Enthalpy recovery

Figure 1-14 shows a simplified layout for an SOFC-based APU. The air for reformer operation and cathode requirements is compressed in a single compressor and then split between the unit operations. The external water supply shown in figure 1-14 will most likely not be needed the anode recycle stream provides water. Unreacted anode tail gas is recuperated in a tail gas burner. Additional energy is available in a SOFC system from enthalpy recovery from tail gas effluent streams that are typically 400-600°C. Current thinking is that reformers for transportation fuel based SOFC APUs will be of the exothermic type (i.e. partial oxidation or autothermal reforming), as no viable steam reformers are available for such fuels. 

When the compression process in the diffuser involves heat loss, the total enthalpy decreases from hoa to ho2- The enthalpy recovery factor, r, j, is defined as... 

Glass transitions, both in frozen systems and in freeze-dried solids, can be difficult to detect. This may be caused by the small heat capacity change associated with the glass transition, a broad glass transition region, or both. Interpretation is made more uncertain by baseline drift or other noise. In addition, other thermal events at temperatures close to the glass transition, such as enthalpy recovery or crystallization, may disguise the heat capacity... 

As indicated earlier, the enthalpy balance method is a valuable tool for making an account of the pathways operating during cellular metabolism (reviewed by Kemp, 1993). In this way, it was shown by Eftimiadi and Rialdi (1982) that 36% of the heat dissipation by human neutrophils was due to the pentose phosphate pathway and the remainder (64%) to glycolysis, resulting in lactate production. The enthalpy recovery of 1.0 indicated that there was no measurable respiration, which is consistent with the almost complete absence of mitochondria from these cells. 

PM A). Neutrophils stimulated in this way produced a 40-minute heat burst of 23.5 nW per cell, approximately fourfold more than resting cells over a similar period. The rate of glycolysis, as measured by lactate evolution, was not altered substantially but the flux through the pentose phosphate pathway was increased by nearly 500% to give the necessary NADPH. All of the heat dissipated was accounted for by measurements of oxygen consumption, lactate production and C02 evolution in the glucose carbon 1/carbon 6 ratio. Enthalpy recovery was, therefore, 1.0 which indicated that no other pathway was induced by neutrophil activation—an enhanced flux in the pentose phosphate pathway to produce NADPH was responsible solely for the observed metabolic burst. 

The same techniques cannot be applied to the case of sPS/aPS blends, as the two components have similar Tg values (less than 10 °C difference). A higher resolution of close Tg values can be derived from the isothermal heat capacity curves, measured in the vicinity of Tg by modulated DSC [20]. Furthermore, sPS and aPS, when annealed separately below Tg, exhibit in both DSC and modulated DSC distinct endothermic transitions owing to the enthalpy recovery [20,21]. Both methods, when applied to the sPS/aPS blends, give a single temperature for all compositions in agreement with the presence of a miscibility between the components. 

Figure 6. Influence of cooling rate on enthalpy recovery peak in AZA9M4200. From top to bottom cooling rates are . 62 2.5 5 10 20 K/min quenched.

Although, ethanol fermentation (equation 1) is known to have high conversion efficiency (97% estimated from the ideal enthalpy recovery), the real efficiency falls to around 50% if we consider the distillation energy (Table 1). This is the non improvable efficiency. 

While the agreement between the experimental data and the theoretical calculation is very satisfying, other types of volume and enthalpy recovery experiments show that the single-ordering parameter model is not sufficiently flexible to rationalize many of the important aspects of the glass transition phenomenon. As a result, more complex models based on multiple ordering parameters are now under development.8... 

Differential scanning calorimetry was used to measure both the extent of cure as well as the progress of enthalpy recovery in the neat epoxy resin. A Perkin Elmer DSC-2 differential scanning calorimeter equipped with a scannlng-auto-zero unit for baseline optimization was utilized to measure the heat capacity of the... 

Zelko R, Siivegh K (2004) Comparison of the enthalpy recovery and free volume of polyvinylpyrrolidone during anomalous glassy to rubbery transition. J Pharm Sci 21 519-523. 

Kovacs AJ, Aklonis JJ, Hutchinson JM, Ramos AA (1979) Isobaric volume and enthalpy recovery of glasses II. A transparent multiparameter theory. J Polym Sci Polym Phys Ed 17 1097-1162... 

Kovacs, A. J., Hutchinson, J. M., Aklonis, J. J., and Ramos, A. R., Isobaric volume and enthalpy recovery of glasses 2. Transparent multi-parameter theory, J. Polym. Sci. Polym. Phys. Ed., 17,1097-1162(1979). 

FIGURE 5.16 Enthalpy recovery results for o-terphenyl aged at Tj — 11°C in (a) bulk state and (b) confined in an 11.6-nm pore diameter controlled pore glass material showing much smaller buildup of enthalpy overshoot upon aging of the confined material. Originally, similar data were interpreted [McKenna et al. [1992] to imply reduced aging in confined systems. (Data from Simon et al. [2002].)... 

FIGURE5.17 Enthalpy recovery as 7) — rTest temperatures are at Tg — 8 C. Importantly, Tf — Ta does not go to zero for the confined materials. See the text. (After Simon et al. [2002].)... 

McKenna, G. B., Jackson, C. L., O Reilly, J. M., and Sedita, J. S., Kinetics of enthalpy recovery near the glass transition of small molecule glasses at nanometer size scales, Polym. Prepr, 33(1), 118-119(1992). 

Simon, S. L., Park, J. Y., and McKenna, G. B., Enthalpy recovery of a glass-forming hquid constrained in a nanoporons matrix negative pressure effects, Eur. Phys. J. E, 8, 209-216 (2002). 

Figure 4 shows the temperature dependence of the shift factors resulting from the reduction of the equilibrium creep data and the isothermal enthalpy recovery data shown in Figures 1, 2, and 3. The fit of equations 5 and 6 are also shown. Tj is taken as 207.5 C. The parameters used in the fits are, for equation 5 D/R = 1920 and T = 162 C and for equation 6 D/Ra =780, b/a = -1/560K and T2 = 151 C. Equation 6 seems to be better able to describe the temperature dependence in the glass due to the additional parameter. For modeling entMpy recovery, however, the results are expected to be identical with either equaticxi since the temperature range of interest is... 

Figure 5 Experimental (data points) and calmdated (lines) enthalpy recovery for heating at lO CVnun after cooling at coding rates of 0.1 C7nun and 10 C7niin. Temperature gradients were not incmporated into the calculaticxis.

---