Patent GB-945077-A (GB)
Title: Device for measuring the heat-conductivity of fluids
Inventor: ELBERG SALOMON
IPC: G01N27/18
Filed: 1961-12-15
Abstract: 945,077. Measuring thermal conductivity electrically. COMMISSARIAT A L'ENERGIE ATOMIQUE. Dec.15, 1961 [Dec. 16, 1960], No. 45002/61. Headings G1D and G1N. Heat conductivity of a fluid is measured by an immersible probe 1 connected in one arm of a Wheatstone bridge 3 one diagonal of which is connected to an amplifier 5 feeding a differentiation circuit 6 itself connected across first and second fixed terminals of a potentiometer 9, the slider of which is driven at constant speed thus providing a desired variation of resistance with time and which is synchronized so as to switch "on" a power supply 4 feeding the other diagonal of the Wheatstone bridge when the slider passes the first terminal, an indicating or recording instrument 12 being connected between this terminal and the slider. A step function of power q, Fig. 1 is applied per unit length of platinum resistance wire immersed in the fluid and causes a rise in wire temperature # # in time t according to the curve shown in Fig. 2, a portion of which is linear and of slope S. The Specification states that (1) where # is the conductivity of the fluid, and the invention is directed to determining d(##)/d(log t) automatically, ## beingmeasured by the change in probe resistance. As shown in (Fig. 3) the platinum wire probe 1 is immersed in liquid 2 both initially at temperature #. The bridge output is connected to an amplifier 5 having gain A feeding a differentiation circuit 6 of gain B, itself connected to terminals 7, 8 of a circular potentiometer 9, the slider 10 of which is driven by synchronous motor 11. A standard resistance Re in conjunction with a potentiometer-type voltmeter P is used to obtain the value of current I flowing through the probe arm of the bridge. Power supply 4 is switched "on" when the slider 10 passes the zero of potentiometer 9 by a contact fitted to the potentiometer shaft. It is shown that when power is applied to the bridge 3 resulting in a bridge output voltage e, the voltage U appearing at the instrument 12 is (2) and that the heat conductivity of the liquid is (5) where D is a characteristic constant of the probe and the total equipment. The output voltage U shown in Fig. 4 is the differential of the curve shown in Fig. 2, the reference 13 indicating the value of the slope s and being proportional to The instrument is first calibrated on a liquid of known heat conductivity and the value of q and U noted. The liquid to be evaluated is then used and the value of q progressively altered until the same value of U as obtained from the known liquid is arrived at, # for the unknown liquid then being determined. Equipment shown in Fig. 5 enables heat conductivity of organic liquids to be measured at temperatures up to 500‹C. and at inert gas pressures of up to 20kg/cm<SP>2</SP>. A silver, stainless steel or precious metal receptacle 14 for the liquid under test is supported within a heating element 16, by a heat insulating block 23 and a rod 24 terminating in a block 25 of magnetic material, able to move up and down a stainless steel tube 26 in accordance with movement of a permanent magnet 27 driven by a mechanism 28. A pipe 29 is connected to a vacuum pump, a pressure gauge or a supply of pressurising inert gas. Temperature probes are disposed at 32. At the instant of measuring, the receptacle 14 is lifted by members 24, 28 until a probe 15 comprising wires 19 protected by a cylinder 21 is immersed in the fluid to be evaluated.