Numerical model for solar thermal collectors and thermal energy storages based on phase change slurry

The efficiency of conventional solar thermal collectors and related thermal energy storages is often reduced by the requirement for high irradiation levels and the heat losses due to the relatively high temperature of the heat transfer fluid. In order to overcome those limitations, a solar thermal system capable of working at low temperatures through the exploitation of latent heat storage is presented in this paper. The proposed system was based on a novel heat transfer fluid and storage media, composed by a mixture of water and micro-encapsulated phase change material (PCM), named Phase Change Slurry (PCS). This paper introduces a numerical model capable of accurately describe the physical process and the dynamics of the proposed technology (collector, thermal energy storage and control logics). Results were validated by means of experimental tests and a long-term monitoring on a real full-scale prototype. Furthermore, experimental tests were performed to carry out the actual PCS thermo-dynamical properties that are strongly dependent on the concentration of micro-capsules in the heat transfer fluid

Overlapping Climate Policies

Major carbon-pricing systems in Europe and North America involve multiple jurisdictions (countries or states). Individual jurisdictions often pursue additional Initiatives – such as unilateral carbon price oors, legislation to phase out coal, aviation taxes or support programs for renewable energy – that overlap with the wider carbon-pricing system. We develop a general framework to study how the climate benefit of such overlapping policies depends on their design, location and timing. Some policies leverage additional climate benefits elsewhere in the system while others backfire by raising aggregate emissions. Our model encompasses almost every type of carbon-pricing system used in practice

Characterization and energy performance of a slurry PCM-based solar thermal collector: a numerical analysis

Flat plate solar thermal collector is the most common technology for solar energy conversion at the building scale. This technology has been established since long time and continuous developments have been achieved as time passed by; significant improvements of flat plate solar thermal collectors are thus now limited. A novel approach to increase further the performance of this technology is based on the exploitation of the latent heat of the heat carrier fluid. In order to assess this strategy, a previously developed numerical model of flat plate solar thermal collector with slurry PCM as heat carrier is herewith used to simulate the technology. The characterization and energy performance of such a system are herewith presented, based on the outcome of the numerical analysis. The results demonstrate that the novel approach is able to improve the performance of the system under different boundary conditions and in different climates: the improvement in the instantaneous efficiency is in the range 5-10%, while during the winter season the converted heat by the slurry PCM-based system is 20-40% higher than that of a conventional water based solar collector, depending on the climates – the colder the climate, the larger the improvement

Theoretical Methods for Wave Propagation across Jointed Rock Masses

Different methods are presently available for the analysis of wave propagation across jointed rock masses with the consideration of multiple wave reflections between joints. These methods can be divided into two categories. One is based on the displacement discontinuity model for representing rock joints, where the displacements across a joint are discontinuous and the tractions are continuous, and the other is the equivalent medium method. For the first category, there are three methods, i.e., method of characteristics (MC), scattering matrix method (SMM) and virtual wave source method (VWS). MC solves the equation of motion by using the theory of characteristic curves. SMM is based on the definition of the scattering matrix in which the reflection and transmission coefficients of a set of joints are stored. VWS method replaces the joints in the rock mass with a virtual concept. For the second category, equivalent medium model treats the problem in the frame of continuum mechanics and simplifies it from an explicit wave propagation equation. The objective of this paper is to review and compare these theoretical methods. The comparison shows that the four solutions agree very well with each other. Some additional considerations about the advantages and disadvantages of these methods are also given in the pape

Fresh vs. frozen embryo transfer in assisted reproductive techniques: a single center retrospective cohort study and ethical-legal implications

OBJECTIVE: Several studies have shown higher pregnancy rates and better perinatal outcomes with frozen embryo transfers than with fresh techniques, with better results in patients with polycystic ovary syndrome (PCOS) but with a higher rate of pregnancy complications such as preeclampsia. This retrospective cohort study aims to compare the cumulative live birth rates, maternal and neonatal complications of fresh embryo transfers (ET) and frozen-embryo transfers (FET) in infertile women who underwent assisted reproduction techniques (ART) at the Azienda Ospedaliera Ospedali Riuniti (AOOR) Villa Sofia Cervello, Palermo, Italy. In addition, the authors have focused on the legislative and ethical complexities which such a procedure entails.PATIENTS AND METHODS: Out of 475 women undergoing in vitro fertilization programs from January 2017 to January 2021, 128 were enrolled; 70 patients underwent ET, and 58 patients FET. The main outcome measure was live birth rates. Secondary outcomes were clinical pregnancy, ongoing pregnancy, pregnancy loss, low birth weight (LBW), ectopic pregnancy, and obstetrical and perinatal complications.RESULTS: The cumulative live birth rates were similar between the fresh transfer (95.7%) and frozen transfer (93.1%). Biochemical pregnancy rates, clinical pregnancy, ongoing pregnancy, and pregnancy loss were similar between the groups.CONCLUSIONS: Obstetrical outcomes were not statistically different between the two groups; a higher preterm delivery rate was reported in the FET group. ET birth weights were notably lower for singletons compared to the freeze-all strategy. ET patients also had higher LBW rates, with a 2.5-fold higher rate compared to FET. No significant differences were found in cumulative live birth rates between ET and FET, which is consistent with earlier studies. FET protocols are linked to higher neonatal birth weight and lower risk of LBW than fresh ET. The ethical and legal quanda-ries inherent in such techniques, as technology moves on and outpaces current legislative frame-works, cannot be discounted

Potentialities of a Low Temperature Solar Heating System Based on Slurry Phase Change Materials (PCS)

Flat-plate solar thermal collectors are the most common devices to convert solar energy into heat. Water-based fluids are commonly adopted as heat carrier for this technology, although their efficiency is limited by some thermodynamic and heat storage constraints. To overcome some of these limitations, an innovative approach is the use of latent heat, which can be available by means of microencapsulated slurry PCMs (mixtures of microencapsulated Phase Change Materials, water and surfactants). The viscosity of these fluids is similar to that of water and they can be easily pumped. In the present work, some of the thermo-physical and rheological properties and material behaviour that interest flat-plate solar thermal collectors with slurry PCM as the heat carrier fluid are analysed. Concepts of solar thermal systems filled with a slurry phase change material are proposed and a prototypal system is presented. Possible advantages and drawbacks of this technology are also discussed