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

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

Method for Determining Air Side Convective Heat Transfer Coefficient Using Infrared Thermography

Air side convective heat transfer coefficients are among the most important parameters to know when modeling thermal systems due to their dominant impact on the overall heat transfer coefficient. Local air side convective heat transfer coefficients can often prove challenging to measure experimentally due to limitations with sensor accuracy, complexity of surface geometries, and changes to the heat transfer due to the sensor itself. Infrared thermography allows local heat transfer coefficients to be accurately determined for many different surface geometries in a manner which does not impact the results. Moreover, when determining convective heat transfer coefficients for a large number of samples, it is less costly in terms of both time and materials than other experimental methods. The method determines the heat transfer coefficient for an arbitrary region by determining the rate at which the surface temperature changes due to a step change in air temperature. To utilize the method a simple calibration is first done to determine the local thermal time constant under natural convection. Alternatively, if the thermal properties of the object are well known, a model may be used. In subsequent tests, the ratio of thermal time constant to that from the calibration test can be determined. As the material properties of the solid object are unchanged, the convective heat transfer coefficient scales inversely with the thermal time constant. A computer script has been created which automates the entire analysis process with the exception of determining the region of interest. The experimental method has been validated by comparison to other experimental methods, values from literature, and numerical simulations

Self-oligomerization regulates stability of survival motor neuron protein isoforms by sequestering an SCF^Slmb degron

Spinal muscular atrophy (SMA) is caused by homozygous mutations in human SMN1. Expression of a duplicate gene (SMN2) primarily results in skipping of exon 7 and production of an unstable protein isoform, SMNΔ7. Although SMN2 exon skipping is the principal contributor to SMA severity, mechanisms governing stability of survival motor neuron (SMN) isoforms are poorly understood. We used a Drosophila model system and label-free proteomics to identify the SCFSlmb ubiquitin E3 ligase complex as a novel SMN binding partner. SCFSlmb interacts with a phosphor degron embedded within the human and fruitfly SMN YG-box oligomerization domains. Substitution of a conserved serine (S270A) interferes with SCFSlmb binding and stabilizes SMNΔ7. SMA-causing missense mutations that block multimerization of full-length SMN are also stabilized in the degron mutant background. Overexpression of SMNΔ7S270A, but not wild-type (WT) SMNΔ7, provides a protective effect in SMA model mice and human motor neuron cell culture systems. Our findings support a model wherein the degron is exposed when SMN is monomeric and sequestered when SMN forms higher-order multimers

Design and Analysis of High-Performance Air-Cooled Heat Exchanger with an Integrated Capillary-Pumped Loop Heat Pipe

We report the design and analysis of a high-power air-cooled heat exchanger capable of dissipating over 1000 W with 33 W of input electrical power and an overall thermal resistance of less than 0.05 K/W. The novelty of the design combines the blower and heat sink into an integrated compact unit (4" × 4" × 4") to maximize the heat transfer area and reduce the required airflow rates and power. The device consists of multiple impeller blades interdigitated with parallel-plate condensers of a capillary-pumped loop heat pipe. The impellers are supported on a common shaft and powered with a low-profile permanent magnet synchronous motor, while a single flat-plate evaporator is connected to the heat load.United States. Defense Advanced Research Projects Agency. Microsystems Technology Office. Microtechnologies for Air-Cooled Exchangers (Grant number W31P4Q-09-1-0007