Temperature recovery

We noted that the presence of hydrogen causes an, at least apparent, lower recovery temperature. It has also been observed that the presence of hydrogen causes a lower damage production rate (e.g., for the (V O)-center) for irradiations at room temperature, which indicates either a passivation of the defects by the hydrogen or competition for the mobile irradiation defects (e.g., the vacancy) by hydrogen-related defects. Judging... 

At high Re and Ma in the free-molecule regime, transfer rates for spheres have been calculated by Sauer (S4). These results, together with others for cylinders and plates, have been summarized by Schaaf and Chambre (Sll). The particles are subject to aerodynamic heating and the heat transfer coefficients are based upon the difference between the particle surface temperature and the recovery temperature (see standard aerodynamics texts). In the transitional region, the semiempirical result of Kavanau (K2),... 

Beckwith, I.E. and Gallagher J.J., Local Heat Transfer and Recovery Temperatures on a Yawed Cylinder at a Mach Number of 4.15 and High Reynolds Numbers , NASA TR-R-104, 1962. 

Here Taw> commonly called the adiabatic wall temperature or the recovery temperature, is the equilibrium temperature the surface would attain in the absence of any heat transfer to or from the surface and in the absence of radiation exchange between the surroundings and the surface. In general the adiabatic wall temperature is dependent on the fluid properties and the properties of the bounding wall. Generally, the adiabatic wall temperature is reported in terms of a dimensionless recovery factor r defined as... 

The value of r for gases normally lies between 0.8 and 1.0. It can be seen that for low-velocity flows the recovery temperature is equal to the free-stream temperature Tf. In this case,... 

The adiabatic wall temperature (recovery temperature) is given by... 

Ideal Gases at High Temperatures. The speeds of modem military aircraft, missiles, or reentry bodies are so high that the resulting recovery temperatures are several times to orders of... 

Nonuniform Surface Temperature. Nonuniform surface temperatures affect the convective heat transfer in a turbulent boundary layer similarly as in a laminar case except that the turbulent boundary layer responds in shorter downstream distances The heat transfer to surfaces with arbitrary temperature variations is obtained by superposition of solutions for convective heating to a uniform-temperature surface preceded by a surface at the recovery temperature of the fluid (Eq. 6.65). For the superposition to be valid, it is necessary that the energy equation be linear in T or i, which imposes restrictions on the types of fluid property variations that are permitted. In the turbulent boundary layer, it is generally required that the fluid properties remain constant however, under the assumption that boundary layer velocity distributions are expressible in terms of the local stream function rather than y for ideal gases, the energy equation is also linear in T [%]. 

Derham [38] has investigated many of the factors affecting test performance. Test piece history is important, especially with filled rubbers, since prestressing reduces the creep rate and there need not be a full recovery. Temperature control is also essential, since thermal cycling can significantly increase creep. 

As compared to metallic compounds used as shape memory materials, shape memory polymers have low density, high shape recoverability, easy processability, and low cost. Since the discovery by Mitsubishi in 1988, polyurethane SMPs have attracted a great deal of attention due to their unique properties, such as a wide range of shape recovery temperatures (— 30°C to 70°C) and excellent biocompatibility, besides the usual advantages of plastics. A series of shape memory polyurethanes (SPMUs), prepared from polycaprolactone diols (PCL), 1,4-butanediol (BDO) (chain extender), and 4,4 -diphenylmethane diisocyanate (MDI) or toluene diisocyanate (TDI) have recently been introduced [200—202]. 

SMPUs are basically block copolymers of soft segments, which are polyols, and hard segments built from diisocyantes and chain extenders (see Figure 4.31). Depending on the types and compositions of soft and hard segments, and preparation procedures, the structure-property relationships of SMPUs are extremely diverse and easily controlled, and hence shape recovery temperature can be set at any... 

To prevent this problem, all control sensors should be close to the level of the tops of the loads. Input control sensors should be within about one-fourth of their zone length from the load entry end of their zones. Over-temperature sensors should be 5 to 10% of their zone length from the exit end of their zones, and set at the maximum furnace temperature allowed. With such a sensor-positioning arrangement, a modem quick-recovery temperature control has a chance to avoid a heat delay following a mill delay. 

It is interesting to note that, while the CP content has a significant effect on the stress recovery, its effect on shape recovery is comparatively small. The reason is that shape recovery is basically a global or macroscopic behavior, while stress recovery is dependent more on the microstmeture and internal parameters. For instance, the recovery stress depends on the stiffness at the recovery temperature, while the recovery strain does not. Therefore, the shape recovery ratio and the stress recovery ratio usually do not have the same value and the stress recovery ratio is usually lower than the strain recovery ratio. In this sense, the stress recovery ratio is a more rigorous indicator of shape memory functionality. 

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