Climate change has become a huge challenge faced by all mankind. In production and operation, people are inevitably exposed to the outdoor environment of high temperature and insolation, so it is urgent for people to realize the outdoor protection with zero energy consumption. How to avoid the harm caused by heat stress to human body with high efficiency and low energy consumption? In a paper recently published in the international top academic journal "Science", The tao Guangming team of Huazhong University of Science and Technology, Professor Ma Yaoguang's team of Zhejiang University, Tao Guangming Smart Fabric Studio of China Textile Research Institute and other scientific research and industrial units carried out interdisciplinary joint innovation to overturn the traditional refrigeration concept. A zero energy consumption optical metamaterial refrigeration fabric with significant cooling effect under direct sunlight was developed. It is reported that the fabric can cool the human body surface by nearly 5℃ in the outdoor exposure environment, with excellent daytime radiation cooling capacity, which is of great significance for the realization of efficient outdoor personal heat management.

A refrigerated fabric developed by researchers

Body heat is transferred from the subcutaneous tissue to the skin, and then dissipated to the surrounding environment through clothing, thus maintaining dynamic heat balance and relatively stable body temperature. Therefore, personal thermal management through clothing is an effective way to maintain the individual thermal comfort needs of human body. However, the existing cooling clothing has the problems of poor cooling effect, heavy not light, high energy consumption. So in recent years, fabrics based on radiant heat regulation have attracted more and more attention from academia and industry. Because the infrared radiation range of human body (7-14 μm) overlapses with the transparent window of atmosphere (8-13 μm), the thermal radiation of human body can be directly cooled to outer space through the transparent window of atmosphere, thus achieving zero energy consumption cooling. Therefore, radiation cooling using human wearable fabric can significantly improve the thermal comfort performance of human body without any external energy input, which is a potential alternative and supplement to traditional energy dissipation thermal management technology.

It is understood that the intelligent refrigeration fabric developed by researchers has a hierarchical morphological structure. According to the fabric spatial structure, fiber structure, fiber internal nano structure, the classification of different space and scale, forming a macroscopic ordered, microscopic random morphological classification system.

Schematic diagram of metamaterial refrigerating fabric for daytime radiation cooling

The researchers combined the photoelectric metamaterial technology with the batch fiber preparation technology, and selected the green and biodegradable poly (lactic acid) (PLA) as the fiber raw material. After further processing, uniform and continuous metamaterial fibers were obtained. The fiber strength is sufficient for sewing machine to embroider any text and shape on commercial fabrics. Based on this, the researchers further utilized spinning weaving and lamination techniques to obtain metamaterial fabrics with a reflectivity of 92.4% in the sunlight band and 94.5% in the mid-infrared band.

Cooling performance test of metamaterial fabric:

(a) Schematic diagram of test equipment and photographs of samples; (b) Metamaterial fabric 24 hours continuous cooling performance test curve

In addition, the researchers tested simulated human bodies and found that the temperature of simulated skin covered by metamaterial fabrics was 5 to 7℃ lower than that of cotton, Spandex and hemp fabrics at midday.

Comparison test of cooling performance between metamaterial fabric and commercial fabric:

(a) Schematic diagram of test device and sample photo (b) Comparison test curve of metamaterial fabric refrigeration performance

In the cooling test of the automobile model, the temperature difference between the automobile model covered with metamaterial refrigerating fabric and the automobile model covered with cover can reach up to 27℃, and the temperature difference between the automobile model without cover can reach up to 30℃.

Comparison test of cooling performance between metamaterial fabric and commercial car cover:

(a) Simulated physical vehicles and infrared photographs; (b) Comparison test curve of refrigeration performance

Metamaterial fabrics cost little more than ordinary clothes, which means they could make the technology more accessible to more people than liquid and air-cooled clothes, the researchers said. The metamaterial fabric has also been successfully used in medical protective masks and protective clothing, which can effectively cool outdoor temperatures compared with traditional medical protective materials. It is reported that the production of metamaterial fabric has low requirements for equipment, zero energy consumption, low cost, industrialized mass production and other characteristics, suitable for large-scale promotion of preparation and industrial application. (This article is from open data collection)

(Source: Official Account of Textile Herald)