The biaxial mechanics of thermally denaturing skin - Part I: Experiments

The mechanics of collageneous soft tissues, such as skin, are sensitive to heat. Thus, quantifying and modeling thermo-mechanical coupling of skin is critical to our understanding of skin's physiology, pathophysiology, as well as its treatment. However, key gaps persist in our knowledge about skin's coupled thermo-mechanics. Among them, we haven't quantified the role of skin's microstructural organization in its response to superphysiological loading. To fill this gap, we conducted a comprehensive set of experiments in which we combined biaxial mechanical testing with histology and two-photon imaging under liquid heat treatment. Among other observations, we found that unconstrained skin, when exposed to high temperatures, shrinks anisotropically with the principle direction of shrinkage being aligned with collagen's principle orientation. Additionally, we found that when skin is isometrically constrained, it produces significant forces during denaturing that are also anisotropic. Finally, we found that denaturation significantly alters the mechanical behavior of skin. For short exposure times, this alteration is reflected in a reduction of stiffness at high strains. At long exposure times, the tissue softened to a point where it became untestable. We supplemented our findings with confirmation of collagen denaturation in skin via loss of birefringence and second harmonic generation. Finally, we captured all time-, temperature-, and direction-dependent experimental findings in a hypothetical model. Thus, this work fills a fundamental gap in our current understanding of skin thermo-mechanics and will support future developments in thermal injury prevention, thermal injury management, and thermal therapeutics of skin.

Physicochemical Properties of the System N,N-Dimethyl-dipropylene-diamino-triacetonediamine (EvA34), Water, and Carbon Dioxide for Reactive Absorption

Aqueous solutions of N,N-dimethyl-dipropylene-diamino-triacetonediamine (EvA34)are promising solvents for CO2 capture. Therefore, in the present work, a compre-hensive experimental study was carried out to determine data on physico-chemicalproperties of EvA34 and its mixtures with H2O and CO2. The liquid density and thedynamic viscosity was studied for pure EvA34, as well as for unloaded and CO2-loaded aqueous solutions of EvA34. The liquid heat capacity was studied for pure EvA34and unloaded aqueous solutions of EvA34. Furthermore, data on the vapor pressure ofpure EvA34 was recorded. The pH-value was measured for unloaded and CO2-loadedaqueous solutions of EvA34 and the dissociation constants of EvA34 were determinedfrom titration curves. Moreover, data on the solubility of CO2 in aqueous solutions ofEvA34 and data on the CO2-containing species in the liquid phase of these solutionswere recorded. Most of the new data was taken at temperatures between 293 and 393K. The mass fraction of EvA34 in the unloaded aqueous solutions was either ~ w0EvA34= 0.1 g/g or ~ w0EvA34 = 0.4 g/g. The CO2-loading was up to ~?CO2 = 6.2 mol/mol. Thenew data were compared to corresponding data of two standard amines that are usedfor CO2 capture: monoethanolamine (MEA) and a blend of methyl-diethanolamineand piperazine (MDEA/PZ). The comparison revealed that EvA34 combines favorableproperties of MEA and MDEA/PZ in one molecule.

Numerical Analysis of Liquid–Liquid Heat Pipe Heat Exchanger Based on a Novel Model

Heat pipe heat exchangers (HPHEXs) are widely used in various industries. In this paper, a novel model of a liquid–liquid heat pipe heat exchanger in a countercurrent manner is established by considering the evaporation and condensation thermal resistances inside the heat pipes (HPs). The discrete method is added to the HPHEX model to determine the thermal resistances of the HPs and the temperature change trend of the heat transfer fluid in the HPHEX. The established model is verified by the HPHEX structure and experimental data in the existing literature and demonstrates numerical results that agree with the experimental data to within a 5% error. With the current model, the investigation compares the effectiveness and minimum vapor temperature of the HPHEX with three types of HP diameters, different mass flow rates, and different H* values. For HPs with a diameter of 36 mm, the effectiveness of each is improved by about 0.018 to 0.029 compared to HPs with a diameter of 28 mm. The results show that the current model can predict the temperature change trend of the HPHEX well; in addition, the effects of different structures on the effectiveness and minimum vapor temperature are obtained, which improve the performance of the HPHEX.

Mathematical modeling of moisture removal from granules

With modern world trends in the growth of consumption of products of various industries and the environmental situation, the problem of rational use of energy and raw materials in industrial production in order to obtain the maximum amount of finished product of a given quality. An important step in solving this problem is to create an adequate mathematical model of the process. A simplified model of the process of dehydration of the aqueous solution film on the surface of a single granule in the production of multilayer composites in a granulator dryer has been developed. Simulation of pellet dehydration includes analysis of heat distribution in a spherical material and in a film of liquid (heat exchange) covering the sphere, and the process of evaporation of the mixture film (mass transfer), which take place simultaneously. The results can be applied at the stages of design and testing of the granulator.

Performance analysis of a Brayton Pumped Thermal Electricity Storage (PTES) with a liquid sensible heat storage

A pervasive Renewable Energy Source (RES) exploitation poses a wide range of issues to electric grids, which the enhancement of the electric grid flexibility may mitigate. There are several approaches to improve grid flexibility, and a significant help will come from efficient, reliable, durable and cheap electric storage technologies. Inevitably, different storage technologies will be needed since different power and energy spectra characterise RES issues. In the category of high capacity-to-power ratio technologies, Pumped Thermal Electricity Storage (PTES) is becoming more and more popular. Such technology aims at replacing Pumped Hydro Energy Storage (PHES), and it is suited for daily cyclic operation (load shifting). In this paper, a Brayton PTES with liquid sensible heat storages is studied. Compared to the standard system equipped with packed beds, the liquid heat storage allows for a more straightforward state of charge estimation, control and, potentially, for a better usage of storage volume. Through a parametric analysis involving the main design specifications, the system performance is assessed under realistic assumptions. The resulting figures provide an exhaustive characterisation of the performance achievable by the system, which may be useful for a fair comparison between PTES and other competing storage technologies.

Design Improvement of Water-Cooled Data Centres Using Computational Fluid Dynamics

Data centres are complex energy demanding environments. The number of data centres and thereby their energy consumption around the world is growing at a rapid rate. Cooling the servers in the form of air conditioning forms a major part of the total energy consumption in data centres and thus there is an urgent need to develop alternative energy efficient cooling technologies. Liquid cooling systems are one such solution which are in their early developmental stage. In this article, the use of Computational Fluid Dynamics (CFD) to further improve the design of liquid-cooled systems is discussed by predicting temperature distribution and heat exchanger performance. A typical 40 kW rack cabinet with rear door fans and an intermediate air–liquid heat exchanger is used in the CFD simulations. Steady state Reynolds-Averaged Navier–Stokes modelling approach with the RNG K-epsilon turbulence model and the Radiator boundary conditions were used in the simulations. Results predict that heat exchanger effectiveness and uniform airflow across the cabinet are key factors to achieve efficient cooling and to avoid hot spots. The fundamental advantages and limitations of CFD modelling in liquid-cooled data centre racks were also discussed. In additional, emerging technologies for data centre cooling have also been discussed.

Using CFD to improve the performance of a heat exchanger from a gasifier

In this paper, a Computational Fluid Dynamics (CFD) analysis is performed on a gas-liquid heat exchanger fitted on a gasification equipment. The flow and temperature patterns are preliminary investigated using SolidWorks Flow Simulation software, in order to gain insight into the involved physical processes, and to find the exchanger weak points before being manufactured and tested. The analysed equipment tranfers heat from the flue gasses generated by a gasification system, towards a liquid heat transfer medium. This is subsequently sent to a second liquidliquid heat exchanger used to heat water from a boiler. As a result of the analysis, solutions aiming at performance improvement of the equipment are discussed and proposed.