ZEMCH 2019 International Conference Proceedings April.2020 | Page 117
1. Introduction
An energy consumption has been emerged as social problem. According to several researches [1‐
3], the building energy consumption takes about 40 % of total energy consumption. To reduce an issue
of building energy consumption, several efforts are made by BIPV [4‐6], PV [7, 8], Geothermal heat
pump [9‐11], which are mainly for reducing end energy use.
These days, new approach has been introduced as the use of high‐efficiency components in
construction. Phase change materials (PCM) has been investigated as a possible application to
construction materials in the concept of zero energy [12‐14]. In this paper, we investigate the application
of PCM to concrete with light weight aggregate shape (PCM‐LWA), which possibly mitigates leakage
problem [14].
To validate PCM‐LWA as construction materials, several researches have been performed [15‐17].
Kim et al. evaluate thermal characteristics of mortar, wherein PCM behaves as heat storage in building
[15]. Besides monitoring thermal capacity of PCM, more importantly mechanical behaviors are studies
numerically [16] and physically [17]. While numerical efforts suggest theoretical analysis of material
behaviors, physical experiments guide a proper use of the material. However, the mechanical
experiment might occur some damages on the component [18] or fully destroy it [19, 20]. In addition,
these methods have limitation on numbers of data based on samples.
To overcome this problem, while at the same time making use of the advantages provided by
physical experiment, non‐destructive testing is used in this work. Among the non‐destructive
evaluation testing methods, ultrasonic methods are not harmful, which is different from X‐ray method
[21]. Especially, fully contactless ultrasonic method is applied to evaluate mortar plates with PCM‐
LWA samples, which provides mechanical behaviors of the materials in real time without physical
contact [22].
In this study, we evaluate the change of Rayleigh waves from the PCM‐LWA mortar plates, which
simulate a radiant floor heating (RFH) system of apartments in Korea. The results possibly represent
the change of elastic modulus under various thermal condition, which provides a better understanding
of material behavior in use.
2. Experimental Method
2.1. Experimental set‐up
The contactless ultrasonic system consists of three parts; Transducer (ultrasonic emission),
Receiver (Micro‐electro‐mechanical systems (MEMS)), and Supporter (steel frame). The schematic
drawing of this system is as shown Figure 1. The transducer emits acoustic waves into the PCM‐LWA
mortar plates, and transmitted waves are measured by MEMS sensor. Mechanical waves propagate the
medium based on its physical properties such as density, Poisson’s ratio and elastic modulus. In this
regard, we measure the leaky portion of Rayleigh waves, which contains mechanical properties of the
PCM‐LWA plates while it is measured in air.
The signal data are obtained by NI 6366‐USB through Signal Express, where sampling rate and
number of samples are set to 2 MHz and 2000, respectively. Additionally, time‐averaging is conducted
at 100 times in order to improve signal‐to‐noise ratio. Mainly 50kHz narrow‐band ultrasonic transducer
(PID‐615089, Senscamp) and 8ch MEMS sensors (SPU0410LR5H, Knowles Acoustics) are used. The
spacing of MEMS sensor is 5 mm. The transducer and MEMS sensors are placed 35 mm above from the
sample, and the incident angle of the transducer set to 5 degrees. The distance between center of
transducer and first channel of MEMS is 230 mm. In addition to the contactless ultrasonic system,
thermal imaging camera (FL‐IR T 420) is used for validating a thermal performance of the PCM‐LWA
mortar plates, where the size of pixels is 320 by 240. The thermal images are automatically obtained
every 30 minutes during the experiments.
In order to control stable thermal condition, experiment and data measurement are conducted
inside thermal controlled room, which is surrounded by 30 and 150 mm thickness thermal insulation
Evaluation of PCM-LWA Mixed Plates Using Contactless Ultrasonic Method
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