For a start HR should be in brackets:

An improved heat transfer tube (10) having an inner surface, an inner diameter (Di), a longitudinal axis (aT) and a plurality of ribs and grooves formed on said inner surface, each of said ribs having a base, two opposite sides, an apex angle ( beta ) between said sides, a height (HR) and an angle of inclination ( alpha ) with respect to said longitudinal axis, in which the improvement comprises: said angle of inclination being between 30 and 45 degrees; the ratio of said rib height to said tube inner diameter being between 0.018 and 0.03; the width (WR) of said base being between 0.127 and 0.254 mm (0.005 and 0.01 inch); said apex angle being between 0 and 60 degrees; and the number of ribs per unit length of said tube's inner circumference ( pi Di) being between 10 and 24 per cm (26 and 60 per inch).

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Note added at 14 mins (2008-08-28 18:33:24 GMT)
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HR

probably =

height ratio

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Note added at 15 mins (2008-08-28 18:33:42 GMT)
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Here is the site:

http://www.freepatentsonline.com/EP0591094.html

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Note added at 16 mins (2008-08-28 18:35:13 GMT)
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V-ribbed belt and method for fabricating the same - US Patent 6350182
In this belt, the number of bottom-face-side ribs 3 was three, the number of ... Further, the height hr (hr1 or hr2) of each rib 3, 4 was 2.5 mm, ...
www.patentstorm.us/patents/6350182-description.html - Similar pages

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Note added at 17 mins (2008-08-28 18:36:21 GMT)
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Here is something else:


Aa = web area (mm2)
Af = flange area (mm2)
Al = sheet area (mm2)
Ar = rib area (mm2)
b = spacing between ribs (mm)
E = elasticity modulus (N/mm2)
Er = reduced elasticity modulus (N/mm2)
ea = web thickness (mm)
eb = base thickness (mm)
ef = flange thickness (mm)
Gr = shearing elasticity modulus (N/mm2)


h = height between flange and base center (mm)
ha = web height (mm)
hr = rib height (mm)
If = flange index (mm)
It = torsional inertia momentof rib (mm)

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Note added at 18 mins (2008-08-28 18:37:03 GMT)
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Yep:

Results 1 - 10 of about 2,840,000 for height rib height. (0.23 seconds)
Search Results

1.
Effects of Rib Height on Heat Transfer Performance Inside a High ...
The experiments were performed for three rib heights—h = 3 mm, h = 2 mm, and h = 1 mm (h-rib height)—for two rib arrangements, transverse (90°) and inclined ...
www.begellhouse.com/journals/4c8f5faa331b09ea,6c6e1f58370cb... - 19k - Cached - Similar pages

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Note added at 24 mins (2008-08-28 18:43:23 GMT)
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Rib, armadura, puntal, refuerzo (de placa), nervadura, varenga (de buque), costilla , ( Ingeniería aeroespacial ) Miembro transversal de la estructura que le da forma a la sección y resistencia a una porción de una superficie aerodinámica ; rib flange, chapa de nervadura; rib motor, motor con nervaduras; rib nose, borde de costilla; bearing rib , reborde, talón (ferrocarril); centre rib , alma de carril, barra de carril, cuerpo de carril; cutaway rib , nervadura vaciada; glued rib , nervadura pegada; hollow rib , nervadura hueca; ¡ron rib , cuaderna de hierro; longitudinal rib, nervio longitudinal; metal rib , nervio metálico; nose rib , costilla del borde de ataque; ribs of a ship, varenga de un buque; solid rib , nervadura llena; stiffening rib, nervadura de refuerzo; strengthened rib , nervadura reforzada; tacked rib , nervadura clavada; trailing edge rib , nervadura de borde de fuga; transversal rib , nervadura transversal; ventilated rib motor, motor con nervaduras ventiladas; web of rib , alma de nervadura.