Yogesh Jaluria

Mercury and freon: temperature emulation and management for server systems

Power densities have been increasing rapidly at all levels of server systems. To counter the high temperatures resulting from these densities, systems researchers have recently started work on softwarebased thermal management. Unfortunately, research in this new area has been hindered by the limitations imposed by simulators and real measurements. In this paper, we introduce Mercury, a software suite that avoids these limitations by accurately emulating temperatures based on simple layout, hardware, and componentutilization data. Most importantly, Mercury runs the entire software stack natively, enables repeatable experiments, and allows the study of thermal emergencies without harming hardware reliability. We validate Mercury using real measurements and a widely used commercial simulator. We use Mercury to develop Freon, a system that manages thermal emergencies in a server cluster without unnecessary performance degradation. Mercury will soon become available from http://www.darklab.rutgers.edu.

Reducing electricity cost through virtual machine placement in high performance computing clouds

In this paper, we first study the impact of load placement policies on cooling and maximum data center temperatures in cloud service providers that operate multiple geographically distributed data centers. Based on this study, we then propose dynamic load distribution policies that consider all electricity-related costs as well as transient cooling effects. Our evaluation studies the ability of different cooling strategies to handle load spikes, compares the behaviors of our dynamic cost-aware policies to cost-unaware and static policies, and explores the effects of many parameter settings. Among other interesting results, we demonstrate that (1) our policies can provide large cost savings, (2) load migration enables savings in many scenarios, and (3) all electricity-related costs must be considered at the same time for higher and consistent cost savings.

A COMPARISON OF DIFFERENT SOLUTION METHODOLOGIES FOR MELTING AND SOLIDIFICATION PROBLEMS IN ENCLOSURES

Abstract A comparison of two frequently used computational techniques for solving phase-change problems is presented. The governing equations for the conservation of mass, momentum, and energy are solved using a control-volume-based discretization scheme. In Ike first approach, the physical space is mapped onto a simpler domain and the moving boundary is immobilized using Landau transformation. The computations are carried out on a uniform orthogonal grid in the transformed space using the stream function-vorticity formulation. The need to retain all the terms in the governing equations arising from the transformation, for an accurate simulation, is investigated. Simplifications in the governing equations have been used in the literature and are discussed. Both implicit and explicit methods are used to track the phase front. In the second approach, the computations are carried out on a uniform fixed grid in the physical space with primitive variables. The enthalpy-porosity formulation, with appropriate so...

MIXED CONVECTION FROM AN ISOLATED HEAT SOURCE IN A RECTANGULAR ENCLOSURE

Abstract The mixed convection transport from an isolated thermal source, with a uniform surface heat flux input and located in a rectangular enclosure, is studied numerically. The enclosure simulates a practical system such as an oven or an air-cooled electronic device, where an airstream flows through the openings on the two vertical walls. The heat source represents a heater or an electronic component located in such an enclosure. The interaction of the cooling stream with the buoyancy-induced flow from the heat source is of interest in this work. Laminar, two-dimensional flow is assumed, and the problem lies in the mixed convection regime, governed by the buoyancy parameter GrIRe1 and the Reynolds number Re. Other significant variables include the locations of the heat source and the outflow opening. The inflow is kept at a fixed position. The mathematical model is developed with vorticity and stream function, along with temperature, as the dependent variables. The unsteady terms are retained in the vo...

Fluid Flow and Mixed Convection Transport From a Moving Plate in Rolling and Extrusion Processes

The heat transfer arising due to the movement of a continuous heated plate in processes such as hot rolling and hot extrusion has been studied. Of particular interest were the resulting temperature distribution in the solid and the proper imposition of the boundary conditions at the location where the material emerges from a furnace or die. These considerations are important in the simulation and design of practical systems. A numerical study of the thermal transport process has been carried out, assuming a two-dimensional steady circumstance. The boundary layer equations, as well as full governing equations including buoyancey effects, are solved employing finite difference techniques. The effect of various physical parameters, which determine the temperature and flow fields, is studied in detail. The significance of these results in actual manufacturing processes is discussed.

Mixed convection from a localized heat source in a cavity with conducting walls: A numerical study

Mixed convection is studied numerically in the case of an isolated, constant source of heat input within a rectangular enclosure. An external flow enters the enclosure through an opening in the left vertical wall and exits from another opening in the right vertical wall. This configuration leads to a conjugate heat transfer problem and simulates the air cooling of electronic components. Various parameters arise in this problem, particularly the Reynolds number, the buoyancy parameter Gr/Re2, the ratio of the thermal conductivity of the wall material to that of the fluid taken as air, and several geometric parameters. The time-dependent continuity and Navier-Stokes equations are transformed into a system of equations with the stream function and the vorticity as the dependent variables. The energy equation is solved over the entire domain, using the corresponding properties for the solid and fluid regions. The control volume approach is employed in order to discredit the governing equations for their numer...

Recirculating mixed convection flow for energy extraction

Abstract Energy may be extracted from the sensible heat stored in a body of fluid by means of a recirculating flow. A numerical study of the time-dependent, two-dimensional, laminar, convective flow that arises is carried out. The hot fluid is withdrawn at the top and the cold fluid discharged at the bottom of the storage region to preserve the thermal stratification. The nature of the flow is found to be very strongly affected by the buoyancy and the flow configuration. Numerical results are presented over a wide range of governing parameters, that arise from the inflow conditions, flow configuration and the heat transfer mechanisms at the boundaries.

Thermal and fluid flow effects during solidification in a rectangular enclosure

Abstract An analysis is carried out for the solidification in a rectangular enclosure whose top and bottom surfaces are kept adiabaticand sides are kept at a constant temperature. The transient effects of solidification accompanied by natural convection have been studied in detail. The governing equations are written for the temperature, vorticity, stream function and velocity in the melt along with the heat conduction equations through the solid and the mold. The non-linear coupled equations have been non-dimensionalized and solved with the aid of the Alternating Direction Implicit finite difference method. The velocity profiles in the melt, and the temperature distribution in the melt, the solid and the mold are shown. Isotherms and streamlines in the melt are plotted for different Rayleigh numbers. The dependence of the melt-solid interface movement upon various non-dimensional parameters, such as Rayleigh number (5 × 10 2 −5/s 10 5 Prandtl number (0.1–100), aspect ratio (1.1–5.5), Stefan number (0.5–10) and a parameter indicating the effect of superheat (0.67–2.33) are also studied.

Heat Transfer in Nanofluids

1Dipartimento di Ingegneria Aerospaziale e Meccanica, Seconda Universita degli Studi di Napoli, Via Roma 29, 81031 Aversa, Italy 2Department of Mechanical and Aerospace Engineering, Rutgers, The State University of New Jersey, Piscataway, New Brunswick, NJ 08901-8554, USA 3Laboratory of Thermodynamics in Emerging Technologies, Department of Mechanical and Process Engineering, ETH Zurich, 8092 Zurich, Switzerland

On transition mechanisms in vertical natural convection flow

An experimental investigation has been made of the processes occurring during the natural transition from laminar to turbulent flow of natural convection flow of water adjacent to a flat vertical surface where the surface heat flux is uniform. Measurements of both the velocity and temperature fields were made over wide ranges of the heat flux and at various downstream locations. Of principal interest were the definitions of the boundaries of the transition regime and their determination at several values of the surface heat flux. The interaction of the velocity and temperature fields during transition was measured. Our results show that transition events are not correlated in terms of the Grashof number G *. The form G */ x n , where n is of order ½ was found to give satisfactory correlations. Measurements of the frequency and growth rate of disturbances indicate the primacy of the velocity field during transition and show that the growth of turbulence in the temperature field lags behind that in the velocity field. The study of the turbulence growth, in terms of intermittency factors in both the velocity and temperature fields, resulted in unambiguous criteria for the boundaries of the transition regime. Our results suggest a kinetic energy flux parameter E and a single value closely correlates both our measurements of the onset of transition as well as those from all past studies known to us, for both different fluids and heating conditions.