A detailed knowledge of the flow structure and the heat transfer within blade-disc cavities is required for designing safe and efficient aero-engine compressors with a useful operating range. This paper presents the results from temperature field measurements obtained from the Multiple Cavity test facility at the University of Sussex. This emulates part of the secondary air system in an aircraft engine high-pressure compressor. It comprises four externally heated disc-cavities and is supplied by a cool bore flow. The heat transfer is studied with the help of a finite-element method using measured temperatures as boundary conditions. A validated 2D steady-state heat conduction analysis methodology is presented. Results are presented for a range of values of Rossby number, rotational and axial Reynolds numbers and the buoyancy parameter. The curve-fit type that is best suited for the temperature boundary condition specification is established using an independent Ansys APDL based study. The sensitivity of the overall cavity heat transfer to major driving mechanisms has been described. The Monte-Carlo analysis is used to reveal how a ±0.5 K uncertainty in temperature affected the Nu estimation.

AbstractFollowing its exceptional response to the 2003 severe acute respiratory syndrome (SARS) outbreak, the World Health Organization (WHO) gained new powers to securitise infectious disease outbreaks via the revised 2005 International Health Regulations (IHRs) and the ability to declare a Public Health Emergency of International Concern (PHEIC). This article investigates the declaration of a PHEIC in relation to the 2009 H1N1 flu pandemic, the 2014–16 Ebola outbreak, and the ongoing COVID-19 pandemic. It argues that the securitisation of these outbreaks was dependent upon global surveillance networks that utilised genetic technologies to visualise the molecular characteristics and spread of the pathogen in question. Genetic evidence in these cases facilitated the creation of a securitised object by revealing the unique and ‘untypable’ nature of the H1N1 and SARS-CoV-2 viruses and made visible the widespread prevalence of Ebola across the population of West Africa. The power of this evidence draws from a societal perception of science as producing objective ‘facts’ about the world that objectivise their objects of concern and empower political actors in the implementation of their security agendas. As a result, scientific evidence provided by genetic technologies now plays a necessary and indispensable role in the securitisation of infectious disease outbreaks.

A new correlation model is examined for capturing the combined influences of surface-to-nozzle distance , coolant flow rate on critical heat flux associated with spray evaporative cooling of vibrating surfaces. The correlation model is constructed using dimensional analysis by applying the Generalized Buckingham Pi-Theorem. The model is calibrated using experimentally-measured spray evaporative cooling data, taken from an electrically-heated horizontal flat circular test-piece excited by a shaker through a range of low and high frequencies of vibration, from small to large amplitude. To understand the combined effect of frequency, amplitude , surface-to-nozzle distance, at critical heat flux, Vibrational Reynolds Number, Acceleration Number, and Dimensionless Surface-to-Nozzle Distance are used. The results show that surface-to-nozzle distance, in the presence of dynamic effects, significantly influences the critical heat flux, whereas vibration amplitudes and frequencies have differing effects in response to variations in both surface-to-nozzle distance and flow rate. Surface-to-nozzle distance can either increase or decrease the heat transfer, depending on the vibration range. The calibrated correlation model is capable of predicting the effect of surface-to-nozzle distance on the critical heat flux with errors in the range -4.8% and + 10.5%.

A temperature control approach using evaporative spray cooling of vibrating surfaces in the nucleate boiling region is proposed and verified experimentally. This is relevant to temperature control of heat-generating automotive vehicle components. By exploiting an experimentally calibrated dynamic correlation model to represent evaporative spray cooling of a flat test-piece, a PID controller has been adopted with emphasis focused on the choice of gain parameters to ensure both stability of temperature control, and favourable responses in terms of relevant performance measures. Optimum linearisation of the correlation model has been achieved by solving an appropriate Wiener-Hopf equation, mainly to undertake a practical stability assessment of the closed-loop temperature control system. To verify the predicted control system performance, experimental measurements have been obtained from an instrumented, and spray-evaporatively-cooled, flat test-piece exposed to displacement vibration from a shaker. Experimental testing, appropriate to automotive vehicle component applications, includes large-amplitude, low frequency vibration at 12 mm and 1.9 Hz, and low amplitude, high-frequency vibration at 0.02 mm and 400 Hz. To assess the effects of different PID controller gains on the thermal performance of the thermal management system, a coefficient of performance (COP) is used, defined as the ratio of heat power removal to the required pumping power. To achieve a reduction in the settling time, and an increase in the rise time of stable control, a PID controller with a negative proportional gain showed most promising results. A 10.5% increase in COP was achieved in comparison to a PID controller with positive gains. This information is useful for the design and optimization of thermal management systems using evaporative spray cooling.

This paper presents local Nusselt numbers computed from experimental measurements of surface temperature of compressor disks in a multiple rotating cavity test rig with axial throughflow. A validated two-dimensional (2D) steady-state heat conduction analysis methodology is presented, using the actual test geometry, and 95% confidence intervals calculated using Monte Carlo simulation. Sensitivity of the solution to curve fitting types, geometric simplification, and surface instrumentation are explored. The results indicate that polynomial curves fits, while computational simple, are unsuitable especially at higher orders. It is shown that geometric simplifications, that typically simplify the algorithmic implementation, may also omit significant variation in heat flux at critical stress relieving locations. The effect of reducing measurement points in the analysis is to both overpredict heat transfer and increase the uncertainty of the results. Finally, the methodology is applied to previously published thermal data from the University of Sussex, facilitating qualitative discussion on the influence of the governing parameters. While this study does not overcome the inherent uncertainty associated with inverse solutions, it is intended to present a methodology that is readily available to the wider community for the analysis of thermal test data and suggests some guidelines at the planning and postprocessing stages. The range of experiment reported here covers: 1.13 × 105 < Rez < 5.14 × 105, 1.65 × 106 < Reθ < 3.16 × 106, 0.10 < Ro < 0.60, and 3.40 × 1011 < Gr < 1.25 × 1012.

A new simulation capability is presented to enable the performance of a hardware-based temperature control system to be assessed in thermally-managing heat-generating automotive vehicle powertrain parts. Temperature control is assumed to involve spray evaporative cooling of powertrain parts exposed to vibration. Two hypotheses are proposed to enable construction of a practical simulation that is both accurate and computationally efficient. The first is that a dynamic correlation model for single-nozzle spray evaporative cooling of a flat test-piece exposed to vibration, can be used as a reasonable model for multiple-nozzle spray evaporative cooling of component parts with curved cooling surfaces of non-horizontal orientation. The second is that the transient heat diffusion properties of a particular 3-dimensional component can be replaced by a 1-dimensional (1D) equivalence. To test this hypothesis, Finite Element models for two representative parts have been constructed and used to demonstrate the quality of the 1D heat diffusion equivalence, for which a fast Finite Difference solution can be exploited. To test the accuracy of test-piece surface temperature control simulation, an experimental test facility has been built in hardware, in which the temperature of two instrumented test-pieces exposed to vibration (from a shaker) are controlled by spray evaporative cooling. Each test piece is electrically-heated and the hardware control system is configured using PID control, for which appropriate gains are selected. Detailed comparisons of temperature control by hardware and simulation are given for the two test-pieces under static and dynamic conditions. Good agreement is generally obtained between simulated surface temperatures compared with measurements taken from both test-pieces. The paper shows that temperature control of a hardware-based control system using spray evaporative cooling of powertrain parts can be confidently simulated.

An experimental investigation of the effect of surface vibration on spray evaporative cooling has been undertaken using a dynamic test rig.The horizontal circular test section involved a spray nozzle on top of a shaker being shaking at different frequencies and amplitudes to examine the effect of vibration on the nucleate boiling regime.The combination of the two-phase spray cooling and dynamic surface conditions has not previously been studied.The results clearly show that dynamic surface conditions influence nucleate boiling.In general, the evidence shows that vibration impedes heat transfer.The influence of amplitude and frequency are shown however not to have the same trend for all the excess temperatures.Depending on the mechanism, combinations of amplitude and frequency can either increase or decrease the heat transfer coefficient compared with the static cooling surface.

This paper presents Laser-Doppler Anemometry (LDA) measurements obtained from the Sussex Multiple Cavity test facility. This facility comprises a number of heated disc cavities with a cool bore flow and is intended to emulate the secondary air system flow in an H.P compressor. Measurements were made of the axial and tangential components of velocity over the respective range of Rossby, Rotational and Axial Reynolds numbers, (Ro, Reθ andRez),0.32<Ro<1.28,Reθ=7.1×105, 1.2×104<Rez<4.8×104 and for the values of the buoyancy parameter (βΔT) :0.50<βΔT<0.58. The frequency spectra analysis of the tangential velocity indicates the existence of pairs of vortices inside the cavities. The swirl number, Xk, calculated from these measurements show that the cavity fluid approaches solid body rotation near the shroud region. The paper also presents results from Unsteady Reynolds-Averaged Navier-Stokes (URANS) calculations for the test case where Ro = 0.64. The time-averaged LDA data and numerical results show encouraging agreement.

Prediction models have been constructed to investigate the effect of vibrating surfaces on the critical heat flux (CHF) and its associated temperature in spray evaporative cooling. Dimensional analysis has been used to construct the models to account for the influence of key dynamic parameters. Experimental measurements have been obtained from a flat, electrically-heated, copper test-piece, located inside a spray-chamber mounted on top of a shaker. A wide range of large-amplitude and high-frequency measurements have been obtained which correspond to test conditions for a piece of hardware mounted on board a light-duty automotive vehicle with vibration amplitudes ranging from 0 to 8 mm and frequencies from 0 to 200 Hz. Three nozzle types have been fed with distilled water at flow rates ranging from 55 to 100 ml/min being used to cool with subcooling degrees ΔTsub ranging from 10°C to 45°C. Measured data for both static and dynamic cases have been used to explore the influence on the CHF and the surface-to-fluid saturation temperature at which this occurs, of subcooling degrees, surface vibration amplitude and frequency, vibrational Reynolds Number and vibrational Acceleration Number. The measured data has also subsequently been used to calibrate the predictive models for use in thermal management systems. Static measurements (without vibration) show that the influence of flow rate, volumetric flux, and subcooling are largely in agreement with published literature. For dynamic cases, the influence of vibration is best explained in terms of the nondimensional parameters: Vibration Reynolds Number and Acceleration Number. The effect of vibration on CHF and associated temperature is assessed in detail for the three nozzle types at different flow rates and degrees of subcooling. Predictions of CHF and associated excess temperature, using the calibrated correlation models for the dynamic conditions, are very reasonable, and suitable for the intended purpose of ensuring safe operation of thermal management systems using spray evaporative cooling.

A detailed knowledge of the flow structure and heat transfer within the rotor disc cavities is required for designing safe and efficient aero-engine compressors with a useful operating range. This paper presents the results from temperature field measurements obtained from the Multiple Cavity test facility at the University of Sussex. This emulates the secondary-air disc-cavity system in an aircraft engine high-pressure compressor. It comprises four externally heated disc-cavities and is supplied by a cool bore flow. The heat transfer is studied with the help of finite-element method using measured temperatures as boundary conditions. A validated 2D steady state heat conduction analysis methodology is also presented alongside Monte Carlo simulations. Results are presented for a range of values of Rossby number, Rotational and Axial Reynolds number and the buoyancy parameter.

Understandings of the nature or inherent workings of molecular life in the field of biopolitical security studies have today been characterized predominantly in terms of contingency. This article challenges this characterization. It does so by identifying a particular logic of operation that organizes political action and intervention at both the level of the population and the molecular in response to the threats of smallpox, Ebola and pandemic influenza. It argues that, in fact, rather than securing by instantiating a general economy of the contingent, governing practices rely upon the characterization of the nature of molecular life in terms of its constant biological dynamics. Governments around the world, and the US government in particular, have reacted to the increased likelihood of the emergence of disease through the stockpiling of new pharmaceuticals, including the antivirals ST-246, ZMapp and Tamiflu. Antivirals represent a pharmaceutical tool stockpiled by governments to ensure that they can respond to the emergence of novel biological threats. The characterization of the nature of molecular life in terms of its constant biological dynamics is so important, then, as it is this that underpins political programmes of preparedness that utilize antivirals in the prevention of disease.

New empirical correlation models are constructed to characterise heat transfer associated with spray evaporative cooling of vibrating surfaces - a process involving complex two-phase physics well beyond current numerical simulation capabilities. The proposed correlation models, which account for dynamic, rather than just static surface conditions as in existing models, are constructed using dimensional analysis involving the Generalized Buckingham Π-Theorem. Experimentally-measured spray evaporative cooling data is used to fit the model using the Vibrational Reynolds number and a dimensionless acceleration number which better correlate the influence of surface frequency and amplitude in the nucleate boiling regime. Different coolant flow-rates through a full-cone spray nozzle are used to cool a flat circular test-piece acting as a horizontal surface. The test-piece surface is excited by a shaker through a range of low and high vibration frequencies and amplitudes. The results show that surface dynamic effects certainly influence nucleate boiling, but they also show that surface vibration does not have the same effect for all excess temperatures - dynamic effects can either increase or decrease heat transfer depending on the heat transfer mechanism. These new models are important for thermal management in several areas, particularly involving batteries, power electronics, and electrical machines in automotive and aerospace applications.

Abstract Could the most miniscule of objects, imperceptible to the human eye, enact whole new political economies? The suggestion may seem odd, but this article shows that tiny molecules are already engendering new regimes of value across the fields of global health and biodefense. Delving genealogically into the onto-epistemology of the life sciences, the article thus traces the protracted molecular reconfigurations of state-market relations underpinning the global bioeconomy and civilian biodefense today. Using methodological precepts developed through assemblage thinking, this evolving patchwork of new constellations is conceptualized as a global molecular assemblage. Attending to the lively play of molecules in the world advances the post-Foucauldian, molecular study of biopolitics by exploring how scientific shifts in our ‘vital epistemics’ contour state-market relations. It further contributes to the development of a post-human international political economy that is more sensitive to the ways in which artefacts (like molecules) too exhibit particular kinds of ‘agency’ and ‘force’ in the world. Finally, it also enhances the field’s ability to make unconventional, hitherto overlooked and multi-scalar connections in the study of political economy through the creative use of assemblage thinking. In the case of molecules, such assemblage thinking can – quite literally – reveal the value of ‘life’.

How have advances in the molecular sciences reshaped our understandings of resilience? This article argues that a novel form of resilience emerges out of the US government's response to the threat of bioterrorism. This response has focused on the development and stockpiling of new pharmaceutical defences known as medical countermeasures. Medical countermeasures allow the body to 'bounce back' from an attack by enhancing at a molecular scale. The obstacles involved in reshaping molecular life into viable countermeasures has led to the creation of a government backed bio-economy formed of public-private partnerships. In doing so, the US government has taken on an extended role accepting the risk that arises in this area. The result is a new scale at which resilience can be implemented and in contrast to many conclusions in the field of International Relations, the responsibilisation of the state rather than citizens in the face of crises.

A novel approach is proposed for precise control of two-phase spray evaporative cooling for thermal management of road vehicle internal combustion (IC) engines. A reduced-order plant model is first constructed by combining published spray evaporative cooling correlations with approximate governing heat transfer equations appropriate for IC engine thermal management. Control requirements are specified to allow several objectives to be met simultaneously under different load conditions. A control system is proposed and modeled in abstract form to achieve spray evaporative cooling of a gasoline engine, with simplifying assumptions made about the characteristics of the coolant pump, spray nozzle, and condenser. The system effectiveness is tested by simulation to establish its ability to meet key requirements, particularly concerned with precision control during transients resulting from rapid engine load variation. The results confirm the robustness of the proposed control strategy in accurately tracking a specified temperature profile at various constant load conditions, and also in the presence of realistic transient load variation.

The accuracy of computational fluid dynamic (CFD)-based heat transfer predictions have been examined of relevance to liquid cooling of IC engines at high engine loads where some nucleate boiling occurs. Predictions based on (i) the Reynolds Averaged Navier-Stokes (RANS) solution and (ii) large eddy simulation (LES) have been generated. The purpose of these simulations is to establish the role of turbulence modeling on the accuracy and efficiency of heat transfer predictions for engine-like thermal conditions where published experimental data are available. A multiphase mixture modeling approach, with a volume-of-fluid interface-capturing method, has been employed. To predict heat transfer in the boiling regime, the empirical boiling correlation of Rohsenow is used for both RANS and LES. The rate of vapor-mass generation at the wall surface is determined from the heat flux associated with the evaporation phase change. Predictions via CFD are compared with published experimental data showing that LES gives only slightly more accurate temperature predictions compared to RANS but at substantially higher computational cost.

IC engine spray evaporative cooling system design is discussed starting with a review of existing evaporative cooling systems that automotive applications are required to address. A component-level system design is proposed culminating in a simulation model of a PID strategy used to control transient gasside metal temperatures with varying engine load. The model combines a spray evaporation correlation model with 1D finite-difference equations to model the transient heat transfer through a 7 mm thick metal slab which represents the wall of a cylinderhead. Based on the simulation results, the particular changes required of existing engine cooling jacket designs are discussed.

This paper presents new experimental measurements, at conditions representative of an aero engine, of heat transfer from the inner peripheral surface (shroud) of a rotating cavity. The results are taken from the University of Sussex Multiple Cavity Rig, which is designed to be similar to a gas turbine high pressure compressor internal air system. The shroud Nusselt numbers are shown to be dependent on the shroud Grashof number and insensitive to throughflow axial Reynolds number. The magnitude of the shroud Nusselt numbers are consistent with accepted correlations for turbulent free convection from a horizontal plate, yet show a trend (gradient of Nusselt to Grashof numbers) that is similar to laminar free convection. A supporting high-resolution 3D unsteady RANS simulation was conducted to investigate the cavity flow structure with particular attention paid to the near shroud region. This demonstrated flow structures that are consistent with published work but also show the existence of a type of Rayleigh-Bénard flow that manifests as a series of streaks that propagate along the periphery of the cavity. These structures can be found in the literature albeit in different circumstances. Whilst these streaks have been shown in the simulation their existence cannot be ratified without experimental confirmation.