Segmented rapid heating of fluid

Abstract

A fluid heating apparatus has a fluid flow path from an inlet to an outlet, with multiple heating sections positioned along the flow path. Each heating section is at least one pair of electrodes between which an electric current is passed through the fluid to resistively heat the fluid during its passage along the flow path. At least one of the heating sections has a segmented electrode made up of a plurality of electrically separable segments. This allows an effective active area of the segmented electrode to be controlled by selectively activating the segments. A controller determines a required voltage and current to be delivered to the fluid by each heating section, and allows for input conductivity as well as variations in fluid conductivity with temperature. The controller activates selected segments of the segmented electrode to effect delivery of desired current and voltage by the segmented electrode to the fluid.

1 . A method for heating fluid, the method comprising:
 passing the fluid along a flow path from an inlet to an outlet, the flow path comprising at least first and second heating sections positioned along the flow path such that fluid passing the first heating section subsequently passes the second heating section, each heating section comprising at least one pair of electrodes between which an electric current is passed through the fluid to resistively heat the fluid during its passage along the flow path, and wherein at least one of said heating sections comprises at least one segmented electrode, the segmented electrode comprising a plurality of electrically separable segments allowing an effective active area of the segmented electrode to be controlled by selectively activating the segments such that upon application of a voltage to the activated electrode segment(s), current drawn will depend upon the effective active area;   measuring fluid conductivity at the inlet;   determining from measured fluid conductivity a required voltage and current to be delivered to the fluid by the first heating section to raise the fluid temperature by a first desired amount;   determining an altered fluid conductivity resulting from operation of the first heating section;   determining from the altered fluid conductivity a required voltage and current to be delivered to the fluid by the second heating section to raise the fluid temperature by a second desired amount; and   activating segments of the segmented electrode in a manner to effect delivery of desired current and voltage by the segmented electrode.   
     
     
         2 . The method of  claim 1 , wherein variations in fluid conductivity are substantially continually accommodated in response to measurements of incoming fluid conductivity. 
     
     
         3 . The method of  claim 1  wherein fluid conductivity is determined by reference to the current drawn upon application of a voltage across one or more electrodes of one or more heating sections. 
     
     
         4 . The method of  claim 1  further comprising using the measured conductivity value to initially select an established, commensurate combination of electrode segments before allowing the system to operate in order to prevent variations in fluid conductivity from causing the peak current to exceed a rated value. 
     
     
         5 . The method of  claim 1  further comprising deactivating the electrodes if the measured fluid conductivity falls outside a predetermined range of acceptable fluid conductivity. 
     
     
         6 . The method of  claim 1  further comprising measuring a fluid flow rate to assist in determination of appropriate current, voltage and electrode segment activation under varying fluid flow rates. 
     
     
         7 . The method off  claim 1  further comprising measuring fluid temperature at the outlet to permit feedback control of the fluid heating. 
     
     
         8 . The method of  claim 1  further comprising measuring the temperature of the fluid between the first and second heating sections and controlling power to the first and second heating sections in accordance with the measured temperatures and a desired fluid temperature increase in each respective heating section. 
     
     
         9 . The method of  claim 1  wherein the fluid flow path comprises three or more heating sections, each section having an inlet and an outlet, the sections being connected in series, the method further comprising the control means initially selecting electrode segments in accordance with the measured incoming water conductivity and controlling power to an electrode pair of each section in accordance with measured inlet and outlet temperatures of each section and a predetermined desired temperature difference for each section. 
     
     
         10 . An apparatus for heating fluid, the apparatus comprising:
 a fluid flow path from an inlet to an outlet;   at least first and second heating sections positioned along the flow path such that fluid passing the first heating section subsequently passes the second heating section, each heating section comprising at least one pair of electrodes between which an electric current is passed through the fluid to resistively heat the fluid during its passage along the flow path, and wherein at least one of said heating sections comprises at least one segmented electrode, the segmented electrode comprising a plurality of electrically separable segments allowing an effective active area of the segmented electrode to be controlled by selectively activating the segments such that upon application of a voltage to the segmented electrode current drawn will depend upon the effective active area;   a conductivity sensor for measuring fluid conductivity at the inlet; and   a controller for determining from measured fluid conductivity a required voltage and current to be delivered to the fluid by the first heating section to raise the fluid temperature by a first desired amount, for determining an altered fluid conductivity resulting from operation of the first heating section, for determining from the altered fluid conductivity a required voltage and current to be delivered to the fluid by the second heating section to raise the fluid temperature by a second desired amount, and for activating segments of the segmented electrode in a manner to effect delivery of desired current and voltage by the segmented electrode.   
     
     
         11 . The apparatus of  claim 10 , wherein each heating section comprises a segmented electrode. 
     
     
         12 . The apparatus of  claim 10  wherein each segmented electrode is divided into segments of varying size, to permit combinations of segments to be selected to provide an increased accuracy of selection of desired effective area. 
     
     
         13 . The apparatus of  claim 12  wherein the segmented electrode is divided into n segments having relative effective areas in a ratio of 1:2: . . . :2 (n-1) . 
     
     
         14 . The apparatus of  claim 10 , wherein each electrode segment of the segmented electrode extends substantially perpendicularly to a direction of fluid flow, so as to subject fluid across substantially the entire fluid flow path to resistive heating. 
     
     
         15 . The apparatus of  claim 10  further comprising flow rate measuring means for measuring a fluid flow rate to assist in determination of appropriate current, voltage and electrode segment activation under varying fluid flow rates. 
     
     
         16 . The apparatus of  claim 10  further comprising outlet fluid temperature measuring means for measuring fluid temperature at the outlet to permit feedback control of the fluid heating. 
     
     
         17 . The apparatus of  claim 10  further comprising fluid temperature measuring means for measuring the temperature of the fluid between the first and second heating sections and controlling power to the first and second heating sections in accordance with the measured temperatures and a desired fluid temperature increase in each respective heating section. 
     
     
         18 . The apparatus of  claim 10  wherein the fluid flow path comprises three or more heating sections, each section having an inlet and an outlet, the sections being connected in series.