Heat exchangers metal resistances

Explosion-bonded metals are produced by several manufacturers in the United States, Europe, and Japan. The chemical industry is the principal consumer of explosion-bonded metals which are used in the constmction of clad reaction vessels and heat-exchanger tube sheets for corrosion-resistant service. The primary market segments for explosion-bonded metals are for corrosion-resistant pressure vessels, tube sheets for heat exchangers, electrical transition joints, and stmctural transition joints. Total world markets for explosion-clad metals are estimated to fluctuate between 30 x 10 to 60 x 10 annually. 

As the measurements show, the small heater without an electrical separation (from the boiler) is not detrimental to cathodic protection. However, with the uninsulated built-in Cu heat exchanger without an electrical separation, cathodic protection was not achieved. As expected, the polarization increased with increasing conductivity of the water. It should be pointed out that the Cu tube was tinned and that the tin could act as a weak cathodic component. Apart from the unknown long-term stability of such a coating, the apparent raising of the cathodic polarization resistance of tin is not sufficient to provide cathodic protection with such a large fixture. This applies also to other metal coatings (e.g., nickel). 

Copper is attacked by mineral acids, except cold, dilute, unaerated sulphuric acid. It is resistant to caustic alkalies, except ammonia, and to many organic acids and salts. The brasses and bronzes have a similar corrosion resistance to the pure metal. Their main use in the chemical industry is for valves and other small fittings, and for heat-exchanger tubes and tube sheets. If brass is used, a grade must be selected that is resistant to dezincification. 

The sample introduction unit was constructed from inert materials, which minimizes the introduction of metal contamination into the system. The samples or digestion acids make contact only with PTFE, Kel-F, glass, acid-resistant rubber and platinum-iridium (9 + 1) alloy. In addition, the construction materials were Hmited to acid-grade Arborite (ureaformaldehyde laminate). Perspex and stainless-steel. The unit was constructed in three continuous sections a heated sample compartment, a turntable mechanism and heat-exchanger compartment, and a pump compartment. 

Composition 60% copper and 40% zinc. It is used in the manufacture of screws, valve stems, brazing rods, condenser tubes, condenser heads, and heat exchanger baffles and plates. Muntz metal is strong, ductile, and corrosion resistant. 

A liquid-hquid heat exchanger uses metal tubes that are of 30 mm inside diameter and 34 mm outside diameter. The values of h for the liquid 1 flowing inside the tubes ( i) = 1230 kcal h m °( V and h for the liquid 2 flowing outside the tubes = 987 kcal h m" °( V. Estimate based on the outside tube surface and U, for the inside tube surface, neglecting the heat transfer resistance of the tube wall and the dirty deposit. 

In the case of gas-gas or liquid-liquid heat exchangers, the film coefficients for the fluids on both sides of the metal wall are of the same order of magnitude, and can be predicted by correlations, for example, with Equation 5.8a or 5.12a. Neither of the fluid film resistances can be neglected. In a gas-liquid heat exchanger, the controlling resistance is on the gas side, as mentioned before. 

The temperature controller consists of a simple electrical resistance if only heating is required. Otherwise a heating/cooling jacket, or a heat exchanger inside the cell is used (see Fig. 9.10-2). This is the most widespread method, as the metallic thermal inertia is very high, and does not permit a suitable temperature-control in the other cases. 

From a corrosion viewpoint, the metal with the most outstanding promise for seawater heat exchangers is titanium. Laboratory experiments starting with sea water, and heating under pressure to above the critical temperature, have indicated titanium to be greatly superior to Hastelloy C and Monel, under these conditions (4). All indications suggest that titanium is the most resistant of the commercially available metals to sea water at temperatures up to 750° F. 

The practical heat-transfer coefficient is the sum of all the factors that contribute to reduce heat transfer, such as flow rate, cocurrent or countercurrent, type of metal, stagnant fluid film, and any fouling from scale, biofilm, or other deposits. The practical heat-transfer coefficient ((/practical) is, in reality, the thermal conductance of the heat exchanger. The higher the value, the more easily heat is transferred from the process fluid to the cooling water. Thermal conductance is the reciprocal of resistance (/ ), to heat flow ... 

Most other metals in the cooling system are subject to similar corrosive influences, although of reduced intensity, as they will have been selected in part due to their more corrosion-resistant (or noble) properties, albeit at a higher purchasing cost. Although some of these metals and alloys may be quite exotic (and therefore more expensive), they will be used because of a particular suitability for heat exchangers or as components for special types of pumps or valves they may also tend to be inherently noble. 

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