Dynamic Heat Transport Research Articles

Orbit Induced Journal Temperature Variation in Hydrodynamic Bearings

A method for evaluating the asymmetric heat input into the synchronously vibrating journal of a hydrodynamic bearing is presented. CFD techniques are used to analyze the dynamic flow and heat transport in the lubricant film and the heat input into the journal is obtained by orbit time averaging. The procedure is applied to a two-inlet circular bearing with backward and forward circular whirl journal orbits over a range of rotational speeds. The steady asymmetric heat input into the journal is found to have a sinusoidal component, which causes a steady surface temperature differential across the journal. The maximum temperature on the journal surface is always upstream of the minimum film point for forward whirl orbits and downstream for backward whirl orbits. The results provide a greater understanding of the nature of rotor thermal bending.

Mathematical Simulation of Heat and Moisture Transfer in a Human-Clothing-Environment System

A mathematical model has been developed to describe the dynamic heat and moisture transport behavior of clothing and its interaction with the human thermoregulation system under transient wear conditions. A modification of Gagge's two-node model is used to simulate the human physiological regulatory responses. In clothing, heat and moisture transport is coupled with the sorption or desorption of water vapor in the fibers and the associated energy changes. If the physical activity and ambient conditions are specified, the model can predict the thermoregulatory responses of the body, to gether with the temperature and moisture profiles of the clothing. Experimental mea surements with garments made from fibers with different levels of hygroscopicity are compared with predictions by the model. There is good agreement between prediction and experiment for skin and fabric temperatures and the relative humidity of the cloth ing microclimate.

Dynamic Water Vapor and Heat Transport Through Layered Fabrics

In Parts I and II, we reported that during nonsteady-state transport of water vapor through layered fabrics, the temperature between two fabrics rose. In this study, we measure the surface temperature of the first-layer fabrics in similar experiments. The mass of the first layer is changed by tightly stacking the same fabrics, and the surface temperature rise is measured as a function of the mass and the kind of polymers. The rise of surface temperature is proportional to the mass of fabrics and the water ab sorption characteristics of the polymers. We can confirm that the temperature rise that occurs in the space between layered fabrics is mainly due to the heat of absorption of water vapor by the polymers (fabrics).

Dynamic Water Vapor and Heat Transport through Layered Fabrics

Dynamic water vapor and heat transport in the transient state was investigated for fabrics made of polyester, acrylic, cotton, and wool fibers. The overall dissipation rate of water vapor depends on both the vapor transport rate and the vapor absorption by fibers, which are mutually interrelated. Water vapor transport is governed by the vapor pressure gradient that develops across a fabric layer. When a fabric is subjected to given environmental conditions, the actual water vapor transport rate greatly differs depending on the nature of the fibers, even when other parameters are nearly identical, such as density, porosity, and thickness. The actual differential vapor pressure that develops across a layer depends on the water vapor absorption characteristics of the fibers. The higher the water vapor absorption rate, the lower the differential vapor pressure for water vapor transport and thus the lower the overall water vapor transport rate. However, the water vapor transport rate (when considering the actual differential vapor pressure across a fabric layer) is nearly identical regardless of fiber type, providing the fabric structures are kept nearly the same. Water vapor transport occurs through the open air spaces confined by fibers, and the nature of fibers does not greatly affect the characteristic vapor transport rate through these spaces. The temperature of the air space between two layers of fabric rises when water vapor transport occurs. This rise is nearly proportional to the water vapor absorption rate of a fabric, which is determined by the chemical nature of the constituent fibers.

Dynamic Water Vapor and Heat Transport Through Layered Fabrics

An experimental apparatus has been developed to permit simultaneous measurement of temperature change and moisture flux through fabrics during the transient period after one set of fabrics has been exposed to humidity and temperature gradients. Both the water vapor method and the sweat method were used to study the transport of water vapor and water vapor emanating from liquid water in contact with the bottom layer of fabric through several fabrics. Tested fabrics included single fiber and blended fiber fabrics, treated either by hydrophobically or hydrophilically. Analysis of the ex perimental results verified that after either hydrophobic or hydrophilic treatment, the fabrics did not show any significant change in moisture flux when compared to their untreated counterparts using the water vapor method, but did show a significant dif ference when measured by the sweat method. In the sweat case, the dominant factor that controls the water vapor transfer rate is considered to be the wicking ability of the fabric.

Laser heating of semiconductors—effect of carrier diffusion in nonlinear dynamic heat transport process

An analytic theory is presented to describe the nonlinear dynamic heat transport process in a semiconductor irradiated by a pulsed laser beam. The input rate of laser energy to the lattice is sensitively influenced by the ambipolar diffusion of the dense, laser-produced excess charge carriers. Additionally, the high heating rate of the laser beam significantly changes the material transport coefficients during the pulse. This nonlinear laser beam-solid interaction is examined from the viewpoint of the transport process, using a parametrized perturbation technique in Green′s function formulation. An explicit, analytical solution of the lattice temperature rise is presented and the threshold pulse energy for the onset of surface melting for the case of amorphous Si is calculated as a function of laser beam intensity as well as the carrier diffusion length. Our results are compared with both the melting and nonthermal models for laser annealing.