Matthew D. Determan

Experimental assessment of a compact branched tray generator for ammonia–water desorption

An experimental investigation of heat and mass transfer in a miniaturized ammonia–water desorber utilizing microscale geometries is presented. The desorber, sized for a 3.5-kW space-conditioning system, is of a branched tray design consisting of an array of alternating plates with integral microscale features enclosed between cover plates. The desorber is hydronically coupled to a heat transfer fluid that is heated by the combustion of natural gas. An adiabatic analyzer and solution cooled rectifier are integrated into the same envelope as the desorber. The component is tested as part of a single-pressure system on a breadboard test facility and is studied over a range of heat transfer fluid inlet temperatures, flow rates, and concentrated solution flow rates. Desorber performance is experimentally investigated over a wide range of test conditions to improve the understanding of performance at design and off-design conditions and the potential for flow instabilities.

Dynamic model for small-capacity ammonia-water absorption chiller

Optimization of the performance of absorption systems during such transient operations as start-up and shut-down to minimize lifetime costs is particularly important for small-capacity chillers and heat pumps. Dynamic models in the literature have been used to study responses to step changes in single parameters, but more complex transient processes, such as system start-up, have not been studied in detail. A robust system-level model for simulating the transient behavior of an absorption chiller was developed here. Individual heat and mass exchangers were modeled using detailed segmental models. System parameters used in the model were representative of a 1-RT (3.5-kW cooling) absorption chiller currently under development. Representative simulations were performed for the full “cold start-up” process and for system responses to step changes in the desorber coupling-fluid temperature and valve settings. Results from this analysis can be used to optimize start-up and steady-state performances.