Formulation of a 1D finite element of heat exchanger for accurate modelling of the grouting behaviour: Application to cyclic thermal loading

This paper presents a comprehensive formulation of a finite element for the modelling of borehole heat exchangers. This work focuses on the accurate modelling of the grouting and the field of temperature near a single borehole. Therefore the grouting of the BHE is explicitly modelled. The purpose of this work is to provide tools necessary to the further modelling of thermo-mechanical couplings. The finite element discretises the classical governing equation of advection-diffusion of heat within a 1D pipe connected to ground nodes. Petrov-Galerkin weighting functions are used to avoid numerical disturbances. The formulation is able to capture highly transient and steady-state phenomena. The proposed finite element is validated with respect to analytical solutions. An example consisting of a 100 m depth U-pipe is finally simulated. A first continuous heating simulation highlights the nonsymmetric distribution of temperature inside and near the borehole. An estimation of the error on the results as a function of the resolution parameters is also carried out. Finally simulations of cyclic thermal loading exhibit the need to take into account all daily variations if the grouting behaviour must be modelled. This is true especially in case of freeze-thaw damaging risk.Geotherwa

Technological pedagogical content knowledge of mathematics teachers and the effect of demographic variables

With increasing global requirements for the use of technological tools and resources in K-12 settings, there is a need to examine the technological pedagogical content knowledge (TPACK) levels of mathematics teachers because technology use in class may enhance students’ engagement and motivation in learning mathematics. Hence, the purpose of this study was to develop and validate a TPACK scale to be used in investigating mathematics teachers’ knowledge levels in TPACK components, and investigate if mathematics teachers’ TPACK levels differed in terms of gender, teaching experience and level of school. This study is based on survey research design. Data were collected from 202 mathematics teachers in the spring semester of 2016-2017 academic year. MANOVA was used for data analysis. As a result of exploratory and confirmatory factor analysis, the TPACK instrument was developed as a valid and reliable 39-item 5-point Likert scale consisting of six scales: 1. Technological Knowledge, 2. Pedagogical Knowledge, 3. Content Knowledge, 4. Technological Content Knowledge, 5. Pedagogical Content Knowledge and 6. TPACK. The results also revealed that there were significant differences between gender and technological knowledge domain in favor of male teachers. However, it was found that teaching experience and level of school had no significant effect on TPACK domains. © 2019, Anadolu University, Faculty of Communication Sciences. All rights reserved

Views Of Freshmen Students On Foreign Language Courses Delivered Via E-learning

With the increasing number of foreign language courses via e-learning in higher education institutions, it is important to investigate whether the quality of e-learning is up to the standard. This study aimed at finding out the views of freshmen students on foreign language courses delivered via e-learning and revealing whether there were any statistically significant differences between students' views in terms of age, gender, time spent on using e-learning system and the faculty they studied at. This research was designed using the survey model. The sample of the research consisted of 478 freshmen students who were studying at four faculties and one vocational college in a state university in Turkey. The research data were collected through a scale, proposing a sixdimensional assessment of e-learning systems, which was developed by Ozkan and Koseler (2009) and tested for its reliability by the researchers. Data were analyzed using frequencies, mean, standard deviation, independent samples t-test and one-way Anova. The results indicated that the students' views on foreign language courses delivered via e-learning were negative with an 'overall' part mean score of 2,14 (Std=1,17). Also, the students disagreed 'learners' perspective' dimension (x =2,24) and partially agreed 'instructor attitudes', 'system quality', 'information content quality', 'service quality' and 'supportive issues' dimensions. Furthermore, it was revealed that there were no significant correlations between students' views and age and the time spent on using elearning. However, statistically significant differences were found between students' views and gender and the faculty students were studying at (p<0.05). The e-learning system should be developed in order for students to have valuable e-learning experiences and benefit from e-learning more

Thermo-Mechanical Radial Expansion of Heat Exchanger Piles and Possible Effects on Contact Pressures at Pile-Soil Interface

This letter shows that the increase of heat exchanger pile capacity in response to heating, observed in several small-scale laboratory studies, cannot be directly attributed to the increase of contact pressure at the soil-pile interface. The main thermo-hydro-mechanical processes that influence the capacity and behaviour of heat exchanger piles include thermal hardening of the soil, thermally induced water flow, excess pore pressure development and volume changes upon thermal consolidation. Due to the lack of understanding of the behaviour around the soil-pile interface, thermo-mechanical interactions between the heat exchanger pile and the ground are not taken into account appropriately in energy foundation design. However, in situ and reduced-scale experiments provide evidence about temperature-induced changes in pile capacity, presumably as a result of the altered stress state around the test pile. A finite-element analysis was conducted to quantitatively assess the radial stresses and strains undergone by a heated pile embedded in deformable soil. The study indicates that radial contact pressures typically increase less than 15 kPa, which cannot fully explain the increase in shaft resistance observed in heating tests. Further analyses are underway to characterise the mechanisms that govern pile load-displacement behaviour and the limit state

Encapsulation of in vitro-derived propagules of two genotypes of Capparis spinosa (L.) from Pantelleria Island

Encapsulation technology, combining the advantages of zygotic or gamic seed with those of micropropagation, has recently attracted the interest of researchers as a new propagation approach, mainly due to the unsatisfying results of the traditional propagation strategies. The encapsulation of uninodal microcuttings (3-4 mm long) from two Sicilian Capparis spinosa (L.) genotypes (from Pantelleria Island: Tracino and Scauri) was evaluated, observing the influence of the calcium alginate coating and of three different growth regulators (PGRs): 6-Benzylaminopurine (BAP), Meta-Topolin (MT) and Zeatin (ZEA), on viability, regrowth and conversion of the propagules. Caper microcuttings were dissected and placed in different Murashige and Skoog-based artificial endosperms, enriched of MT or ZEA or BAP. The synthetic seeds obtained were sown on a medium with full strength salts concentration, enriched with 0,4 mg/L of naphtalene acetic acid and 0,7 mg/L of gibelleric acid. After 60 days, the following parameters were detected: viability, regrowth, number and length of the shoots and roots, conversion. The results confirm that encapsulation did not negatively affect the viability, which showed the highest percentage with BAP (100%) in Tracino and with ZEA (100%) in Scauri. Similar results were obtained in regrowth, with statistically significant differences among the three PGRs tested: Tracino showed the best regrowth on capsuled enriched with BAP (100%), Scauri with ZEA (100%). In addition, the synseed conversion was greatly affected by the PGR, and it was higher in artificial endosperm added with BAP in Tracino (56.6%) and ZEA in Scauri (23.3%) genotype