Theoretical and experimental study of absorption and absorption/diffusion refrigerating machines using ammonia as a refrigerant: simulation under steady-state and dynamic regimes and experimental characterization of a pilot

Identifier:  TDX:2460

Handle: https://hdl.handle.net/20.500.11797/TDX2460

Authors:  Mansouri, Rami

Abstract:
ASPEN-Plus was used to carry out steady-state investigations on a commercial 3-ton gas-fired absorption chiller (10 kW cooling capacity) and a small capacity (7.5W cooling capacity) diffusion-absorption refrigerator (DAR). Before starting the simulations, the adequate thermodynamic properties model for the ammonia/water fluid mixture over wider ranges of temperature (273.16 ≤ T ≤ 613.15 K) and pressure (0 < P ≤ 210 bar) was selected among nine candidates from the ASPEN-Plus model library. It was found that the Peng-Robinson-Boston-Mathias equation of state (PR-BM) is the most suitable for the ammonia/water working pair in the temperature and pressure ranges encountered in absorption refrigerating machines. The ASPEN-Plus simulation models developed for the absorption chiller were able to reproduce and predict quite well the experimental findings. First experimental tests on the commercial diffusion-absorption refrigerator showed that a heat supply of greater than 35 W in the generator is required to ensure the functioning of the machine and its stability. Further, all the essential features of the refrigerator were determined experimentally, especially the overall heat transfer coefficients of the refrigerated room cabinet and the evaporator, which were (UA)_cab=0.554 WK^(-1) and (UA)_int=0.3 WK^(-1), respectively. The best performance of the refrigerator was reached experimentally with an electric power supply of 46 W and a generator temperature of 167°C. The machine COP was found to be 0.159. The predictions of the ASPEN-Plus models of the DAR showed good agreement with the experimental data. Finally, a dynamic black-box model was developed for the diffusion-absorption refrigerator (DAR) using Matlab Simulink® environment. It was found that a first order transfer function with delay describes correctly the relationship between the power input to the generator and the cooling capacity. The unsteady-state behavior of the refrigerator predicted by the black-box developed agreed well with the experimental data.