Bemcoil Shrouds and Baseplates
Bemcoil’s distinguished history includes almost every major space program in the United States. The liquid nitrogen circuited shroud shown at left housed the Apollo Astronauts and the Apollo Capsule running at -185 C. The shroud is 18 feet in diameter. Many Bemcoil shrouds made in the 1960’s are still functioning reliably, without leaks, today.
Bemcoil, is a proprietary Bemco stainless steel shroud material proven in high vacuum service for over 50 years. This material is available in both single and double embossed versions. It is made from 18 gauge roll welded stainless steel with welded edges.
Because each panel is made to order, circuiting can be optimized to match both the fluid or gas in the shroud and the shape of the enclosing space. Starting with shrouds as small as 12 inches in diameter, Bemcoil is available for installation in systems as large as 50 feet in diameter. Bemco also makes the matching fluid (the Bemco PCL Series) and gas conditioners (the Bemco HPG Series).
Imitators sometimes use uncircuited, spot welded, waffle shrouds in an attempt to duplicate the precise flow patterns that are easily achievable with Bemcoil. Waffle shrouds often suffer from random fluid flow tunneling due to uneven loading or local gas build-up in flooded shrouds. Why compromise when you can have optimized circuiting as well as the superior pressure and helium mass spectrometer tested long term leak tight integrity of a stainless steel Bemcoil shroud?
Bemcoil is pressure expanded in a controlling die. Unlike many aluminum shrouds that depend on conduction for heat transfer, Bemcoil has over 95% of its surface in contact with the circulating fluid. Even through stainless steel is typically not a good conductor, users report outstanding temperature uniformity due to Bemcoil’s high wetted surface-to-fluid ratio.
Stainless steel’s great advantage versus aluminum is its resistance to strain cracking and porosity induced by thermal expansion and contraction. Many users prefer Bemcoil to any other type of thermal shroud. Bemcoil thermal shrouds are usually polished on the outside and painted with high emissivity black epoxy paint on the inside to optimize heat transfer.
Bemcoil-DE (double embossed) is made from roll and continuous welded 18 gauge 304 stainless steel sheet. Each tube passage is almost equivalent to a 7/8 inch OD tube.
It is available in three finishes. A number 2B (semi-reflective) finish on the inside face and a number 4 (polished unidirectional) finish on the outside surface, specified when one side of the shroud is to be painted with black epoxy. A number 4 finish on both sides, specified when both sides will remain unfinished with an electropolish on one or both sides. Bemcoil-DE’s minimum roll diameter is 18 inches. The maximum diameter is unlimited. Sheets can be as small as 4 inches wide with a maximum width of 44 inches. Length of each sheet is limited only by the available material.
Assembled shrouds can be round or square. They can have any number of penetrations. Circuiting is optimized to the intended use and pressure drop is matched to the conditioning system. Each plate or assembly is tested under pressure at 150 psig and with a helium mass spectrometer.
Bemcoil-FOS (Flat One Side) is made from 18 gauge, 304 stainless steel sheet combined with 11 gauge (0.120 inch thick), 304 stainless steel plate.
Bemcoil-FOS can be circuited to allow tapped or clearance hole penetrations for mounting. This material is sometimes specified as a liquid nitrogen cooled water getter plate material in optical testing systems.
Bemcoil-DE and Bemcoil-FOS can be specified for use as a heat transfer surface.
Bemcoil can be used to heat or cool reservoirs, tanks, and mixing kettles. It can be radiused, bent, curved, and have any number of penetrations. It can be formed into troughs and pans, arranged in banks, and enclosed inside heat exchangers. It can be furnished for use as a drum warmer, cylinder heater, or attached to existing vessels. Available in both 304 and 316 series stainless steel, it can be furnished in number 2B, number 4, or electropolish finishes. It can be pressure or vacuum checked with a helium mass spectrometer. It can be painted on one or both sides. Any type of weldable stainless steel connector can be furnished attached.
A technical paper describing the heat transfer characteristics of Bemcoil is available. Please request a copy from your Bemco Applications Engineer.
Stepped, pump opening spacer plates made from Bemcoil-DE and stainless steel or copper chevron baffles are provided to cover pumping port openings while maintaining test object optical density. Stepped ports include a spacer plate and are not optically dense near the shroud edges.
Chevron baffles can be furnished as 60 degree, 45 degree, and 30 degree full chevrons, and louver plates (half chevrons) can be furnished over the same angular range. Variation in louver and chevron geometry modifies the effective net pumping speed of the opening. A full wall chevron from the inside of a Bemcoil shroud, prior to painting is shown. Your Bemco Applications Engineer can help you optimize the pumping port baffle selection for your selected pumping system and needs.
Thermally conditioned baseplates for conductive testing are offered. Baseplates can be fixed or can move on slides.
Base plates are fabricated from Bemcoil-FOS (Flat-One-Side) and machined or gun-drilled aluminum tool plate combined with copper or stainless steel tubes. The plates can be mounted on slides and connected with flexible stainless steel bellows tubing if desired. Base plates are available with pre-drilled stainless steel threaded inserts mounted in regular patterns to allow test item mounting.
Bolt down hole patterns with reinforced threaded inserts are offered in any pattern. Two standard attachment patterns are 3 inches x 3 inches x 1/4-20 grid and 4 inches x 4 inches x 3/8-16 grid. Other patterns are available. 3-inch x 3-inch patterns begin 1-1/2 inches from the edge of the plate and 4-inch x 4-inch patterns begin 2 inches from the edge of the plate. All plates are precision machined smooth and flat, cleaned, and furnished without a finish unless otherwise specified.
Baseplates can be circuited for use with heat transfer fluids, liquid nitrogen, or gaseous nitrogen. Temperature conditioning can share the primary thermal shroud conditioning system fluid or gas system or operate from an independent system to allow different process temperatures on the plate versus the primary shroud. Your Bemco Applications Engineer can help you to optimize a baseplate for your needs.
Shown below is a cutaway drawing of a Bemco BC8-55/150C thermal shroud. The inside is shown in blue for clarity but is actually painted with black epoxy.
When combined with a thermal conditioner such as the Bemco PCL3L-III or PCL3M-III, this shroud converts a 24 inch inside diameter by 30 inch high vacuum only vertical bell jar into a 19 inch inside diameter by 20 inch high thermal vacuum testing system. With a convenient clam shell door, test objects are easily loaded by simply raising the bell jar above the top of the door opening.
The BC8-55/150C Bell Jar Thermal Shroud is made from a combination of Bemcoil-DE (the walls, ceiling and door) and Bemcoil-FOS (the floor and the pump port spacer plate). The clam shell door is piped to the main shroud circuiting using flexible stainless steel bellows tubing.