Demand Flow

Demand Flow is a variation on the theme of postponement. Costanza has described Demand Flow in his book, The Quantum Leap. He uses DFT as an acronym for demand flow technology.  

DFT is an organized approach to matching production with demand, as the term implies. It envisions taking a pile of parts that is assembled to order. So, DFT works well with products designed around modules or common parts. DFT incorporates many of the concepts ascribed to the Toyota Production System and other approaches. 

Our conclusion is that DFT techniques must move back into the supply chain to have the greatest impact. Dealing with final assembly, particularly in a complex supply chain, is the tip of the iceberg. The roots should spread backward into the supply base to have the greatest impact. This also includes design for commonality to maximize the potential for postponement. 

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Air line respirators are similar to hose respirators, except that they are supplied with compressed air from a clean air source and compressor. They provide complete protection, and because they offer little in the way of breathing resistance, they are more suitable than hose respirators for prolonged use. There are two basic types continuous flow and demand flow. 

Nearer, through establishing customer loyalty by offering added-value services like customized products, responsiveness to demand, flow trace-ability, order tracking via the internet, etc. 

Demand Flow is the registered trademark of the John Costanza Institute of Technology. 

Demand flow A technique to speed product final assembly. Demand flow uses the concept of a pile of parts that can be assembled in response to actual customer orders. The term is trademarked by the John Costanza Institute of Technology. 

Examination of Equations (3.57) and (3.58) for the frictional and dynamic pressure losses indicates that both are functions of length and width of the channel, liquid temperature, and demand flow rate. Because both of these contributions are essentially third-order effects in a 1-g environment, the horizontal configuration was chosen to null out hydrostatics to even be able to measure these small pressure drops. At all points within the channel the hydrostatic pressure is constant, and according to the FTS model, pressure drop across the screen would be constant as well. 

The solution shows that the velocity inside the channel becomes more concentrated near the outlet as the demand flow rate increases. At low Reynolds numbers, the resultant pressure drop across the screen is fairly linear, and at high Re numbers, the pressure field inside the channel becomes highly nonlinear. The implication is that, as demand flowrate increases, the nonlinear pressure distribution causes a higher susceptibility to breakdown near the channel outlet. Increasing both channel width and height acts to prolong the breakdown point at the cost of a higher channel mass. 

Table 13.6 Required Minimum Screen Area and Channel Width for Two Different Liquid Hydrogen Depot Concepts at a Demand Flow Rate of 2.75 kg/s...

Table 14.1 Comparison of Model Predicted Percent of Screen Exposed to Pressurant Gas atBreakdown in 1-g and Microgravity fora 325 x 2300 Screen and Channel in Liquid Hydrogen at a Demand Flow Rate of 0.01 kg/s...

FIGURE 14.7 Flow-through-Screen Pressure Drop as a Function of Distance along the Liquid Acquisition Device Channel for Varying Demand Flow Rates. Channel length is 2.23 m. 

Finally, to examine the effect of channel dimensions and demand flow rate on channel performance in microgravity. Figure 14.9 plots the velocity profile as a function of various channel geometries and flow rates. Channel dimensions and corresponding exit Re numbers are shown on the right. It is noticeable that at a smaller height and width, the velocity... 

FIGURE 14.12 Upstream Radius of Curvature as a Function of Downstream Radius of Curvature for a Demand Flow... 

For a given propellant, liquid temperature and pressure, and demand flow rate, the height of the sump constrains the minimum allowable downstream radius of curvature. 

For the vanes, tank drain simulation was not required since the model already considers an EOL configuration. To size the vanes, the height and number of vanes were varied to submerge the sump fully, the liquid filet volume was calculated (following the method outlined in Section 14.3), and expulsion efficiency and PMD mass were obtained. Vanes were also sized to maximize expulsion efficiency at a given demand flow rate. If multiple vane systems could achieve the same expulsion efficiency, the system with the lowest mass was chosen. 

To examine basic trends in the model, tank drains were simulated for a screen channel LAD with a fixed height and width of 2.54 cm each at a demand flow rate of 0.01 kg/s for a 325 X 2300 screen in LH2, using GHe to pressurize, varying the three main thermodynamic properties of liquid temperature, pressure, and pressurant gas temperature. All screen parameters are taken from Chapter 3. 

Table 14.2 Screen Channel Liquid Acquisition Device Expulsion Efficiencies for Variable Thermodynamic Conditions, Demand Flow Rates, and Screen Types...

To determine how the IADs scale with flow rates, in order to compare performance with the vane PMD, simulations were also run at multiple flow rates between 1 x 10 and 2.76 x 10 kg/s for a 325 x 2300 screen in LH2 at a fixed liquid and pressurant gas temperature of 20.3 K each and a tank pressure of 101 kPa. Table 14.4 presents the resultant expulsion efficiencies and PMD mass for the screen channel LAD cases at different demand flow rates. The results show that up to a mass flow rate of 0.0049 kg/s, the LAD can achieve a maximum expulsion efficiency of 98.1% of the small-scale LH2 tank. This upper limit is due to the fact that the gallery arm cannot access the small residual propellant pool in between consecutive arms at very low fill levels due to the closed flow... 

Table 14.4 Screen Channel Liquid Acquisition Device Sizing as a Function of Demand Flow Rate for Case A Ullage Bubble Growth...

FIGURE 14.17 Recommended Propellant Management Device fora Given Demand Flow Rate Range for a Small Scale Liquid Hydrogen Storage Tank in Microgravity. 

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