Analysis of Transient Boiling Processes during Steel Quenching in Water PAG Solutions to Decrease Distortion

The paper discusses results of testing standard cylindrical probe 12.5 mm diameter in water polymer solutions which was additionally instrumented with a surface thermocouple. It is shown that central thermocouple cannot depict many physical phenomena taking place during quenching in polymer solutions such as shoulder formation, self- regulated thermal process establishing, surface temperature transient from film boiling to nucleate boiling process. Moreover, it is shown that experimental data depicted by central thermocouple cannot be used for solving inverse problem to analyze quenching process in liquid media. Along with analyzing film and nucleate boiling processes during quenching, the paper discusses the possibility of quality quench process control via using sonar system. It is established an equation for evaluating duration of transient nucleate boiling process. As an example, the cooling characteristics of fresh and old polyalkylene glycol (PAG) polymer solutions are analyzed. It is shown that with passing time the critical heat flux density of polymer decreases and inverse solubility effect disappears. That is while the method and apparatus were developed to control in industrial condition the quality of quenched steel parts during hardening in liquid media.

Simultanous Transient Surface Temperature and Heat Flux Measurements in a Large Bore Two-Stroke Diesel Engine

Surface temperature measurements were performed in a large bore two-stroke diesel engine used for ship propulsion. A specially designed fast-response surface thermocouple was used together with an embedded standard K-type thermocouple to measure surface temperature and heat flux with high temporal resolution. Heat flux calculations were carried out both analytically and numerically showing good agreement between the results. Measurements were carried out at three different engine load conditions (25%, 30% and 50% load) in one of the fuel atomizers in the cylinder head. Cyclic surface temperature variations of up to approximately 80 K with a peak temperature of 860 K were observed. The magnitude of the perturbation of the temperature field due to the presence of the thermocouples was investigated by three dimensional CFD simulations.

An inverse method to estimate stem surface heat flux in wildland fires

Models of wildland fire-induced stem heating and tissue necrosis require accurate estimates of inward heat flux at the bark surface. Thermocouple probes or heat flux sensors placed at a stem surface do not mimic the thermal response of tree bark to flames. We show that data from thin thermocouple probes inserted just below the bark can be used, by means of a one-dimensional inverse heat conduction method, to estimate net heat flux (inward minus outward heat flow) and temperature at the bark surface. Further, we estimate outward heat flux from emitted water vapor and bark surface re-radiation. Estimates of surface heat flux and temperature made by the inverse method confirm that surface-mounted heat flux sensors and thermocouple probes overestimate surface heat flux and temperature. As a demonstration of the utility of the method, we characterized uneven stem heating, due to leeward, flame-driven vortices, in a prescribed surface fire. Advantages of using an inverse method include lower cost, ease of multipoint measurements and negligible effects on the target stem. Drawbacks of the simple inverse model described herein include inability to estimate heat flux in very moist bark and uncertainty in estimates when extensive charring occurs.

The Effects of Thermocouple Materials and Insulating Mica in an Erodable Surface Thermocouple

A finite-difference model of a surface thermocouple (erodable-ribbon type) of a heat flux sensor was built to analyze the transient response of the thermal junction and the two-dimensional effects created by the insulation between the thermocouple materials and the body material of the sensor. Such transient heat flux sensors have previously been used for measurements in internal combustion engines. It is commonly assumed that the heat transfer within these devices is one-dimensional even though the sensors are constructed from at least two different materials. It is common practice to calculate the transient heat flux using properties of body material and this leads to a substantial error as demonstrated by the model. With these sensors, low thermal capacity thermocouple junctions are formed near the surface by abrasion and response times as low as 30μs have been reported. Experiments were performed on an E type surface thermocouple heated at 11W by means of a copper vapor laser pulsating at 10kHz. Measurement of surface thermocouple temperature was performed at a 100kHz sampling rate. A finite-difference model was used to analyze the response of these sensors to the pulsed laser heating operating at 10 kHz. The insulation between the thermocouples and the body material was mica and the body material was AISI 316 stainless steel. The experimental measurements and simulation results are reported in this work. The analysis and comparison of experimental and simulation results showed that for such thermocouples two-dimensional effects exist due to the presence of mica sheets. The temperature decay between pulses was better matched using thermal properties of mica sheets rather than the thermal properties of the body material. However the body material still dominates the temperature swing of the thermocouple junction.

The Influence of Additives on the Temperature, Heat Transfer, Wear, Fatigue Life, and Self Ignition Characteristics of a 155 mm Gun

The temperature and heat transfer per round was measured at the bore surface of a 155 mm AS90 extended range ordnance. The ammunition was fired with and without wear-reducing additive and the measurements were made using an eroding-type surface thermocouple having response time of about a microsecond. The heat transfer was computed from the measured temperature-time curves. It was found that the wear-reducing additive gradually reduced the surface temperature fluctuation from about 950°C to about 600°C, and reduced heat transfer per round from about 950 kJ/m2 to about 600 kJ/m2, over a period of 50 rounds. From these measurements an assessment was made of the wear rate, the number of rounds to cook-off, and the increase in barrel fatigue life. Similar experiments on 30 mm RARDEN and 40 mm Bofors guns, using different additives, resulted in comparable reductions in bore temperature and heat transfer, but the mechanism for these reductions was different and it is still not clear exactly how these additives reduce barrel temperature and heat transfer.

Determination of the heat transfer coefficient at the workpiece—die interface for the forging process

This paper describes an investigation of the determination of the heat transfer coefficient at the workpiece-die interface for the forging process. A surface thermocouple has been constructed to measure the temperature at the die surface, where a high pressure occurs, for the simple upsetting forging process. The process was also simulated by a commercial finite element package. The measured and predicted temperatures were then used in an inverse algorithm with an iterative approach to determine the interface heat transfer coefficient (IHTC). The results show that the predicted temperatures modelled by a constant IHTC at the rest-on-die stage were in good agreement with the experimental measurement. However, for the forging stage, the IHTC values vary significantly during the process. This has important consequences in the implementation of simulation software.