Wednesday, September 18, 2019

Resistive Heating Elements for Gas Chromatography

Gas Chromatography Heater
Custom gas chromatograph heater by BCE.

What is Gas Chromatography?

The most basic understanding of gas chromatography (GC) is that of a separation technique. It is used in analytical chemistry for the prompt separation, identification and quantification of compounds that can be vaporized without decomposition. Common uses of GC include testing the purity of a substance or separating and identifying the different components of a mixture.

The basic components of the GC system are:
  1. A long thin tube, referred to as a "column", and an oven or direct heating element that provides accurate temperature control and profiling. 
  2. The injector, which provides the means for the sample to enter the column.
  3. The detector, which provides the means for the sample to exit the column.
  4. The temperature control system.

Basic Understanding of Gas Chromatography

The sample (analyte) is transported through the column by the flow of an inert, gaseous mobile phase (typically nitrogen, helium, argon, or carbon dioxide). The GC column contains a liquid referred to as the "stationary phase" which, as it traverses the column, is repeatedly adsorbed onto the surface of an inert solid and desorbed back into the carrier gas stream. Based on an adsorbent's composition, it can have varying affinities to "hold". Because some constituent components are likely to spend more time in the stationary phase, while others are likely to spend less time, the separation process occurs.

Constant demand for optimized analytical throughput, GC portability, and less costly analysis propels the development of new gas chromatography designs and technologies. In recent decades, resistive heating technologies designed for the sample column heating have become commercially available and have grown in popularity. Resistive heaters have clear advantages over traditional air bath ovens, most notably direct, low-mass heating through conduction. The growth of portable GC systems has also benefitted from small, compact, low power resistive heaters.

The temperature control system is at the heart of gas chromatography accuracy, sensitivity and speed. This system is comprised of the electric heating elements, temperature controllers, and temperature sensors. All are critical in sample and column temperature regulation.

Gas Chromatography Heaters

This specialized category of electric heating element is designed to provide extremely uniform temperature profiles across the length of the GC column. This uniformity accommodates a stable temperature environment for the capture of repeatable and consistent data between runs. Gas chromatograph heaters allow for very precise temperature ramping and set point control to very tight tolerances. This is critical because the slightest fluctuation in column temperature during analysis will have significant effect on analysis outcomes.

Controlling the Temperature of the GC Column

Once the temperature profile of the column is established, a precision thermal control system is required to provide precision temperature control during the operation of the profile. The control system must be highly accurate and responsive, and must include advance control algorithms to handle a wide variety of column profiles.


Temperature Programmed Elution

In most cases, a ramping temperature profile is required when the analyte enters the column. The ramping temperature profile starts at a lower temperature and increases over time in a precise and linear fashion. At different points along the temperature profile, compound movement changes according to temperature exposure. This precise exposure to changing temperature enhances analyte separation and reduces cycle time.  Considering this, the heating element must be sized properly and have sufficient wattage to sustain the power requirements of the ramping temperature profile at all points along the ramp.

For more information about the application of resistive heaters for gas chromatography, contact a BCE applications engineer.

Thursday, September 12, 2019

High Temperature 16 Pair Type J Thermocouple Feedthrough

Type J Thermocouple Feedthrough
16 Pair, High Temp Type J Thermocouple Feedthrough
BACKGROUND

A 3D Printer company specializing in Aerospace parts provided BCE a challenge in creating a High Temperature Feedthrough for their new composite 3D printer.  The 3-D composite company needed a high enough temperature in the sealed area with a vacuum chamber being essential in printing aircraft components.  They had difficulties integrating their existing thermocouple design into their expanded chamber with an off the shelf feedthrough.

SCOPE

The 16 (32-wire) Pair Thermocouple feedthrough needed to satisfy the following:
  • Operating temperatures between -25 C to 300 C
  • Low vacuum leak rate of 10^-9 ATM-CC/S or better
  • Able to withstand a 450 C Bake-out temperature
  • Type J thermocouples (customer preference) with ring terminations 
  • Fiberglass lead wires to withstand the high temperature
OUTCOME

BCE successfully designed a Thermocouple Feedthrough with a type J T/C extension wire so that the customer could integrate the component with ease into their 3D Printer. The High Temperature Feedthrough went through extensive pressure and temperature cycling before being shipped.  One final helium leak check was made and a polarity verification for all connectors was done too.

For more information, contact BCE by calling 510-274-1990 or by visiting https://bcemfg.com

Monday, September 2, 2019

Copper Flange Heater for Gas Chromatograph

Copper Flange Heater
A gas chromatography application was brought to BCE involving a custom heater to ramp a cell end plate to 105°C. The customer had issues finding a solution due to the small surface area that needed to be heated (~ 0.75” diameter).  The requirement was a 25-Watt 120-Volt source, which resulted in a high resistance value (576 ohms) eliminating many heater options for this size and surface area.

Scope:
  • Heater plate to be 105°C 
  • Good temperature uniformity (+/- 1.5%C)
  • 25 W 120 V
  • 1/8” Plate thickness max
  • Geometry to allow for three tubes to exit
  • 0.75” Diameter
Outcome:

Since etched foil polyimide heaters were not an option for this application, BCE engineers designed a 110 copper plate with a rod heater welded within the groove.  The rod style heater allowed for a higher resistance value and was more robust compared to other types of heaters.  Additionally, the cold section and lead orientation can be easily modified by the customer to accommodate their assembly.  BCE’s Copper Flange Heater was able to efficiently heat the small surface and save the customer from an expensive assembly redesign.

For more information, contact BCE by calling 510-274-1990 or by visiting https://bcemfg.com

Friday, August 23, 2019

High Temp Heater Chuck – 200mm

High Temp Heater ChuckA semiconductor equipment company in the Atomic Layer Deposition (ALD) market approached BCE in need of a custom high temperature heater solution.  Their application involved a thin-film deposition using a sequence of various chemical processes.  Repeating these processes results in a thin film being slowly deposited. 

SCOPE

High Temperature Heater Chuck needed to satisfy the following:

  • Temperature <700°C   
  • Internal element must be able to withstand higher than 700°C
  • Thermal break between flange and base reducing heat transfer to flange area 
  • 316 Stainless steel base, sleeve, and flange must pass all required vacuum specifications
  • 240Volt 1450Watt
  • Built-in thermocouple type “K” inside internal element grounded with RF screening 


OUTCOME
High Temp Heater Chuck
Click for larger view.


BCE produced a highly effective high temperature heater with exceptional uniformity.  The design was able to compress the internal element enough to allow for optimal temperature transfer.  The weld around the outside periphery of the base plate and the (3) lift–pin-hole-standoffs were essential in the design for vacuum integrity, ramp rate, and temperature stability. 

For more information, contact BCE. Call them at 510-274-1990 or visit their web site at https://bcemfg.com.

Tuesday, August 20, 2019

Fiber Optic Feedthrough

Fiber Optic Feedthrough
A company contacted BCE to design a fiber optic feedthrough for their new assembly. They required (4) x 100 inch single mode coupler fibers to reach a narrow area within their assembly. The customer had a difficult time finding a compatible solution due to the specific thread type and the long fiber length so they approached BCE to create a custom feedthrough. Due to the sensitive nature of fiber optic cable, a BCE Epoxy Feedthrough was the optimal solution.

REQUIREMENTS:
  • 4x single mode Acrylate coated fibers
  • ¾”-16 threaded 316 SS fitting
  • Helium leak test: 5 x 10-8 atm-cc/s or better
  • Temperature range: 0°C - 65° C
  • Long lead length ~100”

Click for larger view.
OUTCOME

The small outer diameter (245 µm with an 8 µm core) of the fibers and the long length, required the addition of Hytrel furcation tubing to prevent breakage by reducing the bend radius. This created a robust feedthrough to withstand a wide range of vacuum and temperature conditions. The fiber optic feedthrough exceeded expectations and achieved a 10 x 10-10 atm cc/s helium leak rate.

For more information, contact BCE. Call them at 510-274-1990 or visit their web site at https://bcemfg.com.

Wednesday, August 14, 2019

Mini Clean Flow - Stream Heater

Mini Clean Flow Heater
Mini Clean Flow Heater
A biotechnology company approached BCE in need of a custom heating solution. Their application required that the media must be heated to 75 °C in order to eliminate any pathogenic bacteria that may be present. Their current system was not heating the medium efficiently requiring a high watt density solution causing heater failure and carbonization of the material.

SCOPE

The Mini Clean Flow - Stream heater needed to satisfy the following:
  • Outlet of temperature of 75 °C (± 2 °C) to eliminate bacteria
  • Ability to place heater in a series flow configuration if necessary
  • Built in thermocouple for accurate temperature measurement
  • 185 Watt, 120 Volt
  • All wetted surfaces must be 304 Stainless Steel
  • Watt density below 30 WSI to avoid damage to the fluid or system
OUTCOME

Test Results
Test Results - Click for larger view.
BCE designed a double wall inline heater with exceptional heat uniformity and reduced heat losses. The Mini Clean Flow Stream heater was built with internal components designed to turbulate the medium to increase efficiency and minimize watt density. This compact, low mass heater had the ability to precisely control the inner temperature for either over-temp or process medium control. The Mini Clean Flow – Stream was the ultimate solution for this application resulting in a more efficient process to eliminate pathogenic material.

For more information, contact BCE by calling 510-274-1990 or visit their web site at https://bcemfg.com.

Monday, July 29, 2019

Electric Heating Elements: Cartridge Heaters

Cartridge Heater
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Cartridge Heater Basics

Cartridge heaters are cylindrical in shape, consisting of an element made of resistance wire wound around a ceramic core. Within a metal sheath tube, the wound core is precisely centered and surrounded by granular magnesium oxide material. This isolates the resistance element from the tube electrically and provides a heat transfer medium to the sheath tube. At one end are electrical terminations. In order to enhance internal heat transfer and electrical insulation characteristics, higher performance, longer-lived cartridge heaters are swaged (a rotary hammer compacting process). Swaging compacts and densifies the granular insulating material, improving its thermal conductivity. Cartridge heaters are commonly used and are produced in a broad range of lengths, diameters, wattages, watt densities, lead agreements, and optional internal sensors.


Cartridge Heater Applications

Cartridge Heater
Specialized Cartridge Heater (BCE)
The following equipment utilizes cartridge heaters: chromatography equipment; medical laboratory equipment, including chemistry analyzers; plastic molds and runners; platens; barrels on extrusion equipment; hot melt glue systems; packaging seal bars; labeling and marking systems; food-warming equipment and steamers; autoclaves; ovens; photographic processing equipment.

Cartridge heaters are capable of operating at elevated temperature as well as high watt density, but care must be taken to apply cartridge heaters at appropriate watt density and sheath temperature levels.

Temperature Capability

A maximum of 1600°F (870°C) sheath temperature is recommended.

Watt Density Capability

A maximum of 400 W/in. and higher under special conditions.  As a rule, cartridge heaters can operate at 1600°F at 40W/in.

Heater Life

Operating at 1600°F internal temperature with modest cycling and with the proper hole fit, a properly designed and constructed cartridge heater will provide approximately a one-year life.

Voltage

Usually 120/240V, with 480V and custom voltages requiring special design or sizing considerations.

Thermal Response/Application

Cartridge heater's thermal response is dependent on conductive heat transfer in most applications.  Optimum conduction requires close fit between the heater and the work to be heated. As heater looseness increases, watt density must be decreased accordingly, to prevent internal overheating. Watt densities of liquid-immersion cartridge heaters vary according to the liquid's viscosity and heat capacity.  When heating liquids, care must be taken to prevent "film boiling" where vapor bubbles create a thermal insulating effect and raise the heaters internal temperatures.

Heater Efficiency

Cartridge heaters are 100% efficient when immersed.

For more information about electric heating elements, contact BCE by calling 510-274-1990 or by visiting https://bcemfg.com.