Assessment of vapour chamber heat spreader implementation for avionic module thermal management

Thermal management of aircraft heat loads is quickly becoming a limiting factor of vehicle performance and reliability. This paper details improvements in forced-convection cooled avionic module heat removal efficiency with the implementation of two-phase high thermal conductivity Vapour Chamber Heat Spreaders (VCHS). A bespoke test rig provides experimental thermal comparisons of an aluminium and embedded VCHS avionic heat exchanger. The experimental results validate a numerical thermal resistance network, which is utilised to simulate more representative avionic chassis geometries. The VCHS dramatically reduces thermal variation in circuit card and avionic heat exchanger exhaust temperatures. Increased isothermalisation of the heat exchanger greatly increases effective heat transfer area in comparison to a traditional aluminium chassis. The VCHS acts as a very effective thermal buffer between the avionic circuit cards and coolant airflow, allowing a more predictable avionic thermal behaviour irrespective of circuit card architecture. The improved heat rejection capability allows either a substantial increase in avionic growth capacity (increased power output for a fixed exhaust temperature) or a substantial reduction in mass flow rate (reduced demand on vehicle thermal management system). An avionic growth capacity of up to 58% is achieved with representative thermal loading conditions

Experimental assessment of vapour chamber heat spreader implementation in avionic cooling

Avionic thermal management is quickly becoming the limiting factor of aircraft performance and reliability, particularly prevalent with ageing airframes. While the increasing power density of avionic components requires a greater heat removal capacity for a given geometric module size, supplementary generation of cooling airflow is detrimental to engine and aircraft performance. This paper looks at improving the heat removal efficiency of forced convection cooled avionic modules by reducing the thermal resistance between the avionic component and module heat exchanger. The implementation of two-phase high thermal conductivity materials, such as Vapour Chamber Heat Spreaders (VCHS), embedded within the avionic module chassis act to improve heat exchanger isothermalisation, improving the effective heat transfer area. A bespoke test rig has been manufactured to experimentally compare a pure aluminium and embedded VCHS avionic chassis for heat removal capability. When considering a single circuit card, a direct mass flow rate reduction of between 22% and 65% is achieved with embedded VCHS over a pure aluminium chassis. Base plate isothermalisation is improved by 9%, generating a reduction in component temperature of 8% to 12%. As the number of heat sources increase, the performance improvements decrease. When testing with three circuit cards mass flow rate savings are reduced to between 14% and 26%. The concluding performance characteristic of the embedded VCHS avionic base plate is the insensitivity to the way thermal energy is coupled to it. Across all testing, the localised heat removal was never further than 3.5% from the averaged plate performance

Evaluating environmental control system thermal response to degraded operating conditions

This paper documents an investigation into the performance and thermal efficiency of an air-cycle Environmental Control System (ECS) artificially injected with common operational failure modes. A two-wheel bootstrap system is taken from an in-service military fast-jet and installed in a bespoke Ground Test Facility (GTF) at the ECS Research Facility, Loughborough University, UK. The failure modes investigated are bleed air blockages in the intercooler and in the low-pressure water extractor, as well as positional inaccuracy in cycle bypass control valves. The full range of degradation in each fault is considered, allowing the quantification of overall system performance degradation. The performance of the system is found to be insensitive to moderate bleed air blockages (up to 80% by pipe cross-section area), whilst blockages at low pressure are more detrimental to cycle performance than blockages at high pressure. The cycle and/or control system will self-regulate around most degrading-type faults. This particular system is most sensitive to a failure at one bypass valve, where the hardware allows partial redundancy of the valve but the control system does not

A study into refrigeration cycle working fluids using an air cycle machine environmental control system

This study is the experimental analysis of a fast-jet military aircraft Environmental Control System (ECS) to the variation in Absolute Humidity (AH) of bleed air working fluid. A genuine fast-jet ECS operates within a ground test facility. The thermodynamic performance of the ECS is evaluated with two main metrics, Coefficient of Performance (CoP, a first law efficiency) and cooling capacity (function of exhaust temperature and mass flow rate). The ECS features Low Pressure Water Extraction (LPWE) with the use of a coalescing sock and centrifuge; the operation, efficiency and performance of this component are discussed in depth. The ECS inlet conditions (temperature, pressure and humidity) are typical of flight and atmospheric envelopes of the donor aircraft for all testing. A linear relationship is witnessed between increasing AH and decreasing CoP, while the cooling capacity of the system exhibits a step change in performance based on induced phase change at the Cold Air Unit (CAU) turbine. The lack of visibility regarding working fluid phase change with traditional first law efficiency measures highlights the often misleading nature of this commonly used performance metric. While phase change is a fundamental requirement for water extraction, it is found to be thermodynamically expensive to system capability as the ECS has no mechanism to recover the energy released during the formation of condensate. This is typical of several complex system dynamics and thermodynamic trade-offs not apparent with dry working fluid. A number of time-dependent transient effects of water extractor coalescing sock blockage have been measured and discussed. The most extreme of these is the complete icing of this component causing a degradation in system performance and finally triggering the LPWE pressure release valve; replication of a typical operational problem. The difficulties of accurately modelling these behaviours is discussed and demonstrated to validate the experimental methodology utilised in this paper. It is concluded that an improved system performance is attainable through the accurate control of condensate generation and separation in the high pressure region of the CAU

Development of a full scale experimental and simulation tool for environmental control system optimisation and fault detection

This paper documents the installation of a fast jet military aircraft Environmental Control System (ECS) ground test facility. The system used in this case is a bleed-air driven two-wheel bootstrap cycle with low pressure water extraction. The facility allows the ECS to be run at conditions similar to those in the aircraft during ground operation. Data from the rig is presented and used to validate a 1-D thermodynamic model. The relationships between aircraft altitude and speed against ECS Coefficient of Performance and system heat rejection are presented, seamlessly utilising both experimental and modelled data. Furthermore, a scenario depicting a ram air blockage in the secondary heat exchanger demonstrates the system’s ability to mask faults. The physical system is used for component-level analysis, whilst the model extends this to system-level. General attributes of the system operation are discussed

Equine cartilage secretome 5 days IL-1 treatment in vitro;'Neopeptide Analyser' output files

<div>Neopeptide Analyser output files.</div><div><br></div><div>Experiment n=8 equine metacarpophalangeal cartilage explants from grossly normal joints treated in vitro with 10ng/ml IL-1 for 5 days. Secretome samples collected and pooled for 5 days. Media samples tryspin digested and run on an Orbitrap-Velos mass spectrometer. Raw files input into Progenesis QIP and label-free quantification undertaken with Mascot used to search for semi-tryptic peptides. Peptide measurements output file from ProgenesisQIP is then used as the  input file into the 'Neopeptide Analyser' for neopeptide identification. The files here are the output files from the 'Neopeptide Analyser'. They are suffixed _filter and _processed.</div

Equine cartilage secretome 5 days IL-1 treatment in vitro; Progenesis semi tryptic peptides measurements file for input into the Neopeptide Analyser

<div>Progenesis semitryptic peptide file for use as input into Neopeptide Analyser.</div><div><br></div><div>Experiment n=8 equine metacarpophalangeal cartilage explants from grossly normal joints treated in vitro with 10ng/ml IL-1 for 5 days. Secretome samples collected and pooled for 5 days. Media samples trypsin digested and run on an Orbitrap-Velos mass spectrometer. Raw files input into Progenesis QIP and label-free quantification undertaken with Mascot used to search for semi-tryptic peptides. Peptide measurements output file from ProgenesisQIP is then used as the  input file into the 'Neopeptide Analyser' for neopeptide identification. Progenesis QIP peptide measurements file is for input into Neopeptide App for neopeptide identification.</div

Thermal sensitivity analysis of avionic and environmental control subsystems to variations in flight condition

The operation of fast jet military aircraft spans a large flight and atmospheric envelope. This study is the analysis of an avionic thermal management system for a typical fast jet military aircraft across changing operating conditions. The system which governs avionic module temperature is only partially active; therefore the efficiency and heat rejection capability is almost completely dependent on the system inputs of flight and atmospheric conditions. The thermal sensitivity to variation in system inputs is assessed with the use of experimental testing, one-dimensional thermodynamic modelling and energy flow calculations. The avionic module is the final component of the thermal management flow path and to understand the performance at component level, every subsystem upstream must be considered through a complete systemic approach. The facility used to deliver this analysis considers the total system energy consumption, Environmental Control System (ECS), cabin and three avionic subsystems as a single airflow path. The system is subjected to a typical fast jet flight profile, including a take-off, climb, cruise, combat, landing and ground operation cases. The flight profile is considered across three atmospheric conditions; ISA standard, hot and cold. It is found that the system heat rejection is stable with variations in flight conditions; therefore the system efficiency is inversely proportion to total energy consumption. The highest system efficiency is delivered at high altitude low load cruise conditions, with the lowest efficiency found at high speed low attitude flight. The system is most efficient when thermal safety factor is lowest. This is hot atmospheric and low load conditions, where the ECS bypass flow rate is low and avionic module exhaust temperatures are high. The ground ops condition in a hot atmosphere is the worst case scenario for avionic module exhaust and cabin temperatures. Considerable system gains could be made by introducing an element of active control, such as limiting bleed and ram air consumption when avionic temperatures are low and ECS bypass flow rate is high