Development of a standard laboratory testing method for thermal diffusivity measurements of building walls: Combined use of Infrared thermography and guarded hot box

Öz

The thermal diffusivity value of a building wall can be calculated theoretically by using the thermophysical properties of its materials listed in standards and literature. In these lists, building materials in the same category can be defined by different thermal properties; therefore, the theoretically-calculated thermal diffusivity values can be misleading. In this study, an experimental setup was developed that can directly measure the thermal diffusivity (α) value of building walls by the combined use of infrared thermography and guarded hot box methods. A 19cm-thick wall sample made of lightweight concrete block with pumice aggregate and mortar was prepared; this wall is positioned between a controlled warm ambient on its one side and a cold ambient on the other side, where its surfaces were monitored by sequential IR imaging. The thermal diffusivity value of the sample wall was calculated using the data showing temperature change versus time and the relevant theoretical equation. The reference thermal diffusivity value (αREF) of the sample wall, calculated using thermal properties measured by standard laboratory tests, is 3.4014x10-7 m2/s. The thermal diffusivity (αIRT) of the same wall, measured with the proposed IRT-GHB experimental setup, is 3.3813x10-7 m2/s. The value measured with that new setup is similar to the reference thermal diffusivity value. The results show that the new experimental setup can directly measure the thermal diffusivity of a wall. Compared to the existing ones, the proposed experimental setup presents a measurement technique that saves time and sets the basis of a scientific, practical, and more economical analytical method.

Anahtar Kelimeler

• Thermal diffusivity
• Lightweight concrete unit with pumice aggregate
• infrared thermography
• guarded hot box

Proje Numarası

BAP 07/2018-21

Yapı duvarlarının ısıl yayınırlık ölçümleri için standart bir laboratuvar test yönteminin geliştirilmesi: Kızılötesi ısıl görüntüleme ve korumalı sıcak kutunun birlikte kullanımı

Öz

Bir yapı duvarının ısıl yayınırlık değeri, bu duvarı oluşturan malzemelerin standartlarda ve/veya basılı yayınlarda listelenen termofiziksel özellikleri kullanılarak teorik olarak hesaplanabilmektedir. Bu listelerde, aynı kategoride yer alan yapı malzemeleri, farklı ısıl özellikleri ile tanımlanabilmekte; dolayısıyla teorik olarak hesaplanan ısıl yayınırlık değerleri, yanıltıcı olabilmektedir. Bu çalışmada, kızılötesi ısıl görüntüleme ve mahfazalı sıcak kutu yöntemleri bir arada kullanılarak yapı duvarlarının ısıl yayınırlık (α) değerini doğrudan ölçebilen bir deney düzeneği geliştirilmiştir. Pomza agregalı hafif beton blok ve harç ile 19cm kalınlığında bir duvar örneği hazırlanmış; bu duvar iklim koşulları takip edilen korunaklı sıcak ortam ve ardışık ısıl görüntüleme ile takip edilen soğuk ortam arasına yerleştirilmiştir. Örnek duvarın ısı yayınırlık değeri, zamana karşı sıcaklık değişimi verileri ve ilgili teorik denklem kullanılarak hesaplanmıştır. Bu duvarın standart laboratuvar testleri ile belirlenen ısıl özellikleri esas alınarak hesaplanan referans ısı yayınırlık değeri (αREF) 3,4014x10-7 m2/s’dir. Aynı duvarın, önerilen IRT-GHB deney düzeneği ile ölçülen ısıl yayınırlık değeri (αIRT) 3,3813x10-7 m2/s’dir. Yeni düzenek ile ölçülen değer, referans ısıl yayınırlık değeri ile benzerdir; sonuçlar, yeni deney düzeneğinin bir duvarın ısıl yayınırlık değerini doğrudan ölçebildiğini göstermiştir. Bu düzenek, mevcut ölçüm tekniklerine kıyasla zaman kazandıran ve ölçümler için mali yükü azaltan, bilimsel ve pratik bir analiz yönteminin temelini oluşturmaktadır.

Anahtar Kelimeler

• Isıl yayınırlık
• pomza agregalı hafif beton blok
• kızılötesi ısıl görüntüleme
• mahfazalı sıcak kutu

Destekleyen Kurum

Gazi Üniversitesi

Proje Numarası

BAP 07/2018-21

Teşekkür

Bu çalışma, Gazi Üniversitesi BAP 07/2018-21 kodlu “Yapı duvarlarının ısıl yayınırlık (termal difüzivite) değerinin belirlenmesi için kızılötesi ısıl görüntülemenin kullanıldığı standart ölçüm yöntemlerinin geliştirilmesi” başlıklı proje ile desteklenmiştir.

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