Glassy materials are not thermodynamically stable and during storage below the glass transition temperature (Tg), they are subjected to the time dependent changes towards the equilibrium. These changes are known as physical ageing, which is the basic feature of glassy materials below Tg. During ageing process, physical properties such as ENTHALPY and volume decrease and these changes are accompanied by important changes in mechanical properties such as change to modulus, compliance and mechanical relaxation, which are of great technological importance. The aim of this study is to investigate the occurrence of the mechanical relaxation in the glassy gelatin and compare it to the ENTHALPY relaxation phenomenon and try to correlate the rate of mechanical relaxation to the rate of ENTHALPY relaxation, which is the more reliable and frequent way for studying physical ageing. The extent of ENTHALPY relaxation of gelatin films with different water contents of 8%, 12 and 17%, measured by differential scanning calorimetry (DSC), was found to increase with increasing the ageing time. The mechanical behaviour of the gelatin films was measured, using dynamic mechanical thermal analysis (DMTA). The mechanical behaviour of gelatin showed time and frequency-dependent changes. Storage modulus increased during isothermal ageing and gelatin became harder and stiffer at higher frequency than that at low frequency. In order to assess the rate of mechanical relaxation, the classical time-ageing time superposition was applied to the results. The rate and extent of mechanical ageing were increased at higher water contents. A good agreement was found between the rate of the ENTHALPY relaxation and the changes to the mechanical properties at different water contents, suggesting that DSC measurements of ENTHALPY relaxation, which can be more easily implemented, can be used as indicator of mechanical changes.  

In view to better understand the interactions of aminoacids and peptides with metallic cations, in the isolated state, the model system glycylglycine–Zn2+has been theoretically studied.Structures and energetic of complexes between glycylglycine dipeptide and zinc cation were investigated applying density functional theory (DFT). Zn2+cation was allowed to interact with different sites of glycylglycine and six stable isomers were obtained. Calculation for six different glycylglycine-Zn2+isomers were performed at BLYP and B3LYP level of theory using 6-31G* and 6-31G** basis sets. Relative energy calculations at different levels indicated that the most stable complex holds the structure, in which zinc cations are bound to the oxygen sites of carbonyl groups and the dipeptide of glycylglycine which acts as a bidentate ligand that has a structure of six-membered ring. Vibration frequency of most stable isomer is calculated by BLYP level and ENTHALPY, entropy and Gibbs energy of reaction was obtained.

Having calculated the exergy loss for all pieces of process equipment, it is possible to show the thermodynamic irreversibility, which makes certain guidelines for modifying the process industries and improving their performance. In this study the exergy loss is calculated using Omega Composite Curves, which is a novel graphical tool for calculating exergy loss in heat exchanger networks. Unlike other current tools, this graph is linear and calculation of exergy loss using the rectangular shaped area is so easy. The Omega-ENTHALPY diagram is used to calculate exergy loss for other unit operations. First, how to achieve this diagram is explained and then the diagrams are used for exergy loss calculation in two case studies. In the first study, each of a PRICO process (LNG production) equipment was investigated especially the multi-stream heat exchanger. The results showed that in the whole process 27. 66 MW of exergy is wasted. In the second study, the heat exchanger network of Shazand thermal power plant was investigated and exergy loss of this network was calculated by 8. 14 MW.

The use of phase change materials (PCMs) for the building sector is increasingly attracting attention from researchers and practitioners. Several research studies forwarded the possibility of incorporating microencapsulated PCM in plastering mortars for building facades, in pursuit of increased energy efficiency associated with the heat storage capacity of PCM. However, most of these studies are centred in the use of a single type of PCM, which is bound to be more adequate for a given season of the year (e.g. winter or summer) than for all the seasons.The study proposed in this work regards the evaluation of the possibility of using more than one kind of PCM, with distinct melting ranges, here termed as hybrid PCMs, in plastering mortars, to achieve adequately advantageous performance in all seasons of the year. To characterize the PCM, the specific ENTHALPY and phase change temperature should be adequately measured. The main purpose of this study was to show the conceptual feasibility of combining PCMs in mortars and to evaluate the behaviour of the resulting mortars with differential scanning calorimeter.The results showed that the behaviour of the mortar that contains more than one type of PCM can be predicted through the superposition of effects of the independent PCMs and no interaction occurs between them. The knowledge obtained from the experimental testing established bases for a framework of numerical simulation of real-scale applications, which can be used to ascertain the feasibility of the hybrid PCM concept for decreases in energy consumption of heating/cooling demands in the buildings.

In this paper, the absorbent carryover effect in a designed counter-flow ENTHALPY exchanger is investigated. In a built prototype of the liquid desiccant dehumidifier, air and the absorbent solution are in contact and flow through a packed multi-channel polymer tower in a counter-flow pattern. To avoid the absorbent carryover, the tower is equipped with an eliminator. Experimental measurements show that applying wick of hydrophilic type material to the channels' surfaces of the eliminator and the ENTHALPY exchanger, while increasing the rate of dehumidification, reduces the solution carryover effect, however, it does not eliminate it. To eliminate the effect, pumping the solution into the tower is interrupted periodically. It was found that by adjusting the pump switching frequency, the carryover effect can be eliminated. The best result is achieved when the period of switching on state is about a quarter of the off state one and the total period is about 25 seconds. Since the solution pump is turned off frequently, the cost of electrical power is reduced significantly. Also, the measurements show that while the dehumidification ability of the tower is improved in a steady state operation its regeneration performance is not.

Structural and thermochemical properties of boron-nitride analogues of organic azides and benzotrifuroxan, as novel high energetic nitrogen-rich precursors, were studied using M06-2X/6-311G (d, p) and B3LYP/6-311G (d, p) density functional methods. The influence of azido (N3) group was investigated for the stability, molecular volume, molecular surface area, crystal density, positive, negative and total average potentials, variances, average deviation and electrostatic balance parameter on the molecular surface. It was found that crystal density and ENTHALPY of sublimation of azidoborazines are distinctly augmented by increasing the numbers of azido substituents. Meanwhile, the stability of these compounds decreases significantly. The B-substituted azidoborazines are more stable than N-substituted ones. Crystal densities of B-substituted di- and triazidoborazines are also larger than N-substituted compounds. Since the condensed-phase enthalpies of formation of azidoborazines are more positive than nitro and nitraminoborazines, these compounds have greater detonation performance. Detonation pressure and velocity of both triazidotrinitroborazines and boron-nitride analogue of benzotrifuroxan are larger than 2, 4, 6-trinitrotoluene (TNT). Detonation performances of these compounds are also between cyanuric triazide and triazidotrinitrobenzene.