Abstract
The air temperature variation of a closed room, well insulated, during the initial time of operation of air-conditioning systems up to temperature stabilization, is simulated by a two-dimensional integral model as a quasi-steady-state phenomenon. The model equipped with a conservation equation for tracer concentration or relative temperature, including the stratification parameter, is well qualified. The flow leaving the air conditioning device forms an inclined buoyant jet which bends over and meets the room floor, where it spreads sideways forming a layer with jet temperature. A sequence of layers, which affect the jet temperature through entrainment, are produced by a novel bottom-up technique. The layer air temperatures are calculated through the bulk dilution of a near bottom jet cross-section, which feeds each new layer. The model simulated a real case and predicted the transient variation of room air and buoyant jet temperatures up to stabilisation. It also predicted the time needed for stabilisation, the cooling rates of the room and jet air temperatures, the Brunt-Väisälä frequency occurring during the temperature transitions, and more. The results are promising as they agree with observations. Thus, the model could be used to evaluate the effectiveness of relevant HVAC systems operating in such rooms.
Highlights
IntroductionBuoyancy-driven flows are very common in everyday life
(2D) stratification mode of the escaping mass approach (EMA) integral model [45], its is fixed on the wall at the level h at the centre of the smaller side of the room of width qualification and implementation for simulating the progressive temperatures of an airThe room air inlet is on the top side of the device and the outlet of the cooled air is in the conditioned environment of a closed and well-insulated room
The total time needed to integrate the uniform room-air temperature to be equal to the exit temperature of 27 ◦ C depends on the inclination angle θ0 and it is given in Table 1 along with the lengths l1 and l2 of the trajectories, cycle times t1 and t2 at the first and last simulation cycle, and total time ttot for all cycles of simulation, correspondingly
Summary
Buoyancy-driven flows are very common in everyday life. These flows are produced by the discharge of wastewater, thermal effluent, or desalination brine into the sea, by emission of air pollutants from chimneys or car exhausts in the atmosphere, and from air emission by heating, ventilation, or air-conditioning systems (HVAC) into rooms. If the density of the discharging fluid is less than that of the receiving fluid, and the initial momentum is zero, or the jet discharges with purely horizontal momentum, the buoyant jet has positive buoyancy; while if the density of the discharging fluid is greater than that of the receiving fluid, the buoyant jet has negative buoyancy. A typical example of negatively buoyant flows is brine discharges that emitted usually positively inclined so that the jets rise to a maximum height and fall downwards, reaching the seabed. Baines & Turner [1,2]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
