Search Results

The two-phase flow modeling is done using the level set method to identify the interface of vapor and liquid. The modifications to the incompressible Navier-Stokes equations to consider surface tension, viscosity, gravity and phase change are discussed in detail. The governing equations are solved using finite difference method. In the present work, investigations on the effect of thermal conductivity and latent heat of vaporization of liquid on heat transfer in a 44 µm thick liquid film containing vapor bubble with droplet impact is investigated. The importance of thermal conductivity and latent heat of vaporization of liquid on heat transfer is identified. The variation of heat flux with thermal conductivity and latent heat is plotted. The computed liquid and vapor interface, velocity vector and temperature distributions at different time instants are also visualized for better understanding of the heat removal.

Lithium ion conductivity of a lithium compound is known to be influenced by an inert, non-lithium ion conductor additive. This paper reports an investigation of the effects of boron nitride (BN) addition to the conductivity of lithium iodide (Lil). The Lil:BN stoichiometry and heat treatment parameters (temperature and time) have been used as variables. It will be shown that lithium conductivity is strongly dependent upon heat treatment parameters. The activation energy for lithium ion transport also decreases with the addition of BN. Further analysis of activation energy data suggests that lithium ion motion takes place through interfacial regions of Lil and BN phases.

This paper describes the development, operation and testing of an across-gimbal ambient thermal transport system (GATTS) for carrying cryocooler waste heat across a 2-axis gimbal. The principal application for the system is space-based remote sensing spacecraft with gimbaled cryogenics optics and/or infrared sensors. GATTS uses loop heat pipe (LHP) technology with ammonia as the working fluid and small diameter stainless steel tubing to transport 100–275 W across a two-axis gimbal. The tubing is coiled around each gimbal axis to provide flexibility (less than 0.68 N-m [6 lbf-in] of tubing-induced torque per axis) and fatigue life. Stepper motors are implemented to conduct life cycling and to assess the impact of motion on thermal performance. An LHP conductance of approximately 7.5 W/C was demonstrated at 200 W, with and without gimbal motion. At the time this paper was written, the gimbal had successfully completed over 500,000 cycles of operation with no performance degradation.

Loss mechanisms in 1-10 kW spark-ignition, two-stroke engines may be grouped into five categories: thermal losses, frictional losses, sensible enthalpy in the exhaust gases, incomplete combustion, and short-circuiting of fresh fuel and air mixture. These loss mechanisms cause small two-stroke engines to have fuel conversion efficiencies 50%-70% lower than similar larger engines. Previous studies of loss scaling in small engines have estimated the short-circuiting using heuristics derived for larger engines or grouped it with other combustion losses to complete the energy balance. This work describes and compares two methods for measuring short-circuiting on a commercially available, two-stroke, naturally aspirated, spark ignition engine with 55 cm3 displacement. One method used oxygen as an analyte (the Watson method), nitrogen as an internal standard, and gas chromatography with a thermal conductivity detector for quantification.