850 



GEOPHYSICAL WELL TESTING 



IChap. 11 



fitted with thermocouples or resistance thermometers. If S is the surface 

 of the plate and (62 — ^\)/x is the temperature gradient, the thermal 

 conductivity 



Q 



c = 



S 62 — 61 ' 



(11-6) 



where Q (cal. sec. ) is the heat current which may be calculated from the 

 current and the resistance of the heater circuit. Another absolute method^* 



ra) 



Ca 

 Cu 

 Cu 



1 



(0 



J I ^L 



hot 



(b) 



Bi 



\ci <f,\ 



'St 



Vt <h 



TTTH 



'ft 



cold 



\ 



Fig. 11-20. Arrangements for measuring thermal conductivities of rocks: {<i) 

 absolute method, (fc) and (c) relative methods. 



uses a thermocouple in the center of a slab whose two faces are exposed 

 to constant temperature for twenty-four hours and then abruptly chilled 

 to and kept at 0° C. The conductivity is calculated from the time required 

 for the center temperature to fall to its hal|- value. 



A simple relative method for comparison with a material of known con- 

 ductivity is shown in Fig. 11-206. Two plates of triangular shape are 

 joined with their hypotenuses and covered with a wax film. If heat is 



" Ingersoll, Phys. Rev. 24, 92 (1924). 



