Thermal conductivity, construction materials

AH 103 EPS 303 Guidelines for Reporting Thermal Transmission Properties of Polystyrene Foam Insulating Materials, Thermal Conductance, and Transmittance of Built-Up Construction Systems. 

The heat transfer-coefficients and fouling factors are listed in Table 7.2.1. Because of the acetic acid, select SS316 as the material of construction. The thermal conductivity, k, of SS316 and the wall thickness of the reactor, xw, are given in Table 7.2.1. 

Because of their low thermal conductivity, high temperature capability, low cost, and neutron tolerance, carbon materials make ideal thermal insulators in nuclear reactor environments. For example, the HTTR currently under construction in Japan, uses a baked carbon material (Sigri, Germany grade ASR-ORB) as a thermal insulator layer at the base of the core, between the lower plenum graphite blocks and the bottom floor graphite blocks [47]. 

Cooler Absorbers When the absorption of a gas is accompanied by the evolution of heat, an important function of the absorption equipment is the removal of the heat generated. This may be accomplished by using a number of towers in series, the liquid from each tower being circulated through an external cooler. There are different types of cooler-absorbers in which processes of this type can be carried out in a single unit. The materials of which these cooler-absorbers are constructed should be of high thermal conductivity and resistant to corrosion by the substances used in the process. As an example, in the manufacture of hydrochloric acid of the... 

Conducted heat is that going in through cold store surfaces, tank sides, pipe insulation, etc. It is normally assumed to be constant and the outside temperature an average summer temperature, probably 25-2/°C for the UK, unless some other figure is known. Coldroom surfaces are measured on the outside dimensions and it is usual to calculate on the heat flow through the insulation only, ignoring other construction materials, since their thermal resistance is small. 

GP 1[ [R 1[ A change from aluminum to platinum as construction material results in reduced micro-reactor performance concerning oxidation of ammonia, decreasing N2O selectivity by 20% [28]. This is explained by the lower thermal conductivity of platinum, which causes larger temperature differences (hot spots) within the micro channels, i.e. at the catalyst site, e.g. due to insufficient heat removal from the channels or also by non-uniform temperature spread of the furnace heating. 

This is explained by a possible higher activity of pure rhodium than supported metal catalysts. However, two other reasons are also taken into account to explain the superior performance of the micro reactor boundary-layer mass transfer limitations, which exist for the laboratory-scale monoliths with larger internal dimensions, are less significant for the micro reactor with order-of-magnitude smaller dimensions, and the use of the thermally highly conductive rhodium as construction material facilitates heat transfer from the oxidation to the reforming zone. 

Thermal conductivity and heat capacity In practical applications, refractory materials processing high thermal capacity as well as low thermal conductivity are required, depending upon (of course) the functional requirements. In most situations, a refractory that serves as a furnace wall should have a low thermal conductivity in order to retain as much as heat as possible. However, a refractory used in the construction of the walls of muffles or retorts or coke ovens should have a high thermal conductivity in order to transmit as much heat as possible to the interior. The charge remains separated from flame in these specific examples of installations. 

Since the thermally thick case will predominate under most fire and construction conditions, the conductance can be estimated from Equation (11.10). Values for the materials characteristic of Table 11.1 are given in Table 11.2. As time progresses, the conduction heat loss decreases. 

For the handling of corrosive fluids, forced-circulation evaporators have been constructed in a variety of inert materials, and particularly in graphite where the unique combination of chemical inertness coupled with excellent thermal conductivity gives the... 

The problems associated with direct reaction calorimetry are mainly associated with (1) the temperature at which reaction can occur (2) reaction of the sample with its surroundings and (3) the rate of reaction which usually takes place in an uncontrolled matmer. For low melting elements such as Zn, Pb, etc., reaction may take place quite readily below S00°C. Therefore, the materials used to construct the calorimeter are not subjected to particularly high temperatures and it is easy to select a suitably non-reactive metal to encase the sample. However, for materials such as carbides, borides and many intermetallic compounds these temperatures are insufficient to instigate reaction between the components of the compound and the materials of construction must be able to withstand high temperatures. It seems simple to construct the calorimeter from some refractory material. However, problems may arise if its thermal conductivity is very low. It is then difficult to control the heat flow within the calorimeter if some form of adiabatic or isothermal condition needs to be maintained, which is further exacerbated if the reaction rates are fast. 

Part AM This part lists permitted individual construction materials, applicable specifications, special requirements, design stress-intensity values, and other property information. Of particular importance are the ultrasonic-test and toughness requirements. Among the properties for which data are included are thermal conductivity and diffusivity, coefficient of thermal expansion, modulus of elasticity, and yield strength. The design stress-intensity values include a safety factor of 3 on ultimate strength at temperature or 1.5 on yield strength at temperature. 

The thermal conductivities of the most common insulation materials used in construction are shown in Table 2. Values at different mean temperature are necessary for accurate design purposes at representative temperatures encountered during winter or summer. For example, under winter conditions with an outside temperature of -20 to -10°C, the mean temperature is 0—5°C. For summer, mean temperatures in excess of 40°C can be experienced. 

A wall 2 cm thick is to be constructed from material which has an average thermal conductivity of 1.3 W/m °C. The wall is to be insulated with material having an average thermal conductivity of 0.35 W/m °C, so that the heat loss per square meter will not exceed 1830 W. Assuming that the inner and outer surface temperatures of the insulated wall are 1300 and 30°C, calculate the thickness of insulation required. 

A plane wall is constructed of a material having a thermal conductivity that varies as the square of temperature according to the relation k = fc0(l + /3T1). Derive an expression for the heat transfer in such a wall. 

A furnace of 1 by 2 by 3 ft inside dimensions is constructed of a material having a thermal conductivity of 0.5 Btu/h ft °F. The wall thickness is 6 in. The inner and outer surface temperatures are 1000 and 200°F, respectively. Calculate the heat loss through the furnace wall. 

The heat exchange function of the mold leads to a conflict of interest. Thermoforming is carried out at relatively low pressures, very low pressures in the case of vacuum forming, so molds can be constructed from light, inexpensive, easily shaped materials such as wood, plaster, or epoxy resins. However, these materials have poor thermal conductivity. Thus such molds do not function well as heat exchangers. 

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