Two dimensional transient heat flux analysis through platinum plate

The transient response of an erodable ribbon element heat flux gauge has been assessed using a two-dimensional finite element (FE) analysis. Such transient heat flux gauges have previously been used for measurements in internal combustion (IC) engines. To identify the heat flux from the measurements of surface temperature, it is commonly assumed that the heat transfer within these devices is one-dimensional. A corollary of the one-dimensional treatment is that only one value of the thermal product, , is needed for identification of the transient heat flux, even though erodable heat flux gauges are constructed from at least two different materials. The current results demonstrate that two-dimensional transient heat conduction effects have a significant influence on the surface temperature measurements made with these devices. For the ribbon element gauge and timescales of interest in IC engine studies, using a one-dimensional analysis (and hence a single value of ) will lead to substantial inaccuracy in the derived heat flux measurements.

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

Heat Transfer: Volume 3 ◽

10.1115/ht2008-56090 ◽

2008 ◽

Author(s):

Alan Grech ◽

Tonio Sant ◽

Mario Farrugia

Keyword(s):

Heat Flux ◽

Thermal Properties ◽

Finite Difference ◽

The Body ◽

Two Dimensional ◽

Difference Model ◽

Dimensional Effects ◽

Surface Thermocouple ◽

Simulation Results ◽

Transient Heat Flux

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.

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