Quantifying Fluid Shear Stress in a Rocking Culture Dish

Fluid shear stress (FSS) is an important stimulus for cell functions. Compared with the well established parallel-plate and cone-and-plate systems, a rocking “see-saw” system offers some advantages such as easy operation, low cost, and high throughput. However, the FSS spatiotemporal pattern in the system has not been quantified. In the present study, we developed a lubrication-based model to analyze the FSS distributions in a rocking rectangular culture dish. We identified an important parameter (the critical flip angle) that dictates the overall FSS behaviors and suggested the right conditions to achieving temporally oscillating and spatially relatively uniform FSS. If the maximal rocking angle is kept smaller than the critical flip angle, which is defined as the angle when the fluid free surface intersects the outer edge of the dish bottom, the dish bottom remains covered with a thin layer of culture medium. The spatial variations of the peak FSS within the central 84% and 50% dish bottom are limited to 41% and 17%, respectively. The magnitude of FSS was found to be proportional to the fluid viscosity and the maximal rocking angle, and inversely proportional to the square of the fluid depth-to-length ratio and the rocking period. For a commercial rectangular dish (length of 37.6 mm) filled with ∼2 mL culture medium, the FSS at the center of the dish bottom is expected to be on the order of 0.9 dyn/cm2 when the dish is rocked +5° at 1 cycle/s. Our analysis suggests that a rocking “see-saw” system, if controlled well, can be used as an alternative method to provide low-magnitude, dynamic FSS to cultured cells

Combustion characterization of hybrid methane-hydrogen gas in domestic swirl stoves.

Combustion of hybrid natural gas (methane) and hydrogen mixture in domestic swirl stoves has been characterized using hot-state experiments and numerical analysis. The detailed combustion mechanism of methane and hydrogen (GRI-Mech 3.0) has been simplified to obtain reduced number of chemical reactions involved (82% reduction). The novel simplified combustion mechanism developed has been used to obtain combustion characteristics of hybrid methane-hydrogen mixture. The difference between the calculations from the detailed and the simplified mechanisms has been found to be < 1%. A numerical model, based on the simplified combustion model, is developed, rigorously tested and validated against hot-state tests. The results depict that the maximum difference in combustion zone's average temperature is < 13%. The investigations have then been extended to hybrid methane-hydrogen mixtures with varying volume fraction of hydrogen. The results show that for a mixture containing 15% hydrogen, the release of CO due to combustion reduces by 25%, while the combustion zone's average temperature reduces by 6.7%. The numerical results and hot-state tests both confirm that the temperature remains stable when hybrid methane-hydrogen mixture is used in domestic swirl gas stoves, demonstrating its effectiveness in cooking processes

Theoretical and experimental investigations on the combustion characteristics of three components mixed municipal solid waste.

The combustion characteristics of Mixed Municipal Solid Waste (MMSW) play a vital role in dictating the efficiency of the incineration process. At present, few studies on combustion characteristics of three components MMSW and the establishment of corresponding comprehensive kinetic model of single component waste have been reported. In the present study, based on the law of mass action and Badzioch's relation, the mathematical expressions for describing the TG (Thermogravimetric) curves and the DT (Differential thermal) curves of single component MMSW are derived. A comprehensive kinetic model for the combustion characteristics of single component MMSW is developed and the appropriateness of the model is confirmed by the experimental results. The calculated TG curves closely agree with the experimental curves; the maximum deviation between the experimental and calculated curves is within 5%. Based on the principle of mixture experiments, the co-combustion characteristics of MMSW composed of food bag, disposable chopstick and cotton cloth are studied by using TGA (Thermogravimetric Analysis) and DTA (Differential Thermal Analysis). It has been found that the activation energy of three components MMSW is lower than that of single component. Finally, based on multiple regression analysis for the design of mixture experiments and the corresponding data, an empirical formula for calculating activation energy of three components MMSW is obtained. The experimental and calculated values match closely; the maximum deviations between them is within 7%. The empirical formula provides a robust way to calculate activation energy of three components MMSW

Design of a novel α-shaped flue gas route flame incinerator for the treatment of municipal waste materials.

In order to improve the combustion characteristics of municipal waste materials and reduce excess pollutants generated during the incineration process, this study develops a novel waste incinerator with an α-shaped flue gas route. This has been achieved through the application of momentum vector synthesis theory in order to modify the secondary air structure in a conventional incinerator, resulting in enhanced combustion efficiency of the incinerator. Computational fluid dynamics (CFD)-based cold-state test results demonstrate that, with appropriate modifications to the design of the incinerator, the flue gas propagates through a longer α-shaped route rather than conventional L-shaped route. Hot state tests have been carried out on a full-scale 750 tons/day waste incinerator. Test rests show that the temperature of the flue gas increases by 138% under the front arch when secondary air supply is being incorporated into the design of the incinerator, resulting in better combustion of the municipal waste materials, lower emissions and higher thermal efficiency of the incinerator. The results obtained in this study confirm the rationality and feasibility of momentum flow rate method for better design of waste incinerators

Numerical Investigation of Wave Slamming of Flat Bottom Body during Water Entry Process

A numerical wave load model based on two-phase (water-air) Reynolds-averaged Navier-Stokes (RANS) type equations is used to evaluate hydrodynamic forces exerted on flat bottom body while entering ocean waves of deploying process. The discretization of the RANS equations is achieved by a finite volume (FV) approach. The volume of fluid (VOF) method is employed to track the complicated free surface. A numerical wave tank is built to generate the ocean waves which are suitable for deploying offshore structures. A typical deploying condition is employed to reflect the process of flat bottom body impacting waves, and the pressure distribution of bottom is also presented. Four different lowering velocities are applied to obtain the relationship between slamming force and wave parameters. The numerical results clearly demonstrated the characteristics of flat bottom body impacting ocean waves

The innovative design of air caps for improving the thermal efficiency of CFB boilers.

Air caps are an effective way of ensuring uniformity of air flow in Circulating Fluidized Bed (CFB) boilers. Published literature on the design and configuration of these air caps is severely limited. In this study, extensive theoretical as well as experimental investigations have been carried out to design novel air caps in order to improve efficiency of CFB boilers. A small-scale test bench of 220 t/h CFB boiler has been developed, integrated with novel air caps. It has been observed that inhomogeneity in air flow velocity decreases from 65.79% to 21.25%, while the pressure drop decreases by 20%. A mathematic model of air caps has been derived and its accuracy verified through cold tests. Two empirical correlations for calculating the pressure drop and the air jet penetration length of the novel air caps have been obtained and verified. Finally, in order to validate the innovative design of air caps, this methodology has been implemented to a full-scale 220 t/h CFB boiler. The hot test results depict that the thermal efficiency of the boiler has increased from 86.4% to 91.8% when tested with the novel air caps in-place, which is equivalent to a saving of 6000 tons of coal per year