New Electric Heater Design Maintains High Flow Rate of Cold Propellants and Optimizes Flow in Space Launches

Ideally a rocket engine would capitalize on internal heat dissipations to create a self-regulating thermal environment. However, in the majority of instances, maintaining a high flow rate of cold propellants can obstruct the flow path. Thus, it becomes essential to integrate resistive heaters inside the flow path’s valves and manifolds. Surface-mounted patch heaters are generally used for this application. These are polyimide/silicone sheathed resistive elements with one side adhered directly to the valves and manifolds. Although patch heaters may present a viable solution, the BCE HEM Sealed Heater™ outperforms as heat flows uniformly from inside the cartridge directly to the heated bodies.

This is because they are secured directly to components by the means of an integrated flange. In essence, the BCE HEM Sealed Heater™ incorporates both the cartridge heaters’ wire wound resistive element encased in a metal sheath and the vacuum compatibility of a feedthrough. Furthermore, the BCE proprietary epoxy seal allows the heater to pass strict electrical tests ensuring the purity of the dielectric materials and hence, preventing shorting.

SCOPE

• Easy mounting of heaters into manifolds and valve bodies
• Mounting to be compatible with standard hardware
• 6 to 36V electrical specifications
• Resistance tolerance to be +/-5%
• < 1,500 VDC or greater on the Hi-pot test
• < 4,000 Megohm at 500 to 1000 VDC on the Megohm test
• < .010 sheath thickness
• Sheath can be Inconel or 300 series stainless material
• Sealing Epoxy to meet NASA ASTM E595 Low Outgassing Standard
• Maximum operating temperature of heater <200°C

OUTCOME

The BCE HEM Sealed Heater™ proved to be the most optimal design for the heating of fast-flowing liquid propellants. The heater incorporated all engineering requirements and was mounted into the manifold through an integrated flange using custom hardware. In addition, the heater’s vacuum compatibility was ensured through BCE’s proprietary black epoxy meeting NASA ASTM E595. Furthermore, successful rocket launches into lower to high earth orbit validate that the BCE HEM Sealed Heater™ is rocket ready and capable of high vacuum applications. BCE, the ultimate partner for resistive vacuum applications.

For more information on the HEM Sealed Heater visit this link.

Everything You Wanted to Know About Cartridge Heaters ...

Cartridge Heater (Hotwatt Backer)

Reprinted with permission of Backer Hotwatt

WHAT ARE CARTRIDGE HEATERS?
Cartridge heaters originally consisted of a ceramic-supported heating wire inserted into round metal tube, making them look like cartridges (the likely source of their name). They provide localized heat to restricted working areas requiring close thermal control. Their power density is less than 60 W/in2 and they generate temperatures up to 1,200°F. They range in diameter from 1/8 to 2 in. and vary in length from less than an inch to over four feet. Although they are usually round, they can have square or rectangular cross sections. Standard cartridge heaters account for an estimated 20% of all electric heaters made.

Compacted cartridge heaters were developed about 60 years ago and feature inorganic powder tightly compacted onto the heater wire. This increases their power density to nearly 500 W/in2 and maximum temperatures approach 1,800°F. The need for higher quality tubing and precision-fired crushable ceramics makes compacted heaters cost 1.5 to 3 times the cost of a standard cartridge. They are available in diameters from 1/8 to 1 in. and lengths from 1 inch to over 3 feet.

HOW ARE CARTRIDGE HEATERS MADE?

Cartridge Heater Internal View

For standard cartridge heaters, nickel / chromium heating coils are inserted in a ceramic tube inside a metal housing or sheath. Magnesium oxide filler is then vibrated into the hole to fill any voids. This increases heat transfer to the metal exterior. An end cap is welded on the bottom and insulated leads are installed at the opposite end. For swaged cartridge heaters, the nickel / chromium wire is wound around a ceramic core, placing the wire closer to the metal housing. Magnesium oxide is vibrated in and the heater swaged to a specific diameter. This compresses the MgO so it becomes a better conductor of heat while maintaining its dielectric properties. This improves heat transfer and allows for higher watt densities. Swaging also lets the heaters operate at higher temperatures and better withstand vibrations.

HOW CAN YOU GET THE MOST EFFICIENT HEAT TRANSFER AND LONGEST OPERATIONAL LIFE OUT OF A CARTRIDGE HEATER?
There are several steps users can take. On installation, for example, cartridge heaters should be installed in holes drilled and reamed to no more than 0.002 inches larger than needed. The heaters are routinely sized to never be 0.005 less than the nominal diameter and always at least .001 under the nominal diameter for a slide fit. These close fits ensure rapid heat transfer from the heater to the housing and helps keep the heater as cool as possible, which contributes to a long life. Heaters should not be cycled from low to high temperatures as it shortens their life considerably. Instead, designers should calculate the proper wattage for their applications. The best wattage results in a 50/50 off/on cycle. For temperatures over 750°F, off/on control can be replaced by input voltage regulation through variable transformers or proportioning controllers to minimize temperature fluctuations. If a heater is going to be turned off routinely, the air around it should be kept dry and no impurities (oil, gas,) should be in contact with the heater. That’s because the ceramic material used in cartridge heaters is hygroscopic. Every time power to the heater is switched off, it creates a vacuum inside the cooling housing which draws in air and any nearby impurities from the surrounding area. The moisture or impurities, once inside the housing, can cause a short circuit and result in heater failure.

If a thermostat is used to control the temperature, it should be no more than 0.5-in. from the heater. Mounting it any farther away could let the unit run hot and thereby shorten its life. Another cause of failures is too high a watt density. If the heater was incorrectly specified for an application and provides too much heat, the heater will not be able to dissipate the heat and will fail. Similarly, if the heater is designed for 120 V but is being powered by 240 V, the output wattage will be four times greater than it should be, which can, again, lead to failure.

WHAT OPTIONS ARE AVAILABLE ON CARTRIDGE HEATERS?
There are several options and variations available. Heaters may be three-phase or multiple wattage in a single unit. For instance, an application might need quick heat ups and then a standby circuit to maintain a relatively low temperature using different wattages based on changing thermal loads. Heaters can have wattage outputs that vary over their lengths in order to even out temperatures over a platen or a large surface. Heaters can also have built-in thermocouples, usually at the bottom of the heater and type J or K grounded or ungrounded. If a precision fit is needed, companies can supply centerless ground diameters. They can also supply certain heaters at higher voltages (300 to 600 V).
Heaters used in corrosive environments can be Teflon coated or electro-polished. Heaters that need hermetic sealing or will be used in a vacuum application can be ordered with ceramic-to-metal seals that withstand temperatures to 1,000°F.

CAN CARTRIDGE HEATERS BE USED IN LIQUIDS AS IMMERSION HEATERS?
Yes, when applied with a mount- ing fitting. Not all cartridge heaters made as immersion heaters are completely moisture sealed. The heater and bushing are submersible but the termination end is not necessarily sealed. If an application is in a high humidity area, however, the termination area should be sealed. Seals can be silicone rubber or Teflon which are good to 400°F, or epoxy potting which can handle temperatures to 265°F.

WHAT ARE SOME OF THE TERMINATION OPTIONS OFFERED ON CARTRIDGE HEATERS?
There are multiple options for cartridge heaters, almost too many to list. Standard options start with straight internally connected leads. External connections are optional on larger sizes, recommended when repairable leads are required. There are also post terminals available on cartridges 15⁄16-in. and larger. For applications with limited space, manufacturers can supply right-angle leads.

There are also several options for protecting leads. Fiberglass or silicone rubber sleeving, as well as ceramic bead insulation, protect against temperatures up to 1,000°F. Additional protection can be provided using flexible conduit or stainless steel braid.

Have a requirement for cartridge heaters? Call BCE now at 510-274-1990 or visit https://belilove.com

Understanding Thermal Control Systems

Example of an integrated heater and thermowell with multiple
sensors to be matched with a control system for
highly accurate heating. Courtesy of BCE.

The control system is one of the primary components of a thermal system, along with the heating source (ex. electric heater) and the sensing element (ex. thermocouple or RTD). Proper selection of the control system is critical to accurate control, efficiency and performance.

Temperature gradients and fluctuations occur during heat up, cool down, and when process load is applied. These are mitigated by proper placement of the heating source, location of the sensing element, and control mode chosen.

Thermal system stability is maintained by carefully balancing the energy applied to the process media in opposition to the energy adsorbed by the process and all the radiant, conductive, and convective losses in the system.

For example, an electric heater's "power" is rated in watts, and the power density is stated in watts per square inch. In an ideal thermal system, the energy provided by the electric heater (in watts) would equal the energy lost from all the surfaces and work-related losses at the desired temperature. However, the world is not ideal, and additional external variables affect close temperature control. Hence, the need for control systems.

Control systems regulate in two ways: 1) by regulating the amount of energy (electricity or fuel) added to a process; and 2) by regulating the time the full energy source is applied. When talking about electric heaters, an example of power regulation is the use of thyristor power controllers that modulate the voltage delivered to the heater. An example of time-based power control is the use of solid state (or mechanical) relays and proportioning the amount of time-on, versus time-off, that full power is applied.

Recommendations for optimal thermal system control:

1. Use adequate insulation when and where possible to reduce radiant and convective surface losses.
2. Design the thermal system with the heating source, sensing element and process media as compact and near one another as possible.
3. For thermal systems that are likely to have large overshoot, consider using cascading control that governs the power output based upon multiple sensing locations.
4. Carefully consider the thermal system control mode you choose for the application, i.e. simple on-off control or some variety of energy proportioning.
5. Sensor position is very important. The sensor should be placed as close to, or immersed in, the critical area of your process media, or where a good average temperature can be obtained.
6. Consider the thermal conductivity of your process media and base your sensor location accordingly. You may have to test several locations.

Contact BCE with any question or requirement for electric heaters or thermal system design. Call 510-274-1990 or visit https://belilove.com.

Electric IR Heating To Peel Tomatoes: A Water Saving, Cost-effective, and Eco-friendlier Alternative

For almost a decade now the development of non-chemical peeling technology has recently been identified as a top priority at the for the California Food Processing and Beverage Industry.

Lye peeling is the most industrially used method for processing tomatoes in the U.S. However, due to the pressure of cost and environmental regulations, some tomato processors were forced to use steam peeling to reduce chemical contamination of water. Unfortunately, steam peeling produces undesirable products with deteriorated peeling appearance, high loss in firmness and lowered yields.

Existing studies about the success of IR radiation heating for peeling of potatoes prompted interest in using the same technology for tomatoes. Initiatives for pilot plants and testing began.

A pilot-scale infrared tomato dry-peeling system was designed, built, and tested. It consisted of a section for feeding of the tomatoes, the infrared heating section, a peel eliminator, and the discharge section.

The IR heating unit is equipped a number of IR emitters and an automatically controlled variable speed conveyor system.  Surface temperature of tomatoes was measured immediately after IR heating using non-contact IR thermometers that gathered three different measurements on each tomato. The controlled temperatures were in the range of 103 deg. C to 110 deg. C. In this range, a yield of 70%- 85% fully peeled tomatoes could be obtained for all tomatoes sizes, depending on variety and maturity stage.

Since IR heating does not use water as a heating medium, the process can be referred to as “IR dry-peeling”. Early results showed infrared (IR) heating for peeling tomatoes as having "remarkable and promising" potential for commercialization by the food industry.

Because no water and salt are used in the new peeling process, IR dry-peeling could be the solution for long-term water supply and salinity problems caused by lye peeling. IR dry-peeling also reduced the tomato peeling loss significantly and resulted in similar or better firmness of the product with similar heating time compared to hot lye peeling. The reduced peeling loss and high product quality mean that more valuable and premium products can be produced. Because no salt is used in the peeling, the skins do not contain added salt and can be easily utilized as value-added food products.

Major Advantages to Infrared Dry Peeling:

• The average percentage of fully peeled tomatoes obtained from the IR peeling system was much higher than that from steam peeling. 
• The IR peeled tomatoes had a much better texture than the steam peeled ones.
• A commercial infrared peeling system is predicted to save about 22 percent and 28 percent of the energy when compared to energy used by steam and lye peelings.
• No water and chemicals are required for the infrared peeling system so there will be no need to treat any wastewater after the peeling process. 

Vacuum Feedthroughs for University Research and Development

Public research universities play a significant role in the advancement of many industries, including medicine, composite materials, semiconductor development, analytical equipment and alternative energy sources. Every day, we benefit from discoveries made, or knowledge advanced, from the engineering and scientific research done by our universities.

Scientific research almost always involves the careful and accurate control of pressure (vacuum), temperature, level, and flow. Included in most labs are an assortment of testing and monitoring chambers, all with an wide array of peripheral support equipment such as vacuum feedthroughs, thermocouples, heaters, and connectors.  Equipment size, shape, and material selection vary widely, and many times compromises in component specifications vs. design requirements are made, with component purchases being driven by off-the-shelf-parts. These decisions are driven by the assumption of favorable cost and delivery time over those of a custom solution. Any downside to design compromise is chalked up to schedule and budget.

There's good news on the custom feedthrough front though. One manufacturer, Northern California's BCE, has adopted processes and techniques that deliver prototypes and low production-run custom feedthroughs quickly and inexpensively.

Below are some examples of custom feedthroughs from BCE that better fit the desired design requirements, and still were produced quickly and affordably:


Novel feedthrough design used in methane sensing systems incorporating a brass bushing with an O-ring seal. Vacuum leak tight assembly with limited outgassing due to BCE’s proprietary black epoxy seal. Cost-effective 18 wire configuration with a small footprint. Threaded assembly for easy installation into a universal vacuum port.


Effective feedthrough design ideal for extremely confined spaces. Less than 3/16” in diameter incorporating 6X 20 AWG Teflon insulated wires sealed in a 1” long stainless steel shell. Precisely manufactured and engineered to supply power and signals to delicate instruments.



Epoxy-free, robust laser welded assembly ideal for power supply in high temperature and vacuum environments. Standard 9X Beryllium-Copper Alloy contacts hermetically sealed with ceramic. Rated for 750VAC. Mating UHV connector and cables available.




Hermetically sealed 50 pin feedthrough for easy integration in complex electrical circuits. Stainless steel contacts sealed with a clear epoxy engineered to fit into any electrical port. Contacts mounted to FR4 board with standard through holes for easy installation with readily available hardware.



Stainless steel contacts sealed in a standard CF flange with an O-ring groove for effective supply of signals inside a vacuum chamber. Proprietary BCE Epoxy seal meeting NASA ASTM E595 Low Outgassing Specification. Additional sleeve on rear for easy installation and grip.

For more information visit https://belilove.com/feedthrough or call (510) 274-1990

18 Wire Vacuum Feedthrough: Pioneering Advanced Methane Sensing Systems

18 Wire Vacuum Feedthrough (BCE)

Domestic natural gas production from shale resources is proving to be more economical and environmentally sustainable for the United States. Unfortunately, part of this gas resource is lost through methane leaks, which is also a greenhouse gas detrimental to the environment. Thus, in order to increase the efficiency of this process, it is vital to monitor methane emissions to keep them at an absolute minimum. It is for this precise development that BCE was approached by a large American University requesting a feedthrough that would be used as part of an elaborate methane sensing device. The feedthrough needed to meet specific requirements in order to become an integral part of the existing assembly.

SCOPE

• Cost effective design 
• Brass body construction 
• ½” BSPP Male Threads to mate feedthrough 
• Hermetically sealed wires 
• 16X 20AWG solid wires, Teflon insulated 
• 2X 26AWG solid wires, Teflon insulated 
• Limited outgassing 
• 1’ wire length on vacuum side 
• 1.5’ wire length on atmosphere side 
• Vacuum Compatible to 10-9 atm.cc/sec 
• All materials operable at 150°C 

OUTCOME

BCE proposed its 18 wire vacuum feedthrough configuration for this specific application. All conductors were sealed into a brass bushing adapter with ½” BSPP mating male threads. Moreover, BCE’s proprietary black epoxy was used; meeting NASA ASTM E595 low outgassing standards to prevent contamination. The requested wire configuration was also respected and the feedthrough was tested to ensure its vacuum compatibility meeting customer demands. Furthermore, all requirements were met to ensure a seamless integration to the existing methane sensing device. 

https://belilove.com
510-274-1990

Replaceable, (10) Type K Thermocouple, Vacuum Feedthrough

Thermal sensing inside a vacuum chamber is essential in many processes. It is therefore necessary to have a feedthrough that not only ensures vacuum compatibility, but which also allows easy replacement and maintenance of thermocouples and components. This is precisely what BCE’s Replaceable 10X Thermocouple Feedthrough renders.

With 10 thermocouples installed inside stainless steel compression fittings, multiple temperature readings can be taken from inside the vacuum chamber simultaneously. As the thermocouples are compressed, they can be easily extracted for maintenance or replacement purposes. The compression fittings in turn are threaded into a standard CF flange with an O-ring groove that mates directly to the chamber port. Thus, they can also be removed and replaced with ease. 

The entire construction is stainless steel for added durability and cost effective machining of parts. Thermocouple leads are available in multiple materials including Kapton for higher temperature applications. Hence, there is virtually no contamination.

Specifications

• CAD modelling and Engineering Design Consultation for R&D 
• Vacuum Compatible to 10-9 atm.cc/sec 
• Maximum Operating Temperature up to 400°C (dependent on lead insulation and O-ring materials) 
• 10X Thermocouple, Type K, Grounded, SS304 sheath (multiple options available) 
• 10X 316 SS compression fittings (multiple options available) 
• 304 SS standard CF flange with O-ring groove (multiple options available) 
• 24” standard Teflon leads (multiple options available) 
• All features and materials can be customized