Wetting balance curve

FIGURE 8.18 Wetting balance curve. Fmm Joint Industry Standard.)... 

FIG. 8 Wetting balance force vs. time wetting balance curve. Drawings at the top of the figure correspond to the labeled points on the curve. (From Ref. 26.)... 

The PCB surface finishes all have their unique wetting curves and shapes. Understanding what a good curve should look hke for a given surface finish is very important, especially when using the wetting balance to detect subtle changes that are process indicators of potential problems to come. A test that does not provide numerical data will never be able to achieve this. 

In general, a complete understanding of the wetting balance force-time curve for solders awaits a rigorous theoretical analysis capable of resolving aU the dynamic aspects of the solder flow noted above. 

This result (which is far from obvious) allows us to perform adiabatic cooling calculations with relative ease using the psychrometric chart. First locate the initial state of the air on the chart then locate the final state on the constant wet-bulb temperature line that passes through the initial state (or on the 100% humidity curve if cooling below the adiabatic saturation temperature takes place) and finally perform whatever material and energy balance calculations are required. Example 8.4-7 illustrates such a calculation for an adiabatic humidification operation. 

The psychrometric chart for most gas-liquid systems would show a family of adiabatic saturation curves in addition to the families of curves shown on Figures 8.4-1 and 8.4-2. However, for the air-tvater system at 1 atm, the adiabatic saturation curve through a given state coincides with the constant wet-bulb temperature line through that state, so that Tas = Twb- The simple material and energy balance procedure for adiabatic cooling outlined in this section is possible only because of this coincidence. 

To apply the mass balance to the Sound, the details of the sand distribution were studied in a small area along the north shore. A series of short cores were taken along the tracks shown in Fig. 3. The top 20 cm of these samples was wet sieved and the shell removed with dilute HCl. The material that passes a 1-mm screen but is retained on a 0.064-mm screen is defined as sand. The volume of material retained on the fine screen was measured after a standard settling time (1 hr) and was compared to the initial volume of sediment to define the sand-mud ratio. The weight-percent sand was found to be about 1.2 times the sand-mud ratio. Harbors along the north shore in the study area have mud floors with a lower sand content than the offshore sediments. South of the harbors, however, the curves of constant sand fraction run nearly north and south... 

Heparin was released from 1% heparin-PVA gel "beads at 1.7 x 10 yg/g wet gel/min. This rate was determined from the approximately linear portion of the heparin content versus PBS (phosphate buffered saline, pH 7.4) wash time curve (between 300 and 500 hours) by using the toluidine blue method ( ). This release rate was 1/1000 of the minimum rate considered necessary for thromboresistance ( ). After washing, the remaining heparin content was determined indirectly by mass balance to be approximately 7.1 mg/g wet gel for 1% heparin gels and 14 mg/g wet gel for 2% heparin gels. 

One of the most familiar consequences of surface tension, capillary rise, may be understood in terms of this equation. If a tube of narrow diameter is dipped into a liquid and the liquid wets the inside of the tube, a curved meniscus will be formed (figure 2.3). Just below the meniscus, the internal pressure inside the liquid will be less than the pressure in the bulk, by virtue of equation (2.2.12). Equilibrium is attained by the liquid rising up the tube imtil the extra hydrostatic pressure due to gravity balances the discrepancy. At any point a distance z above the minimum of the meniscus this balance is expressed by... 

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