Rigorous CO₂ absorption models were developed for aqueous 4.5 m K+/4.5 m PZ, monoethanolamine (7m - 9m), and piperazine (8m) in Aspen Plus® RateSepTM. The 4.5 m K+/4.5 m PZ model uses the Hilliard thermodynamic representation and kinetics based on work by Chen. The MEA (Phoenix) and PZ (5deMayo) models incorporate new data for partial pressure of CO₂ vs. loading and kinetics from wetted wall column data. They use reduced reaction sets based on the more relevant species present at the expected operating loading. Kinetics were regressed to match reported carbon dioxide flux data using a wetted wall column (WWC). Density and viscosity were satisfactorily regressed to match newly obtained experimental data. The activity coefficient of CO₂ was also regressed to include newly obtained CO₂ solvent solubility data. The models were reconciled and validated using pilot plant data obtained from five campaigns conducted at the Pickle Research Center. Performance was matched within 10% of NTU for most runs. Temperature profiles are adequately represented in all campaigns. The calculated temperature profiles showed the effect of the L/G on the location and magnitude of the temperature bulge. As the L/G is increased the temperature bulge moves from near the top of the column towards the bottom and its magnitude decreases. Performance improvement due to intercooling was validated across the campaigns that evaluated this process option. Absorber intercooling was studied using various solvent rates (Lmin, 1.1 Lmin and 1.2 Lmin). It is most effective at the critical L/G where the temperature bulge without intercooling is in the middle of the column. In this case it will allow for higher absorption by reducing the magnitude of the bulge temperature. The volume of packing to get 90% removal with L/Lmin =1.1 at the critical L/G is reduced by 30% for 8m PZ. For MEA and a solvent flow rate of 1.1 Lmin packing volume is increased with intercooling at constant L/G. This increase is compensated by higher solvent loadings that suggest lower stripping energy requirements. The critical L/G is 4.3 for 8m PZ, 6.9 for 9m MEA and 4.1 for K+/PZ. / text

 There are two concentrations in this project. One is to explore the possibility to construct negative acoustic impedance by electronic techniques, and the other is to see whether such method can be utilized to build effective sound absorber using electromagnetic actuator (here we adopt the moving-coil loudspeaker as sample) with a shunt circuit. Our study begins with analytical analysis, and the result shows that it is impossible to gain independent control of basic acoustic impedance components (mass, stiffness and damping) by simple circuits. Two alternative designs are put forward as a compromise. One is the series circuit with NIC to simulate the negative acoustic impedance, and another is the series-parallel circuit with NIC. Theoretical prediction shows that we can indeed obtain broadband negative mass and local negative stiffness by these two types of circuits, and that we can achieve broadband noise control with simple electronic shunt circuits despite fact that completely independent control over each parameter is not possible. We argue that these conclusions represent significant technological and economic advantage worthy of further development. All analytical results are validated by experiments with satisfactory agreement. The sample loudspeaker with shunt circuit is tested with acoustic impedance tube. The rig consists of a DC powered op-amp circuit and a loudspeaker. An efficient Matlab code controls the excitation sound generation and data acquisition with AD/DA cards. Two typical and most interesting results are summarized here. In the first, a series type circuit with NIC is used to construct negative equivalent mass and local (banded in frequency domain) negative stiffness. We experimentally demonstrated that it is rather easy to reduce original mass of the loudspeaker to half of its original value and it could be reduced to almost zero. This is evidenced by a very flat sound absorption coefficient curve from 100 Hz to 1000 Hz. The second circuit is a series-parallel circuit. It’s an improved design from the first type. This type of circuit can, to a certain extent, decouple the stiffness and mass controls. The results show that we can reduce mass globally (in the frequency domain) and stiffness at low frequencies. The original mass of the sample loudspeaker is almost eliminated and the stiffness at low frequencies is reduced too. In terms of the spectrum of sound absorption coefficient, it manifests itself through a broadband absorption with prominent improvement in the low frequency region. Finally, potential applications for our designs are discussed. A tunable low frequency resonance absorber is designed. Prediction results point out that, by choosing the right parameters of the circuit, we can achieve 100% absorption at any given low frequency. Thin absorber is another potential application. With the same dimension, the performance of a thin absorber is much better than that of the standard sound absorption construction. A 90% noise absorption from 300Hz-600Hz and 50% absorption from 250Hz-1000Hz is achieved by our new design. The dimension can be further reduced in theory. Finally, a broad-band absorber with 50% or more absorption over 80Hz-1000Hz is demonstrated. / published_or_final_version / Mechanical Engineering / Master / Master of Philosophy

Not available / text

Not available / text

A detailed investigation of novel air-coupled absorbers for use in a diesel engine exhaust-driven ammonia-water absorption system operating in extreme ambient conditions was conducted. Electrically driven vapor-compression systems are under scrutiny due to the environmental impact of synthetic refrigerants and the exacerbation of electric utility loads during peak demand periods. One alternative to vapor-compression systems is the absorption heat pump that uses environmentally benign working fluids and can be driven by a variety of heat sources, including waste heat and solar thermal processes. Direct air coupling of the absorber and condenser instead of indirect hydronic coupling can reduce absorption system size, complexity, and inefficiency, but materials compatibility issues with ammonia-water and the poor heat transfer properties of air present challenges. Heat and mass transfer modeling was used to predict the performance of round-tube corrugated-fin and compact tube-array absorbers designed for a 2.64-kW absorption chiller operated in high ambient temperature (51.7°C) conditions. A single-pressure ammonia-water test facility was constructed and used in conjunction with a temperature- and humidity-controlled air-handling unit to evaluate the absorbers at design and off-design operating conditions. Absorber performance was recorded over a range of air temperatures (35-54.4°C), air flow rates (0.38-0.74 m3 s-1), inlet solution temperatures (92-102°C), concentrated solution flow rates (0.006-0.010 kg s-1), and concentrated solution concentrations (38-46%). At design conditions, round-tube corrugated-fin absorbers of 394 and 551 Fins Per Meter (FPM) demonstrated comparable performance (Q394-FPM,exp = 4.521±0.271 kW; Q551-FPM,exp = 4.680±0.260 kW), and measured heat transfer rates were 0.7-1.9% AAD higher than those predicted through modeling. The measured heat transfer rate in the prototype tube-array absorber was significantly lower than the values predicted at design conditions (Qprot,exp = 2.22±0.24 kW; Qprot,mod = 4.33 kW). Maldistribution of the two-phase flow in the tube array is the probable cause of the disparity between the prototype absorber data and model predictions. Results from this investigation can be used to guide the development of air-coupled heat and mass exchangers for compact absorption heat pumps.

Not available / text

No description available.

No description available.

No description available.

No description available.