Hydro-thermal performance of fabric air duct (FAD): Experimental and CFD simulation assessments

Abstract

Nowadays, fabric air duct (FAD) systems are the most cost-effective, and aesthetically appealing way to evenly distribute heated or cooled air to large open interior spaces. There is a need to develop a proper procedure to calculate the friction factor and Nusselt number of the air flow inside these types of fabric air ducts because of their great impact on the design of central air conditioning systems. Therefore, the main objective of this research is to carry out laboratory and numerical experiments to establish a certain technique of calculation of the friction factor and Nusselt number inside fabric air ducts and to develop validated CFD air distribution model capable of predicting the air flow pattern and heat transfer parameters inside different configurations of fabric air ducts. By controlling these parameters, FAD systems can be balanced and designed. For this purpose, three fabric air ducts made of porous and non-porous polyester with different outlet ports distribution and have a diameter of 60 cm and a length of 3 m have been experimentally assessed under variation of inlet Reynold numbers ranging from 9.9x103 to 1.47x105. The results showed that the maximum error between laboratory and numerical values for the mean friction factor and mean Nusselt number was 4.9% and 4.8% respectively, which was within an acceptable range according to previous studies. Based on the results analysis empirical correlations were obtained for their importance in achieving a well-balanced FAD system. One of the most significant equations that were obtained in this research was the relationship between the Nusselt number and Reynold number. For porous duct was Nu=127.69Re0.148, non-porous duct 4,8 o'clock air slots was Nu=4.51Re0.49 and non-porous duct 3,9 o'clock air slots was Nu=40.82Re0.139. The relationship between friction factor with Reynold number for porous duct was f=0.251e−0.0000067Re, non-porous duct 4,8 o'clock air slots was f=0.397e−0.000017Re and non-porous duct 3,9 o'clock air slots was f=0.529e−0.000025Re. All correlations are valid only within the range of conditions considered in current experimental study.