Steel, density, thermal conductivity

Niobium is always found in nature associated with tantalum and it closely resembles tantalum in its chemical and mechanical properties. It is a soft ductile metal which, like tantalum, work hardens more slowly than most metals. It will in fact absorb over 90% cold work before annealing becomes necessary, and it is easily formed at room temperature. In addition, welds of high quality can be produced in the metal. In appearance the metal is somewhat similar to stainless steel it has a density slightly higher than stainless steel and a thermal conductivity similar to 1% carbon steel. 

The pure metal has a very high melting point (2996°C) and is blue-grey and like lead in appearance. It has a density of about twice that of carbon steel (16.6 g/cm ) and a similar thermal conductivity. It is one of the refractory metals and suitable for high temperature application under protective conditions. 

Liquid 4He, above 2.2 K (He I), because of its low density, shows transport properties similar to those of a classic gas (Fig. 2.12). The same happens for 3He above 0.1 K. Above the A-point, 4He has a low thermal conductivity (a factor of 10-4 compared to Cu and a factor of 10-1 compared to stainless steel) and boils with strong bubbling. 

A fermentation broth contained in a batch-operated stirred-tank fermentor, 2.4m in inside diameter D, is equipped with a paddle-type stirrer of diameter (L) of 0.8 m that rotates at a speed Af = 4s -. The broth temperature is maintained at 30 °C with cooling water at 15°C, which flows through a stainless steel helical coil that has a 50 mm outside diameter and is 5 mm thick. The maximum rate of heat evolution by biochemical reactions, plus dissipation of mechanical energy input by the stirrer, is 51000 kcal h , although the rate varies with time. The physical properties of the broth at 30 °C were density p = 1000 kg m " , viscosity p = 0.013 Pa s, specific heat Cp = 0.90 kcal kg °C , and thermal conductivity K = 0.49 kcal h m °C = 0.000136 kcals m °C . ... 

Different grades of chopped low-carbon steel fibers are used as reinforcements and friction enhancers in formulations. Steel fibers have good reinforcing properties and thermal resistance but high density, poor corrosion resistance, and high thermal conductivity. Chopped stainless steel fibers have found limited application in friction materials and backing layers. Some manufacturers have developed annealed and softer grades of steel fiber to reduce rotor and drum wear. 

Fig. 1. Temperature dependence of critical property ratios for uniaxial composite laminates and annealed stainless steel (a) ratio of thermal conductivity to Young s modulus (b) ratio of thermal conductivity to tensile yield strength (c) ratio of Young s modulus to density (d) ratio of tensile yield strength to density.

Thermal conductivities and diffusivities of solids vary greatly with temperature. Specific heats and densities vary little, except for steels at their phase transition point. The thermal conductivities of solid pure metals drop with increasing temperature, but the conductivities of solid alloys generally rise with temperature. 

The Cooling of Steel Plates In an annealing process—a process wherein materials such as glass and metal are heated to hi temperatures and then cooled slowly to toughen them—thin steel plates k = thermal conductivity = 40 W/m K, p = density = 7800 kg/m and c = specific heat - 400 J/kg IQ are heated to temperatures of900°C and then cooled in an enviroiunent with temperature of 35°C and a heat transfer coefficient of A = 25 W/m K. Eadi plate has a thickness of = 5 cm. We are interested in determining what die temperature of the plate is after one hour. 

Aluminum. Aluminum has a density about one-third that of steel, high resistance to corrosion, and excellent electrical and thermal conductivity. Moreover, this nontoxic metal reflects light and heat well. 

Zirconium is a lustrous, grayish white, ductile metal. A listing of the physical properties of zirconium is given in Table 22.1. However, a few comments can be made. First, zirconium s density is considerably lower than those of iron-and nickel-based stainless alloys. Second, zirconium has a low coefficient of thermal expansion, favoring equipment that requires a dose tolerance. The coefficient of thermal expansion of zirconium is about two-thirds that of titanium, about one-third that of type 316 stainless steel (S.S.), and about one-half that of Monel. Third, zirconium has high thermal conductivity that is more than 30% better than those of stainless alloys. These properties make zirconium very fabricable for constructing compact, efficient equipment. 

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