NUMERICAL INVESTIGATION OF VENTILATION PROBLEMS USING DISCRETE HEAT AND CONTAMINANT SOURCES

Abstract

This thesis addresses the detailed numerical investigation of double di usive mixed convection

ow within ventilated enclosures equipped with di erent thermal and solutal boundary conditions. Geometric modulations are included by considering di erent sizes and locations of inlet port, outlet port, heat sources and contaminant sources. The ow of

uid, heat and contaminants are analyzed by streamlines, isotherms and isoconcentrations for a wide range of ow governing parameters. The trends of average Nusselt number, Sherwood number, entropy generation and cooling e ciency are investigated with the variation of Reynolds number, Richardson number and buoyancy ratio to improve the performance of the ventilated system. In this thesis, two air distribution forms are studied: one is displacement ventilation and other is mixing ventilation to drive and control the indoor air environment. The mathematical model is formulated based on the pre-assumptions that the uid is Newtonian, viscous and incompressible and the ow is laminar. A control volume based SIMPLE algorithm is used to solve the ow governing equations, that are represented by a coupled set of non-linear partial di erential equations. Chapter-1 of the thesis includes the basic de nitions and various solution algorithms used for uid ow problems. Chapter-2 deals with the double di usive mixed convection ow inside a ventilated enclosure due to the presence of thermosoluted square block at the middle region. The block is at higher temperature and concentration as compared to the inlet cold uid which is at lower temperature and concentration and is passed through various slots of the left vertical wall and ush-out through the right vertical wall. E ective heat and mass transfer performance is studied by changing the locations of inlet and outlet port with the variation of ow governing parameters which is mostly applicable for building ventilation and cooling of equipments. Chapter-3 is focused on the numerical simulation of uid i ii

ow, heat and mass transfer in a ventilated enclosure where a thermo-contaminated square block is placed inside the enclosure. Simulations are performed for di erent locations and di erent sizes of the thermo-contaminated block with xed inlet and outlet port along the vertical walls where coolant air is supplied and contaminated air is ushed out. The heat and contaminant transfer rate along the surface of the block are compared for di erent block locations with the variation of Richardson number, Reynolds number and buoyancy ratio and found that maximum cooling inside the enclosure is obtained when thermocontaminated block is placed near the outlet port. Mixed convection ow in a parallelogrammic shaped ventilated system lled with air- CO2 mixture with uniform discrete heat and CO2 contaminant sources is numerically studied in Chapter-4. The impact of inclination angle of horizontal walls on average rate of heat transfer and mass transfer, average temperature, entropy generation, Bejan number, cooling e ciency and performance evaluation criterion inside the system is evaluated with respect to the location of inlet port, outlet port and heat sources. Chapter-5 is focused on maximizing the removal rate of heat and contaminants due to wall heater and a thermosoluted block in a slot-ventilated enclosure. Cold fresh air is in ltrated into the enclosure through an inlet port located along right vertical wall and polluted air is expelled through the chimney shaped outlet port located along the upper wall. The best suited inlet port location along with inclination angle of outlet chimney is determined in terms of maximum heat transfer rate with minimum entropy generation. Subsequently, a numerical simulation of three-dimensional mixed convection due to thermosolutal gradients in a slot-ventilated enclosure is presented in Chapter-6 due to discrete heat and contaminant sources under di erent ow conditions. The numerical simulations are performed for a wide range of ow governing parameters to nd the e ects of inlet and outlet port locations for achieving acceptable average temperature inside the enclosure to obtain maximum heat and mass transfer rate with minimum entropy generation.