Warmer Ice Cream?

April 24, 2023 by Lewin Day 52 Comments

What if you could tweak the recipe on ice cream to keep it frozen at higher temperatures? The idea comes from massive conglomerate Unilever. Among other things, the brand owns a wide variety of ice cream brands, from Ben & Jerry’s to the Magnum and Cornetto lines. Instead of running freezers at the industry standard of -18 °C (0°F), the company is experimenting with upping the temperature to -12 °C (10 °F) instead.

First off, you’d save a lot of electricity. Thanks to the way the industry works, the company actually owns the vast majority of the three million or so display freezers that are used to sell its stock to customers. Running at a higher temperature could slash the freezer’s energy use by 20% to 30%, according to the company’s calculations. The company also estimates that the energy used by these freezers makes up around 10% of its total greenhouse gas footprint, so it’s better for the environment too.

Of course, there’s savvy commercial reasons behind the idea. Unilever had noticed its ice cream sales dropping in 2022. The company believes this was in part due to retailers unplugging their freezers earlier than usual as winter approached, due to high energy bills. If the company’s freezers aren’t humming, they’re doing less business. If shaving down the freezer’s energy use helps retailers keep them plugged in and the lights on, that’s a net bonus to the company’s bottom line. It could also make their freezers unhospitable places for rival products, giving them an edge in the marketplace.

But this is all business intrigue. Let’s instead take a deeper look at ice cream.

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Does Hot Water Freeze Faster Than Cold? Debate Continues Over The Mpemba Effect

July 2, 2022 by Donald Papp 92 Comments

Does hot water freeze faster than cold water? On its face this idea seems like it should be ridiculously simple to test, and even easier to intuit, but this question has in fact had physicists arguing for decades.

Erasto Mpemba’s observations initiated decades of research into the Mpemba effect: whether a liquid (typically water) which is initially hot can freeze faster than the same liquid which begins cold.

There’s a name for the phenomenon of something hot freezing faster than something cold: the Mpemba effect, named for Erasto Mpemba (pictured above) who as a teenager in Tanzania witnessed something strange in high school in the 1960s. His class was making ice cream, and in a rush to secure the last available ice tray, Mpemba skipped waiting for his boiled milk-and-sugar mixture to cool to room temperature first, like everyone else had done. An hour and a half later, his mixture had frozen into ice cream whereas the other students’ samples remained a thick liquid slurry.

Puzzled by this result, Mpemba asked his physics teacher what was going on. He was told “You were confused. That cannot happen.” Mpemba wasn’t convinced by that answer, and his observations ultimately led to decades of research.

What makes this question so hard to nail down? Among many of the issues complicating exactly how to measure such a thing is that water frankly has some odd properties; it is less dense as a solid, and it is also possible for its solid and liquid phases to exist at the same temperature. Also, water in the process of freezing is not in equilibrium, and how exactly things act as they relax into equilibrium is a process for which — physics-wise — we lack a good theory. Practically speaking, it’s also a challenge how to even accurately and meaningfully measure the temperature of a system that is not in equilibrium.

But there is experimental evidence showing that the Mpemba effect can occur, at least in principle. How this can happen seems to come down to the idea that a hot system (having more energy) is able to occupy and explore more configurations, potentially triggering states that act as a kind of shortcut or bypass to a final equilibrium. In this way, something that starts further away from final equilibrium could overtake something starting from closer.

But does the Mpemba effect actually exist — for example, in water — in a meaningful way? Not everyone is convinced, but if nothing else, it has sure driven a lot of research into nonequilibrium systems.

Why not try your own hand at investigating the Mpemba effect? After all, working to prove someone wrong is a time-honored pastime of humanity, surpassed only in popularity by the tradition of dismissing others’ findings, observations, or results without lifting a finger of your own. Just remember to stick to the scientific method. After all, people have already put time and effort into seriously determining whether magnets clean clothes better than soap, so surely the Mpemba effect is worth some attention.

Cryogenic Machining: Custom Rubber Parts

September 22, 2014 by Marsh 43 Comments

Fashioning a custom, one-off rubber part for your project isn’t usually an option, but [Ben Krasnow] has an alternative to injection molding and casting: machining frozen rubber.

As [Ben] points out, you can’t exactly pop a sheet of rubber on your mill and CNC the needed shape; the bit will push the material around rather than cut it. Freezing the rubber first, however, allows you to carve into the now-hardened material.

His initial setup consisted of a sheet of aluminum with water drizzled on top, a square of neoprene placed on the water, and a steady stream of -60 to -80C alcohol flowing directly onto the rubber. The water underneath freezes, holding the neoprene in place. This proved problematic as the ice-clamp gives way before the milling is complete. [Ben] later adds some bolts to clamp the pieces down, allowing the milling process finish as planned.

A small plastic tray sits underneath this assembly to capture the alcohol as it runs off, feeding it back with some tubing. [Ben] recommends against a submersible aquarium pump—his initial choice—because the pump stopped working after a few minutes immersed in the chilly alcohol. An external, magnetically-driven pump solved the problem although it does require manual priming.

Stick around after the jump for the video and check out some of [Ben’s] other projects, like his quest for the perfect cookie, or CT scanning a turkey.

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Cold Climate Solar Water Heater

January 11, 2010 by Mike Szczys 30 Comments

Here’s a solar water heater setup that augments your home’s water heater instead of replacing it. The system monitors a solar collector panel on the roof for temperature. If the temperature is warm enough, a photo voltaic cell powered pump circulates cold water through the system. The heated water returns to the top of the home’s water heater. Unlike the warm-climate solar heater we saw earlier, this one can withstand freezing because it uses silicone tubing in the collector.

[Thanks Marius]