الفهرس Only 14 pages are availabe for public view
 |  | from | 137 |  |  |
| | | from | 137 | | |
Abstract
In this thesis, a steady-state model for variable-speed centrifugal chillers is presented. The model is useful for studying the performance of chiller’s components under various operating conditions and design parameters. The chiller sub-models are developed based on the first principles and used the suitable heat transfer correlations. Thereby, the results of the model can be used with confidence to develop a complete performance map for the variable-speed centrifugal chillers.
The centrifugal compressor model in this study is built upon a series of thermo dynamical processes for the sub-components of the centrifugal compressor; the nozzle, impeller, vaneless space, vaned diffuser, and the collector. The model utilized mass, momentum, and energy balances in addition to thermodynamics relations, to describe the performance for each centrifugal compressor’s component. The incidence and friction losses in the impeller and vaned diffuser are considered. The losses in vaneless space are considered by an empirical correlation which is generated in this study by using manufacturer’s data. The generated empirical correlation is introduced in a form which almost makes it unrestricted to manufacturer’s data.
In the condenser model, the condensing heat transfer coefficient takes into account the combined effects of the tube surface geometry, condensate inundation from the tubes above, and condensing vapor velocity (vapor shear effects). The influences of gravity and forced convection components on the condenser overall conductance are investigated. In the evaporator model, the forced convection boiling model is used to predicate the boiling heat transfer coefficient. The influence of the chilled water leaving temperature (setting point) on the variable-speed chiller performance is studied in order to explain the limits of increase in the setting point temperature. Also, the manufacturer’s data are used to develop an empirical polynomial for a combined motor and transmission efficiency. Therefore, the actual chiller power is estimated, and the additional cooling load for the motor and VFD cooling purposes is considered.