Additive Hydroxide Sodium Simulation Performance COP a b s t r a c t Adding NaOH to ammonia/water... more Additive Hydroxide Sodium Simulation Performance COP a b s t r a c t Adding NaOH to ammonia/water improves the separation of ammonia in the generator and reduces both chiller driving temperature and rectification losses. In this paper the main disadvantages for the implementation of these new mixtures are addressed: a) few experimental data or reliable correlations of the fluid mixture properties exist; b) selection of an adequate system for separating the hydroxide; and c) evaluation of potential corrosion problems. Our results show that the separation of NaOH from an ammonia/water solution with a maximum approximate mass fraction of 0.05 (5% weight) is viable when reverse osmosis is used with membranes BW30 and SW30HR LE. Cycle simulation using experimental data to calculate the vapour-liquid equilibrium properties shows that the COP is approximately 20% higher than with a conventional ammonia/water chiller working under the same conditions and using a hydroxyl separation efficiency of 99% for NaOH, which is feasible according to the experimental tests. (J.C. Bruno). w w w . ii fi i r .o r g a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / i j r e f r i g 0140-7007/$ -see front matter ª i n t e r n a t i o n a l j o u r n a l o f r e f r i g e r a t i o n 3 2 ( 2 0 0 9 ) 5 7 7 -5 8 7
New simple and accurate correlations of the equilibrium properties and solution enthalpies for NH... more New simple and accurate correlations of the equilibrium properties and solution enthalpies for NH 3 /H 2 O/alkaline hydroxide mixtures are presented for use in the modeling and design of absorption chillers in a temperature range between 273.15 and 353.15 K. The correlations are used to calculate the PÀTÀx diagrams and show the effect of hydroxide on the liquidÀvapor equilibrium. Finally, the correlations presented are used to estimate the improvement in the cycle performance in absorption chillers when NH 3 /H 2 O mixtures containing NaOH are used instead of the conventional NH 3 /H 2 O mixture. Results show that the addition of hydroxide can significantly decrease the generator temperature of ammonia/water absorption refrigeration cycles while simultaneously increasing the Coefficient of Performance (COP). For a NaOH concentration of 12%, the temperature at the generator decreases by about 17°C, the COP increases by 28%, and the size of the rectifier can be up to 46% less than that required when the conventional NH 3 /H 2 O cycle is used.
The conventional working fluids used in absorption chillers (water/lithium bromide and ammonia/wa... more The conventional working fluids used in absorption chillers (water/lithium bromide and ammonia/water) present several disadvantages that limit their effective application. Recently, some works have reported the addition of NaOH to the ammonia/water working pair to improve the separation of ammonia in the generator, reducing the chiller driving temperature by taking advantage of the common ion effect. However, the presence of NaOH in the absorber has a negative impact on the absorption process. This study analyzes the technical viability of separating NaOH from ammonia/water/NaOH mixtures by using reverse osmosis membranes to incorporate this separation method into future chiller designs that work with these mixtures. The concentration range analyzed covers the solution concentration values of interest for absorption chiller applications (approximate 0.02-0.05 mass fraction of NaOH and 0.3 mass fraction of NH 3 ). The results obtained show that, by using an in-series configuration of the modules, reverse osmosis technology is suitable for separating NaOH from the ternary mixtures studied.
Additive Hydroxide Sodium Simulation Performance COP a b s t r a c t Adding NaOH to ammonia/water... more Additive Hydroxide Sodium Simulation Performance COP a b s t r a c t Adding NaOH to ammonia/water improves the separation of ammonia in the generator and reduces both chiller driving temperature and rectification losses. In this paper the main disadvantages for the implementation of these new mixtures are addressed: a) few experimental data or reliable correlations of the fluid mixture properties exist; b) selection of an adequate system for separating the hydroxide; and c) evaluation of potential corrosion problems. Our results show that the separation of NaOH from an ammonia/water solution with a maximum approximate mass fraction of 0.05 (5% weight) is viable when reverse osmosis is used with membranes BW30 and SW30HR LE. Cycle simulation using experimental data to calculate the vapour-liquid equilibrium properties shows that the COP is approximately 20% higher than with a conventional ammonia/water chiller working under the same conditions and using a hydroxyl separation efficiency of 99% for NaOH, which is feasible according to the experimental tests. (J.C. Bruno). w w w . ii fi i r .o r g a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / i j r e f r i g 0140-7007/$ -see front matter ª i n t e r n a t i o n a l j o u r n a l o f r e f r i g e r a t i o n 3 2 ( 2 0 0 9 ) 5 7 7 -5 8 7
New simple and accurate correlations of the equilibrium properties and solution enthalpies for NH... more New simple and accurate correlations of the equilibrium properties and solution enthalpies for NH 3 /H 2 O/alkaline hydroxide mixtures are presented for use in the modeling and design of absorption chillers in a temperature range between 273.15 and 353.15 K. The correlations are used to calculate the PÀTÀx diagrams and show the effect of hydroxide on the liquidÀvapor equilibrium. Finally, the correlations presented are used to estimate the improvement in the cycle performance in absorption chillers when NH 3 /H 2 O mixtures containing NaOH are used instead of the conventional NH 3 /H 2 O mixture. Results show that the addition of hydroxide can significantly decrease the generator temperature of ammonia/water absorption refrigeration cycles while simultaneously increasing the Coefficient of Performance (COP). For a NaOH concentration of 12%, the temperature at the generator decreases by about 17°C, the COP increases by 28%, and the size of the rectifier can be up to 46% less than that required when the conventional NH 3 /H 2 O cycle is used.
The conventional working fluids used in absorption chillers (water/lithium bromide and ammonia/wa... more The conventional working fluids used in absorption chillers (water/lithium bromide and ammonia/water) present several disadvantages that limit their effective application. Recently, some works have reported the addition of NaOH to the ammonia/water working pair to improve the separation of ammonia in the generator, reducing the chiller driving temperature by taking advantage of the common ion effect. However, the presence of NaOH in the absorber has a negative impact on the absorption process. This study analyzes the technical viability of separating NaOH from ammonia/water/NaOH mixtures by using reverse osmosis membranes to incorporate this separation method into future chiller designs that work with these mixtures. The concentration range analyzed covers the solution concentration values of interest for absorption chiller applications (approximate 0.02-0.05 mass fraction of NaOH and 0.3 mass fraction of NH 3 ). The results obtained show that, by using an in-series configuration of the modules, reverse osmosis technology is suitable for separating NaOH from the ternary mixtures studied.
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