IEEE Spectrum July, 2014 - 38

1. iN this
Gas broiler,

jul 2014

north american

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1
3

3. the
teMperature
seNsor
in the upper back corner
is in a spot that's often
tens of degrees hotter
than the bottom front
corners.

starts doing a fair amount of the heat transfer. At 800 °C, radiation overwhelms convection. Why couldn't we have an oven
designed to cook primarily by convection
at low temperatures that switches to radiant heating for high-temperature baking?
And you're not going to be able to stop
a cook from opening the oven door on
occasion-peek ing through a g reasesplattered window just doesn't cut it. But
designers could prevent that blast of cold
air by building a blower into the door frame
that generates a "curtain" of air whenever

PrevIous Page: ryan matthew smIth/modernIst cuIsIne;
thIs Page: melIssa lehuta/modernIst cuIsIne

The problems with ovens start as soon
burning fuel
as you turn them on. Preheating always
spreads across a
wide screen.
seems to take an unreasonably long
time because ovens waste most of the
hot air they generate. The actual amount
of energy required to reach baking temperature is quite small: Just 42 kilojoules
will heat 0.14 cubic meters of air to 250 °C.
The heating element in a typical domestic
electric oven supplies this much energy in
a mere 21 seconds.
It's the oven walls you want to preheat,
however, not the air. Unfortunately, the heat,
which originates in the heating coils of
an electric oven or the burner of a
2. the heat
gas oven, must pass through the
oriGiNates
air to get to the walls, and air is
at the main gas burner
an awful conductor of heat, only
and reaches the food
slightly better than Styrofoam.
through radiation, air
convection, and direct
Even worse, air expands when
conduction.
heated, so much of it flows out of
the vent, heating the kitchen rather
than the oven. And if you try to save
that heat by closing the vent and adding a
latch to the door, the oven might explode.
The time it takes an oven to heat up, however, is the least of the problems. Oven walls
radiate heat unevenly because they vary
in thickness and in their proximity to the
heating elements. So the temperature can
fluctuate by tens of degrees from one spot
to another. And many oven doors contain a
window, which radiates a lot less heat into
the oven cavity than the walls do.
BRawN NOT BRaINs:
Traditional ovens, like
At low temperatures, these fluctuations
the one in this Viking
don't matter much, because radiant heat
range, are impressive
is weak compared to the heat transferred
in their brawn, less so
in their brains.
through conduction and convection;
at high baking temperatures, the unevenness matters a lot. The power of radiant
heat emitted from part of an oven wall at
270 °C is 16 percent more intense than the
power coming from part of a wall that is
the oven door to adjust or check on the
slightly cooler, at 250 °C.
food, nearly all the hot air spills out. The
Food itself also absorbs radiant heat puny electric element or gas burner is no
unevenly, which exacerbates the prob- match for such large surges of cool air, so
lem. Some parts of the surface naturally the temperature in the oven plummets,
dry faster and brown earlier. Because dark and it recovers slowly.
surfaces absorb more radiant heat than
light surfaces do, small variations quickly Oven designers could do a lot to make
grow. If a darkening part of the food is par- ovens heat more evenly by taking advanticularly close to an intense spot of radiant
tage of the different ways ovens transfer
heat, that part of the food will likely burn. heat at different cooking temperatures. At
And you, the cook, will inevitably make 200 °C or below, convection moves most
the situation worse. As soon as you open
of the heat. But at 400 °C, radiant energy

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Table of Contents for the Digital Edition of IEEE Spectrum July, 2014