Electric Heating Systems for Liquid-Gas Vaporization

Electric Circulation Heater

Hydrocarbon and non-hydrocarbon based gas products are transported and stored at low temperatures. The most common examples of liquified gasses are liquified natural gas, butane, propane, nitrogen, and oxygen. In liquid form gases are more convenient and efficient to transport, however once at their destination, they must be changed back to the gaseous state.

There are many ways to accommodate the phase change from liquid to gas and picking the best option is dependent on many criteria including plant location, climate conditions, available energy sources, and infrastructure available.

Transitioning from liquid phase to gas phase is a gradual process usually taking place at higher pressures, through several containment vessels, heat exchangers or heating coils which slowly warms the liquified gas.

Some thermal heat exchanging systems use fluids such as hot oil, hot water or a glycol-water solution to efficiently transfer heat to the liquified gas.

Happy Holidays and Happy New Year from Belilove Company-Engineers

We at Belilove Company-Engineers believe the magic of the holidays never really ends, and the most important gifts we share are family and friends. Thank you for a wonderful 2014 and we wish you peace, love, and prosperity in the upcoming year.

Advantages of Epoxy Electrical Feedthroughs Over Glass-to-Metal and Ceramic Seals

Epoxy Electrical
Vacuum Feedthrough

Advances in semiconductor and medical device development has continually challenged manufacturing processes in ultra-clean environments. Getting power and control signals into high vacuum chambers has always been difficult. The vacuum seal has to be tight and not allow any contamination so that product quality is maintained.

Historically glass-to-metal seals for wire feedthroughs have been the choice in these industries, but are constrained in size, geometry, flexibility and electro-magnetic shielding. At the same time, semiconductor and medical device equipment have an increasing need for higher power, more control, better monitoring, and increased signal shielding. These ever changing requirements, which push the capability of glass-to-metal seals,  open up opportunity for an alternative technology - epoxy electrical vacuum feedthroughs.

Engineered epoxy electrical feedthroughs offer the best of all technologies. Shapes, angles and curves are not a problem. Virtually any kind of shielded wire or cable can be used and still maintain a tight seal. And as equipment design requirements continue to challenge vacuum seals with space and shielding requirements, the advantages of epoxy vacuum seals look to be a promising solution as the technology itself continues to advance.

While glass-to-metal feedthroughs have advantages in high temperature and corrosive applications, many of todays semiconductor and medical device applications don’t see these conditions. In these lower temperature, and non-corrosive applications, the lower cost, easy prototyping and more flexible design capability of epoxy feedthroughs make them very attractive alternatives.

The epoxy's ability to flow and fill spaces completely make it an excellent choice for any special shapes and sizes a vacuum chamber may require for access.  For the most part, epoxy feedthroughs can be used in most applications where glass-to-metal or ceramic feedthroughs are used (with the exception of temperature and corrosion issues outlined above). In some applications, organics are not allowed, and the epoxy feedthrough would be excluded from these as well.

One additional advantage is that custom epoxy vacuum feedthroughs can be quickly provided in very small quantities for prototyping and R&D.

For more information on epoxy feedthroughs, visit this page.

Advancements in Electric Resistance Heaters - Ceramic Heating Elements

Aluminum nitride, high performance electric heating elements using Tungsten traces on ALN. Product manufactured by Durex and Oasis Materials.

• Power Densities up to 2500 Watts per square inch
• 0-400º C in a quarter of a second
• Extreme temperature uniformity
• Inert in acidic solutions
• Custom line widths and resistance values available
• Encapsulated Tungsten RTD trace
• 3D shapes and configurations
• Thermal conductivity of Oasis' Aluminum Nitride (ALN) is 190 W/mK
• Thermal conductivity of pure tungsten is 170 W/mK

Basics of OEM and Industrial Electric Heating Elements - Part 2

This blog entry, reproduced from an electric heating element basics white-paper from Hotwatt, a leading US manufacturer of OEM and industrial heating elements. To download the PDF version, click this link.

Basic Heat Equations

Electric Heating Elements

It would appear at first that calculating all of the heat transfers and losses in a design would be a daunting task. Fortunately a number of equations were developed that help simplify this task. First the equations were divided into three tasks: the wattage needed to heat a material to a specific temperature in a given amount of time; the wattage needed to overcome the losses at operating temperature; and a special calculation needed to reach a melting or vaporizing point.

This equation calculates the amount of wattage (W) needed to raise the temperature of a material a specific amount in °F (ΔF) in a given number of hours (T), you first need to know the mass (m) of the material being heated and its specific heat value (c):

m × c ×ΔF

W=  -------------------

3.412 × T

The mass and specific heat of some materials may be found at www.hotwatt.com/table1.htm for metallic solids, www.hotwatt.com/table2.htm for solids other than metals, and www.hotwatt.com/table3.htm for certain liquids and gases.

Basics of OEM and Industrial Electric Heating Elements - Part 1

This blog entry, reproduced from an electric heating element basics white-paper from Hotwatt, a leading US manufacturer of OEM and industrial heating elements. To download the PDF version, click this link.

Electric heating elements
for OEM and Industry
(courtesy of Hotwatt)

The simplest definition of an electric heater is any device that changes electrical energy into heat energy. But from that simple explanation, electric heaters explode into a myriad of types, sizes, applications, and designs depending upon what’s being heated, the degree of heating needed, and the method by which the heat is applied.

The measure of electrical energy is called the Joule after its discoverer, James Prescott Joule. Through numerous experiments, Joule determined that the quantity

(Q) of heat transferred from electrical energy is proportional to the square of the current (I² ) multiplied by the resistance (R) for the period of time (t) through which it passes:

Q ∝ I² × R × t

However, one seldom sees a reference to Joules used in modern electric circuits. Instead, the controlling factor becomes that of power (P):

P = I² × R

You’ll note the only difference between the formula for determining power and that of determining Joules is the time component. The time factor in heating becomes readily apparent in any device that gets hot when an electric current flows through it: its temperature rises as time passes.

Thermal Solutions for Condensate and Particulate Control in Semiconductor Vacuum Pumps and Lines

Semiconductor Gas & Pump
Line Heaters (courtesy of Durex)

Low vapor pressure gas delivery lines must be held at elevated temperatures (higher than the gas vaporization point) in order to prevent condensation that adversely effects process yields. Similarly, sublimation (transition of a substance directly from the solid to the gas phase) occurs when the vapor phase materials are allowed to cool in a vacuum line.  The most common types of sublimation in the semiconductor process is of ammonium chloride (AlCl2) and nitrides (NH4) (NH4Cl).

The more common semiconductor processing applications requiring unique thermal solutions for condensate and sublimation prevention are PECVD, LPCVD, MOCVD, ALD, plasma etch and other vacuum applications.

Keeping temperatures elevated along the vacuum lines, and in the vacuum pump, assures gas temperature above the vapor condensation point, thus keeping condensate at bay.  Heating the vacuum lines, vacuum pumps, and forelines, also substantially reduces sublimation in these areas.

By controlling condensate and sublimation, the need for frequent preventive maintenance is dramatically reduced and subsequently, the costs. Additionally, the life of associated valves and vacuum pumps is increased as well.

The ideal heater should be self contained, be easy to install and remove,  fit tightly on the lines and pumps, and provide optimum heat transfer. It should be powered by readily available voltages (120, 240), have built-in fasteners, and provide over-temperature limit control. It should provide process temperatures up to 200°C and have the ability to distribute wattage along the length of the process line to compensate for colder line sections. The backside of the heater should include thermal insulation that can withstand the operating temperatures, while still providing good thermal insulation.

For more information on semiconductor line, pump and valve heating contact Belilove Company-Engineers at (510) 274-1990 or at sales@belilove.com.

2-Wire and 4-Wire Transmitters and Control Loops

Digital Meters

Industrial process control transmitters commonly provide analog signals, such as 4-20 milliamps (mA), 1-5 volts DC, and 10-50 milliamps as outputs which can be scaled to the control range of the process variable they are sensing. Industrial transmitters are either “4-wire” or “2-wire” which defines how the transmitter gets its supply or “excitation” voltage.

4-wire transmitters have four wires exiting the device. Two wires are for the supply power of the device, typically 120 volts AC, 240 volts AC or and external 24 volts DC supply. The other two wires provide the analog output signal provided by the transmitter circuitry.

2-wire, loop power example

2-wire transmitters have only two wires exiting the device and rely upon the control “loop” for the excitation voltage - typically 24 volts DC which normally comes from the loop controller, PLC or DCS.

4-wire devices are also classified as “active” (supplying power) devices, while 2-wire devices are classified as “passive” (loop powered) devices.

For example, a digital meter (active) may provide loop power to a pressure transmitter. The pressure transmitter regulates the current on the loop to send the signal back to the digital meter, but since the transmitter does not provide power to the control loop, it is deemed passive. In another example, a passive (loop powered) digital meter and a passive pressure transmitter may be used in the same loop, but uses a 24 V battery as the active device to power the loop.

Industrial Electric Immersion Heaters

Screw plug and flanged
immersion heaters
(courtesy of Durex)

Electric immersion heaters are used in a myriad of industrial applications. From drying industrial gasses, to freeze protecting cooling tower sumps, to heating acids in plating applications, the versatility of electric heating element can save time, energy and space.

Industrial immersion heaters are used to directly heat a standing or moving fluid by using electric heating elements. There are three primary types of industrial electric immersion heaters; screw-plug heaters, flanged immersion heater, and over-the-side heaters.

At the heart of industrial immersion heaters are the individual heating elements, normally constructed from a stainless steel or Inconel tube containing a magnesium oxide filler and a nichrome resistance wire. Current is applied to the wire which produces the heat, while the compacted magnesium oxide powder provides the electrical insulation, and the metallic tube provides the physical protection.

Custom Electric Heaters for Unique Thermal Systems Require the Right Thermal System Partner

OEMs in the analytical, semiconductor, biomedical, life-science, food service and environmental industries continually design new pieces of equipment offering their customers greater efficiencies, smaller foot prints and greater production rates. When the piece of OEM equipment requires precise heating, consultation with an experienced thermal systems engineer will provide significant time savings and budget control.

More specifically, working with an experienced thermal system consultant provides these important benefits: front-end, practical design review to optimize manufacturability; timely prototype development; partnerships and alliances with platers, brazers, casters and heating element manufacturers; single source responsibility; testing and calibration; inventory management; value-added assembly; and cleaning and packaging.

Aluminum Nitride Ceramic Heaters Open Doors to Better Machine Design

Aluminum Ceramic Heaters
(Courtesy of Durex)

Aluminum Nitride (AlN) Ceramic heaters are a relatively new entry in the very high watt density heater market and are an attractive alternative to traditional metal sheathed heaters. Capable of achieving up to 2000 watts per square inch, and operating temperatures of up to 1000 deg. C, these heaters show great promise for semiconductor processing applications such as crucible heating, fluid and gas handling and chemical vapor deposition. 

The heaters are made by "tracing" a resistance material (Tungsten) on a the ceramic base at various thicknesses, corresponding to the performance requirements of the heater. The Tungsten and AIN expand and contract at very similar rates, which greatly reduces the mechanical concerns of delamination. Binders and trace additives are added to the ceramic and Tungsten for additional strength. The resulting construction allows for some pretty impressive thermal cycling - one example is an application with a 200 deg. C temperature swing every 30 seconds.

AIN ceramic heaters offer significant advantages over metal sheathed heaters and their inherent performance limitations. Material compatibility, fatigue, outgassing and thermal lag must be considered when applying metal sheath heaters. Ceramic heaters combine excellent thermal conductivity with outstanding chemical resistance, strength, inertness and design flexibility. Additionally, RTD sensors can be deposited right on the ceramic heater itself for optimum control. 

Capable of forming virtually any shape, along with their excellent mechanical, thermal, dielectric, chemical resistant and embedded sensors, Aluminum Nitride Ceramic heaters open the doors for engineers to design equipment to new levels of performance.

Mass Flow Controller Calibration, Accuracy Check and Maintenance Solution

An innovative solution to solving the high cost and downtime caused when servicing mass flow controllers (MFC's).

Introduction to Programmable Logic Controllers (PLC)

Typical Modular PLC

Programmable logic controls, or PLC's, are used for plant automation and control. The PLC is a specialized, industrial computer which includes onboard random access memory (RAM) and read only memory (ROM). As with any other computer, the PLC has a central processor unit (CPU) for data processing. A single PLC has the switching and logic capability to replace thousands of control relays. PLC's are ubiquitous and are used in many different applications in all industries including semiconductor manufacturing, pharmaceutical production, chemical processing, food production, primary metals, and HVAC. Because of their wide industry use, they are manufactured in many shapes and sizes.

Basic Concepts of PID Control

PID control loop diagram
(courtesy of Wikipedia)

PID is short for "proportional plus integral and derivative control", the three actions used in managing a control loop. Process loop controllers use one, two or all three of these to optimally control the process system. PID control is used in a wide variety of applications in industrial control and process system management.

Many types of PID controllers exist on the market and are used for controlling temperature, pressure, flow, and just about every other process variable. Here is a brief explanation of the three actions that make up PID.

Proportional Control Action (P):  The controller output responds in proportion to error signal. The characteristic equation for this action is:

• Where, Kp is called proportional gain, e is the error magnitude and B is the output from controller when there is no error. It is also called bias. 
• In a proportional controller, the value of gain is set as required by the process and can be varied from 0 to ∞. 

Integral Control Action (I): The control system will respond if the error is present over a period of time. This type of control action is called Integral Control Action. The integral action is defined mathematically as:

• Where, e= error, Ti= Time interval of integral action.
• Purpose of integral action is to provide adequate control action on varying demands of process. In this type of action, output varies as per the time integral of error. This action does not exist independently and always associated with proportional control. 

Derivative Control Action (D): To achieve a stable process, wide proportional band and low integral action are set. Due to these settings, the control system can be too slow. If large system disturbances occur over a wide interval, PI controllers are inadequate. These large system disturbances can be managed if the controller output responds not only to the magnitude of deviation, but also to the rate of change of deviation. Derivative control action is that control action. 

Today's loop controllers are much easier to set the PID, thanks to auto-tuning algorithms. What used to be a very time consuming and tedious job can now be done with the push of a button and allowing the controller to "learn" the process dynamics. PID controllers minimize error and optimize the accuracy of any process.

Bi-Metal Thermostats

Bi-metallic Thermostats

Bi-metallic (bi-met) temperature controls (thermostats) have been around for a very long time, but their simplicity, dependability, size and cost still make them a good choice for certain applications.

Also known as "thermoswitches", bi-metal thermostats come in  two primary styles - a "disk" type, which looks more like a button, and a "cartridge" style. Both operate on the same basic principle of differential expansion. Disk type devices are used in many household appliances, such as clothes dryers or coffee pots, as temperature control or as hi-limits. Cartridge style thermostats are used in more industrial applications and OEM equipment.

Thermocouples, RTD's and Thermistors

This post explains the basic operation of the three most common temperature sensing elements - thermocouples, RTD's and thermistors.

A thermocouple is a temperature sensor that produces a micro-voltage from a phenomena called the Seebeck Effect. In simple terms, when the junction of two different (dissimilar) metals varies in temperature from a second junction (called the reference junction), a voltage is produced. When the reference junction temperature is known and maintained, the voltage produced by the sensing junction can be measured and directly applied to the change in the sensing junctions' temperature.

High Purity Fluid Electric Heaters

Transfer Line
Heater Assembly

In many biomedical, pharmaceutical, semiconductor, electronics or R&D laboratory applications, special purpose electric heaters are required for heating high purity fluids. These heaters typically must be ruggedly designed, made from materials immune to process contamination and be vacuum tight. They can be subject to high temperatures, harsh solvents, and corrosive gases. Many times they must maintain a seal for full vacuum, demonstrate a unique or even heating profile and be able to be closely controlled.

The misapplication of screw plug immersion heaters, screwed into a stainless steel welded vessel, offer more problems than solutions due to leaks, material compatibility, poor controllability, and bulky size.

Transfer line
heater assembly

The answer is in a custom high purity fluid heater designed with the process in mind.

Custom electric heating elements are available designed to handle high vacuum, high temperatures, utilize glass liners for ultra-pure gases, offer 316 stainless steel parts, provide internal RTDs for control and can be temperature profiled.

General Specs for these types of custom fluid heaters are:

• Variety of voltages.
• Wide range of watt densities.
• Temperatures up to 350°C.
• Heater length can be profiled to generate a liner temperature profile.
• Vacuum compatible up to 1.0 x 10-8  STD. CC/SEC Helium.
• Can be provided with internal sensors (RTD or thermocouples).
• Can be glass lined for ultra pure gas application.

Careful review of the application is important and the help of an experienced application engineer is required, but the outcome of the test, process or product will be infinitely improved.

Have You Considered a Cast-in Heated Part?

Cast-in semiconductor chuck heater

When OEMs (original equipment manufacturer's) look for the best way of adding heat to their equipment, they're faced with the same choices - clamping, bonding or inserting. But there's another, more efficient and productive way to go - cast-in aluminum or bronze heaters.

Custom-Fabricated, Mass Flow Controller (MFC) Flow Validation Cart Allows for Easy Servicing, Reduced Downtime, and Reduced Inventory

The process of calibrating, servicing and troubleshooting mass flow controllers is a time consuming and expensive endeavor. The typical scenario requires stopping the process and removing the MFC for accuracy checks. The downtime and labor required is very costly, and the advantages for in-situ (without removing it from the process) flow accuracy checks and troubleshooting is quite clear.

An innovative approach for in-place accuracy checks has been developed by Belilove Company. Their solution is a mobile station that includes multiple thermal mass flow meters connected via RS-485, power supplies, software and all the necessary plumbing.

Flow, Pressure, Pneumatics, and Process Control Basics Tutorials Videos

If you're interested in the principles of pressure control, flow control, pneumatics, hydraulics and other process control subjects, the Columbia Gorge Community College offers a wonderful selection of videos. They are presented by a teacher named Jim Pytel who does a very nice job. We'll repost one on flow control valve basics here and suggest you recommend them to any new engineering student, tech, or service rep you know.

Custom Epoxy Vacuum Feedthroughs - A Great Alternative

Epoxy feedthrough on circuit board

Custom epoxy feedthroughs offer some excellent advantages when compared to ceramic and metal seals and should be considered whenever the need for a high integrity feedthrough is required. Below is a rundown of the advantages and specification for epoxy vacuum feedthroughs:

Common Ways to Electrically Heat a Semiconductor Chuck - The Basics

A semiconductor wafer platform, know as a chuck, is used to support and hold in place (usually by means of applied vacuum), a silicon wafer. A chuck heater is used to uniformly and accurately distribute heat (and cooling) to a semiconductor wafer chuck.  This is done during the manufacturing, characterization, testing, and failure analysis of semiconductor wafers.

Semiconductor wafers contain many electronic devices or electronic circuits, known as dies. Each die has to be carefully tested through a range of temperatures. Precise and uniform temperature control is a requirement. The simplest, and most common way to apply heat (and cooling) is through a chuck incorporating an electric resistance heating element.