• Energy Research
• Restricted close
• Open Source close
• CA close

The main objective of this paper is to study the possible use of D-mannitol as phase change material (PCM) for thermal energy storage. PCM are materials that have high phase change enthalpy and this thermophysical property gives them the ability to store energy as latent heat. D-mannitol is a material which has different morphological phases (polymorphism); here were studied b-form and d-form. Different polymorphic forms produce changes on melting point of D-mannitol. For this reason it is necessary to establish a suitable working temperature range for the use of D-mannitol as phase change material. The thermal characterization was performed with DSC analysis using 0.5 K min-1 slow-dynamic method. Polymorphism analysis of D-mannitol was analyzed to associate the thermal behavior obtained by DSC with a specific polymorphic phase. D-mannitol presented three different thermal behaviors: the first one had a melting peak at 167 oC, the second was a double melting peak at 155 oC and 166 oC, and the third a single peak at 155 oC. Due to irregular results, two working range were studied and through the thermal characterization, it was possible to define a working range where Dmannitol could be used as PCM for energy storage: this range is between 135 and 175 oC. Furthermore, it was possible to differentiate two crystalline phases of D-mannitol applying FT-IR analysis and to link them with thermal behavior observed in DSC. The percentage of times each thermal behavior is observed in DSC analysis was calculated. d-form is obtained 15.8% of analyzed cycles, the b-form appears 44.7% of times, and an intermediate transition between the two phases is found 39.5% of cycles.

Elevated environmental carbon dioxide (pCO2) levels have been found to cause organ damage in the early life stages of different commercial fish species, including Atlantic cod (Gadus morhua). To illuminate the underlying mechanisms causing pathologies in the intestines, the kidney, the pancreas and the liver in response to elevated pCO2, we examined related gene expression patterns in Atlantic cod reared for two months under three different pCO2 regimes: 380 μatm (control), 1800 μatm (medium) and 4200 μatm (high). We extracted RNA from whole fish sampled during the larval (32 dph) and early juvenile stage (46 dph) for relative expression analysis of 18 different genes related to essential metabolic pathways. At 32 dph, larvae subjected to the medium treatment displayed an up-regulation of genes mainly associated with fatty acid and glycogen synthesis (GYS2, 6PGL, ACoA, CPTA1, FAS and PPAR1b). Larvae exposed to the high pCO2 treatment upregulated fewer but similar genes (6PGL, ACoA and PPAR1b,). These data suggest stress-induced alterations in the lipid and fatty acid metabolism and a disrupted lipid homeostasis in larvae, providing a mechanistic link to the findings of lipid droplet overload in the liver and organ pathologies. At 46 dph, no significant differences in gene expression were detected, confirming a higher resilience of juveniles in comparison to larvae when exposed to elevated pCO2 up to 4200 μatm.

For the design of ground-source heat-pump systems, the local subsoil is an invariant factor. To improve the evaluation of the local heat exchange capability, significant efforts recently have been devoted to identifying the ground thermal conductivity vertical profile. In recent years, an innovative method using hybrid optic fiber cables inserted into the ground has been developed. The technique relies on copper wires that thermally stimulate the ground. Optical fibers measure the temperature variation over time all along the cable at a high spatial and temporal resolution. In this work, the hybrid cable was grouted into a 125-m well located in the Po Plain in Northern Italy. The provided core defined the geological environment as a continuous succession of unconsolidated alluvial deposits of very limited thickness, grouped in 15 different granulometric units. Three enhanced thermal response test (ETRT) data sets were acquired in different seasons; for 5 days of heating followed by 5 days of recovery, the soil temperature was recorded continuously along the well, with a spatial resolution of 1 m. A new approach using a multiple linear regression is proposed to analyze the data sets to distinguish the thermal conductivity of each individual granulometric unit. The obtained thermal conductivity values were compared and discussed considering the standard thermal response test outputs and the thermal conductivity data obtained from direct measurements performed on the cores. The analytical method's reliability stands due to the high repeatability of the obtained results, despite the increased complexity of the treated geological setting.

Abstract A heat pump coupled to thermal energy storage (TES) tanks is experimentally tested under simulated summer conditions and the results are presented in this paper. The cold TES tank is used for shifting the cooling load of a small house-like structure. The study evaluates the thermal behaviour of the TES tank for cold storage and the application of the system for space cooling. For the analysis, two different configurations of the tanks are compared: a water tank and a PCM tank. The PCM tank is filled with a commercial macro-encapsulated PCM, which has a phase change temperature of 10 °C. The results point out that the PCM tank is able to supply 14.5% more cold and to maintain the indoor temperature within comfort 20.65% longer than the water tank. However, it needs 4.55 times longer to charge the tank.

Abstract Life Cycle Assessment (LCA) has been conducted for seven experimental cubicles located in Puigverd de Lleida (Spain). The objective of this experimental set-up is to test different constructive solutions in order to point out the most sustainable solution with lower energy demand during the operational phase. Therefore, different building, insulation and Phase Change Materials (PCMs) have been tested under controlled temperature conditions to examine the thermal performance of the whole system. Although some of these materials are able to reduce the energy demand and consequently the environmental impact during the operational phase, they still have high embodied energy that can cause high environmental impact during the manufacturing phase. Therefore the LCA study in this paper focuses on assessing the impact of the embodied energy needed during the manufacturing and disposal phase by highlighting and comparing the effect of using different building materials, insulating materials, and phase change materials.

There remains conflicting evidence on the relationship between P supply and biological N(2)-fixation rates, particularly N(2)-fixing plant adaptive strategies under P limitation. This is important, as edaphic conditions inherent to many economically and ecologically important semi-arid leguminous tree species, such as Acacia senegal, are P deficient. Our research objective was to verify N acquisition strategies under phosphorus limitations using isotopic techniques. Acacia senegal var. senegal was cultivated in sand culture with three levels of exponentially supplied phosphorus [low (200 μmol of P seedling(-1) over 12 weeks), mid (400 μmol) and high (600 μmol)] to achieve steady-state nutrition over the growth period. Uniform additions of N were also supplied. Plant growth and nutrition were evaluated. Seedlings exhibited significantly greater total biomass under high P supply compared to low P supply. Both P and N content significantly increased with increasing P supply. Similarly, N derived from solution increased with elevated P availability. However, both the number of nodules and the N derived from atmosphere, determined by the (15)N natural abundance method, did not increase along the P gradient. Phosphorus stimulated growth and increased mineral N uptake from solution without affecting the amount of N derived from the atmosphere. We conclude that, under non-limiting N conditions, A. senegal N acquisition strategies change with P supply, with less reliance on N(2)-fixation when the rhizosphere achieves a sufficient N uptake zone.

Energy storage can facilitate the transition process from the actual energetic model to a model based on renewable energies. A lot of attention has been put in such technology, being the use of phase change materials (PCM) of high interest. However, design methodologies for PCM storage systems are still a limiting factor for its deployment. This paper compiles and structures the most common and promising design methodologies and highlights their usefulness and limitations. These methodologies are classified in six types: (1) empirical correlations and characterizing parameters, (2) dimensional analysis and correlations, (3) effectiveness–NTU, (4) Log Mean Temperature Difference (LMTD), (5) Conduction Transfer Functions (CTF), and (6) numerical models. Dimensionless correlations and effectiveness–NTU are the most common and straight-forward methods as well as the ones that offer more possibilities for general solutions. Empirical correlations and numerical models are problem based and difficult to generalize. On the other hand, the adaptation of LMTD and CTF to PCM systems still requires detailed research.

Abstract A comprehensive non-isothermal, three-dimensional computational model of a polymer electrolyte membrane (PEM) fuel cell has been developed. The model incorporates a complete cell with both the membrane-electrode-assembly (MEA) and the gas distribution flow channels. With the exception of phase change, the model accounts for all major transport phenomena. The model is implemented into a computational fluid dynamics code, and simulations are presented with an emphasis on the physical insight and fundamental understanding afforded by the detailed three-dimensional distributions of reactant concentrations, current densities, temperature and water fluxes. The results show that significant temperature gradients exist within the cell, with temperature differences of several degrees K within the MEA. The three-dimensional nature of the transport is particularly pronounced under the collector plates land area and has a major impact on the current distribution and predicted limiting current density.