Tuesday, October 27, 2015

The Three Body Styles of Industrial Thermowells

Industrial thermowells
Industrial thermowell styles
(courtesy of REOTEMP)
There are three common shanks used on thermowells: the straight shank, the taper shank, and the step shank.

The straight shank has the same diameter throughout its entire immersion length. Because of its greater diameter and thicker tip, it usually has the slowest response time compared to other shank styles. However, the extra metal allows it to have a high corrosion and high abrasion resistance. Common installations for a straight well are tanks or pipes to have low pressure, low-velocity and/or a high abrasion process.  Although the straight shank has the best mechanical strength properties, it should not be used in high-velocity flow systems. Its larger surface area can be overly disruptive to flow, or it may fail due to vortex shedding.

The second design is the tapered shank, which has an outside diameter that gradually decreases from the point just under the process connection, down to the tip.  This taper allows for a very high mechanical strength, with a faster response time than a straight well. This design has very good vibration resistance and is commonly used and high-velocity flow applications. Common installations for a taper well are applications with a very high flow rate, high vibration, high-pressure and are high temperature.

The final type of shank is the stepped shank. Usually this type of well is a straight shank from the process connection down to about two and a half inches from the tip, with the final two and a half inches a smaller diameter straight shank. The reduction in diameter allows for a faster response - usually the fastest response out at three different shank designs. There is however a reduction in strength because of the diameter change, and less mechanically rugged as a straight or tapered shank style. Common installations for a step well are where rapid response is needed, but without high-velocity flow or where there is a possibility of being physically damaged from the process media.

Monday, October 26, 2015

Custom Heating Elements and Controls

custom heating element
Custom heating element.
Many types of industrial and manufacturing equipment, including analytical instrumentation, semiconductor, photovoltaic, medical, plastics processing, foodservice packaging, and aerospace equipment require some kind of custom electric heater, controller, and sensor.

For instance here, in semiconductor processing, you can find a need for electric heating in all these areas:  Bake platen heaters, bake/chill pedestal & platen heaters, hot chuck heaters, high temperature platen heaters, standard pedestal heaters, vacuum chamber heaters, and aluminum pedestal heaters.

A well engineered thermal system considers overall heat load, maintenance power requirements, control method, and sensor location. Working with a vendor who has the experience and background in this kind of product development is critical. Careful consideration of form, fit, and function requires the guidance an experienced applications engineer to avoid wasted time and money. 

Tuesday, October 20, 2015

Custom Epoxy Vacuum Feedthroughs

Equipment manufacturers and scientific researchers are continually challenged with supplying power, fiber-optic, control, and monitoring cables through sealed vacuum vessels. Whether due to space restrictions, special geometries, or number and type of conductors, standard glass-to-metal or ceramic feedthroughs never quite fit the bill. Unfortunately, because of limited options, many designers are forced to compromise and go for an off-the-shelf solution.

During the past decade, new epoxy compounds have been developed that rival glass and ceramic in performance. With modern epoxy feedthroughs, any kind of standard or custom connector is sealed in a completely potted, high-performance, clear epoxy compound. Epoxy seals offer countless design options, and most amazingly, performance equal to or better than glass or ceramic. Better yet, pricing is very competitive and quick turn-around for prototypes and short production runs are not a problem.

Wednesday, October 14, 2015

Electric Heating Element Technical Reference Guide

Carnot engine diagram
Carnot engine diagram
(courtesy of Wikipedia)
Here’s a very handy reference document (courtesy of Hotwatt) for the application of electric heating elements in industrial and OEM applications such as extruding, vulcanizing, laminating, curing, bonding and thermoforming.

The heater application guide provides all the important technical look-up tables required to properly apply electric heaters, such as wattage calculation formulas and examples, properties of metals properties of non-metallic solids, properties of liquids and gases, suggested watt densities, estimates of wattage required, guide for heat losses, suggested sheath materials, installation,  Ohms Law, and typical wiring diagrams. The reference document is also very helpful when designing custom electric heating elements and designing a thermal system.

Tuesday, October 6, 2015

The Virtues of a Cone Meter for Your Next Challenging Flow Application

V cone meter
"V" shaped cone meter for controlling flow.
A cone meter, also referred to as a "V Cone" (trademark of McCrometer), is an advanced differential pressure instrument, ideal for liquids, steam or gas in rugged conditions where accuracy, low maintenance and cost are important.

Cone meters operate on the same physical principle as other differential pressure flowmeters, such as orifice plates, flow nozzles or venturi tubes, using the theorem of conservation of energy in fluid flow through a pipe.

The cone interacts with the fluid flow and reshapes the fluid’s velocity profile, which in-turn creates a region of lower pressure immediately downstream. The pressure difference between the upstream side and the downstream side of the cone can be measured via two pressure sensing ports. One port is placed slightly upstream of the cone, the other is located just downstream of the cone. The pressure difference can then be calculated to determine the fluid flow rate. Because the cone is positioned in the center of the flow, the velocity profile is automatically optimized at the point point of measurement, which assures highly accurate, reliable flow measurement irrespective of the upstream flow.

The theories behind differential pressure type measurement are based on Bernoulli’s theorem for the conservation of energy in a closed pipe. The theorem states that for a constant flow, the pressure in a pipe is inversely proportional to the square of the velocity in the pipe. Simply put, the pressure decreases as velocity increases.

In real life situations, pipe flow profile is never ideal. Flowmeters are rarely installed in well developed, planned situations. Changes to piping, like elbows, valves, reductions, expansions, pumps, and tees will corrupt well-developed flow. Measuring disturbed flow is difficult for other flowmeter technologies because of the errors introduced. The cone flow meter overcomes by using its contoured shape and localized position to reshape the velocity profile upstream of the cone. As the flow approaches the cone, the flow profile flattens and becomes much better developed, even under extreme conditions. This ensures there will always be a predictable flow profile at the cone which in-turn ensures accurate measurement.

Contrary to popular opinion, cone meters measure much more than just gas. They also measure steam and a wide variety of liquids in many industries including oil/gas, chemical, electric power, food/beverage, HVAC systems, metals and mining, pulp/paper, water and wastewater treatment, and more.

The following video illustrates more on how cone meters work, how their flow control is superior to other devices, and why their design is so beneficial in today's industrial applications.