Bain Marie or Steam Jacket?

dad

While I understand the physical difference, I fear some science escapes me here.

A Bain Marie has a thicker jacket, than a Steam Jacketed boiler. While the Steam Jacket has a layer of insulation on the outside.

Is the BM thicker jacket strictly to allow for electrical elements to be placed inside it?

I imagine the Bain Marie would take longer to heat up and to cool. While the SJ would take more power. And that power would have to be supplied by a boiler, either electric or gas.

What am I missing?

Myles

Sizes are very variable, as is the outer insulation. In general the bain marie style are self heating with immersion elements and may not be vapour tight between the inner pot and water jacket.

For those that are sealed they are typically not pressure vessels and are often rated at less than 1 barr. You do get some bain marie boilers with pumped circulation and external heaters. Final temperature depends on the thermal transfer fluid that is used.

Steam jackets are pressure vessels and can be self heated or take their steam from an external source. Final temperature is pressure dependent.

Choice of jacket or bain marie is often a simple case of availability of steam. If you already have steam available in the process you might as well use it. It may not be financially viable to put in a steam generator just for the boiler.

Also many steam jacketed boilers are intended to opperate at high temperature for processes other than distillation of alcohol.

If you but a thick mash in a jacketed boiler at 150 degC it will probably be just as likely to burn as if you directly heated it.

Both are nice to have - if you already have the infrastructure available. Steam might be your solution if you don't have an adequate equivalent power source available.

I like my glycol boiler for some applications but can't really justify using it all the time.

dad

Thanks Myles.

I found an older post.

I still have questions about the dif between the two, but having trouble formulating the questions.

Myles

The way I look at is this. Both systems let you increase the thermal gradient so that when the boiler charge is boiling, the bath or jacket is at a higher temperature than 100 degrees C.

If you just use water in the jacket then the energy input into the boiler charge is not efficient because the thermal gradient is so low.

Use steam in a pressurised jacket or a thermal transfer fluid in a Bain Marie and you could get to 150 degrees C if you wanted. The only difference is high pressure or atmospheric pressure.

The thermal transfer fluid would probably be my choice for a small scale opperation.