Analyses of an Improved Double-Absorber Absorption Refrigeration System at Low Temperatures

An auto-cascade absorption refrigeration(ACAR)system could achieve a-60℃ refrigeration temperature by low-grade heat.For an ACAR system,its performance is mainly affected by energy and mass coupling of the auto-cascade processes.A novel ACAR system with double-absorber was proposed to get higher-efficient refrigeration as low as-60℃ in this context,which used R23-R134 a-DMF(N,N-Dimethylformamide)as its working fluids.Theoretical calculation and analyses were conducted under different working conditions.From the calculated results,the new system gained a COP value 20%higher than that of an ACAR system with single-absorber under the same generating,condensing,absorbing and refrigerating temperatures.Compositions of a refrigerant mixture showed key influences on energy and mass coupling of the auto-cascade processes,and an optimal composition of the mixed refrigerants was obtained for the new ACAR system.In addition,it was clearly found that absorbing processes of the new system had great effects on energy and mass coupling of the auto-cascade processes.Based on the difference of absorbing characteristics among R23,R134 a and DMF,the absorbing processes were intensified under the different absorbing pressures.As a result,an optimal matching pressure was obtained for the new ACAR system.Energy and mass coupling of the auto-cascade processes were further optimized,and the highest COP value was obtained.The theoretical analyses showed that performance of the innovative ACAR system could be superior to that of an ACAR system with single-absorber at a refrigeration temperature from -55℃ to -60℃.

An auto-cascade absorption refrigeration(ACAR) system could achieve a-60°C refrigeration temperature by low-grade heat. For an ACAR system, its performance is mainly affected by energy and mass coupling of the auto-cascade processes. A novel ACAR system with double-absorber was proposed to get higher-efficient refrigeration as low as-60°C in this context, which used R23-R134 a-DMF(N,N-Dimethylformamide) as its working fluids. Theoretical calculation and analyses were conducted under different working conditions. From the calculated results, the new system gained a COP value 20% higher than that of an ACAR system with single-absorber under the same generating, condensing, absorbing and refrigerating temperatures. Compositions of a refrigerant mixture showed key influences on energy and mass coupling of the auto-cascade processes, and an optimal composition of the mixed refrigerants was obtained for the new ACAR system. In addition, it was clearly found that absorbing processes of the new system had great effects on energy and mass coupling of the auto-cascade processes. Based on the difference of absorbing characteristics among R23, R134 a and DMF, the absorbing processes were intensified under the different absorbing pressures. As a result, an optimal matching pressure was obtained for the new ACAR system. Energy and mass coupling of the auto-cascade processes were further optimized, and the highest COP value was obtained. The theoretical analyses showed that performance of the innovative ACAR system could be superior to that of an ACAR system with single-absorber at a refrigeration temperature from-55°C to-60°C.