Evaluation of a solar assisted combined ejector-absorption refrigeration system with flash tank / Ranj Sirwan Abdullah.

Cd yang disertakan adalah duplikasi kepada tesis bercetak dan tidak boleh dirujuk/dipinjam.

Thesis (P.hD.) - Universiti Kebangsaan Malaysia, 2013.

References : page [167]-177.

A solar assisted absorption air conditioning system with combined ejector-flash tank have been designed, fabricated and tested. The main objective of this thesis is to enhance the performance of the existed solar assisted combined ejector-absorption cooling system. Adding flash tank to the combined ejector-absorption cycle will enhance the overall coefficient of performance of the system. It will also increase the cooling effect inside the evaporator. The flash tank can improve the quality of the liquid refrigerant that enters the evaporator, optimize the ejector efficiency and finally allow the system to work under higher condenser temperature (ability to run sufficiently under wider operating conditions). The main components of the modified combined ejector-absorption cooling system are generator, rectifier, ejector, condenser, flash tank, evaporator, absorber, solution heat exchanger, expansion valves and pump. The modified cycle works with multi pressure level because the flash tank operates under an intermediate pressure. The performance of the system has been investigated theoretically and experimentally under the climate conditions of Malaysia. The effect on the components operating parameters; generator, condenser, evaporator and absorber temperatures and the effectiveness of heat exchanger on the thermal load, coefficient of performance and entrainment ratio of the ejector have been investigated theoretically. The performance of the proposed cycle has been investigated and compared with basic and ordinary combined cycle (absorption-ejector). The results showed a significant improvement in the COP of the modified combined cycle at different operating conditions. The flash tank has successfully improved the cooling effect of the evaporator. In addition, the flash tank enhanced the ejector entertainment ratio and consequently increased in critical condenser pressure since the pressure of the secondary flow is higher (pressure in the flash tank). The first and second law of thermodynamic has been used to evaluate and compare the cycle performance before and after modification. A comprehensive mathematical model of the entire system using FORTRAN 90 has been developed to calculate the entropy generation in each component and the total entropy generation of the system, as well as to evaluate the exergy losses. Under operating conditions that match the ambient conditions and a certain application in Malaysia Tgen = 85 °C, Tcond = Tabs = 30 °C, and Tevp = 0 °C, the coefficient of performance (COP) and exergetic efficiency (COPexe) values before and after modification are (0.844, 0.875) and (0.459, 0.476), respectively. The maximum exergy losses were found in the evaporator in both cycles, followed by the condenser and the absorber. A statistical t-test is carried out to establish the significance of the differences in the COP and the COPexe before and after modification. It found that there was a significant improvement in the combined-cycle performance after modification. The results of the experimental tests indicated that the COP of the system with and without adding ejector-flash tank unit was 0.87 and 0.64 respectively at the same operating conditions. The improvement of the COP of the system has increased to 36% more than the basic absorption unit. The cooling effect increased as a result of improvement in the quality of the liquid ammonia entering to the evaporator. This study indicated that the technical ability of optimizing the performance of the absorption cooling system significantly by adding ejector-flash tank unit to the basic absorption cycle. Overall, adding the flash tank to the combined cycle can be considered to be a novel enhancement.