"Sun God Clothes" are here! Chinese universities develop 24-hour constant temperature smart clothing, it's so cool

This winter is too cold. On December 16, the Central Meteorological Observatory issued a yellow low temperature warning, the first low temperature warning this year . In the next week, the temperature in most parts of China will continue to be low.

At such a temperature, it seems that no matter how many clothes you wear, you can't resist the cold weather. Perhaps, the wearable thermal regulation clothing from Nankai University can help us "add clothes to keep warm" .

Recently, a research team from Nankai University has developed a two-way temperature regulation clothing system that can be powered by solar energy throughout the day . The system can expand the thermal comfort zone from 22°C to 28°C to 12.5°C to 37.6°C through rapid thermal regulation, and has a fast body temperature regulation rate, thereby ensuring the safety and comfort of the human body in various complex and unstable environments.

Furthermore, since the device is self-powered by solar energy, no additional power source is required .

The related research paper, titled "Self-sustaining personal all-day thermoregulatory clothing using only sunlight", has been published in Science.

A related viewpoint article published at the same time wrote: "Wang et al.'s comprehensive device opens up broad prospects for the development of actively controlled, self-powered and wearable local thermal management systems, while providing multiple possibilities for expanding human adaptability to harsh environments . This innovation shows a future vision of a thermal management system that does not need to worry about energy supply constraints around the clock, and even under special conditions, the additional energy harvested can be used to power electronic devices ."

Cooling down, keeping warm, proficient in everything

Clothing plays an important role in maintaining body heat balance and thermal comfort. If you cannot adapt quickly from a comfortable indoor environment to a hot or cold outdoor environment, you may feel uncomfortable or sick. This is even more challenging in harsh environments, such as in cold polar regions or space travel. Therefore, wearable thermal regulation clothing has been a long-sought but challenging goal in smart clothing systems .

At present, humans have developed many thermal regulation systems, which are mainly divided into passive systems and active systems . However, in passive systems, most solar-driven systems can only achieve unidirectional thermal regulation, and bidirectional thermal regulation systems need to improve efficiency, response speed and adjustable temperature range; while active systems have disadvantages such as mechanical complexity, high energy consumption and low efficiency.

Therefore, to achieve sustainability, flexibility, and lightweight in thermal-regulating clothing, the researchers successfully designed and fabricated a wearable thermal management system (OETC) by combining organic photovoltaic cells and electrocaloric effect cells into a single device with the required flexibility .

The study selected recently developed electrocaloric effect (EC) devices, which are highly efficient, low energy consumption, have bidirectional thermal regulation performance, and are non-polluting. For example, the flexible EC thermal regulation device has a very low energy cost, can achieve a coefficient of performance of 13, and has a specific cooling power of 2.8 watts per gram.

In addition, OETC achieves two-way thermal management, providing 10.1°C cooling to the skin in hot weather, while keeping the human body 3.2°C warmer than bare skin in the dark or at night through additional energy harvested by the organic photovoltaic unit. In addition, within the first 5 seconds, the maximum skin heating rate can reach 15.6°C/minute and the maximum cooling rate can reach 14.0°C/minute, achieving rapid thermal regulation.

Figure | Working mode when wearing a flexible OETC, cycling between hot (in the sun) and cold (in the dark) environments to achieve personal thermal comfort as needed (Source: the paper)

Even when the ambient temperature varies between 12.5°C and 37.6°C, the OETC maintains the human skin temperature in the thermal comfort zone of 32.0°C to 36.0°C.

Benefiting from the low energy consumption of EC devices, the OETC system can operate 24/7 with 12 hours of sunlight energy input . Therefore, the system has comprehensive characteristics such as controllable, 24/7 dual mode and significant thermal regulation performance, making individuals more comfortable in harsh environments using only sunlight as energy.

In addition, the system successfully conforms to human skin. Through the bending state test coordinated with the human body, the study proved its stability in different postures . The researchers observed the thermal regulation performance of OETC in different bending states, and the results showed that OETC achieved maximum and stable thermal regulation performance when running at a frequency of 0.75 Hz for 10 seconds. This flexibility makes OETC have superior adaptability in wearable devices, able to coordinate with the movement and changing posture of the human body, ensuring effective thermal regulation in various scenarios.

Figure｜Wearable thermal regulation performance of OETC (Source: the paper)

Increasing human survival in harsh environments

This two-way thermal regulation capability using solar energy makes the device even more attractive, especially for integration into traditional space suits to help reduce overall power consumption.

During an individual's space travel, the theoretical area of ​​a space suit is about 1.85 square meters. In space, the magnitude of solar radiation pressure depends on the solar radiation flux near the Earth's surface, and the solar constant of 136.7 mW/cm2 is usually used to calculate the solar radiation flux within 1 astronomical unit.

Figure | Thermoregulation performance of OETC and cotton clothing and the prospects of personal space travel (Source: the paper)

As solar cell performance continues to improve, the solar cell modules required to provide human thermal regulation throughout the day are estimated to require only 1.12 square meters of area, assuming a 45% photovoltaic conversion efficiency solar cell device.

As the review article states: “With its excellent thermal management performance, ability to easily switch directions, and the ability to adjust the thermal management temperature range for optimal temperature control, Wang et al. demonstrated a garment that enables the human body to adapt to changes in ambient temperature.”

Taking advantage of the low energy consumption of EC equipment, OETC can achieve controllable and all-weather dual-mode thermal regulation. Coupled with other excellent features such as simple and compact structure, high efficiency and strong adaptability.

With more optimization, the researchers say the OETC could show potential applications in high-end thermal regulation and could even increase human survivability in harsh environments such as polar regions and individual spacewalks .

However, it is worth noting that this system still needs to be optimized in terms of performance and practicality, including the temperature span of the system and the thermal conductivity of the materials .

The review article states: “The device of Wang et al. can be further improved by increasing the entropy change of the material, while the thermal conductivity of the material can be improved by adding inorganic fillers. In addition, by building a cascade device in which multiple electrocaloric effect devices operate in synergy, the thermal management performance of the entire system can be optimized and the temperature span of the entire system can be increased.”

Reference Links:

https://www.science.org/doi/10.1126/science.adj3654

https://www.science.org/doi/10.1126/science.adl5650