Discussion Closed This discussion was created more than 6 months ago and has been closed. To start a new discussion with a link back to this one, click here.
Convective Heat Transfer
Posted 2 ott 2013, 11:20 GMT-4 4 Replies
Please login with a confirmed email address before reporting spam
Dear Friends,
plz have a look at my model.
I am having a horizontal cylinder filled with Argon and an offset heater at center. I have modeled heat transfer only by convection. The gas gets heated and moves up which is heating the cylinder wall. The gas temperature is very high in the vicinity of the wall but the wall temperature is very less. Ofcourse, the wall temperature is very much dependent on the thermal conductivity of the wall, but still i suspect the temperature of the wall. whether there is anything wrong in the modeling?
Warm Regards
plz have a look at my model.
I am having a horizontal cylinder filled with Argon and an offset heater at center. I have modeled heat transfer only by convection. The gas gets heated and moves up which is heating the cylinder wall. The gas temperature is very high in the vicinity of the wall but the wall temperature is very less. Ofcourse, the wall temperature is very much dependent on the thermal conductivity of the wall, but still i suspect the temperature of the wall. whether there is anything wrong in the modeling?
Warm Regards
4 Replies Last Post 3 ott 2013, 00:03 GMT-4
Please login with a confirmed email address before reporting spam
Posted:
1 decade ago
Hi,
Yes, temperature should be higher but you have forgot radiation from you model. Natural convection heat transfer isn't very effective method but if you add radiation situation will change. In these temperatures radiation plays major role in heat transfer.
Best regards
Tero Hietanen
Yes, temperature should be higher but you have forgot radiation from you model. Natural convection heat transfer isn't very effective method but if you add radiation situation will change. In these temperatures radiation plays major role in heat transfer.
Best regards
Tero Hietanen
Please login with a confirmed email address before reporting spam
Posted:
1 decade ago
Seems like your model is correct. I can't really comment on the quantitative importance of radiation as it has been pointed out. Qualitatively radiation will increase the heat exchange between inner and outer parts, so it will affect the kinetics of the system (how long it takes to reach one temperature) but not the general behavior : if you expect the temperature of the wall increase more rapidly, radiation will help.
This is a case where there is no stationary solution : the temperature will raise up towards infinity (at least in the model -I doubt this can be true in the real life...) At the same time, you can see that the average fluid velocity reaches a maximum and then decreases, because the temperature of the system gets more homogeneous : the difference of temperature between the heater and the external part decreases due to the action of the convection, so does the Archimede's force (estimate your Grashof number, this is the relevant non dimensional number regarding convection).
You might want to introduce a heat loss by convection (something like h*(T_inf - T) = convective heat flux) instead of a thermal insulation at external boundaries. In such case the system will reach an equilibrium temperature and the convection will be of greater importance. I suspect that this would be closer to a real device but I might be wrong : you should know this better than anyone!
For those that are interested in a similar model, see the "light bulb", in the heat transfer module.
Good luck,
Eric
This is a case where there is no stationary solution : the temperature will raise up towards infinity (at least in the model -I doubt this can be true in the real life...) At the same time, you can see that the average fluid velocity reaches a maximum and then decreases, because the temperature of the system gets more homogeneous : the difference of temperature between the heater and the external part decreases due to the action of the convection, so does the Archimede's force (estimate your Grashof number, this is the relevant non dimensional number regarding convection).
You might want to introduce a heat loss by convection (something like h*(T_inf - T) = convective heat flux) instead of a thermal insulation at external boundaries. In such case the system will reach an equilibrium temperature and the convection will be of greater importance. I suspect that this would be closer to a real device but I might be wrong : you should know this better than anyone!
For those that are interested in a similar model, see the "light bulb", in the heat transfer module.
Good luck,
Eric
Please login with a confirmed email address before reporting spam
Posted:
1 decade ago
Thank you very much Tero Hietanen for the comments.
Yeah you are right that radiation should be included. I have done that also. Actually in this model i just wanted to see the heat transfer by convection only which seems to be correct by the discussions here.
Thank you.
Yeah you are right that radiation should be included. I have done that also. Actually in this model i just wanted to see the heat transfer by convection only which seems to be correct by the discussions here.
Thank you.
Please login with a confirmed email address before reporting spam
Posted:
1 decade ago
Seems like your model is correct. I can't really comment on the quantitative importance of radiation as it has been pointed out. Qualitatively radiation will increase the heat exchange between inner and outer parts, so it will affect the kinetics of the system (how long it takes to reach one temperature) but not the general behavior : if you expect the temperature of the wall increase more rapidly, radiation will help.
This is a case where there is no stationary solution : the temperature will raise up towards infinity (at least in the model -I doubt this can be true in the real life...) At the same time, you can see that the average fluid velocity reaches a maximum and then decreases, because the temperature of the system gets more homogeneous : the difference of temperature between the heater and the external part decreases due to the action of the convection, so does the Archimede's force (estimate your Grashof number, this is the relevant non dimensional number regarding convection).
You might want to introduce a heat loss by convection (something like h*(T_inf - T) = convective heat flux) instead of a thermal insulation at external boundaries. In such case the system will reach an equilibrium temperature and the convection will be of greater importance. I suspect that this would be closer to a real device but I might be wrong : you should know this better than anyone!
For those that are interested in a similar model, see the "light bulb", in the heat transfer module.
Good luck,
Eric
Thank you Eric, your suggestions and comments are really valuable. I also thank you for referring me to "light bulb" model.
Warm Regards