Does the water level in the jacket of a kettle affect its effeciency?

[ectofix]

It certainly DOES affect the efficiency.  Keeping in mind that pure steam is the intended medium for delivering heat to the food.

 

For a properly functioning kettle, here’s some basic points to remember:

 

Heat transferred by steam is LATENT heat – given up when the steam condenses back into water.  Just like in a refrigeration cycle, heat transfer (measured in BTUs) is FAR greater during a phase transition (change of state) of a substance. EXAMPLE: The amount of LATENT heat absorbed by 1 lb of water to turn it all into steam is around 960 BTUs. That’s also the amount of heat given up by that steam as it condenses back to a liquid.

 

Although water has tremendous capacity for carrying heat when compared to other substances – it still doesn’t come even CLOSE to giving up the same quantity of heat as steam does during a phase transition.  Water in the bottom of the steam jacket only contains SENSIBLE heat (vice LATENT heat). In essence, what BTUs water can give up while in contact with the inner jacket vessel – would simply rapidly sub-cool the water (below saturation temp). EXAMPLE: 1 lb of water needs to only give up 1 measly BTU in order to drop its temperature 1°F.

 

Higher pressure causes a higher boiling point (saturation temperature).  Conversely, that also translates to a higher condensing temperature of the steam back into water at that given pressure.  So proper steam jacket pressure is crucial since it directly affects the temperature at which steam will condense back to water. A steam jacket pressure of 0 psi (equal to atmospheric) only gets to 212°F.  At about 20 psi, it’ll get nearly 240°F and at 35 psi, it’s pushing nearly 280°F.

 

Now with regards to your question:

If the water level is too low, effectively you may have a lesser volume of steam being generated in order to deliver heat to the product (my theory).  I’d also be concerned on relying too much on the water sensors.  Those are there primarily to prevent dry-firing and cracking the jacket.  Of course if there’s air trapped in in the jacket, it offer very little (if any) heat transfer and will also impact operation by having higher-than-designed jacket pressure and cause the safety valve to blow off.

 

If the water is too high, then any cooking surface below the water line would offer extremely poor heat transfer to cook the product.

 

I recommend keeping the water level between the lines in the site glass.  Additionally, if it’s possible that air is leaking into the jacket (overnight after it’s cooled down), then you’ll need to replace the safety valve.  After replacing that, heat the kettle to above 10 psi and then burp the jacket for about ten seconds to get the air out.

[olivero]

Hey Ectofix, Thank you for the extensive answer.

 

I am aware the pressure makes a big difference, no doubt. I keep my jackets well vacuumed whenever I work on them and they are calibrated to stop heating when the pressure is around 40-45 PSI on the gauge.

 

My question was mainly on the water level in the jacket if it makes a difference in heating efficiency when the jacket is right above the low line, to the center between low and high or at high, etc. I am just curious.

 

IT would make sense for there to be a sweet spot allowing for just the right amount of expansion for the steam and keeping everything toasty. When I refill, I put it right below the high line, like when the kettles first came.

 

I doubt there is a leak, I have replaced the PRV before and keep one on the shelf but I will know tomorrow if the needle crawls up.

[ectofix]

I tend to go into more detail because I don’t know what you don’t know.  For that matter, I don’t know what I don’t know as WELL!    So I go a little overboard for the sake of promoting understanding.  I guess that stems from my many years as an instructor while in a military technical field.

 

My boss just hired a guy who claims to have received HVAC/R training at some point, but readily admits that he’s never practiced it.  Our shop happens to only do hot-side (in-house), but as you well know – HVAC/R knowledge & experience is good core knowledge in order to do hot-side as well.

 

So when he first started with us, I’d grilled the guy with all matters of simple questions to test his knowledge.  Well, he has MUCH to learn…and falls way short of what I’d expected!  At some point, I’d specifically asked him the effects of pressure upon the boiling point of a liquid.  He had a 50/50 chance of getting it right…and chose the wrong 50%!

 

So it is what it is.  I’ve committed many hours going over the basics of gas and steam systems with him.  I’m happy to say he’s picking it up quickly.  I need to assess his electrical knowledge next, in order to make sure he’s prepared for troubleshooting it on his own.

[olivero]

HA, yeah. I tend to do the same. Not knowing if that one piece of information you gave him solved the riddle.

 

HVAC/R is very good knowledge to have in any subject, as well as gas, plumbing, combustion, welding, water pipe,etc. It all comes together in the kitchen and gives you the ability to fix so much more. That’s how I look at it and why I decided to get into every subject.

 

Not to get too far off subject, so what would your conclusion be on the water levels?

 

No doubt the pressure is the main variable in the temperature and effeciency, I am just wondering about the water level in the jacket.

[ectofix]

Well, the manual DOES specifically state that the water should be refilled to the high mark, so I’d recommend that.  Just don’t above the high mark.  So if it’s at the high mark, the jacket is burped, there’s no air leaking in after the jacket is cooled and the pressure gauge stays in the green – then I’d say it’s at optimum operating condition in that respect.  All that could go wrong then would be a temperature control or burner issue.

 

How much efficiency it loses between there and the low water mark really isn’t spelled out, so I theorized that in my earlier post. 

 

Been awhile since I’ve fooled with self-contained kettles (ours are all live steam), but I just remembered that the temperature control potentiometer is the ONE component that I’ve replaced the most of on Cleveland kettles.  Seems like I was always at a Cracker Barrel somewhere replacing one of those.  A bad spot in the potentiometer or a little moisture intrusion will cause them to become inconsistent.  They get allot of abuse, sticking out there like that.

If you go to replace one, definitely have a new knob to go with it.  You’ll probably have to destroy the old knob to get the old potentiometer out.  OH…and you’ll need a wire soldering kit.