Authors:N. Ben Ezzine, M. Barhoumi, K. Mejbri, and A. Bellagi
Summary This paper deals with the modeling, thermodynamic analysis and comparison of irreversibility in two configurations of the double generator absorption chiller. First a computer simulation model is developed for each configuration on the basis of mass and energy balances. Simulation results were then used to analyse the entropy generation and irreversibility (or exergy destruction) of each component. It is found that the parallel flow configuration is more powerful than the serie flow configuration. Exergy losses in the parallel flow configuration are lower than that of the serie flow. The results indicate that the absorber and the solution heat exchangers have the most potential to improve the chiller energy efficiency. Also they indicate that focusing on irreversibility is more direct way of analysing the potential for improving the efficiency of ammonia-water absorption chiller.
A new method is presented to analyze the irreversible melting kinetics of polymer crystals with a temperature modulated differential
scanning calorimetry (TMDSC). The method is based on an expression of the apparent heat capacity,
. The present paper experimentally examines the irreversible melting of nylon 6 crystals on heating. The real and imaginary
parts of the apparent heat capacity showed a strong dependence on frequency and heating rate during the melting process. The
dependence and the Cole-Cole plot could be fitted by the frequency response function of Debye's type with a characteristic
time depending on heating rate. The characteristic time represents the time required for the melting of small crystallites
which form the aggregates of polymer crystals. The heating rate dependence of the characteristic time differentiates the superheating
dependence of the melting rate. Taking account of the relatively insensitive nature of crystallization to temperature modulation,
it is argued that the ‘reversing’ heat flow extrapolated to ω → 0 is related to the endothermic heat flow of melting and the
corresponding ‘non-reversing’ heat flow represents the exothermic heat flow of re-crystallization and re-organization. The
extrapolated ‘reversing’ and ‘non-reversing’ heat flow indicates the melting and re-crystallization and/or re-organization
of nylon 6 crystals at much lower temperature than the melting peak seen in the total heat flow.
Reversible and irreversible crystallization and melting of high-density polyethylene at low temperature has been re-evaluated
and is discussed in terms of the concept of the specific reversibility of a crystal. The concept of the specific reversibility
links reversible and irreversible melting of a specific crystal such that reversible melting occurs only at slightly lower
temperature than irreversible melting. In this study evidence for irreversible crystallization at low temperature in high-density
polyethylene is provided, non-avoidable by primary crystallization and extended annealing at high temperature. The simultaneously
observed reversible crystallization and melting at low temperature can be attributed to lateral-crystal-surface activity in
addition to the well-established reversible fold-surface melting, dominant at high temperature, and evidenced by small-angle
X-ray data available in the literature.
New approaches to the analysis of differential scanning calorimetry (DSC) data relating to proteins undergoing irreversible
thermal denaturation have been demonstrated. The experimental approaches include obtaining a set of DSC curves at various
scanning rates and protein concentrations, and also reheating experiments. The mathematical methods of analysis include construction
of a linear anamorphosis and simultaneous fitting of a theoretical expression for the dependence of the excess heat capacity
on temperature to a set of experimental DSC curves. Different kinetic models are discussed: the one-step irreversible model,
the model including two consecutive irreversible steps, the Lumry and Eyring model with a fast equilibrating first step, and
the whole kinetic Lumry and Eyring model.
Authors:G. D. Manetto, C. La Rosa, D. M. Grasso, and D. Milardi
Summary We assessed the applicability of the extrapolation procedure at infinite scanning rate to differential scanning calorimetry (DSC) data related to irreversible protein unfolding. To this aim, an array of DSC curves have been simulated on the basis of the Lumry-Eyring model N↔U→F. The results obtained confirmed that when the apparent equilibrium constant Kapp (T=T1/2) is lower than 3, the application of the extrapolation procedure provides accurate thermodynamic parameters. Although this procedure applies only to monomeric proteins for which the Lumry-Eyring model is a reasonable approximation, it will hopefully contribute to increase the potential of DSC in obtaining reliable thermodynamic information regarding the folding/unfolding equilibrium.
Calorimetric measurements were carried out on the electrorefining of copper using different current densities with a Calvet
type microcalorimeter at room temperature. The ratio (R) of the measured heat (Qm orWm) to the input electric energy (Qin orWin) and the excess heat (Qex orWex), i.e. the difference betweenQm (orWm) andQin (orWin) during the electrorefining process were discussed in terms of general thermodynamics. It was found thatR andQex were related to the current density employed in the experiment and varied as a logarithmic function. The results obtained
here indicate that the heat generation under different conditions, such as different currents or voltages, may be caused partially
by the irreversibility of the process or by some unknown processes.
Authors:Z. Zhang, M. Zhong, J. Liu, F. Liu, Z. Wang, F. Zhong, and F. Wu
In this work some calorimetric measurements were also carried out on the electrorefining silver by using different current densities with a Calvet type microcalorimeter at room temperature. The ratio (R) of the measured heat (
ex for silver were related with the current density or cell voltage employed in the experiment. The results obtained here also indicate that the heat generation under different conditions, such as different currents or voltages may be caused partially by the irreversibility of the process or by some unknown processes.
Authors:Maria Kulawska, Henryk Moroz, and Aleksandra Kasprzyk
rates. A maximum limiting value of the flow was thus established, above which further increase in the flow rate has no effect. Under these conditions the reaction 2 can be assumed as irreversible.
Conversion of phthalic anhydride was calculated