Parallel Disk System Research Articles

Effects of groove orientation on transmission characteristics of hydro-viscous film in the parallel-disk system

The disk groove can greatly influence the hydrodynamic behaviors of the rotating film, especially on the cooling performance and the transmission efficiency. In the present work, the effects of groove orientation on the hydro-viscous transmission of the parallel-disk system are investigated. The Reynolds equation and thermal equation, considering tangential Coriolis effect and temperature–viscosity dependency, are derived and solved. The effects of the groove orientation on the shear stress, load-carrying capacity, viscous torque, and transmission efficiency are analyzed. The results reveal that the Coriolis resisting torque can be restrained but the load-carrying capacity declines if the groove orientation is consistent with the rotating direction, and the variation of the transmission efficiency can even be inverted at the turning point of the groove orientation. Therefore, the effects of groove orientation must be paid more attention in the hydro-viscous transmission.

Coriolis effects on torque transmission of hydro-viscous film in parallel disks with imposed throughflow

The imposed throughflow into rotating parallel disk system is to decrease temperature rise of hydro-viscous film flow, but the induced Coriolis effects are usually underestimated on torque transmission. The analytical expressions of thin-film parameters are obtained based on Navier-Stokes equations with the method of approximate analytical iteration. The Coriolis force and the corresponding influence on torque transmission are analyzed by analytical calculation and experimental verification. The results show that the tangential Coriolis force serves as resistance to the viscous torque transmission and the Coriolis torque loss can lead to primary reduction of efficiency among all motion effects. Therefore, the Coriolis effects should be paid more attention for the practical designs and applications of rotating hydro-viscous parallel-disk systems with imposed throughflow.

Experimental Study of Single Phase Heat Transfer and Pressure Loss in a Spiraling Radial Inflow Microchannel Heat Sink

This paper presents an experimental study of the heat transfer and pressure drop characteristics of a single phase high heat flux microchannel cooling system with spiraling radial inflow. The heat sink provides enhanced heat transfer with a simple inlet and outlet design while providing uniform flow distribution. The system is heated from one conducting wall made of copper and uses water as a working fluid. The microchannel has a 1 cm radius and a 300 μm gap height. Experimental results show, on average, a 76% larger pressure drop compared to an analytic model for laminar flow in a parallel disk system with spiral radial inflow. The mean heat transfer coefficients measured are up to four times the heat transfer coefficient for unidirectional laminar fully developed flow between parallel plates with the same gap height. Flow visualization studies indicate the presence of secondary flows and the onset of turbulence at higher flow rates. Combined with the thermally developing nature of the flow, these characteristics lead to enhanced heat transfer coefficients relative to the laminar parallel plate values. Another beneficial feature of this device, for high heat flux cooling applications, is that the thermal gradients on the surface are small. The average variation in surface temperature is 18% of the total bulk fluid temperature gain across the device. The system showed promising cooling characteristics for electronics and concentrated photovoltaics applications with a heat flux of 113 W/cm2 at a surface temperature of 77 °C and a ratio of pumping power to heat rate of 0.03%.

Strip-oriented asynchronous prefetching for parallel disk systems

Sequential prefetching schemes are widely employed in storage servers to mask disk latency and improve system throughput. However, existing schemes cannot benefit parallel disk systems as expected due to the fact that they ignore the distinct internal characteristics of the parallel disk system, in particular, data striping. Moreover, their aggressive prefetching pattern suffers from premature evictions and prolonged request latencies. In this paper, we propose a strip-oriented asynchronous prefetching (SoAP) technique, which is dedicated to the parallel disk system. It settles the above-mentioned problems by providing multiple novel features, e.g., enhanced prediction accuracy, adaptive prefetching strength, physical data layout awareness, and timely prefetching. To validate SoAP, we implement a prototype by modifying the software redundant arrays of inexpensive disks (RAID) under Linux. Experimental results demonstrate that SoAP can consistently offer improved average response time and throughput to the parallel disk system under non-random workloads compared with STEP, SP, ASP, and Linux-like SEQPs.

Thermal Nanofluid Property Model With Application to Nanofluid Flow in a Parallel Disk System—Part II: Nanofluid Flow Between Parallel Disks

This is the second part of a two-part paper which proposes a new theory explaining the experimentally observed enhancement of the thermal conductivity, knf, of nanofluids (Part I) and discusses simulation results of nanofluid flow in an axisymmetric jet-impingement cooling system using different knf-models (Part II). Specifically, Part II provides numerical simulations of convective nanofluid heat transfer in terms of velocity profiles, friction factor, temperature distributions, and Nusselt numbers, employing the new knf-model. Flow structures and the effects of nanoparticle addition on heat transfer and entropy generation are discussed as well. Analytical expressions for velocity profiles and friction factors, assuming quasi-fully-developed flow between parallel disks, have been derived and validated for nanofluids as well. Based on the numerical simulation results for both alumina-water nanofluids and pure water, it can be concluded that nanofluids show better heat transfer performance than convectional coolants with no great penalty in pumping power. Furthermore, the system’s entropy generation rate is lower for nanofluids than for pure water.

Thermal Nanofluid Property Model With Application to Nanofluid Flow in a Parallel-Disk System—Part I: A New Thermal Conductivity Model for Nanofluid Flow

This is a two-part paper, which proposes a new theory explaining the experimentally observed enhancement of the thermal conductivity, knf, of nanofluids (Part I) and discusses simulation results of nanofluid flow in a radial parallel-plate channel using different knf-models (Part II). Specifically, Part I provides the derivation of the new model as well as comparisons with benchmark experimental data sets and other theories, focusing mainly on aluminum and copper oxide nanoparticles in water. The new thermal conductivity expression consists of a base-fluid static part, kbf, and a new “micromixing” part, kmm, i.e., knf = kbf + kmm. While kbf relies on Maxwell’s theory, kmm encapsulates nanoparticle characteristics and liquid properties as well as Brownian-motion induced nanoparticle fluctuations, nanoparticle volume fractions, mixture-temperature changes, particle–particle interactions, and random temperature fluctuations causing liquid-particle interactions. Thus, fundamental physics principles include the Brownian-motion effect, an extended Langevin equation with scaled interaction forces, and a turbulence-inspired heat transfer equation. The new model predicts experimental data for several types of metal-oxide nanoparticles (20 < dp < 50 nm) in water with volume fractions up to 5% and mixture temperatures below 350 K. While the three competitive theories considered match selectively experimental data, their needs for curve-fitted functions and arbitrary parameters make these models not generally applicable. The new theory can be readily extended to accommodate other types of nanoparticle-liquid pairings and to include nonspherical nanomaterial.

PRE-BUD

A critical problem with parallel I/O systems is the fact that disks consume a significant amount of energy. To design economically attractive and environmentally friendly parallel I/O systems, we propose an energy-aware prefetching strategy (PRE-BUD) for parallel I/O systems with disk buffers. We introduce a new architecture that provides significant energy savings for parallel I/O systems using buffer disks while maintaining high performance. There are two buffer disk configurations: (1) adding an extra buffer disk to accommodate prefetched data, and (2) utilizing an existing disk as the buffer disk. PRE-BUD is not only able to reduce the number of power-state transitions, but also to increase the length and number of standby periods. As such, PRE-BUD conserves energy by keeping data disks in the standby state for increased periods of time. Compared with the first prefetching configuration, the second configuration lowers the capacity of the parallel disk system. However, the second configuration is more cost-effective and energy-efficient than the first one. Finally, we quantitatively compare PRE-BUD with both disk configurations against three existing strategies. Empirical results show that PRE-BUD is able to reduce energy dissipation in parallel disk systems by up to 50 percent when compared against a non-energy aware approach. Similarly, our strategy is capable of conserving up to 30 percent energy when compared to the dynamic power management technique.

Quality of security adaptation in parallel disk systems

In the past decade, parallel disk systems have been highly scalable and able to alleviate the problem of disk I/O bottleneck, thereby being widely used to support data-intensive applications. Although a variety of parallel disk systems were developed, most existing disk systems lack a means to adaptively control the quality of security for dynamically changing workloads. We address this gap in disk technology by designing, implementing, and evaluating a quality of security control framework for parallel disk systems, or ASPAD for short, that makes it possible for parallel disk systems to adapt to changing security requirements and workload conditions. The ASPAD framework comprises four major components, namely, a security service middleware, a dynamic data-partitioning mechanism, a response time estimator, and an adaptive security quality controller. The framework is conducive to adaptively and expeditiously determining security services for requests submitted to a parallel disk system in a way to improve security of the disk system while making an effort to guarantee desired response times of the requests. We conduct extensive experiments to quantitatively evaluate the performance of the proposed ASPAD framework. Empirical results show that ASPAD significantly improves the overall performance of parallel disk systems over the same disk systems without using the ASPAD framework.

Nanofluid convective heat transfer in a parallel-disk system

Inherently low thermal conductivities of basic fluids form a primary limitation in high-performance cooling which is an essential requirement for numerous thermal systems and micro-devices. Nanofluids, i.e., dilute suspensions of, say, metal-oxide nanoparticles in a liquid, are a new type of coolants with better heat transfer performances than their pure base fluids alone. Using a new, experimentally validated model for the thermal conductivity of nanofluids, numerical simulations have been executed for alumina-water nanofluid flow with heat transfer between parallel disks. The results indicate that, indeed, nanofluids are promising new coolants when compared to pure water. Specifically, smoother mixture flow fields and temperature distributions can be achieved. More importantly, given a realistic thermal load, the Nusselt number increases with higher nanoparticle volume fraction, smaller nanoparticle diameter, reduced disk-spacing, and, of course, larger inlet Reynolds number, expressed in a novel form as Nu = Nu(Re and Br). Fully-developed flow can be assumed after a critical radial distance, expressed in a correlation R crit = fct(Re), has been reached and hence analytic solutions provide good approximations. Nanofluids reduce the system’s total entropy generation rate while hardly increasing the required pumping power for any given Re in. Specifically, minimization of total entropy generation allows for operational and geometric system-optimization in terms of S gen = fct (Re and δ).

Generalizations of Ruby's formula for the geometric efficiency of a parallel-disk source and detector system

Ruby's formula for a parallel-disk source and detector system has been generalized to include non-coaxial disks and a source disk with an arbitrary radial distribution of surface emissivity. The results in all cases are given as one-dimensional integrals of products of Bessel functions and exponentials. For the case of coaxial disks, the solution can always be expressed in closed form as a sum of complete elliptic integrals. For the coaxial case with constant emissivity treated by Ruby, the solution is also given as a simple numerically friendly angular integral.

A hierarchical disk scheduler for multimedia systems

An integrated storage platform for open systems should be able to meet the requirements of deterministic applications, multimedia systems, and traditional best-effort applications. It should also provide a scheduling mechanism fitting all those types of applications. In this paper, we propose a two-level hierarchical disk scheduling scheme, named 2-Q, which can guarantee deterministic deadlines, maximize the number of statistic real-time streams processed by the disk system, and minimize the average latency for best-effort requests. The upper level of the scheduling architecture, server level, is divided into three queues: deterministic, statistic, and best-effort requests. Each server may have its own scheduling algorithm. The lower level, disk driver, chooses the ready streams using its own scheduling criteria. We also propose an adaptive admission control algorithm relying on worst and average values of disk server utilization. Only streams satisfying the admission algorithm criteria are accepted for further processing by the disk server. The solution is extended to a parallel disk system by using a third hierarchical level, named meta-scheduler, briefly described in the paper. The performance evaluations demonstrate that our scheduling architecture is adequated for handling stream sets with different deterministic, statistic, or best-effort requirements.

Performing out-of-core FFTs on parallel disk systems

The Fast Fourier Transform (FFT) plays a key role in many areas of computational science and engineering. Although most one-dimensional FFT problems can be solved entirely in main memory, some important classes of applications require out-of-core techniques. For these, use of parallel I/O systems can improve performance considerably. This paper shows how to perform one-dimensional FFTs using a parallel disk system with independent disk accesses. We present both analytical and experimental results for performing out-of-core FFTs in two ways: using traditional virtual memory with demand paging, and using a provably asymptotically optimal algorithm for the Parallel Disk Model (PDM) of Vitter and Shriver. When run on a DEC 2100 server with a large memory and eight parallel disks, the optimal algorithm for the PDM runs up to 144.7 times faster than in-core methods under demand paging. Moreover, even including I/O costs, the normalized times for the optimal PDM algorithm are competitive, or better than, those for in-core methods even when they run entirely in memory.

Z -iteration

Multiple-class multiple-resource (MCMR) systems, where each class of customers requires a particular set of resources, are common. These systems are often analyzed under steady-state conditions. We describe a simple method, referred to as Z-iteration , to estimate both transient and steady-state performances of such systems. The method makes use of results and techniques available from queueing theory, network analysis, dynamic flow theory, and numerical analysis. We show the generality of the Z-iteration by applying it to an ATM network, a parallel disk system, and a distributed batch system. Validations against discrete-event simulations show the accuracy and computational advantages of the Z-iteration.

A study parallel disk organizations

In this paper, several issues related to designing a parallel disk system are discussed. Results of performance evaluation of several parallel disk organizations are presented. A characterization of the disk systems is also presented. Issues such as scalability, networking etc. are discussed. Several problems for future research on improving the I/O performance are pointed out.

Effect of Rotation and Coolant Throughflow on the Heat Transfer and Temperature Field in an Enclosure

Measurements were performed to determine the local heat transfer coefficients along the heated shroud of a shrouded parallel disk system. The temperature field within the enclosure formed by the shroud and the disks was also measured. One of the disks was rotating, whereas the other disk and the shroud were stationary. Coolant air was introduced into the enclosure through an aperture at the center of the stationary disk and exited through a slot at the rim of the rotating disk. The coolant entrance-exit arrangement differed from that of previous studies, with the additional difference that the incoming coolant stream was free of rotation. The coolant flow rate, the disk rotational speed, and the aspect ratio of the enclosure were varied during the experiments. The heat transfer coefficients were found to be increasingly insensitive to the absence or presence of rotation as the coolant flow rate increased. There was a general increase of the transfer coefficients with increasing coolant flow rate, especially for low rotational speeds. The temperature field in the enclosure differed markedly depending on the relative importance of rotation and of coolant throughflow. When the latter dominates, the temperature in the core is relatively uniform, but in the presence of strong rotation there are significant nonuniformities. A comparison was made between the present Nusselt number results and those of prior experiments characterized by different coolant entrance—exit arrangements. The positioning of the coolant exit slot relative to the direction of the boundary layer flow on the shroud emerged as an important factor in the comparison.

Experiments on a shrouded, parallel disk system with rotation and coolant throughflow

The heat transfer and fluid flow characteristics of a cylindrical enclosure having both rotating and stationary walls have been investigated in the presence of coolant throughflow. The research was motivated by cooling applications in cavities and enclosures which may be situated adjacent to the rotating shaft in gas turbines, compressors, and similar devices. The test section walls consisted of a heated rotating disk, a heated stationary cylindrical shroud, and an insulated stationary disk. The coolant passing through the enclosure was air. The experiments were performed over a range of disk rotational speeds, coolant flow rates and spacings between the disks. The local heat transfer coefficients on the rotating disk were found to increase with increasing rotational speed, increasing coolant flow rate, and decreasing spacing. The shapes of the radial distributions of the transfer coefficients suggested the existence of laminar, transition, and turbulent regimes. In the laminar regime, the transfer coefficients were relatively insensitive to the coolant flow rate. For the shroud, the trends with rotational speed, coolant flow, and spacing were generally similar to those for the rotating disk. However, owing to backflows along the shroud at the lower rotational speeds, the trends were more complex in that range. Flow visualization, accomplished by smoke injection, revealed a succession of flow patterns which could be ordered according to the ratio of the coolant flow rate to the disk rotational speed.