Measurements of Thermal Conductivity of LWC Cement Composites Using Simplified Laboratory Scale Method

The implementation of low-energy construction includes aspects related to technological and material research regarding thermal insulation. New solutions are sought, firstly, to reduce heat losses and, secondly, to improve the environment conditions in isolated rooms. The effective heat resistance of insulating materials is inversely proportional to temperature and humidity. Cement composites filled with lightweight artificial aggregates may be a suitable material. Selecting a proper method for measuring the thermal conductivity of concrete is important to achieve accurate values for calculating the energy consumption of buildings. The steady state and transient methods are considered the two main thermal conductivity measurement approaches. Steady state is a constant heat transfer, whereby the temperature or heat flow is time independent. In the transient method, temperature changes over time. Most researchers have measured the conductivity of cement-based materials based on transient methods. The availability and cost of equipment, time for experimental measurements and measurement ability for moist specimens may be some of the reasons for using this method. However, considering the accuracy of the measurements, the steady state methods are more reliable, especially for testing dry materials. Four types of composites were investigated that differed in filler: natural aggregate, sintered fly ash filler, sintered clay and granular foam glass aggregate. The method of preparing the samples for testing is especially important for the obtained results. The samples, with a specific surface roughness, will show a lower coefficient of thermal conductivity by 20–30%; therefore, the selection of the type of contact layer between the plate of the measuring device and the sample is of particular importance.

Spectral Properties of Laser Dyes at varying Temperature

Spectral properties of laser dyes 4-methyl-7-(4-morpholinyl)-2 H pyrano [2,3-b] pyridin-2-one (LD – 425) and 6,7,8,9-tetrahydro-6,8,9-trimethyl-4-(trifluoromrthyl)-2H-pyrano[2,3b][1,8]naphthyridin-2-one (LD – 489) have been investigated in the temperature range 250C - 650C by steady state and transient methods. Fluorescence intensity decreases with increase in temperature with fluorescence band maxima shifted towards shorter wavelength in both the dyes. Further, fluorescence lifetime has decreased with increase in temperature for LD - 425, whereas remained constant with change in temperature for LD - 489. The possible deactivation mechanisms are discussed. The quenching effect of these dyes in the presence of aniline at different temperature has been studied and the Stern-Volmer (S-V) plots are non-linear showing positive deviation. It has been observed that dynamic quenching constant increases with temperature, whereas static quenching constant is independent of temperature.

Leakage Detection in Pipeline using Wavelet Transform Method

This research project is focusing on the leakage detection in the pipelines using wavelet and cepstrum analysis. To fully complete this research project, experimental and analysis by using signal processing are required. This research project proposed a technique which is a transient method. The basic principle is the fact that water spouting out of a leak in a pressurized pipe generates a signal, and this signal contains information to whether a leak exists and where it is located. The present transient methods for finding leaks are mainly based upon correlation analysis, where one sensing device is installed at each side of a leak. This method is hard to operate because it needs many operators to operate it due to equipment in different place. This research project proposed a wavelet transform method to detect leakage in the pipeline system. The experimental results show appears to improve the ability of the method to identify features in the signal.

Unravelling steady-state bulk recombination dynamics in thick efficient vacuum-deposited perovskite solar cells by transient methods

By evaluating perovskite solar cells up to 820 nm thick using charge extraction and transient photovoltage, first and second order recombination dynamics can for the first time be identified under operational conditions in complete devices.