Relationship between pressure and flow is to achieve the optimum heat loss? 1

[MattJackson]

Hello All,

I have been asked to look into artificially cool a steel ‘chill’ within a sand mould. The chill by nature conducts heat out of the liquid casting aiding direction solidification. I have been asked to look into maintaining/prolonging the thermal differential between the chill and casting solidifying by using compressed air as the working fluid. I have fluid dynamics software that I can use to model this problem.

I am a mechanical engineer and have not done much thermo work since uni and am a bit rusty.

Could anyone explain to me the relationship between pressure and flow to achieve the optimum heat loss?

Many thanks in advance.

Matt

 

[willard3]

You will do better to hire an Engineer familiar with the problem.

 

[zekeman]

I think you are asking how to continuously remove heat from this "chill",
which is a steel jacket.
Please post a detailed diagram of the setup , including the sand mold ,so we can see the problem.

 

[rmw]

The relationship is this: Q = M(dot)*Cp* delta T. But also, Q = M(dot)*U*A*LMTD. The first is a heat in/heat out book keeping equation and he second is a function of the heat transfer coefficients and the terminal temperature differences.

So you need to know how much heat you need to remove, and calcualte the air flow that will accomplish that and figure the rate at which that heat transfers based on temperature differences, film coefficients of the heat transfer fluid flowing along the metal surfaces, etc. etc.

You could do this by a bunch of fancy calculations or hire it done as Willard suggests, or you oculd just do some testing and develop an empirical solution.

rmw

 

[MattJackson]

Many thanks everyone.

Zekeman i will post an image etc. when i have one.

rmw thanks, i did think it was something like that but wasnt sure. I'm guessing the LMTD is the log mean temp. difference? Is that something to do with the natural logs of the radius ratio's in the pipe etc?

Thanks.

 

[MattJackson]

Hello All,

Please see attached a 3D image of the chiller set-up.

The chiller is fed with air at ambiant temperature at a rate of 7.06 m^3/hr at 100 psi into the inlet and through the steel chiller.

The chiller that is manufactured from steel is used to cool the casting (steel) more quickly on the lower contact surface (to do with material properties but not relevent to my problem). The contact area between the chiller and casting is 0.305m x 0.407m (0.14335 m^2).

The casting loses heat to the sand and has a contact area of 1.65 m^2 and the sand loses heat to the surronding air.

Could someone assist me in calculating the thermal conductivity (k), surface heat transfer coefficients (h) and overall heat transfer coeeficients (U) for the various contacting surface so that i can input these into my CFD programme.

The idea is to show the thermal gradients with and without the steel chiller for the casting (no solidification processes are necessary).

Any help would be greatly appreciated.

Matt

 

[MortenA]

Matt,

Quite frankly i think that if you need detailed calculation you should go to a consultant. How are you going to explain yourself if something goes wrong (you to your boss after an epic failure of the chiller) "i talked to these guys on the internet, ok maybe not alked - it was more like typing, and then somebody who calledhimself "thebestengineer" said that i needed to...".

Best regards

Morten