Warm-up Rates Research Articles

Influence of oil service life on selected performance parameters of an aircraft piston engine

This article presents an analysis of the influence of oil service life on the performance parameters of an aircraft piston engine lubrication system used in an ultralight aircraft. The ageing of oil between oil changes causes a change in its parameters (such as density, viscosity ...). These parameters have a strong influence on the level of protection of the lubricated components. Currently, in aircraft, oil changes are carried out according to a time schedule - oil is changed every fixed period (residual life) regardless of its actual condition. The task of this article is to test the possibility of indirect assessment of oil condition based on analysis of changes in selected parameters of engine lubrication system operation during normal operation. The oil warm-up speed during the pre-start procedure and the dependence of oil pressure on engine speed were assumed for the analysis. The study was conducted on an ultralight rotorcraft during normal operation. Selected first daily flights directly after oil change, and after 17, 32, 50, 66 hours of operation were analysed. It was shown that the warm-up rate changes in the samples analyzed, but that this change may also be due to factors other than oil operating time. In the case of the oil pressure vs. speed characteristics, different characteristics were shown for different operating time, but no specific dependencies were found.

Optimisation of a recirculating domestic hot water system to minimise wait time and heat loss

Many houses suffer from a delay in hot water arrival, after opening the hot tap, due to the length of pipe work from the boiler or thermal store. Measurements in three properties showed delays of up to 46 s. A recirculation system could maintain the water in the pipe at a suitable temperature and for a 15 m pipe is expected to use 30 W less electrical power than a local thermal store at the delivery point. Time-steady eigenvector solutions to the linked temperature equations allow optimisation of the recirculation flow rate, pipe diameters and insulation thickness. The pumping power is <1 mW and a pumpless thermo-syphon system should be possible in some installations. Heat loss coefficients have been calculated for a pair of pipes in a common insulation sleeve to minimise the losses. A plug flow transient advection model for water and pipe temperature based on a sliding 1-D grid has been developed and validated for a single pipe, then extended to also model recirculating systems. Heat losses in a pumped system may be reduced using a timer so the system can cool overnight. The transient model predicts the relationship between flow and warm-up rate to optimise pump size and timing.

Investigation of the transient freeze start behavior of polymer electrolyte fuel cells

Understanding the water management in polymer electrolyte fuel cells during sub-zero operation is crucial for designing effective freeze start strategies. This study uses sub-second operando X-ray tomographic microscopy to study the effect of warm-up rate and pre-drying on the water dynamics during non-isothermal freeze starts from −30 °C. A faster warm-up rate and cell pre-drying before freezing improved the cell performance during the freeze start. Imaging showed that during the freeze starts no new water clusters were formed in the cathode gas diffusion layer. Temporary catalyst layer detachment from the micro-porous layer was also observed between −20 to 18 °C due to the hygro-mechanical stresses during the sub-zero operation. Isothermal freeze starts were also performed to study the effect of membrane conductivity and local water flux in the catalyst layer during the sub-zero operation. Higher temperatures and lower operating current densities resulted in an increase in the operation time. Imaging results showed water clusters in the cathode gas diffusion layer for the isothermal freeze starts from −15 to 0 °C after 6 C/cm2 charge was produced.

High-temperature fatigue behavior of a steam turbine rotor under flexible operating conditions with variable loading amplitudes

This study investigated the high-temperature fatigue behavior of a steam turbine rotor under long-term operation with multiple startup types including one cold, three warm and 16 hot-startups at intervals of 45 days. To better describe the mechanical behavior of the rotor material, a unified viscoplastic constitutive model was experimentally validated then implemented with a user-defined material. Analysis initially focused on the inlet region, where thermal loads dominated. Next, the stress and damage at three selected positions with differences in temperature and load were compared and analyzed in detail. The effect of different startup types on the fatigue damage was statistically assessed. The equivalent hot startup (EHS) ratio was calculated to compare the risk level of each position under each startup type in flexible operation mode. Investigation of the inlet region showed that the warm startup conditions adopted here were more damaging than cold startup due to the higher warmup rate. The analysis of fatigue damage showed a temperature-dependent characteristic of the thermo-mechanical load-dominated positions. The EHS ratio of Groove-1 was larger than that of Groove-4, indicating a higher risk level in Groove-1 under flexible operating conditions. For the inlet region, the accumulation of viscoplastic strain made this region a fatigue-damageable position.

Influence of poor preparation and sleep deficit on injury incidence in amateur small field football of both gender.

Amateur small-field football tournaments are rather common worldwide. Adequate preparation is essential for injury prevention. The consequences of insufficient injury preparation at this level are still unclear. This study investigates the factors influencing injuries in this football population. In 2017, medical students participating in a national amateur football tournament were analysed in a prospective cohort study. Injury incidence, injury pattern and factors influencing injuries were investigated according to the statement on data collection and injury definition of Fuller et al. (Br J Sports Med 40:193-201, 2006). Preparation for the tournament was assessed for both sexes by means of hours of sleep, alcohol consumption, training level and warm-up performance. II. Of 694 amateur football players (423 men and 271 women) with a mean age of 23years (SD 2.5), 321 (21.1%) injuries happened during the tournament. 60% of injuries affected the lower extremity. The most common types of traumatic injury were skin abrasions (40.0%) and muscle strains (23.3%). The injury incidence of male players during match exposure was 469 per 1000h football and significantly higher than in female players 313 (p = 0.025). One potential reason for the higher injury rate of male players as measure for inadequate preparation was significantly higher alcohol consumption the evening before the tournament (p < 0.001) and the after-effects on match day (p < 0.001). Additionally, male players reported less and inadequate sleep the night before the tournament (p < 0.007) and a lower warm-up rate before the matches compared to female players (p < 0.001). Small-field tournaments in football have a high injury incidence. Male players have a higher injury incidence than female players and show additionally a lack of sleep and alcohol consumption the night before the tournament and poor warm-up performance on match day. Adequate preparation for a football tournament is the key factor for preventing injuries, also in recreational football.

Utilizing low airflow strategies, including cylinder deactivation, to improve fuel efficiency and aftertreatment thermal management

Approximately 30% of the fuel consumed during typical heavy-duty vehicle operation occurs at elevated speeds with low-to-moderate loads below 6.5 bar brake mean effective pressure. The fuel economy and aftertreatment thermal management of the engine at these conditions can be improved using conventional means as well as cylinder deactivation and intake valve closure modulation. Airflow reductions result in higher exhaust gas temperatures, which are beneficial for aftertreatment thermal management, and reduced pumping work, which improves fuel efficiency. Airflow reductions can be achieved through a reduction of displaced cylinder volume by using cylinder deactivation and through reduction of volumetric efficiency by using intake valve closure modulation. This paper shows that, depending on load, cylinder deactivation and intake valve closure modulation can be used to reduce the fuel consumption between 5% and 25%, increase the rate of warm-up of aftertreatment, maintain higher temperatures, or achieve active diesel particulate filter regeneration without requiring dosing of the diesel oxidation catalyst.

SHS reaction and explosive crystallization in thin films: Resemblance and distinction

The SHS waves in multilayer Ni/Al nanofilms and the explosive crystallization waves in Sb films deposited onto a thin copper substrate were comparatively explored by IR imaging and SEM. Despite a markedly lower thermal effect of crystallization, the waves of chemical reaction and crystallization were found to have much in common in their temperature–time histories: warmup rate, temperature gradient in the wave front, and duration of heat release. Observed was a micro-scintillation mode of the propagation of explosive crystallization wave in Sb films.

A novel filtration device for point of care preparation of cellular therapies

Many biological samples are stored at cryogenic temperatures (i.e. temperatures below -1500C) to preserve their viability. Typically, these samples are stored in liquid nitrogen vapor-phase freezers. The underlying assumption is that biological samples show highly reduced degradation and metabolic activity while below Tg (the glass transition temperature). On the other hand, every time a sample is manipulated or temporarily removed from an LN2 freezer, the sample will experience thermal excursions marked by warm-up rates of several degrees per second. In these cases, the risk of harming a sample by inadvertently crossing the Tg threshold is very likely. This paper’s objective is to provide supporting data to fully characterize the thermal excursions of cryogenically frozen single vials filled with H2O during typical transient temperature events. Specifically, we focus our attention on the cold-chain steps that involve transferring a single vial from an LN2 vapor environment to either an ambient temperature or transportable dry ice (-800C) environment. In general, the warm-up rates experienced by the biological sample correlate to the thermal energy exchanged with the warmer environment via convective and conductive heat transfer. The magnitude of the heat transfer is driven by multiple factors: the warmer environment temperature and the overall time of exposure, the size and shape of the vial, its placement in a cryobox, the type of handling (manual or automated), the handling speed, etc. In this paper, we rationalize all the above factors and present experimental measurements supported by calibrated finite elements simulations showing typical expected warm-up rates. As a result, best-practice time constants for handling vials of biological samples without risking excessive thermal excursions above Tg are suggested.

Thermal excursions of cryogenically frozen single vials below -150°C) and the risk of rising above Tg: analyzing warm-up rates from cryogenic storage to both dry ice and ambient temperature environments

Thermal excursions of cryogenically frozen single vials below -150°C) and the risk of rising above Tg: analyzing warm-up rates from cryogenic storage to both dry ice and ambient temperature environments

Cryogenics for Super-FRS at FAIR

The challenge of cooling down the huge cold mass up to 1100 tons (dominated by iron) to 4.5K is addressed as one of the most important features for Super-FRS cryogenics at FAIR. For such large cold mass precooling with LN2 is necessary due to the reason that approximately 80% of the cool down load is from 300K to 80K. The capacity of the LN2 precooler at 80K as well as the 4.5K cooling power have been specified in order to reach a reasonable cooldown time of three to four weeks. In the paper we will also discuss the technical issues for Super-FRS magnet testing at CERN in terms of the limitations of the cooldown / warmup rates on magnets, interface definition, and the magnet cryostat protection against over-pressure under worst-case scenarios, i.e., quench and insulation vacuum sudden loss to air, which are the key issues for the cryogenic test facility planning and machine protection at FAIR. Meanwhile the important features of the refrigerator and the cryogenic distribution system for the Super-FRS at FAIR will be discussed.

Experimental Investigation of Effect of Meteorology and Turbidity on Operation of Salt Gradient Solar Pond in the Tropics

The experimental studies are carried out at the location having tropical climate. An underground pond of size 1m x 1 m x 2.5 m is constructed. Meteorology has strong influence on the thermal performance of pond. This study has reported that starting day is an important consideration in thermal performance analysis. Starting day affects the rate of warm-up and cumulative heat collection significantly. Estimated the rate of turbidity accumulation and observed that the turbidity can be effectively removed, but cannot be reduced to zero level. Results are of practical importance as a data base for the pond operators and researchers.

Meteorologically efficient commissioning of salt gradient solar pond

Salt gradient solar pond has thermal performance parameters as rate of warm-up, highest achievable temperature, and cumulative heat collection. All these are strongly influenced by the meteorology. Consequently, specific to the meteorology of a geographic location, there is a best starting day for the as pond defined by Singh et al. [1]. The present work has done rigorous analysis of influence of meteorology on pond’s thermal performance. It is found that the starting day has strong influence in initial stage of pond warm-up; however the effect diminishes in long-term. Finally pond started on any day of the year acquires same highest temperature. It is also found that in order to retrieve maximum heat, waiting for the best starting day to commission a pond is not judicious, rather it is always more beneficial commission the pond at the earliest possible day. This finding is of practical significance while planning to put a pond in operation.

Systems optimisation of an active thermal management system during engine warm-up

Active thermal management systems offer a potential for small improvements in fuel consumption that will contribute to upcoming legislation on carbon dioxide emissions. These systems offer new degrees of freedom for engine calibration; however, their full potential will only be exploited if a systems approach to their calibration is adopted, in conjunction with other engine controls. In this work, a design-of-experiments approach is extended to allow its application to transient drive cycles performed on a dynamic test stand. Experimental precision is of crucial importance in this technique since even small errors would obscure the effects of interest. The dynamic behaviour of the engine was represented mathematically in a manner that enabled conventional steady state modelling approaches to be employed in order to predict the thermal state of critical parts of the engine as a function of the actuator settings. A 17-point test matrix was undertaken, and subsequent modelling and optimisation procedures indicated potential 2–3% fuel consumption benefits under iso-nitrogen oxide conditions. Reductions in the thermal inertia appeared to be the most effective approach for reducing the engine warm-up time, which translated approximately to a 1.3% reduction in the fuel consumption per kilogram of coolant. A novel oil-cooled exhaust gas recirculation system showed the significant benefits of cooling the exhaust gases, thereby reducing the inlet gas temperature by 5 °C and subsequently the nitrogen oxide emissions by 6%, in addition to increasing the warm-up rate of the oil. This suggested that optimising the thermal management system for cooling the gases in the exhaust gas recirculation system can offer significant improvements. For the first time this paper presents a technique that allows simple predictive models of the thermal state of the engine to be integrated into the calibration process in order to deliver the optimum benefit. In particular, it is shown how the effect of the thermal management system on the nitrogen oxides can be traded off, by advancing the injection timing, to give significant improvements in the fuel consumption.

Review of the systems analysis of interactions between the thermal, lubricant, and combustion processes of diesel engines

A review of technologies surrounding the thermal management system of the modern diesel engine with increased attention on fuel consumption is presented. A system-based approach has been adopted, looking at the interaction with other key systems. Previous innovation has aimed at reducing the power consumption of the cooling system or incorporating different cooling strategies and improving the engine warm-up rate for improved fuel consumption by higher operating temperatures. Electrical pumps can operate independently of the engine speed, and precision cooling and nucleate boiling have improved the heat transfer within the engine, reducing coolant flow requirements by 90 per cent. Improved warm-up rates have been demonstrated by using reduced thermal inertia or energy recovery systems either simulated on the test rig or through heat exchangers with exhaust gases. The resultant reduction in the fuel consumption is a result of various effects of the temperature on both the lubricating system and the combustion process. Despite difficulties in accurately measuring the engine friction, studies suggest that an increase in the engine temperature from 50°C to 80°C reduces the engine friction by 44 per cent because of 67 per cent lower oil viscosity. Simultaneous reduction in the emissions of nitogen oxides (NO x) and the fuel consumption of 13.5 per cent and 0.7 per cent respectively have been achieved by including the engine thermal system in the calibration procedure. However, in-cylinder data needs to be studied to understand fully the mechanisms involved. Hotter engine temperatures reduce ignition delay, making combustion occur earlier in the cycle, which has a positive effect on the fuel consumption but a negative effect on the NO x emissions. Engine thermal management requires a system-based approach if the effects are to be fully understood but offers potential as an additional parameter in engine calibration.

Hydrocarbon storage modeling for diesel oxidation catalysts

A simple hydrocarbon (HC) storage model was proposed which represents the adsorption–desorption processes in zeolites incorporated in a diesel oxidation catalyst (DOC). Using four experiments in which the HC was stepped up and the reactor run until steady state, a Langmuir isotherm was generated that was sufficient to represent the equilibrium data, and the remaining rate constant capturing the adsorption time scale was obtained by fitting. The model thus developed was validated using reactor data which was obtained by stepping the inlet HC concentration to zero after outlet reached equilibrium. A typical DOC which contained both a storage component (zeolite) and noble metal component (for oxidation) was studied using a full scale 1D reactor model which includes the storage kinetics developed here with the oxidation kinetics developed in our previous work [ Sampara et al., 2008. Global kinetics for a commercial diesel oxidation catalyst with two exhaust hydrocarbons. Industrial & Engineering Chemistry Research 47, 311–322]. Simulations of a simplified warm-up process indicated that the zeolite storage component reduces the overall cold start HC emissions by at least a factor of two if the warm-up rate achieves 45 – 65 ∘ C min - 1 , a range commonly observed during start-up. Modeling results also showed that the HC oxidation for these reactors commonly starts at the rear end of the reactor due to reduced CO inhibition. The rates of the individual processes during cold start were analyzed in detail and compared with the rate of inlet temperature increase provided from the exhaust.

Size evolution of palladium nanoparticles from low-temperature solvated atoms

Palladium nanoparticles were synthesized by the chemical liquid deposition method. In this method Pd atoms, produced by resistive heating, were co-deposited at 77 K with 2-propanol vapors to obtain a frozen metal-organic matrix, which is then melted to obtain a colloidal dispersion. In this work, we study the effect of the melting or warm-up rate of the frozen matrix on the characteristics of nanoparticles. The colloidal dispersions were characterized by FTIR, TEM and HRTEM techniques. The FTIR spectra reveal that the carbonaceous fragments are anchored on Pd particles. Studies in TEM and HRTEM micrographs reveal higher mean particle size (∼5 nm), broader size distributions and irregular shapes when the melting process is faster, whereas for a slower warm-up process, it was found smaller particle sizes (∼2 nm), narrower size distributions and regular particle shapes like cuboctahedron, tetrakaidecahedron and icosahedron.

Optimum size of non-convective zone for improved thermal performance of salt gradient solar pond

The salt gradient solar pond is a long-term heat storage system with a considerable warm-up time. A pond is efficient when it reaches the desired temperature quickly and maximum heat is subsequently retrieved at steady state. This requires optimum sizing of the non-convective zone. In the present work, the optimum size of the non-convective zone for fast warm-up is determined. This is found to differ considerably from the optimum size of the steady state criterion. The possibility of achieving both performance parameters, i.e. fast warm-up and maximum heat collection later on, is analyzed. It is suggested that when commissioning a pond, the size of the non-convective zone should at first be the optimum value from the warm-up rate criterion, but may later be changed to the optimum size from the steady state criterion.

The development of a fully portable, cryocooled HTS SQUID NDE instrument

Commercial realisation of the full potential of HTS SQUIDs in NDE will only come about with the development of fully portable systems that operate on a turn-key approach. Existing cryogenic solutions rely on invertible cryostats which can be both cumbersome and are typically custom-fabricated. With the use of cryocoolers becoming more widespread, there is a possibility to dispense with the need for a liquid cryogen. Here we report on progress towards such a system that will incorporate a cryocooler which can be disengaged from a copper thermal battery once the base temperature has been reached. The battery has been designed with a two-stage inner and outer core system to extend the SQUIDs operating time. The cool-down and warm-up rates for the system are presented along with a discussion of SQUID packaging.

Temperature and water relations in desert bees

1. 1. Desert bees do not show significant differences in most thermal parameters; mean endothermic warm-up rates are similar to those of temperate species, with no special cooling mechanisms, and normal upper critical temperatures (unlike desert ants and beetles). Thermoregulatory abilities may however be improved. 2. 2. They show the whole range of possible water balance problems; small species are acutely water-stressed when foraging, but large bees suffer from excessive generation of metabolic water in flight. 3. 3. Activity patterns are therefore either matinal, crepuscular or bimodal; essentially desert bees avoid heat and adapt to cold desert dawns and dusks. Desert plants must be coevolved to offer appropriate rewards and match the physiological constraints on their pollinators. 4. 4. Endothermy in bees may have evolved primarily in arid zones, and served as a pre-adaptation for subsequent invasion of cool temperate biomes.

Effect of Humidity on the Drying Rates of Carpet Tiles

The effects of humidity on the drying rates of carpet tile depend on both gas stream temperature and flow rate, and are much larger in the warm-up and constant rate periods than in the falling rate period. The existence of inversion temperatures is investigated for carpet tile drying. For a given flow condition, an inversion temperature is the temperature at which the drying rate in a superheated steam environment equals that in air. Inversion temperatures are 177°C and 214°C for the low flow and high flow conditions of this study, respectively.