Thread Subject: Modeling of condensation/evaporation process in simscaope with thermal blocks

Dear community,

I am trying to model a simple heat exchanging process that features a hot temperature source to simulate a condensating hot fluid and a cold working fluid that is going to be heated up.

Withing simscape I inserted one heat flow source, one temperature source with a convective heat transfer in between. Additionally there is a thermal mass to simulate the "warming up" of the cold water in the tubes.

However the temperature of the cold fluid exceeds the surface temperature of the condensate and this is theoretically not possible, since the fluid cannot get hotter than its heat source.

I uploaded the corresponding files to my profile in order to provide a firt draft.

Regards,
Stefan Smolik

"Stefan Smolik" <ssmolik@gmx.de> wrote in message <h58ghp$he2$1@fred.mathworks.com>...
> Dear community,
>
> I am trying to model a simple heat exchanging process that features a hot temperature source to simulate a condensating hot fluid and a cold working fluid that is going to be heated up.
>
> Withing simscape I inserted one heat flow source, one temperature source with a convective heat transfer in between. Additionally there is a thermal mass to simulate the "warming up" of the cold water in the tubes.
>
> However the temperature of the cold fluid exceeds the surface temperature of the condensate and this is theoretically not possible, since the fluid cannot get hotter than its heat source.
>
> I uploaded the corresponding files to my profile in order to provide a firt draft.
>
> Regards,
> Stefan Smolik

Hi,

I assume you are referring to the file you uploaded on the file exchange:
http://www.mathworks.com/matlabcentral/fileexchange/24918

You'll notice that I commented that the definition of the parameters is missing, e.g.:

Error evaluating parameter 'Value' in 'Thermal_HExchanger/Cooling Plate heat exchanger/"cold" fluid': Undefined function or variable 'm_dot'.

Can you provide the MATLAB code which defines those parameters?

Thanks,

Arnaud

"Arnaud Miege" <arnaud.miege@nospam.mathworks.co.uk> wrote in message
news:h5ru83$rue$1@fred.mathworks.com...
> "Stefan Smolik" <ssmolik@gmx.de> wrote in message
> <h58ghp$he2$1@fred.mathworks.com>...
>> Dear community,
>>
>> I am trying to model a simple heat exchanging process that features a hot
>> temperature source to simulate a condensating hot fluid and a cold
>> working fluid that is going to be heated up.
>>
>> Withing simscape I inserted one heat flow source, one temperature source
>> with a convective heat transfer in between. Additionally there is a
>> thermal mass to simulate the "warming up" of the cold water in the tubes.
>>
>> However the temperature of the cold fluid exceeds the surface temperature
>> of the condensate and this is theoretically not possible, since the fluid
>> cannot get hotter than its heat source.
>>
>> I uploaded the corresponding files to my profile in order to provide a
>> firt draft.
>>
>> Regards,
>> Stefan Smolik
>

I think that you need to remove the heat flow source. If you do and run the
model for long enough (50e7), the temperature of the cold fluid tends
towards the hot temperature of the surface. I think the heat flow is if you
were actively cooling/heating something, whereas here, it's just thermal
inertia that allows heat to be exchanged between the cold fluid and hot
surface. Note that the Simscape thermal blocks are designed to model thermal
effects in solids and non-flowing fluid systems. It is therefore not
recommended for things like heat exchanger design. For this would have to
create your own thermal hydraulics domain and associated blocks using the
Simscape language, so that could couple the thermal effects with the fluid
dynamics ones. Have a look at the following:

http://www.mathworks.com/products/demos/simscape/model_projector/index.html
http://www.mathworks.com/products/demos/simscape/Simscape_Demo_Language_Hydraulic_Orifice/
http://www.mathworks.com/company/events/webinars/wbnr31004.html

HTH,

Arnaud

"Arnaud Miege" <arnaud.miege@nospam.mathworks.co.uk> wrote in message
news:h5uqcg$ggc$1@fred.mathworks.com...
>
> "Arnaud Miege" <arnaud.miege@nospam.mathworks.co.uk> wrote in message
> news:h5ru83$rue$1@fred.mathworks.com...
>> "Stefan Smolik" <ssmolik@gmx.de> wrote in message
>> <h58ghp$he2$1@fred.mathworks.com>...
>>> Dear community,
>>>
>>> I am trying to model a simple heat exchanging process that features a
>>> hot temperature source to simulate a condensating hot fluid and a cold
>>> working fluid that is going to be heated up.
>>>
>>> Withing simscape I inserted one heat flow source, one temperature source
>>> with a convective heat transfer in between. Additionally there is a
>>> thermal mass to simulate the "warming up" of the cold water in the
>>> tubes.
>>>
>>> However the temperature of the cold fluid exceeds the surface
>>> temperature of the condensate and this is theoretically not possible,
>>> since the fluid cannot get hotter than its heat source.
>>>
>>> I uploaded the corresponding files to my profile in order to provide a
>>> firt draft.
>>>
>>> Regards,
>>> Stefan Smolik
>>
>
> I think that you need to remove the heat flow source. If you do and run
> the model for long enough (50e7), the temperature of the cold fluid tends
> towards the hot temperature of the surface. I think the heat flow is if
> you were actively cooling/heating something, whereas here, it's just
> thermal inertia that allows heat to be exchanged between the cold fluid
> and hot surface. Note that the Simscape thermal blocks are designed to
> model thermal effects in solids and non-flowing fluid systems. It is
> therefore not recommended for things like heat exchanger design. For this
> would have to create your own thermal hydraulics domain and associated
> blocks using the Simscape language, so that could couple the thermal
> effects with the fluid dynamics ones. Have a look at the following:
>
> http://www.mathworks.com/products/demos/simscape/model_projector/index.html
> http://www.mathworks.com/products/demos/simscape/Simscape_Demo_Language_Hydraulic_Orifice/
> http://www.mathworks.com/company/events/webinars/wbnr31004.html
>
> HTH,
>
> Arnaud
>

Actually, after thinking about it, you can leave the heat flow source to
represent the cold fluid stream, but I think you need to change the sign of
the constant block connected to it. With a positive sign, you are injecting
heat into the system, i.e. actually warming the fluid rather than cooling
it. If you change the sign of the constant block, you'll notice that the
temperature of the cold fluid actually drops with time, i.e. it gets colder.
I think this is because there is not enough heat exchanged with the hot
surface. If you multiply by 100 the heat transfer in your convection block
between the thermal mass of the fluid and the hot surface, you'll see that
the cold fluid temperature reaches that of the hot surface in approx. 6e6s.

HTH,

Arnaud