Turbulent and Transitional Modeling of Drag on Oceanographic Measurement Devices

Computational fluid dynamic techniques have been applied to the determination of drag on oceanographic devices (expendable bathythermographs). Such devices, which are used to monitor changes in ocean heat content, provide information that is dependent on their drag coefficient. Inaccuracies in drag calculations can impact the estimation of ocean heating associated with global warming. Traditionally, ocean-heating information was based on experimental correlations which related the depth of the device to the fall time. The relation of time-depth is provided by a fall-rate equation (FRE). It is known that FRE depths are reasonably accurate for ocean environments that match the experiments from which the correlations were developed. For other situations, use of the FRE may lead to depth errors that preclude XBTs as accurate oceanographic devices. Here, a CFD approach has been taken which provides drag coefficients that are used to predict depths independent of an FRE

HT2008-56233 Slip-flow and Conjugate Heat Transfer in Rectangular Microchannels

ABSTRACT Slip-flow and conjugate heat transfer in rectangular microchannels are studied numerically for thermally developing laminar flow subjected to constant wall temperature (T) and constant wall heat flux (H2) boundary conditions. A three-dimensional numerical code based on finite volume method is developed to solve the coupled energy equations in the wall and fluid regions together with temperature jump at the wall-fluid boundary. A modified convection-diffusion coefficient at the wall-fluid interface is defined to incorporate the temperature-jump boundary condition. The numerical code is validated by comparing the present results with the published data. The effect of rarefaction and wall conduction on the heat transfer in the entrance region is analyzed in detail. Results show that the wall conduction has a considerable influence on the developing Nusselt number along the channel for the H2 boundary condition, particularly at low Knudsen numbers. In the case of the T thermal boundary condition, negligible influence of wall conduction on the Nusselt number is observed for all Knudsen numbers considered

Improved perturbation solutions for laminar natural convection on a vertical cylinder

The method of extended perturbation series is applied to solve for laminar natural convection from an isothermal, thin vertical cylinder. The series in terms of the transverse curvature parameter ξ extended to five terms and is subsequently improved by applying the Shanks transformation twice. The validity of the solution is extended up to ξ =10 and possibly even beyond. Up to ξ =10, the results for wall shear as well as the local and average Nusselt numbers agree very closely with those of local nonsimilarity and finite difference solutions. The ease of computation coupled with high accuracy makes the present approach far more attractive than the currently popular local nonsimilarity and finite difference methods. Its success with the present problem should motivate applications to a host of nonsimilar boundary layer flows. Die Methode der erweiterten Störungsserien wird auf die laminare freie Konvektion am isothermen senkrechten dünnen Zylinder angewendet. Die Serien in Ausdrücken des Krümmungsparameters ξ werden auf 5 Terme ausgedehnt und weiter durch doppelte Auswertung der Shank-Transformation verbessert. Die Lösung gilt mindestens bis ξ =10, vielleicht sogar weiter. Bis ξ =10 stimmen die Lösungen für die Wandschubspannung und die örtliche und mittlere Nußelt-Zahl gut überein mit jenen, die auf der örtlichen Nicht-Ähnlichkeit und finiten Differenzen beruhen. Die leichte Berechenbarkeit und die hohe Genauigkeit machen diesen Lösungsweg attraktiver als die heute populären Verfahren der örtlichen Nicht-Ähnlichkeit und der finiten Differenzen. Der hier aufgezeigte Erfolg sollte zur Anwendung auf nicht-ähnliche Grenzschichtströmungen motivieren.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46653/1/231_2005_Article_BF01459764.pd

A review of global ocean temperature observations: Implications for ocean heat content estimates and climate change

The evolution of ocean temperature measurement systems is presented with a focus on the development and accuracy of two critical devices in use today (expendable bathythermographs and conductivity‐temperature‐depth instruments used on Argo floats). A detailed discussion of the accuracy of these devices and a projection of the future of ocean temperature measurements are provided. The accuracy of ocean temperature measurements is discussed in detail in the context of ocean heat content, Earth's energy imbalance, and thermosteric sea level rise. Up‐to‐date estimates are provided for these three important quantities. The total energy imbalance at the top of atmosphere is best assessed by taking an inventory of changes in energy storage. The main storage is in the ocean, the latest values of which are presented. Furthermore, despite differences in measurement methods and analysis techniques, multiple studies show that there has been a multidecadal increase in the heat content of both the upper and deep ocean regions, which reflects the impact of anthropogenic warming. With respect to sea level rise, mutually reinforcing information from tide gauges and radar altimetry shows that presently, sea level is rising at approximately 3 mm yr−1 with contributions from both thermal expansion and mass accumulation from ice melt. The latest data for thermal expansion sea level rise are included here and analyzed

Entropy analysis on convective film flow of power-law fluid with nanoparticles along an inclined plate

Entropy generation in a two-dimensional steady laminar thin film convection flow of a non-Newtonian nanofluid (Ostwald-de-Waele-type power-law fluid with embedded nanoparticles) along an inclined plate is examined theoretically. A revised Buongiorno model is adopted for nanoscale effects, which includes the effects of the Brownian motion and thermophoresis. The nanofluid particle fraction on the boundary is passively rather than actively controlled. A convective boundary condition is employed. The local nonsimilarity method is used to solve the dimensionless nonlinear system of governing equations. Validation with earlier published results is included. A decrease in entropy generation is induced due to fluid friction associated with an increasing value of the rheological power-law index. The Brownian motion of nanoparticles enhances thermal convection via the enhanced transport of heat in microconvection surrounding individual nanoparticles. A higher convective parameter implies more intense convective heating of the plate, which increases the temperature gradient. An increase in the thermophoresis parameter decreases the nanoparticle volume fraction near the wall and increases it further from the wall. Entropy generation is also reduced with enhancement of the thermophoresis effect throughout the boundary layer

Theoretical and numerical predictions of the thermal conductivity of thermal protection systems

The present work evaluates the effective thermal conductivity of an ablative composite in the state of virgin material and in three different paths of degradation. The material is assumed to undergo ablation with formation of void pores and with formation of char and void pores. The one dimensional effective thermal conductivity is evaluated theoretically by the solution of heat conduction under two extreme assumptions, i.e. parallel isotherms and parallel heat fluxes. The paper presents the theoretical model applied to an elementary cubic cell of the composite material made of two crossed fibres and matrix. A numerical simulation is carried out to compare numerical results with the theoretical ones for different values of the filler volume fraction

Theoretical and numerical predictions of the thermal conductivity of thermal protection systems

The present work evaluates the effective thermal conductivity of an ablative composite in the state of virgin material and in three different paths of degradation. The material is assumed to undergo ablation with formation of void pores and with formation of char and void pores. The one dimensional effective thermal conductivity is evaluated theoretically by the solution of heat conduction under two extreme assumptions, i.e. parallel isotherms and parallel heat fluxes. The paper presents the theoretical model applied to an elementary cubic cell of the composite material made of two crossed fibres and matrix. A numerical simulation is carried out to compare numerical results with the theoretical ones for different values of the filler volume fraction