Radiation Barrier Question

[gilberts]

I am building a carrier design to keep food hot. I have a chamber made with food grade urethane FDA approved, wall thickness ¼”. Around and on the outside I want to wrap a material that would serve as “radiation barrier”.
Any suggestion as the most effective and low cost material to use?
I have been successful with Reflective Aluminum Foil Insulation.
The outside shell will be another 1” blow molded urethane.
The objective is to keep the most heat as possible inside the chamber.

 

[dvd]

Radiation barriers need to "see" the hot object in order to reflect the radiation. Having a urethane interior will not reflect the radiant energy, the urethane will warm up and store energy, this in turn will be conducted toward the outside. If you could get a shiny surface on the inside it would be better. Short of that it would be best to use a good quality insulation on the outside of your unit.

 

[IRstuff]

1/4" of urethane just doesn't sound like it's going to cut the mustard. But, how long do you need to keep something hot? And how hot do you need to keep it?

A more effective system would be aluminum foil on the inside, 1/8" urethane, 1/4" styrofoam or other expanded foam, 1/8" urethane. The foam has only about 1/10 the thermal conductivity of the denser materials, so 1/4" is equivalent to about 2.5" of the denser material.

TTFN

FAQ731-376

 

[gilberts]

This is how it works: I preheat a casserole dish to 300 degrees and place the freshly prepared hot food in it, then insert the dish in the chamber and quickly close the door. I want the food to be still over 150 degrees after two hours.
I must have the carrier approved NSF to be commercialized.
Because of the low cost budget to start with until the concept is proved to work, I have access to a local urethane factory who is willing to work with me.
That's why the urethane chamber.

I have done numerous tests, fabricating my own carrier with aluminum chamber wrapped with reflective Aluminum Foil Insulation and a one inch low density "roof type" urethane. Results: 170 degrees after two hours. Victory!!
My problem now is manufacturing at the lowest cost possible two hundred units that will hold for at least one year of daily traffic.
The aluminum chamber was not accepted by the local health department, The chamber must be all in one piece. I had parts folded.

Thanks for your help.

 

[gilberts]

To: DVD, you are right. I should have said Thermal Barrier instead.
Do different density material slows the heat escaping?

 

[IRstuff]

Yes, see:

http://www.engineeringtoolbox.com/thermal-conductivity-d_429.html

Just about any foamed plastic/urethane/styrene will result in something like 0.03 W/m*K thermal conductivity.

The simplest solution would be to double the thickness of your insulator and forego the reflector and see what you get. It might also help to use some sort of airgap on the bottom to minimize the direct thermal conduction going on there. A 1/2" raised ribbing or waffling would cut done the thermal conduction considerably.

TTFN

FAQ731-376

 

[dvd]

The possibilities of how to make your carrier are endless. You might be able to convince a nearby mechanical engineering school professor to make this a project for a design class and see what evolves. I would recommend that you only provide a minimum of information, i.e., the starting and ending temperature and minimum total cost. A cash reward to the best solution would be an incentive also.

 

[gilberts]

dvd, Time does not permit that, but it's a good idea for down the road.
I have signed a lease on a kitchen thinking it would be easy to come up with a carrier. Because we are dealing with food and heat, it's not that easy. I want the carrier to be a one hand held, so that it will be practical to use in a household environment. Diner for two delivered hot, safe to eat and completely table ready.
By now you can guess, engineering is not my field, I am a chef.

I have a CAD, is it safe to post it here?

Gilbert

 

[dvd]

You can post a sketch.

If you want something "quick and dirty" I would suggest an expanded bead foam cooler like frozen foods are shipped in. You could get one that would fit a stainless steel pan with cover similar to those used for a steam table. The stainless steel pan would hold the casserole dish and all of these would fit inside of the foam cooler. This way no food is in contact with the foam and the stainless steel can be washed easily.

The foam coolers are made from expanded bead foam. A quick search turned up lots of hits. Here is an example:

http://www.styrotek.com/index.php?id=products

 

[gilberts]

dvd, the stainless steel pan is of the commercial type. The size would be way too big for two entrees, and would not fit on a dining table without embarrassment. It would not be practical for the operator or the consumer.
I need something that has class, I am going to upper-income households.
The cost for the mold would be in a range of $15,000.

Here is the picture of the casserole.

 

[dvd]

Best of luck. I am sure you can invent something. You may want to modify an existing product to get off of the drawing board and back into the kitchen.