Void Fraction and Flow Pattern of R-290 in A Horizontal Evaporator: Effects of Pipe Diameter and Cooling Capacity

Void fraction and flow pattern play important roles in the performance of evaporator in an air conditioning system. In this paper, the behaviors of void fraction and flow pattern of refrigerant R-290 in a horizontal evaporator are discussed. To simplify the analysis, the evaporator was divided into 10 segments. The void fraction was calculated based on the refrigerant flow quality and the flow pattern was determined on the basis of superficial gas and liquid velocity plotted in the flow pattern map. The calculation was carried on air conditioning machines with nominal capacities of 2.64 kW, 3.62 kW, and 5.28 kW using the evaporator pipe diameters of 3/8 in and 5/16 in. Generally, the lower evaporating temperature results in the higher void fraction, higher gas superficial velocity, and lower liquid superficial velocity. For all ranges of evaporator diameter and cooling capacity, annular flow is found to be the dominant flow pattern. The wavy flow is only found in the lower cooling capacity and larger evaporator diameter. Meanwhile, the slug flow occupies 16.7% to 25.8% of evaporator segment.

Deformation characteristics of a single bubble in immiscible fluids

In order to investigate characteristics of bubble deformation in immiscible fluids, the bubble shape change during the interface and the relationship between aspect ratio(E) and dimensionless number of forces is obtained. A three-dimensional model is established and the free-floating behavior of a single bubble in immiscible fluids is numerically simulated by phase-field method. The simulation results are in good agreement with experimental results. The research shows that, in the lower liquid, the relationship between E and We, Ta, Re is distributed between two intersecting lines. In the upper liquid, the relationship between E and We, Ta, Re is distributed between two parallel lines. Comparing the bubble deformation and the influence of the forces. Compared with gravity, the inertial force plays a leading role in the bubble shape in the lower liquid and upper liquid. Compared with the viscous force, the surface tension dominates the bubble shape in the lower liquid.

PHYSICAL MODELING OF STEEL HOMOGENIZATION DURING FINISH ALLOYING IN THE MOLD

The article describes the method of finish alloying steel in molds in top and bottom casting. Due to the reduction of oxygen activity in the metal due to the relatively lower casting temperature than the previous stages of steelmaking redistribution, it is achieved the reduction of the ferroalloys loss and increasing the yield of useful elements of ferroalloys. An important indicator of the implementation of the proposed technology is the alloying of steel in the mold to obtain steel of a certain brand in small volumes. The aim of the study is to determine the rational place of addition of alloys into the volume of the melt and the method of casting, for the best dissolution of alloys in steel directly in the mold. To solve this problem, the method of physical modeling on a water transparent model using a fluorescent dye that glows brightly in ultraviolet light was used. The experiment consisted of three series of with different methods of casting and introduction of dye: 1) top casting with the introduction of dye into the mold; 2) bottom casting with the introduction of dye into the mold; 3) bottom casting with the introduction of dye in the trumpet. It was analyzed that the averaging of the dye is more efficient at a lower liquid level in the mold, because mixing occurs due to the flow of liquid in the mold, the higher the liquid level in the mold, the weaker the mixing flows. The research revealed minimization of averaging time at the optimal fluid level. For top and bottom casting with the addition of dye to the mold, the optimal level is 33%. When the dye is introduced into the center, there is a slight directly proportional increase in the time of complete homogenization with an increase in the liquid level in the mold. Among the analyzed methods of steel casting, the most effective in terms of homogenization of the alloying additive is bottom casting. The color of the liquid at different stages of filling the mold with the introduction of the dye at the level of 25% of the height of the mold is analyzed.

Energy Saving through Efficient BOG Prediction and Impact of Static Boil-off-Rate in Full Containment-Type LNG Storage Tank

Boil-off gas (BOG) from a liquefied natural gas (LNG) storage tank depends on the amount of heat leakage however, its assessment often relies on the static value of the boil-off rate (BOR) suggested by the LNG tank vendors that over/under predicts BOG generation. Thus, the impact of static BOR on BOG predictions is investigated and the results suggest that BOR is a strong function of liquid level in a tank. Total heat leakage in a tank practically remains constant, nonetheless the unequal distribution of heat in vapor and liquid gives variation in BOR. Assigning the total tank heat leak to the liquid is inappropriate since a part of heat increases vapor temperature. At the lower liquid level, BOG is under-predicted and at a higher level, it is over-predicted using static BOR. Simulation results show that BOR varies from 0.012 wt% per day for an 80% tank fill to 0.12 wt% per day at 10% tank fill.

Study on the impregnation quality of rubberwood (Hevea brasiliensis Müll. Arg.) and English oak (Quercus robur L.) sawn veneers after treatment with 1,3-dimethylol-4,5- dihydroxyethyleneurea (DMDHEU)

The efficacy of chemical wood modification is closely related to the permeability of the wood species and the cell wall deposition of the reagent, causing a permanent swelling (“bulking effect”). This study aimed to analyze how rubberwood (Hevea brasiliensis Müll. Arg.) and English oak (Quercus robur L.) may be affected by chemical wood modification, although they are known to show either variations in permeability or being less permeable. Thin clear veneers were treated with 1,3-dimethylol-4,5- dihydroxyethyleneurea (DMDHEU) which resulted in significantly reduced moisture-induced swelling and increased the resistance to static and dynamic indentation loads. The results evidenced significantly lower liquid uptakes in English oak compared to rubberwood, which directly affected the weight percent gains (WPGs) and restricted the range for potential improvements of the material properties. Surprisingly, rubberwood showed a lower cell wall bulking, which, in comparison with English oak, indicated less DMDHEU monomers entering the cell walls and rather being located in the cell lumens. Atypical for treatments with cell wall penetration chemicals, no further decrease in maximum swelling (SM) was detected with increasing bulking in rubberwood specimens. English oak showed higher variations in DMDHEU distribution within treated veneers and between earlywood and latewood areas, effecting a less homogeneous performance.

Partial Upgrading of Athabasca Bitumen Using Thermal Cracking

The current industry practice is to mix bitumen with a diluent in order to reduce its viscosity before it can be pumped to refineries and upgraders. The recovery of the diluent and its recycling to the producers, on the other hand, pose major environmental and economic concerns. Hence, onsite partial upgrading of the extracted bitumen to pipeline specifications presents an attractive alternative. In this work, thermal cracking of Athabasca bitumen was carried out in an autoclave at 400 °C, 420 °C and 440 °C in presence and absence of drill cuttings catalyst. At 400 °C, despite no coke formation, the reduction in viscosity was insufficient, whereas at 440 °C, the coke yield was significant, ~20 wt.%. A balance between yield and viscosity was found at 420 °C, with 88 ± 5 wt.% liquid, ~5 wt.% coke and a liquid viscosity and °API gravity of 60 ± 20 cSt and 23 ± 3, respectively. Additionally, the sulfur content and the Conradson carbon residue were reduced by 25% and 10%, respectively. The catalytic thermal cracking at 420 °C further improved the quality of the liquid product to 40 ± 6 cSt and 25 ± 2 °API gravity, however at slightly lower liquid yield of 86 ± 6 wt.%. Both catalytic and non-catalytic cracking provide a stable liquid product, which by far exceeds pipeline standards. Although small relative to the energy required for upgrading in general, the pumping energy requirement for the partially upgraded bitumen was 3 times lower than that for diluted bitumen. Lastly, a 5-lump, 6-reaction, kinetic model developed earlier by our group successfully predicted the conversion of the bitumen to the different cuts.

Temperature dependence of Gilbert damping in manganite/normal metal heterostructure

The temperature dependence of the spin-pumping effect on the Gilbert damping in a bilayer based on epitaxial manganite film grown on neodymium galate substrate was investigated by measuring of the linewidth of the ferromagnetic resonance spectrum (FMR). Ferromagnetic resonance in thin ferromagnetic manganite La0.7Sr0.3MnO3 (LSMO) films is used to produce a spin current at the interface between a metallic and a ferromagnetic layer. Pt/LSMO/NGO, Au/LSMO/NGO and LSMO/NGO heterostrucutres were measured. An increase of the linewidth in FMR spectrum at the temperature lower liquid nitrogen temperature (77K) is observed .

Experimental Study on Separation of CO2 by Using Hollow Fiber Membrane Contactors with Amino Acid Salts Solutions

Experimental on CO2 removal from flue gas using polypropylene hollow fiber membrane contactors were conducted in this study. Absorbents including aqueous PG, SG were used to absorb CO2 in the experiments, and comparing with aqueous MEA. The experimental results showed that the mass transfer rate of PG and SG increased gradually in experiments while the absorbent concentration can not be elevated without limitation. That may show the mass transfer rate will be eventually saturated at a certain concentration value. The aqueous PG can be selected to absorb CO2 in membrane contactors at a lower liquid flow rate to reduce the potential to wet the membrane. Comparing PG and SG with MEA. The performance of PG is superior to SG and MEA under the same operating conditions.

Oscillating Micromixers on a Compact Disc

In this study, mixing efficiencies of oscillating micromixers based on a compact disc under various operating conditions and geometric parameters were analyzed. By alternating the direction of rotation, stirring of liquids inside the chamber can be used for mixing. The experimental results showed that under the same operating conditions, deeper chamber and lower liquid filling ratio resulted in better mixing efficiency. Under the same distance of motion, oscillating frequency had more impact on the mixing efficiency than the oscillating amplitude. In addition, the experimental results also demonstrated that this batch mixing mechanism can also be utilized to achieve satisfactory mixing of liquids with viscosity of 100 cp within 10 seconds.

Spin-coating of vertically stratified thin liquid films

Spin-coating is a process used to fabricate thin films for device applications. In this paper, lubrication theory is used to derive an axisymmetric model for the spin-coating of two immiscible vertically stratified Newtonian thin films. The model includes gravitational, van der Waals, capillary and viscous forces, differences in liquid layer properties and evaporation/condensation effects. Thinning calculations focus on the effects of viscosity and condensation/evaporation. In this case, for layers of uniform thickness, the lower layer thins monotonically yet never reaches zero thickness. With evaporation mass loss the upper layer disappears in finite time, whereas with condensation effects the upper layer approaches a steady-state thickness. Fully nonlinear calculations are carried out for films with non-uniform thickness and the deviation of the interfaces from the flat state is monitored. In general, disturbances to the lower layer have a greater effect on the upper layer than those of disturbances of the upper layer on the lower layer. Disturbances along the upper gas–liquid free surface propagate outward more rapidly than those along the lower liquid–liquid interface and disturbances that decrease the film thickness tend to dissipate more slowly.