Uniform temperature distribution

The sterilizers or retorts used to process canned or prepackaged foods must be designed in such a way as to assure uniform temperature distribution throughout. Adequate venting permits complete air removal. The air vent is located at the opposite end from the steam inlet (24). The retorts may be horizontal or vertical in design. 

In this study, an integrated methanol reformer including an evaporator and a combustor was fabricated and tested. Previous tests of the reformer with a number of on-off cycles revealed that non-uniform temperature distribution caused hot spots within the combustion plate, resulting in cracking of the welded region of the reformer. Therefore, emphasis was made to achieve a uniform temperature distribution within the reformer. In addition, start-up characteristics of the complete reforming system were investigated. 

The crucible, which is usually platinum, is rotated to obtain a uniform temperature distribution within the melt-compound solution. 

Non-uniform temperature distribution in a reactor assumed model based on the Fourier heat conduction in an isotropic medium equality of temperatures of the medium and the surroundings assumed at the boundary critical values of Frank-Kamenetskii number given. 

Figure 2.22 [2.6] demonstrates the method of a cooling circuit with recirculated flow An injector pump operated with just evaporated LN2 aspirates the warmer N2 coming from the condenser and feeds the mixture back in the condenser. The desired condenser temperature can be controlled by a throttle valve. To achieve a uniform temperature distribution, the gas mixture is alternately fed to one or the other end of the condenser. No results of such a system are given. 

A thermal explosion is the third type of chemical explosion. In this case, no reaction front is present, and it is therefore called a homogenous explosion. Initially, the material has a uniform temperature distribution. If the temperature in the bulk material is sufficiently high so that the rate of heat generation from the reaction exceeds the heat removal, then self-heating begins. The bulk temperature will increase at an increasing rate, and local hot spots may develop as the thermal runaway proceeds. The runaway reaction can lead to overpressurization and possible explosive rupture of the vessel. 

The inner chamber of the oven has curved walls for smooth circulation of air the radiant heat from the sample injection port units and the detector oven is completely isolated. These factors combine to provide demonstrably uniform temperature distribution. (The temperature variance in a column coiled in a diameter of 20cm is less than 0.75°K at a column temperature of 250°C). 

In a similar method, Ramousse et al. [248] designed a technique wherein the sample material is placed between two copper plates that have thermocouples located at their centers. Copper plates were chosen due to the high thermal conductivity of copper and to ensure a uniform temperature distribution. Fluxmeters to measure the thermal flux between both plates were located beside each copper plate. At each end of fhe apparatus, end plates... 

All types of catalytic reactors with the catalyst in a fixed bed have some common drawbacks, which are characteristic of stationary beds (Mukhlyonov et al., 1979). First, only comparatively large-grain catalysts, not less that 4 mm in diameter, can be used in a filtering bed, since smaller particles cause increased pressure drop. Second, the area of the inner surface of large particles is utilized poorly and this results in a decrease in the utilization (capacity) of the catalyst. Moreover, the particles of a stationary bed tend to sinter and cake, which results in an increased pressure drop, uneven distribution of the gas, and lower catalyst activity. Finally, porous catalyst pellets exhibit low heat conductivity and as a result the rate of heat transfer from the bed to the heat exchanger surface is very low. Intensive heat removal and a uniform temperature distribution over the cross-section of a stationary bed cannot, therefore, be achieved. The poor conditions of heat transfer within... 

Norman113 gave a valuable discussion of the problems with curemeters, pointing out that there is no one level of cure which gives optimum values for all physical properties and no satisfactory procedure for dealing with a "marching modulus". He also listed problems such as non-uniform temperature distribution, possible slip of the test piece over rotor or cavity and porosity. 

Other experimental difficulties not directly related to the nature of high polymers are a non-uniform temperature distribution on the outer... 

This non-uniform temperature distribution is enhanced by the unreacted hydrogen undergoing the afterburning reaction. Comparing the two operating conditions,... 

If a hot steel ball were immersed in a cool pan of water, the lumped-heat-capacity method of analysis might be used if we could justify an assumption of uniform ball temperature during the cooling process. Clearly, the temperature distribution in the ball would depend on the thermal conductivity of the ball material and the heat-transfer conditions from the surface of the ball to the surrounding fluid, i.e., the surface-convection heat-transfer coefficient. We should obtain a reasonably uniform temperature distribution in the ball if the resistance to heat transfer by conduction were small compared with the convection resistance at the surface, so that the major temperature gradient would occur through the fluid layer at the surface. The lumped-heat-capacity analysis, then, is one which assumes that the internal resistance of the body is negligible in comparison with the external resistance. 

We have already noted that the lumped-capacity type of analysis assumes a uniform temperature distribution throughout the solid body and that the assumption is equivalent to saying that the surface-convection resistance is large compared with the internal-conduction resistance. Such an analysis may be expected to yield reasonable estimates when the following condition is met ... 

By comparison with a fixed-bed gas-liquid reaction, a three-phase fluidized-bed reactor offers the advantage of very high effective thermal conductivity and, therefore, a more uniform temperature distribution in the reactor. Van Driesen and Stewart139 have demonstrated this for large-scale catalytic desulfurization and hydrocracking of heavy petroleum fractions. 

Prior to each test, the reactor was preheated to a temperature of SOO°C and primary air was preheated to 350 - 400°C. In combustion, secondary air injection was started immediately after initiating friel feed to the reactor. Temperature equilibrium and uniform temperature distribution were achieved typically within IS min from start. Sampling was conducted only after reaching steady operating conditions. 

Tunnel kilns are usually heated with gas or liquid fuels, and in some instances by means of electrically heated metal or SiC or M0S12 elements. The firing schedule can be controlled directly by burners and draught, and by adjusting the car speed. More uniform temperature distribution over the cross-section-is attained in small tunnel kilns which find application in the firing of special ware however, kilns with large cross-section arc used in normal ceramic operation. The functioning of a tunnel kiln is shown in Fig. I86. 

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