ASTM D518 PDF

More C It must be recognized, therefore, that the selection of typical values of thermal transmission properties representative of a material in a particular application should be based on a consideration of these factors and will not apply necessarily without modification to all service conditions. Even more basic is the dependence of the thermal properties on variables, such as mean temperature and temperature difference. These dependencies should be measured or the test made at conditions typical of use.

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More C It must be recognized, therefore, that the selection of typical values of thermal transmission properties representative of a material in a particular application should be based on a consideration of these factors and will not apply necessarily without modification to all service conditions.

Even more basic is the dependence of the thermal properties on variables, such as mean temperature and temperature difference. These dependencies should be measured or the test made at conditions typical of use.

The use of a heat flow meter apparatus when there are thermal bridges present in the specimen may yield very unreliable results. If the thermal bridge is present and parallel to the heat flow the results obtained may well have no meaning.

Special considerations also are necessary when the measurements are conducted at either high or low temperatures, in ambient pressures above or below atmospheric pressure, or in special ambient gases that are inert or hazardous.

In all cases the accuracy of the heat flow meter apparatus can never be better than the accuracy of the primary standards used to calibrate the apparatus. The average of two calibrations shall be used as the calibration factor and the specimen s certified with this average value.

This precision is required to identify changes in calibration and is desirable in quality control applications. Scope 1. The precision and bias of the heat flow meter apparatus can be excellent provided calibration is carried out within the range of heat flows expected. This means calibration shall be carried out with similar types of materials, of similar thermal conductances, at similar thicknesses, mean temperatures, and temperature gradients, as expected for the test specimens.

Properties of the calibration specimens must be traceable to an absolute measurement method. The calibration specimens should be obtained from a recognized national standards laboratory. By appropriate calibration of the heat flux transducer s with calibration standards and by measurement of the plate temperatures and plate separation. Many advances have been made in thermal technology, both in measurement techniques and in improved understanding of the principles of heat flow through materials.

These advances have prompted revisions in the conceptual approaches to the measurement of the thermal transmission properties Other test methods, such as Test Methods C or C should be used if needed. Thus users of this test method shall have sufficient knowledge to satisfactorily fulfill their needs. For example, knowledge of heat transfer principles, low level electrical measurements, and general test procedures is required.

The Annex is critically important in addressing equipment design and error analysis. No other units of measurement are included in this standard.

It is the responsibility of the user of this standard to consult and establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

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