Chemical Engineering in Daily Life – Question 13: Why does wearing less clothing make one feel warmer while sleeping in cold environments? Standard answer already available

As someone who has always slept naked, I really find it very warm to sleep that way:$; I feel uncomfortable sleeping with clothes on. As for the chemical mechanisms involved, I would appreciate it if the teacher could provide some guidance. It seems to be similar to the previous ones, concerning the processes of air flow and moisture transformation, but I can’t explain it in detail. Sleeping naked allows one to sense the temperature difference with the environment immediately, whereas when wearing clothes, there is a layer of clothing between the body and the environment, resulting in a gradual cooling process. It’s like the story of the frog in warm water – the temperature drops slowly, so by the time one notices it, it’s already too cold. It’s similar to the principle of heat exchangers; for example, when sleeping naked, there is direct heat exchange, and when the ambient temperature drops, it’s necessary to cover oneself with a blanket to regain heat ； Sleeping while dressed is like having dirt on a heat exchanger, which slows down heat transfer, reduces the rate at which temperature drops, and weakens the sensation.

In fact, the clothes we wear, especially underwear, are wet – their humidity level is much higher than that of the surrounding environment – as they contain moisture emitted by the human body. Sleeping in clothes doesn’t feel warm because the body’s heat is used to heat the clothes, causing moisture to evaporate. Evaporation requires heat, and since the clothes are humid and contain water, this process takes place. Sleeping naked eliminates these heat losses.

Boss, when the indoor temperature is lower than body temperature, we cover ourselves with blankets not to warm up, but to reduce the heat loss from our bodies. In chemical terms, this is insulation; the human body is the heat source, not the blanket. I believe everyone agrees that sleeping under a blanket without wearing clothes is more comfortable than sleeping under a blanket while wearing clothes; focusing solely on the heat transfer process is far from sufficient and may lead to misunderstandings.

If you sleep naked or in very little clothing, the blanket acts as an insulating layer; most of the heat lost by the body is trapped within the blanket, which is why the sleeping area remains warm and comfortable. When a person sleeps in pajamas, the pajamas act as an insulating layer for the body, slowing down the loss of heat from the body’s surface. As a result, the pajamas remain warm. However, the bed covers take longer to warm up, and it might even feel a bit cold, leaving the person unwarm while sleeping.

This post was last edited by yjqin1 on 2015-8-22 at 19:11. Standard answer: The human body is a heat source; the oxidation of sugars, the ultimate breakdown of proteins, and the digestion of fats all generate heat. Gut peristalsis produces heat, blood flow generates heat, heartbeats produce heat, and brain activity as well as dreaming also produce heat. The human body is essentially a reactor for exothermic reactions. In terms of area, where is there the most heat dissipation? Of course, it’s the torso and head (there are many heat sources inside). The limbs come next, with the extremities of the limbs being even less so, as less heat is produced there. So when sleeping in cold places, cover your head (but not your mouth and nose). As for whether sleeping naked keeps one warmer, the main factor to consider is heat transfer. If you wear long underwear, or even thick long undergarments, different parts of your body have to function independently. The torso is definitely warm, and the hands placed on the chest won’t get too cold either. But what about the feet and calves? If the temperature of the environment outside the blanket is low, the temperature of your feet depends on the heat generated locally in the feet, the heat brought by blood circulation, and the heat lost to the outside through the blanket. Due to the very low thermal conductivity of the still air inside underwear and blankets, there is almost no heat exchange between the body’s torso and feet (unless you curl up like a baby, in which case some heat transfer does occur). Compared to wearing thick underwear, if you sleep naked, the air inside the bed is warmer. And air at different temperatures is convective, resulting in convective heat transfer. In other words, more of the heat generated in your chest is transferred to your feet. Some people might still not believe it. Would that be good? Have your mother make a one-piece pajama set as thick as a quilt using cotton and cotton cloth (similar to the kind worn by one-year-old children in the rural areas of northern China in the past, without a split in the crotch area), so that you can sleep with your whole body tightly covered from head to toe. I guarantee that when you wake up, you’ll feel colder than when you went to bed in your pajamas under the covers. In this case, the heat generated by your torso certainly cannot be transferred to your hands and feet through the outside of your body. Even though the upper body is sweating, the feet remain cold. What is plug flow, and what is a completely mixed reactor?