Instant water heater with PTC plastic conductive electrodes

Abstract

An instant water heater utilizing positive temperature coefficient plastic electrically conductive material structures for electrodes. The heating of the water is not generated by the electrodes, but instead by the resistance of the water to the electrical current flowing between them. The material of the electrodes undergoes a phase change at certain temperatures when whereby it converts from electrically conductive to electrically non-conductive at a predetermined temperature. The output temperature of the water is determined by a combination of the area of the electrodes that confront one another, the water's conductivity, the flow rate of the water and the current limiting capability of the conductive electrode materials positive temperature coefficient, which reduces or stops the heating of the water when the intended water temperature is achieved.

1 . An electrode for an instant water heater, said electrode being intended for submersion in water to be joule heated for conducting electricity for heating water disposed and in contact between itself and a confronting similar electrode, said electrode comprising: a polymer which at a lower temperature is conductive of electricity, and which inherently has a positive temperature coefficient, whereby said electrode loses at least some of its electrical conductivity and becomes non-conductive or nearly non-conductive at and above a temperature at which said polymer undergoes a phase change from crystalline to amorphous, whereby to reduce or substantially prevent passage of electrical current through it at and above said phase change temperature, thereby to prevent heating of water in which it is submerged to a higher temperature, and to remain in said crystalline phase at lower temperatures, and 
 a conductive package of carbonaceous material distributed throughout said polymer to provide enhanced electrical conductivity at temperatures below said phase change temperature and less enhanced at temperatures above said temperature, said conductive package comprising carbonaceous material in a plurality of particle sizes, whereby more intimately to pack the carbonaceous material into the polymer to facilitate molding of the electrode by injection molding.    
   
   
       2 . An electrode according to claim w in which said polymer and carbonaceous material are being substantially devoid of contaminant material so that the concentration of contaminant in the electrode is sufficiently low that seeds of insoluble salts formed from the water are unlikely to be formed on the surface of the electrode.  
   
   
       3 . An electrode according to  claim 1  in which said carbonaceous material comprises two or more of the following: natural graphite, synthetic graphite, purified graphite, expandable graphite, expanded graphite, graphite flake and graphite fiber, and carbon as carbon black, purified carbon, carbon fiber, carbon fibrils, and carbon nano tuber, thereby to reduce the bulk electrical resistance of the electrode, provide suitable conductivity for the electrode, and to provide for enhanced connectivity with the water.  
   
   
       4 . An electrode for an instant water heater, said electrode being intended for submersion in water to be joule heated for conducting electricity for heating water disposed and in contact between itself and a confronting similar electrode, said electrode comprising: a polymer which at a lower temperature is conductive of electricity, and which inherently has a positive temperature coefficient, whereby said electrode loses at least some of its electrical conductivity and becomes non-conductive to nearly non-conductive at and above a temperature at which said polymer undergoes a phase change from crystalline to amorphous, whereby to reduce or substantially prevent passage of electrical current through it at and above said phase change temperature, thereby to prevent heating of water in which it is submerged to a higher temperature, and to remain in said crystalline phase at lower temperatures; 
 a conductive package of particles of carbonaceous material distributed throughout said polymer to provide enhanced electrical conductivity at temperatures below said phase change temperature and less enhanced at temperatures above said temperature;    said polymer and said carbonaceous material being substantially devoid of contaminant material so that the concentration of contaminant in the electrode is sufficiently low that seeds of insoluble salts formed from the water are unlikely to be formed on the surface of the electrode.    
   
   
       5 . An electrode according to  claim 2  in which contaminant material is contained in said electrode in total amount no greater than about 100 parts per million of the electrode.  
   
   
       6 . An electrode according to  claim 5  in which said contaminant material is contained in said electrodes in total amount no greater than between about 10 ppm and 100 ppm.  
   
   
       7 . An electrode according to  claim 4  in which contaminants to be excluded are among the following: ions of calcium, iron, aluminum and silicone, and silicates and carbonates, especially calcium carbonates.  
   
   
       8 . In combination: a pair of electrodes according to  claim 4 , spaced apart from one another in a chamber adapted to submerge them and apply an electrical potential between them to heat the water by joule heating.