Steve Armfield

Direct simulation of weak laminar plane fountains in a homogeneous fluid

Abstract The behaviour of weak laminar plane fountains that result from the injection of dense fluids upwards into a large container of homogeneous fluid of lower density is studied numerically by using a time-accurate finite volume code. The study is an extension of a previous numerical study on weak laminar axisymmetric fountains. Weak laminar plane fountains with both a uniform and a parabolic profile of the discharge velocity at the source have been investigated. The initial, temporary and final characteristic fountain heights and the times for the fountain front to reach these heights have been determined and scaled. At steady state, a height scale as well as a horizontal length scale for the fountain width are determined. The vertical distribution of the vertical velocity and temperature on the symmetry line are shown to scale with this height. The height and horizontal length scales have been used to scale the horizontal variation of both the horizontal and the vertical velocity in the fountain core at steady state.

Analysis of exergy destruction in data centres

IT equipment and systems, housed in data centres, consume a considerable amount of electricity. Most of the electrical energy consumed by the data centre IT equipment is released in the form of heat. From a second law of thermodynamics analysis point of view, the mixing of hot and cold air streams in the room caused by hot air recirculation is an irreversible process, leading to wasted work potential in data centres. In the work presented here, a numerical analysis of flow and temperature distribution of a raised-floor data centre is conducted in order to evaluate the thermal performance of the data centre. Subsequently, from flow patterns and temperature profiles, a detailed exergy analysis of the data centre is performed to get a better understanding of the room airspace irreversibilities. The amount of the exergy as well as the exergy destroyed in the airspace is evaluated in order to cast a light on the nature of the irreversibilities. Finally, new performance metrics based on the second law of thermodynamics are proposed and used to assess the performance of a data centre. A comparison between the performance metrics based on the first and second law of thermodynamics as well as the limitations of the newly derived performance metrics are discussed.

Combined natural convection cooling of a drink can

We investigate natural convection cooling of the fluid in a drink can placed in a refrigerator by simulating the full combined boundary layer system on the can wall. The cylindrical can is filled with water at initial nondimensional temperature 0, and located within a larger cylindrical container filled with air at initial temperature −1. The outer container walls are maintained at constant temperature −1. Initially both fluids are at rest. Two configurations are examined: the first has the inner can placed vertically in the middle of the outer container with no contact with the outer container walls, and the second has the inner can placed vertically at the bottom of the outer container. The results are compared to those obtained by assuming that the inner can walls are maintained at a constant temperature, showing similar basic flow features and scaling relations, but with very different proportionality constants. doi:10.1017/S1446181111000538

Addressing Thermal Challenges in Design of Data Centres

Aggregation of small networking hardware has led to an ever increasing power density in data centres. The energy consumption of IT systems is continuing to rise substantially owing to the demands of electronic information and storage requirements. Energy consumption of data centres can be severely and unnecessarily high due to inadequate localised cooling and densely packed rack layouts. However, as heat dissipation in data centres rises by orders of magnitude, inefficiencies such as air recirculation causing hot spots, leading to flow short-circuiting will have a significant impact on the thermal manageability and energy efficiency of the cooling infrastructure. Therefore, the thermal management of high-powered electronic components is a significant challenge for cooling of data centres. In this project, an operational data centre has been studied. Field measurements of temperature have been performed. Numerical analysis of flow and temperature fields is conducted in order to evaluate the thermal behaviour of the data centre. A number of undesirable hot spots have been identified. To rectify the problem, a few practical design solutions to improve the cooling effectiveness have been proposed and examined to ensure a reduced air-conditioning power requirement. Therefore, a better understanding of the cooling issues and the respective proposed solutions can lead to an improved design for future data centres.© 2010 ASME