Thermodynamic performance assessment of an indirect intercooled reheat regenerative gas turbine cycle with inlet air cooling and evaporative aftercooling of the compressor discharge

This study provides a computational analysis to investigate the effects of cycle pressure ratio, turbine inlet temperature (TIT), and ambient relative humidity (φ) on the thermodynamic performance of an indirect intercooled reheat regenerative gas turbine cycle with indirect evaporative cooling of the inlet air and evaporative aftercooling of the compressor discharge. Combined first and second‐law analysis indicates that the exergy destruction in various components of gas turbine cycles is significantly affected by compressor pressure ratio and turbine inlet temperature, and is not at all affected by ambient relative humidity. It also indicates that the maximum exergy is destroyed in the combustion chamber; which represents over 60% of the total exergy destruction in the overall system. The net work output, first‐law efficiency, and the second‐law efficiency of the cycle significantly varies with the change in the pressure ratio, turbine inlet temperature and ambient relative humidity. Results clearly shows that performance evaluation based on first‐law analysis alone is not adequate, and hence more meaningful evaluation must include second‐law analysis. Decision makers should find the methodology contained in this paper useful in the comparison and selection of gas turbine systems. Copyright © 2006 John Wiley & Sons, Ltd.     

A comprehensive design and performance evaluation study of counter flow wet cooling towers

Fouling of cooling tower fills is one of the most important factors affecting its thermal performance, which reduces cooling tower effectiveness and capability with time. In this paper, the fouling model presented in an earlier paper using the experimental data on fill fouling, is used to investigate the risk based thermal performance of the cooling tower. It is demonstrated that effectiveness of the cooling tower degrades significantly with time indicating that for a low risk level (p=0.01), there is about 6.0% decrease in effectiveness for the given fouling model. The sensitivity analysis of the cooling tower is investigated for both rating and design calculation for different values of mass flow rate ratios. The effect of atmospheric pressure on the thermal performance of the cooling tower is also demonstrated.     

Toward the modeling of data provenance in scientific publications

In this paper, we implement a provenance-aware system for documenting publications, called PADS. It employs a three-layered provenance hierarchy, which can output diverse types of provenance data related to the research life cycle. From this, we generate different profiles for research ventures, reviewers, and authors. PADS employs the standard Open Provenance Model (OPM) specification for capturing provenance data, and stores this data as ontological instances. We show that data is retrieved without any apparent delay in the execution time of the queries. We also demonstrate how this data can be used to make useful recommendations to the organizers, in order to manage upcoming research ventures.     

The effect of SiO2 addition on the development of low-Σ grain boundaries in PTC thermistors

Electron backscatter pattern analysis has been used to characterise, using the coincidence site lattice model, the distribution of grain boundary structures in a series of BaTiO₃ based positive temperature coefficient of resistance (PTC) thermistors, prepared with 0, 1.0, 2.0 and 3.0 at.% SiO₂ additions. As the SiO₂ content was raised, the proportion of random, high-angle grain boundaries in the microstructure increased steadily from 85.7% to 89.6%, while the proportion of grain boundaries indexable in the range Σ3–Σ29 decreased from 14.3% to 10.4%, and the Σ3 grain boundary population fell from 5.9% to 3.6%. At the same time the proportion of Σ3 twin boundaries remained approximately constant at 3.0 ± 0.3%. Significantly more Σ3 grain boundaries than would be expected in a randomly oriented, untextured material were observed in all samples. The variation in grain boundary types with SiO₂ addition is discussed in terms of grain boundary energy and its effect on PTC performance.     

Fabrication and positive temperature coefficient of resistivity properties of semiconducting ceramics based on the BaTiO3–(Bi1/2K1/2)TiO3 system

BaTiO₃–(Bi_1/2K_1/2)TiO₃ (BT–BKT) ceramics have a low ρ_RT of 10¹–10² Ω cm like that of semiconducting materials prepared by sintering in a N₂ flow with low O₂ concentration. By annealing in air, the BT–BKT ceramics show an abrupt increase in their resistivity near the T_c, namely, a positive temperature coefficient of resistivity (PTC) characteristic. With 5 mol% and 10 mol% BKT added to BT, the ceramics display the PTC characteristic at 155 °C and 165 °C, respectively. Furthermore, the ratio, ρ_max/ρ_RT, of the highest resistivity (ρ_max) and the resistivity at room temperature (ρ_RT) of the ceramics increased on adding a small amount of Mn and a sintering aid.     

Prediction of Evaporation Losses in Wet Cooling Towers

The accurate prediction of all aspects of cooling tower behavior is very important. Accurately predicting evaporation losses is significant because water in cooling towers is cooled primarily through the evaporation of a portion of the circulating water, which causes the concentration of dissolved solids and other impurities to increase. An empirical relation is developed on the basis of ASHRAE's rule of thumb that is simple and accurate with a wide range of applicability. The predicted values are in good agreement with experimental data as well as predictions made by an accurate mathematical model.     

Exergy analysis of double effect vapor absorption refrigeration system

Energy and exergy analyses previously performed by the authors for a single effect absorption refrigeration system have been extended to double effect vapor absorption refrigeration system with the expectation of reducing energy supply as well as an interest in the diversification of the motive power employed by HVAC technologies. The total exergy destruction in the system as a percentage of the exergy input from a generator heating water over a range of operating temperatures is examined for a system operating on LiBr–H₂O solution. The exergy destruction in each component, the coefficient of performance (COP) and the exergetic COP of the system are determined. It is shown that exergy destructions occur significantly in generators, absorbers, evaporator2 and heat exchangers while the exergy destructions in condenser1, evaporator1, throttling valves, and expansion valves are relatively smaller within the range of 1–5%. The results further indicate that with an increase in the generator1 temperature the COP and ECOP increase, but there is a significant reduction in total exergy destruction of the system for the same. On the other hand, the COP and ECOP decrease with an increase in the absorber1 temperature while the total exergy destruction of the system increases significantly with a small increase in the absorber1 temperature. The results show that the exergy method can be used as an effective criterion in designing an irreversible double effect absorption refrigeration system and may be a good tool for the determination of the optimum working conditions of such systems. Copyright © 2007 John Wiley & Sons, Ltd.     

Role of Pb substitution and a study of synthesizing procedure for Bi-based superconductors

Bulk superconductors of the (Bi_1–x Pb _x )₂Sr₂Ca₂Cu₃O _y system have been synthesized by changing the Bi/Pb ratio. The effect of Pb substitution onT _c has been studied by standard d.c. resistivity measurements. An appropriate thermal procedure and time for the preparation of the 110 K phase has also been studied at length. The experiments indicate that the best results are obtained forx=0.2 and that a slow cooling process is necessary for a better control of the thermal process. Indexed X-ray diffraction patterns indicate the lattice parameters of low- and high-T _c phases asa _L=0.54004 nm,b _L=0.5445 nm,c _L=3.084 nm anda _H=0.5483 nm,b _H=0.5339 nm,c _H=3.772 nm, respectively. The observed superconducting behaviour is stable on thermal cycling between 77 and 300 K.     

A probabilistic fouling and cost model for plate‐and‐frame heat exchangers

Fouling in plate‐and‐frame heat exchangers (PHEs) may be defined as the deposition of unwanted material on the heat transfer surface that reduces heat‐transfer and increases the resistance to fluid flow. Once the thermal–hydraulic performance decreases to a minimum acceptable level, cleaning of the equipment has to be done to restore the performance. The decision regarding periodic off‐line maintenance of the heat exchangers is generally based on a thermal–economic performance of the process. In this paper, we discuss a probabilistic maintenance model for PHE by incorporating the risk level and scatter parameter of the four random fouling growth models, namely linear, power law, falling rate and asymptotic models, which are integrated in the dimensionless cost model for a heat exchanger used in a steel plant. All the results are presented in terms of non‐dimensional plots. The results show that there is a strong relationship between t_down and the uptime, particularly in the region where the costs of operation and maintenance are minimum. Copyright © 2005 John Wiley & Sons, Ltd.     

Conductivity enhancement of PEDOT:PSS thin film using roll to plate technique and its characterization as a Schottky diode

The conductivity of poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) was improved by pressing the PEDOT:PSS thin film using roll to plate system. PEDOT:PSS thin film was deposited on polyethylene terephthalate using electrohydrodynamics atomization technique. The physico-chemical properties of the pressed thin film at different loads were compared with an un-pressed sample. The electrical properties show that the film conductivity has been increased by four times. An optimized pressing load was found to have good conductivity and transmittance of the thin film. A hybrid device (PEDOT:PSS/F8BT/ZnO/Ag) was fabricated using layer by layer method with PEDOT:PSS as anode. The I–V characterization showed that the device with pressed PEDOT:PSS showed higher current densities. The results give a promising future of PEDOT:PSS in electronics device applications using printed electronics techniques.