Designing domestic mini fridge

[irafi]

Hi

I need to calculate the rough design point for a domestic mini fridge. I have calculated the cooling requirement to be 400W, the evaporator temperature of -1C and a condenser temperature no higher than 50C. So far I have just done hand calculations to determine the compressor work required, condenser capacity, mass flow rate and the pressure ratio as well as the COP. How would i use these values to find suitable compressors and evaporator. I was so far been looking at the stated cooling loads on the compressor manufactures datasheets and matching them to my calculated values.

I have assumed a super heat of 10C in my calculations as the system will be using a TEV as a throttling device.
How would I calculate the sub cooling of such a system.

The refrigerant has to be non-flammable aswell as have a low GWP. I have been looking at R-415a and R-513a as my refrigerants.

The minifridge is designed to keep the cavity temperature at either 4C or -18C. The cooling load at 4C is 400W. The cooling load at -18C can be lower.

And does anyone know of any components they would recommend? size and weight is the main limiting factors.

I do not mind sacrificing some efficiency if it means a reduction in mass or size.

 

[berkshire]

For miniature fridge applications, these are good people to talk to :

https://www.aspencompressor.com/company

B.E.

You are judged not by what you know, but by what you can do.

 

[irafi]

How would you calculate the charge required from the mass flow rate?

I would assume you would need to know the dimensions of the piping of the system etc, but I have not gotten that far into designing the product yet.

I am thinking of using R-1234yf, but that has a maximum charge limit.

 

[berkshire]

You have to calculate the total volume of the system including piping, condenser, evaporator, receiver and compresser volume. You may have to do some trial and error on initial charge of your prototype.
B.E.

You are judged not by what you know, but by what you can do.

 

[irafi]

Once I have found the total system volume would I just use mass flow rate=rho*A*u with rho being the critical density of the refrigerator? or is there a more elegant solution? Sorry for asking such simple questions. If this is a trivial solution, would appreciate it if you could direct me to better sources.

This is my first job out of college.

 

[berkshire]

You could look at the,

https://en.wikipedia.org/wiki/Darcy–Weisbach_equation

.
B.E.

You are judged not by what you know, but by what you can do.

 

[IRstuff]

The cooling load at -18C can be lower.

This does not compute. Typical load is dependent on the delta temperature between ambient and the internal temperature. If the internal temperature is cooler, then the load must be higher, not lower, than that of a 4C interior

TTFN (ta ta for now)
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[irafi]

I meant to say, a cooling load of 380W at 4C is the design point for the refrigerator.

But the refrigerator must be capable of pulling down to -18C

 

[IRstuff]

Then, the cooling load at -18C is going to be larger, so sizing it for 4C likely won't get you down to -18C

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

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