Thermal transmission testing

Thermal transmission testing is an excellent way of detecting various types of anomalies such as surface corrosion under paint before the corrosion becomes visually evident. Thin, single-layer structures, such as aircraft skin panels, can be inspected for surface and subsurface discontinuities. This test is simple and inexpensive, although materials with poor heat-transfer properties are difficult to test, and the joint must be accessible from both sides. For nonmetallic materials, the defect diameter must be on the order of 4 times its depth below the surface to obtain a reliable thermal indication. For metals, the defect diameter must be approximately 8 times its depth. Some bright surfaces such as bare copper and aluminum do not emit sufficient infrared radiation and may require a darkening coating on their surface. 

Tye, R. P., ed. (1977). Thermal Transmission Measurements of Insualtion (STP 660). West Conchohocken, PA American Society for Testing and Materials. 

ASTM Cl77, 2004, Standard test method for steady state heat flux measurements and thermal transmission properties by means of the guarded hot plate apparatus. 

ASTM C177-85, Standard Test Method for Steady-State Heat Flux Measurements and Thermal Transmission Properties by Means of the Guaxded-Hot-Plate Apparatus , Annual Book of ASTM Standards, American Society for Testing and Materials, Philadelphia, PA. 

Thermal transmission methods are relatively new techniques for adhesive inspection. Heat flow is determined by monitoring the surface temperature of a test piece a short time immediately after external heating or cooling has been applied. Subsurface anomalies alter the heat flow pattern and, thereby, affect the surface temperature. The surface temperature difference can be detected by thermometers, thermocouples, or heat-sensitive coatings. Liquid crystals applied to the joint can make voids visible if the substrate is heated. 

Dix and Lavan conducted studies to measure the effectiveness of draperies and other indoor shading devices on the coefficient of thermal transmission, U, under winter and summer conditions (89)- With the aid of two environmentally controlled chambers and thermistors located near a test window, they determined that a medium-colored drapery with a white plastic backing reduced conductive heat loss in the winter by 6-1%, and conductive and radiant (solar) heat gains in the slimmer by 33%. Because shades inside casements were more effective than draperies in reducing heat loss under winter conditions, they concluded that the ability of the material to block air flow was more important than other properties of the material used (8 ). 

Dechow, F. I. Epstein, K. A. ASTM STP660, Thermal Transmission Measurements of Insulation, American Society for Testing and Materials Philadelphia, PA, 1978, p. 234. 

Thermal conductivity test JIS A 1412 (Test Method for Thermal Transmission Properties of Thermal Insulations). 

C 518 Standard Test Method for Steady-State Thermal Transmission Properties by Means of the Heat Flow Meter Apparatus... 

Steady State Heat Flux Measurement and Thermal Transmission Properties by Measure of Heat Flow Meter Apparatus, ASTM C518, Am. Soc. Testing and Materials. Goodrich B, Toyama B. Liquid encapsulation considerations. Dexter Technology Paper, Dec. 1994. 

ASTM F 1769-97, Standard Test Method for Measurement qfDiffusivity, Solubility, and Permeability of Organic Vapor Barriers Using a Flame Ionization Detector (Philadelphia, 1997) ASTM C177-93, Steady-State Thermal Transmission Properties by Means of the Guarded Hot Plate (Philadelphia, 1993)... 

Thermal impedance of the composites was tested per ASTM D5470, Standard Test Method for Thermal Transmission Properties of Thin Thermally Conductive Solid Electrical Insulation Materials. Test method A calls for a specimen to be compressed between two masses of metal. A measured amount of heat energy is put in the metal and once equilibrium is obtained, the temperature of the metal masses is measured. These temperatures are used to calculate thermal impedance. This relationship is seen in equation 12. 

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