Active Thermal Protection Research Articles

Topology optimization of regenerative cooling channel in non-uniform thermal environment of hypersonic engine

Regenerative cooling technology is widely used in the active thermal protection system of hypersonic airbreathing engine. However, the overall efficiency of active cooling with limited total coolant quantity needs to be improved due to flow non-uniformity, hydrocarbon fuel pyrolysis and other factors. This paper presents a fluid–structure coupled topology optimization design of the regenerative cooling channel to improve heat transfer efficiency. To further verify the advantages of topology-optimized cooling channels under real operating conditions, detailed three-dimensional numerical simulations were conducted to investigate the supercritical flow and heat transfer processes of hydrocarbon fuel in the topology-optimized channels. Results reveal that compared to the traditional straight cooling channel, the topology-optimized channel has improved the heat transfer efficiency and flow distribution significantly. Many micro-channels perpendicular to the mainstream direction which can be termed as “capillary-like” zone in the optimized channel distribute the inlet fuel to the adiabatic walls, thus significantly improving the overall heat transfer. Remarkable cooling capacity robustness of the topology-optimized cooling channels has been found under different non-uniform heat flux conditions. Comparing to the straight channels, the averaged temperature of the heated wall in the optimized channels can be decreased up to 5.8% and the pressure drop can be decreased up to 20.6%. The uniformity of the fuel temperature distribution is about 2 times better than that of the straight channel. However, although overall heat transfer efficiency is high, complex flow and heat transfer phenomenon occurs in the topology-optimized cooling channel, such as the reverse flow phenomenon induced by adverse pressure gradient near the entrance and the stagnated flow in the “capillary-like” zone near the exit, which impair the local heat transfer and cause the existence of high temperature regions.

Thermal Protection Mechanism of a Novel Adjustable Non-Ablative Thermal Protection System for Hypersonic Vehicles

In order to improve the thermal protection performance of the active thermal protection system (TPS) based on the spike and jet, an adjustable non-ablative thermal protection system, of which the spike can be rotated in the direction of the free stream, is proposed in this paper. The thermal protection mechanism and the optimal installation angle are analyzed by adopting the numerical method. The results show that the angle of attack has great influence on the peak heat flux of hypersonic vehicles, the dangerous point is on the windward side of the vehicles at the non-zero angle of attack. With the increase in angle of attack, the heat flux of the windward side of the vehicles rises rapidly, leading to the decrease in the global thermal protection efficiency. The adjustable non-ablative TPS in this paper greatly reduces the aeroheating of the windward side through the installation angle between the spike and nose cone, thus improving the global thermal protection efficiency. The optimal installation angle can be obtained by numerical or experimental methods in engineering design, and the difference between the angle of attack and the optimal installation angle is about 2.4° for the proposed model. Therefore, the installation angle can be automatically adjusted based on the angle of attack to achieve the highest thermal protection efficiency.

Aerodisk Effect on Hypersonic Boundary Layer Transition and Heat Transfer of HIFiRE-5 Vehicle

The substantial aerodynamic drag and severe aerothermal loads, which are closely related to boundary layer transition, challenge the design of hypersonic vehicles and could be relieved by active methods aimed at drag and heat flux reduction, such as aerodisk. However, the research of aerodisk effects on transitional flows is still not abundant. Based on the improved k-ω-γ transition model, this study investigates the influence of the aerodisk with various lengths on hypersonic boundary layer transition and surface heat flux distribution over HIFiRE-5 configuration under various angles of attack. Certain meaningful analysis and results are obtained: (i) The existence of aerodisk is found to directly trigger separation-induced transition, moving the transition onset near the centerline upstream and widening the transition region; (ii) The maximum wall heat flux could be effectively reduced by aerodisk up to 52.1% and the maximum surface pressure can even be reduced up to 80.4%. The transition shapes are identical, while the variety of growth rates of intermittency are non-monotonous with the increase in aerodisk length. The dilation of region with high heat flux boundary layer is regarded as an inevitable compromise to reducing maximum heat flux and maximum surface pressure. (iii) With the angle of attack rising, first, the transition is postponed and subsequently advanced on the windward surface, which is in contrast to the continuously extending transition region on the leeward surface. This numerical study aims to explore the effects of aerodisk on hypersonic boundary layer transition, enrich the study of hypersonic flow field characteristics and active thermal protection system considering realistic boundary layer transition, and provide references for the excogitation and utilization of hypersonic vehicle aerodisk.

Numerical simulation study of transpiration cooling with hydrocarbon fuel as coolant

Transpiration cooling is an advanced active thermal protection technology, which has been studied widely. The effects of cracking reaction on transpiration cooling are considered in this paper when n-decane is used as coolant. The porous wall temperature is reduced and the cooling efficiency is improved due to the cracking reaction. The cracking of n-decane produces a large number of small molecular products, and the random motion of the small molecular products increases the turbulent kinetic energy near the wall. The synergistic effect of the flow field and the total enthalpy near the porous wall is analyzed. The energy fluctuation caused by the cracking reaction is not enough to change the momentum distribution at the porous wall. The pressure increase caused by the small molecular gas generated by the cracking of n-decane can block the flow inside the porous media. The cooling effect brought by the cracking reaction is more obvious when increasing the coolant inlet temperature and the mainstream temperature.

Effects of particle diameter and plate thickness on transpiration cooling for double-layer porous plates

Transpiration cooling is a highly efficient active thermal protection technology, which has a great application prospect in the thermal protection of hypersonic vehicles. Nevertheless, the problem of large injection pressure caused by porous structure in transpiration cooling system has been ignored in previous studies. In this work, the transpiration cooling performance of double-layer sintered metal particle plates with different particle diameter combinations and plate thickness were simulated. The results showed that the cooling effectiveness of double-layer plates was improved when the particle diameter of the porous plate in direct contact with the main stream decreased. The inner plate particle diameter and plate thickness had little effect on cooling performance. By increasing inner plate particle diameter, the coolant injection pressure can be lowered by 41% while the structural thickness was maintained. Further reducing the thickness of the outer plate to 1/4 of the total thickness can reduce the injection pressure to 38% of the single plate, which provided an optimization direction for reducing engine power consumption caused by heat dissipation.

Prevention of occupational diseases of diving specialists while performing underwater works under low ambient temperatures: prospective study

OBJECTIVE: To assess the impact of applying active thermal protection by diving specialists based on electric heating to ensure thermal comfort as a part of a series of measures to prevent occupational diseases while performing underwater works under low ambient temperature.MATERIALS AND METHODS: The test evaluated the time spent by divers in the water maintaining thermal comfort without active heating and using the system of electric heating. The diver’s thermal comfort was estimated according to subjective sensations. The test was held using the diving equipment SLVI-71, SSP-М, SN-21, GVS ХС1200, SVG-200, SVC «Amphora», SVU-5/1, SVU-3 with АВМ-12к, at depth from 2 m to120 m, at a water temperature from +1° С to +16° С.RESULTS: The test determined the compatibility of the electric heating developed system for divers with components of special diving equipment of the above types; showed the necessity of applying the elements of hands and feet’s warming as a part of the heating system; proved the positive impact of the heating system on divers in the period of maintaining thermal comfort while performing diving works, including different levels of heating power.DISCUSSION: Diver’s hypothermia predisposes to oxygen starvation, contributes to the emergence of decompression sickness, oxygen and carbon dioxide poisoning. The average time of providing divers thermal comfort by using FEC at a water temperature from +1° С to +4° С exceeds 3,5–4,6 times the period of the diver’s staying in the water without using active heating. Using elements of hands and feet’s warming in the electric heating suit provides decrease in appearance of primary hypothermia signs of the extremities, contributing to the maintenance of the diver’s optimum heat sensation for a long time. Applying electric heating system significantly reduces the risk of hypothermia while performing diving works under low ambient temperatures and helps to prevent occupational diseases, directly or indirectly related to the impact of low ambient temperatures on the body.CONCLUSION: The application of electric heating system for divers significantly reduces the risk of hypothermia while performing diving works under low ambient temperatures, enables to increase allowable time in water in the diving suit 3,5–4,6 times and helps to prevent occupational diseases, directly or indirectly related to the impact of low ambient temperatures on the body.

Analysis and optimization of flow and heat transfer performance of active thermal protection channel for hypersonic aircraft

This paper presents a numerical simulation on the thermal–hydraulic performance of multiple parallel cooling channels to realize active thermal protection of hypersonic aircraft. The fluid velocity is set in the range of 0.5–2.5 m/s, with the corresponding Reynolds number of 4300 to 22,000, and results show that the rectangular and triangular channel have the best cooling performance on outer wall and inner wall with water as coolant, respectively. Further, “Diamond” channel is proposed to improve the cooling performance, and aviation kerosene RP–3 is used as coolant. Three inlet temperatures (243, 253 and 263 K) are applied to investigate the thermal protection performance of Diamond channel. The cooling performance of RP–3 is better than water, and total pump power of RP–3 is only 60% of water. It is found that the conspicuous symmetric longitudinal swirls generated at the leading edge effectively enhance the heat convection performance. Under the studied ranges of fluid velocity and inlet temperatures, outer and inner wall temperatures can be controlled below 700 K and 330 K, respectively. Subsequently, the preliminary parameters of the “Diamond” are investigated and optimized. Model with L = 16 mm, Yc = 3 and X = 8.8 mm has better thermal protection performance and mechanical properties.

Concept of an Active Thermal Protection System with a Three-Layer Design–Force Scheme and a Discrete Filler for a Hypersonic Aircraft

Concept of an Active Thermal Protection System with a Three-Layer Design–Force Scheme and a Discrete Filler for a Hypersonic Aircraft

Practical Experience in the Application of Energy Roofs, Ground Heat Storages, and Active Thermal Protection on Experimental Buildings

Research Area: Building components with integrated energy-active elements (BCEAE) are generally referred to as combined building-energy systems (CBES). Aim: Research on the application of energy (solar) roofs (ESR), ground heat storage (GHS), active thermal protection (ATP), and their cooperation in different modes of operation of energy systems with an emphasis on the use of renewable energy sources (RES) and waste heat. Methodology: The analysis and synthesis of the state of the art in the field, the inductive and analogical form of the creation of an innovative method of operation of combined building-energy systems, the development of an innovative solution of the envelope panel with integrated energy-active elements, the synthesis of the knowledge obtained from the scientific analysis and the transformation of the data into the design and implementation of the prototype of the prefabricated house IDA I and the experimental house EB2020. Results: The theoretical analysis of building structures with active thermal protection results in the determination of their energy potential and functionality, e.g., thermal barrier, heating/cooling, heat storage, etc. New technical solutions for envelopes with controlled heat transfer were proposed based on the implementation of experimental buildings. Conclusions: The novelty of our research lies in the design of different variants of the way of operation of energy systems using RES and in upgrading building envelope panels with integrated energy-active elements.

Oesophageal protection during AF ablation: real world registry data and mechanisms behind the therapeutic effect of tissue cooling

Abstract Funding Acknowledgements Type of funding sources: None. Background Oesophageal protection using a dedicated device to provide controlled active thermal protection of the oesophagus during atrial fibrillation ablation has been shown to be effective at reducing endoscopically detected oesophageal lesions. Real world registry data of this device and established evidence on the effect of cooling on localized tissue after thermal injury have been under review. Purpose To determine the safety of an oesophageal temperature control device by a review of real-world registry data on its clinical use during catheter ablation procedures and to clarify basic mechanisms of its therapeutic action by a literature review of scientific studies on cooling in the context of thermal injury. Methods The United States Food and Drug Administration (FDA) Manufacturer and User Facility Device Experience (MAUDE), FDA Medical and Radiation Emitting Device Recalls, the Medicines and Healthcare products Regulatory Agency (MHRA) Medical Device Alerts and SwissMedic records of Field Safety Corrective Actions (FSCA) databases were reviewed for any device-related adverse events. A systematic literature review was conducted to clarify the findings from studies investigating the physiological processes behind the therapeutic effect of cooling after tissue thermal injury. Results Of over 20,000 oesophageal temperature control devices clinically used, 7976 were recorded as having been used for the purpose of oesophageal protection during left atrial catheter ablations. No adverse events occurred related to its use during left atrial catheter ablations. No case of clinically significant oesophageal injury was reported in a patient who had been protected by the oesophageal temperature control device. 208 research articles retrieved from PubMed and MEDLINE that met the search criteria were reviewed. The common finding in all the studies was that cooling had an anti-inflammatory and restorative effect via modulation of several immune-mediated pathways, local cellular function and genetic expression. Conclusions There have been no adverse events reported to date in real world clinical use of an oesophageal temperature control device during left atrial catheter ablations, for the purpose of active thermal protection. Literature review data suggests that there are complex biophysical and cellular effects from cooling that leads to its therapeutic effect but further work is required to define the mechanisms of action of thermal protection in this specific context.

Contribution to research on ground heat storages as part of building energy systems using RES

Contribution to research on ground heat storages as part of building energy systems using RES

CA-528-03 A REGISTRY REVIEW UPDATE OF 7120 CATHETER ABLATIONS FOR ATRIAL FIBRILLATION USING A DEDICATED ESOPHAGEAL TEMPERATURE CONTROL DEVICE FOR PROTECTION

Esophageal protection using a dedicated device to provide controlled active thermal protection of the esophagus during atrial fibrillation ablation has been shown to be effective. Randomized evidence from the IMPACT trial showed an 83.4% reduction in endoscopically detected esophageal lesions compared to standard care. Real world registry data of this device has been under review. To determine the safety of an esophageal temperature control device by an updated review of real-world registry data on its clinical use and any reported device-related adverse events. The following databases were reviewed for any reported esophageal temperature control device-related complications: The United States Food and Drug Administration (FDA) Manufacturer and User Facility Device Experience (MAUDE), FDA Medical and Radiation Emitting Device Recalls, the Medicines and Healthcare products Regulatory Agency (MHRA) Medical Device Alerts and SwissMedic records of Field Safety Corrective Actions (FSCA). An internal registry (post-marketing follow up) database maintained by the manufacturer of the device was used to quantify the number used for each indication. Reported events underwent an updated review including any instances of device-related adverse events when used during catheter ablations. Of the 20,000 oesophageal temperature control devices used, 7120 were recorded as having been used for the purpose of esophageal protection during left atrial catheter ablations. A total of 5 events associated with the device were identified, all from the MAUDE database. Three were from 2017, one from 2018, and one from 2019. All involved its use in critical care or trauma patients and were related to user error or contraindicated patient selection; none resulted in serious harm to the patient. No adverse events occurred related to its use during left atrial catheter ablations. No case of clinically significant esophageal injury was reported in a patient who had been protected by the esophageal temperature control device. Real world registry data has shown no adverse events reported to date in 7120 uses of an esophageal temperature control device during left atrial catheter ablations, for the purpose of active thermal protection.

Mathematical modeling of thermal stabilization systems based on phase transitions

At present, first of all, due to success of biotechnologies, tasks have arisen in which it is required to ensure the thermal regime of the protected product within strictly defined and fairly close temperature limits. Most traditional thermal protection, cooling and heating systems have proven to be ill-suited to such tasks. Among the principles of thermal protection used in modern practice, active thermal protection technologies based on the latent heat of phase transitions are considered to be the most effective. It seems to be quite natural to use the same principle in new thermal stabilization systems in a narrow temperature range. To do this, sufficiently small inclusions of a different phase with a phase transition temperature close to one of the limiting temperatures of the required range should be introduced into the heat-shielding layer. As the geometric dimensions of the inclusions of a different phase are significantly smaller than the dimensions of the object as a whole, a multiscale problem is generated with all the difficulties inherent in solving such problems. To overcome the difficulties associated with the multiscale nature of the problem, the thermal effects of inclusions of a different phase were modeled by point heat sources. The thermophysical properties of the heat-shielding coating material were assumed to be constant due to the narrowness of the considered temperature range. Boundary conditions for the heat equation at the outer boundary of the heat-shielding layer were set of the first, second, or third kind. On the inner surface of the heat-shielding layer, conditions were set for conjugation with the temperature field of the protected body. In this case, two limiting models of the protected body were considered: a solid body with some effective thermal conductivity and an integral heat capacity with a temperature constant over the volume. In the first case, the conditions of the fourth kind were set, and in the second, the condition of the first kind. To calculate the temperature field in the system under consideration, the boundary element method was used, which easily takes into account the presence of point heat sources. Thus, a mathematical model and the corresponding calculation scheme of the thermal stabilization system based on the latent heat of the phase transition were constructed in the work. The obtained results of numerical calculations could not be confirmed either by comparison with analytical results, or with experimental studies, or with the works of other authors, since the latter were not found. With an increase in the number of inclusions, the material of the heat-shielding layer begins to resemble a heterogeneous medium, which inspires hope for the possibility of comparison with asymptotic results. Prospects for further research are related to the optimization of thermal stabilization systems based on the latent heat of phase transitions. The illustrative calculations carried out confirm the conclusion about the high efficiency of this approach.

Сравнительная оценка теплового состояния клина с термостойким покрытием в высокоскоростном воздушном потоке

The efficiency and maximum height, speed and duration characteristics of the flight path of high-speed atmospheric aircraft are largely determined by the temperature regime of the most heat-stressed structural elements, suchas the edges of airframe airfoils. Their active thermal protection systems contribute to solving a number of complex scientific and technical problems, the most promising and simple solution being heat-resistant inorganic materials of the oxide class. However, their use for the structural design of the edge as a monolithic structural element is difficult both in terms of technology and strength characteristics, especially in the heat shock mode. In this regard, a promising solution is an edge in the form of a core made of heat-resistant and heat-conducting materials with a high-temperature oxide ceramic lining, which protects from the environmental oxidative effects and provides the permissible temperature regime of the core due to thermal resistance determined by the thickness of the lining. The study examines the temperature conditions of the wedge-shaped edge with a heat-conducting core and a heat-resistant ceramic lining. When choosing materials for the core and lining, it is important to preliminary calculate and estimate the parameters of the edge performance, taking into account the data on the thermophysical and physicomechanical properties of the materials. The study comparatively analyzes the thermal state of a prefabricated wedge with a heat-conducting core made of hafnium boride, which is an advanced heat-resistant material, and molybdenum and nickel, which are more technological and cheap metal materials, with a lining of oxide heat-resistant ceramics

Numerical investigation on flow and film cooling characteristics of coolant injection in rotating detonation combustor

The film cooling is a possible active thermal protection solution for the rotating detonation engines. As the rotating detonation wave is of high periodic and unsteady features, the film cooling characteristics inside the rotating detonation combustor are very complicated. To illustrate the influence of rotating detonation wave on the flow dynamics of coolant jets and the thermal protection performance of film cooling in the rotating detonation combustor, a numerical investigation is performed in the current study, on the base of a simplified physical model wherein only single row of film cooling holes in the axial direction is concerned. The results show that both the blocking effect and oscillating effect occur in the transverse jet injection, upon the impact of sweeping of detonation wave and oblique shock wave. Due to the occupancy of momentary combusting flow invasion into the film cooling hole during one cycle of wave sweeping, the inward flow from the film cooling hole to the combustor chamber is not the pure ‘coolant jet’ but instead of a ‘mixed’ jet. The blocking effect of sweeping oblique shock wave front on the coolant jet injection is significantly weaker when compared to the detonation wave front. With the use of film cooling, the time-averaged temperature on the outer wall of the combustor chamber is reduced effectively, especially in the middle and rear sections of the rotating detonation combustor. The coolant jet injection does not change propagation speed of the rotating detonation wave but reduces a little the peak pressure and peak temperature of each cycle.

On the feedback inertia effects impact on the temperature field of a system with active thermal protection

On the feedback inertia effects impact on the temperature field of a system with active thermal protection

A Calculation Model for Temperature Responses of Active Cooling Lattice Sandwich Structures for Thermal Protection

Aimed at the active thermal protection with lattice sandwich structures, an unsteady heat transfer theoretical model coupling facesheet and core heat conduction with coolant convection in the sandwich structure, was established. The model equations were discretized with the finite volume method and solved iteratively in MATLAB; the constriction thermal resistance between the facesheet and the lattice struts was considered for the first time in the model, and the approximate analytical solution of the constriction thermal resistance was obtained with the variable separation method; based on the unit-cell model and periodic boundary conditions, heat transfer coefficients <i>h</i>_b and <i>h</i>_fin required by the model were first obtained through numerical simulation. Finally, a case study with a multi-cell structure was carried out to compare the numerical and theoretical results, and the influence of the constriction thermal resistance on the prediction accuracy was discussed. The results show that, the theoretical model can accurately predict the temperature variations of the sandwich structure and the internal fluid, and the maximum deviation between theory and simulation is less than 1%. As the external heat flux increases, the error of theoretical prediction rises with the constriction thermal resistance ignored. Compared with the numerical simulation, the theoretical model can significantly reduce the calculation time and save calculation resources, thus it is especially suitable for active cooling lattice sandwich structures subjected to complex, non-uniform and unsteady thermal loads.

Design and Optimization Study of Discrete Inclined Ribs Enhanced Bend Tube Based on “Diamond” Active Cooling Thermal Protection Systems of Hypersonic Aircraft

Design and Optimization Study of Discrete Inclined Ribs Enhanced Bend Tube Based on “Diamond” Active Cooling Thermal Protection Systems of Hypersonic Aircraft

Study on influence of forced vibration of cooling channel on flow and heat transfer of hydrocarbon fuel at supercritical pressure

The cooling channel of a scramjet is the fundamental structure of the active thermal protection for an engine. Till now, studies have focused mainly on the steady-state flow and heat transfer process in the cooling channel. However, the vibration intensity of an engine increases sharply as the flight speed increases, because of which, the flow and heat exchange mechanisms based on the cooling channel under stable conditions cannot be applied under vibration. In this study, experimental methods are used to study the characteristics of the forced vibration of a cooling channel on the flow and heat transfer of hydrocarbon fuel at supercritical pressure. In addition, the influences of different vibration frequencies and vibration amplitudes on the flow and heat transfer are analyzed. The research results show that at supercritical pressure, when the fuel temperature is below the critical temperature and the inner wall temperature is above the critical temperature, external vibrations would enhance the heat transfer characteristics of the cooling channel. However, when the pressure and temperature are unstable, the forced vibration of the cooling channel would suppress the instability of temperature and pressure while strengthening the heat exchange.

Analysis and Optimization of Flow and Heat Transfer Performance of Active Thermal Protection Channel for Hypersonic Aircraft

Analysis and Optimization of Flow and Heat Transfer Performance of Active Thermal Protection Channel for Hypersonic Aircraft