Heat transport delayed

Delayed Heat Transport Through the Monolayer Film... 

The term "lag" refers to the delay in transporting heat from one part of the extruder to another. For example, "Lag 11" refers to the delay in heat conduction from the "OPl" heater to the first measurement, node number 5 ("Tn5"), in the model. Similarly, "Lag 12" refers to the delay in heat conduction from the "OPl" heater to the second measurement, node number 55 ("Tn55"), in the model. 

To explain the imbalance, O Nions and Oxburgh (1983) and Oxburgh and O Nions (1987) proposed that a barrier, which is suggested to exist between the upper and the lower mantle from seismic observation, has trapped helium in the lower mantle and retarded the heat transport from the lower mantle to the upper mantle. O Nions et al. (1983) suggested, from a semiquantitative discussion, that delayed heat transfer from the lower mantle to the upper mantle with a time constant of about 2Ga would enhance the present heat flow by a factor of two. McKenzie and Richter (1981) made numerical calculation on a two-layered mantle convection and showed that heat transfer from the lower mantle to the upper mantle is considerably retarded to give rise to an enhancement of the present surface heat flow up to a factor of two. If the thermal barrier not only retards the heat transfer and hence enhances the present surface heat flow but also essentially prevents the 4He flux from the lower to the upper mantle, this would qualitatively explain the imbalance. If this indeed were the case, we would expect a large amount of 4He accumulation in the lower mantle. However, it is difficult to conclude such a large accumulation of 4He in the lower mantle from the currently available scarce noble gas data derived from mantle-derived materials. 

The ignition time for each test, in which a constant heat flux was impinging on the sample, was obtained by examining the second derivate of the mass loss data or the first derivative of the HRR data. Both methods yield similar results after the time delay for transporting the hot gas to the HRR analyzer in the hood is accounted for. A summary of the ignition time for all the tests conducted is... 

In thermally non-homogeneous supercritical fluids, very intense convective motion can occur [Ij. Moreovei thermal transport measurements report a very fast heat transport although the heat diffusivity is extremely small. In 1985, experiments were performed in a sounding rocket in which the bulk temperature followed the wall temperature with a very short time delay [11]. This implies that instead of a critical slowing down of heat transport, an adiabatic critical speeding up was observed, although this was not interpreted as such at that time. In 1990 the thermo-compressive nature of this phenomenon was explained in a pure thermodynamic approach in which the phenomenon has been called adiabatic effect [12]. Based on a semi-hydrodynamic method [13] and numerically solved Navier-Stokes equations for a Van der Waals fluid [14], the speeding effect is called the piston effecf. The piston effect can be observed in the very close vicinity of the critical point and has some remarkable properties [1, 15] ... 

Insofar as diffusion is concerned, stirring can accelerate the relaxation processes. But even in the case of an ideally rapid mixing of the reagents, heat transport is necessarily hindered and delayed by the vessel walls or by the insulation of the thermometer. Moreover, the very act of stirring generates additional heat (and entropy), thus perhaps distorting the measurement. 

The peak rate of heat rejection demanded may be reduced for the heat transport systems directly associated with the ultimate heat sink by storing the heat and by delaying the time when use of the ultimate heat sink is necessary. 

Attaching the sensor in this way would require a known relationship between the temperature of the gas and the temperature of the outer pipe. The sensors need to see the temperature of the gas or an equivalent temperature from the pipe surface to make an accurate reading. The reason for the hot leg piping concept is to limit the amount of heat transferred between the inner and outer pipe. This would then reduce the amount of heat transported to the sensor causing the sensor temperature to lag behind the gas temperature significantly, see Section 9.4.6.3.5.1 for a quantification of the sensor delay time. 

A similar problem affects the heat exchange jacket and may be reduced by using a coil, in which a plug flow can be assumed for the heat exchange fluid. When the reaction temperature is controlled by an external heat exchanger or condenser [17], the recirculation of the fluids introduces a transport delay that may strongly affect the control action. 

Curve No. 1 shows freezing of the pure component. On the curve, only one delay can be seen, which is caused by the evolution of the crystallization heat of the component. At melting temperature, this one-component system has no degree of freedom, since two phases coexist the solid compound and its melt k= l,/= 2, v = 0). The temperature of the system therefore stays constant until its whole solidification. In practice we can, however, observe at the end of the delay a temperature decrease caused by the transport of bigger heat amounts to the surroundings, than it could be evolved at crystallization of the compound. 

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