Effect of refrigerant charge on the performance of air conditioning systems

An air conditioning system operates in an optimal condition if the system is fully charged with a specified amount of refrigerant. Poor field maintenance or refrigerant leakage causes low level of charge resulting in a lower thermal performance and higher operating cost. An experimental investigation was conducted to study the effect of low charge level of R‐22 on the performance of a 3‐ton residential air conditioning system. The experimental results show that if a system is undercharged to 90 per cent then the effect is small: a 3.5 per cent reduction in cooling capacity and a 2 per cent increase in the coefficient of performance (COP). However, the system performance suffers serious degradation if the level of charge drops below 80 per cent. An ice layer formed on the outer surface of the cooling coil impedes the heat transfer between the warm air and cold refrigerant vapour. An economic analysis shows that the cost of properly charging an under‐charged system which is at an 85 per cent charge level, can pay for itself in savings in a short period of 3–4 months. Copyright © 2001 John Wiley & Sons, Ltd.     

Comment on ‘extended depth of field in hybrid imaging systems: circular aperture’

A recent paper by Sherif et al. (S.S. Sherif, E.R. Dowski, W.T. Cathey, J. Mod. Opt. 51 1191 (2004).) reported the derivation of an aspherical phase plate, which when placed at the exit pupil of a conventional imaging system and combined with digital processing of the recorded images, increases the depth of field by an order of magnitude. An error in the derivation of this phase plate has been identified, which makes the reported extension of depth-of-field sub-optimum rather than invalid. In this comment, an optimum phase plate is obtained and the relevant results are repeated.     

Instant synthesis of mesoporous monolithic materials with controllable geometry,dimension and stability: a review

The development of the nanoscale structures and their integration into components, systems, and natural architectures (such as monoliths), and large-scale devices, is one of the most promising areas in the emerging field of nanotechnology. We believe that it is time to write a review that focused on the rapid synthesis and the functional properties of HOM mesoporous monoliths. Thus, we here introduce comprehensive and up-to-date reports on the instant synthesis (within minutes) of a range of mesoporous silica monoliths (HOM-type, High-Order-Monolith) by means of a direct-templating method of lyotropic and microemulsion liquid crystalline phases. A number of nonionic n-alkyl-oligo(ethylene oxide), namely, Brij-type (C _x EO _y ), and Triton- and Tween-type and cationic alkyl trimethylammonium bromide or chloride (C _n TMA-B or -C, where n = 12, 14, 16 and 18) surfactants were used as soft templates. A variety of 1D, 2D and 3D mesostructure geometries were successfully fabricated by using this simple, fast and yet reproducible design strategy. This is the first and detailed review of using rapid synthesis to fabricate disordered and ordered silica/surfactant mesophases with supermicro- and meso-pore engineering systems. In this review, we also addressed the prominent factors affected the formation of the large-scale ordered and worm-like structures (HOM): (1) the phase composition of domains, (2) the extent of solubilization of hydrocarbons, and (3) the nature of surfactant molecules (corona/core features). Significantly, due to large morphological particle sizes, these HOM monolithic structures exhibited considerable structural stability against longer hydrothermal treatment times. Such retention is crucial in industrial applications.     

Adaptive allocation of resources and call admission control forwireless ATM using genetic algorithms

In wireless ATM-based networks, admission control is required to reserve resources in advance for calls requiring guaranteed services. In the case of a multimedia call, each of its substreams (i.e., video, audio, and data) has its own distinct quality of service (QoS) requirements (e.g., cell loss rate, delay, jitter, etc.). The network attempts to deliver the required QoS by allocating an appropriate amount of resources (e.g., bandwidth, buffers). The negotiated QoS requirements constitute a certain QoS level that remains fixed during the call (static allocation approach). Accordingly, the corresponding allocated resources also remain unchanged. We present and analyze an adaptive allocation of resources algorithm based on genetic algorithms. In contrast to the static approach, each substream declares a preset range of acceptable QoS levels (e.g., high, medium, low) instead of just a single one. As the availability of resources in the wireless network varies, the algorithm selects the best possible QoS level that each substream can obtain. In case of congestion, the algorithm attempts to free up some resources by degrading the QoS levels of the existing calls to lesser ones. This is done, however, under the constraint of achieving maximum utilization of the resources while simultaneously distributing them fairly among the calls. The degradation is limited to a minimum value predefined in a user-defined profile (UDP). Genetic algorithms have been used to solve the optimization problem. From the user perspective, the perception of the QoS degradation is very graceful and happens only during overload periods. The network services, on the other hand, are greatly enhanced due to the fact that the call blocking probability is significantly decreased. Simulation results demonstrate that the proposed algorithm performs well in terms of increasing the number of admitted calls while utilizing the available bandwidth fairly and effectively     

Critical pathways to enhanced innovation diffusion and business performance in Australian design firms

This paper presents a study that extends on previous empirical research, which examined the role of enabling ‘climate for innovation’ constructs in determining the level of innovation diffusion outcomes, and subsequent business performance in architectural and engineering design (AED) firms. Whilst this previous study elucidated the relationships between broad theoretical constructs, the present study was focused on targeting the significant enabling factor interrelationships with the core outcomes that result from the innovation diffusion process. To achieve this objective, a sequential mixed-method research design combining quantitative and qualitative analysis techniques was employed. The quantitative techniques included a correlation analysis to identify the strong factor relationships, followed by Structural Equation Modelling (SEM) to determine the critical pathways for enhancing innovation diffusion and ultimately heightened levels of client satisfaction. Following path model extraction, qualitative interviews with five Australian AED firms were conducted. The interview findings confirmed the uncovered significant pathways, and provided in-depth insights into how the improvement of critical enabling factors could leverage improved innovation diffusion outcomes and business performance.     

The electroremoval of copper from dilute waste solutions using Swiss-roll electrode cell

Copper is usually present in concentrations less than 5 g/L⁻¹ in dilute waste solutions. The low concentrations make these solutions unsuitable for the electro-flow owinning processes via conventional electrolysis cells. Unconventional, two-and three-dimensional electrode cells with relatively large cathodic area are essential for such treatment. Different types of cells are mentioned in the literature. Among these cells, the two-dimensional Swiss-roll cell (SR) is considered in this study. The effects of cathodic current densities, initial copper concentrations, free sulfuric acid concentration, the presence of iron and zinc cations, and the rate of flow of the solution on both the cathodic current efficiency and power consumption were studied. Copper was removed from synthetic and industrial mixtures of Cu/Fe/Zn sulfate solutions to less than 5 ppm with power consumptions of 10.326 kWh/kg⁻¹ and 8.61 kWh/kg⁻¹, respectively. The correlation between the SR cell and packed-column cell on such treatment was also considered.     

The search for quality: The case of planned obsolescence

Planned obsolescence involves a design plan that is intended to hasten existing products to become undesirable (not necessarily below that of competitive offerings) either functionally or psychologically and consequently to be replaced by new products. Many manufacturing companies since the last decade have adopted the policy of planned obsolescence in their products. Their main objective is to cut costs, increase profits and secure continuous consumption and production. When this policy is abused, however, so that customers are not getting products which can perform adequately and safely for a reasonable amount of time, the end result may prove to be more detrimental than beneficial, not only to producers and consumers but to the nation as a whole. In this age of scarce resources, energy shortages and new challenges, this paper re-examines planned obsolescence and searches for quality in todays products.     

Overview of wideband packet protocols

Wideband packet networks operate at rates equal to, or higher than, 64 kb/s, but lower than the basic broadband rate of 150 Mb/s, on cables or satellite links. Wideband packet protocols are the transmission protocols for these networks. They define open interfaces that can be used for public and private ISDNs. The protocols are defined in CCITT Recommendations G.764 and G.765. This paper describes the objectives of the wideband protocols, and how the objectives were achieved.     

Improving software quality through formal inspections

Software safety is a relatively new concept in the software reliability and quality assurance disciplines. Several techniques for conducting software safety analysis are available, and include the following: Peer Circuit Analysis, Software Fault Trees, Nuclear Safety Cross-Check and Petri Nets. This paper puts forward Technical Walkthroughs as an effective method of the Peer Circuit Analysis technique. The paper emphasizes the characteristics of efficient technical walkthroughs that improve the safety and quality assurance function of software in each phase of its life cycle development process. The paper identifies walkthroughs objectives, responsibilities, participants, rules agendas and feedback protocols.     

A novel approach for the modeling of advanced photovoltaic devices using the SILVACO/ATLAS virtual wafer fabrication tools

In this paper a new method for developing a realistic model of any type of solar cell is presented. Taking into account the high cost of research and experimentation involved with the development of advanced cells, we present here this novel methodology. In our opinion, the introduction of this modeling technique to the photovoltaic community will prove to be of great importance in aiding in the design and development of advanced solar cells. Two models of a single GaAs and an InGaP/GaAs/Ge multi-junction solar cell are prepared and are fully simulated. The major stages of the process are explained and the simulation results are compared to published experimental data to demonstrate the accurate results produced by the model utilizing this technique. The flexibility of the proposed methodology is illustrated and example results are shown throughout the whole process, demonstrating some of the different parameters effects on the model performance.