Study On Isothermal Jet Characteristics Of Square Ceiling Diffuser

For an air-conditioning system, the air inlet is an important factor to the indoor airdistribution. Since the late seventies of last century, air distributor type, quantity and material,produced by domestic manufacturers become increasingly rich, design and production hasalso been greatly improved. But the jet theory for a single type of inlets is not describedsufficient in the manual. Based on this, paper will first design an air distributor performancelaboratory, according to relevant standards and product samples. Then take square ceilingdiffusers as the research object; paper establishes a theoretical model according to jetcharacteristics of the ceiling diffuser to solve the throw and make an experimental study ofjet characteristics. Finally, the paper uses mathematical models to calculate and analyze jetcharacteristics.Laboratory is equipped with air supply system and testing system. There are three airsupply methods in the air supply system, including sidewall air supply，ceiling air supply andfloor air supply. The design air volume of supply system is0~4000m3/h. Testing system ismainly flow test device and the terminal wind speed testing device. Flow test equipment is aMean Velocity Tube Flowmeter, total uncertainty of which is±4.12%. Wind speed testingdevice consists of universal anemometer probe and the Agilent data logger, total uncertaintyof which is±0.092m/s.Paper verifies a theoretical model to discribe the jet of a ceiling diffuser. Experimentsshow that theoretical model is well consistent with the experimental results. Comparedvalues calculated by the model with experimental results, the maximu m error of impingingpoint is0.10m, and the maximum error of throws was3.10%. The maximum error of throwsbetween values calculated by empirical formula and experimental value is9.17%. Applicatethe mathematical model to analysis the jet, and we find that the throw of the jet is mainlyaffected by wind speed and size of the air inlet, and the jet axis orbit is mainly affected byinstallation distance from ceiling.Jet characteristics and envelopes of square ceiling diffusers are obtained by experiments.The results show that: Jet cross-section gradually changes from the flat into a semi-circular,and through a period of air entrainment, the jet cross section becomes flat again.The spreadand drop of square ceiling diffuser increase linearly with the increase of the wind speed. Thelarger the dimension of a diffuser, the longer its spread and drop are. The maximum drop ofsquare ceiling diffuser is0.87m in the experimental conditions, so that the jet forms a goodwall attachment jet under the ceiling. The axial velocity measured by experiments through dimensionless transformation, axial velocity dimensionless values of4square ceilingdiffusers are well described by a single straight line, all within the curve calculated in the aas1.16,1.94. The coefficient of square ceiling diffusers resistance is a good linearrelationship with their dimension.The research results improve the jet theory and jet data of square ceiling diffuser, andprovide a theoretical basis for further research about ceiling diffuser non-isothermal jet.