The Physics of Hot Pockets

StartsWithABang (3485481) writes "You've all had the experience: you're all excited to microwave your favorite snack. So you pull it out of the freezer, you throw it in, and you let it rip. A minute or two later, you pull it out, and there it is: boiling on the outside, frozen in the middle. Finally, a physicist answers the eternal question: why do microwaved foods remain frozen on the inside when they reach scalding temperatures on the outskirts? Starts With A Bang explains the whole phenomenon. Bonus for the crisping sleeve explanation!"

Comments

Microwave trays

[Travis Mansbridge]

Also those with rotating microwave trays (because microwaves tend to heat unevenly) ought to be aware that anything at the center of the tray will not get the benefit of rotation and heat at the same rate the entire time. To roll around in a (relatively) even distribution, none of your food should sit in the center of the tray.

Re:Microwave trays

[Anonymous Coward]

Of course there are microwaves made with competent stirrers and well-placed feeds. Panasonic makes microwave ovens that feature both (the feed is at the bottom of the cavity), so no rotation is necessary. They also use variable fast pulse width modulation to drive the magnetron, resulting in a smooth output power, thus avoiding another common contribution made by on-off duty cycles to burnt skin / frozen middle problems especially at lower power settings. (Triac controlled magnetrons can only go on and off; most PWM microwave ovens not driven by an inverter supply do a cycle on the order of 30 seconds.) There is work on continuous phase shifting, which will avoid heating the same islands in food even in pessimal cases (like poorly conducting food put in the centre of a rotating tray). Finally, there is still substantial research going into probes inserted into food so as to provide feedback to the driver logic (dynamically or for capture into programs which take food type mass as variables) and whether non-invasive probes can provide useful dynamic feedback every time the oven is in use.

The main problem is that the cheapest microwave ovens are just good enough to follow recipes that call for some number of seconds on the high setting while being unreliable at other settings, and the food industry targets its instructions accordingly. This is a global problem, not unique to the USA. However, as large-cavity combination microwave/grill/convection ovens become more popular in densely populated areas (why waste space having two or three ovens? why not coat your microwave with pyrolytic surfaces that you clean by simply baking or roasting something? why not cook with microwaves and brown with the grill simultaneously?) this is likely to change faster than patents expire, especially as several key manufacturers (Panasonic, GE) will not be cannibalizing conventional oven products. The critical path and most visible extra cost to the first time buyer is mainly in the design of trays and dishes which work well under arbitrary conditions in a combo oven, and avoiding damage when someone uses the wrong tray, dish or tool for a given programme.