Modeling and performance analysis of an absorption chiller with a microchannel membrane-based absorber using LiBr-H₂ O, LiCl-H₂ O, and LiNO₃ -NH₃

Abstract

Summary In order to develop compact absorption refrigeration cycles driven by low heat sources, the simulated performance of a microchannel absorber of 5‐cm length and 9.5 cm3 in volume provided with a porous membrane is presented for 3 different solution‐refrigerant pairs: LiBr‐H2O, LiCl‐H2O, and LiNO3‐NH3. The high absorption rates calculated for the 3 solutions lead to large cooling effect to absorber volume ratios: 625 kW/m3 for the LiNO3‐NH3, 552 kW/m3 for the LiBr‐H2O, and 318 kW/m3 for the LiCl‐H2O solutions given the studied geometry. The performance of a complete absorption system is also analyzed varying the solution concentration, condensation temperature, and desorption temperature. The LiNO3‐NH3 and the LiBr‐H2O solutions provide the largest cooling effects. The LiNO3‐NH3 can work at a lower temperature of the heating source, in comparison with the one needed in a LiBr‐H2O system. The lowest cooling effect and coefficient of performance are found for the LiCl‐H2O solution, but this mixture allows the use of lower temperature heating sources (below 70°C). These results can be used for the selection of the most suitable solution for a given cooling duty, depending on the available heat source and condensation temperature.

Absorption Refrigeration Systems Based on Ammonia as Refrigerant Using Different Absorbents: Review and Applications

“…Several studies have investigated and analyzed compact heat exchangers as a way to reduce the amount of working fluid, as well as reducing the global size of the system, and therefore costs, by the use of compact components in absorption refrigeration systems to use low-temperature sources for the activation [26,85]. Additionally, due to the increasing performance of the refrigeration systems and reduction in energy consumption, new configurations are possible, such as adding multiple absorbers [77], compact heat exchanger components [26,27,76,88] or including ejectors of the systems [84], or combining sorption and mechanical compression systems [80,89], or integrating different systems to use polygeneration plants [67,90].…”

“…The search for systems with better thermal performance, not only of the fluid used, but with the modification of the cycle through the introduction of a component has been done, as shown by Zacarías et al [77] with the addition of several absorbers, or with the use of more compact exchangers [26,27,76,88] or by the integration of ejectors into the system [84], or simply through joining refrigeration systems by vapor compression and absorption [80,89], integration of cycles in the production of electricity and cold [136], and obviously in the use of these ARS in energy polygeneration plants, analyzed and verified technically and financially [67,137].…”

“…For the NH 3 /LiNO 3 mixture, Figure 16 shows the COP values for a single-, double-, triple-effect chiller, and the COP values of the advanced modified absorption chiller, respectively [11,16,17,41,42,[45][46][47][49][50][51][52]55,56,58,59,64,69,80,88,90,92,93,101,125,130,131]. The results are coherent with the conventional COP values of the single effect absorption chiller, which are 0.6-0.7, but the most important fact is that those values were obtained with driving temperatures (60-90 • C), which suits the use of solar energy as an input source.…”

“…This prototype was built with an intermediary process to increase the system's performance to attend the residential district heating's thermal demands because conventional absorption heat pumps undergo significant performance deterioration at low ambient temperatures. This prototype with an intermediate process could offer up to 30 kW heating capacity to heat the water, leading to an increased coefficient of performance around 1.66 (Figure16).For the NH 3 /LiNO 3 mixture, Figure16shows the COP values for a single-, double-, triple-effect chiller, and the COP values of the advanced modified absorption chiller, respectively[11,16,17,41,42,[45][46][47][49][50][51][52]55,56,58,59,64,69,80,88,90,92,93,101,125,130,131]. The results are coherent with the conventional COP values of the single effect absorption chiller, which are 0.6-0.7, but the most important fact is that those values were obtained with driving temperatures (60-90 • C), which suits the use of solar energy as an input source.The COP values for the double-effect absorption chillers proposed in the literature are similar to the conventional ARS (LiBr/H 2 O and NH 3 /H 2 O) but have lower driving temperatures.…”

Role of Membrane Technology in Absorption Heat Pumps: A Comprehensive Review

“…In the adiabatic operation mode, cooling water was not required, which is one of the most relevant advantages, since avoiding the used cooling towers; however, smaller channel lengths were suggested. The LiBr-H 2 O, LiNO 3 -NH 3 , and LiCl-H 2 O mixtures were analyzed with the same absorber configuration [ 116 ]. A membrane absorber with 13 microchannels of 0.15 mm height, 1.5 mm width, and 50 mm length was simulated.…”