Development of an air-cooled, loop-type heat pipe with multiple condensers

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2012.Cataloged from PDF version of thesis.Includes bibliographical references (p. 169-172).Thermal management challenges are prevalent in various applications ranging from consumer electronics to high performance computing systems. Heat pipes are capillary-pumped devices that take advantage of the latent heat of vaporization of a working fluid to achieve low thermal resistance (~0.1 °C/W), and have been of particular interest to address these thermal management needs for cooling solutions such as air-cooled heat sinks. This thesis reports the design, fabrication, and characterization of a novel loop-type heat pipe with multiple condensers for a high performance air-cooled heat sink. While multiple-condenser heat pipes have been developed in the past, this heat pipe layout is the first to ensure equal operation of the individual condensers. The layout incorporates wicks in both evaporator and condenser; the wick in the evaporator supplies the capillary pressure to drive the circulation and the wick in the condenser uses capillary pressure to separate the vapor and liquid phases for controlled condensation. Additionally, methods of liquid and vapor pressure control are developed to modulate the capillary pressure in the condenser. The heat pipe was first evaluated using an analytical model to determine the required thermophysical properties and geometries of the capillary wicks in the evaporator and condenser. The model results were subsequently used to obtain a detailed evaporator design that is compatible with the multiple-condenser layout. The evaporator was fabricated with a multi-step metal sintering process, characterized, and integrated into both single-condenser and six-condenser prototypes. The prototypes successfully operated in a wide range of angles, with automatic heat pipe startup and with a heat pipe thermal resistance as low as 0.0065 °C/W with equal condenser performance. The air-cooled, six-condenser prototype demonstrated removal of 500 W from a heat source at 75 °C. The heat pipe cycle developed in this study enables the use of multiple condensers in a loop-type heat pipe to achieve a large surface area with little thermal resistance for heat sink applications.by Harumichi Arthur Kariya.Ph.D

A user's guide to the Langley 16- by 24-inch water tunnel

The Langley 16 x 24 inch Water Tunnel is described in detail, along with all the supporting equipment used in its operation as a flow visualization test facility. These include the laser and incandescent lighting systems; and the photographic, video, and laser fluorescence anemometer systems used to make permanent records of the test results. This facility is a closed return water tunnel capable of test section velocities from 0 to 0.75 feet per second with flow through the 16 x 24 inch test section in a downward (vertical) direction. The velocity normally used for testing is 0.25 feet per second where the most uniform flow occurs, and is slow enough to easily observe flow phenomena such as vortex flow with the unaided eye. An overview is given of the operational characteristics, procedures, and capabilities of the water tunnel to potential users of the facility so that they may determine if the facility meets their needs for a planned study

Development of a multi-regime tribometer and investigation of zinc dialkyldithiophosphate tribofilm development in the presence of overbased calcium sulfonate

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2009.Includes bibliographical references.A custom tribometer was developed to investigate the production of nano-scale films from the anti-wear additive zinc dialkyldithiophosphate (ZDDP). The tribometer was designed to operate in various conditions of lubrication severity, from boundary to hydrodynamic lubrication regimes. A cylinder-on-plate layout, in which a cylinder rotates and rubs against a plate in a line contact, was employed for this purpose. ZDDP, a wear preventative additive universally used in engine and gear oil formulations, was studied in detail with respect to tribofilm production. As typical oil formulations contain an assortment of additives, the development of these films in the presence of other additives was studied. Of these, overbased detergents have recently been under scrutiny with mixed findings of synergetic and antagonistic effects. This project investigates the effects of overbased calcium sulfonate, a basic detergent used to neutralize acids and solubilize contaminants in oil, using electrical contact resistance (ECR), Auger electron spectroscopy (AES) and 31-phosphorous nuclear magnetic resonance (P₃₁NMR). Oil blends of 2.4% (mass) ZDDP with varying concentrations of calcium sulfonate were mixed for rubbing and heating tests. ECR was used to monitor the development of the tribofilm in-situ of the tribometer and AES was used in postmortem analysis to measure the film thickness. Analysis with P₃₁ NMR was employed for a series of heating experiments to characterize the chemical interactions between the two additives. Tests in light boundary lubrication show a trend of suppression of ZDDP tribofilm formation with the introduction of the detergent.by H. Arthur Kariya.S.M