Digitized by Kansas Correctional Industries

The performance of two innovative collector-loop heat exchangers used in pumped circulation solar water heaters was investigated experimentally and numerically, and TRNSYS simulation models were developed for evaluating long-term performance. The heat exchangers evaluated are a narrow gap mantle on a vertical tank and a falling film system in a standard gas hot water tank. The falling film system is based on minor changes to a mass produced tank and does not require the addition of a special purpose heat exchanger. The heat exchangers were assessed for a range of operating conditions to quantify the overall heat exchanger UAhx value and the effect of thermal stratification in the tank. Flow visualisation experiments and CFD modelling were also performed to provide detailed understanding of the operation characteristics of the heat exchangers. For each heat exchanger, the measured and computed collector loop side heat transfer coefficients were correlated by developing new Nusselt number versus Reynolds and Prandtl number functions. New heat transfer correlations were developed for both types of heat exchanger and have been implemented into full solar water heater simulation models in TRNSYS. Predictions of tank stratification conditions in each heat exchanger were in good agreement with experimental data. Compared to a standard direct circulation system, the annual performance of the mantle system and falling film system are 8% and 18% less respectively. The decrease in system performance is due to the heat exchanger penalty and reduced thermal stratification in the storage tank, however they have the added features of freeze protection and suitability for hard water areas. They are also cheaper to manufacture than convectional heat exchange systems. The annual performance of a falling film solar water heater was shown to be affected by de-stratification if an in-tank electric booster was used. However, improved performance can be achieved if an advanced switching controller is used to modulate the flow rate such that the collector return temperature is always higher than the temperature in the top of the tank.

Bibliography: leaves 273-287. / xviii, 289 leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / The aim of this thesis is to develop a new method for the conceptual design of heat exchanger networks. The initial designs can be optimized using conventional non-linear optimization techniques in the subset of the problem's initial dimensionality. / Thesis (Ph.D.)--University of Adelaide, Dept. of Chemical Engineering, 1994

Thesis (M.S.)--University of Nevada, Reno, 2006. / "May 2006." Includes bibliographical references (leaves 46-48). Online version available on the World Wide Web.

Thesis (M.S.)--University of Nevada, Reno, 2004. / "December 2004." Includes bibliographical references (leaves 43-46). Online version available on the World Wide Web.

An experimental study was performed in which an ammonia-water solution was desorbed within a branching fractal-like microchannel array. The solution entered in the center of a disk, and flowed out radially until discharging in to a gravity-driven separation chamber. Heat was added to the ammonia-water through a thin wall, above which flowed heat transfer oil in a separate branching fractal-like microchannel array. Such arrays have been shown to utilize the increased heat transfer coefficients seen in parallel channel arrays; however, they do so with a lower pressure drop. An experimental flow loop consisting of ammonia-water and heat transfer oil sub-loops was instrumented along with a test manifold for global measurements to be taken. Temperature, pressure, density and mass flow rate measurements permitted calculation of desorption and heat transfer characteristics. Parameters included oil mass flow rate, oil inlet temperature, and strong solution flow rate, while strong solution concentration, temperature, and weak solution pressure were kept constant. The desorber was assumed to achieve equilibrium conditions between the vapor and weak solution in the separation chamber. The exit plenum was large and acted as a flash chamber, making the assumption reasonable. The vapor mass fraction was determined from knowledge of the weak solution saturation temperature. Heat exchanger analyses (LMTD and ε-NTU) were done to determine the heat transfer characteristics of the desorber. Calculated values of UA are shown to be as high as 5.0 W/K, and desorber heat duties were measured as high as 334 W. Strong solution, at 0.30 mass fraction, was desorbed into weak solution and vapor with concentrations ranging from 0.734 to 0.964. Circulation ratios, defined as strong solution mass flow rate per unit desorbed vapor mass flow rate, varied in this study from 3.4 to 20. A method for specifying desorber operating conditions is described, in which a minimum desorber heat input per unit vapor flow rate is determined at an optimum circulation ratio. A description of how the circulation ratio behaves as a function of strong solution mass flow rate, oil flow rate, and the maximum temperature difference between oil and ammonia-water solution is shown. / Graduation date: 2006

The Oregon State University (OSU) Radiation Center (RC) is the location of a one quarter scale model of the Westinghouse Electric Corporation advanced light-water nuclear reactor design called the AP-600. The full scale AP-600 is a 600 megawatt electric nuclear power plant that incorporates unique passive systems to perform the safety functions currently required of all existing nuclear power plants. Passive safety refers to a system's ability to perform its desired function using natural forces such as gravity and natural circulation. This reduces the reliance on active systems to assure plant safety. The Advanced Plant Experiment (APEX) at the OSU RC is an electrically heated simulation of the AP-600 that includes the Nuclear Steam Supply System (NSSS) and all of the passive safety systems. The APEX facility was funded by the United States Department of Energy and the Westinghouse Electric Corporation. The facility was built to perform the long term cooling tests necessary for design certification of the AP-600. The data taken will be used to benchmark the thermal hydraulic computer codes applied in the design certification process and to better understand the phenomena involved in the full scale AP-600. This paper presents the analysis of the Passive Residual Heat Removal System (PRHR) and in particular the PRHR's "c"-shaped heat exchanger (PRHR Hx). This paper includes analysis and modeling of the PRHR Hx including: hydraulic flow parameters, heat rejection capability, an empirical correlation for determining pressure drop, and an examination of the flow phenomena that occurs in the tank in which the heat exchanger is installed. / Graduation date: 1997

Dissertation (Ph. D.)--University of Stellenbosch, 1992. / Bibliography. Also available via the Internet.

The fouling characteristics of a desalted crude oil were investigated in a systematic investigation. There are two main parts in this study, the dry bulk tests (dehydrated crude oil) and the wet bulk tests (to which desalter brine was added). Three barrels of desalted crude oil provided by Amoco Oil Company were studied. For the dry bulk tests, no brine was added to the crude oil. The effects of fluid velocity and surface temperature on fouling were investigated. The higher the surface temperature the greater the fouling was observed. Fouling decreased with an increase of fluid velocity. Fluid velocity had a stronger effect on fouling at low surface temperatures than at high surface temperatures. It was also observed that the fouling behavior of crude oil depended on small difference in composition. The threshold surface temperatures for the initiation of fouling were 400-450 °F (3.0 ft/sec), 525-550 °F (5.5 ft/sec), 550-600 °F (8.0 ft/sec) and about 600 °F (10.0 ft/sec) for Barrel No. 2 and Barrel No. 3. For Barrel No. 1 however, the threshold surface temperatures were about 550 °F (3.0 ft/sec) and 600 °F (5.5 ft/sec). For the wet bulk tests, a certain amount desalter brine (weight percentage = 0.8%) was added to the crude oil for each run. The effects of fluid velocity, surface temperature and the presence of brine on fouling were investigated. Higher surface temperature enhanced fouling considerably. Fouling was reduced as fluid velocity was increased. It was shown that brine had a strong effect on fouling. No fouling occurred for velocities of 5.5 and 8.0 ft/sec at a surface temperature of 350 °F which was a condition for which an aqueous phase was present and the salt remained in solution. Significant fouling occurred for velocities of 5.5 and 8.0 ft/sec at a surface temperature operated at a low 400 °F (Tb = 300 °F) which was a condition for which the aqueous phase at the heat transfer surface was dissolved or boiled to extinction and the salt was deposited on the heat transfer surface. / Graduation date: 1991

Thesis (M.S.)--Mississippi State University. Department of Mechanical Engineering. / Title from title screen. Includes bibliographical references.