Exergetic analysis of a desiccant cooling system: searching for performance improvement opportunities

The current increase of the energy consumption of buildings requires new approaches to solve economic, environmental and regulatory issues. Exergy methods are thermodynamic tools searching for sources of inefficiencies in energy conversion systems that the current energy techniques may not identify. Desiccant cooling systems (DCS) are equipments applied to dehumidifying and cooling air streams, which may provide reductions of primary energy demand relatively to conventional air‐conditioning units. In this study, a detailed thermodynamic analysis of open‐cycle DCS is presented. It aims to assess the overall energy and exergy performance of the plant and identify its most inefficient sub‐components, associated to higher sources of irreversibilities. The main limitations of the energy methods are highlighted, and the opportunities given by exergy approach for improving the system performance are properly identified. As case study, using a pre‐calibrated TRNSYS model, the overall energy and exergy efficiency of the plant were found as 32.2% and 11.8%, respectively, for a summer week in Mediterranean climate. The exergy efficiency defect identified the boiler (69.0%) and the chiller (12.3%) as the most inefficient components of the plant, so their replacement by high efficient systems is the most rational approach for improving its performance. As alternative heating system to the boiler, a set of different technologies and integration of renewables were proposed and evaluated applying the indicators: primary energy ratio (PER) and exergy efficiency. The heating system fuelled by wood was found as having the best primary energy performance (PER = 109.6%), although the related exergy efficiency is only 11.4%. The highest exergy performance option corresponds to heat pump technology with coefficient of performance (COP) = 4, having a PER of 50.6% and exergy efficiency of 28.2%. Additionally, the parametric analyses conducted for different operating conditions indicate that the overall irreversibility rate increases moderately for larger cooling effects and more significant for higher dehumidification rates. Copyright © 2013 John Wiley & Sons, Ltd.     

Reducing the uncertainty in real-time impedance measurements

This paper arises from the exigency of enhancing the performance of a VXI-based digital meter designed for real-time tracking of impedance. Specifically, the metrological characterization of the meter has put into evidence that the experienced measurement uncertainty is mostly due to wide-band noise corrupting the acquired signals. With the aim of reducing its noise susceptibility without compromising the measurement rate, two digital signal-processing solutions are proposed. The first one pre-processes the acquired signals by means of predictive digital filtering for improving zero-crossing detection and, consequently, granting more reliable phase displacement measurements. The second solution evaluates the inner product of the signals of interest in order to average noise during the course of measurement, thus limiting its effect on the overall uncertainty. Many impedance measurements are carried out to draw a proper comparison between the proposed solutions.     

Desiccant wheel regenerated by thermal energy from a microcogenerator: Experimental assessment of the performances

Hybrid desiccant HVAC systems have shown several advantages, compared to conventional cooling and dehumidification systems. Therefore, their use is also spreading for tertiary and residential buildings, especially when the regeneration of the desiccant can be obtained by using available waste heat.     

The Effect of Different Sterilization Methods on the Mechanical Strength of Magnesium Based Implant Materials

The research on the development and characterization of potential magnesium biomaterials is a steadily expanding. Commonly, implants present a high risk of infection for their recipients. For this reason, a pre‐operative sterilizing process is required. Due to the temperatures and media which are used while sterilizing, effects may occur which cause a change in the mechanical strength of certain magnesium alloys. Four commonly used sterilization methods (autoclave sterilization, dry heat sterilization, gamma sterilization and ethylene oxide sterilization) were investigated to gain information about their influences on the quasi‐static mechanical behavior of LAE442 (Mg 90 m.%, Li 4 m.%, Al 4 m.%, RE 2 m.%), MgCa0.8 (Mg 99.2 m.%, Ca 0.8 m.%) magnesium alloys as well as pure magnesium. The mechanical properties exhibited by the sterilized and non‐sterilized alloys refer to susceptibilities of the mechanical strengths to the investigated sterilization methods. Such susceptibilities appear to be dependent on the combination of alloy and method of sterilization. However, the maximum changes in mechanical strength appear in the range of ±10%. Within this study, ETO sterilization caused the least changes in the mechanical strength of the alloys and appears to be the best performer.     

Accurate self-synchronizing technique for measuring transmitterphase and frequency errors in TDMA digitally encoded cellular systems

Measurement of phase and frequency errors, affecting the transmitted signal in digitally encoded cellular systems, is discussed here. To this aim, a new, cost-effective technique, particularly suitable in time domain multiple access (TDMA) systems, is proposed. In contrast to other measurement methods or instruments, the proposed technique gains burst synchronization on the analyzed signal through digital signal-processing, thus avoiding the need of sophisticated and expensive analog triggering solutions. Only a general-purpose data acquisition system is, in fact, required to capture a proper time window of the transmitted signal, preliminarily down-converted to intermediate frequency. Furthermore, in the same way as other methods or instruments, phase and frequency errors are evaluated according to a standard digital signal-processing procedure, which applies both for the actual and reference phase trajectory of the transmitted signal. The technique makes both trajectories available just at the end of the aforementioned burst synchronization stage, thus also optimizing the computational burden     

Fluoride and calcium-phosphate coated sponges of the magnesium alloy AX30 as bone grafts: a comparative study in rabbits

Biocompatibility and degradation of magnesium sponges (alloy AX30) with a fluoride (MgF₂ sponge, n = 24, porosity 63 ± 6 %, pore size 394 ± 26 μm) and with a fluoride and additional calcium-phosphate coating (CaP sponge, n = 24, porosity 6 ± 4 %, pore size 109 ± 37 μm) were evaluated over 6, 12 and 24 weeks in rabbit femurs. Empty drill holes (n = 12) served as controls. Clinical and radiological examinations, in vivo and ex vivo μ-computed tomographies and histological examinations were performed. Clinically both sponge types were tolerated well. Radiographs and XtremeCT evaluations showed bone changes comparable to controls and mild gas formation. The μCT80 depicted a higher and more inhomogeneous degradation of the CaP sponges. Histomorphometrically, the MgF₂ sponges resulted in the highest bone and osteoid fractions and were integrated superiorly into the bone. Histologically, the CaP sponges showed more inflammation and lower vascularization. MgF₂ sponges turned out to be better biocompatible and promising, biodegradable bone replacements.     

Development and characterization of cube-textured Ni–Cu–Co substrates for YBCO-coated conductors

Ni–Cu–Co alloys were studied for the development of textured substrates for YBCO-coated conductor application. Three compositions were obtained by adding a fixed amount of 3 at.% Co to the binary Ni_xCu_100?x, where x = 40, 50 and 60. Cube texture was induced by conventional cold rolling followed by high-temperature annealing. The structural, microstructural, morphological, electrical, magnetic, mechanical and oxidation properties were evaluated and compared with those exhibited by the binary Ni–Cu alloy, as well as by Ni–W and pure Ni. A low Ni content is detrimental for the development of the cube texture with respect to higher concentrations. Nevertheless, the use of high annealing temperatures enabled an area fraction of cube orientation as high as 95% to be obtained for x = 40, and >97.5% in the case of Ni-richer alloys. Compared with Ni and Ni–W, Ni–Cu–Co alloys oxidize more easily and exhibit higher electrical resistance. In addition, the presence of copper enables the Curie temperature to be reduced to 60 K for x = 40 and to 155 K for x = 50. Furthermore, the introduction of cobalt reduces the oxidation rate at temperatures normally used for the deposition of ceramic buffer layers, thus allowing the successful development of a CeO₂/YSZ/CeO₂ architecture on ternary Ni–Cu–Co alloy. YBCO/buffer multilayer architecture deposited by pulsed laser deposition on a selected alloy tape exhibits a critical current density exceeding 1 MA cm^?2 at 77 K in self-field, indicating that this alloy substrate is suitable for YBCO-coated conductor application.     

A digital signal-processing approach for phase noise measurement

A digital signal-processing method for phase noise measurement is presented. By properly over-sampling the input signal and adopting an optimized quadrature demodulation scheme, the method grants acceptable performance in analyzing sinusoidal carriers, the frequencies of which range from fractions of hertz up to hundreds of megahertz. Moreover, the method shows itself a valid alternative both to analog measurement systems, especially for the evaluation of close-to-the-carrier phase noise and time interval analyzers, particularly for carrier frequencies greater than a few units of megahertz. At first, the fundamental stages of the proposed method are described in detail. Its theoretical performance is then derived and compared to that offered by other measurement solutions already available on the market. Finally, the results of experiments carried out on actual signal sources are presented     

The effects of handling and storage on magnesium based implants — First results

The present work aimed to investigate the influence of acetone and formalin as well as the duration and type of storage on magnesium based implants by means of microscopic, μ-computed tomographic, scanning electron microscopic, EDX and metallographic investigations.In contrast to storing in acetone, storage in formalin led to an increase in surface to volume ratio, and a decrease of the volume and the density. The various types of storage exerted no differing effects on the implants but with increasing storage duration, a spreading of oxygen rich areas on the surface, increased precipitations and a decrease in grain size could be observed.     

Measuring Time-Varying $I/Q$ Impairments in Digital Transmitters

Impairments affecting the baseband modulator of digital transmitters, which are commonly called I/Q impairments, are responsible for the deviations of symbols from their original position on the I/Q diagram. They cause a reduction in the noise margin and ultimately worsen the probability of error. This is why their measurement is so important in all stages in the life cycle of digital transmitters. This paper presents an original method for the evaluation of the I/Q impairments based on a discrete extended Kalman filter (DEKF). In the same way as alternative solutions already presented in the literature, the method exhibits good performance in the presence of time-invariant impairments. Differently from them, it allows accurate measurements of time-varying impairments, thus making real-time tracking of their evolution feasible. After a few theoretical notes on the I/Q impairments and DEKF, the operative stages of the proposed method are described in detail. Several experiments are then conducted on radio frequency signals to assess the performance of the method; the obtained results are given and discussed.