Transient temperature response

Fig. 19. Transient temperature response to step-input change of T0 from 573 to 593 K and x 0 from 0.06 to 0.07, type II conditions.

Figure 9.9 Transient temperature response at the specimen back face after laser flash absorption at the the front face.

Fig. 3 Transient temperature response for CH30H-NaX, pressure step 48-80 Pa (step A, run 13) showing conformity between experimentally observed temperature and theoretical curve, calculated from diffusion model with Do = 2.6 x 10 m s h = 2.3 Wm" From Grenier et al. [27]...

Fig. 2 a System for surface temperature infrared (STIR) measurements, b Transient temperature response upon methanol sorption into Na-X zeolite as a function of the square root of time [17]... 

Functions that exhibit time delay play an important role in process modeling and control. Time delays commonly occur as a result of the transport time required for a fluid to flow through piping. Consider the stirred-tank heating system example presented in Chapter 2. Suppose one thermocouple is located at the outflow point of the stirred tank, and a second thermocouple is immersed in the fluid a short distance (L= 10 m) downstream. The heating system is off initially, and at time zero it is turned on. If there is no fluid mixing in the pipe (the fluid is in plug flow) and if no heat losses occur from the pipe, the shapes of the two temperature responses should be identical. However, the second sensor response will be translated in time that is, it will exhibit a time delay. If the fluid velocity is 1 m/s, the time delay ( o = L/v) is 10 s. If we denote /( ) as the transient temperature response at the first sensor and fd(t) as the temperature response at the second sensor. Fig. 3.3 shows how they are related. The function/ = 0 for t < to. Therefore,/ and/are related by... 

The thermal transient studied was a gas temperature increase from 900 K to 1150 K over a period of 1 second. A plot of the transient temperature response of the Inner and outer walls is provided in Figure 9-52. As shown in the plot, there is a very large time lag in temperature response of the outer wall. It takes approximately 5000 seconds ( 1.5 hr) for the outer wall to come within 2 degrees of its final steady state temperature. The inner wall responds more rapidly, coming to within 2 degrees of its final steady state value in 415 seconds. 

In [119], the hydrogen adsorption and desorption reactions in thin palladium electrodes were studied using the potential step method in order to analyze the mechanism of phase transformation. Transient current responses were recorded at the onset of the potential step for 47 pm thick Pd electrodes in 1 mol dm H2SO4 at ambient temperature. A model based on a moving boundary mechanism was proposed to account for the experimental i-t curves. It was found that the hydrogen adsorption reaction shows interfacial kinetic limitations and only numerical solutions can be obtained. Such kinetic limitations were not found for the desorption reaction and a semianalytical solution that satisfactorily fits the experimental data was proposed. 

For linear thermorheologically simple materials a single temperature-dependent shift factor, aT T), can be used to predict the transient thermal response [20]. The mechanical response is history dependent and involves the use of reduced times, ( ) and (t), which can be found from the shift factor as... 

HEAT EXCHANGER TEMPERATURE RESPONSE FOR DUTY-CYCLE TRANSIENTS IN THE NGNP/HTE... 

Heat exchanger temperature response for duty-cycle transients in the NGNP/HTE... 

Vilim, R.B. (2008), Heat Exchanger Temperature Response for Duty-Cycle Transients in the NGNP/HTE, ANL-GenIV-114, September. 

Fig. 5.2 Comparison of creep behavior and time-dependent change in fiber and matrix stress predicted using a 1-D concentric cylinder model (ROM model) (solid lines) and a 2-D finite element analysis (dashed lines). In both approaches it was assumed that a unidirectional creep specimen was instantaneously loaded parallel to the fibers to a constant creep stress. The analyses, which assumed a creep temperature of 1200°C, were conducted assuming 40 vol.% SCS-6 SiC fibers in a hot-pressed SijN4 matrix. The constituents were assumed to undergo steady-state creep only, with perfect interfacial bonding. For the FEM analysis, Poisson s ratio was 0.17 for the fibers and 0.27 for the matrix, (a) Total composite strain (axial), (b) composite creep rate, and (c) transient redistribution in axial stress in the fibers and matrix (the initial loading transient has been ignored). Although the fibers and matrix were assumed to exhibit only steady-state creep behavior, the transient redistribution in stress gives rise to the transient creep response shown in parts (a) and (b). After Wu et al 1...

The effects of space velocity, partial pressure, temperature, and catalyst crystallite size on the coke formation and the resulting deactivation in both MTO and the coke forming reactions were easily obtained in the TEOM experiments (39,40,86). Furthermore, the mass desorbed from the catalysts was determined by the transient mass response this information is important for the design of the stripping process in such applications as FCC and MTO. 

In this technique, the transient heat flux to a relatively large uncooled body is determined indirectly. The temperature profiles in the target are measured by an array of imbedded thermocouples, usually at or near the impingement surface. The flux is then calculated from the measured temperature responses, using inverse conduction heat transfer computational techniques... 

Evaluation of the data requires time constants for both the heat transfer and diffusion under nonisothermal conditions. It turns out that the initial part of the response curve is mainly determined by the mass transport (transport diffusion), whereas the descending part is mainly governed by the heat transfer. The STIR technique avoids intrusion by the evolution of heat, in that it measures the transient temperature, and has a rapid response (time constant about 10 s). Results obtained for the diffusion of CH3OH into Na-X were essentially consistent with those derived from the ZLC and PFG NMR... 

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