Amount Of Heat Loss Research Articles

산소부화용 공업로의 운전조건이 열효율에 미치는 영향

After a reheating furnace installation, the modification of the size and the heat capacity is very difficult. Therefore, the development of design package tool is required for the computation on the correct specifications before the design and the installation. Prior to development of the design tool, a module that calculates the amount of heat loss of each part according to the specifications for determining the thermal efficiency of a continuous heating furnace was developed and applied to the oxy-fuel industrial furnace. Through this, the effects of fuel type, oxygen fraction and recirculation on the efficiency of the furnace of which the output is 110Ton/hour were analyzed. In oxy-fuel combustion condition, the efficiency was 15% higher than air combustion conditions. With the using COG(Coke Oven Gas) instead of LNG, the efficiency was slightly increased. In the air combustion condition, the efficiency was increased about 33% with the preheated air. But, in oxy-fuel condition, the amount of exhaust gas was reduced, so the efficiency was increased about 7%.

Analysis of Reversed Trapezoidal Fins using a 2-D Analytical Method

This paper presents a two-dimensional analysis of reversed trapezoidal fins with variable fin base thickness. Heat loss from the reversed trapezoidal fin is presented as a function of the fin shape factor, fin base thickness, and fin base height. The relationship between the fin tip length and the convection characteristic number, as well as that between the fin tip length and the fin base height for equal amounts of heat loss are analyzed. In addition, the relationship between the fin base thickness and the fin shape factor for equal amounts of heat loss is presented. One of the results shows that the heat loss decreases linearly with the increase in the fin shape factor.

Analysis of the heat losses associated with the SAGD visualization experiments

Dealing with the heat losses associated with steam-assisted gravity drainage (SAGD) experiments has been an issue for which different heat loss prevention techniques have been developed and utilized in the literature. The aim is to minimize the amount of heat losses from the porous medium to the surrounding environment. Excessive heat losses negatively affect quantifying the energy requirements of the SAGD experiments. In this study, an inverted-bell vacuum chamber was employed to minimize the excessive heat losses while steam was injected under different superheating levels. Local temperatures along the glass micromodels’ height and width were recorded on a real time basis. Details of the heat losses associated with our pore-scale SAGD visualization experiments are described in this paper. According to the results presented, employing extremely low vacuum conditions resulted in effective heat loss prevention in a sense that the convective element of heat loss could be neglected. As a result, radiation heat transfer was the only mechanism of heat transfer that contributed to the heat loss from the micromodels’ surfaces. In each pore-level SAGD experiment, the overall steam consumption to produce one unit of the mobile oil was corrected based on the heat loss analysis of the process to account for the additional volume of steam which was condensed because of the heat loss. The net cumulative steam consumed, corrected for the heat losses, was in very good agreement with the predictions made based on the theory of gravity drainage and its application in performance analysis of the SAGD process.

Determining heat loss into the environment based on comprehensive investigation of boiler performance characteristics

A refined procedure for determining heat loss into the environment from heat-generating installations is presented that takes into account the state of their lining and heat insulation quality. The fraction of radiative component in the total amount of heat loss through the outer surfaces is determined. The results from experimental investigations of the thermal engineering and environmental performance characteristics of a foreign hot-water boiler in firing wood pellets are presented. A conclusion is drawn about the possibility of using such hot-water boilers for supplying heat to low-rise buildings, especially for the conditions of the North-Arctic region. The results from a thermal engineering investigation of wood pellets and furnace residue carried out on installations of a thermal analysis laboratory are presented together with the grain-size composition of fuel and indicators characterizing the mechanical strength of wood pellets. The velocity fields, flue gas flow rates, and soot particle concentrations are determined using the external filtration methods, and the composition of combustion products is investigated using a gas analyzer. The graphs of variation with time of boiler external surface temperature from the moment of achieving the nominal mode of operation and heat loss into the environment for stationary boilers are presented.

Extended Heat Loss and Temperature Analysis of Three Linear Fresnel Receiver Designs

Heat loss prediction models for parabolic trough receivers do not consider the thermal effect of a secondary mirror. As an extension a Thermal Resistance Model (TRM) has been developed at Fraunhofer ISE for the prediction of the heat loss of three different Linear Fresnel Collector (LFC) receiver configurations. In previous investigations we have found the energy balance of a LFC receiver to be strongly influenced by the amount of solar radiation absorbed by the secondary mirror. This absorption provokes an increase of temperature of the secondary mirror and hence a decrease in the total amount of heat loss of a LFC. The size of this effect depends on the receiver geometry and diverse ambient parameters. Investigated parameters are wind velocity, ambient temperature and Direct Normal Irradiance (DNI). This dependency and its effect on heat loss and secondary mirror temperatures are analyzed for three different LFC receiver configurations. As the radiation absorbed by the secondary mirror is affected by the aperture area of the LFC, studies are performed for small-scale and for large-scale collectors.

ARC FURNACE WATER COOLED ELEMENTS HEAT WORK ESTIMATION AT DIFFERENT CONSTRUCTION ELECTRODES APPLICATION

The article discusses the increase in efficiency of the water-cooled heat elements of modern electric arc furnaces using mathematical modeling using electrodes of different design, namely conventional (solid) and hollow (tubular). In the mathematical modeling showed that the use of hollow (tubular) electrodes can significantly improve the thermal performance of water-cooled elements arc steel furnaces, reduce the amount of heat loss of 120 kW/m2. The results of computer simulations are in qualitative agreement with the data on physical models, thus promising applications of hollow (tubular) electrodes in a production environment.

Pilot Study on In-depth Water Saving and Heat Recovery from Tail Flue Gas in Lignite-fired Power Plant

In lignite-fired power plants, the high water content of lignite (35-40%) is responsible for significant reductions in boiler efficiency due to the large amounts of heat loss experienced through water evaporation during coal combustion. Installation of a water condensation device in the outlet of the desulfurization absorption tower can recover substantial amounts of water and latent heat from the flue gas that containing saturated steam. In the present study, a pilot test platform was built into a 600MW lignite-fired power plant, and a 50,000m3/h flue gas flow was been extracted and cooled by 5°Cduring the test. Using our theoretical model for this energy efficiency innovation, the test results demonstrate that 129.5GJ/h of latent heat can be recovered and 61.6t/h condensate water can be collected from the flue gas (2,500,000m3/h) for the600MWlignite-fired power plant. The wet flue gas desulphurization system (wet FGD) consumes the supplemental water of 60-80 t/h for this power plant. Consequently, the water recovery quantity of 73 t/h demonstrate that zero net water consumption can be achieved by returning the recovered water back into wet FGD.

외기온도 변화에 따른 지역난방 공동주택 다중 열공급제어 알고리즘 개발에 관한 해석적 연구

In this study, we developed a heat supply control algorithm that minimizes the heat loss in the heat distribution pipelines used for supplying heat energy to shared group housing. Controlling the temperature and flow rate of the hot water supplied to the heat exchanger for shared group housing enables us to develop a heat supply control technique that meets the heating load required by each household in a shared apartment building in accordance with changes in the outdoor air temperature, and that minimizes the heat loss occurring in the heat distribution pipeline. A one-year study in 2008 on a 1,473-household D-apartment building in Hwaseong, Gyeonggi-do, South Korea, compared the heat capacity used by each household, as well as the heat capacity supplied to the heat exchanger room of the apartment housing building, to calculate the amount of heat loss in the heat distribution pipeline. The results confirmed that 24.1% of the heat supplied was lost in the piping.

The Wall Heat Transfer Phenomenon of Premixed CH4/Air Catalytic Combustion in a Pt Coated Microtube

In this paper, a 2D model with detailed heterogeneous chemical mechanism has been employed to investigate the heat transfer phenomenon of premixed CH4/air catalytic combustion in a Pt coated microtube. Especially, the thermal processes such as coupled heat transfer between the internal surface of the microtube and the gas phase, thermal conduction along the solid structure, convection and radiation between the external surface and the environment are comprised in the simulation. The results show that the thermal conductivity of different solid wall materials dramatically affects the uniformity of temperature distribution of the catalytic surface. To maintain stable combustion in the microtube, the thermal conductivity should exceed 0.49 W/m/K at least and conductive walls (FeCr alloy and corundum ceramic) are more appropriate to manufacture microcombustors. The extremely small Biot number at the external surface indicates that convective heat transfer coefficient and emissivity to the environment are the key factors determining the heat loss of the microtube. The amount of heat loss influences the reaction rate and residence time of the mixtures in the microtube, which would affect the conversion of CH4. An increase of the wall thickness improves the heat transfer along the solid structure, also increases the total heat loss.

Global Effects of MWCNT-W Nanofluid in a Shell & Tube Heat Exchanger

Global warming and other problems can be reduced by effectively using the available materials and facilities. Heat exchangers play an important part of the field of energy conservation, conversion and recovery. Shell & tube heat exchangers are widely using in industrial processes and power plants. Suspension of small amounts of nanoparticles into the base fluid called nanofluid can reduce the global energy losses. Thermal conductivity of Multi Walled Carbon Nanotube (MWCNT) is highest among the different nano materials [1]. Therefore, in this paper, the overall performance of a shell & tube heat exchanger has been analytically investigated by using MWCNT-W nanofluid with 0.02-0.1 vol. fractions of MWCNT and compared with water. Mathematical formula, specifications of heat exchanger and nanofluid properties were taken from the literatures to analyze the energy performance and other effects within the system. It is found that for certain mass flow rates of nanofluid and base fluid, the convective heat transfer coefficient increased around 4% to 17% compared to pure water, respectively for 0.02-0.1 vol. fractions of MWCNT in water. However, for constant vol. fractions of MWCNT, convective heat transfer coefficient of the above nanofluid negligibly changed for different mass flow rates. Furthermore, energy effectiveness of the heat exchanger also improved approximately by 3% to 14%, respectively. This energy effectiveness again improved with the decrease of the mass flow rates of nanofluids (tube side) and increase of the mass flow rates of base fluid (shell side). As energy effectiveness is increased by using MWCNT-W nanofluid, therefore, a significant amount of heat losses will be reduced. As a result, with the reduced heat emissions, global warming and greenhouse effects can be reduced by using MWCNT-W nanofluid as working fluid in shell & tube heat exchanger system.

Cooling Coffee without Solving Differential Equations

SummaryA classic textbook problem is to show, assuming Newton's law of cooling, that if cold milk is added to coffee that has been cooling down, the result will be colder than if the milk was added at an earlier time. We formulate and prove a theorem that shows this holds when the linear function of Newton's law is replaced by any function satisfying a certain weak convexity condition. This is relevant to the real-world problem, since Newton's law is not an adequate model for cooling liquids; it ignores the large amount of heat loss due to evaporation, as well as the smaller loss due to radiation.

Analysis of Heat Losses of Absorber Tubes of Parabolic through Collector of Shiraz (Iran) Solar Power Plant

In this article heat losses of absorber tubes of parabolic trough collectors for the collector field of 250 kW Shiraz (Iran) solar thermal power plant is evaluated for various conditions. For analysis, both experimental measurements and numerical modeling are made to find the impact of failure of heat collecting tubes. The amount of heat losses are compared numerically for 3 different types of tubes; vacuum, lost vacuum (air) and broken glass (bare) tube. The experimental measured data are used to validate the numerical simulation. For temperature measurements around the glass tube and absorber tube an infrared thermograph (IR) camera is used. Thermal images are calibrated with measuring some local temperatures. For theoretical simulation a commercial code for thermal analysis of parabolic collectors are used. An absorber tube with vacuum reduces significantly the heat losses in comparison with broken tube or tube without vacuum. During power plant operation poor isolation or any glass tube failure should be avoided for any solar thermal power plants.

Comparison of Heat Losses for Different Shapes and Size Volumes

The shape of a house significantly affects the amount of heat loss. Compact building, especially without various projections, has a smaller proportion of the cooled surface of the floor surface area and its volume. The ideal shape is a sphere, but in terms of practical use in the cube or block layout is preferable. For this purpose, were created on the same ground plan standards areas and various levels of the circuit. These demonstrate the amount of heat loss, depending on the shape of the object.

Research of Bilayer Stacked Resistance Switching Memory Structure Based on Pt/NiO/TiO2/Pt

The large power consumption and the wide distribution of switching parameters for unipolar resistance switching are major hurdles to non-volatile memory application. In this letter, the stacked structure Pt/NiO/TiO2/Pt was investigated to overcome the mentioned problems. TiO2 thin film was formed on NiO by oxidation of metallic Ti thin film through rapid thermal process (RTP) in oxygen atmosphere. The sharp TiO2 (202) peak and NiO (200) peak observed by the X-ray diffraction measurement. This stacked bilayer structure is favorable for reducing reset current in comparison with single layer structure. This is attributed to a small amount of heat loss during rupturing process of conductive filaments. It is suggested that the conductive filament rupture and rejuvenation was happened at the interface between TiO2 and NiO by controlling switching sequence. Furthermore, the diffused Ti in NiO also can result in stabilization of switching parameters.

Factors Regulating the Air–Sea Heat Fluxes Regime over the Aegean Sea

Abstract The authors examine the impact of low-frequency atmospheric forcings on the air–sea heat fluxes over the Aegean Sea. The correlation between the air–sea heat flux components and three established [North Atlantic Oscillation (NAO), east Atlantic–western Russian pattern (EAWR), and North Sea–Caspian pattern (NCP)] and two testing climatic indices of potential effect over the eastern Mediterranean Sea region underlines significant discrepancies between the radiative (shortwave and longwave radiation) and the turbulent (sensible and latent heat) components. The NAO index affects the air–sea heat fluxes over the Aegean Sea region much less than the two innovative indices, the “Mediterranean index” and the “Eastern Europe index,” which play more effective roles. Moreover, the influence of the sea level atmospheric pressure (SLP) variability over an extended area (Europe and North Africa) on surface fluxes regime is investigated. The SLP anomalies are corroborated as a prominent regulating factor of the air–sea heat fluxes over the Aegean Sea region, especially during the cold season of the year. The analysis of the extreme values in the heat exchange anomalies for the period 1958–2001 highlights the role of SLP field on determining the air–sea heat fluxes regime, mainly during winter, when, occasionally, large amounts of heat loss from the sea surface trigger the mechanism of intermediate- and deep-water formation. It is suggested that wind regime and turbulent components are the modulators of the net air–sea heat flux anomalies throughout the year.

Toughness improvement in coarse grain heat affected zone of X70 pipeline steel by accelerated cooling

For in-service welding, a large amount of heat loss through the pipe wall is created by the flowing gas, resulting in accelerated cooling of the weld. In the present paper, the thermal simulated specimens were used to investigate the microstructure and mechanical properties in coarse grain heat affected zone (CGHAZ) of in-service welding X70 pipeline steel. The simulated results indicate that the embrittlement phenomenon in the CGHAZ is not serious for X70 pipeline steel at cryogenic temperature by accelerated cooling. Microstructure analysis suggests that the improvements in CGHAZ toughness can be explained not only by the amount of martensite–austenite constituents, but also by the presence of austenite films. From all the results obtained, a mechanism for toughness improvement among CGHAZs is proposed and discussed.

Comparative study on carbon monoxide stratification and thermal stratification in a horizontal channel fire

Carbon monoxide (CO) stratification and its relationship with thermal stratification are quite important for dealing with issues related to building fire safety. This experimental study compares the CO stratification and thermal stratification in channel fires. The results show that the relationship between CO stratification and thermal stratification depends on heat loss intensity from smoke flow to walls. In the conditions with considerable amount of heat loss, the vertical gradients of CO volume concentration are smaller than those of temperature rise beneath the ceiling. However, in the conditions with negligible heat loss, the vertical profile of dimensionless CO volume concentration becomes similar with dimensionless temperature rise. The longitudinal ventilation, as a prevailing smoke control or ventilation method, has a strong effect on the relationship between CO stratification and thermal stratification. A larger longitudinal air flow velocity leads to smaller heat loss intensity from smoke flow to walls and thus a higher similarity between CO stratification and thermal stratification.

Thermal transmittance measurements with the hot box method: Calibration, experimental procedures, and uncertainty analyses of three different approaches

A large amount of heat loss through building envelopes takes place via inhomogeneous components such as windows, doors, and thermal bridges. This loss can be approximated by measuring in lab the actual thermal transmittance of these components with the use of a hot box. The calibration and experimental procedures can be performed, taking into account three standards for calibrating hot boxes: the European EN ISO 8990; the American ASTM C1363-05; and the Russian GOST 26602.1-99. An experimental setup for testing the accuracy of these standards has recently been created at the University of Perugia; after a measurement campaign for the validation of the test rig, the differences of the approaches were evaluated. Results showed that although the EN ISO 8990 and ASTM C1363-05 are similar in terms of procedures definition, methodology of thermal transmittance calculation, and level of uncertainty, the GOST 26602.1-99 differs from the others since it adds individual measurements of the thermal characteristics of each sample component. The analysis highlighted that the ideal procedure should include the Russian method to define the thermal behavior of each component under analysis, with a contemporary validation of the global results to be performed with one of the other two approaches.

INVESTIGATION OF HEAT INSULATION PERFORMANCE OF DIFFERENT WALL VARIETIES USED IN BUILDINGS

In this study, the most preferred types of wall heat insulation performance are determined experimentally. For this purpose, with the actual construction features 1/3 of a reinforced concrete structure can be manufactured and column spans are built with six different wall element. These materials are extensively used in the production of housing; horizontal hollow brick, the vertical hollow brick, pumice, aerated concrete blocks, brick and sandwich wall. A heat source placed inside the model building, with the help of thermo couples fixed to the internal heat is provided. The building operated for 30 days with a heat source to provide heat balance and every wall surface of the thermal images were taken with the camera. The images and heat values are interpreted, heat efficiency of the wall varieties are defined. Consequently, the wall varieties's thermal conductivity resistance, thermal conductivity coefficient and the amount of heat loss have been identified.

ANALYSIS OF A REVERSED TRAPEZOIDAL FIN USING A 2-D ANALYTIC METHOD

A reversed trapezoidal fin is analyzed using a two-dimensional analytical method. Heat loss from the reversed trapezoidal fin is presented as a function of the fin shape factor, fin base thickness and the fin base height. The relationship between the fin tip length and the convection characteristic number as well as that between the fin tip length and the fin base height for equal amounts of heat loss are analyzed. Also the relationship between the fin base thickness and the fin shape factor for equal amount of heat loss is presented. One of the results shows that the heat loss decreases linearly with the increase of the fin shape factor.