Working under the hot sun and in high humidity can be very challenging, seriously affecting health while reducing work efficiency. Some argue that suitable clothing is imperative, but just how effective is fabric for cooling the body? Can materials be engineered for these conditions?
An MSFEA research team led by Professors Kamel Ghali and Nesreen Ghaddar is doing just that. By studying the body's thermal characteristics, its reaction to extremes of heat or cold, and the causes of sweat, Ghaddar and Ghali's team found that more than 80% of the body's heat is released through the torso. Yet which parts of the upper body contribute most to cooling? They tackle this question by modeling the physical processes involved.
Cloth ventilation study
While studying human physiology, Ghaddar, Ghali, and PhD student Nagham Ismael, all at MSFEA's Department of Mechanical Engineering, investigated textile properties such as porosity, thickness, and water retention capacities. They correctly predicted that ventilation of the trunk relies on surrounding airflow, air penetration through the cloth pores, and air flow from other body parts. By testing types of clothing ventilation in standing and walking positions, the team was able to predict the heat lost with different clothes and conditions. Through validation experiments, good agreement was found between the predicted ventilation and experimental values (their research was published in the Textile Research Journal).
Hybrid cooling vests
Cooling vests help improve thermal sensation for people working outdoors in fields such as firefighting, construction, military, and the police, effectively cooling the torso unless the environment is very dry or humid. Some cooling vests use Phase Changing Materials (PCM), which are capable of absorbing large amounts of heat energy produced by the human body. MSFEA researchers designed two types of hybrid vests: one with micro-fans attached to PCM in strategic areas, and a second type based on the bio-heat model employing bags of desiccant (humidity absorbent) materials attached to PCM packets distributed in specific segments of the vests.
The vests were tested for various levels of humidity, temperature, and human activity. Experimental results show that PCM vests are efficient for cooling body temperatures of 35°C, while vests with PCM and fans are better for temperatures of 40° to 45°C and in moderately or very dry environments. For very humid environments, results indicate the best choice is PCM-desiccant vests.
Part of this research was carried out in collaboration with Dr. Djamel Ouahrani of Qatar University, and funded by the Qatar National Research Fund (QNRF). Among the publications resulting from the research are: