heat loss | andreacollo

Imagine you’re in the bus leading you home. Outside it’s snowing, the bus is stuck in traffic, you’re damn freezing. Well, soon you’ll just have to touch something on your wrist in order to feel warmer almost instantaneously. This magic something is called Wristify and is one of the thousands awesome technological inventions made day by day at MIT. Press and official images can be found on the official webpage of the project. In this post we’ll see its basic working principle.

wristify

Technically, Wristify is a thermoelectric bracelet based on the principle that heating or cooling the skin on one part of the body can make the entire body feel warmer or colder. Developed by four MIT engineering students who adopted the motto “thermal comfort, reimagined“, this interesting device is supposed to help cutting the amount of energy currently used to heat or cool entire buildings. Logically, if everyone could be able to autonomously tune their body temperature according to their preferences, there wouldn’t be need to continuously heat, for example, huge rooms for conferences or shopping malls areas. Ideally, in the long term, it would be reasonable to expect significant savings.

Currently at working prototype stage (15 models have been developed up to now), this portable mini-heater looks like a wristwatch. The key difference is the custom copper-alloy-based heat sink on which Wristify’s working principle depends. Readings from embedded thermometers measure external and body temperature. With such information, an automated control system automatically adjusts the intensity and duration of thermal pulses that are delivered to the wrist via the heat sink. Thanks to a lithium polymer battery, the current prototype can run for up to 8 hours. As previously said, the team found that minute, rapid changes in temperature on one part of the human body can affect the whole body. They discovered that a change of 0.1° C per second is the minimum rate required to make the entire body feel several degrees warmer or colder (the current prototype is capable of a rate of change of up to 0.4° C per second).

The team recently took out the first prize in MIT’s annual Making And Designing Materials Engineering Competition MADMEC (USD 10,000). They plan to use the money to continue development of the device, aiming to develop more advanced algorithms and improve the automation of the thermal pulses.

wristify-1

sources: this, that and another one

Seriously, it’s too hot outside. All of a sudden I’ve turned the heating off in my small apartment, started watering plants daily and begun the countdown for the first bath of 2013!

Inspired by such a summerish weather, I thought it could be interesting to read something about Hypothermia and its causes. Hope this post will help cooling down a bit – but not too much, it wouldn’t be nice to freeze down completely 🙂

The first notion to know is that of Body Temperature (BT), the temperature that a living being autonomously keeps more or less constant through biologic processes such as homeostasis or thermoregulation. BT is about 37 °C for a human being, 38.5 °C for a pig, 39 °C for cats and cows, between 34 °C and 40 °C for camels and dromedaries, 42 °C for birds (whoa!) and so on… There is a sort of threshold, different for each single species, for the minimum temperature required to allow normal metabolism and body functions. Now, cows hypothermia is for sure an awesome topic and could raise kind of interesting discussion, but we’ll focus on the human being. For a normal healthy man, the threshold value is 35.0 °C. If our core temperature (i.e. “the temperature of an organism at which it is meant to operate”) drops below such 35 °C, we start feeling bad since our body does not like working in suboptimal conditions.

Wiki says that “Hypothermia usually occurs from exposure to low temperatures, and is frequently complicated by alcohol. Any condition that decreases heat production, increases heat loss, or impairs thermoregulation, however, may contribute”.

That’s the point! We lose our body heat in many ways, as shown in this nice image. Or better, we continouosly exchange our body heat with every single thing that surrounds us in daily life. In a sense, we are nothing more that walking heaters. Our internal mechanisms, normally, are enough to keep a constant BT. But in the case of, for example, prolonged exposure to cold, our body might become unable to replenish the heat that is being lost. As a consequence, a drop in core temperature occurs. This change causes a host of characteristic symptoms (according to the hypothermia degree), such as:

shivering,
mental confusion (difficulty in speaking, sluggish thinking, and amnesia),
muscle mis-coordination,
cyanosis (exposed extremities become blue),
decreased heart rate, respiratory rate and blood pressure.

If you ever plan to swim or dive in cold water, to explore snowy landscapes, to drink alcohol and smoke outside at night (alcohol and tobacco -> vasodilatation -> sensation of warmth while, instead, heating loss is rapidly increasing), to chase russians in their homeland in 1812 and so on… well, you’d better take your time and think about all the risks you’re going to take.

A subject found in hypothermic conditions needs to be rewarmed. Rewarming can be achieved in three main ways:

passive external rewarming: the subject is moved to a warm environment and provided with properly insulated dry clothing. Then, their own heat generating ability will be enough to restore proper BT conditions.
active external rewarming: external warming devices, such as warmed forced air or hot water bottles placed in both armpits and groin, are employed to help the subject warming up faster.
active internal rewarming: it involves the use of intravenous warmed fluids, irrigation of body cavities with warmed fluids or inhalation of warm humidified air.