Abstract
A technique is reported for simultaneous, time- and space-resolved measurements of temperature using laser-induced thermal grating scattering, LITGS, from four points on a 1-D line. Signals from four separate points on the line, separated by 1 mm, in toluene-seeded nitrogen flows, were imaged onto a fibre-optic array and delivered to separate photodiode detectors to record their temporal evolution from which the temperatures at each point were derived with a spatial resolution of 1 mm and a precision of 0.7% at atmospheric pressure. Effects of variation of composition on the accuracy of the measurements were compensated by a calibration method providing good agreement with values inferred from thermocouple measurements. Temperature gradients at the boundary between parallel gas flows and at the surface of hot and cold surfaces were measured with a resolution of 5 K mm−1. Extension of the technique to more measurement points and improvements in spatial resolution are briefly discussed.
Highlights
The temperature of combusting and non-combusting flows is an important parameter in a wide range of problems including heat transfer to surfaces in internal combustion engines, cooling of turbine blades in aero-engines and studies of thermal boundary layers in hypersonics and the physics of spacecraft entry or re-entry into atmospheres. (Lucht 1991; Kays and Crawford 1993; Heppenheimer 2006) Of particular concern is the measurement of temperature gradients close to surfaces exposed to hot or cold gas flows
The variation in signal strength is accounted for by the difference in absorber concentrations at the edges of the flow as a result of dilution by entrained air and lower intensity of the pump beams at the edges of the beams. These data show the typically high signal-to-noise ratio of the single-shot LITGS signals from which the temperature can be derived at each point on the line
The simultaneous measurement of temperature using LITGS at four points along a line has been demonstrated in this work
Summary
The temperature of combusting and non-combusting flows is an important parameter in a wide range of problems including heat transfer to surfaces in internal combustion engines, cooling of turbine blades in aero-engines and studies of thermal boundary layers in hypersonics and the physics of spacecraft entry or re-entry into atmospheres. (Lucht 1991; Kays and Crawford 1993; Heppenheimer 2006) Of. The streak camera image provided a spatially resolved LIGS signal, showing the temporal oscillations in signal intensity at each point on the line, from which the temperature was derived with an uncertainty of 0.3% and a spatial resolution of 150 μm along the line. These measurements were taken in a cell at uniform temperature, and so no temperature gradient was probed. The precision of 0.3% was achieved only by “stitching together” a sequence of LIGS signals recorded at increasing delay times to cover the entire signal duration This limitation is inherent in the design of most streak cameras. Some future applications of the technique and extensions to more measurement points are discussed
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