Simulation Of Heat Balance Research Articles

Influence of Radiative Components and Meteorological Conditions on Simulation of Slope-Specific Heat Balance

Fields have uneven surfaces, such as ridges, and the shortwave radiation of fields differs depending on the orientation of the slope of the unevenness, resulting in variations in the distribution of moisture on the ground surface. Therefore, it is necessary to estimate the heat and water balances spatially, taking into account the variation of the moisture distribution on the ground surface. Previously, one-dimensional simulations have been used to estimate the heat and water balance of non-sloping surfaces. To estimate the heat and water balance spatially while taking into account ground surface roughness, it is necessary to first estimate the heat and water balance of the ground surface on the basis of slope orientation. The purpose of this study was to clarify those factors, in addition to shortwave radiation, that affect the heat balance of a bare sloping surface at different orientations. To achieve this, the heat balance calculated using observational data of bare ground, including unevenness, was compared with the heat balance estimated by HYDRUS-1D simulation for each slope orientation. Additionally, the brightness index of RGB images was calculated and compared with the relative ground surface brightness and the estimated heat balance for each slope orientation. The estimated results at night and at sunrise/sunset were extremely small in comparison with the calculated results, and the heat balance simulation in the absence of shortwave radiation remained an issue. The relationship between ground surface brightness and ground conduction heat was completely different depending on slope direction, suggesting that ground surface heat transfer is affected substantially by factors other than shortwave radiation related to slope orientation. The findings indicate that it is necessary to examine the effects of heat transfer in detail to estimate the heat balance related to slope orientation.

Influence of Lubricant Supply on Thermal and Efficient Performances of a Gear Reducer for Electric Vehicles

Abstract The amount of lubricating oil in a gear reducer greatly influences components’ temperature and efficiency of the reducer. A thermal network simulation model of a gear reducer for electric vehicles based on amesim software was built for thermal and efficiency analysis of the reducer, where heat production and transfer processes of each component in the reducer are considered. Moreover, secondary development submodels were developed to calculate the convection coefficients in real time based on different lubricating oil temperatures and working conditions. Next, the experiments were conducted to verify the developed model regarding transmission efficiency and lubricating oil equilibrium temperature in the reducer. The deviation between the numerical and experimental results is less than 5%, which indicates high accuracy of the developed thermal network model. Thereafter, efficiency and heat balance simulation tests under different working conditions were performed to determine an optimal lubricating oil supply, which is 14 mm gear-oil-immersion oil supply in this study. Finally, a comparison between the reducer with the optimal oil supply and that with normally used 22 mm gear-oil-immersion supply in the NEDC cycles in low temperature was done. The reducer with the optimal oil supply shows 1.032% energy saving. The method presented in this article provides a good guide to design and optimization of the gear reducer for electrical vehicles.

Heat balance simulation for evaluating a 315 MW low rank coal-fired power plant performance

The domination of coal-fired power plant as power generation due to its feasibility to ensure a stable supply of electricity to customer. Unfortunately, the use of coal as power plant fuel faces an issue of air pollution. Some efforts have been proposed to make the operated coal-fired power plant meeting the environmental regulations. One of the most potential ways to solve the problem is by improving the coal-fired power plant efficiency and then equate to a greenhouse gas reduction. Thus, heat balance simulation of coal-fired power plant which operates in different conditions have to be studied in order to analyse the power plant performance. In this paper, the heat balance of a 315 MW low rank coal-fired power plant is simulated by Cycle-Tempo. The simulations are carried out for several different operation conditions of the power plant. The Heat Rate will increase of 3.66% when all HPH are on off-duty while it increases by 2.63% when all LPH are on off-duty. Furthermore, the increasing of Superheater temperature of 5 °C will decrease the Heat Rate of 0.59% and it will decrease of 0.39% when the temperature of Reheater increases of 5 °C.

Conceptual design for combined ocean thermal energy conversion using computational fluid dynamics and heat balance analysis

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.

Modeling and simulation of heat balance and internal heat recovery targets through a combination of stream specific minimum temperature difference and polynomial temperature coefficients of specific heat capacities using pinch analysis

Existing heat balancing and energy targeting model in Pinch Analysis rely on use of interpolated values of specific heat capacities and global values of minimum temperature difference ∆Tmin, respectively. Even though this model is useful in estimation of the maximum internally recoverable heat recoverable in processing plants, it does not adequately represent the actual state properties of industrial processes. Specific heat capacities of fluids are polynomial functions of temperature of material under processing. The values of ∆Tmin also vary depending on the nature of the process stream under analysis. In this study, improvement to the heat balancing and energy targeting processes of pinch analysis was proposed. The study combined the use of stream specific values of ∆Tmin and polynomial temperature functions of specific heat capacities for heat targeting model. This was coded and executed using a PHP program. The model performance was tested using data from three thermochemical plants, Plant A, B and C, which process linear alkyl benzene sulphonic acid, dairy products and ethanol, respectively. The proposed method for heat balancing computed more heating requirements for plant A, B and C by 0.37%, 0.65% and 0.72% respectively, compared to the traditional method of heat balancing. The cooling loads for Plant A and B were less by 2.23% and 32.52% respectively, while for Plant C, they were more by 0.64%. The computed internally recoverable heat targets were more by 1.5%, 4.5% and 2.2% for Plants A, B and C. Simulations of the proposed model were carried out over a range of temperature targets, for different process streams. For gaseous process streams, heating and cooling load requirements were less. Reverse behavior was observed in liquid and steam containing streams, where the heating and cooling load requirements were more.

Finite element modeling of geothermal source of heat pump in long-term operation

Heat pumps become more and more popular heat source. They can be an alternative choice for obsolete coal fired boilers which are emissive and not ecological. During heat pump installation designing process, especially for heat pumps with higher heating capacity (for example those suppling larger buildings), a simulation of heat balance of ground heat source must be provided. A 3D heat transport model and groundwater flow in the geothermal heat source for heat pump (GSHP) installation was developed in FEFLOW according to Finite Element Modelling Method. The model consists of 25 borehole heat exchangers, arranged with spacing recommended by heat pump branch guidelines. The model consists of both a homogeneous, non-layered domain and a layered domain, which reflected differences in thermal properties of the ground and hydrogeological factors. The initial temperature distribution in the ground was simulating according to conditions typical for Europe in steady state heat flow. Optimal mesh refinement for nodes around borehole heat exchangers were calculated according to Nillert method. The aim of this work is to present influence of geological, hydrogeological factors and borehole arrangement in the energy balance and long term sustainability of the ground source. The thermal changes in the subsurface have been determined for a long term operation (30 years of operation period). Some thermal energy storage applications have also been considered.

某重载型商用车动力舱气液联合热平衡仿真与优化

某重载型商用车动力舱气液联合热平衡仿真与优化

外皮・躯体と設備・機器の総合エネルギーシミュレーションツール「BEST」の開発（その173） 自然換気併用外気制御システムをもつゾーンの熱平衡計算

外皮・躯体と設備・機器の総合エネルギーシミュレーションツール「BEST」の開発（その173） 自然換気併用外気制御システムをもつゾーンの熱平衡計算

自然換気併用外気制御システムをもつ空調室の熱負荷計算法に関する研究

This paper presents a thermal load simulation method for spaces conditioned by heating, cooling and fresh air control systems combined with natural ventilation. Fresh air control systems enables free cooling, demand control ventilation and energy recovery ventilation. Natural ventilation may be carried out while spaces are conditioned by cooling equipment. For simulation of natural ventilation, many conditions which must be satisfied for natural ventilation can be considered and the under limit of space air temperature is supposed to be controlled by regulating ventilation opening area. On the other hand, natural ventilation rate is calculated under the simple conditions where airflow balance is not solved and the location of the neutral zone is assumed to be fixed. Space air temperature control by free cooling and heat recovery ventilation can be simulated. In demand control ventilation, ventilation rate is estimated in proportion of occupancy rate For heat balance simulation of multi zones where fresh air control systems combined with natural ventilation are used, a new method was developed in order to enable speedy simulation and to avoid complicated procedure. In the proposed method for iterative solution of heat balance and fresh air rate which means sum of natural ventilation rate and forced ventilation rate for free cooling, space air temperature control by regulating fresh air rate is replaced for control by a virtual heater and cooling and heating capacities are intentionally increased. This procedure suppresses iteration of calculating fresh air rate and the solution such as heating rate, cooling rate and fresh air rate can be obtained by correcting the calculated results. The proposed simulation method was applied to the building simulation engine in BEST which is a whole building energy and thermal load simulation program and the simulations for a typical office building located in Tokyo were performed. The basic effects of fresh air control techniques and natural ventilation on space thermal environment and thermal load were presented. The interaction effects of energy saving strategies such as high performance building facades, natural ventilation and fresh air control techniques were evaluated through simulations in two buildings. One is a low-performance building and the other is a high-performance building. The energy saving rate for a low-performance building is defined as the thermal load reduction achieved by adding an energy saving strategy, and that for a high-performance building is defined as the thermal load increase resulted by removing the strategy employed in the high-performance building. Although some strategies provide lower energy savings for the high-performance building than for the low-performance building, a few strategies are more effective for the high-performance building.

Estimating heat transfer losses caused by alkali salt deposits in biomass combustion

The results of a simulation of heat balance in the tube side of a heat exchanger operating in the superheated steam zone of a biomass combustion boiler are presented. The alkali salt deposits on the surface of the exchanger interfere with the heat transfer from hot gases to the superheated steam. A theoretical model has been used to assess the layer growth of these deposits depending on different operational parameters and to study the influence on the heat transfer rate. The weight of some variables such as the superheated steam temperature and pressure, the diameter of the heat exchanger tube or the particle diameter on the heat transfer losses is low (<1%) in the studied range. Other parameters, such as the hot gas temperature, concentration of alkali salts or gas speed, have a higher influence up to 4, 10 and 15%, respectively.

The influence of doping on flash sintering conditions in SrTi1−xFexO3−δ

Joule heating in flash sintering depends on the sample resistance, which is linked to the charged defects concentration. To study the contribution of defects on the flash sintering mechanism, this link should be untied. In SrTi1−xFexO3−δ (STFO) system, point defect concentration can be pinned while the resistance is influenced by the oxygen partial pressure (pO2). SrTi0.97Fe0.03O2.985 onset temperature at different pO2 was examined at constant oxygen vacancy concentration. The furnace onset temperature decreases with increasing pO2. The onset temperature of five STFO samples was predicted based on resistance-temperature dependency of the porous green ceramics in a dynamic heat balance simulation. High compatibility of model and experimental results showed reduction of onset temperature with increasing doping. Ex-situ impedance measurements of green samples reveal an overlapping Nyquist plots close to the sample onset temperature. This indicates that the onset is determined by the green body resistance regardless how it has been achieved.

Development of the Vertical Swirling Melting Furnace with Multistage Air Nozzles for a Municipal Solid Waste Gasification and Melting System

The melting furnace of a municipal solid waste gasification and melting system must have a high slag recovery rate and low dioxin emission. In this study, we developed a vertical swirling melting furnace with multistage air nozzles which can be used in the gasification and melting system. Three stage nozzles for feeding air and fuel are installed on a cylindrical furnace. Each nozzle is arranged in a tangential direction to generate swirling flow. The fuel is supplied by the primary nozzle which is located at the lowest level among the nozzles. Combustion air is supplied by the secondary and tertiary stage nozzles. The flow pattern of this furnace is similar to that of a cyclone separator. Most of the fuel goes down to the bottom of the furnace and burns in the swirl flow. The furnace design was done using a one-dimensional heat balance simulation tool. In this simulation, distribution of air mass flow in the furnace was determined by an air flow model experiment. The simulation results were compared with measured data from a 20t/day demonstration plant, and accuracy of the developed design tool was verified. The temperature prediction error was less than 40 degC. In the demonstration plant, the slag recovery rate of the melting furnace was higher than 90%, and the dioxin concentration in the flue gas at the chimney was lower than the government regulation value.

STUDY OF ENVIRONMENTAL DESIGN APPROACH USING THE HEAT BALANCE SIMULATION TOOL IN COLD REGIONS

This research studies the application of the evaluation technique of thermal comfort in the outer spaces of urban areas, focusing on thermal environment evaluation indexes, i.e. HIP, MRT and thermal storage (thermal insulation), to the heat balance simulation tool in cold regions in Ulaanbaatar, Mongolia, climatically characterized by extreme cold and dry where urbanization is rapidly spreading. In addition, the research presents whether the environmental design of city blocks using the heat balance simulation tool in cold regions will help restrain the consumption of resources and reduce environmental burdens, and the methodology and the concept of creating living environments.This paper reports the research frame and technique to apply the heat balance simulation tool, which was developed as a design support and environmental design tool mainly for reducing the heat island effect and cooling the city, to the cold regions, the results of a field survey on the information about buildings and the surface of the ground, and the collection and preparation of data required to perform heat balance simulations.

DEVELOPMENT OF A NUMERICAL SIMULATION METHOD FOR PREDICTING AND EVALUATING THE MICROCLIMATE IN THE DEVELOPED URBAN LOCATIONS WITH EVAPORATIVE VOID-BRICK WALLS

The present paper describes a coupled method of CFD and heat balance simulation for predicting and analyzing the microclimate in the developed urban locations where void-brick walls with evaporative cooling effect were applied. The heat balance simulation is performed using the 3D CAD-based thermal environment simulator developed by the authors’ group. A methodology of data transfer between the heat balance simulation and CFD simulation was proposed in this study. In order to present the usefulness of the proposed method, a case study was carried out for quantifying the microclimatic modifying effect of the void-brick wall applied to a rest station.

Thermal design tool for outdoor spaces based on heat balance simulation using a 3D-CAD system

This paper focuses on the development of a thermal design tool for use in planning outdoor spaces by combining a heat balance simulation for urban surfaces, including buildings, the ground and greenery, with a 3D-CAD system that can be run on a personal computer. The newly developed tool is constructed by improving the previous simulation model, which uses the geographic information system (GIS) for the input data. The simulation algorithm is constructed so as to predict the surface temperature distribution of urban blocks while taking into account the actual design of the outdoor space using the 3D-CAD system. A method of multi-tracing simulation to calculate the sky view factor and radiative heat transfer is established. The optimal mesh size is examined for the tool so as to provide detailed spatial geometry within a suitable calculation time. The simulation model is integrated with an all-purpose 3D-CAD software, and the pre-processing method are constructed for practical use. The results obtained by applying this simulation tool to an area of detached houses reveals that the tool is able to evaluate the effects of building shape, materials, and tree shade on the surface temperature distribution, as well as the MRT and HIP, which are evaluation indices of the outdoor thermal environment.

大学校舎のソーラーチムニーの換気性能評価と設計法に関する研究

A sustainable college building with 2 solar chimneys was completed in the Spring of 2004. Since then, authors have continued to measure natural ventilation rate using SF6 and C2H4 as tracer gases to know those of class rooms and whole building. At the same time, thermal conditions, air flow directions and pressure differences were also measured.Based on these data, multi rooms ventilation calculation models were developed, by which effects of some improvements for chimney systems were examined. At the next step, the authors have developed heat balance simulation model around chimney, which showed good accordance with measured values and adequate heat capacities of construction materials were studied to get constant ventilation rate through a day.

屋外の空間形態と構成材料を考慮した建築伝熱シミュレーションモデルの開発

Numerical simulation for calculating the heat transmission between indoor and outdoor spaces was developed in order to simulate the indoor air temperature and the heat load of building considering the effects of spatial form and material in outdoor space. This method was realized by combining the heat load calculation method with the heat balance simulation on external building surfaces. Calculation method of heat transmission and way of data transfer between the two simulation models were established. Influences of error factors of the heat balance simulation on the indoor air temperature, calculated by the heat load simulation, were confirmed. The application results of the developed simulation model showed that this simulation could predict the effects of spatial shape and material in outdoor space, tree's arrangement and size, on the indoor air temperature of the adjacent house.

土地利用と熱環境対策からみた都市街区におけるヒートアイランドポテンシャルの特徴

In this study, characteristics and variations of Heat Island Potential (HIP) on urban blocks were examined from a viewpoint of land use and countermeasure for thermal environment in order to obtain knowledge about the influence factor on sensible heat flux from all surface of urban blocks. First, four types of land use, commercial/business, residential, industrial and main road, were selected for analysis. All surface temperature and HIP of urban block was calculated by heat balance simulation at 28 cases on clear sky day in summer. It was clarified that HIP of each model was different characteristically, and material of urban block, planting method and room temperature of building influenced largely on that. Especially, drop of HIP by tall trees planting was remarkable.

Analysis of the influence of urban form and materials on sensible heat flux — a case study of Japan's largest housing development “Tama New Town”

In this study, the relationship between the form and materials of urban blocks and sensible heat flux from total surfaces was analyzed in the case of `Tama New Town', which is one of the largest housing developments in Japan and is under continuing development. First, urban blocks were divided into five categories depending on the building plot types. The characteristics of the form and thermal properties of each building, as well as the land cover condition (area of vegetation, bare soil, asphalt pavement, and built area) of each category was considered. Furthermore, 6 urban blocks were selected for numerical simulation of heat balance of the total surfaces, and sensible heat flux from the total surfaces of each urban block on clear sky summer day was calculated. It was confirmed that the influence of the direction that buildings faced and floor area ratio was as great as that of building materials upon the amount of sensible heat flux in each urban block.

スムージング技術を用いた熱画像シミュレーションによるサーモグラフィー法の適用限界に関する解析的研究

The thermographic survey using thermal imager is considered to be a method for detecting the surface temperature differences between the delaminated area and the sound area of finishing materials on building walls. So, there exist some analytical studies using heat balance simulation on this method. However the numerical result obtained by a heat balance simulation can not always represent the easiness of judgement. In this study, by making simulated thermal image using finite element method with smoothing technique, the limitations of the method are discussed from a visual standpoint