Xita Ring

Xita Ring

Xita ring is the Chinese name for the Dixon ring, also called the theta ring — a high-efficiency packing made from knitted stainless-steel wire mesh. It was invented in 1947 by the British scientist Dr. Dixon, whose name it carries (and, from the way it is pronounced, is sometimes spelled Dixson); the theta name comes from its cross-section, a mesh cylinder with a mesh diaphragm across the middle that looks like the Greek letter θ. Each piece is a small, uniform cylinder of fine mesh — typically 60 to 100 mesh — and it is this mesh construction that makes it work: it holds a thin film of liquid over an enormous area of wire and keeps the vapour in close contact with it, so a short bed separates extremely sharply. It is a laboratory and small-column packing, used where the purity of the separation matters more than the throughput — bench distillation, small-batch production, and demanding high-purity duties. It is made in a range of small sizes, each matched to a column bore; the full data are in the table below. Model RJ-903.

Xita ring = Dixon ring / theta ring: knitted stainless wire-mesh high-efficiency packing.
Small mesh cylinder with a central mesh diaphragm (the θ cross-section); 60–100 mesh.
Invented by Dr. Dixon in 1947; a benchmark laboratory-distillation packing.
Very sharp separation in a short bed; for high-purity and small-column work.
Made in small sizes matched to the column bore; data in the table; model RJ-903.

Technial Parameters

Size	Fits column dia. (mm)	Theoretical plates (per m)	Bulk density (g/L)	Surface area (m²/m³)	Porosity (%)	Pressure drop (mbar/m)
φ1.5×1.5	φ2–10	70–90	1960	4700	90	32
φ2×2	φ10–20	60–70	1710	3900	91	30
φ3×3	φ25–40	50–60	1140	3000	93	15
φ4×4	φ40–70	45–50	830	2200	95	10
φ5×5	φ50–70	30–40	650	1700	95	9
φ6×6	φ60–90	20–30	520	1200	95	7

Property	Value
Product Type	Xita ring / Dixon ring / theta ring (wire-mesh column packing)
Function	High-efficiency mass transfer in small-diameter columns
Model NO.	RJ-903
Material	Knitted stainless-steel wire mesh (typically 60–100 mesh)
Structure	Small uniform mesh cylinder with a central mesh diaphragm (θ cross-section)
History	Invented 1947 by Dr. Dixon (hence Dixon / Dixson / theta ring)
Sizes	φ1.5×1.5 to φ6×6 mm (also up to about 8×8 mm)
Fits Column Diameter	φ2–90 mm
Theoretical Plates	20–90 per metre
Surface Area	1200–4700 m²/m³
Porosity	90–95%
Pressure Drop	7–32 mbar/m (also depends on gas/liquid rates and fluid properties)
Advantages	Very high separation efficiency, low pressure drop, corrosion-resistant
Applications	Laboratory distillation, small-batch production, high-purity separation (e.g. isotope enrichment)
Trademark	RONGJIAN
Origin	China
HS Code	8419909000
Transport Package	Steel drum / ton bag / carton box

FAQs

What is a Dixon (theta) ring, and where does the name come from?

A Dixon ring, Xita in Chinese, from the Greek letter theta, and so also called the theta ring, is a small, high-efficiency packing made of knitted wire mesh. It has a genuine pedigree: it was developed in 1947 by a British scientist, Dr. Dixon, and is named after him. Because his surname is pronounced Dixson, you will occasionally see it spelled that way too, and because a piece viewed end-on looks like the Greek letter θ, a ring of mesh with a straight strip of mesh across the middle, theta ring has become the other common name. Physically it is a tiny, uniform cylinder of fine stainless mesh with that internal mesh partition. It is one of the classic high-performance laboratory packings, the yardstick against which small-column packings are often judged, and it is used wherever a separation in a small column has to be as clean as possible. In short, it is a mesh ring, invented by Dr. Dixon, shaped like a θ, for very sharp separations in small equipment.

What is the wire-mesh θ structure, and why does it separate so well?

The whole design is about spreading liquid thinly over a lot of wire and holding the vapour against it. Each ring is knitted from fine wire mesh, commonly in the range of 60 to 100 mesh, meaning that many wires to the inch, so its surface is not a smooth wall but a dense weave of tiny threads. Liquid clings as a thin film across all of that wire, presenting a huge, constantly renewed area for the rising vapour to exchange with, and the internal mesh partition across the cylinder adds still more surface and breaks up the flow so the two phases keep re-mixing. Fine mesh also wets easily and drains evenly, so the liquid spreads rather than channelling. The upshot is a very high separation efficiency for the size of the packing, a large number of ideal separation steps in a short height of bed, while the open weave keeps the resistance to flow low. It is that combination, a lot of finely divided wetted surface with an open, low-resistance structure, that makes the mesh ring the high-efficiency choice it is. The exact figures for each size are tabulated above.

Why is it used for isotope enrichment and high-purity separation?

Because it separates so cleanly. Some separations are extraordinarily hard, the two things to be separated being almost identical, so each theoretical stage moves you only a hair closer and you need a great many stages to get a pure product. The extreme example is isotope separation, such as enriching one isotope of an element over another, where the difference between what you are separating is tiny; jobs like that demand a packing that packs the maximum number of separation stages into a column, which is exactly what the mesh Dixon ring does. The same logic applies to producing very high-purity chemicals and solvents, and to research separations of close-boiling mixtures, all of which are typically done at laboratory or small-batch scale where a compact, ultra-efficient column is wanted. The Dixon ring earns its place in these because it delivers the plate count that such separations need in a manageable column height, and does so consistently, piece to piece, thanks to its uniform manufacture. Tell us the separation and how pure the product must be and we will advise.

How is it run, and what affects its pressure drop?

It is used as a dumped packing in small columns: the rings are poured in loosely to a chosen bed height, and the liquid and vapour pass through as in any packed column, just at the fine, high-efficiency end of the scale. Being mesh, it is best kept to clean fluids, since the fine weave can foul if the liquid carries solids, and to the moderate flow rates typical of laboratory and small-batch work. Its pressure drop, how much resistance the bed offers to the vapour, is low for the efficiency it gives, but it is not a single fixed number: it rises with the gas velocity and the liquid spray rate, and it depends on the properties of the fluids themselves, particularly their viscosity and surface tension, so the figures in the table are typical values that shift with the duty. In practice you choose the ring size for the column bore, set the bed height for the number of stages you need, and keep the vapour and liquid rates within the packing's efficient range. Send us the column and the separation and we will specify the ring and the bed.

A Xita ring is the Dixon ring, or theta ring — a high-efficiency packing knitted from fine stainless-steel wire mesh, invented in 1947 by Dr. Dixon and named after him; the theta name comes from its θ-shaped cross-section, a mesh cylinder with a mesh strip across the middle. Its dense weave holds a thin film of liquid over a large area of wire and keeps it in close contact with the vapour, so it separates very sharply in a short bed while offering little resistance to flow. It is a laboratory and small-column packing, made in small uniform sizes matched to the column bore.

Where the Dixon (theta) ring is used:

Use	Why the mesh ring suits it
Laboratory distillation	Many separation stages in a short bench column
Small-batch production	High purity from a compact, efficient column
High-purity separation	Sharp resolution of close-boiling or near-identical components
Isotope enrichment	The very high plate count that extreme separations need

Made of knitted stainless mesh (typically 60 to 100 mesh) in sizes from φ1.5×1.5 to φ6×6 mm, it is a dumped packing for small columns, best on clean fluids at moderate rates. The per-size surface area, plate count and pressure drop are in the table above. Tell us your column and the separation, and we will choose the ring size and the bed height.