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Heat pipes: space age tech to halve roasting times

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The space race trickled into kitchens in the 60s and 70s, including one curious tool that's faded away in the years since: the thermal pin, a heat pipe skewer that can halve cooking times for roasts:

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Heat pipes are thermal superconductors, transferring heat 500-1000 times more effectively than solid copper (some people in the sous vide thread have discussed copper pins). They're hollow tubes with the air evacuated and a small amount of working fluid, often water. The usable temperature range is limited by the triple point and the critical point, with additional constraints near the edges. Water is effective from 20C-280C /70F-530F, which comfortably spans most cooking temperatures.

 

Modernist Bread has an excellent section on how bread bakes, including a diagram of the internal heat pipes that develop, summarized here. (click for a good photo!)

Quote

“A Harvard professor once asked me, ‘If I’ve got a roast about this size’ ” – Myhrvold holds up his hands about half a metre apart – “ ‘it takes me a few hours to cook. If I’m cooking the same amount of bread, it’s done in 20–30 minutes. Why?’ It turns out it has to do with heat transport.” As Myhrvold explains, while heat flows into a roast by conduction, in bread it flows more because the bursting bubbles open “heat pipes” through which heat can move by convection. The two have different scaling laws.

 

Sous-vide solves the overcooking side of the gradient problem, but it's still limited by total heat diffusion time-- doubling the size of a cut quadruples the time needed for the center to reach temperature. Heat pipe pins should make larger cuts practical, or normal cuts cook faster. Here's a graph from "The heat pipe and its potential for enhancing the cooking and cooling of meat joints", showing average temperatures over time for 1kg joints of meat convection baked at 190C/375F for 110 minutes (foil removed for the last 30 minutes):

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Thermal pins were sold commercially from 1956 to about 1990. They're listed occasionally for about $20 on ebay. They even made potato baking racks with heat pipes-- though now you can easily par-cook a potato in the microwave and finish it in the oven.

 

I don't know why production of thermal pins stopped, or what fundamental problems limited their usage. It seems like pans and commercial griddles would be improved by adding heat pipes to spread heat throughout and avoid hot or cold spots. Perhaps roasts fell out of favor as the culture of entertaining shifted away from monolithic centerpieces to smaller, more precisely cooked portions.

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I guess the ubiquitous "potato nail" for baked potatoes is a small-scale version of the same. 

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9 hours ago, chromedome said:

I guess the ubiquitous "potato nail" for baked potatoes is a small-scale version of the same. 

Somewhat, though note that potato nails -- even the aluminum ones -- conduct heat >100x slower than a heat pipe. In a heat pipe, the liquid vaporizes at the hot end, travels through the tube (by convection/density), and condenses at the cold end, depositing its thermal energy. This moves heat inwards faster than metallic conduction (atoms colliding).

 

 

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I theory the heat pipe sounds great, but in reality no.

 

I have been playing with heat pipes for cooking for many years and have found that there are issues.

The heat collecting end is too small to collect heat, and the contact surface between the pipe and the meat is also not big enough to be of any significance. 

The biggest problem is without the heat pipe, you always insert your thermometer into the center to check temperature,  but if you cook with the heat pipe, where do you insert the thermometer to make sure that you have reached safe temperature?

 

Heat pipes have been in use for many years, in practically every laptop computer to evacuate CPU heat. They are very inexpensive.

 

dcarch

 

 


Edited by dcarch (log)
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