Simplified Analyses of Some Vapour Power Cycles

1996 ◽  
Vol 210 (3) ◽  
pp. 191-202 ◽  
Author(s):  
J H Horlock
Keyword(s):  
Thermal Efficiency ◽  
Low Pressure ◽  
Power Cycles ◽  
Turbine Expansion ◽  
The Difference

A range of vapour power cycles is analysed, using the assumption originally made by Schaff that along a turbine expansion line the difference between the (local) enthalpy (h) and the liquid enthalpy at the same pressure ( hL) may remain unchanged (β = h – hL is constant). The thermodynamics of the assumption are critically examined and it is found to be valid only over strictly limited ranges of properties (usually low-pressure levels). However, if such limitations are accepted, the analyses provide understanding of the effects of various key parameters on thermal efficiency, and of measures (such as feed heating, reheat, dual pressure boilers, etc.) that are taken to raise that efficiency.

Analysis and calculation of the process of low-pressure reverse osmosis during recycling of hygienic water

2019 ◽  
pp. 28-36
Author(s):  
Leonid S. Bobe ◽  
Nikolay A. Salnikov
Keyword(s):  
Mass Transfer ◽  
Reverse Osmosis ◽  
Life Support ◽  
Space Station ◽  
Low Pressure ◽  
Operating Pressure ◽  
Life Support System ◽  
Cleaning Agent ◽  
The Difference ◽  
Pressure Channel

Analysis and calculation have been conducted of the process of low-pressure reverse osmosis in the membrane apparatus of the system for recycling hygiene water for the space station. The paper describes the physics of the reverse osmosis treatment and determines the motive force of the process, which is the difference of effective pressures (operating pressure minus osmotic pressure) in the solution near the surface of the membrane and in the purified water. It is demonstrated that the membrane scrubbing action is accompanied by diffusion outflow of the cleaning agent components away from the membrane. The mass transfer coefficient and the difference of concentrations (and, accordingly, the difference of osmotic pressures) in the boundary layer of the pressure channel can be determined using an extended analogy between mass transfer and heat transfer. A procedure has been proposed and proven in an experiment for calculating the throughput of a reverse osmosis apparatus purifying the hygiene water obtained through the use of a cleaning agent used in sanitation and housekeeping procedures on Earth. Key words: life support system, hygiene water, water processing, low-pressure reverse osmosis, space station.

scholarly journals Thermal Efficiency Gains Enabled by Using CO2 Mixtures in Supercritical Power Cycles

Energy ◽  
2021 ◽  
pp. 121899
Author(s):  
F. Crespi ◽  
P. Rodríguez de Arriba ◽  
D. Sánchez ◽  
A. Ayub ◽  
G. Di Marcoberardino ◽  
...  
Keyword(s):  
Thermal Efficiency ◽  
Efficiency Gains ◽  
Power Cycles

Performance Comparison and Parametric Analysis of sCO2 Power Cycles Configurations

2018 ◽  
Author(s):  
Ali S. Alsagri ◽  
Andrew Chiasson ◽  
Ahmad Aljabr
Keyword(s):  
Power Output ◽  
Thermal Efficiency ◽  
Performance Comparison ◽  
Specific Power ◽  
Brayton Cycle ◽  
Computationally Efficient ◽  
Power Cycles ◽  
Optimization Study ◽  
Specific Power Output ◽  
Improve Calculation

A thermodynamic analysis and optimization of four supercritical CO2 Brayton cycles were conducted in this study in order to improve calculation accuracy; the feasibility of the cycles; and compare the cycles’ design points. In particular, the overall thermal efficiency and the power output are the main targets in the optimization study. With respect to improving the accuracy of the analytical model, a computationally efficient technique using constant conductance (UA) to represent heat exchanger performances is executed. Four Brayton cycles involved in this compression analysis, simple recaptured, recompression, pre-compression, and split expansion. The four cycle configurations were thermodynamically modeled and optimized based on a genetic algorithm (GA) using an Engineering Equation Solver (EES) software. Results show that at any operating condition under 600 °C inlet turbine temperature, the recompression sCO2 Brayton cycle achieves the highest thermal efficiency. Also, the findings show that the simple recuperated cycle has the highest specific power output in spite of its simplicity.

scholarly journals A Subglacial Boundary-layer Regelation Mechanism

1990 ◽  
Vol 36 (124) ◽  
pp. 263-268 ◽  
Author(s):  
E.M. Shoemaker
Keyword(s):  
Boundary Layer ◽  
Heat Input ◽  
High Water ◽  
Low Pressure ◽  
Critical Value ◽  
High Water Content ◽  
Overburden Pressure ◽  
Basal Ice ◽  
The Difference ◽  
Linear Nature

AbstractHeat input to basal ice at subglacial low-pressure regions, such as exist on the lee side of bed bumps including regions of ice-bed separation, is shown to melt basal ice internally in a narrow boundary layer at most centimeters thick. Before ice at the ice-bed interface can begin to melt, the heat input Q must exceed a critical value Q*. Q* increases rapidly with an increase in the difference ΔΡ between the nominal (global) overburden pressure and the magnitude of the (local) normal stress acting between the ice and bed or ice and water pocket. Because of the non-linear nature of the flow law, the thickness of the boundary layer decreases rapidly with increasing ΔΡ. The ice in the boundary layer is likely to be soft with a high water content. Under certain conditions, a regelation cycle may exist between the boundary layer and the water in a subglacial cavity. The boundary layer is sufficiently narrow that the processes can reach steady state while ice traverses subglacial low-pressure regions of length the order of 0.01–0.1 m. The regelation phenomenon may preserve or aid the formation of narrow debris-rich ice layers at the base of temperate glaciers.

Construction and Experimental Study of an Elevation Linear Fresnel Reflector

2016 ◽  
Vol 138 (3) ◽  
Author(s):  
J. D. Nixon ◽  
P. A. Davies
Keyword(s):  
Heat Loss ◽  
Thermal Efficiency ◽  
Theoretical Models ◽  
Loss Coefficient ◽  
Heat Transfer Fluid ◽  
Stagnation Temperature ◽  
Model Predictions ◽  
The Difference ◽  
Predicted Values ◽  
Linear Fresnel Reflector

This paper outlines a novel elevation linear Fresnel reflector (ELFR) and presents and validates theoretical models defining its thermal performance. To validate the models, a series of experiments were carried out for receiver temperatures in the range of 30–100 °C to measure the heat loss coefficient, gain in heat transfer fluid (HTF) temperature, thermal efficiency, and stagnation temperature. The heat loss coefficient was underestimated due to the model exclusion of collector end heat losses. The measured HTF temperature gains were found to have a good correlation to the model predictions—less than a 5% difference. In comparison to model predictions for the thermal efficiency and stagnation temperature, measured values had a difference of −39% to +31% and 22–38%, respectively. The difference between the measured and predicted values was attributed to the low-temperature region for the experiments. It was concluded that the theoretical models are suitable for examining linear Fresnel reflector (LFR) systems and can be adopted by other researchers.

Phosphorus Kinetics in Lake Water: Influence of Membrane Filter Pore Size and Low-Pressure Filtration

1976 ◽  
Vol 33 (12) ◽  
pp. 2800-2804 ◽  
Author(s):  
D. R. S. Lean
Keyword(s):  
Membrane Filter ◽  
Lake Ontario ◽  
Low Pressure ◽  
Total Radioactivity ◽  
Pressure Filtration ◽  
Membrane Filters ◽  
Pressure Method ◽  
Carrier Free ◽  
Algae And Bacteria ◽  
The Difference

Radiotracer kinetics using carrier-free 32P-PO4 were conducted on samples of water from Heart Lake, Ontario. Results obtained using 0.45-μm membrane filters were compared with those for 0.1 μm at vacuums of 400 mm Hg and to those for 0.45-μm filters using very low-pressure (4 mm Hg) filtration. The difference between 0.45 and 0.1 can reach 8–20% of the total radioactivity during the first 10 min of the experiment. After 60 min the fraction removed by 0.1, but not 0.45-μm filters, declines to only 1% of the total radioactivity, but this may represent as much as 50% of that which goes through 0.45 μm. The low-pressure filtration techniques provided similar results to those for normal filtration when kinetics were monophasic. Later in the season, the low-pressure method was shown to provide confusing artifacts that were explained by the hypothesis that tiny filaments extend from the surfaces of some species of aquatic algae and bacteria and are often dislodged during filtration.

Availability Balance of Steam Power Plants

1959 ◽  
Vol 81 (1) ◽  
pp. 35-42 ◽  
Author(s):  
C. A. Meyer ◽  
G. J. Silvestri ◽  
J. A. Martin
Keyword(s):  
Thermal Efficiency ◽  
Power Plants ◽  
Heat Rate ◽  
Development Effort ◽  
Combustion Gases ◽  
Steam Power Plants ◽  
Reheat Steam ◽  
Temperature Combustion ◽  
The Difference ◽  
Average Plant

The well-known expression for availability, b = h − T0s, is developed in a simple yet general manner. The changes in availability throughout several typical single and double reheat steam plants having different steam conditions have been calculated. Balances of availability are presented for each of the several plants. These balances show the net plant output as the difference between the availability added in the boiler and the various losses in availability throughout the plant. The maximum plant thermal efficiency (or minimum heat rate) is easily obtained from the ratio of the increase in availability to the heat added in the boiler. The availability balances present in fine detail the loss distribution throughout the plant. Some very interesting results are obtained. For example, an assumed average plant will have a calculated maximum thermal efficiency of about 75 per cent based on the ratio of the availability and the heat in the high temperature combustion gases. Due to the heat transfer through a temperature difference, this value is reduced to 50 per cent when based on the ratio of the availability and the heat added to the steam in the boiler. This average plant will lose an additional 10 points in thermal efficiency, due to internal losses in availability, resulting in a 40 per cent thermal efficiency (excluding boiler and auxiliary losses). These latter 10 points due to internal losses are roughly divided as follows: Pressure drop: 0.9 Turbine blading: 5.0 Turbine leakage: 0.6 Turbine leaving and hood: 1.0 Mechanical and generator: 0.7 Feed and healing system: 1.3 and Feed pump and motor inefficiency: 0.5 Total: 10.0 An availability balance enables one to make an accurate assessment of the losses in any power plant and therefore serves as a very accurate guide in directing development effort toward reducing the more significant losses.

Effect of Carbon Dioxide Recirculation and Pressure on Efficiency of the TIPS and ENEL Oxy-Coal Power Cycles

2019 ◽  
Vol 142 (6) ◽  
Author(s):  
Md. Moheiminul I. Khan ◽  
Mehrin Chowdhury ◽  
A. S. M. Arifur Rahman Chowdhury ◽  
Jad Aboud ◽  
Norman Love
Keyword(s):  
Flow Rate ◽  
Flue Gas ◽  
Thermal Efficiency ◽  
Pressure Range ◽  
Aspen Plus ◽  
Dominant Factor ◽  
Power Cycles ◽  
Thermodynamic Cycles ◽  
Coal Power ◽  
Cycle Efficiency

Abstract This paper presents the results of thermal efficiency of two coal based oxy-combustion thermodynamic cycles that are modeled using aspen plus. The objective of the present study is to perform a parametric analysis, investigating the effect of different recirculation ratios at different pressures on the efficiencies of the cycle named for the company, ENEL, and the thermo energy power system, TIPS, cycles using aspen plus® software. Variables include the flue gas recycle flow rate, the combustor temperature, and the operational pressure. Five recirculation ratios were investigated, ranging from 20% to 75%. It was determined that as the amount of recycled gas into the combustor increased, the thermal efficiency increased for both the TIPS and ENEL cycles. The highest thermal efficiency for TIPS is 37% and for ENEL is 38%, both occurring at a 75% recirculation ratio. After investigation, since combustion temperature and specific heat capacity decreases at higher recirculation ratios, the mass flow rate was the dominant factor that contributes to the increase in thermal efficiency of the cycle. At each recirculation ratio, the effect of pressure is also determined. For ENEL, the increase in cycle efficiency is 10% over the pressure range of 1–12 bar at a recirculation ratio of 20%, while the increase in cycle efficiency is only 1.5% at a higher recirculation ratio of 75%. For TIPS, the cycle efficiency increases by 4% at the recirculation ratio of 20% and increases by 3% at the recirculation ratio of 75% for a pressure range of 50–80 bar.

Effects of Tooth Width on Gas Labyrinth and Windback Seals Operating at Low Pressure Ratios

2007 ◽  
Author(s):  
Gerald L. Morrison ◽  
Chae Hwan Lim
Keyword(s):  
Low Pressure ◽  
Labyrinth Seal ◽  
Screw Thread ◽  
Tooth Width ◽  
Accepted Standard ◽  
Additional Amount ◽  
The Difference ◽  
Low Pressures

The difference in leakage rates for labyrinth and windback seals is studied. It is determined that the leakage under the teeth of a windback seal is within ± 3% of a labyrinth seal with the same cavity/tooth design. The windback leaks an additional amount due to fluid passing through the long conduit composed of the continuous screw thread like channel. At low pressures and low differential pressures across the seal, the effect of tooth width upon the leakage in labyrinth and windback seals is opposite to the normal accepted standard of thinner teeth leak less.

scholarly journals Molecular Indications of Protein Damage in Adenoviruses after UV Disinfection

2010 ◽  
Vol 77 (3) ◽  
pp. 1145-1147 ◽  
Author(s):  
Anne C. Eischeid ◽  
Karl G. Linden
Keyword(s):  
Cell Culture ◽  
Viral Proteins ◽  
Low Pressure ◽  
Protein Damage ◽  
Uv Disinfection ◽  
Medium Pressure ◽  
The Difference ◽  
Uv Lamp ◽  
Detailed Work

ABSTRACTAdenoviruses are resistant to monochromatic, low-pressure (LP) UV disinfection—but have been shown to be susceptible to inactivation by polychromatic, medium-pressure (MP) UV—when assayed using cell culture infectivity. One possible explanation for the difference between UV lamp types is that the additional UV wavelengths emitted by MP UV enable it to cause greater damage to viral proteins than LP UV. The objective of this study was to examine protein damage in adenoviruses treated with LP and MP UV. Results show that MP UV is more effective at damaging viral proteins at high UV doses, though LP UV caused some damage as well. To our knowledge, this study is the first to investigate protein damage in UV-treated adenovirus, and the overview presented here is expected to provide a basis for further, more detailed work.

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