18 May 2017

P.4.3.9 Resorption Heat Transformers Operating with the Ammonia-Lithium Nitrate Mixture

Absorption heat transformers (AHT) are interesting devices for recovering and upgrading thermal energy which consume very low amount of primary energy. To date, H2O-LiBr is the most common working pair used in absorption heat transformers. However, H2O-LiB mixture has several well-known drawbacks. On the other hand, heat transformers operating with NH3-H2O are not so common because they should operate at very high pressures. The use of a resorption circuit in heat transformers is an interesting alternative to reduce the high pressure level. A resorption heat transformer (RHT) is very similar to an absorption heat transformer, where the evaporator-condenser circuit is replaced by a second desorber-absorber circuit. In the literature it has been reported very few studies about resorption heat transformers operating with the NH3-H2O working pair. In this paper, the modeling and thermodynamic analysis of a single stage absorption heat transformer (AHT) and a single stage resorption heat transformer (RHT) operating with the NH3-LiNO3 mixture is presented. The systems using the NH3-LiNO3 do not require rectification process; therefore the systems using this mixture are simpler than those operating with NH3-H2O. In the present study the coefficients of performance, the exergetic efficiencies and the gross temperature lifts are analyzed as function of the main operating system temperatures.