Transient Thermography Method Research Articles

In-situ heat loss measurements of parabolic trough receivers based on transient infrared thermography

The design lifetime of parabolic trough receivers is at least 25years. However, depending on the specific operating conditions, this expected lifetime may be shortened. A periodic inspection of receivers mounted in a solar field is thus recommended. Several field methods with distinct depth of information and field throughput exist to estimate receiver thermal performance. This paper gives an overview of these field methods and presents the application of a transient infrared thermography method, which combines dynamic temperature measurements with a numerical heat transfer model in order to derive specific receiver heat losses and separate internal heat loss mechanisms. This method has been previously investigated under laboratory test conditions and is here applied under field test conditions for in-situ thermal measurements on mounted receivers.The transient thermography method allows a correct estimation of specific heat losses within a precision range below ±10% for all tested receivers under field test conditions. Relevant separation of heat loss mechanisms could be derived for evacuated PTRs with solar selective absorber coating, while partially biased diagnoses could be observed for partially or non-evacuated PTRs with highly emissive absorber coatings. Active thermography is considered as a relevant tool for receiver field inspection, in combination with a complementary field screening measurement technique.

A Transient Thermography Method to Separate Heat Loss Mechanisms in Parabolic Trough Receivers

This paper describes a transient thermography method to measure the heat loss of parabolic trough receivers and separate their heat loss mechanisms. This method is complementary to existing stationary techniques, which use either energy balances or glass envelope temperature measurements to derive overall heat losses. It is shown that the receiver heat loss can be calculated by applying a thermal excitation on the absorber tube and measuring both absorber tube and glass envelope temperature signals. Additionally, the emittance of the absorber selective coating and the vacuum quality of the annulus can be derived. The benefits and the limits of the transient method are presented and compared to the established stationary method based on glass envelope temperature measurements. Simulation studies and first validation experiments are described. A simulation based uncertainty analysis indicates that an uncertainty level of approximately 5% could be achieved on heat loss measurements for the transient method introduced in this paper, whereas for a conventional stationary field measurement technique, the uncertainty is estimated to 17–19%.

Nondestructive Evaluation of Polyurethane Materials Using Transient Thermography

The aim of this work is to investigate the potential of transient thermography in the nondestructive evaluation of structural defects of NECURON 1001 using the FLIR thermographic system. Necuron is a polyurethane material used for applications like: fixture and gauges, master and copy models, models with high mechanical stress, etc. Transient thermography is a thermographic method which implies the investigation of materials that are of a different (often higher) temperature than the ambient. The heat flow into the sample is altered in the presence of a subsurface defect or feature, creating a temperature contrast at the surface that is recorded by the infrared system. Results show that this method of evaluation can indicate, in necuron, defects of small sizes that can be overlooked in the manufacturing process. Also, it was shown that the transient thermography method presented can be an important tool in evaluating structural defects of materials.

Lateral heat flow method for thickness independent determination of thermal diffusivity

A pulsed transient thermography method is described where a high-intensity light pulse is used to heat a long, uniform stripe on the surface of a plate. A high spatial resolution, high frame rate focal plane array infrared camera is used to monitor surface temperature. We explain the theoretical model and data analysis framework used to experimentally determine all three thermal diffusivity components from the temperature measurements. The analysis does not require any fitting to the temperature profile and is based on the creation of thermal time-of-flight (tof) images from the temperature data and the relationship between tof and the distance from the stripe edge. The in-plane components of thermal diffusivity are obtained without the need for thickness information. Experimental validation of this procedure was carried out using anisotropic carbon fiber reinforced polymer composites.