Critical Operating Conditions Research Articles

Influence of Propeller–Ice Loads on the Wear Development in Stern Tube Bearings of Marine Propulsion Systems and Identification of Critical Operating Conditions

Abstract Increasing ship traffic in ice-covered waters leads to more frequent collisions between ship propellers and sea ice which causes extreme impulse loads on the propeller. These loads are transferred through the propeller shaft to the sliding bearings of the stern tube, especially, the aft stern tube bearings. Extreme bearing loads can lead to mixed friction regimes that cause wear in the bearings and eventually result in a failure of the entire propulsion system. The effect of ice-induced loads on the contact conditions in the sliding bearings is widely unknown. Thus, a study of the influence of these loads on the contact conditions and wear behavior in stern tube bearings resulting from observed sea ice conditions and operating conditions of the ship is necessary. This article aims to investigate the influence of ice collision loads on the contact conditions in the bearings of the stern tube of the research vessel SA Agulhas II. For this purpose, an elastohydrodynamic simulation and a multibody simulation based on field measurements were performed. As a result, this article identifies the operating condition thresholds (i.e., propeller torque and rotational speed) during propeller–ice collisions that cause mixed friction conditions in the bearings. On the basis of these conditions, a risk map is generated to assess the actual wear risk by including the frequency of occurrence of the corresponding mixed friction condition over the duration of a voyage.

Prediction of voltage stability index in buses without measurement in distribution systems

AbstractIn power systems, voltage collapse during overload can be a significant threat. Accurate forecasting of critical operational conditions within power grids is crucial for preventing such situations. Precise predictions of voltage collapse enable operators to monitor the system closely and implement necessary corrective measures promptly, avoiding potential issues. However, monitoring networks can be costly due to the numerous loads and transformers in the distribution system. A comprehensive approach known as the voltage stability index (VSI) forecast without measurement buses (VFWMB) has been introduced to address this challenge. This approach involves innovative methods, including the seeking observation zone with weight least square (SOZWLS) technique for determining the number and location of measurements in the network based on its topology. Additionally, short‐term load forecasting is performed using the long short‐term memory (LSTM) forecasting method, followed by voltage estimation for buses without measurements. Finally, the proposed method calculates the modern voltage stability index for distribution systems (MVSIDS) for upcoming hours. All indicators and techniques in the VFWMB method have been validated. The algorithm has been thoroughly tested on various networks, including small and large, balanced and unbalanced, and both real and test networks, showing high efficiency in the electricity industry.

Sensitivities of critical operating conditions on proton exchange membrane fuel cell performance: an experimental study

Abstract The performance of the Proton Exchange Membrane Fuel Cell (PEMFC) is subject to substantial influence from operating conditions. In this paper, the impact of various operating conditions on the polarization curves is examined through single-variable polarization curve tests. Notably, it is observed that the polarization curves intersected within the range of 1.0 A/cm2 to 1.5 A/cm2 under varying cathode inlet humidity and working pressure conditions. Expanding upon this observation, an orthogonal experiment is designed and executed to evaluate the sensitivity of PEMFC performance to diverse operating conditions under two distinct current densities of 1.0 A/cm2 and 2.0 A/cm2. Consequently, it is revealed that the output voltage, charge transfer impedance, and mass transfer impedance are most significantly influenced by three specific operating conditions: temperature, cathode inlet humidity, and stoichiometric ratio. Furthermore, as the current density increases, the dominant factors governing PEMFC performance have evolved from temperature-dominated charge transfer impedance to cathode stoichiometric ratio-dominated mass transfer impedance.

A data-driven multi-objective optimization approach for enhanced methanol yield and exergy loss minimization in direct hydrogenation of CO[formula omitted]

The stability and control of process industries have historically faced obstacles due to inherent uncertainties in their operations. This work focuses on leveraging machine learning models as a surrogate to facilitate real-time optimization of operating conditions of the direct hydrogenation of CO2 to enhance methanol production while minimizing exergy losses. Numerous studies have explored steady-state exergy analysis and the impact of various process conditions on methanol production. However, there is a notable absence of research investigating the influence of exergy destruction on methanol production under dynamic conditions. Initially, a commercial software Aspen HYSYS was utilized to design, model, and simulate the methanol synthesis plant. Exergy analysis was conducted to quantify the process exergy losses, exergy efficiency, and potential areas for improvement. The process model transitioned to a dynamic mode by incorporating ±5% uncertainty into critical operating conditions, i.e., temperature, pressure, and molar flow rate, simulating real-world variability and resulting in a dataset of 370 samples. Two machine learning models; the Gaussian process regression (GPR) and artificial neural network (ANN) model were developed using the data samples to predict the process exergy losses and molar flow rate of methanol produced. To enhance the predictive capabilities of these deployed models, Bayesian optimization was employed for hyperparameter tuning. The developed models were employed as surrogates in multi-objective genetic algorithm (MOGA) environments with the aim of maximizing the production of methanol with minimum exergy losses under uncertainty. The optimized process conditions, derived from MOGA-based methods, underwent cross-validation using the Aspen model. This analysis revealed that the methanol synthesis plant exhibited an exergy loss of 2425 kW, an exergy efficiency of 97.78%, and an improvement potential of 53.74 kW. The GPR and ANN models demonstrated high correlation coefficients (R2) of 0.9928 and 0.9375, and root mean square error (RMSE) values of 38.93 and 1.122, respectively. Incorporating these machine learning models as surrogates within the optimization frameworks notably outperformed the base case, achieving maximum methanol production while minimizing exergy losses in the process.

Influence of operating conditions in nonlinear vibration of a drill-string

In this work, the vibrational analysis of an oil drill-string is carried out concerning nonlinear and nonsmooth dynamical model with coupled axial-torsional modes. This study aims to investigate the influence of operating conditions to avoid bit-bounce and stick-slip phenomena. A discrete lumped dynamic model with two degrees of freedom is considered. Dry friction and the possibility of loss of contact between the bit and the formation introduce two nonsmooth conditions into the system. Numerical simulations are performed to obtain the dynamic responses and to evaluate critical operating conditions. A parametric analysis is carried out to determine the influence of the weight on the drill bit and the angular velocity of the rotary table on the severity of critical vibrations for different drilling depths. A map is obtained, where normal operation, stick-slip, and bit-bounce responses are defined, allowing a choice of suitable parameters so that the drill-string does not experience critical vibration issues. The results indicate that the safety region, where normal operation is realized, depends on the drilling depth. However, when the angular velocity of the rotary table is equal to 10 rad/s and the weight on the drill bit is greater than 55 kN ensures normal operation for any drilling depth.

Optimisation of the biological production of levulinic acid in a mixed microbial culture fed with synthetic grape pomace.

Levulinic acid (LA) is a polymer with a vast industrial application range and can be co-produced as a minor by-product during the biological production of polyhydroxyalkanoates (PHA). However, the influence of key parameters as tools for favouring the production of LA over PHA is still unclear. In this study, we investigated how several critical operational conditions, i.e., carbon-nitrogen ratio (C/N), organic loading rate (OLR) and airflow, can be optimised to favour LA accumulation over PHA production by a mixed microbial culture (MMC), using synthetic grape pomace (GP) hydrolysate as the substrate. The results showed that it was possible to direct the MMC towards LA accumulation instead of PHA. The maximum LA yield was 2.7 ± 0.2g LA/(L·d) using a C/N of 35, an airflow of 5L/min and an OLR of 4g sCOD/(L·d). The OLR and, to a lesser extent, the C/N ratio were the main factors significantly and positively correlated with the biological synthesis of LA.

Analysis of the Influence of Calculation Parameters on the Design of the Gearbox of a High-Power Wind Turbine

As wind turbine power requirements have evolved from the order of kilowatts (kWs) to the order of several megawatts (MWs), wind turbine components have been subjected to more demanding and critical operating conditions. The wind turbine must cope with higher wind loads due to larger blade sizes, which are also time-varying, and, ultimately, higher power levels. One of the challenges in the manufacture of high-power wind turbines lies in the gearbox and consists of achieving ever-greater power density without compromising efficiency, i.e., greater load capacity with lower weight (and production cost) and reduced power losses. Epicyclic geartrains are used to build the gearbox due to various advantages in relation to conventional gear systems, such as higher feasible gear ratios, higher efficiency, compactnesss, and lower weight. In this paper, several epicyclic geartrains with different structures will be analysed to reveal the influence that certain design parameters have on the size and weight of the gearbox components in the selected model and, therefore, of the gearbox itself. For this purpose, the theoretical model of the gearbox will be planned and the influence of the calculation parameters on the gearbox design will be analyzed following ISO 6336. Special emphasis is placed on the influence of the material used; the modulus and tooth width on the size and weight of the gearbox will be observed. Critical stresses are also calculated. The goal is to prepare the theoretical basis for an optimization process subject to geometric, kinematic, and dynamic constraints that will result in a gearbox as compact, energy-dense, and light as possible without compromising the service life of the components.

Experimental study on hydro- thermal behavior of journal bearing oil film profile in a slow speed diesel engine

Utilizing universal journal bearing test rig, the performance of a heavy-loaded main journal bearing has been investigated based on tracing operational behavior of oil film temperature and pressure profiles. Test trials were conducted observing the loading program of slow speed diesel engine. Examining the effect of different oil grades, it turned out that oil grade of higher viscosity index enhances journal bearing performance and maintains oil film temperature profile stability at both maximum speeds and heavy loads. Further, medium viscosity grade oil reduces fuel consumption and costs from power production for all operational conditions. Regarding the impact of heavy loads on shaft power performance with medium viscosity oil grade, the differences between optimal and heavy loads get lower as the shaft speed increases. Those were 22 %, 9.7 % and 2.1 % corresponding to the shaft speeds of 43 rpm, 90 rpm and 104 rpm respectively. Additionally, the lower the value of the maximum oil film pressure Pmax difference between optimal and heavy load, the higher the ability of the lubricant to promote performance and provide enhanced operating condition stability. Yet, at part load operating conditions entailing running journal shaft at slow speeds during ship maneuverability, it cannot be considered as the best selection due to the heavy loads often applied in such critical operating conditions. Finally, the test-trial based experimental outcomes can provide useful guidance regarding the proper selection of a lubricant for enhanced performance, cost saving and prolonged journal bearing working life.

Toxic heavy metal ions removal from wastewater by ion flotation using a nano collector

Industrial wastewater treatment containing heavy metal ions has been a challenge in the ion flotation process development in recent years due to the high collector consumption required to achieve maximum ion removal. To address this issue, a nano collector consisting of functionalized graphene oxide (FGO) was synthesized and applied to increase the removal of heavy metal ions (lead, copper, nickel, cadmium, and zinc) from wastewater. This study evaluated the effect of various critical operating conditions including pH, collector/frother type and concentration, gas type, gas flowrate, and energy input on ion flotation performance to improve the efficiency of the process in this investigation. It was found that using FGO not only increased the ion removal percentage but also decreased collector consumption and water recovery, all of which improved the ion flotation process performance. Under the optimum chemical and hydrodynamic conditions using FGO with much lower concentration than stoichiometry concentration resulted in the maximum removal of lead, copper, nickel, cadmium, and zinc ions with percentages of 97.07, 99.02, 98.38, 95.20, and 98.94, respectively. In optimum condition, water recovery was 8 %. The use of FGO in the ion flotation process for wastewater treatment offered significant benefits, including high adsorption efficiency, low collector consumption, recyclability, and the absence of critical micelle concentration (CMC) and frothing properties.

Enhanced ship cross-section design methodology using peridynamics topology optimization

In this study, peridynamics topology optimization (PD-TO) framework is implemented to reduce the total weight of ship structures and increase their structural endurance against cracks. PD-TO is a general nonlocal optimization strategy that performs the minimization of strain energy density as the objective function and uses pre-defined volume fractions as optimization constraints. To analyze ship structures herein, both the optimality criteria (OC) algorithm and the proportional (PROP) approach are implemented into the PD-TO solver. As the initial design domain, a reference bulkhead geometry of trailing suction hopper dredger (ship) is modeled. This web frame is optimized according to critical wave/loading conditions such as hogging and sagging. Different volume fractions are investigated to obtain lighter designs based on OC and PROP methods. In addition, different cracked scenarios are created by locating the cracks into various positions on the reference ship cross-section. Optimized results for cracked cases shows that the proposed method can create alternative web frames for specific definitions of the possible damaged regions on the board. To prove the efficiency of the proposed method, maximum displacements and compliance of the reference and optimized structures are compared. The results proves that topologically optimized designs offered stiffer structures as compared to conventional designs under the same loading conditions. Finally, some of the optimized results are smoothed to demonstrate the practical utility of the PD-TO for manufacturing. Overall, it is revealed that the PD-TO can be effectively utilized to design marine structures to achieve a higher strength/weight ratio while considering critical operation conditions and possible damaged regions.

Studies on Shock Wave Structures in Supersonic Ejector and Its Influence on Ejector Performance

Supersonic ejectors are an economically feasible and environmentally friendly technology. Shock wave structures significantly affect the ejector performance. In the present work, the first shock wave structures in a supersonic ejector were analyzed with experimental and numerical methods. The experimental results by the Schlieren method were used to verify the accuracy of the numerical simulation results. Then the influence of the inlet pressure on the first shock wave structures inside the ejector was analyzed under critical operating conditions. The numerical simulation results showed that the dimensionless length and height of the first shock wave inside the ejector increase with the increase of the primary pressure and decrease with the increase of the secondary pressure. Meanwhile, the relationship between the performance of the ejector and the shock structures was established, the entrainment ratio is positively correlated with the first shock wave aspect ratio and has a good linear relationship. The results may be beneficial to reveal the ejector’s working mechanism and design high performance ejectors in the future.

Effect of curtailment scenarios on the loads and lifetime of offshore wind turbine generator support structures

Curtailment is a known phenomenon for wind turbine operators of both onshore and offshore wind turbine generators (WTG). Curtailment refers to the situation in which the power output of all WTG’s within a windfarm is forced below the expected power output at the occurring environmental conditions. A direct consequence of curtailment is the loss of power production. In the present contribution further consequences of curtailment of an offshore wind farm (OWF) are studied from the perspective of the support structure, in specific the foundation. In relation to curtailment a couple of potentially critical operational conditions impacting the fatigue consumption of the support structure can be identified. Besides the standstill during operational windspeed conditions, in specific damaging for the +7MW generation WTG’s, curtailment introduces repeated transitions between operational conditions. Since transitions between operational conditions of a WTG are known to be a cause of high fatigue loads in the structural components of the WTG, their increased occurrence due to curtailment might also have an impact on the fatigue consumption of the support structure. With the growing interest of the industry to quantify and potentially optimize the structural lifetime consumption in view of potential lifetime extension of OWF assets, any potential fatigue damaging operational condition is to be investigated. The present work focusses on the investigation of the impact these transitional load cycles may have on the structural lifetime of the WTG foundation. To assess the impact on lifetime, the assessment of the damage equivalent loads (DEL) derived from structural health monitoring (SHM) data are used as a data-driven alternative for model-based load simulations. In the present work such data-driven lifetime assessment studies the impact of curtailment regimes with different frequency of stop and start cycles on the structural lifetime. The study is performed based on 1 year of SHM data collected from two OWF’s. The assessment demonstrates that the impact of additional transitional load cycles on the structural fatigue life consumption is to be considered when defining a long-term curtailment strategy for an OWF.

АСПЕКТИ ПРОГНОЗУВАННЯ ТЕМПЕРАТУРНИХ РЕЖИМІВ АСФАЛЬТОБЕТОННОГО ПОКРИТТЯ В ЦІЛЯХ ПРОЄКТУВАННЯ НЕЖОРСТКОГО ДОРОЖНЬОГО ОДЯГУ

Introduction. The introduction to the paper describes the impact of critical temperatures and temperature loadings on the performance of the asphalt pavement layer and also on the entire flexible road pavement construction. Problem statement. The issues of the paper concern significant aspects of the pavement temperature regimes prediction used in various systems of the flexible road pavement designing. Purpose. The main goal of the paper is to review and compare the flexible road pavement designing approaches based on predicted temperatures of the asphalt pavement layer which may be reached under critical road pavement operating conditions. Results. The application of the theory of thermal diffusion as the framework for the description of establishing the asphalt pavement layer temperature equilibrium was reviewed. As it is assumed, when the maximum asphalt pavement layer temperature is reached exists the equilibrium between outgoing and incoming flows such as outgoing and incoming longwave radiation, shortwave incoming radiation, convection losses and heat transfer. After wide investigations carried out by an SHR program, the maximum asphalt pavement layer temperatures calculated on that heat flows balance were proposed to be used in the flexible road pavement designing. Also, the results of investigations carried out to develop the proposed theory of temperature equilibrium were analyzed and it was stated that under certain meteorological conditions the maximum asphalt pavement layer temperature will not be accompanied by the temperature equilibrium; the subsequent redistribution of heat flows may led to the values of temperature that significantly overcome the calculated maximum.

Optimal design of lithium ion battery thermal management systems based on phase change material at high current and high environmental temperature

The market of electric storage systems is widely dominated by Lithium ion batteries, whose peculiarity is the need for a thermal management system, whose proper design is complicated by the interaction. among different design and operating parameters. A specific methodology for carrying out the task is still lacking. In this context, the present paper proposes a systematic framework for the design of passive and hybrid thermal management systems (TMSs) of Li-ion batteries. Thermal tests were carried out on Lithium-Titanate-Oxide cells under realistic operating conditions in a controlled environment to characterize the electrical and thermal behaviour. A thermofluid dynamics model of the battery was implemented in COMSOL Multiphysics. The experimentally validated model was used to evaluate the influence of different design and operating parameters (ambient temperature, charge/discharge current, phase change material thickness and melting temperature) using the Taguchi method (orthogonal arrays), and discussing inter-related effects of the studied parameters via interaction plots. Air temperature (45 °C) and/or discharge current (69–92 A) were identified as critical operating conditions beyond which thermal runaway issues occur. Starting from the optimal design conditions for a passive TMS, the same methodology was used to assess a hybrid PCM-liquid cooling system as an alternative configuration. The results indicate that, compared to the baseline case of natural cooling, the optimal designs of standalone PCM and hybrid cooling system led to a reduction in maximum cell temperature of 11 and 22 °C, respectively, showing the high potential of these TMSs.

Динамічні процеси у твердопаливних ракетних двигунах та їх взаємодія з вібраціями конструкції ракети: стан питання та актуальні проблеми

The most critical operating conditions of solid rocket motors (SRMs) are often due to the development of dynamic processes characterized by excess values of operating parameters. Pressure surges and a sharp increase in the combustion product temperature may impair the strength of the combustion chamber structure, cause its failure, and lead to critical conditions of the motor operation, up to extinguishing the propellant combustion in the motor. It is shown that both in steady and in unsteady operating conditions of an SRM, dynamic processes in its combustion chamber feature a complex interrelation of a large number of processes in the gas-dynamic space of the combustion chamber: physical, chemical, and thermodynamic (heat and mass exchange) processes. It is found that current studies of SRM operation instability are aimed at identifying mechanisms of combustion chamber pressure oscillations, which are usually due to combustion product vortex formation in the chamber space and acoustic feedback resulting from collisions of vortices with the SRM’s combustion chamber components or nozzle. Other lines of investigation are the analysis of SRM resonant damping and the establishment of a relationship between aluminum droplet combustion and SRM internal instability. It is noted that accelerations and vibrations of mixed-propellant combustion surfaces may greatly affect the combustion rate and the agglomeration, on-surface confinement, and burn-up of metal additives, which, in its turn, governs the combustion chamber acoustics. It is pointed out that the interaction of SRM combustion chamber pressure oscillations and the response of the SRM structure observed in flight tests of some rockets should be taken into account in predicting the stability of SRM dynamic processes. This interaction may call into question the sufficiency of SRM static tests and subsequent conclusions on the magnitude of its dynamic effect on the rocket structure.

A Study on the Influence of Electrical Discharges on the Formation of White Etching Cracks in Oil-Lubricated Rolling Contacts and Their Detection Using Electrostatic Sensing Technique

In bearing applications, the presence of stray and parasitic currents in combination with lubricants has been studied for almost a century and has been found to cause fluting and corrugation damages under high current densities. However, recent research has suggested that at low current densities (<1 mA/mm2) under specific operating conditions, electrical discharges can substantially reduce bearing life due to the formation of white etching cracks (WECs). To date, limited studies have investigated the critical operating and electrical conditions for WEC formation and demonstrated effective fault detection techniques. This study uses a novel monitoring technique known as the electrostatic sensing technique to detect, monitor and characterise electrical discharges in an oil-lubricated steel–steel rolling contact on a TE74 twin-roller machine. The findings demonstrate that WECs can be formed under the influence of electrical discharges in less than 50 h, and the electrostatic sensors are effective for the early detection of critical electrical discharges related to WEC-induced failures.

Simulation methodology for the identification of critical operating conditions of planetary journal bearings in wind turbines

The usage of journal bearings as planetary bearings in wind turbines instead of roller bearings has become more common in recent years. Their usage is advantageous, due to smaller installation space needed compared to roller bearings allowing for higher power densities of wind turbine drive trains. However, this technology presents a challenge since there is currently no standardized approach for the design of planetary journal bearings regarding wear. Due to varying wind speeds and dynamic operating events a large variation of loads has to be considered in the design process of a planetary journal bearing for wind turbines. Some of these loads are considered potentially critical to the journal bearing in terms of wear. Identifying these critical load areas early in the design phase supports a reliable bearing design and wind turbine operation.This paper introduces a method to identify critical operating conditions for planetary journal bearings using a simulation tool chain, which couples a multi body simulation (MBS) model of a wind turbine with an elasto-hydrodynamic (EHD) model of the planetary journal bearing. Based on the EHD results critical operating conditions are determined for the planetary bearing. Furthermore, methods are implemented to reduce the number of required EHD simulations for analysing the bearing design. The combination of the identification of critical operating conditions, while reducing the computational effort leads to a simulation methodology, which enables a faster bearing design assessment considering the wide variation of wind turbine operating conditions. The applicability of this method is demonstrated by a simplified use case.Firstly, this paper introduces the MBS model and the parameter space that describes possible combinations of bearing loads such as forces, moments and rotational speed. Due to the number of combinations and the EHD computing effort, the identified parameter space is secondly sampled statistically to reduce the simulation effort. A risk map is derived from the EHD results, to easily indicate potentially critical operating conditions for the planetary journal bearing.

A cost-effective algorithm for the co-simulation of unsteady and non-linear aeroelastic phenomena

Increasingly flexible structures force engineers and scientists to improve simulation capabilities incorporating an adequate description of non-linear phenomena. Furthermore, many critical operating conditions of aeronautical and civil structures are associated with unsteady phenomena, which makes it necessary to tackle this kind of problems. A critical aspect to be analyzed is the stability of the system: the determination of, not only the critical flutter speed, but also the post-critical behavior, is fundamental to guarantee the safety of designs and determine mitigation strategies. In this work, a numerical technique that allows simulating the non-linear and unsteady behavior of highly flexible structures immersed in a fluid at high Reynolds numbers is presented. This problem is addressed using a co-simulation approach, coupling the Unsteady Vortex Lattice Method (as the aerodynamic model) with the Finite Element Method using non-linear beams and rigid bodies (as the structural dynamics model). The coupling is achieved through a weak interaction algorithm. The resulting method has a very good compromise between versatility and computational cost, and is not restricted to periodic motions or linear equations of motion. Nonlinearity is included through the possibility to represent large displacements and rotations of the structure, a visco-elastic material behavior, and a nonlinear relation between the aerodynamic loads and the incidence of the incoming flow. The domains considered in the submodels and the temporal and spatial discretizations used for each one are essentially different; the interaction process must take into account these aspects. The computational implementation is carried out by combining a general-purpose structural dynamics code with an aerodynamic tool oriented to the analysis of three-bladed horizontal axis wind turbines. Examples to validate the code and show the potential of the proposed method are presented in the Results section.

Railway Noise Reduction at the Source only. Is this possible or mandatory?

Climate change urges CO2 reduction also in traffic. Electrified Railways are a powerfull CO2 free and energy and space efficient traffic mode already today. Modal shift is demanded but environmental noise of railway hinder rail traffic growth significantly. Noise tunnels are not only expensive but also reduce energy efficency and increase interior noise. Noise barriers are very costly and optical obstacles. TSI-Noise values have many criticisms. They do not cover the most bothering situations, curve running and severe other critical operation conditions are missing. The noise limit values are very high. Many standard measures in all other technical fields, construction machines or road vehicles do not exist in the railway context. Even worse is the situation of the track noise. There are nearly no measures except the demand for smooth surfaces. But the noise radiation of rails and sleepers is not constant but can be reduced significantly. Even good railway practice in other countries does not push the noise reduction without legislatve demands. Exemple are quiet high speed pantographs and tamping machines in Japan. With general measures and low noise barriers and skirts on each track side the immision limt even at densly operated lines of LDEN 55 dBA is possible.

Limiting the temperature at the chimney-roof penetration: Innovative roof passage with fins and case to meet the latest European standards and enhance heat recovery

To prevent overheating and consequent fires, European regulations prescribe thermal tests to determine the distance between chimney and combustible materials. Traditional installations are characterized by insulating material at the chimney-roof penetration; however, under critical conditions, including high gas temperatures, thick and insulating roofs, this does not ensure safety. A recent revision of the regulations has been made in light of the increased thermal resistance of building elements. The paper describes an experimental campaign on a marketable device that ensures low temperatures at chimney-roof penetration, limits thermal bridges, and improves heat recovery. Besides the thermal and energy issues, other relevant aspects have been considered, such as marketability, ease of installation, and cost. This device consists of conductive and insulating elements enclosed in a case: the conductive elements reduce the roof temperature by dissipating part of the heat from the chimney and conveying it to both the outdoor and indoor environments. By analyzing the roof temperatures detected in a test where the critical chimney operating conditions have been reproduced, its effectiveness has been experimentally demonstrated. A second test on a similar device without the conductive elements has been also conducted. Finally, results have been compared to those in the literature about tests performed on similar elements. Since results reveal that the external case strongly influences heat transfer, very thick roofs must have chimney-roof penetrations carefully designed to accommodate the latest devices. Designers of timber houses, manufacturers of chimney flues, and standards organizations can benefit from the results presented in this study.