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pratikmehta September 28, 2010 16:07

ice melting simulation
 
Hello Friends,

I am trying to perform a simulation for ice melting

Here is the Problem definition:

I have a aluminium hollow pipe ( 1mm thickness ) . Through this pipe water at 80 C is flowing at constant flow rate . Re number is about 20K
The ice deposition over this pipe is about 2mm thick .

My quest is to know how much time does it take for the ice at -5 C gets converted to water at 5 C . I just need to know when does water reach 5C.


What I have done so far:

I have got geometry and meshed it :).I have the fluid domain ( water )and solid domain ( Ice ) .I am using CFX 12.1v. Material in fluid domain is water & material in Ice domain is user created material as CHT solid & thermodynamic state as solid.

My doubts,,,
1) How should I treat the interface ??. Should I keep it as conservative interface flux as the boundary condition and should I create a thin wall of 1 mm aluminium ,so as to save my meshes to aviod the extra physical 1mm thickness of the pipe.

2) Variables like Density, Thermal conductivty & Sp heat capacity as all function of temperature. Regarding the thermal conductivity & density I have used step function CEL expression that will suitably feed in the right number at the existence of ice or water. My biggest worry is to specify Cp variation as the ice start to heat up from -5C .

I need to know how should I specify Cp that will consider the Cp of Ice from -5C to -1C approx 2kJ/KgK , then it must consider Cp as 166kJ/KgK frmo -1C to +1 C and later from 1C onwards Cp as 4kJ/KgK .

I tried to use the step function in order to get this variation but could not get it correct.

So how would you suggest me to go forward .


Thanks for your suggestions

Best regards
Pratik

10mmet21 February 29, 2012 05:41

Freezing of an ice cream
 
Dear all,

I am Working On an interesting M. Tech Project. Description is discussed bellow.

It is a Two phase problem in which convection takes place through air flowing outside and conduction in the ice cream. Further description is given bellow.

1 litter rectangular Ice cream packet is placed in air blast freezer.
Air is flowing at the velocity of 2.5 m/s. from one side of rectangular duct and leave at the other end of the freezer. It flows over the Rectangular ice cream box. The Temperature of an air is (-30 C)

Initial Temperature of an ice cream is (-4 C)
initial freezing temperature is (-5.6 C)
specific heat above freezing point is 3.22 kJ/Kg K and bellow freezing Point is 2.74Kj/kg K
latent heat of fusion is 204 kj/kg
density 550 kg/cubic meter
conductivity of unfrozen ice cream is 0.518 w/m K and frozen ice cream is 1.8203 w/m k

I have to find that what time will it take to reach the center temperature of an ice cream to (-18 C)

Air properties are available. heat transfer coefficient h=15 w/m2*K

conductivity of an ice cream box which is made up of paper can be taken as 0.05 w/m k. Thickness of wraper is 0.5 mm.

If any one has related tutorial of freezing then please send it to me or upload on the forum.

I wanted to plot graph of Temperature vs time as an Output.

Please Help me.

ashish1676 April 7, 2013 02:33

Quote:

Originally Posted by pratikmehta (Post 276991)
Hello Friends,

I am trying to perform a simulation for ice melting

Here is the Problem definition:

I have a aluminium hollow pipe ( 1mm thickness ) . Through this pipe water at 80 C is flowing at constant flow rate . Re number is about 20K
The ice deposition over this pipe is about 2mm thick .

My quest is to know how much time does it take for the ice at -5 C gets converted to water at 5 C . I just need to know when does water reach 5C.


What I have done so far:

I have got geometry and meshed it :).I have the fluid domain ( water )and solid domain ( Ice ) .I am using CFX 12.1v. Material in fluid domain is water & material in Ice domain is user created material as CHT solid & thermodynamic state as solid.

My doubts,,,
1) How should I treat the interface ??. Should I keep it as conservative interface flux as the boundary condition and should I create a thin wall of 1 mm aluminium ,so as to save my meshes to aviod the extra physical 1mm thickness of the pipe.

2) Variables like Density, Thermal conductivty & Sp heat capacity as all function of temperature. Regarding the thermal conductivity & density I have used step function CEL expression that will suitably feed in the right number at the existence of ice or water. My biggest worry is to specify Cp variation as the ice start to heat up from -5C .

I need to know how should I specify Cp that will consider the Cp of Ice from -5C to -1C approx 2kJ/KgK , then it must consider Cp as 166kJ/KgK frmo -1C to +1 C and later from 1C onwards Cp as 4kJ/KgK .

I tried to use the step function in order to get this variation but could not get it correct.

So how would you suggest me to go forward .


Thanks for your suggestions

Best regards
Pratik



Dear Pratik
how you define ice as solid because we can not set liquidus ,solidus temperature properties etc if we define it as fluid

vagantes April 17, 2013 09:52

Quote:

Originally Posted by pratikmehta (Post 276991)
Hello Friends,

I am trying to perform a simulation for ice melting

Here is the Problem definition:

I have a aluminium hollow pipe ( 1mm thickness ) . Through this pipe water at 80 C is flowing at constant flow rate . Re number is about 20K
The ice deposition over this pipe is about 2mm thick .

My quest is to know how much time does it take for the ice at -5 C gets converted to water at 5 C . I just need to know when does water reach 5C.

Hi Pratik,

if the only thing you wish to get is time needed for ice to be melted into water and this amount of water to be heated up to 5C, then I would suggest you to use FLUENT Pressure Based Solver instead of CFX.
There, you can choose to solve only Energy (heat) equation and pose boundary conditions that would imitate heat exchange between the fluid in the pipe and ice (i.e., you consider only heat exchange problem, no fluids flows). You can read more in Chapter 17 of FLUENT Theory Guide (Solidification and Melting).

I have successfully applied this FLUENT PBS for the transient thermal phase transition problem, but I had to define User-Defined functions for heat capacity and thermal conductivity dependences on temperature (that was probably the most challenging part:))

best regards!


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