Why does my canned chili splatter in 700 W microwave but not in 1000W?

[sevensages]

TL;DR Summary

My microwaveable chili sometimes will fly up in the air and splatter all over the ceiling of my 700 Watt microwave. Why does my microwaveable chili never fly up in the air and splatter all over the ceiling in my 1000 Watt microwave?

I am a truck driver. I have a 700 watt microwave in my truck that is powered by an inverter. At my house, I have a 1000 Watt microwave that just plugs into a regular wall outlet.

I like to eat Campbell's Microwaveable Chili. Campbell's microwaveable chili comes in a can with a plastic lid that has six little bitty holes in the top. The six holes in the top of the lid for the Campbell's microwaveable chili are each about 2 millimeters in diameter. Both at my house and in my semi-truck I microwave the Campbell's Microwaveable Chili with the plastic lid on top of the chili. The instructions instruct a person to microwave the chili with the lid on top of the chili.

When I microwave the chili in my semi-truck, I always have the engine of the truck running. When I microwave the Campbell's Microwaveable chili in my semi-truck, the can of chili will hop up into the air and splatter onto the ceiling of my microwave about half of the time. When I microwave the Campbell's microwaveable chili at my house, the can of chili never hops up into the air, and the chili never splatters onto the ceiling of my microwave. This is counter-intuitive because one would expect the chili to be more likely to overheat and fly up in the air on a higher wattage microwave than a lower wattage microwave. I believe that the higher wattage microwaves heat up food faster than lower wattage microwaves.

Why does my microwaveable chili frequently fly up in the air and splatter in my 700 watt microwave in my semi-truck but never in my 1000 Watt microwave at my house?

 

[berkeman]

Do both ovens have a turntable?

 

[sevensages]

Do both ovens have a turntable?

Yes

 

[berkeman]

What cook times do you use for each oven?

 

[Borek]

My - to some extent random - bet would be on the shape of the microwave working box (whatever it is called).

Microwaves used in mw ovens have length comparable with the oven box. That means plenty of interference and reflections, possible standing waves and whatnot. That in turn means there are places inside that heat much faster, and places that heat much slower. Turntable moves your food to average the heating, but it can be still not enough and there can be still some hotspots.

So yes, what you observe is counterintuitive, but probably can be explained by the energy density distribution inside (which is far from uniform).

 

[sevensages]

What cook times do you use for each oven?

In the microwave in my semi-truck, I first microwave the chili for 90 seconds on high. Then I microwave the chili for an additional 50 seconds on 50% power.

In the microwave at my house, I microwave the chili for 90 seconds on high. I do not microwave the chili a second time at 50% power at my house.

The only time that the chili hops up in the air and splatters on the ceiling of the microwave in my semi-truck is when I microwave the chili the first time for 90 seconds on high. The chili never hops up in the air and splatters on the ceiling when I microwave the food the second time on 50% power.

I didn't mention the cook times in the OP because I first cook the chili for 90 seconds on high at both my house and in the semi-truck. So I don't think that the cook times could be the explanation for why the chili splatters in my semi-truck but not at my house.

 

[sevensages]

My - to some extent random - bet would be on the shape of the microwave working box (whatever it is called).

Microwaves used in mw ovens have length comparable with the oven box. That means plenty of interference and reflections, possible standing waves and whatnot. That in turn means there are places inside that heat much faster, and places that heat much slower. Turntable moves your food to average the heating, but it can be still not enough and there can be still some hotspots.

So yes, what you observe is counterintuitive, but probably can be explained by the energy density distribution inside (which is far from uniform).

You might be on to something here.

The oven box in my 1000 watt microwave in my house is about 50% larger in cubic feet than the oven box in my 700 watt microwave in my semi-truck. What does that indicate to you?

 

[sevensages]

The answer to the question of the OP is probably what Borek wrote in post #5 on this thread. I hope Borek or someone else can elaborate on Borek's post #5 in light of the fact that I wrote that the oven box in the 1000 watt microwave at my house has an oven box approximately 50% larger than the oven box in the 700 watt microwave in my semi-truck.

Before I created this thread, i thought that the answer to the question of the OP had something to do with the fact that the 700 watt microwave in my semi-truck runs off an inverter and/or the fact that I keep the truck's engine running while I microwave the food in my semi-truck.

I always run the engine while I microwave the food in my semi-truck because I am worried that if I don't run the engine while I microwave the food in the semi-truck that one of the four following things might happen:
1# the microwave might not properly heat the food
2# it might damage the batteries of the semi-truck
3# it might damage the inverter
4# it might damage the microwave.

 

[Averagesupernova]

I always run the engine while I microwave the food in my semi-truck because I am worried that if I don't run the engine while I microwave the food in the semi-truck that one of the four following things might happen:
1# the microwave might not properly heat the food
2# it might damage the batteries of the semi-truck
3# it might damage the inverter
4# it might damage the microwave.

I can't disagree that running the engine while you zap your food is a good idea. It is certainly the way to go. But I would hate to think the batteries would be so poor as to cause that to make them give their last breath. On a three battery setup it's not alot of drain per battery. Maybe your rig uses four, I don't know.
-
One thing I have found with chili I warm up in the microwave is that it is almost easier to do it on the stovetop. The liquid warms up quickly, will come to a boil actually. In a few minutes it's cold. The beans, hamburger, etc in the chili does not absorb the heat fast enough. Just the nature of the beast.

 

[sevensages]

I can't disagree that running the engine while you zap your food is a good idea. It is certainly the way to go. But I would hate to think the batteries would be so poor as to cause that to make them give their last breath. On a three battery setup it's not alot of drain per battery. Maybe your rig uses four, I don't know.
-
One thing I have found with chili I warm up in the microwave is that it is almost easier to do it on the stovetop. The liquid warms up quickly, will come to a boil actually. In a few minutes it's cold. The beans, hamburger, etc in the chili does not absorb the heat fast enough. Just the nature of the beast.

What do you have to say about Borek's theory that the length of the microwaves (determined by the size of the oven box) determines whether or not the chili splatters?

 

[marcusl]

It sounds quite reasonable to me. Your truck MW is 50% narrower and is probably shorter and shallower, too. Let’s say it has 40% of the volume of the big one. The power is 70% of the big one, so the average power density (watts/cubic meter) is 70/40=1.75 or 75% higher! You can work out the actual value by measuring all dimensions of your ovens.

 

[Averagesupernova]

What do you have to say about Borek's theory that the length of the microwaves (determined by the size of the oven box) determines whether or not the chili splatters?

Possibly could be related. We usually assume that 100% of the power coming out of the magnetron ends up in the food minus some losses in reflections, etc. It is not impossible though that some of that power is actually dissipated elsewhere in the oven. So maybe if you put two cans of soup in at the same time which would put a larger load in the oven maybe the two would behave more similarly while accounting for differences in power? It's a place to start. Maybe a cup of water in along side the can of soup would show something. This is essentially matching the load better to the source.

 

[marcusl]

You say that all of the power ends up in the food, but doesn't it depend on the size of the load (a single chicken thigh vs. a whole roasted turkey), composition (percent liquid content, thawed vs. frozen) and other factors?

 

[Averagesupernova]

You say that all of the power ends up in the food, but doesn't it depend on the size of the load (a single chicken thigh vs. a whole roasted turkey), composition (percent liquid content, thawed vs. frozen) and other factors?

Try putting a half cup of water in the microwave for a minute. Now do the same with a quart. The half cup will become much warmer.

 

[Tom.G]

Or you could try 50 (or 60) seconds on High and 90+ seconds on Medium.

 

[Borek]

What do you have to say about Borek's theory that the length of the microwaves (determined by the size of the oven box) determines whether or not the chili splatters?

That's not what I wrote.

Length of the waves depends on the magnetron frequency only. What happens to these waves, how they interfere, depends on the shape/size of the oven.

 

[marcusl]

Try putting a half cup of water in the microwave for a minute. Now do the same with a quart. The half cup will become much warmer.

Of course. The quart has a much higher heat capacity. The small container can still have smaller absorption--or not, depending on the locations of hot and cold spots created by standing waves, etc. Standing wave patterns are striking Vollmer [2004]

Here are a simulation and measurement of the volume effect:

The paper shows a complicated dependence on many factors. Zhang [2003]

 

[Averagesupernova]

So based on post #17, what I said is correct. The power generated by the magnetron is not necessarily all absorbed in the food. I said it was often assumed to absorb it all. I also said:

It is not impossible though that some of that power is actually dissipated elsewhere in the oven.

Or the size of the food loads the magnetron less or more. I did not say all the power ends up in the food:

You say that all of the power ends up in the food

Do not put words in my mouth.

 

[Borek]

That's what I was aiming at - plus the fact the heat map will vary between ovens.

 

[Borg]

I would try switching the microwaves and see if anything changes. The fact that the 700 watt appliance is in a running truck (i.e. vibrations, potential voltage anomalies, etc.), might have something to do with it. Switching them might point to a different cause.

I would also be curious about the alignment of the appliance and whether placement on an uneven surface could affect it due to steam building up on one side of the lid and not escaping evenly. Even if it's perfectly level in the truck, parking on an uneven surface would cancel that. To test this, you would have to use a mini-level to check alignment each time that you cook and keep a record to see when it explodes or not.

 

[Klystron]

Or you could try 50 (or 60) seconds on High and 90+ seconds on Medium.

From a cooking viewpoint:
If your truck oven has heat settings such as 1 to 10, consider warming the chile at 7 or 8 for the same time. Pop the top and stir the contents. Replace top and finish heating at this setting for desired temperature and food safety (internal temperature ~165 degrees F.).

If truck oven only has time setting, divide cooking time as suggested by Tom, but also stir contents between heating.

Presuming the splatter is caused by steam pockets forming in the chile, stirring the contents tends to mitigate buildup while also mixing sauce, meat, beans, etc. for better flavor. At home I prepare stews and soups in advance, divide into portions in glass containers then refrigerate or freeze. I microwave the container much as you describe but at around 80% of full power to avoid steam pockets, stirring the contents after initial warming (or defrosting frozen item).

 

[256bits]

That's what I was aiming at - plus the fact the heat map will vary between ovens.

And the smaller rotating plate increases the chance that a particular spot of the food will be always, or nearly always lie within two of the nodes, leading to a hot spot. Best to put the food container nearer the rim rather than the centre of the rotating plate for a better sweep.

 

[sophiecentaur]

My - to some extent random - bet would be on the shape of the microwave working box (whatever it is called).

Cavity?

Microwaves used in mw ovens have length comparable with the oven box.

I think it's the other way round. The frequency is chosen to match the absorption bands of the food (water / fat? ) and the cavity dimensions should be chosen to get a suitable set of mode patterns. The food can affect the pattern, especially if it's absorbing well. Then there will be 'design features' to fit a cavity into the box. If the oven is conveniently small for mobile use then the cavity may not be ideal.

The OP could try putting the chilli in a different shaped container (say shallow bowl) to see if things change. But then there's the washing up to deal with . . . .

Do not put words in my mouth.

Just put the chilli! Har har.

 

[marcusl]

I think it's the other way round. The frequency is chosen to match the absorption bands of the food (water / fat? ) and the cavity dimensions should be chosen to get a suitable set of mode patterns.

Actually, water has an extremely broad absorption spectrum. Rather than exciting a particular resonance, heating occurs through dielectric loss. See the blue curves below.

[Wikipedia]
The frequency at which microwave ovens work, shown by the bold vertical line, is not near a peak, indicating that efficiency could be improved by going up in frequency.

2.45 GHz is chosen because it lies in the FCC's unregulated ISM band (industrial, scientific and medical). Devices there are allowed to operate without requiring an individual transmit license, although there is a strict limit on radiated and/or leakage power. (Imagine if every microwave oven required its own license, like KCBS!) Other common uses for the ISM band are WiFi and Bluetooth devices.

EDIT: I should add that the ISM band has been dedicated for these uses throughout the world by international treaties, not just by the FCC in the USA. Microwave ovens work at the same frequency everywhere.

 

[sevensages]

That's not what I wrote.

Length of the waves depends on the magnetron frequency only. What happens to these waves, how they interfere, depends on the shape/size of the oven.

Okay. So how does the fact that my 700 watt microwave oven's having a 50% smaller oven box cause

Cavity?

I think it's the other way round. The frequency is chosen to match the absorption bands of the food (water / fat? ) and the cavity dimensions should be chosen to get a suitable set of mode patterns. The food can affect the pattern, especially if it's absorbing well. Then there will be 'design features' to fit a cavity into the box. If the oven is conveniently small for mobile use then the cavity may not be ideal.

The OP could try putting the chilli in a different shaped container (say shallow bowl) to see if things change. But then there's the washing up to deal with . . . .

Just put the chilli! Har har.

Could you take a stab at answering the question of the OP?

 

[256bits]

Actually, water has an extremely broad absorption spectrum. Rather than exciting a particular resonance, heating occurs through dielectric loss. See the blue curves below.

The frequency at which microwave ovens work, shown by the bold vertical line, is not near a peak, indicating that efficiency could be improved by going up in frequency

Depth of penetration is reduced at the efficient 20GHz frequency for 20 degree C water. At the 2.45 GHz, the waves heat farther into the material than just the surface, which is probably a good thing for cooking of food.
https://water.lsbu.ac.uk/water/microwave_water.html

 

[256bits]

Okay. So how does the fact that my 700 watt microwave oven's having a 50% smaller oven box cause

Could you take a stab at answering the question of the OP?

You mentioned a rotating platter.
Have checked if it is actually rotating, or dead.
Is there a microwave stirrer on the ceiling of the cavity?
If so, is that dead too?
My stirrer is dead ( no rotating platter in this model ) and I quickly get definite hotspots.

 

[JT Smith]

Microwave ovens aren't really all that great at heating things evenly, at least in my experience. I don't know how many messes I've had to clean up. The fact that one manages the task and another messes it up is hardly a surprise.

And as for canned chili, splatter has been an issue for me as well. :-)

 

[sophiecentaur]

Could you take a stab at answering the question of the OP?

I thought I mentioned size and shape. Not relevant?
There may be another issue of where and how the microwaves are fed into the cavity. I would imagine that the design of a budget device might not be optimal for all foods / containers / masses. I can feel an experiment coming on.

If you want to avoid splatter then use a lidded container or cling-film.