Study and Optimisation of Supply Duct Bend and Diffuser in HVAC System for a Classroom

Authors : Shivam Agarwal; Danishq Gera

Volume/Issue : Volume 5 - 2020, Issue 7 - July

Google Scholar : http://bitly.ws/9nMw

Scribd : https://bit.ly/2DEeVxl

DOI : 10.38124/IJISRT20JUL723

This paper presents numerical predictions and results of air flow and pressure distribution in common possible iterations of duct and diffuser having: 1. square, rectangle and circular duct shape, 2. square duct with side 12in, 15in and 18in and 3. bend radius to width ratio of 0, 0.5, 1 and 2. The system is designed to develop an optimal system to reduce the noise levels in a classroom which are far above the recommended value of 35dB by WHO in an engineering institution designed according to the Common Public Works Department(CPWD) norms while also bridging the gap between the industry and the consumer. The iterations were designed on fusion 360 and tetrahedron meshing was done in ANSYS after defining the boundaries of geometry of CAD design. The inlet velocities varied as per the different diffuser size, shape and angles. The inlet velocity lies in the range of 1.5m/s to 3m/s. After setting up the solver and choosing k-omega SST model for solving, calculation was performed for 3000 iterations using hybrid initialization to reduce the residuals as much as possible for the results to converge for accurate results. Material properties of aluminum and properties of the fluid were set. Among different groups, results based on different shapes showed that circular duct displayed gradual pressure and velocity drop at the lower bend of the wall than in the case of rectangle or square. While, in case of duct with different sizes, as size of duct increased, frictional losses increased, while pressure drop, noise levels and eddy current formation significantly reduced. In case of different bend radius to width ratio(r/W), as r/W increased, eddy formation and boundary layer separation, pressure drop, turbulence and noise levels decreased. Therefore, the study showed that a circular duct, with a diameter of 15in having r/W ratio of 2 would significantly reduce the sound levels and be the optimum solution for the classroom and adding 2-3 vanes would further improve the performance of the system and maximize the required effort.

Keywords : HVAC; Ansys; CFD; Duct; Diffuser; Pressure drop

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