Thesis (M.S.)--University of Massachusetts Amherst, 2009. / Open access. Includes bibliographical references (p. 59-64).

Optimization of the performance of absorption systems during transient operations such as start-up and shut-down is particularly important for small-capacity chillers and heat pumps to minimize lifecycle costs. Dynamic models in the literature have been used to study responses to step changes in a single parameter, but more complex 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 is developed here. Individual heat and mass exchangers are modeled using detailed segmental models. The UA-values and thermal masses of heat exchangers used in the model are representative of a practical operational chiller. Thermal masses of the heat exchangers and energy storage in the heat exchanging fluids are accounted for to achieve realistic transient simulation of the heat transfer processes in the chiller. The pressure drop due to fluid flow across the heat exchangers is considered negligible in comparison to the pressure difference between the high- and low-side components (~ 1.5 MPa). In components with significant mass transfer effects, reduced-order models are employed to decrease computational costs while also maintaining accurate system response. Mass and species storage in the cycle are modeled using storage devices. The storage devices account for expansion and contraction of the refrigerant and solution in the cycle as the system goes through start-up, shut-down, and other transient events. A counterflow falling film desorber model is employed to account for the heat and mass transfer interactions between the liquid and vapor phases, inside the desorber. The liquid film flows down counter to the rising vapor, thereby exchanging heat with the counterflowing heated coupling fluid. A segmented model is used to account for these processes, and a solver is developed for performing rapid iteration and quick estimation of unknown vapor and liquid states at the outlet of each segment of the desorber. Other components such as the rectifier, expansion valves and solution pump are modeled as quasi-steady devices. System start-up is simulated from ambient conditions, and the coupling fluid temperatures are assumed to start up to their steady-state values within the first 90 s of simulation. It is observed that the system attains steady-state in approximately 550 s. The evaporator cooling duty and COP of the chiller during steady-state are observed to be 3.41 kW and 0.60, respectively. Steady-state parameters such as flow rates, heat transfer rates and concentrations are found to match closely with results from simulations using corresponding steady-state models. Several control responses are investigated using this dynamic simulation model. System responses to step changes in the desorber coupling fluid temperature and flow rate, solution pumping rate, and valve setting are used to study the effects of several control strategies on system behavior. Results from this analysis can be used to optimize start-up and steady state performances. The model can also be used for devising and testing control strategies in commercial applications.

The closed shell structures of certain all-carbon fragments originally observed in mass spectroscopy experiments leads to the enhanced stability of these species, known as fullerenes, which have excited sufficient interest amongst chemists and physicists over the last decade to warrant the award of the 1996 Nobel Prize for Chemistry to their discoverers. ¶ Studies of the stability, symmetry, and consequent remarkable properties of fullerenes began in earnest in 1991 with the development of a technique enabling the production and purification of macroscopic quantities of material. The best known and most widely studied fullerene is the truncated icosahedral C[subscript 60] molecule, which forms the basis of the present work. ¶ One important property of C[subscript 60] is that it forms salts with sufficiently electropositive species, such as the alkali metals. The resulting salts contain C[subscript 60] anions and are known as fullerides. Certain of these salts display metallic behaviour, and some superconduct at temperatures as high as 33 K. ¶ Three aspects of fulleride research are addressed in this work. These are: i) the preparation, crystal structure determination and superconductivity characterization of several new fullerides, particularly those including ammonia as an additional intercalant; ii) the electronic structure of the C[superscript n-, subscript 60] (n = 1 - 6) anions, as probed by solution-phase near infrared absorption spectroscopy; and iii) the molecular dynamics of a number of fullerides, superconducting and non-superconducting, by inelastic neutron scattering. ¶ This work has grown out of an Honours project also concerning C[subscript 60], the combined duration of the two studies covering essentially the entire history of this widely and competitively studied field.

Thesis (M.S.)--Duquesne University, 2006. / Title from document title page. Abstract included in electronic submission form. Includes bibliographical references (p.72) and index.