<p>Computer-Aided Concurrent Engineering Design (CACED) is an emerging field which stems from the realization that a holistic design approach, simultaneously considering all requirements, will result in systems that can be fielded quickly, and at the lowest practical lifetime cost. The philosophy inherent to CACED is that in a multi-faceted design arena, requirements such as cost, performance, reliability, produceability, size and supportability will conflict. Traditionally, designs are established then "audited" for compliance with various requirements. Subsequent "corrections" might then create new problems, but they certainly would slow the process and probably result in a less than optimum solution from the overall, long-term view.</p> <p> To concurrently (or simultaneously) consider numerous interdependent design issues, in order to optimize within constraints, requires an application-specific model and considerable computing power. The thrust of CACED is to develop appropriate models that allow designers to quickly establish and judge alternatives, simultaneously evaluating the compromises between often conflicting requirements.</p> <p>Computer hardware is readily available to perform design evaluation tasks--the challenge lies in establishing appropriate equations and a framework in which they are to be effectively used. This report explains CACED structure, illustrates a practical application to refrigeration system design, and suggests areas of further study.</p> / Master of Science

This dissertation presents experimental data correlations for the spatially - averaged convective heat transfer coefficient for thin walled closed containers during and after gas injection. The different modes of heat transfer were identified, and correlations were made for each. Correlations are presented for the injection period, post-top injection, post-bottom injection, post- tangential, post-radial injection, and post-ejection heat transfer for various tank geometries. Of special significance are the very high heat transfer rates that were shown to be present in some cases immediately after injection. Heat transfer rates were shown to be, for a short period, up to almost two orders of magnitude higher than the natural convection predictions would indicate.

Modifications to the quasistatic Carnot cycle are developed in order to formulate improved theoretical bounds on the thermal efficiency of certain refrigeration cycles that produce finite cooling power. The modified refrigeration cycle is based on the idealized endoreversible finite time cycle. Two of the four cycle branches are reversible adiabats, and the other two are the high and low temperature branches along which finite heat fluxes couple the refrigeration cycle with external heat reservoirs. This finite time model has been used to obtain the following results: First, the performance of a finite time Carnot refrigeration cycle (FTCRC) is examined. In the special case of equal heat transfer coefficients along heat transfer branches, it is found that by optimizing the FTCRC to maximize thermal efficiency and then evaluating the efficiency at peak cooling power, a new bound on the thermal efficiency of certain refrigeration cycles is given by $\epsilon\sb{m} = (\tilde\tau\sp2\sb{m}\ (T\sb{H}/T\sb{L}) - 1)\sp{-1},$ where $T\sb{H}$ and $T\sb{L}$ are the absolute high and low temperatures of the heat reservoirs, respectively, and $\tilde\tau\sb{m}=\sqrt{2}$ + 1 $\simeq$ 2.41 is the dimensionless cycle period at maximum cooling power. Second, a finite time refrigeration cycle (FTRC) is optimized to obtain four distinct optimal cycling modes that maximize efficiency and cooling power, and minimize power consumption and irreversible entropy production. It is found that to first order in cycling frequency and in the special symmetric case, the maximum efficiency and minimum irreversible entropy production modes are equally efficient. Additionally, simple analytic expressions are obtained for efficiencies at maximum cooling power within each optimal mode. Under certain limiting conditions the bounding efficiency at maximum cooling power shown above is obtained. Third, the problem of imperfect heat switches linking the working fluid of an FTRC to external heat reservoirs is studied. The maximum efficiency cycling mode is obtained by numerically optimizing the FTRC. Two distinct optimum cycling conditions exist: (1) operation at the global maximum in efficiency, and (2) operation at the frequency of maximum cooling power. The efficiency evaluated at maximum cooling power, and the global maximum efficiency may provide improved bench-mark bounds on thermal efficiencies of certain real irreversible refrigeration cycles.

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The performance of a flashing flow nozzle was quantified by efficiency and metastability measurements. Efficiency was calculated over a range of operating conditions, by using both inlet and exit conditions and the nozzle thrust. Metastability was quantified by a parameter that compared the experimental mass flow rate with homogeneous equilibrium and frozen state flow rates. The efficiency of the flashing flow nozzle was found to be less than half the efficiency of the nozzle while operating at near thermodynamic equilibrium. Attempts were made to improve nozzle performance by lowering the piping diameter immediately upstream of the nozzle to increase flow turbulence and encourage a uniform bubbly flow. Bubbly flow helps two-phase flows become less metastable, by generating a uniform distribution of bubbles that act as nucleation sites for flashing inception. Low flow metastabilities were found with high inlet qualities and small upstream piping diameters. These conditions also resulted in the highest flashing flow nozzle efficiencies; however, the efficiency showed a much less pronounced response to upstream piping diameter. The homogeneous equilibrium model was found to be an inaccurate predictor of nozzle performance. To satisfy this model, a shock must be positioned in the nozzle's divergent section, severely limiting nozzle efficiency. The effects of phase slip on nozzle efficiency were investigated with recommendations made for further research in this area. / Master of Science

This thesis summarises the work performed within the project known as ICE-COOL at the Royal Institute of Technology (KTH) on low tem-perature applications of ice slurry. The ICE-COOL project is a Euro-pean Community funded project within the 5th Framework Program. The task given to KTH was to find and characterize the best possible aqueous solution with a freezing point of -25 °C applicable for ice slurry with an operating temperature of -35 °C. The circumstances differ for low temperature ice slurry from medium temperature as a result of for example the change in thermo-physical properties due to increased addi-tive concentration and the lower temperature. Ice slurry is a mixture of fine ice crystals, water and freezing point de-pressant additives. The typical ice crystal size ranges between 0.1 to 1 mm in diameter. The main purpose of using ice slurries is to take advan-tage of the latent heat. More than a few requirements are to be fulfilled by an ideal ice slurry fluid. It should have good thermo-physical proper-ties, high heat transport and transfer abilities, as well as low pressure drop to facilitate small pumping power. The ice content of ice slurry af-fects all the mentioned abilities. Apart from the mentioned factors of the fluid, there are other aspects that have to be taken into consideration such as environmental pollution and toxicity, flammability, material compatibility, corrosion, handling security and cost. This thesis reports on the experiences accomplished and the initial ex-periments performed on low temperature ice slurry. The thesis also gives the background and fundamentals necessary for a discussion and com-parison of different aqueous fluids suitable for ice slurry in general and for low temperature in particular. In addition to the low temperature ap-plication, the thesis also reports on an initial energy consumption com-parison between using ice slurry and single-phase fluid in supermarkets by means of the simulation program CyberMart developed by Jaime Arias at the Department of Energy Technology at KTH. / QC 20101202

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A computer model of a fin and tube air-to-air heat exchanger is presented. The model incorporates a computational scheme to account for latent effects due to small amounts of moisture in one or both fluid streams. A testing program is described which was performed in order to mathematically characterize the heat transfer and pressure drop relationships of the tube with turbulator used in the heat exchanger. These relationships are included in the computer model. A comparison of the computer model to heat exchanger test data indicates that the computer model may be relied upon to provide design and analysis information. Finally, a parametric study is performed using the computer model in order to explore the characteristics of the heat exchanger and to demonstrate its usefulness to the heat exchanger designer. It is concluded that, in addition to presenting an analysis tool for heat exchanger design, there are several important secondary results. These include: verification of the modelling techniques, the analytical description of the tube with turbulator and, identification of a problem area in the header design.

Refrigeration systems employing the NH3-H2O absorption cycle provide cooling using a thermal energy input. This cycle relies on the zeotropic nature of the refrigerant - absorbent pair: because of the difference in boiling temperatures between NH3 and H2O, they can be separated through selective boiling in the desorber. Desorbers with counter-current flow of the solution and generated vapor enable efficient heat and mass transfer between the two phases, reducing the absorbent content in the generated vapor. Flow visualization experiments at temperatures, concentrations and pressures representative of operating conditions are necessary to understand the heat and mass transfer processes and flow regime characteristics within the component. In this study, a Flooded Column desorber, which accomplishes desorption of the refrigerant vapor through a combination of falling-film and pool boiling, was fabricated and tested. Refrigerant-rich solution enters the top of the component and fills a column, which is heated by an adjacent heated microchannel array. The vapor generated within the component is removed from the top of the component, while the dilute solution drains from the bottom. Flow visualization experiments showed that the Flooded Column desorber operated most stably in a partially flooded condition, with a pool-boiling region below a falling-film region. It was found that the liquid column level was dependent on operating conditions, and that the pool-boiling region exhibits aggressive mixing between the vapor and solution phases. Heat transfer coefficients were calculated from the data for the pool-boiling region, and were compared with the predictions of several mixture pool-boiling correlations from the literature. The correlations from the literature were in general unable to predict the data from this study adequately. It was found that the Flooded Column desorber yielded higher heat transfer coefficients within the pool-boiling region than those predicted by these correlations. Therefore, modifications to existing mixture boiling correlations are suggested based on the findings of this study. The resulting modified correlation predicts 33 of the 35 data points from this study within ±40%, with an average absolute error of 19%.