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Sea breezes are important in a coastal urban climate; however, the impact of urban development on the effects of sea breezes, which decrease air temperature and increase humidity, has not been understood quantitatively. To quantitatively evaluate this impact in Sendai, Japan over the past twenty years, this study analyzed the heat balance mechanisms in urban spaces based on the simulation results of the Weather Research and Forecasting (WRF) model coupled with Local Climate Zone (LCZ) maps. Compared to the observation data on air temperature, specific humidity, and wind in August 2002, results of the numerical simulation, using the 2002 LCZ map and the meteorological conditions of August 2002, confirmed that the WRF model could reproduce meteorological factors well. Thereafter, two numerical simulations using the LCZ maps from 2002 and 2022 were conducted based on the same meteorological condition, from 25 July to 1 September 2008, to extract the impact of urban development on the effects of sea breeze. Consequently, when land use changed from urban built-up land to natural land cover, both the effects of sea breeze—decreasing air temperature and increasing humidity—decreased. Additionally, increases in LCZ 3 (compact low rise), mainly from LCZ 6 (open low rise) and LCZ 9 (sparsely built), decreased the effects of sea breeze (decreasing air temperature and increasing humidity) by 5% and 10%, respectively, in areas around Sendai Station. This was because the consumption of the sea breeze's potential to decrease air temperature and increase humidity increased and the wind speed of sea breezes decreased in the windward areas of Sendai Station. These results provide new insights into the impact of urban development on the effects of sea breeze and quantitatively reveal changes in the effects of sea breeze. [ABSTRACT FROM AUTHOR]

Short-term reliability of transmission lines is related to prediction time and operating conditions. The reliability model based on constant unavailability is no longer applicable. Hence， a temperature-dependent reliability model of transmission lines is established based on PHM （proportional hazard model）. The model consists of baseline hazard function and concomitant variable. The baseline hazard function takes account of tensile strength loss of transmission lines caused by temperature. Weibull distribution is used to describe the aging process and characterize the influence of temperature on failure rate. The ratio of real-time temperature to the rated temperature of lines is adopted as the concomitant variable to quantify the effect of real-time temperature on the short-term reliability of transmission lines. A Case study compares failure rate change of transmission lines with different service life in 24 hours. The result verifies the effectiveness of the model that can be applied to short-term reliability assessment for transmission lines to help operators make rational decisions in short-term operation and planning and online operation.

Sea breezes are important in a coastal urban climate; however, the impact of urban development on the effects of sea breezes, which decrease air temperature and increase humidity, has not been understood quantitatively. To quantitatively evaluate this impact in Sendai, Japan over the past twenty years, this study analyzed the heat balance mechanisms in urban spaces based on the simulation results of the Weather Research and Forecasting (WRF) model coupled with Local Climate Zone (LCZ) maps. Compared to the observation data on air temperature, specific humidity, and wind in August 2002, results of the numerical simulation, using the 2002 LCZ map and the meteorological conditions of August 2002, confirmed that the WRF model could reproduce meteorological factors well. Thereafter, two numerical simulations using the LCZ maps from 2002 and 2022 were conducted based on the same meteorological condition, from 25 July to 1 September 2008, to extract the impact of urban development on the effects of sea breeze. Consequently, when land use changed from urban built-up land to natural land cover, both the effects of sea breeze—decreasing air temperature and increasing humidity—decreased. Additionally, increases in LCZ 3 (compact low rise), mainly from LCZ 6 (open low rise) and LCZ 9 (sparsely built), decreased the effects of sea breeze (decreasing air temperature and increasing humidity) by 5% and 10%, respectively, in areas around Sendai Station. This was because the consumption of the sea breeze’s potential to decrease air temperature and increase humidity increased and the wind speed of sea breezes decreased in the windward areas of Sendai Station. These results provide new insights into the impact of urban development on the effects of sea breeze and quantitatively reveal changes in the effects of sea breeze.

A numerical study of aerodynamics in a deteriorated gas turbine was carried out. In the present study, a hybrid method of CFD simulation and heat balance analysis were used to estimate entire performance of the gas turbine cycle and local flow characteristics in the turbine section. Using this analysis method, flows in a deteriorated gas turbine were simulated under an operating condition, which was designated using the same procedure with that used in a real power plant. In our previous study, the degradation of the gas turbine performance due to blades deterioration had been observed. In the present study, flow patterns were observed and mechanisms underlying the degradation of the gas turbine performance were discussed in detail. Influences of two kinds of deterioration on flow patterns were examined: the first was thinning of nozzle guide vanes in the first stage and the second was increase of rotor tip gap in the first stage. The results showed that the deterioration of nozzle guide vanes leaded to decrease of the Mach number through the nozzle, and this leaded to increase of the turbine isentropic efficiency due to decrease of the friction loss. The increase in the rotor tip gap affected a loss generation of the following stage. Changes of flow patterns and its effects were discussed varying operating points of a gas turbine.

Summary: To overcome the limited efficiency of ocean thermal energy conversion (OTEC), particularly in the mid‐latitudes, combined OTEC (C‐OTEC) could use power extracted from the latent heat of a power plant condenser. Past research in South Korea has demonstrated the feasibility of a 10 kW C‐OTEC system using R134a as a working fluid. As the next phase, a 200 kW C‐OTEC demonstration facility with a thermal efficiency of greater than 3% is proposed. This paper presents the engineering design process for kW‐scale C‐OTEC within a 100 MW‐scale thermal power plant. The design process is divided into two stages. First, to predict patterns in steam flow to a connected external evaporator with a porous medium, computational fluid dynamics are calculated. The results show a conservative margin suitable for the conceptual design. Second, an iterative heat balance simulation method simultaneously evaluates the heat balance analysis of the C‐OTEC design and the thermal impact of the existing power plant. The design stages are then integrated in terms of heat transference capacity. [ABSTRACT FROM AUTHOR]

An analysis of energy balance and greenhouse gas emissions was conducted to compare alternative systems for the disposal and recycling of sewage sludge and food waste. Although the conversion of dewatered sludge to solid fuel has been a recent research focus, it is difficult to ensure that the solid fuel is needed and can be delivered to plants that can use it, such as coal-fired power plants. We therefore evaluated the effects of introducing various collaborative systems when updating existing sewage treatment plants and municipal solid waste incineration plants in Japan. Several cases were proposed and compared with a base case. In case Y, low-temperature carbonization equipment is introduced into a sludge conversion plant and dewatered sludge is converted into solid fuel. In case Z, dewatered sludge is dried to a moisture content of 40% with useable steam heat in a municipal solid waste incineration plant; the dried sludge is then combusted with municipal solid waste. Relative to the base case, greenhouse gas emissions were reduced by 25% in case Y and 26% in case Z. Therefore, a similar level of greenhouse gas reduction can be achieved by introducing a co-combustion system in a municipal solid waste incineration plant, even if there is no production of solid fuel to use in collaboration with coal-fired power plants. [ABSTRACT FROM AUTHOR]

Aiming at the security and economy problem of transmission line rating, a transmission line rating method based on security constraint and economy analysis was proposed. This transmission line rating method consisted of three main steps: temperature verification, failure rate verification and economy analysis. The real-time temperature of transmission line could be calculated by heat balance differential equation. A short-term reliability model of transmission line based on the PHM(proportional hazard model) was presented in this paper. A computing method of relative aging rate of transmission line based on empirical formula of tensile strength loss was proposed. The economy of transmission line rating was described from three terms including transmission profit, transmission loss cost and life loss cost. The results indicate that the proposed transmission line rating method can achieve a balance between security and economy. The final rating plan obtaines by the method satisfies the constraints of temperature and failure rate, and it is economical in the meanwhile. [ABSTRACT FROM AUTHOR]

Municipal solid waste (MSW) management has shifted to include multiple functions, especially energy recovery and reduction of greenhouse gas emissions, other than sanitary treatment of waste. In China, two main MSW treatment options exist: landfill and incineration. The objective of this study was to evaluate the landfill and incineration methods in terms of two important indicators, energy balance and greenhouse gas (GHG) emissions, and to discuss the advantages as they relate to decarbonization policy. We set up two landfill cases: LF-Anaero, which adopted an anaerobic landfill structure, and LF-SAero, which adopted a semi-aerobic landfill structure. Two incineration cases were also established: INC-Non, where the MSW was not subjected to separated collection of non-burnable waste, and INC-Sep, where separated collection was conducted. Two conditions were also established. In the one-year condition, waste was assumed to entirely decompose in one year, whereas in the variable decomposition condition, the rate varied. Under the one-year condition, INC-Sep gave the best results for both energy balance and GHG emission reduction. When the decomposition rate of landfilled waste was considered, LF-SAero and INC-Sep had very similar cumulative amounts of GHG emissions after 50 years. However, in INC-Sep, the emissions all occurred in the first 20 years. In LF-SAero, about one-third of the emissions were accounted for in the last 30 years (after the landfill was out of service). Thus, this landfill method must be considered as a GHG emission source for a longer period when considering the total global warming impact. We concluded that INC-Sep is the superior technological option. • We studied both semi-aerobic and anaerobic municipal solid waste landfills. • The half-life of biodegradable waste was included in analyses of landfill methods. • The effect of MSW composition on incineration method was evaluated. • Greenhouse gas emissions and energy balance were used as the evaluation indicators. • Incineration with separated collection is the superior technological option. [ABSTRACT FROM AUTHOR]