The investigation is concerned with the effect of entrained oil on the heat transfer characteristics of a direct expansion evaporator coil. A modified refrigeration system, in which the oil content of the refrigerant could be varied, was used in conjunction with an air conditioning system, which supplied the evaporator load. The heat transferred to the refrigerant was measured for different concentrations of oil in the refrigerant. The load to the evaporator was supplied by 500 cfm of air maintained at 80°F dry bulb and 61°F wet bulb by a washer and an electric heater. The heat transferred to the refrigerant was determined by measuring the temperature of the liquid refrigerant entering the expansion valve and the suction temperature and pressure of the superheated vapor at exit from the evaporator. A sample of the liquid refrigerant flowing to the evaporator during the test was trapped in a sample collector and channeled to an expansion chamber, where the oil and refrigerant were separated and the oil concentration was determined. The results of the investigation showed that oil tends to reduce heat transfer across the evaporator tube wall. At 25°F suction temperature, the reduction in the heat transferred was 5% with an oil concentration of 0.84% by volume compared to the refrigerant with an oil concentration of 0.063%. At 30°F suction temperature the reduction in the heat transferred was 3% with an oil concentration of 1.52% by volume. The range of suction temperatures for the investigation was from 24°F to 31.9°F, The maximum average oil concentration obtained during the investigation was approximately 1.75% by volume of oil in the refrigerant. / Master of Science

Oil ring seals are one major source of instability in high pressure centrifugal compressors. This thesis presents a method for analysis of an improved seal concept that has been used in very high pressure designs (900 PSI). The improved design uses a combination of ring seals and tilting pad bearing elements. The stable tilting pad is used to center the heavily grooved seal element. The eight stiffness and damping coefficients which represent the hydrodynamic forces between the journal and the seal assembly are computed by an automated computer code for evaluation of both the standard ring seal and the tilting pad elements. Both synchronous and nonsynchronous steady state characteristics have been included in the analysis. The nonsynchronous whirl of the rotor and its effects on the stiffness and damping coefficients of a 5 tilting pad seal have been given in the form of design curves. The effect of pad inertia which has been neglected in many bearing analysis codes has been incorporated in this seal analysis, and allowed the determination of the exact cross coupling stiffness and damping coefficients. / Master of Science

This thesis describes measurements of the gas-solid flow boundary condition at moderate Knudsen number, i.e., where the dimensions of the flow are similar to the mean free path, and thus partial slip is expected. This regime has become more important with increased focus on nano-scale devices, but there is currently no consensus on how the slip length should vary for different solids and gases, or whether it can be controlled. In this thesis, I describe unambiguous measurements showing that partial slip occurs, that the slip length depends both on gas and solid, and that the slip length can be altered in situ. The slip length is determined from analysis of the vibration of a small sphere adjacent to a solid. I also describe applications of these findings both to the separation of gases, and to inhalants. The effect of water films, gas species, organic films, and electric fields on gas flow was studied. Water films had a large, but complex effect. On bare hydrophobilic glass, the tangential momentum accommodation coefficient (TMAC) for nitrogen on hydroxyl-terminated silica changed from 0.25 to 0.88 when the humidity changed from 0 to 98 %. On hydrophobized glass, TMAC changed from 0.20 to 0.56 in the same range. The effect of the gas on TMAC was measured for five different gases (helium, nitrogen, argon, carbon dioxide, hexafluoride sulfur) on octadecyltrichlorosilane-coated glass surfaces. A lower TMAC occurred for greater molar mass, and this trend was explained using a simple model representing both the gas and the monolayer by spheres. The existence of this gas-dependent difference in TMAC suggests that gases can be separated based on their collisions with surfaces. Methods for controlling the flow boundary condition were also developed by adsorbing monolayers on the solid, and altering the monolayers in situ. Both temperature and electric fields altered the boundary condition, and these changes were attributed to changes in the surface roughness. The effect of roughness was modeled with grooved surfaces. Possible applications of this effect of roughness include changing the flow of aerosol droplets for deeper delivery of therapeutic drugs into the lung. / Ph. D.

Tests were conducted in the Lubrication Laboratory of the Virginia Polytechnic Institute to study the effect of several metals on the deterioration of steam-turbine oils. A special test apparatus was constructed and three commercial turbine oils were tested in the presence of 14 different metal and metal combination. Included in this group of metals were five bearing metals, several metals now extensively used in turbine lubricating systems, and several metals that are not at present used in turbine oiling systems. Oxidation of the oils was accomplished by heating the oil in glass containers at 275°F for 200 hours, in the presence of the metals. The oil samples were then subjected to laboratory inspections to determine the extent of oxidation. It was found that in the case of oil A copper, lead and the copper-lead combination were increasingly effective in increasing the viscosity and acidity. Brass, copper, and copper-lead were increasingly effective in promoting sludge formation. With oil B copper, lead, and the copper-lead combination were increasingly effective in promoting sludge formation and increasing the viscosity. Steel, lead and the copper-lead combination were increasingly effective in producing acidity. Copper, metal No. 9, and the copper-lead combination were increasingly effective in increasing the viscosity of oil C. Copper, metal Ho. 5, and copper-lead produced acidity in increasing amounts. Aluminum, zinc, and cooper were increasingly effective in promoting sludge formation. Tin showed the least effect on solidity in the case of all three oil. It caused the lowest sludge formation with oils A and B and was low with oil C. The viscosity of oil A was least affected by metal No. 6, of oil B by metal No. 8, end of oil C by steel. / Master of Science

The lubrication of ceramic materials is a difficult problem; conventional lubrication techniques are limited or often ineffective. Therefore, the concept of tribopolymerization -- originally proposed by Furey and later modified by Furey and Kajdas -- is used as a new approach to boundary lubrication of ceramics. In this approach, potential polymer-forming compounds are used in minor concentrations in a carrier fluid, which polymerize at the contact region under the sliding action to form a protective layer at the contact. Selected monomers -- including one condensation type, C₃₆ dimer acid/ ethylene glycol monoester, and five addition type, i.e., lauryl methacrylate, diallyl phthalate, vinyloctadecyl ether, vinyl acetate and methyl-2-acrylamido-2- methoxy acetate, were used at 1% concentration in hexadecane in pin-on-disk tests with sliding alumina and zirconia ceramic systems. Results showed that wear reductions of alumina by up to 80% were achieved at room temperature. At elevated temperatures (up to 150°C), the monomers were also effective; one of the monomers reduced wear by over 90% at higher temperatures. In the zirconia system, the monomers in general were also effective in reducing wear, but not to the same extent as with alumina. There was no significant effect of the monomers on friction. Detailed surface analytical studies of the worn surfaces lubricated with the monomer solutions using Fourier transform infrared microspectroscopy, X-ray photoelectron spectroscopy and mass spectrometry showed the complex nature of tribochemistry involved in the antiwear action of these monomers. In addition to the polymerization, evidence of chemical reactions of the monomers with the ceramic substrate was found. Using an advanced infrared microscope system, surface temperatures at the lubricated contacts of alumina-on-sapphireand zirconia-on-sapphiresystems were measured for selected monomers. In general the temperatures were very low. Theoretical estimations of surface temperatures using Vick’s model were also carried out for several systems (including the ones studied in the past) and the role of surface temperature in the anti-wear action of the monomers was examined. The relationship is complex; but the general trend suggests that temperatures are important for tribopolymerization of the monoester, whereas not so much so for the addition monomers. A molecular modeling software -- CHEM-X -- was also used to obtain additional insight into the mechanisms of anti-wear action of the monomers. In this exploratory study, 3-dimensional shapes of the monomers, their polymerization mechanisms, and possible orientation of a selected monomer on polymerization mechanisms, and possible orientation of a selected monomer on a ceramic surface was examined. Possible mechanisms of anti-wear action of these monomers are proposed. For the monoester, the mechanism involves (a) an initial adsorption of the carboxylic end of the molecules on the surface, (b) chemical reaction with the surface to form a soap, and (c) the formation and outward growth of oligomer/polymer chains somewhat similar in structure to a Langmuir-Blodgett multi-layer. The mechanism of anti-wear action of the addition monomers is believed to be connected to the negative-ion radical action mechanism (NIRAM) as proposed by Kajdas. According to this mechanism, exoelectron emitted during sliding initiate tribopolymerization of vinyl monomers, and monomers polymerizing only by anionic or free radical mechanisms are capable of tribopolymerization on the ceramic surfaces. It is proposed that the formed polymeric products act as a binding medium for fine wear debris particles generated during sliding. As a result, a strongly bonded debris layer -- somewhat similar to a ceramic powder reinforced polymer composite -- forms on the surface. This layer provides protection to the sliding surfaces against wear. / Ph. D.

by Ha Fu-Lam. / Thesis (M.B.A.)--Chinese University of Hong Kong, 1989. / Bibliography: leaves 61-63.

<p>Friction is the resistive force that arises when two contacting surfaces move relative to each other. Frictional interactions are important from both engineering and biological perspectives. In this research I focus on the fundamental understanding of friction on polymeric and biological surfaces in aqueous environments. First, I examine the frictional properties of a stimulus-responsive hydrogel, poly-N-isopropylacrylamide (pNIPAAm), to understand how different phase states affect its tribological properties. My measurements indicate that gels in a collapsed conformation at low shear rates, exhibit significantly larger friction than swollen gels. These differences arise from changes in surface roughness, adhesive interactions, and chain entanglements of the gel surfaces associated with the phase transition. Importantly, I show that the changes in friction, triggered by an external stimulus, are reversible. </p><p>Second, I examine details of the boundary lubrication mechanism involved in mediating friction and wear in diarthrodial joints. Specifically, I looked at the constituents of the synovial fluid, lubricin and hyaluronic acid (HA) and examined their interactions on model substrates, (1) to determine the effect of surface chemistry on adsorption using surface plasmon resonance (SPR), and (2) to study normal force interactions between these surfaces using colloidal probe microscopy (CPM). I found that lubricin is highly surface-active, adsorbed strongly onto hydrophobic, hydrophilic and also collagen surfaces. Overall, lubricin develops strong repulsive interactions. This behavior is in contrast to that of HA, which does not adsorb appreciably, nor does it develop significant repulsive interactions. I speculate that in mediating interactions at the cartilage surface, an important role of lubricin is one of providing a protective coating on cartilage surfaces that maintains the contacting surfaces in a sterically repulsive state.</p> / Dissertation

The internal combustion engine is still at the heart of the vast majority of vehicles manufactured worldwide today. For these applications reciprocating pistons are typically employed to convert the pressures generated by internal combustion into mechanical work required by the vehicle. Of the energy supplied to the engine as a whole approximately 17% is lost by means of mechanical friction. The piston ring - liner and piston skirt - liner conjunctions contribute approximately 30% of the overall friction losses in almost equal proportions. It is, therefore, important to note that reduction in piston assembly friction would have a significant effect on the fuel consumption and, therefore, performance of engines manufactured today. In order to reduce the effect of friction it is of critical importance that the model and predictions made alongside the design of engine components accurately represent the real incycle conditions encountered in practice. Much of the published research to date has excluded the effects of global thermo-elastic distortions on the lubrication of the piston skirt. In cases where this effect has been studied, it has been for relatively low engine speeds or loads on relatively stiff conjunctions. In motorsport applications the expected component lifespans are much shorter than in the usual OEM production vehicles. Reduction in component mass, particularly in reciprocating components has been at the centre of these recent gains. The effect of mass reduction coupled with the increased BMEP observed in high performance engines emphasises the importance of underlying mechanisms of lubrication. This thesis develops the modelling methodology for piston skirt-cylinder liner conjunction for the motorsport and high performance engine applications. It presents a multi-body, multiscale approach to the prediction of the lubrication conditions of the skirt-liner conjunction, incorporating realistic measured boundary conditions. It highlights the effect of inertial loading observed at high speeds in such applications. Using the methodology developed in this work, future improvements in friction may be accurately predicted though the use of the modular boundary and component contributions used throughout. Crucially though, the models created have been scrutinised and verified using instantaneous ultrasonic film thickness measurements non-invasively from the conjunction. One of the key findings of the thesis is that the component stiffness profiles have a significant effect on the dynamics of the piston assembly. The shape of the conjunction at a given instant, and thus the contact condition, is largely governed by the interaction between the themo-mechanical distortion of the contiguous solids, as well as changes in lubricant characteristic responses. The iso-viscous elastic mechanism of lubrication has been identified as being the dominant mechanism of lubrication.

The lubricants that are applied during metal cutting acts on the interface between the tool and the nascent surfaces generated by the cutting process. Dispersions of oil in water made using suitable emulsifier(s) are used as metal cutting lubricants. The efficiency of the emulsion in rendering a low friction layer on the freshly cut surface will depend on the composition of the emulsion and on the speed, load and temperature characteristics in the tribological system. A unique tribometer which can perform friction testing on freshly cut surfaces has been designed and built for the experimental investigation. In this experimental facility experiments are conducted by performing cutting operation inside a pool of the lubricant and friction force is measured in-situ. Experiments at different loads and speeds were performed. The surfaces were subsequently subjected to spectroscopic analysis using X-ray Photoelectron spectroscopy and Fourier Transform Infrared Spectroscopy (FTIR). Lubricity of the base oils on nascent and preformed (oxidized) surfaces are compared by performing friction tests on surfaces which are cut and friction tested without exposing them to the environment, and on surfaces which were cut and exposed to the environment. While the freshly cut surfaces were seen to be sensitive to the structure of the base oil, the oxidized surfaces did not differentiate between the oil structures. Amongst the three base oils tested, aromatic oil was found to exhibit the least friction. This is attributed to tendency of the aromatic chains to react with the surface and form a film, due to the formation of radical anion-metal cation complexes. Results from spectroscopic investigations are presented to substantiate these arguments. The thesis then explores the differences in the tribological behavior promoted by an emulsion between, when it acts on a cut surface and is slid just once, and when it acts on a cut surface slid repeatedly. Due to repeated sliding, friction was found to decrease with sliding time (distance), and the transition from a freshly formed surface to a repeatedly slid one was found to follow a smooth transition. The improvement in lubricity is attributed to the formation of carboxylate type structures (C=O) which get generated due to the tribological action under repeated sliding conditions in the presence of water. Under repeated sliding conditions, the friction as a function of emulsifier concentration is found to exhibit a minimum at a value which is much below the critical micellar concentration of the emulsifier (CMC). However, the variation under continuous cutting followed a different pattern, with the friction undergoing a sharp decrease close to the CMC. The effect of speed on the tribological performance was investigated and friction was found to increase dramatically beyond a critical speed which is marked as the onset of starvation. The characteristic time required for a film to develop on a newly created surface, together with the contact pressure conditions dictated by the load and speed dictates starvation. The films formed at speeds corresponding to starvation conditions was found to have a significantly different chemical structure from that corresponding to a speed less than the starvation speed.. The effect of temperature was found to affect the lubricity adversely. At elevated temperature, the nature of the film was found to change to that to starved condition, even at a speed which does not register starvation when operating at a lower temperature. The effect of solubility of the emulsifier on the friction characteristics were explored by using emulsifiers of varying hydrophilic-lypophilic values (HLB). Lower HLB emulsifiers were found to exhibit lesser friction, than those corresponding to high HLB value. The variation in lubricity is examined in the light of the morphology of the micellar structures which evolve using these emulsifiers. The main conclusions of the thesis are: 1 Evaluation of lubricity of metal cutting fluids warrants a testing strategy which tests their lubricity on freshly cut surfaces. 2 The formation of carboxylate structures aids lubricity while using an emulsion; emulsions which can result in the formation of such structures exhibit better lubricity under cutting conditions. 3 Tribofilms which show characteristic peaks related to chemisorbed oxygen is found to exhibit good lubricity under the test conditions. 4 Emulsifiers which form lamellar micellar structures which aid easy shear give better lubricity in cutting than those which yield spherical micelles.

The dissertation thesis deals with an experimental study of an elastohydrodynamic contact under insufficient lubricant supply. Theoretical studies published in this research area focus mainly on the development of theoretical models and there is an insufficient number of experimental studies which validate these models. There are two basic methods of starvation severity control in published theoretical models: by positioning of an inlet meniscus and by setting the thickness of an oil layer in the vicinity of contact inlet. The second method is more suitable when considering a wide range of operating conditions, however it is difficult to ensure experimentally. This thesis presents original experimental results and aims to describe the starvation severity level as a function of the inlet film thickness. Deeper understanding of fundamental processes in starved elastohydrodynamic contacts enables the development of more precise models, better ability of prediction of the starvation and improves the ability to avoid starvation in the early design process of key tribological components.