Transient and steady state simulations of an advanced desiccant enhanced cooling cycle.

摘要

In this thesis, the parabolic concentration profile (PCP) assumption was investigated for use in modeling of a rotary dehumidifier. The transient solution utilized an explicit marching solution method called the Bulirsch-Stoer method. The explicit numerical scheme required very small stepsizes due to stability considerations and as a consequence was found to be rather time consuming. The periodic steady state (PSS) model utilized the Crank-Nicholson discretization scheme. A sparse matrix solving package was used to solve the resulting system of discretized equations. The PSS model was extremely computationally efficient. Comparison of the two models with experimental data revealed that the PCP model accuracy was dependent on the particle's Fourier number for mass transfer. A quartic concentration profile (QCP) assumption was also investigated. For this study, the QCP model did not offer significantly improved predictions over the PCP model in the region of interest.;The PCP model is much more suited for modeling a variety of materials than the commonly utilized pseudo gas side model which uses an empirically degraded mass transfer coefficient on the air side to account for the diffusion resistance of the solid side. The PCP model uses a commonly available adsorption property, the effective diffusivity, to incorporate the effects of mass transfer resistance of the desiccant particle. The PCP model also offers much lower computational effort than the gas and solid side model, which more rigorously accounts for the solid side resistance.;The PCP model was used to perform simulations of an innovative desiccant assisted cooling system proposed by Cromer in 1988 called desiccant enhanced cooling (DEC). The DEC system uses mass transfer in a similar way that a heat pipe system uses heat transfer to enhance the latent capabilities of a cooling coil. The simulations determined that the DEC system experiences a dramatic rise in latent capacity compared with a vapor compression (VC) unit alone. A Second Law analysis was also performed on the DEC system and the major sources of destruction of available energy were identified.;Since heat pipes are currently considered the state of the art technology for controlling the latent load of a conditioned space, it was appropriate to compare the DEC system to a heat pipe system. The DEC system compared favorably to the heat pipe system. The preliminary investigation indicated that the DEC system is promising and could become a contending technology in the area of increased humidity control over the currently favored method of heat pipe technology.