A computational fluid dynamics evaluation of a pneumatic safety relief valve

Safety relief valves are well established components preventing catastrophic failure of pressurised systems when non-normal operating conditions occur. However, it is only recently with developments in CFD techniques that the capability to predict the complex flow conditions occurring in the valves has been possible resulting in only limited studies being found in the literature. This paper presents experimental and theoretical investigations applied to a safety relief valve designed for the refrigeration industry but extended here to consider pneumatic systems since air is the compressible fluid. The discharge flow rate and valve forces are determined both theoretically and experimentally for different valve lift conditions and related to the detailed flow conditions (pressure, temperature and Mach number) in the valve predicted by CFD techniques. The CFD code FLUENT has been used with a two dimensional axisymmetric RANS approach using the k-İ turbulent model to predict the highly compressible flow through the valve. The model has been validated by comparison with experimental measurements and the predicted results show good agreement, providing confidence in the use of CFD techniques for valve design and improvement

Transient thermal analysis of a data centre cooling system under fault conditions

Data centres housing the IT infrastructure of large organisations constitute a considerable technical challenge to ensure 100% operational availability for mission critical IT systems. Specifying plant cooling systems to maintain suitable temperature levels and dissipate the heat generated can be carried out using industry standard design methods. However, accounting for perturbations in cooling due to failure of plant and restart of backup systems requires for faster thermal transients to be addressed than would normally be encountered in building system analysis. It is in this context that this paper describes the modelling and analysis of a 5 MW chilled water cooling system used for the cooling of a recently constructed UK data centre. The model has been developed using the TRNSYS software and includes a full model of the energy transfers for the data centre including chillers, hydraulic network, valve models and each of the 70 Room Air Conditioning Units. The coupling between the data centre air temperature levels and the cooler system has enabled a full assessment of the cooling system design in response to system perturbations. A number of scenarios are examined involving the failure of the chillers and how the inherent thermal inertia of the system plus additional inertia achieved through buffer vessels allowed a suitable design to be achieved. The detailed transient analysis model allowed the sizing of these vessels effectively and to gain a better understanding of the chilled water plant operation, both in normal conditions and in the case of failure

The determination and evaluation of Nitinol constitutive models for finite element analysis

Superelastic Ni-Ti (Nitinol) is a member of the shape memory alloy (SMA) family of metals. The physical properties of Nitinol are highly dependant on a number of factors, including manufacturing method, subsequent processing, operating temperature, and strain rate. These factors complicate the prescription of material constitutive models, leading to complexities in the computational analysis of Nitinol components. The current work explores the limitations in the Nitinol material model available in existing commercial finite element (FE) software using a series of specially design experimental tests and representative FE models

The development and application of time resolved PIV at the University of Strathclyde

This paper describes the development of time resolved particle image velocimetry (PIV) within the Department of Mechanical Engineering at the University of Strathclyde. The Department's first PIV systems were developed on a limited budget and used existing and second hand equipment. The original technique which, employed 16mm high speed cinematography, is described. The introduction and development of low cost systems employing high speed digital video (HSDV) is discussed and, finally, the Department's new time resolved PIV system, supplied by Dantec Dynamics, is introduced. For each of the PIV systems that have been developed a critical analysis of their functionality is given and samples of the data that they have been produced are shown. Data are presented from systems such as de-rotated centrifugal impellers, air bubbles growing in columns of water, pulsatile jets and vortex shedding

Improved prediction of shell side heat transfer in horizontal evaporative shell and tube heat exchangers

This paper presents an improved prediction method for the heat transfer and pressure drop in the shell side of a horizontal shell and tube evaporator. The results from an experimental test program are used in which a wide range of evaporating two-phase shell side flow data was collected from a TEMA E-shell evaporator. The data are compared with shell side heat transfer coefficient and pressure drop models for homogeneous and stratified flow. The comparison suggests a deterioration in the heat transfer data at low mass fluxes consistent with a transition from homogeneous to stratified flow. The pressure drop data suggest a stratified flow across the full test range. A new model is presented that suggests the transition in the heat transfer data may be due to the extent of tube wetting in the upper tube bundle. The new model, which also takes into account the orientation of the shell side baffles, provides a vast improvement on the predictions of a homogenous type model. The new model would enable designers of shell side evaporators/reboilers to avoid operating conditions where poor heat transfer could be expected, and it would also enable changes in process conditions to be assessed for their implications on likely heat transfer performance. (Abstract from WOK

CFD modelling of two-phase mixing/separation flow

Book chapter on Computational Fluid Dynamics modelling off two-phase mixing/separation flow

Norwich Union Data Centre 3 - Transient thermal analysis of the chilled water hydraulic network and the impact of chilled water temperature disturbances on the IT environment

Research report focusing on the transient thermal analysis of the chilled water hydraulic network and the impact of chilled water temperature disturbances on the IT environment

Engineering analysis: a pre-requisite for design

The design element of an engineering curriculum in a higher education degree course is often found to shape the structure and content of the whole course. That is, all other elements ranging from mathematics, applied science to finance and management are devised to provide the engineering student with sufficient knowledge to support the requirements of the design process. The definition and the description of the design process have been given considerable attention in the literature. For example Pugh (1991) discussed the design process in depth and presented what was to become an established view on the multitude of the diverse elements that exist and the skills that are required to be mastered. This diversity is often found to be rather troublesome for engineering teachers and the developers of engineering course curricula due to the different types of subject matter and the provision of effective teaching and learning environments

Experimental characteristcs of steam bubble growth at orifices in sub-cooled liquid

The experimentally determined characteristics of steam bubble growth when generated at a number of 1 mm diameter orifices in sub-cooled water are presented. Three orifices were used with a wide range of flowrates and liquid sub-coolings. Tests were conducted at pressures of 2 and 3 bar absolute and at constant flowrate conditions. A high speed cine camera recordings were used to determine the bubble geometrical characteristics such as volume, surface area, and centroid. This data indicated significant dependencies of flowrate, pressure and liquid sub-cooling as would be expected and these have been used to provide non-dimensional correlation's for bubble detachment volume and bubble formation time. The effect of neighbouring orifices was investigated by imposing combinations of different orifice flowrates adjacent to the orifice under investigation. The results indicated that the effect of neighbouring orifices is small for the conditions tested