Patent GB-625571-A (GB)
Title: Improvements in or relating to heat exchange apparatus
IPC: G05D23/22
Filed: 1946-05-15
Abstract: 625,571. Fluid-pressure servomotor-control systems. TINSLEY (INDUSTRIAL INSTRUMENTS), Ltd., and STEGHART, F. L. May 15, 1946, No. 14703. [Class 135] [Also in Groups XXXV and XXXVIII] A heat-exchange apparatus comprises a circuit for controlling the temperature of the heating medium, thermoelectric devices responsive to temperature change respectively in the heated and the heating medium, and connections for passing current from said devices through said circuit, so that temperature fluctuations of the heating medium effective to vary the control circuit before such fluctuations become effective to alter the temperature of the heated medium substantially. In a system for controlling a milk pasteurising plant, Fig. 2, comprising a heat exchanger 77 with milk supply and discharge pipes 81, 82 and a hot water circuit 75, 76, 78 with a steam make-up pipe 80 controlled by a valve 133, a resistance thermometer 83 is inserted in the pipe 82 and is connected in a Wheatstone bridge 84, and two thermocouples 93, 94, arranged in the pipe 76 in opposition and one of them screened, are connected in series in one bridge-diagonal lead 92 which includes a mirror galvanometer 96 illuminated by a lamp 112. Current variations due to differential heating of the thermocouples are amplified by an amplifier, such as is described in Specification 554,030, [Group XL], including a photo-electric cell 108 exposed to the mirror galvanometer and connected to the grid of a thermionic valve 105, and are imposed on a transformer secondary 102 in circuit with a coil 100. The core 114 of the latter is slidable on the stem 115 of a piston valve 116 and is biassed downwardly by a spring arrangement 134, 140. The valve is urged upwardly by a spring 128 and its stem has a bore 124 the upper opening 126 of which is closable by the core 114. A pump 117 passes oil by a port 120 to the mid-portion of the valve and by a reducing valve 121 and ports 122, 123 above and below the valve. The Figure shows the position with a constant temperature in the milk and heating medium, the opening 126 being partially closed by 'the core so that the pressure above the valve balances the pressure of the spring 128. If over-heating increases the current through the coil 100, the core exposes the opening 126 so that the valve 116 rises. Oil then passes from port 120 through a passage 129 to rotate a vane motor 131 clockwise, so that its shaft 132 closes the steam valve 133. The shaft also rotates a cam 135 which acts, through a stem and dashpot 138, to increase the stress of the spring 134 so as to increase the downward bias on the core 114. Under-heating effects the reverse operation of the motor 131 and valve 133. The thermocouples 93, 94 are designed to give a high E.M.F. for temperature change and the unscreened one has a similar time constant to the resistance thermometer 83. A flow diversion valve operated from the thermocouples may be inserted in the milk pipe 82. In a modification of this arrangement, a single thermocouple is arranged in the milk pipe and is connected across a transformer primary, the secondary of which is connected to an amplifier connected in the main amplifier circuit.