Increased Temperature Levels Research Articles

Experimental research on slip-resistant bolted connections after fire

Slip factor and bolt pre-tension force for slip-resistant bolted connections after fire were investigated experimentally. 74 connections made up of four plates and four class 10.9 bolts were first heated to specified temperature levels, and then cooled to ambient temperature and tested. Slip load tests were conducted to obtain the slip factor and bolt pre-tension force for the post-fire connections. In case of slip factor tests the bolts in connections after fire were replaced by new bolts and the pre-tension in the new bolts was measured, so the slip factor could be determined from the post-fire slip load. While in case of bolt pre-tension tests the old bolts were kept and the residual pre-tension was calculated based on the slip factor data obtained from accompanying tests. Two friction surface treatment methods were considered which were blast-cleaning (Class A) and inorganic zincs paint coated after blast-cleaning (Class B). Nine temperature levels from 200°C to 700°C were considered. Test results show that heating–cooling process has significant effects on both slip factor and bolt pre-tension force. The slip factor after fire increases with increasing temperature level, and residual bolt pre-tension force decreases with increasing temperature level. The increase in slip factor for Class A friction surface is much greater than that for Class B friction surface. Tri-linear models are proposed to calculate the normalized slip factor and bolt residual pre-tension force for slip-resistant 10.9 bolted connections after fire. New suggestions are proposed for post fire checking of slip-resistant bolted connections.

Steady shear rheological characteristics of model system meat emulsions: Power law and exponential type models to describe effect of corn oil concentration.

The effect of oil concentration (57.50, 58.75, 60.00 and 61.25%) and temperature (5, 10 and 15 ºC) on steady shear rheological properties of O/W model system meat emulsions were investigated. The effect of temperature and oil concentration was modeled using power law and exponential type functions. The meat emulsions showed non-Newtonian flow behavior because flow behavior index was lower than unity. Consistency coefficient and flow behavior index values of O/W model system meat emulsions were calculated using Oswald de Waele model with higher coefficients of determination. Apparent viscosities of emulsions at a specified shear rate (50s(-1)) were in the range of 0.652-0.941Pas. Increasing oil concentration provided an increase in apparent viscosity and increase in temperature levels resulted a decrease in consistency coefficient values. The exponential function performed better than the power-law function (R (2) > 0.922) in terms of describing the effect of oil concentration on the steady shear rheological properties of the model system meat emulsions. Higher coefficients of determination (R (2) = 0.979-0.999) were observed in exponential-type function compared to a power law function (R (2) = 0.880-0.946).

Heat transfer and air movement behaviour in a double-skin façade

Theoretical and practical evaluation of a naturally ventilated double skin facade has been undertaken. The study has shown that the double skin facade (DSF) system is capable of supplying adequate ventilation to various levels with little or no additional heating during winter thus saving the bulk percentage of the heating load on the building. However there was an element of overheating in the DSF which may have contributed to an additional cooling load on the building. Even though the operational strategy of mixing return air with trapped air in the cavity helped to minimise the overheating effect, there was still some considerable level of temperature increase in the DSF. Effective thermal management control strategies and systems are therefore encouraged in the design and operation of DSFs.

Thermal habitat constraints on zooplankton species associated with Atlantic cod (Gadus morhua) on the US Northeast Continental Shelf

The US Northeast Continental Shelf is experiencing a period of increasing temperature levels and range, which impacts the quantity of thermal habitats within the ecosystem. With increasing temperatures, the amount of warmer, surface water thermal habitats (16–27°C) has increased while there has been a reciprocal decline in cooler water habitats (5–15°C). These cooler water habitats are the most abundant and comprise the core habitats of the ecosystem. The coldest thermal habitats (1–4°C), however, have increased slightly in amount or have remained constant, reflecting a discontinuity in the progression of warming along a latitudinal gradient. This discontinuity may be the result of recent changes in the circulation of water masses in the northern Gulf of Maine, potentially associated with the Labrador Current. The contraction of core thermal habitats appears to have had biological consequences on multiple trophic levels. In particular, two zooplankton species associated with the larval feeding of Atlantic cod, Gadus morhua, have declined in abundance in the same areas where cod populations have exhibited continually poor recruitment. The zooplankton species group Pseudocalanus spp., which is associated with winter-spawning cod, has declined on Georges Bank and in the Eastern Gulf of Maine. The zooplankton Centropages typicus has declined in the Gulf of Maine during late summer into fall, potentially affecting spring-spawning cod in that area. These observations are consistent with the hypothesis that portions of the population complex of cod have lower reproductive output due to changes in zooplankton abundance, which we associate with the distribution of temperatures within the ecosystem.

Ocean acidification mediates photosynthetic response to UV radiation and temperature increase in the diatom <i>Phaeodactylum tricornutum</i>

Abstract. Increasing atmospheric CO2 concentration is responsible for progressive ocean acidification, ocean warming as well as decreased thickness of upper mixing layer (UML), thus exposing phytoplankton cells not only to lower pH and higher temperatures but also to higher levels of solar UV radiation. In order to evaluate the combined effects of ocean acidification, UV radiation and temperature, we used the diatom Phaeodactylum tricornutum as a model organism and examined its physiological performance after grown under two CO2 concentrations (390 and 1000 μatm) for more than 20 generations. Compared to the ambient CO2 level (390 μatm), growth at the elevated CO2 concentration increased non-photochemical quenching (NPQ) of cells and partially counteracted the harm to PS II (photosystem II) caused by UV-A and UV-B. Such an effect was less pronounced under increased temperature levels. The ratio of repair to UV-B induced damage decreased with increased NPQ, reflecting induction of NPQ when repair dropped behind the damage, and it was higher under the ocean acidification condition, showing that the increased pCO2 and lowered pH counteracted UV-B induced harm. As for photosynthetic carbon fixation rate which increased with increasing temperature from 15 to 25 °C, the elevated CO2 and temperature levels synergistically interacted to reduce the inhibition caused by UV-B and thus increase the carbon fixation.

Temperature, traffic-related air pollution, and heart rate variability in a panel of healthy adults

BackgroundBoth ambient temperature and air pollution have been associated with alterations in cardiac autonomic function, but the responsive patterns associated with temperature exposure and the interactive effects of temperature and air pollution remain largely unclear. ObjectivesWe investigated the associations between personal temperature exposure and cardiac autonomic function as reflected by heart rate variability (HRV) in a panel of 14 healthy taxi drivers in the context of traffic-related air pollution. MethodsWe collected real-time data on study subjects’ in-car exposures to temperature and traffic-related air pollutants including particulate matter with an aerodynamic diameter ≤2.5μm (PM2.5) and carbon monoxide (CO) and HRV indices during work time (8:30–21:00) on 48 sampling days in the warm season (May–September) and cold season (October–March). We applied mixed-effects models and loess models adjusting for potential confounders to examine the associations between temperature and HRV indices. ResultsWe found nonlinear relationships between temperature and HRV indices in both the warm and cold seasons. Linear regression stratified by temperature levels showed that increasing temperature levels were associated with declines in standard deviation of normal-to-normal intervals over different temperature strata and increases in low-frequency power and low-frequency:high-frequency ratio in higher temperature range (>25°C). PM2.5 and CO modified these associations to various extents. ConclusionsTemperature was associated with alterations in cardiac autonomic function in healthy adults in the context of traffic-related air pollution.

Failure analysis of mechanically fastened glass fiber/epoxy composite joints under thermal effects

An experimental failure analysis has been carried out to determine the effects of thermal condition and tightening torque on the failure load and failure behavior of single lap double serial fastener glass fiber/epoxy composite joints. 40, 50, 60, 70, and 80°C temperatures were exposed to the specimens during tensile tests. It was seen that, the load-carrying capacity of the joint is decreased gradually by increasing temperature level. In proportion to the room temperature, the maximum decrease of failure loads occurs at 70°C and 80°C with the rate of nearly 55% and 70% respectively, because of the heat damage to the resin matrix. Besides thermal effects, 0 and 6Nm tightening torques were applied to observe how clamping forces affect the joint strength. The results proved that, tightening torque is effective not only at room temperature, but also at elevated temperatures and contributes to the joint strength.

Thermal–mechanical and isothermal fatigue of 304L stainless steel under middle range temperatures

The present study investigates the crack initiation in a 304L stainless steel under thermal fatigue using volume element tests designed to assess the endurance to engineering crack initiation in real structures under middle range temperature and fairly large number of cycles. The inelastic cyclic strain is significant in most testing conditions for this alloy, even for long tests. Regarding tests, thermal–mechanical fatigue life is compared with low cycle fatigue tests under isothermal conditions. Noteworthy, throughout the different studied ranges of applied temperature cyclic behavior of the alloy has shown an initial hardening followed by a cyclic softening. In addition, no clear effect in lifetime for the high strain range has been discovered. In fact, when exposed to various increasing temperature levels, the material endurance tends to decreases for low strain range (correspond to high number of cycle). A different behavior in cyclic hardening tests is identified between the In-Phase thermal–mechanical fatigue tests and the Out-of-Phase tests at temperature levels ranges between 90 and 165 °C. In-Phase thermal–mechanical test increases lifetime with respect to the Out-of-Phase test. The fracture surfaces for all tested conditions are characterized by a fatigue striation.

Thermal Stresses in Thick Walled Cylinders due to a Periodic Moving Heat Source: Effect of Material Properties

nternal heating of hollow cylinders with moving periodic heat source is examined in relation to surface treatment applications. This study includes three different cylinder materials, namely aluminum, nickel and titanium. Effective stresses in the cylinder wall are found to be mainly attributed to longitudinal temperature gradients. The aluminum cylinder shows sharper longitudinal temperature gradients as compared to the nickel and the titanium cylinders, which is due to the high value of the aluminum specific heat capacity. However, the larger Eα (elasticity modulus × thermal expansion coefficient) values for nickel cylinder result in higher levels of stress although nickel and titanium cylinders exhibit similar longitudinal temperature profiles. During dwelling time for the heating source at a certain spot, titanium cylinder exhibits lower levels of temperature increase as compared to aluminum and nickel cylinders, due to its lower value of thermal conductivity.

Effect of increasing temperature due to depletion of ozone layer caused by CFC on the dynamics of two competing populations: a model

It is well recognized that the greenhouse gas such as Chlorofluoro Carbon (CFC) is responsible for the increase in the average global temperature. The presence of CFC is responsible for the depletion of ozone concentration in the atmosphere due to which the heat accompanied with the sun rays are less absorbed causing increase in the atmospheric temperature of the Earth. The increase in temperature level may directly or indirectly affect the dynamics of interacting species systems. Therefore, in this paper, a mathematical model is proposed and analysed to asses the effects of increasing temperature on the survival or extinction of two competing populations.

Market Study of Whirlpool Air-Conditioners in Chennai

Marketing is the process of planning and executing the conception, pricing, promotion & distribution of ideas, goods & services to create exchanges that satisfy individual and organizational objectives”. The Marketing philosophy of business assumes that an organization can best service, prosper and profit by identifying and satisfying the needs of its customers. This however is a recent thinking. Various definitions of Marketing have been given from different perspectives, exchange and utility being the two important ones.Management must accept the assumption that profit goals will be reached through satisfied customers. Clearly, the path to profit is not a simple one; all business firms compete within a complex environment that demands astute management of organizational resources and efforts. Nevertheless, managers must have confidence that if their material needs by offering quality products at fair prices, their companies will make money. Similarly, not-for-profit organizations will achieve their financial and other goals if they satisfy their customers and members.Air conditioners are become compulsory in ones life due to changing environmental and ecological changes and increased temperature levels of the country. In this context the large number of customers is looking for economy models of air conditioners. Whirlpool is one of the popular brands producing and selling large number of air conditioners in the country. The present study is focused on finding the market potential of whirlpool air conditioners in Chennai city.

Mechanical and fracture properties of normal- and high-strength concretes with fly ash after exposure to high temperatures

This paper mainly reports an experimental investigation on the residual mechanical and fracture properties of normal and high-strength concrete (HSC) with and without fly ash after exposure to high temperatures ranging from 200 to 600°C. The fracture behaviour of concrete was investigated using the three-point bending notched beam test, according to RILEM recommendations. The effects of concrete strength, temperature level and the presence of fly ash on the fracture and mechanical properties of concrete were investigated. Some studies on the aggregate–cement paste transition zone have been made by means of a scanning electron microscope (SEM). The mechanical properties of concrete specimens significantly decreased with increase in temperature level, the extent of which depended on the presence of fly ash in the mix. In general, fly ash concrete performed better in residual mechanical and fracture properties especially at relatively high temperature levels than concretes without fly ash. Also, fewer and finer microcracks were identified in fly ash concrete under the SEM study.

Treatment of wastewater polluted with urea by counter-current thermal hydrolysis in an industrial urea plant

In this paper, the removal of urea from industrial wastewater by thermal hydrolysis was studied via modeling and simulation of counter-current urea thermal hydrolysis reactor. The features of our proposed model are (1) the use of Nakamura equation of state to predict the vapor fugacity coefficients and UNIQUAC equation to describe the non-ideality of liquid phase, (2) the use of multi-stage well-mixed model for the liquid and vapor flows with non-ideal rate-based model for urea thermal hydrolyser, (3) the reactions are assumed to take place in the liquid phase. The model incorporates reaction rates of urea hydrolysis and takes into account the effects of solution non-ideality and back mixing on the urea thermal hydrolyser performance. The rates of reaction are written in terms of activity of reactants which are determined using a thermodynamic framework for system of NH 3–CO 2–H 2O–urea mixture. The model provides temperature and concentrations distribution of different components in the liquid and vapor phases along the height of urea thermal hydrolyser. The predicted data of the model were consistent with the plant data indicating validity of the model. Also the effects of key parameters on the performance of urea thermal hydrolyser such as the temperature and flow rate of the steam and wastewater were examined. The results of this work show each parameter that causes an increase in temperature level along the urea thermal hydrolyser improves the urea removal efficiency.

Changes in wood-water relationship due to heat treatment assessed on micro-samples of three Eucalyptus species

Abstract Wood-water relationship of untreated and heat-treated wood was studied. Specimens of Eucalyptus grandis, E. saligna, and E. citriodora were submitted to five conditions of heat treatment: 180°C and 220°C with air; 220°C, 250°C, and 280°C with N2. The wood-water relationships were accurately studied in a special device, in which the moisture content (MC) of the sample was measured with a highly sensitive electronic microbalance placed in a climatic chamber. The dimensions of the sample were collected continuously without contact by means of two high-speed laser scan micrometers. Sorption curves and shrinkage-MC relationships were observed. To study the effects of heat treatment, the following parameters were also determined: fiber saturation point (FPS), wood anisotropy (T/R ratio), shrinkage slope, reduction in hygroscopicity, and anti-shrink efficiency (ASE). The physical properties were significantly affected only at 220°C and above. At heat temperature levels higher than 220°C, the reduction in hygroscopicity and ASE are higher than 40% and continue to be reduced with increasing temperature level. This work also demonstrates that heat treatment does not change the slope of the curves “shrinkage vs. MC”, proving that heat treatment affects the domain of alterations in wood properties, but not the behavior within this domain.

Habitat shifts of endangered species under altered climate conditions: importance of biotic interactions

AbstractPredicting changes in potential habitat for endangered species as a result of global warming requires considering more than future climate conditions; it is also necessary to evaluate biotic associations. Most distribution models predicting species responses to climate change include climate variables and occasionally topographic and edaphic parameters, rarely are biotic interactions included. Here, we incorporate biotic interactions into niche models to predict suitable habitat for species under altered climates. We constructed and evaluated niche models for an endangered butterfly and a threatened bird species, both are habitat specialists restricted to semiarid shrublands of southern California. To incorporate their dependency on shrubs, we first developed climate‐based niche models for shrubland vegetation and individual shrub species. We also developed models for the butterfly's larval host plants. Outputs from these models were included in the environmental variable dataset used to create butterfly and bird niche models. For both animal species, abiotic–biotic models outperformed the climate‐only model, with climate‐only models over‐predicting suitable habitat under current climate conditions. We used the climate‐only and abiotic–biotic models to calculate amounts of suitable habitat under altered climates and to evaluate species' sensitivities to climate change. We varied temperature (+0.6, +1.7, and +2.8 °C) and precipitation (50%, 90%, 100%, 110%, and 150%) relative to current climate averages and within ranges predicted by global climate change models. Suitable habitat for each species was reduced at all levels of temperature increase. Both species were sensitive to precipitation changes, particularly increases. Under altered climates, including biotic variables reduced habitat by 68–100% relative to the climate‐only model. To design reserve systems conserving sensitive species under global warming, it is important to consider biotic interactions, particularly for habitat specialists and species with strong dependencies on other species.

An experimental study on hydrogen–methane mixtured fuels

In this study, temperature distributions from turbulent chemical reactive flow inside a model combustor have been presented for various mixtured hydrogen–methane fuels. The gas emissions were also obtained at the combustor exit. A platinum–platinum 13% rhodium thermocouple (R type) was used for measurement of axial and radial temperatures. The axial and radial temperature measurements were taken from six various distances and four distances, respectively. Experimental measurements were made at excess air ratios of 1.2 and 1.7, two various thermal powers including 40 and 60 kW and two various hydrogen–methane blending fuels (volumetrically 30% H2–70% CH4 and 70% H2–30% CH4). The results show that the temperature level increases, CO and CO2 emissions decrease when the hydrogen content is increased in mixtured fuel, hydrogen–methane mixtured fuels are successfully used without any important modification in natural gas burner.

Light quality and temperature effects on antirrhinum growth and development

An experiment was carried out to examine the effects of light quality on the growth and development of antirrhinum under three different temperatures 19 degrees C, 24 degrees C and 27 degrees C in glasshouses. Five different colour filters (i.e. 'Red absorbing', 'Blue absorbing', 'Blue and Red absorbing' and two 'partially Blue absorbing' materials) were tested, with one clear polythene as a control. Plant height, internode length and leaf area were significantly affected by the spectral filters as well as the temperature. Analysis of color filter's effect on presumed photoreceptors to exist indicated that antirrhinum plant height was regulated by the action of a blue acting photoreceptor (BAP) and not the phytochrome. There was no evidence for an effect of phytochrome or BAP on time to flowering, however, increasing temperature levels effectively decreased the time to flowering. To predict the effects of different spectral qualities and temperature, simple models were created from data on plant height, internode length and time to flowering. These models were then applied to simulate the potential benefits of spectral filters and temperature in manipulation of growth control and flowering in antirrhinum.

Economic analysis and comparison of chemical heat pump systems

Over the last years great interest has been shown in chemical heat pump systems. Chemical heat pumps represent a new technology with great potential to reduce the energy consumption in very different sectors. They can provide the ability to capture the rejected low-grade heat and to reuse it at increased temperature levels in various industrial processes. Heat can be removed from a heat source at low-temperature by an endothermic reaction and can be boosted to a heat sink at high-temperature by an exothermic reaction. Since chemical heat pumps can operate without compression, with less electrical power and at higher temperature levels compared to conventional heat pumps, they can afford high performance advantages. As an additional advantage, energy storage can also be accomplished so that intermittent energy sources can be utilized in a chemical heat pump system. The objective of this work was to study methanol–formaldehyde–hydrogen, ethanol–acetaldehyde–hydrogen, i-propanol–acetone–hydrogen and n-butanol–butyraldehyde–hydrogen chemical heat pump systems based on catalytic dehydrogenation of alcohols at low-temperature and hydrogenation of aldehydes and a ketone at high-temperature. On the base of economic analysis, the quantity of waste-heat that must be supplied to produce the benefits of the process heat and also the improvement in the net gain reached were determined and compared.

The compression/absorption cycle – influence of some major parameters on COP and a comparison with the compression cycle

This article concerns two main studies: a parameter study and a comparison. In the parameter study, the CAHP is focused upon. Its COP sensitivity to changes in the absorber and desorber falling-film tube length, heat exchanger area distribution, and concentration change of the solution in the absorber is studied. The relative distribution between the desorber and absorber is found to have little impact on COP. The area distributed to the solution heat exchanger and the concentration change in the absorber is found to have a large impact on COP when examined separately, but when they are studied together, and with optimized concentration change for each area distribution, the total impact is low. It is shown that the falling-film tubes should be designed to be as long as possible in order to increase the COP. The comparison involves a new procedure for comparing the performance (COP) of a compression/absorption heat pump (CAHP) with that of a compression heat pump (CHP). In the procedure local heat transfer coefficients and pressure drop are taken into account. Further, the comparison is performed for various heating applications and with specified investment level. The heating applications are typically industrial or district heating cases and are chosen to study impact of three different kinds: size of the sink and source temperature change (glide), temperature lift for a given sink and source glide and temperature level for a given sink and source glide. Ammonia/water is used as working fluid in the CAHP and isobutane in the CHP. A relevant industrial design is assumed for the CHP (including an indirect economizer coupling, suction gas heat exchanger, sub-cooler and surface enhancements in evaporator and condenser), which is not the case in previous comparisons of this type. The absorber and desorber in the CAHP are modeled as vertical falling-film tube-and-shell heat exchangers. The main results for the comparison study are: (1) the COP of the CAHP is as good as that of the CHP when the sink and source glides are 10 K; (2) when the glide of the sink and source is increased to 20 K, the CAHP has a 12% better performance than the CHP; and (3) an increased temperature lift and an increased temperature level give the CAHP a relatively worse COP. Some COP-increasing design parameters to be studied further are proposed for the CAHP.

Thixotropic behaviour of rubber under dynamic loading histories: Experiments and theory

In the first part of this essay we investigate the thermomechanical behaviour of carbon black-filled rubber under dynamic loading conditions. The loadings consist of static predeformations which are superimposed by small sinusoidal oscillations. The frequency was varied between 0.1 Hz and 100 Hz, the deformation amplitude between 0.006 and 0.06, the temperature between 253 K and 373 K and the storage and dissipation moduli measured. The data show that the frequency dependence of the moduli is of the powerlaw type. They also depend on the deformation amplitude and the temperature. If the temperature is constant, increasing amplitudes lead to decreasing moduli. As discussed by Payne (1965), this behaviour can be interpreted in terms of a thixotropic change. If, on the other hand, the deformation amplitude is kept constant, increasing temperature levels lead to decreasing moduli. In the second part of this work we develop a constitutive theory to represent the material behaviour observed. We consider the dissipation principle of thermodynamics and formulate the model for three-dimensional finite deformations. To describe thermal expansion effects, we decompose the deformation gradient into a thermal and a mechanical part as proposed by Lu and Pister (1975). We prescribe the thermal part by a constitutive function and assume the mechanical part to be the driving force for the stress tensor. As motivated in earlier works we split the total stress into an equilibrium stress and a rate-dependent overstress. We represent the equilibrium stress using a modified Mooney-Rivlin strain energy function and the overstress by a series of Maxwell elements whose springs are of Neo-Hookean type. Both the kinematic tensors and the associated stress measures are defined by using the concept of dual variables proposed by Haupt and Tsakmakis (1989). In order to represent the thixotropic effects, the viscosities depend on the temperature and the deformation history. The history dependence is implied by an internal variable which is a measure for the deformation amplitude and has a relaxation property as discussed by Payne (1965). To determine the material parameters, we linearise the constitutive equations with respect to the static predeformation and take the analytical solution for harmonic strain-controlled loadings into account. Numerical simulations demonstrate that the constitutive theory describes all phenomena experimentally observed with a fairly good approximation. The model is compatible with the second law of thermodynamics in the form of the Clausius Duhem inequality.