Abstract:

Significance Phase-change cooling garments are a special functional clothing, which use phase-change materials (PCM) at a specific temperature can change their physical status to absorb or release a significant amount of heat, so as to regulate the comfortable temperature of the clothing microclimate between clothing and the human body. Phase-change cooling garments can effectively improve the conventional liquid cooling and gas cooling garments in terms of large volume, high cost, liquid leakage, explosion, restricted application places, and other related issues.

Progress Despite the many advantages of phase-change cooling garments, problems still exist, such as low cooling rate, high humidity in the microclimate of the garment, short cooling time, and imperfect selection of working conditions. Comprehensive national and international latest research status suggests that the microclimate inside the garments directly affects the human body thermal comfort, and the influencing factors range from phase-change cooling garments, cooling garments structural optimization, and the use of working conditions. In order to keep the microclimate temperature regulated by the cooling garments at (32±1) ℃, relative humidity at (50±10)%, and air velocity at (25±5) cm/s within the standard climate range, phase-change materials are the core structure in the phase-change cooling garments.

The main factors that influence the final use of the cooling suit are the operating environment and human activity level. In order to optimize the overall performance of the cooling suit, the influence of the environment and human activity level on its performance should be considered. In order to select the optimal cooling material, the physical parameters of the PCM, such as phase-change temperature, latent heat of change, thermal conductivity, and so on, should be taken into account. Solutions to common problems of cooling garments are identified through the structural design of the phase-change package cold source system, with their advantages and disadvantages. Phase-change cooling garments address common issues in cooling garment solutions through the structural design of the cold source system, and analyze their advantages and disadvantages:

Low cooling rate of cooling garments: modifying phase change materials to improve thermal conductivity can enhance the cooling rate, but the development process is cumbersome and time-consuming. Additionally, adjusting the temperature gradient (the difference between skin temperature and the melting point of the PCM) can also improve the cooling rate; however, this approach may not be suitable for situations requiring long-term cooling.

High humidity in microclimate: While combining phase change garments with desiccants has an excellent dehumidification effect, it poses a potential heating issue that reduces the cooling duration. Mixing phase change garments with vortex tubes can improve the microenvironment's humidity, but the large size of vortex tubes makes movement inconvenient. Introducing a micro-fan can effectively mitigate humidity problems, but its effectiveness diminishes when the skin temperature equals the external environment temperature. Utilizing moisture-absorbent fabrics can efficiently reduce microenvironment humidity in the short term, but prolonged wear limits its efficacy.

Short cooling duration: adjusting the structure of the packaging layer can extend cooling time to some extent, but only until the phase change package becomes ineffective. Combining different melting points of phase change materials can prolong the cooling duration, although this increases the thickness of the phase change package, which affects wearing comfort. Integrating various cooling mechanisms allows for the recyclability of the phase change package, but results in a larger volume, limiting application to certain insulated areas. Vortex tubes combined with phase-change cooling garments are restricted to specific locations due to these limitations.

Conclusion and Prospect Phase-change cooling garments need to be designed against the working environment. Under the conditions of determining the temperature, humidity, wind speed, and radiation intensity of the working conditions, and according to the comfort needs of the microclimate inside the garment, the existing problems of phase-change cooling garments are solved from the selection of phase change materials, cold source design, and garment structure in three directions, so as to ensure that phase-change cooling garments with the cooling performance, comfort, cost, and other aspects of the optimal effect. The future research focus of phase-change cooling garments includes. (1) Development of a phase-change material with high storage energy (high latent heat of phase change) and high heat absorption efficiency (high thermal conductivity); (2) Integration PCM with melting points with ergonomics for different parts of the human body with the difference in temperature sensitivity; (3) When selecting working conditions, factors such as temperature, humidity, wind speed, and radiation need to be considered to ensure that the cooling performance of the cooling garments is optimized during use.

Key words: functional garment design, phase-change cooling garment, phase-change material, thermal-moisture comfort, clothing microclimate, phase-change package