New absorption air-conditioner

We propose in this paper the use of a mixture of n-butane and n-octane as working fluids for an absorption chiller and the comparison of its performance with the classical ammonia/water mixture. A simulation model is established to calculate the different thermodynamic properties of each point of the cycle such as compositions, flow rates, and temperatures. Heat transfer rates and some performance parameters are calculated using the first law analysis. Compared to an ideal machine, the performances are degraded because of the irreversibilities occurring in the different components of the machine. The second law analysis provides the entropy generation in each element and its contribution at the degradation of the COP as well as the total entropy generation of the system. The performance criteria of the considered mixtures are estimated in the same operating conditions of a simple effect machine. When the condenser and the absorber of the machine are cooled with the ambient air the COP of the n-butane/n-octane system is 0.36. When the machine is cooled with the water the COP is about 0.62. This harmless natural combination is an interesting alternative since the machine working with this mixture can use a heat driven source at moderate temperature such as a thermal waste or vacuum solar panel. The two working pressures are also moderate (less than 5 bar) reducing the necessity of high airtightness in the construction of the machine.