Lois J. Gschwender

Enhancing Heat Capacity of Colloidal Suspension Using Nanoscale Encapsulated Phase-Change Materials for Heat Transfer

This paper describes a new method to enhance the heat-transfer property of a single-phase liquid by adding encapsulated phase-change nanoparticles (nano-PCMs), which absorb thermal energy during solid-liquid phase changes. Silica-encapsulated indium nanoparticles and polymer-encapsulated paraffin (wax) nanoparticles have been made using colloid method, and suspended into poly-alpha-olefin (PAO) and water for potential high- and low-temperature applications, respectively. The shells prevent leakage and agglomeration of molten phase-change materials, and enhance the dielectric properties of indium nanoparticles. The heat-transfer coefficients of PAO containing indium nanoparticles (30% by mass) and water containing paraffin nanoparticles (10% by mass) are 1.6 and 1.75 times higher than those of corresponding single-phase fluids. The structural integrity of encapsulation allows repeated use of such nanoparticles for many cycles in high heat generating devices.

Synthesis and Characterization of Silahydrocarbons—A Class of Thermally Stable Wide-Liquid-Range Functional Fluids

The synthesis and characterization of the silahydrocarbons, a class of functional fluids with excellent viscosity index and thermal stability characteristics, are presented and discussed. Thermal stability data for the silahydrocarbons at temperatures up to 370°C are compared to other functional fluids. The oxidative stability and lubricity characteristics of silahydrocarbon formulations are discussed. Presented at the 36th Annual Meeting in Pittsburgh, Pennsylvania, May 11–14, 1981

Tribological Behavior of Some Candidate Advanced Space Lubricants

Performance of a variety of space lubricants was compared under boundary and elastohydrodynamic lubrication (EHL). The types of fluids studied were naphthenic mineral oil, paraffinic mineral oil, polyalphaolefin, and silahydrocarbon. The silahydrocarbon and the polyalphaolefin lubricants exhibited lower traction under similar conditions. A specific additive package increased the traction of the polyalphaolefin. Volatility characteristics of some of these fluids were also studied. Presented at the 45th Annual Meeting In Denver, Colorado May 7–10, 1990

Characterization of Model Perfluoropolyalkylethers by Miniaturized Thermal Oxidative Techniques–-Part II: Pressure Differential Scanning Calorimetry

Commercially available and model perfluoropolyalkylether (PFPAE) fluids were characterized by pressure differential scanning calorimetry (PDSC). Details of the PDSC method are described and the stabilities determined by PDSC are compared to those obtained from the constant temperature miniaturized oxidation corrosion test described in Part I of this paper (1). Chemical structure-thermal oxidative stability relationships of the fluids as derived from the PDSC method are discussed. The destabilizing effect of an -OCF2-group is confirmed and other more subtle effects are noted.

Compressibility of lubricants at high pressures

Results from a high pressure chamber, recently developed at Lund Institute of Technology, are presented. The compressibility variation with the pressure of five different lubricants is investigated for pressures up to 2.7 GPa. The density variation for each lubricant is presented as a curve fit. The results show that at high pressures when the lubricant has solidified, the density varies linearly with the pressure. It is also concluded that the Dowson-Higginson relationship may be inaccurate when describing the density variation for some lubricants, especially at higher pressures.

Computational Chemistry of Soluble Additives for Perfluoropolyalkylether Liquid Lubricants

Computational chemistry has been applied in a practical manner to a perfluoropolyalkylether (PFPAE) liquid lubricant research and development program. Additives have been previously shown to be effective in a PFPAE liquid lubricant candidate gas turbine engine oil base fluid as oxidation inhibitors/metal deactivators, lubricity additives and antirust additives. In this effort, low energy configuration computer models of the base fluid and of selected additives were created. Simulated docking of the additive molecules in the base fluid media, onto low carbon steel and onto iron oxide substrates, provided information on the strength of the substrate/additive interactions. Also, the visual representation of each additive molecules alignment on the metallic surface has provided insight into selection of the optimnum functionality in designing new additives. Data on the additive/metal attraction and corresponding additive effectiveness are presented. Presented at the 50th Annual Meeting in Chicago, Illinois M...

Characterization of Model Perfluoropolyalkylethers by Miniaturized Thermal Oxidative Techniques—Part I: Modified Oxidation-Corrosion Test

The metal catalyzed thermal oxidative stability of commercially available and model perfluoropolyalkylether (PFPAE) fluids was investigated by oxidation corrosion tests. Using model PFPAE fluids, prepared via direct fluorination of hydrocarbon analogues, a wider variety of specific molecular structures were available for study than previously available from more conventional PFPAE chemistry synthesis procedures. Because of a limited supply of the model fluids, a miniaturized oxidation corrosion test, using only 6 ml of fluid, was devised. This test, conducted at constant temperatures, was compared to a similar test using 20 ml of fluid on the more abundant commercial fluids and then extended to the model fluids. Details of the miniaturized test procedure and apparatus are presented. Also presented are the chemical structure-thermal oxidative stability relationships of the fluids as derived from this study. The destabilizing effect of an -OCF 2 - group is confirmed and other more subtle effects are noted.

Effect of Viscosity Index Improvers on the Elastohydrodynamic Lubrication Characteristics of a Chlorotrifluoroethylene and a Polyalphaolefin Fluid

The film thickness characteristics and traction behavior, two of the more important elastohydrodynamic lubrication (EHL) properties, of two important classes of synthetic lubricants have been studied. The effect of viscosity index (VI) improvers on these properties has been determined for both hydrogenated polyalphaolefin (PAO) base fluids and chlorotrifluoroethylene oligomer (CTFE) base fluids. A polyalkylmethacrylate (PMM) VI improver was studied in PAO and a copolymer of vinylidine fluoride and chlorotrifluoroethylene was studied in CTFE. The VI improvers demonstrated insignificant improvement in the EHL film thickness of both the PAO and CTFE base fluids as determined by comparing the measured film thickness of the VI-improved fluids to the predicted film thickness based on measured pressure-viscosity characteristics and kinematic viscosities determined at low shear rates. Similarly, the traction behavior of VI-improved PAO and CTFE fluids was nearly equivalent to that of the respective base fluids, d...

U.S. Air Force Perfluoropolyalkylether Experiences

The U.S. Air Force Research Laboratory (AFRL) received the first sample of perfluoropolyalkylether (PFPAE) liquid lubricant outside of private industry in the 1960s. The unique behavior of PFPAE fluids includes their excellent thermal stability (up to 345°C with appropriate additives) and excellent viscosity-temperature properties for the linear structures. Military applications are often cutting-edge technology requiring these unique properties, but other undesirable behavior such as tribo-corrosion has required investigations into basic understanding of PFPAE fluids. From the 1960s on, Air Force scientists have investigated many aspects of their behavior as summarized here. This presentation discusses various types of PFPAEs commercially available and highlights studies on elastohydrodynamic lubrication film formation, model compounds, additives, relative humidity relationship to wear, and potential U.S. military program applications.

Hydraulic System Component Storage with Military Hydraulic Fluids

In the military aerospace community, most hydraulic fluid pumps and components are currently being stored in rust inhibited fluids containing barium dinonylnaphthalene sulfonate (BSN). Fluids containing barium are hazardous waste after use, with expensive disposal, and have caused operational problems in aircraft hydraulic systems including helicopters and fighter aircraft. In this program, bearings and pistons were stored in jars containing both operational hydraulic fluids (MIL-PRF-83282, MIL-PRF-87257, and MIL-PRF-5606) and rust-inhibited hydraulic fluids containing BSN (MIL-PRF-46170 and MIL-PRF-6083). In addition, hydraulic pumps were filled with MIL-PRF-83282, MIL-PRF-87257, and MIL-PRF-46170. Hydraulic pumps were not filled with MIL-PRF-5606 or MIL-PRF-6083 because these hydraulic fluids are being phased out of military aerospace applications as operational and storage fluids, respectively. Jars, containing bearings and pistons, as well as hydraulic pumps, were stored for up to three years in a laboratory environment to determine if operational fluids would protect them from rusting during storage. After each year, the bearings, pistons, and pumps were inspected for corrosion. At the end of three years of storage, pumps were endurance tested using fresh operational fluid, MIL-PRF-83282. The bearings, pistons, and pumps showed no rusting for the duration of storage with either operational or storage fluids. The pumps stored with the operational fluids, MIL-PRF-83282 and MIL-PRF-87257, were in better condition than the pump stored with the rust-inhibited fluid. The operational hydraulic fluids, MIL-PRF-83282 and MIL-PRF-87257, provided excellent protection against rusting during storage. Manuscript contributed February 1, 2005 Review led by Paul Bessette