Axial temperature distribution

In this paper, TiCU was oxidized in the flow reactor at various temperature and gas flow rate. The wall scales were characterized by scan electron microscopy and X-ray diffraction. The effects of reactor wall surface state, radial growth of scale layer and reactor axial temperature distribution on scaling formation were discussed. At the same time, the mechanism of scaling on the reactor wall was explored furthermore. 

Specific Remarks. The established dependence of the microkinetics on the oxidation state of the catalyst make clear that a) results of kinetic investigations at lower temperatures are different in respect to the mechanistic scheme from those obtained at higher temperatures, b) in a distributed catalytic system in the steady state a distribution of the catalytic steps is possible as a direct consequence of the ambient gas concentration profile and the axial temperature distribution in an extreme situation it is conceivable that at the reactor inlet, another mechanism dominates as at the reactor exit. These two facts can perhaps explain some contradictory results about the same reaction scheme which have been reported in the past by different authors. As stated recently by Boreskov (19) in a review paper, this conclusion holds true for the most catalytic systems under the technical operating conditions. 

Experimental results (Li et a/., 1991) indicate that the axial temperature distribution is highly dependent on the secondary-to-total air ratio. When this ratio is less than about 0.3, the axial temperature profile is essentially uniform except for the region approaching the exit of the combustor, as shown in Fig. 17. When this ratio exceeds about 0.4, however, the temperature in the middle of the combustor becomes lower than those at the two ends. On the other hand, experimental results also indicate that increasing the secondary air ratio is favorable for supressing NO emission. If this ratio is greater than 0.5, NO emission can be controlled to less than 65 ppm. Therefore, it is necessary to locate the secondary air inlet properly and choose the secondary air ratio in order to optimize between efficient combustion and low NO emission. 

Certain circumferential temperature differences exist on FFB regenerator from the bottom to the top. The temperature of two catalyst streams entering at the diagonal entrances may differ by as much as 200°C, resulting in a 20 to 50°C measured circumferential bed temperature difference at different elevations. The two curves in Fig. 9 show the axial temperature distribution on two sides of a commercial FFB unit with d, 5 m from 3 m upward from the bottom, indicating a circumferential temperature difference of 20°C, which is evidence of reduced mixing. 

Figure 3 shows the axial temperature distributions of fluids under the normal operating condition. Temperature distribution in the ceramic block was analysed with ABAQUS Vcr.6.4. Figure 4 shows a computational grid of a 1/4 sector of the upper half part of the block. 

In the case of heat transfer analysis, axial temperature distribution, shown in Figure 3 are specified for the surfaces of both He and sulfuric flow cannels, considering heat transfer coefficients. And outer surface of block is modeled as adiabatic condition. Figures 5 and 6 show the temperature and the stress distributions in the block, respectively. The stress shown in Figure 6 is a coupled stress with thermal stress and static stress caused by the operating pressure difference between He and sulfuric acid. Analytical conditions are as follows ... 

A constant property fluid having velocity V and upstream temperature To flows steadily through an infinitely long tube of cross sectional area A and periphery P. The upstream half of the tube is insulated, while the downstream half either transfers heat with a coefficient h to an ambient at temperature T,x [Fig. 2.38(a)] or is subjected to a peripheral heat flux q" [Fig. 2.38(b)]. The wall thickness of the tube is negligible. Based on a radially lumped analysis, we wish to know the axial temperature distribution in the fluid. 

The axial temperature rise in the coolant, Eq. (2.183), the radial temperature drop and the axial temperature distribution in the fuel, the gap, the clad, and the coolant, Eq. (2.188), are sketched in Fig. 2.52. Some typical values encountered in practice for the radial temperature drop are ATpuei 1500 °C, AToap 150 — 300 °C, ATaad 50 °C, and ATbooiam 5 °C (for water). Also, some values for the geometry, thermal conductivity and heat transfer coefficient are ... 

Consider an infinitely long pipe with diameter D = 0.2 m. The upstream half of the pipe is insulated and the downstream half is subjected to a uniform heat flux q" = 10 kW/m2. A liquid metal (or = 5 x 10 5 m2/s) with bulk velocity V — 0.01 m/s flows slowly through the pipe. Including the effect of axial conduction, determine the axial temperature distribution within the liquid metal. 

The rate equations, which were formulated on the basis of the reaction model taking account of these inhibition and acceleration effects and the axial temperature distribution of the reactor in each run, were solved. 

The axial temperature distribution of the reactor was measured by inserting a 70cm long Pt-Pt Rh thermocouple into the reactor. The thermocouple was moved at 5cm intervals along the axis of the reactor to obtain the temperature profile. The cross-sectional area of the reactor used in the present study was so small that the temperature measurements thus obtained were assumed to give the gas temperatures within the reactor. 

The UIS is a cylindrical structure located above the core It supports the control rod guide tubes and instrument wells in the event of an earthquake The cylindrical drum is made of 316FR with no vertical weld seam, to allow it to withstand the thermal stress due to the axial temperature distribution near the liquid surface, which changes as the liquid level changes The surface of the UIS near the core outlet is covered with Alloy 718 as a measure against thermal striping, similar to the design of the prototype reactor "Monju"... 

In the middle channel, the axial temperature distribution is somewhat more complicated due to the recirculating flow in the core. The maximum temperature is seen about half way up the channel with much cooler temperatures above this location. This is due to a combination of two phenomena. First, high temperatures occur half way up the channel because flow stagnated in the recirculating pattern is heated to higher temperatures. Secondly, lower temperatures occur at the top of the core due to cooler vapor in the upper plenum flowing into the core. 

In the upper plenum, the radial temperature distribution is similar to that in the core with hotter vapor rising in the center channel and cooler fluid descending at the plenum periphery. The axial temperature distribution in the upper plenum is reversed to that in the core. As the fluid rises in the center channel, the vapor decreases in temperature as energy is transferred to the water cooled guide tube structures. The vapor temperature continues to decrease as it turns and descends down the periphery of the plenum. 

Once the boundary conditions are fixed (i.e., local decay heat generation rate, inlet coolant temperature, channel coolant flow rate, plenum pressure, assembly pressure drop and inlet air void fraction), FLOWTRAN-TF iterates between cells/nodes to obtain an axial temperature distribution for the fuel assembly subchannel surfaces as a function of time. In the calculation for power limits, the assembly power is progressively increased in increments until one of the subchannel surface nodes equals or exceeds the ECS T/H criterion (i. e., the fuel surface temperature exceeds the coolant saturation/boiling temperature for the static pressure conditions at that axial location (T... 

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