Thermal rise

However, information concerning thermal rise is not available for all equipment. Generally, manufacturers of critical machinery, such as centrifugal air compressors and turbines, will include information relating to thermal rise in their installation manuals in the section dealing with alignment. When not available, the only method to determine the exact amount of compensation necessary to correct for thermal rise is referred to as a hot alignment check . 

If the finite thermal rise time Tth cannot be neglected, which means that At P Tt/, is not fulfilled, it may be necessary to sample at a higher rate than the clock rate of the excitation sequence (oversampling) [74]. A detailed discussion of this effect is, however, beyond the scope of this article. 

The paint or ink used must be conductive to laser processing. Standard paints and inks are not predictable nor controllable when exposed to the laser output. The inks bum easily and can mix the underlying plastic while in the molten liquid state. Laser compatible inks are mixed with a silicone based material reflective to the laser output thereby reducing the inks light absorption and rate of thermal reaction. Paints must be suitable for high temperature processing and be free of any contaminants that may absorb the laser wavelength and speed up the thermal rise. 

Clearance between cntont walls and component pins Clearance must be provided between the edge of the pallet cutout and the component pins to be soldered. If the pins are too close to the pallet opening wall, the wave may not contact the pins. Further, the pallet is somewhat of a thermal sink and inhibits the thermal rise necessary for soldering. 

G. S. Bushanam et al., Measuring Thermal Rises Due to Digital Device Overdriving, Proceedings of the International Test Conference, Philadelphia, PA, October 1984, pp. 400-407. 

In tanks with a depth/diameter ratio less than 0.5 (as in very large LNG and LPG tanks), the wall boundary layer flow may not be strong enough, and some of the heat inflow from the tank floor may be concentrated by natural convection into a number of thermals rising through the lower layer. As mentioned in Sects. 3.5.3 and 4.5,... 

Figure 13.16 shows two possible thermal profiles for endothermic plug-fiow reactors. This time the temperature falls for low rates of heat addition and/or high heat of reaction. The temperature rises for the reverse conditions. Under conditions between the profiles shown in Fig. 13.16, a minimum can occur in the temperature profile at an intermediate point between the inlet and exit. 

Measuring the gross heating value (mass) is done in the laboratory using the ASTM D 240 procedure by combustion of the fuel sample under an oxygen atmosphere, in a bomb calorimeter surrounded by water. The thermal effects are calculated from the rise in temperature of the surrounding medium and the thermal characteristics of the apparatus. 

The Morse function rises more steeply ihan ihe harmonic potential at short bonding distances. This difference can be important especially during molecular dynamics simulations, where thermal energy takes a molecule away from a potential minimum. ... 

The controlled thermal decomposition of dry aromatic diazonium fluoborates to yield an aromatic fluoride, boron trifluoride and nitrogen is known as the Schiemann reaction. Most diazonium fluoborates have definite decomposition temperatures and the rates of decomposition, with few exceptions, are easily controlled. Another procedure for preparing the diazonium fluoborate is to diazotise in the presence of the fluoborate ion. Fluoboric acid may be the only acid present, thus acting as acid and source of fluoborate ion. The insoluble fluoborate separates as it is formed side reactions, such as phenol formation and coupling, are held at a minimum temperature control is not usually critical and the temperature may rise to about 20° without ill effect efficient stirring is, however, necessary since a continuously thickening precipitate is formed as the reaction proceeds. The modified procedure is illustrated by the preparation of -fluoroanisole ... 

The variation of Cp for crystalline thiazole between 145 and 175°K reveals a marked inflection that has been attributed to a gain in molecular freedom within the crystal lattice. The heat capacity of the liquid phase varies nearly linearly with temperature to 310°K, at which temperature it rises more rapidly. This thermal behavior, which is not uncommon for nitrogen compounds, has been attributed to weak intermolecular association. The remarkable agreement of the third-law ideal-gas entropy at... 

Where there is a temperature difference between the object to be weighed and the surrounding air, air currents will be induced close to the object s surface (12). These can be significant if extreme accuracy is required. Objects should be allowed to reach thermal equiHbrium in the laboratory before weighing. Just as important, the balance should be designed to minimize the temperature rise inside the weighing chamber. In extreme cases, the object should be placed inside the chamber until it reaches thermal equiHbrium before weighing. Needless to say, drafts must be avoided. 

Thermal Resistance and Flammability. Thermal analysis of PVA filament yam shows an endothermic curve that starts rising at around 220°C the endothermic peak (melting point) is 240°C, varying afitde depending on manufacture conditions. When exposed to temperatures exceeding 220°C, the fiber properties change irreversibly. 

Differential-Temperature Thermal Flow Meters. Meters of this type inject heat into the fluid and measure the resulting temperature rise or, alternatively, the amount of power required to maintain a constant temperature differential. The power required to raise the temperature of a flowing stream by an amount AT is given by the relation ... 

The variation in total thermal conductivity with density has the same general nature for ah. cellular polymers (143,189). The increase in at low densities is owing to an increased radiant heat transfer the rise at high densities to an increasing contribution of k. ... 

Residential Construction. Owing to rising energy costs, the cost and low thermal conductivity are of prime importance in wall and ceiling insulation of residential buildings. The combination of insulation efficiency, desirable stmctural properties, ease of appHcation, abiHty to reduce air infiltration, and moisture resistance has led to use of extmded polymeric foam in residential constmction as sheathing, as perimeter and floor insulation under concrete, and as a combined plaster base and insulation for walls. 

The reaction occurs at essentially adiabatic conditions with a large temperature rise at the inlet surface of the catalyst. The predominant temperature control is thermal ballast in the form of excess methanol or steam, or both, which is in the feed. If a plant is to produce a product containing 50 to 55% formaldehyde and no more than 1.5% methanol, the amount of steam that can be added is limited, and both excess methanol and steam are needed as ballast. Recycled methanol requited for a 50—55% product is 0.25—0.50 parts per part of fresh methanol (76,77). 

With a batch process, such as hot isostatic compaction (HIP), heat exchange as used in a continuous reactor is not possible, and it is common practice to provide a furnace within the pressure vessel which is thermally insulated to ensure that the temperature of the vessel does not rise above 300°C. Most HIP operations involve gas pressures in the range 70—200 MPa (10—29,000 psi) and temperatures of 1250—2000°C, occasionally 2250°C (74). The pressure vessel may have a bore diameter from 27 to 1524 mm (75) and is nearly always provided with threaded closures sealed with O-rings made of elastomer provided the temperature is low enough. 

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