Amélioration de la performance des machines frigorifiques á absorption par l'utilisation de cycles à absorption et désorption étagés

This study deals with staged absorption and desorption cooling systems which increase the performance of absorption cycles that are driven by only low-grade energy, particularly when the working fluids are NH₃H₂0. Instead of working with only one absorber, these systems use a cascade of absorbers composed by one operating at the evaporator pressure, followed by a series of absorbers operating at staged pressures P_j, between P_ev and P_c In the same way, a cascade of generators is used for desorption. For the same operating parameters for other equipment and the same COP, the systems that we propose permit the generators to run at temperatures below those of all other systems offered up to now and using the same working fluids. When T_ev = −10°C, T_a = T_c = 30°C, the temperature of the generators can be as low as 65°C while the COP of the system is 0.258 and the COP_ex 0.317. By increasing the temperature of generators to 85°C while maintaining the other parameters at the same values, COP becomes 0.374 and the COP,, 0.336. These results improve the performance of absorption systems using only low-grade energy (T < 100°C). Particularly, they are better than the performance of two-stage absorption systems which consist of two single-stage absorption cycles coupled with each other through the evaporator of the first cycle and the absorber of the second cycle. With the same operating parameters indicated above for our system at the evaporator, the condenser, and the absorber, these coupled cycles need temperatures at generators of 80 and 100°C, whereas they give a COP of only 0.270     

Amélioration de la performance des machines frigorifiques á absorption par l'utilisation de cycles à absorption et désorption étagésPerformance improvement of absorption cooling systems by using staged absorption and desorption cycles

This study deals with staged absorption and desorption cooling systems which increase the performance of absorption cycles that are driven by only low-grade energy, particularly when the working fluids are NH₃---H₂0. Instead of working with only one absorber, these systems use a cascade of absorbers composed by one operating at the evaporator pressure, followed by a series of absorbers operating at staged pressures P_j, between P_ev and P_c In the same way, a cascade of generators is used for desorption. For the same operating parameters for other equipment and the same COP, the systems that we propose permit the generators to run at temperatures below those of all other systems offered up to now and using the same working fluids. When T_ev = −10°C, T_a = T_c = 30°C, the temperature of the generators can be as low as 65°C while the COP of the system is 0.258 and the COP_ex 0.317. By increasing the temperature of generators to 85°C while maintaining the other parameters at the same values, COP becomes 0.374 and the COP,, 0.336. These results improve the performance of absorption systems using only low-grade energy (T < 100°C). Particularly, they are better than the performance of two-stage absorption systems which consist of two single-stage absorption cycles coupled with each other through the evaporator of the first cycle and the absorber of the second cycle. With the same operating parameters indicated above for our system at the evaporator, the condenser, and the absorber, these coupled cycles need temperatures at generators of 80 and 100°C, whereas they give a COP of only 0.270     

Global Electricity Interconnection

正Sustainability and climate change are the biggest challenges faced by humanity. Innovation is critical to respond to these challenges.Insufficient action against climate change has put the     

Etude comparative de la performance des machines frigorifiques à absorption utilisant de l'energie thermique à très faible valeur exergétiquePerformance study of cooling systems using low grade heat energy for refrigeration

This study deals with cooling systems driven with low grade heat energy delivered by heat sources whose temperature do not exceed 100°C. Since we cannot neglect the irreversibilities associated to heat depreciation, we consider an approach temperature of 10°C for all the heat exchangers. So the temperature of the generators is <90°C to fulfill the approach conditions. For a heat sink temperature of 30°C and an evaporating temperature of −10°C, only two kinds of cycles are concerned: the cycles with staged absorption and desorption (CADE) and the cascade systems (CCAR) in which a series of two cycles is used, the evaporator of the former cooling the absorber of the later.The cycles with staged absorption and desorption are described. They permit a decrease of generators' temperature down to a level no system among those previously offered can run.To point out the importance of the CADE, we compare them to cascade systems. This comparative study shows that the CADE yields better performances. The gap of performance between the two systems increases with the decrease of the heat sink temperature and it is maximal for lower temperature at generators. The comparative study uses five criteria: the coefficient of performance, Σw_p/Q_ev, Q_t/Q_ev, Q_ref/Q_ev and the operating area in a (T_fr, T_g) plane. LiNO₃/NH₃ and H₂O/NH₃ are used as working fluids of the CADE while LiBr/H₂O + LiNO₃/NH₃ and LiBr/H₂O + H₂O/NH₃ are used for the CCAR.The CADE are very suitable for the use of low grade heat energy (70°C T_sc 100°C) in refrigeration (T_ev −10°C) with sink temperature as high as 30°C and a realistic approach of 10°C for all the heat exchangers.     

Etude comparative de la performance des machines frigorifiques à absorption utilisant de l'energie thermique à très faible valeur exergétique

This study deals with cooling systems driven with low grade heat energy delivered by heat sources whose temperature do not exceed 100°C. Since we cannot neglect the irreversibilities associated to heat depreciation, we consider an approach temperature of 10°C for all the heat exchangers. So the temperature of the generators is <90°C to fulfill the approach conditions. For a heat sink temperature of 30°C and an evaporating temperature of −10°C, only two kinds of cycles are concerned: the cycles with staged absorption and desorption (CADE) and the cascade systems (CCAR) in which a series of two cycles is used, the evaporator of the former cooling the absorber of the later.The cycles with staged absorption and desorption are described. They permit a decrease of generators' temperature down to a level no system among those previously offered can run.To point out the importance of the CADE, we compare them to cascade systems. This comparative study shows that the CADE yields better performances. The gap of performance between the two systems increases with the decrease of the heat sink temperature and it is maximal for lower temperature at generators. The comparative study uses five criteria: the coefficient of performance, , and the operating area in a (T_fr, T_g) plane. LiNO₃/NH₃ and H₂O/NH₃ are used as working fluids of the CADE while LiBr/H₂O + LiNO₃/NH₃ and LiBr/H₂O + H₂O/NH₃ are used for the CCAR.The CADE are very suitable for the use of low grade heat energy (70°C ? T_sc ? 100°C) in refrigeration (T_ev ? −10°C) with sink temperature as high as 30°C and a realistic approach of 10°C for all the heat exchangers.