Search on your website doesn't work fyi It times out. -- also do you have everything backed up on a different platform in case RUclips goes down? We want to make sure we never lose all your videos.
I absolutely love your videos and clear explanations. Just one question, why do you use this odd number for h when h = 12*square root(v) where h=thermal transmittance in W/(m²K) and v= airspeed in m/s? When using this, the formula would become more simple and students would actually be able to find the other values of h for other fluids and real world problems.
When it comes to convection, many of these constants were experimentally derived and are continuously updates as new tests show slightly different responses. There is no exact answer, but good approximations.
Thank you that was such a helpful video. If you have the time any hints on answering this question? Home heating is a significant cost for Tasmanian householders. Describe some methods people can use in order to deuce their power bill while maintaining adequate heating, explaining the physical principles behind them. Thank you for your time
Hannah, The old fashion "swamp cooler". Hang rags or towels above a bucket of water with the bottom of the towels submerged in the water. The water will wet the whole towel because of capillary action. Then blow air across the wet towels with a fan. The water will evaporate cooling the air that is blown across the wet towels. That is how people used to stay cool before they had air conditioners.
I want to know if energy from the air (assuming the air is warmer) will transfer into the wall and what equation to use to solve the energy transfer. I'm currently using conduction (Q = kAt) in my model and something isn't right. I've successfully modeled a runaway greenhouse :P
Heat always flows from hot to cold. Since it is colder outside we know the direction of the heat flow. To find out the magnitude fo the heat flow (per unit time) we only need to know the magnitude of the change in temperature.
Convection exists everywhere. What you need is a difference in temperature of the fluid which results in a difference in density, which will cause forces to move the fluid. If the temperature of an object is lower than the temperature of the air, that will also cause convection.
Smail Waltit Just like with any other equation in physics, they give the constant the correct units so that the units work out in the end. Look at Newton's equation of gravity.
How comparable is the Conv. Coeff. you use to the equation h = [ -kf * dT/dy |y=0 ] / [Ts - T∞] from Bergman's Heat transfer book? Mostly i'm wondering if the 1.77*Delta T^0.25 is only for air or could be used roughly for other mediums. Thank you for creating these videos, they have been very helpful for review.
+Kehan Lykaios Note that the convection coefficients depend greatly on a number of factors. They do vary between substances, especially between a gas and a liquid. They also depend on the geometry of the surface and the velocity of the transfer fluid and it also depends whether or not the fluid is forced. Thus the number used is not a "fixed" number.
h is the heat transmission coefficient for heat transfer by convection. That equation is based upon a model that was developed about 70 years ago and still offers a good approximation. We are currently working on a much more detailed analysis and presentation of heat transfer with convection that will show much more information on these models.
Search on your website doesn't work fyi It times out. -- also do you have everything backed up on a different platform in case RUclips goes down? We want to make sure we never lose all your videos.
Yes, something is wrong with the website and we haven't had time to fix it. We do have our videos backed up at home. Thanks for the tip.
I absolutely love your videos and clear explanations. Just one question, why do you use this odd number for h when h = 12*square root(v) where h=thermal transmittance in W/(m²K) and v= airspeed in m/s? When using this, the formula would become more simple and students would actually be able to find the other values of h for other fluids and real world problems.
When it comes to convection, many of these constants were experimentally derived and are continuously updates as new tests show slightly different responses. There is no exact answer, but good approximations.
Thanks. awesome lectures!
thank you
Thank you that was such a helpful video. If you have the time any hints on answering this question?
Home heating is a significant cost for Tasmanian householders. Describe some methods people can use in order to deuce their power bill while maintaining adequate heating, explaining the physical principles behind them.
Thank you for your time
Hannah,
The old fashion "swamp cooler".
Hang rags or towels above a bucket of water with the bottom of the towels submerged in the water. The water will wet the whole towel because of capillary action.
Then blow air across the wet towels with a fan. The water will evaporate cooling the air that is blown across the wet towels. That is how people used to stay cool before they had air conditioners.
Do you still use the convection equation if the air is warmer than the wall?
+Kevron Rees That depends. What question are you trying to answer?
I want to know if energy from the air (assuming the air is warmer) will transfer into the wall and what equation to use to solve the energy transfer. I'm currently using conduction (Q = kAt) in my model and something isn't right. I've successfully modeled a runaway greenhouse :P
The 1.77, where it came from?
It is a constant typically found in an engineering handbook. (I forgot where we got the number from, but we often use the engineering handbook.)
sir where did you get the 1 that you added on the 1/4 power that became 5/4?
We substituted h = 1.77 (delta T)^(1/4)
Michel van Biezen why didn't you do the 5/4 on the horizontal convection video
Everyone asked a question on that video so why not me? Why delta T is not negative?
Thank you both
Heat always flows from hot to cold. Since it is colder outside we know the direction of the heat flow. To find out the magnitude fo the heat flow (per unit time) we only need to know the magnitude of the change in temperature.
what if the temperature of air is higher,would the temperature be transfered through Conduction?
Convection exists everywhere. What you need is a difference in temperature of the fluid which results in a difference in density, which will cause forces to move the fluid. If the temperature of an object is lower than the temperature of the air, that will also cause convection.
Michel van Biezen Thank you sir
hello Mr Michel I cannot get to make the dimensions of the equation accurate. How can power be compatible with Air"T5/4 ?
Smail Waltit
Just like with any other equation in physics, they give the constant the correct units so that the units work out in the end. Look at Newton's equation of gravity.
How comparable is the Conv. Coeff. you use to the equation h = [ -kf * dT/dy |y=0 ] / [Ts - T∞] from Bergman's Heat transfer book?
Mostly i'm wondering if the 1.77*Delta T^0.25 is only for air or could be used roughly for other mediums.
Thank you for creating these videos, they have been very helpful for review.
+Kehan Lykaios Note that the convection coefficients depend greatly on a number of factors. They do vary between substances, especially between a gas and a liquid. They also depend on the geometry of the surface and the velocity of the transfer fluid and it also depends whether or not the fluid is forced. Thus the number used is not a "fixed" number.
Sir, would this explain how a hairdryer works? Is it convection or radiation?
A hair dryer uses convection to transfer heat from the dryer to the hair
is 1 W/mK equals with 1 J/s.m.c ? fast respon please
1 W = 1 J / sec 1 K degree = 1 C degree
great videos :D
Pleaa tell me! what is h mean? Why h = 1.77.(deltaT)1/4 ????
h is the heat transmission coefficient for heat transfer by convection. That equation is based upon a model that was developed about 70 years ago and still offers a good approximation. We are currently working on a much more detailed analysis and presentation of heat transfer with convection that will show much more information on these models.