When loss of material due to sliding of two solids is promoted/prevented, in the presence of chemically reacting liquid or gas, tribochemical wear is said to occur. Tribochemical wear, in which corrosive media promotes material loss, is a serious concern in a variety of applications like machining, bio-implants, gas turbine engines etc. The most pervasive corrosive media encountered in applications are water and air. Air also contains water vapour along with oxygen, both of which adsorb and react with most materials, thus influencing their wear behaviour. The need for higher operating temperatures and compression ratios in gas turbine engines require development of high temperature wear resistant coatings to protect their soft metallic components. Ti based nitride coatings with Ti, Al, Si, Cr, Ta, Nb, V are known for wear resistance because of their high hardness which is second only to diamond and c-BN. High O affinity of these elements, induce the coatings to form passive oxide scale up to reasonably high temperatures and offer superior corrosion and oxidation resistance. However, sliding can remove the passivating layer, exposing the native surface to the environment which can lead to enhanced tribochemical wear. Oxidation resistance under static conditions does not guarantee low tribochemical wear; however, the tribochemical reactions causing the corrosion are of interest. Another concern is that sliding in unison with high temperatures can activate processes like enhanced diffusion, phase transformations in nitride coatings as well as in the substrate. Hence one of our objectives is to perform wear tests at high temperatures to understand the dominant mechanisms that affect wear in nitride coatings. Wear tests in the range of room temperature up to the oxidation limit of these coatings are designed.In this study TiN and high aluminium containing TiAlN coatings are chosen to study understand the wear behaviour as function of temperature up to 800°C [1]–[3]. In order to study wear of coatings, it is necessary to identify the best possible materials and methods. Though under the targeted application the coatings have to perform under fretting tests, pin on disk configuration is used which simplifies the analysis and gives deeper insight into the wear mechanism. Coated ball is used as the pin which is stationary unlike many earlier studies where the coating is applied on the rotating disk. The purpose of keeping the pin stationary is to minimize the counter-face wear and, instead, accelerate wear in these hard coatings. This method also enables easy and accurate measurement of wear depth and volume by using an optical microscope, while the conventional coated disk method requires profilometry and statistically sound measurements. To enable coating performance, substrate should not undergo much loss of strength before 800°C and hence aerospace grade IN718 alloy is chosen as the substrate which softens slowly beyond 650°C. Alumina is used as counter-face, since it has high hardness, excellent mechanical, chemical and thermal stability. In the current study, TiAlN coating is tested for wear in the range of room temperature to 800°C. Figure 1 represents the data obtained from the wear experiments. It is found that the wear is higher with large scatter at room temperature while it remains constant from 200- 750°C. Two important observations are made, firstly that the TiAlN is susceptible to some kind of a corrosive wear at room temperature which depended on the timing of the tests and secondly that the coating shows a surprisingly constant wear behaviour over the temperature range of 200-750°C. The scatter at room temperature is found to be linked with seasonal fluctuation of humidity which is verified by performing tests under controlled humidity conditions. Water vapour and oxygen are potential reacting gases present in air. Oxidation and oxidative wear is known to occur in many materials as temperatures increase which seem to be linked to thermal activation of oxidation. However lower wear at 200°C and above compared to room temperatures suggests something else to be happening .It is evident then that between room temperature and 200°C lies a transition of some kind in the tribochemical reaction which is responsible for the observed wear behaviour of TiAlN. A detailed study to understand this transition is then undertaken for the composition of TiN coatings so that benchmarking and comparison with TiAlN is possible. Also if the wear behaviour of TiN is found similar to TiAlN then it would indicate a general phenomenon which can be extended to Ti based nitrides. Figure 1 Wear rate as a variation of temperature for TiAlN coatings In contrast to low temperature wear behaviour of TiAlN, a constant wear in the range of 200-750°C is surprising because the primary suspect which is oxidation is thermally activated. The oxide scale though expected to be thin at low temperatures, has to increase in thickness with temperature due to increased diffusion and reaction rates. The oxide scale also undergoes a change in morphology and composition which indicate a lower oxidation resistance as temperature increases. A preliminary characterization of the wear scar on the ball shows that the oxide inside the worn region is thinner than the oxide outside at 750°C. The amount of O within the wear scar is similar to levels observed on as deposited surface while the surface outside the wear scar shows oxidation and discolouration. The results suggest that oxidation inside worn region at high temperatures might be slower than the expected parabolic oxidation occurring outside the wear region. It is speculated that a double layer oxide is formed with TiO2 towards the surface and Al2O3 towards the nitride which is responsible for the lower wear at high temperature. This is supported by the fact that larger amount of Ti is found in the wear debris as temperature inceases. Superficial surface cracks appear at higher loads at temperatures as low as 600°C but they affect wear only above 800°C due to substrate softening. This shows that the coatings are still limited by the substrate softening temperature and could be used at higher temperatures. Tribo-reaction in metals, nitrides and carbides can be brought about in the presence of O2 or water vapour. Tribochemical wear of SiN, SiC, TiN, TiAlN, alumina and most other ceramics at room temperature are found to depend on humidity[4]–[6]. But only tribo-oxidation due to O2 is found to operate at high temperatures[7], [8]. Notwithstanding, it is known that SiC and SiN are more resistant to attack from O2 above 800°C than from steam. Hence the role played by water vapour is found to be convoluted. Moreover, relative humidity is the frequently mentioned quantity with regard tribochemical wear at room temperatures. It should be noted that relative humidity is not a measure of chemical activity of water vapour. Rather the water vapour pressure which represents the chemical activity of water, is not given much importance in the earlier studies. In this study, the importance of humidity, water vapour pressure and temperature in influencing wear, is studied by performing controlled wear tests on TiN. To explore the effect of temperature and water vapour pressure, TiN is tested varying temperature range of 28 °C to 90°C and water vapour pressure in the range of 3-35 mm-of-Hg. Wear tests are conducted keeping temperature constant with varying water vapour pressure and vice versa. The results show that, wear increased with humidity/vapour pressure at a fixed temperature but wear dropped drastically with increase in temperature at constant vapour pressure up to a critical temperature beyond which wear remained constant. This is one of the major unexpected findings since temperature is expected to increase wear volume. Also the critical temperature is found to shift to higher temperatures as water vapour pressures increased. It was suspected that capillary condensation was playing a role in the wear which was later verified. The whole wear behaviour is shown to be correlated with the amount of capillary condensed water. The large radius of curvature of the asperities on the polished coating surface and the smooth surface formed on the counter-face due to debris compaction form conditions favourable for capillary condensation. Any two hydrophilic surfaces which come in contact can form capillary condensation to occur at the cusps formed around the contact. However a threshold pore size of about 1nm existed below which condensation did not influence wear. Another observation is that the water vapour did not affect wear significantly in the absence of condensation for TiN coatings. As temperatures increased condensation became unfavourable, but the high vapour pressure present showed no signs of wear enhancement. This is surprising and unexpected compared to earlier reports.[9], [10] On contrary tests in liquid water showed expected behaviour for tribochemical reaction i.e wear increased with temperature. The wear in liquid water is highest when compared studies in air at any given temperature. The X-ray electron emission spectroscopy (XPS) analysis is performed to understand the surface reactions. It appears that O2 forms a barrier oxide which protects the nitride from reacting with water vapour. However when condensation occurs or in water, the oxygen and water collude into forming softer hydroxide layer which is easily removed. Though chemically water and water vapour are same, they affect wear in TiN very differently. Summarising the synopsis, exploration into high temperature wear of TiAlN reveals that it can handle oxidative wear upto 750°C showing constant wear over the temperature range of 200-750°C. Reduction in residual stresses and substrate softening may be responsible for higher wear at higher loads since the cracking is observed at 5N is absent at 3N. The substrate is expected to soften above 650°C but this does not necessarily affect wear until the load is increased or the temperature is sufficiently high. However TiAlN and TiN coatings showed susceptibility to tribo-corrosion in water and high humidity at room temperature. At high humidity, condensation of water leads to increase in wear. The dependence of wear on humidity is found to be because of capillary condensation. The negligible dependence of wear on humidity in the absence of condensation is ascribed to formation of oxide layer due to reaction with O2 and coating. The oxide barrier formed due to atmospheric O2 protects the coating from reacting with the water vapour. The oxide barrier on TiN forms faster indicating O2 reaction to be faster than the reaction with water vapour. In the presence of capillary condensation or water, O2 is depleted from contacting surfaces thus hindering the formation of the barrier oxide, increasing wear. As temperature increases the condensation becomes unfavourable and barrier oxide dominates the wear mechanism upto high temperatures which is dominated by oxidative wear.

The thesis focuses on the way inventories are stored in depositories. Later on, it develops a project of the air-conditioning system in the archive. The last part of the thesis deals with an experiment which examines the interior environment of the depository.

The diploma thesis deals with microclimate of a pool hall. This is divided into three parts. The first part describes the theoretical aspects of the environment in swimming pools in general. The second part of the diploma thesis deals with the calculation of the course of specific moisture concentration during the day in the pool hall. Different humidity concentration curves are assessed based on different electable input parameters. Subsequently, suitable setting options are evaluated in order to achieve acceptable environment in the hall in terms of humidity and optimal operating costs. The last part relates to the experimental part. This examines the measurement of evaporation under different boundary conditions and the subsequent comparison with some calculation methods for the calculation of evaporation.

The work deals with solution of air distribution in swimming pool halls with regard to the dominant influences, which are creating a microclimate in these areas. Results of this work are graphs with evaporation of water and chemicals dependents on changing boundary con-ditions. There is followed with optimal design of air distribution, which is reflecting the critical specific effects of swimming pool halls.

No description available.

Yes / Energy consumption (EC) of consumers primarily depends on comfort level (CL) affirmed by brain sensations of the central nervous system. Environmental parameters such as surroundings, relative humidity, air temperature, solar irradiance, air pressure, and cloud cover directly influence consumer body temperature that in return affect blood dynamics perturbing brain comfort sensations. This CL (either in summer, winter, autumn, or spring season) is a function of external environment and internal body variations that force a consumer toward EC. To develop a new concept of consumer's EC, first the authors described environment parameters in detail with relation to surroundings and EC. Considering this, they tabulated a generic relation of consumer's CL with EC and environment temperature. Second, to build an inter-related bond between the environmental effects on consumer body dynamics, they analysed theoretically and mathematically above mutual relations between medical and environmental sciences. Finally, they present their conceptual EC model based on a closed-loop feedback system. This model is a complex non-linear adaptive system with environmental and surrounding parameters as input to the system resulting in an optimised EC, considering consumer CL as a key parameter for the system.

Call number: LD2668 .T4 1961 I73

Call number: LD2668 .T4 1985 M44 / Master of Science

The ability to sense humidity and wetness is an important sensory attribute for many species across the animal kingdom, including humans. Although this sensory ability plays an important role in many human physiological and behavioural functions, as humans largest sensory organ i.e. the skin seems not to be provided with specific receptors for the sensation of wetness (i.e. hygroreceptors), the neurophysiological mechanisms underlying this complex sensory experience are still poorly understood. The aim of this Thesis was to investigate the neurophysiological mechanisms underpinning humans remarkable ability to sense skin wetness despite the lack of specific skin hygroreceptors. It was hypothesised that humans could learn to perceive the wetness experienced when the skin is in contact with a wet surface or when sweat is produced through a complex multisensory integration of thermal (i.e. heat transfer) and tactile (i.e. mechanical pressure and friction) inputs generated by the interaction between skin, moisture and (if donned) clothing. Hence, as both thermal and tactile skin afferents could contribute significantly to drive the perception of skin wetness, their role in the peripheral and central sensory integration of skin wetness perception was investigated, both under conditions of skin s contact with an external (dry or wet) stimulus as well as during the active production of sweat. A series of experimental studies were performed, aiming to isolate the contribution of each sensory cue (i.e. thermal and tactile) to the perception of skin wetness during rest and exercise, as well as under different environmental conditions. It was found that it is not the contact of the skin with moisture per se, but rather the integration of particular sensory inputs which drives the perception of skin wetness during both the contact with an external (dry or wet) surface, as well as during the active production of sweat. The role of thermal (cold) afferents appears to be of a primary importance in driving the perception of skin wetness during the contact with an external stimulus. However, when thermal cues (e.g. evaporative cooling) are limited, individuals seem to rely more on tactile cues (i.e. stickiness and skin friction) to characterise their perception of skin wetness. The central integration of conscious coldness and mechanosensation, as sub-served by peripheral cutaneous A-nerve fibers, seems therefore the primary neural process underpinning humans ability to sense wetness. Interestingly, these mechanisms (i.e. integration of thermal and tactile sensory cues) appear to be remarkably consistent regardless of the modality for which skin wetness is experienced, i.e. whether due to passive contact with a wet stimulus or due to active production of sweat. The novelty of the findings included in this Thesis is that, for the first time, mechanistic evidence has been provided for the neurophysiological processes which underpin humans ability to sense wetness on their skin. Based on these findings, the first neurophysiological sensory model for human skin wetness perception has been developed. This model helps explain humans remarkable ability to sense warm, neutral and cold skin wetness.

The aim of this thesis was to investigate the difference between containerboard materials strength and stiffness properties in tension and compression, how the mechanisms behind compressive and tensile properties are affected by the relative humidity of the ambient air and how the relative humidity affects the compressive response of the fibre network. These properties are used to predict the lifetime performance of corrugated boxes and to prevent early collapses of the boxes and thereby waste or harm of the transported goods inside. The work also discusses the methods used to evaluate the different properties and how reliable the results are. The experimental part includes testing of linerboard and fluting materials from both virgin and recycled fibres, which have been conditioned at 50% and 90% relative humidity. The compression tests were filmed to evaluate if different compression failure modes can be related to the strength and stiffness of the material. The results indicated that the compressive strength and stiffness differ from the strength and stiffness values in tension at 90% relative humidity. Compressive strength is lower in both 50% and 90% relative humidity compared with the tensile strength. However, the compression stiffness shows a higher value than the tensile stiffness at 90% relative humidity. The study of the method for evaluating the compressive behaviour of the paper does not present a complete picture on what type of failure the paper actually experience.