Suhas V. Patankar

Bio: Suhas V. Patankar is an academic researcher from Innovative Research Inc.. The author has contributed to research in topics: Heat transfer & Raised floor. The author has an hindex of 15, co-authored 36 publications receiving 22350 citations. Previous affiliations of Suhas V. Patankar include University of Minnesota.

Numerical heat transfer and fluid flow

Abstract: This book focuses on heat and mass transfer, fluid flow, chemical reaction, and other related processes that occur in engineering equipment, the natural environment, and living organisms. Using simple algebra and elementary calculus, the author develops numerical methods for predicting these processes mainly based on physical considerations. Through this approach, readers will develop a deeper understanding of the underlying physical aspects of heat transfer and fluid flow as well as improve their ability to analyze and interpret computed results.

Airflow distribution through perforated tiles in raised-floor data centers

Abstract: Raised-floor data centers are the most commonly used facilities for housing computer and telecommunication equipment. To adequately cool this equipment, the cooling air through perforated tiles must be distributed properly. The airflow distribution depends on the pressure distribution or the flow field in the space under the raised floor (plenum); it is a complex function of a large number of variables, including the size of the plenum, the open area of the perforated tiles, the locations and flow rates of the computer room air conditioner (CRAC) units, and the size and location of the under-floor obstructions like cables and pipes. In this article, the effect of these parameters on the airflow distribution is studied using an idealized one-dimensional computational model. Within the one-dimensional framework, the airflow distribution is governed by two dimensionless parameters: one related to the pressure variation in the plenum and the other to the frictional resistance. Results, in terms of distributions of pressure in the plenum and flow rates through the perforated tiles, are presented over a range of values of these two parameters. These results provide an understanding of the fundamental fluid mechanical processes controlling the airflow distribution through the perforated tiles. The one-dimensional model is used to calculate flow rates for two possible arrangements of the CRAC units, and these results are compared with those given by a three-dimensional model.

Use of Computational Fluid Dynamics for Calculating Flow Rates Through Perforated Tiles in Raised-Floor Data Centers

Abstract: This paper describes a computational fluid dynamics model for calculating airflow rates through perforated tiles in raised-floor data centers. The model is based on the assumption that the pressure in the space above the raised floor is uniform, which allows the calculation to be limited to the space below the raised floor. It uses a finite-volume method, the k-∊ turbulence model, and a multigrid method. The model is applied to a real-life data center. The calculated results for velocity and pressure distributions are discussed. The flow rates through the perforated tiles are shown to be in good agreement with the measured values.

Techniques for Controlling Airflow Distribution in Raised-Floor Data Centers

Abstract: In raised-floor data centers, the airflow rates through the perforated tiles must meet the cooling requirements of the computer servers placed next to the tiles. The data centers house a wide range of equipment, and the heat load pattern on the floor can be quite arbitrary and changes as the data center evolves. To achieve optimum utilization of the floor space and the flexibility for rearrangement and retrofitting, the designers and managers of data centers must be able to modify the airflow rates through the perforated tiles. The airflow rates through the perforated tiles are governed primarily by the pressure distribution under the raised floor. Thus, the key to modifying the flow rates is to influence the flow field in the plenum. This paper discusses a number of techniques that can be used for controlling airflow distribution. These techniques involve changing the plenum height and open area of perforated tiles, and installing thin (solid and perforated) partitions in the plenum. A number of case studies, using a mathematical model, are presented to demonstrate the effectiveness of these techniques.

A methodology for the design of perforated tiles in raised floor data centers using computational flow analysis

Abstract: An important aspect of the design of data centers involves sizing of the perforated floor tiles for return of cold air, the size of the space under the raised floor, and placement of the DP equipment and modular chillers. The flow through individual perforated tiles needs to fulfil the cooling requirements of the computer equipment placed adjacent to them. The novelty of this paper lies in the treatment of the volume under the raised floor as a uniformly pressurized plenum. The accuracy of the Pressurized Plenum model is demonstrated with reference to a computational fluid dynamics (CFD) analysis of the recirculating flow under the raised floor and the limits of its validity are also identified. The simple model of the volume under the raised floor enables use of the technique of flow network modeling (FNM) for the prediction of the distribution of flow rates exiting from the various tiles. An inverse design method is proposed for one-step design of the perforated tiles and flow balancing plates for individual chillers. Subsequent use of the FNM technique enables assessment of the performance of the actual system. Further, required design changes to an existing system can also be evaluated using the FNM analysis in a simple, quick, and accurate manner. The resulting design approach is very simple and efficient, and is well suited for the design of modern data centers.

Bubbles, Drops, and Particles

Abstract: The standard κ-ϵ equations and other turbulence models are evaluated with respect to their applicability in swirling, recirculating flows. The turbulence models are formulated on the basis of two separate viewpoints. The first perspective assumes that an isotropic eddy viscosity and the modified Boussinesq hypothesis adequately describe the stress distributions, and that the source of predictive error is a consequence of the modeled terms in the κ-ϵ equations. Both stabilizing and destabilizing Richardson number corrections are incorporated to investigate this line of reasoning. A second viewpoint proposes that the eddy viscosity approach is inherently inadequate and that a redistribution of the stress magnitudes is necessary. Investigation of higher-order closure is pursued on the level of an algebraic stress closure. Various turbulence model predictions are compared with experimental data from a variety of isothermal, confined studies. Supportive swirl comparisons are also performed for a laminar flow case, as well as reacting flow cases. Parallel predictions or contributions from other sources are also consulted where appropriate. Predictive accuracy was found to be a partial function of inlet boundary conditions and numerical diffusion. Despite prediction sensitivity to inlet conditions and numerics, the data comparisons delineate the relative advantages and disadvantages of the various modifications. Possible research avenues in the area of computational modeling of strongly swirling, recirculating flows are reviewed and discussed.

Review on thermal energy storage with phase change materials and applications

Abstract: The use of a latent heat storage system using phase change materials (PCMs) is an effective way of storing thermal energy and has the advantages of high-energy storage density and the isothermal nature of the storage process. PCMs have been widely used in latent heat thermal-storage systems for heat pumps, solar engineering, and spacecraft thermal control applications. The uses of PCMs for heating and cooling applications for buildings have been investigated within the past decade. There are large numbers of PCMs that melt and solidify at a wide range of temperatures, making them attractive in a number of applications. This paper also summarizes the investigation and analysis of the available thermal energy storage systems incorporating PCMs for use in different applications.

Additive manufacturing of metallic components – Process, structure and properties

Abstract: Since its inception, significant progress has been made in understanding additive manufacturing (AM) processes and the structure and properties of the fabricated metallic components. Because the field is rapidly evolving, a periodic critical assessment of our understanding is useful and this paper seeks to address this need. It covers the emerging research on AM of metallic materials and provides a comprehensive overview of the physical processes and the underlying science of metallurgical structure and properties of the deposited parts. The uniqueness of this review includes substantive discussions on refractory alloys, precious metals and compositionally graded alloys, a succinct comparison of AM with welding and a critical examination of the printability of various engineering alloys based on experiments and theory. An assessment of the status of the field, the gaps in the scientific understanding and the research needs for the expansion of AM of metallic components are provided.

Solution of the implicitly discretised reacting flow equations by operator-splitting

Abstract: A non-iterative method for handling the coupling of the implicitly discretised time-dependent fluid flow equations is described. The method is based on the use of pressure and velocity as dependent variables and is hence applicable to both the compressible and incompressible versions of the transport equations. The main feature of the technique is the splitting of the solution process into a series of steps whereby operations on pressure are decoupled from those on velocity at each step, with the split sets of equations being amenable to solution by standard techniques. At each time-step, the procedure yields solutions which approximate the exact solution of the difference equations. The accuracy of this splitting procedure is assessed for a linearised form of the discretised equations, and the analysis indicates that the solution yielded by it differs from the exact solution of the difference equations by terms proportional to the powers of the time-step size. By virtue of this, it is possible to dispense with iteration, thus resulting in an efficient implicit scheme while retaining simplicity of implementation relative to contemporary block simultaneous methods. This is verified in a companion paper which presents results of computations carried out using the method.

Enhancements of the simple method for predicting incompressible fluid flows

Abstract: Variations of the SIMPLE method of Patankar and Spalding have been widely used over the past decade to obtain numerical solutions to problems involving incompressible flows. The present paper shows several modifications to the method which both simplify its implementation and reduce solution costs. The performances of SIMPLE, SIMPLER, and SIMPLEC (the present method) are compared for two recirculating flow problems. The paper is addressed to readers who already have experience with SIMPLE or its variants.