the basics of design

[mark101]

hi everyone,

I have been working as a refrigeration engineer and service manager and have now been given the job of helping to developing new products for customers.

but when prototyping new units i really need to be able to understand how to calculate what load is required and then be able to calculate the size/performance of each of the major working parts, up to now i have been using my knowledge of refrigeration to try different sized evaporators, condensers etc but this can be time consuming and if the prototype does not function efficently i don't how to fix it without putting larger components in but this then becomes very much trial and error.

i feel that i really need to approach this more scientifically, so i was wondering if anyone could suggest any useful websites/books and/or courses in the basics of design to help me understand better, this way i can (hopefully) source the right size components before i begin building the unit

any help you could give me would be gratefully appreciated

thanks

Mark

[Samarjit Sen]

You have approached the correct place. Wait and you will get lot of good guidance from some of the experts. Could you be a bit more specific as to what sort of assitance are required.

If you browse through the Forum, you will get a lot of informations.

[mark101]

sure, thanks for your post

i wrote these questions out for myself so that i could quantify what i really needed to know, the unit i worked on last was an open fronted bottle cooler which i had some eventual success with, but it was just a case of adding different componenets to see what worked and what didn't. at the moment i am working on a blast chiller which needs to cool bottled beers quickly.

the questions below are for the blast chiller i am currently working on

is there a way to calculate the cooling load required? How do I then calculate the size of the evaporator required?

I believe that when deciding on the components in a unit the evaporator should be your my first consideration, after this how do I calculate what size and/or specification the compressor, capillary and condenser should be?

What is the optimum placement position of the evaporators inside the unit? (i.e. either side, on the back wall or flat to the ceiling) what is the optimum placement position of the axial fans inside the unit and how many should be used (as the heat generated by these fans is a consideration in the load calculations)

I need to learn how to calculate the above myself, where can I get this information from/which course can I go on?

many thanks

Mark

[Samarjit Sen]

Hi mark101,

What you require is a bottle cooler. First thing is to know as to how many bottles you propose to chill. Each bottle would be about 1 liter size.

What is the incoming temperature of the beer and what is the temperature required. The time required to pull down the temperature.

If you can give the above informations then I can tell you as to how to go about it.

[US Iceman]

...where can I get this information from/which course can I go on?

Engineering College. Everyone of the questions you have asked about will take a long discussion. In most manufacturing companies what you want to do is performed by product development teams.

You are on the right track though.

You always start with the cooling load requirements.

Then you start to select components to meet the cooling load.

If you have an open display counter you have things such as air curtains so this is a critical aspect to design for. What you might try to do is search the web for other manufacturers and see what they are doing as a starting point.

[mark101]

hi, i am grateful with your help with this

i need to chill 48 bottles of 330ml beer with a product temp of 25 degrees down to a product temp of 2 degrees in 30 minutes

thanks

Mark

[Samarjit Sen]

To chill 48 bottles of beer from 30 Deg. C to 2 Deg. C, you do not need a blast chiller. What you require is a simple chest type bottle coolers or a vertical bottle cooler.

If you need the load for this, I can work out and let you know.

[mark101]

thankyou very much for your offer but this is important project, so i have had to have calculations done for me, this is what they have come up with

The simple heat load calculation for beer in bottles is as follows:

Heat load (kW) = mass (kg) x specific heat capacity (kJ/kg K) x temp change (K) / time (seconds)

I have treated the beer as water (not much difference when it comes to heat load!)

Heat load = 15.84 kg x 4.18 kJ/kg K x 23 / 30 x 60 = 0.84 kW.

This sounds about right (it is exactly the same as if you were heating that amount of water (15.84 litre = 15.84 kg) from 2 to 25degC in 30 minutes).

For the glass bottles:

Heat load = 14.4 kg x 0.84 x 23 / 30 x 60 = 0.15 kW

Total heat load = 0.84 + 0.15 kW = 0.99 kW to reduce the temperature of 48 bottles of beer from 25 to 2degC in 30 minutes.

This is the heat load on the cooling system of just the 48 bottles and beer.

You need to add the fan motor power to this as the cooling system also needs to remove that heat




from this info supplied how do i now spec an evaporator?

thanks Mark

[fridg]

Have a look at some of the specifications of cabinets at this website , it should get you started.

www.tylerrefrigeration.com