 55 MPH

Click For Summary

Discussion Overview

The discussion revolves around the cooling effect of wind on the temperature of a car hood when driving at 55 MPH, particularly starting from an initial temperature of 106 degrees. Participants explore the theoretical and practical aspects of temperature changes due to airflow, considering various influencing factors.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • Some participants argue that there are too many variables to provide a definitive answer without empirical testing, suggesting the use of a thermometer for accurate measurement.
  • Others highlight that the initial temperature of the hood could be influenced by multiple factors, such as engine heat or solar radiation, complicating the analysis.
  • A participant proposes a thought experiment involving a metal sheet and a fan to illustrate how airflow can affect temperature, emphasizing that the cooling effect depends on the temperature difference between the air and the metal.
  • It is noted that if the air is cooler than the metal, it will remove heat, while warmer air will add heat, with the rate of heat exchange being dependent on various factors including humidity and air speed.
  • Some participants express uncertainty about whether the hood temperature at 55 MPH would be significantly lower than at rest, with one suggesting that the engine's heat might still affect the hood temperature during driving.
  • There is a discussion about whether the temperature is in Celsius or Fahrenheit, with concerns raised about the implications of a 106-degree Celsius reading.

Areas of Agreement / Disagreement

Participants generally agree that multiple variables affect the cooling of the hood, and no consensus is reached on the exact impact of wind at 55 MPH on the hood temperature. The discussion remains unresolved regarding the specific cooling effect and the role of the engine heat during driving.

Contextual Notes

Limitations include the dependence on various assumptions such as the initial heat source, ambient conditions, and the duration of driving, which are not fully defined or quantified in the discussion.

JMcGoo
Messages
2
Reaction score
0
If the hood of my at rest car is 106 degrees and I drive at 55 MPH, how much is the hood temparature reduced by the wind so created?
 
Science news on Phys.org
Not even close to enough information to answer this theoretically. By far the easiest way to get this info would be to put a thermometer on the hood of your car and test it out.
 
What Moduspwnd said. Way too many variables to answer. It might even depend on why your hood reaches 106C with the car stationary (eg is it the heat from the engine or the sun?). If you drive for a long time at speed the hood temperature could well fall to air temperature because cooling air goes under as well as over the hood. So the length of time you spend driving may/will effect the results.
 
Sorry if I made the question too full of variables. Take a sheet of metal and place it on the grass in the sun. Blow a fan on it. Assuming the ambiant temp is unchanged, with no other variables such as moisture, is the temp of the metal effected downward by the breeze from the fan?
 
JMcGoo said:
Sorry if I made the question too full of variables. Take a sheet of metal and place it on the grass in the sun. Blow a fan on it. Assuming the ambiant temp is unchanged, with no other variables such as moisture, is the temp of the metal effected downward by the breeze from the fan?

If the air is cooler than the metal, it will tend to remove heat from (cool) the metal as it flows by; and to add heat if it is warmer than the metal. The actual rate of heat exchange will depend on many variables: humidity, the intensity of the sun and the emissivity of the metal, the air speed, the size of the temperature difference, and lots more.

Google for "IR temp gun" - twenty dollars US will buy you the tool you need to answer your question.
 
You said that the hood temperature at rest was 106 degrees. Does it not occur to you that the heat of the engine, driving at 55 mph, will heat the hood?
 
JMcGoo said:
Sorry if I made the question too full of variables. Take a sheet of metal and place it on the grass in the sun. Blow a fan on it. Assuming the ambiant temp is unchanged, with no other variables such as moisture, is the temp of the metal effected downward by the breeze from the fan?

If the air is colder than the metal then heat will be conducted away into the air. The power flowing between metal and air will depend on the thermal resistance between metal and air and the temperature difference between them.

If you blow air over the metal the temperature difference (edit: "Gradient" is a better word) will be increased because the layer of air next to the metal will be colder. This will increase the rate at which power flows from metal to air.

What happens to the temperature of the metal depends on the balance of power going into and out of the metal. Presumably a heat source made the metal hot in the first place? If the power supplied by that heat source is greater than that lost to the air then the temperature will rise. If less then it will fall.

So if the heat source (the sun?) still exists the fan may or may not cause the metal to get colder. All you can say is that it won't be as hot as it would have been without the fan.

PS: Car radiators and the heat sinks in a computer have fans for a reason.
 
CWatters said:
What Moduspwnd said. Way too many variables to answer. It might even depend on why your hood reaches 106C with the car stationary (eg is it the heat from the engine or the sun?). If you drive for a long time at speed the hood temperature could well fall to air temperature because cooling air goes under as well as over the hood. So the length of time you spend driving may/will effect the results.

It's not clear if the hood temp is 106 F or 106 C. If the latter, I would expect serious burns from touching it.
 
HallsofIvy said:
You said that the hood temperature at rest was 106 degrees. Does it not occur to you that the heat of the engine, driving at 55 mph, will heat the hood?
Heat it MORE than sitting still at idle? It won't: a car engine produces only a moderate amount of power at cruise and cools itself vastly better.

So at 55mph, I'd expect the hood temperature to be only a little above ambient.
 

Similar threads

High School Are wind farms stealing the cooling capacity of the wind?
  • · Replies 4 ·
Replies
4
Views
3K
Undergrad How Much Energy is Dissipated When Braking from 75 to 55 mph?
  • · Replies 10 ·
Replies
10
Views
2K
Undergrad Cooling Time for Air Conditioning
  • · Replies 5 ·
Replies
5
Views
2K
Ideas for high school wind tunnel?
  • · Replies 14 ·
Replies
14
Views
3K
VFD for powering a car lift
  • · Replies 31 ·
2
Replies
31
Views
3K
High School Does the Bernouli Effect Work On Cars?
  • · Replies 8 ·
Replies
8
Views
3K
High School Energy Harvesting: Calculating kWh from Motorway Traffic
  • · Replies 4 ·
Replies
4
Views
2K
Automotive Wind Turbine on the grill of the car
  • · Replies 26 ·
Replies
26
Views
14K
Maximum power from a transformer
  • · Replies 8 ·
Replies
8
Views
3K
Undergrad Daytime: Solar->Ice-> Nighttime:Air conditioning
  • · Replies 6 ·
Replies
6
Views
2K