Rules Of Thumb : Evaporators

1. Long tube vertical evaporators with either natural or forced circulation are most popular. Tubes are 19–63 mm dia and 12–30 ft long.
2. In forced circulation, linear velocities in the tubes are 15–20 ft/sec.
3. Film-related efficiency losses can be minimized by maintaining a suitable temperature gradient, for instance 40–458F. A reasonable overall heat transfer coefficient is 250 Btu/(h)(ft2).
4. Elevation of boiling point by dissolved solids results in differences of 3–108F between solution and saturated vapor.
5. When the boiling point rise is appreciable, the economic number of effects in series with forward feed is 4–6.
6. When the boiling point rise is small, minimum cost is obtained with 8–10 effects in series.
7. In countercurrent evaporator systems, a reasonable temperature approach between the inlet and outlet streams is 308F. In multistage operation, a typical minimum is 108F.
8. In backward feed the more concentrated solution is heated with the highest temperature steam so that heating surface is lessened, but the solution must be pumped between stages.
9. The steam economy of an N-stage battery is approximately 0.8N lb evaporation/lb of outside steam.
10. Interstage steam pressures can be boosted with steam jet compressors of 20–30% efficiency or with mechanical compressors of 70–75% efficiency.

Instrumentation Reference Book, Fourth Edition

Instrumentation embraces the equipment and systems used to detect, track and store data related to physical, chemical, electrical, thermal and mechanical properties of materials, systems and operations. While traditionally a key area within mechanical and industrial engineering, it also has a strong presence in electrical, chemical, civil and environmental engineering, biomedical and aerospace engineering.

The discipline of Instrumentation has grown appreciably in recent years because of advances in sensor technology and in the inter-connectivity of sensors, computers and control systems. In turn, this has meant that the automation of manufacturing, process industries, and even building and infrastructure construction has been improved dramatically. And now with remote wireless instrumentation, heretofore inaccessible or widely dispersed operations and procedures can be automatically monitored and controlled.

he new 4th edition of this already well-established reference work, will reflect these dramatic changes with improved and expanded coverage of the both the traditional domains of instrumentation as well as the cutting edge areas of digital integration of complex sensor/control systems.

Thoroughly revised, with up-to-date coverage of wireless sensors and systems, as well as nanotechnologies role in the evolution of sensor technology

Latest information on new sensor equipment, new measurement standards, and new software for embedded control systems, networking and automated control

Three entirely new sections on Controllers, Actuators and Final Control Elements; Manufacturing Execution Systems; and Automation Knowledge Base

Up-dated and expanded references and critical standards

Rules Of Thumb : Filtration

1. Processes are classified by their rate of cake buildup in a laboratory vacuum leaf filter: rapid, 0.1–10.0 cm/sec; medium, 0.1–10.0 cm/min; slow, 0.1–10.0 cm/hr.
2. The selection of a filtration method depends partly on which phase is the valuable one. For liquid phase being the valuable one, filter presses, sand filters, and pressure filters are suitable. If the solid phase is desired, vacuum rotary vacuum filters are
   desirable.
3. Continuous filtration should not be attempted if 1/8 in. cake thickness cannot be formed in less than 5 min.
4. Rapid filtering is accomplished with belts, top feed drums, or pusher-type centrifuges.
5. Medium rate filtering is accomplished with vacuum drums or disks or peeler-type centrifuges.
6. Slow filtering slurries are handled in pressure filters or sedimenting centrifuges.
7. Clarification with negligible cake buildup is accomplished with cartridges, precoat drums, or sand filters.
8. Laboratory tests are advisable when the filtering surface is expected to be more than a few square meters, when cake washing is critical, when cake drying may be a problem, or
   when precoating may be needed.
9. For finely ground ores and minerals, rotary drum filtration rates may be 1500 lb/(day)(sqft), at 20 rev/hr and 18–25 in. Hg vacuum.
10. Coarse solids and crystals may be filtered by rotary drum filters at rates of 6000 lb/(day)(sqft) at 20 rev/hr, 2–6 in. Hg vacuum.
11. Cartridge filters are used as final units to clarify a low solid concentration stream. For slurries where excellent cake washing is required, horizontal filters are used. Rotary disk filters are for separations where efficient cake washing is not essential. Rotary drum filters are used in many liquid- solid separations and precoat units capable of producing
    clear effluent streams. In applications where flexibility of design and operation are required, plate-and-frame filters are used.

Submerged Arc Welding SAW | Submerged Arc Welding Deposition Rates | Submerged Arc Welding Flux Composition

Submerged arc welding: (SAW)

In submerged arc welding also known as hidden arc welding, submerged melt welding, or sub-arc welding the arc is struck between a metal electrode and the work piece under a blanket of granular flux. The welding action takes place under the flux layer without any visible arc, spatter, smoke or flash.

Here the weld arc is shielded by granular flux, consisting of Lime, Silica, Manganese Oxide, Calcium Fluoride, and other elements.

The filler wire used may be bare or slightly copper coated. The consumable electrode is a coil of bare round wire 1.5 to 10 mm in diameter.

Operation of Submerged Arc welding Process:

The welding action can be initiated by introducing a piece of high resistance conducting material like steel wool or carbon between the electrode and the work piece. Once the welding action has been initiated the intense heat produced by the flow of current in the high resistance path melts a path of the flux around the electrode forming a conducting pool. The molten filler displaces the liquid flux and fuses with the molten base metal forming the weld. The molten flux coating over the molten metal pool forms a blanket that eliminates spatter losses and protects the welded joint from oxidation. As welding proceeds, the molten weld metal and the liquid flux cool and solidify under a layer of unused flux. The molten flux on solidification forms a brittle slag layer which can be easily removed.

Unused granular flux material can be reclaimed and reused.

Characteristics of Submerged Arc welding Process:

Electric current is 300 to 2000A.

Power supply is 440 V.

Velocity is 5m / Min

The SAW process provides very high welding productivity, depositing 4 – 10 times the amount of weld metal per hour.

Advantages of Submerged Arc welding Process:

Thin plates can be easily welded in one pass without any edge preparation while only a slight bevelling is necessary in most other cases.

The quality of welds produced in submerged arc welding is very high with good toughness, ductility and uniformity of properties.

Submerged arc welding is most suitable for welding in the down hand or flat position although welds can be made on a straight slope.

Materials successfully welded by the process include low carbon steel, medium carbon steel, heat resistant steel, corrosion resistant steel, high strength steels and non ferrous metals like Monel metal, nickel and others.

High speed of execution due to the use of high currents in one or more electrode wires

No smoke

The arc is concealed, enabling the operator to work without a mask and without disturbing others nearby

Limitations of Submerged Arc welding Process:

Solid flux submerged arc welding can be used only on alloy and non-alloy carbon steel, stainless and refractory steel

The use of a powder flux means that welds must be executed horizontally, unless special measures are taken

The process cannot weld plate less than 1.8 mm thick (due to its high penetration)

It is not possible to butt joint work pieces more than 16 mm thick ; thicknesses greater than 16 mm require special preparation (bevelling).

Application of Submerged Arc welding Process:

Shipbuilding

Heavy Duty Pressure vessels

Off shore engineering