GB855658A - Improvements in and relating to the measurement of thermal conductivity - Google Patents

Abstract

855,658. Determining thermal conductivity. NATIONAL RESEARCH DEVELOPMENT CORPORATION. Nov. 29, 1957 [Nov. 29, 1956], No. 36588/56. Class 40 (1). [Also in Group XX] In apparatus for measuring thermal conductivity the temperature change of a body when brought into contact with the material being tested, the body and the material initially being at different temperatures, is compared with the temperature change of a similar body in contact only with the ambient atmosphere. Fig. 1 shows a section through the apparatus in which two steel balls 11 and 12 are mounted in an insulating block 13. Ball 11 is slightly protuberant in order to contact the material under test, whilst ball 12 is recessed in order that it shall only contact the ambient atmosphere. The block is supported on the test material at only ball 11 and two studs, of which one is shown at 14. The temperatures of the balls are measured by thermocouples recessed into their surface and preferably the connections are such that the output is the difference in the e.m.f's of the thermocouples and hence a function of the temperature difference, Measuring thermal conductivity of a fluid.- A shallow dish 17, Fig. 7, having branch tubes 18 for the introduction of temperature-measuring instruments or the introduction of the fluid under test, has a thin impervious membrane 21, stretched over its top so that a device 13, as described above may be placed on the membrane in good thermal contact with the fluid. In order to limit convection currents a member 25 is placed in the disc to keep the depth of the fluid below the membrane at a suitable value, e.g. 3 mm. For use with gases smaller or hollow balls may be used in order to reduce their thermal capacity.