Temperature spike

The use of integrated reactor and heat-transfer models is essential for scale-up. Figure 11.7 shows an early reactor design for the same chemistry that was developed without the use of integrated models. Other unoptimized designs with temperature spikes have also been reported [12,44]. Integrated models were used to... 

Concerning the reaction pathway, two routes have been proposed the sequence of total oxidation of methane, followed by reforming of the unconverted methane with CO2 and H2O (designated as indirect scheme), and the direct partial oxidation of methane to synthesis gas without the experience of CO2 and H2O as reaction intermediates. The results obtained by Schmidt and his co-workers [4, 5] indicate that the direct reaction scheme may be followed in a monolith reactor when an extremely short contact time is employed at temperatures in the neighborhood of 1000°C. However, the majority of previous studies over numerous types of catalysts show that the partial oxidation of methane follows the indirect reaction scheme, which is supported by the observation that a sharp temperature spike occurs near the entrance of the catalyst bed, and that essentially zero CO and H2 selectivity is obtained at low methane conversions (<25%) where oxygen is not fully consumed [2, 3]. A major problem encountered... 

In Figure 4.42, every trajectory that starts at one of the eight corners of the cube CC of (xa, xn, y) initial values ends up at the optimal stable middle steady state marked by when sufficient feedback K = 10 is used. Most trajectories in this example go through a relatively high temperature spike and xa = xb = 0 phase before reaching... 

Notice in Figure 4.45 that only the set of profiles that emanate from the initial value (xao, xbo, j/o) = (0.0, 0.8, 0.9) reaches the steady state without an explosion. Our other chosen initial value profiles result in explosions with temperature spikes of y around 5, 9, and 3 near 1, 20, and 100 time units, respectively. For all three initial value profiles note the oscillations with shrinking amplitudes around the steady-state values of xa, xb, and y after about 200 time units until convergence in Figure 4.45. On the other hand, the temperature profiles (except around the time of the explosions) settle down to near their steady-state value very smoothly after about 100 time units. This corroborates our 3D image in Figure 4.44 perfectly, in which the trajectory is depicted as oscillating around the steady-state coordinates on a near-level temperature surface. 

Decreases in recycle flow produce similar effects but in the reverse direction. The decrease in flow raises reactor temperatures, and a temperature wave starts to move down the reactor. Since the flowrate is lower, the temperature spike moves more slowly than when the recycle flowrate is increased. This explains the longer period of the cycles. These results demonstrate that the optimal design with the hot reaction is openloop unstable. 

Lattice energy. This energy is essentially the energy which is dissipated through displacements and related phenomena (temperature spikes, lattice defects, etc.) it always corresponds to a very small fraction of the dissipated energy, except for fast neutron and fission fragment irradiations. 

The lattice defects belong to the following four types (a) vacancies, (b) interstitial atoms, (c) replacements, and (d) impurity atoms. The first three types of defects have a common origin, namely, collisions. These collisions have been shown to produce both displacements and temperature spikes. An atom which has received sufficient energy on collision, may leave its normal position in the lattice in this way a vacancy is created. 

We have seen that the temperature spike involves a relatively large number of atoms, which, after having been superheated, undergoes a subsequent rapid cooling. A certain number of atoms are thus quenched in metastable positions, increasing the local density of defects. 

For systems where the adiabatic temperature rise is low (as is the case considered here) the thermal spikes introduced by the flow reversals do not dramatically affect the reactor performance. However, the concentration of feed streams to such treatment reactors can fluctuate to a high level which can result in a high temperature thermal spike developing within the reactor. Pinjala, Chen, and Luss characterized this dynamic response and showed that reactor runaway could occur within the single-pass reactor. Their work is directly applicable to the RFR as the forced oscillations in the gas flow direction can result in a thermal spike formation at the beginning of each half cycle. Thus, there is a need to understand thermal stability within these systems. Further complicating the matter is the fact that the temperature spikes are very narrow and are thus difficult to detect using thermocouples or other sensors imbedded within the reactor. 

Thermal considerations are paramount for ATFs. A great deal of friction is produced, which generates heat and high-temperature spikes at the torque converter this will damage the fluid. ATF is designed to operate at temperatures around 95°C. At the torque converter, under extreme conditions, temperatures can reach 120°C. A transmission fluid should be designed to handle these temperature extremes. The transmission fluid will quickly break down above 120°C. Temperature spikes in the torque converter have been known to go above 120°C. 

Figure 15-9. Oscilloscopic trace of temperature measurement by a dynamic thermocouple. Constantan against steel, 17.8 cm/s. (a) Starting temperature before rubbing, (b) Predominant temperature during rubbing, (c) Temperature spikes. Data by M. J. Furey [16].

Odour Chemical Sensing Temperature Spike-Train... 

Temperature control requiring additional heat input is normally controlled by regulating the flow rate of steam to the process heat exchanger. A desuperheater should be installed to prevent steam quality variation from causing heat exchanger fouling due to temperature spikes at constant flow. 

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