Liquid heating apparatus

Abstract

A method and apparatus for preventing build-up of deposits on internal surfaces ( 6 ) of a water heater ( 1 ). A heat shock treatment is periodically applied to the surfaces ( 6 ) resulting in differential thermal expansion and/or contraction between the internal surfaces ( 6 ) and deposits ( 7 ) adhering thereto that causes the deposits ( 7 ) to crack and break away from the surfaces ( 6 ). The heat shock treatment may include the step of alternatively heating and cooling the internal surfaces ( 6 ) in any order and may be repeated one or more times. The internal surfaces ( 6 ) may be low friction surfaces to reduce adhesion between the surfaces ( 6 ) and any deposits ( 7 ) that facilitates removal of the deposits ( 7 ) during the heat shock treatment.

1 . A method of removing deposits from internal surfaces of water heating apparatus by applying a heat shock treatment to the internal surfaces.  
   
   
       2 . A method according to  claim 1  wherein the internal surfaces are subject to thermal expansion and/or contraction during the heat shock treatment.  
   
   
       3 . A method according to  claim 2  wherein the internal surfaces are caused to expand by heating and/or contract by cooling whereby the differential rate of expansion and/or contraction between the surfaces and the deposits results in cracking of the deposits.  
   
   
       4 . A method according to  claim 3  wherein cooling the surfaces is effected by flushing the apparatus with cold water.  
   
   
       5 . A method according to  claim 3  wherein heating the surfaces is effected by heating water in the apparatus.  
   
   
       6 . A method according to  claim 3  wherein heating the surfaces is effected by heating the surfaces directly.  
   
   
       7 . A method according to  claim 6  wherein the surfaces are directly heated by resistance heater(s) surrounding or embedded in the surfaces.  
   
   
       8 . A method according to  claim 3  wherein the surfaces are alternately heated and cooled in any order.  
   
   
       9 . A method according to  claim 7  wherein one or both steps of heating and cooling the surfaces is repeated.  
   
   
       10 . A method according to  claim 1  wherein deposits that break away from the internal surfaces are collected and periodically removed.  
   
   
       11 . A method according to  claim 1  wherein the internal surfaces are low friction surfaces.  
   
   
       12 . A method according to  claim 1  wherein the internal surfaces are subjected to a change in temperature during the heat shock treatment producing forces that exceed the forces experienced during normal operation of the apparatus.  
   
   
       13 . A method of operating a water heater comprising the steps of heating water in a tank to an elevated temperature, and periodically applying a heat shock treatment to remove deposits adhering to the internal surfaces by switching the water heater off and flushing the tank with cold water to cause thermal contraction of the internal surfaces, and switching the water heater on after the cold flush to heat water in the tank.  
   
   
       14 . A method according to  claim 13  wherein the water heater is operable to maintain the water at the elevated temperature in a stand-by mode between heat shock treatments.  
   
   
       15 . A method according to  claim 14  wherein the water heater is operable during the stand-by mode to provide a source of hot water at a temperature higher than the elevated temperature.  
   
   
       16 . Apparatus for heating water comprising a tank for holding water to be heated and means for heating water in a tank, wherein the tank has low adhesion internal surfaces by means of which deposits adhering to the internal surfaces can be removed by applying a heat shock treatment to the internal surfaces.  
   
   
       17 . Apparatus according to  claim 16  wherein the tank is made of metal provided with low adhesion internal surfaces by a lining of a material to which deposits adhere less strongly than the metal of the tank.  
   
   
       18 . Apparatus according to  claim 17  wherein the lining is inert to water and capable of withstanding temperature changes occurring during operation of the water heater without degrading to any appreciable extent.  
   
   
       19 . Apparatus according to  claim 18  wherein lining material is polytetrafluoreothylene (PTFE).  
   
   
       20 . Apparatus according to  claim 18  wherein the lining is pre-formed for insertion in the tank.  
   
   
       21 . Apparatus according to  claim 18  wherein the internal surfaces of the tank are coated with material to form the lining.  
   
   
       22 . Apparatus according to  claim 16  wherein the tank has a base wall and side walls upstanding from the base wall of which at least the side walls have low adhesion internal surfaces.  
   
   
       23 . Apparatus according to  claim 22  wherein the side walls are inclined relative to the base wall at an angle of less than 90° so as to converge in a direction away from the base wall.  
   
   
       24 . Apparatus according to  claim 16  wherein the heating means is positioned internally or externally of the tank.  
   
   
       25 . Apparatus according to  claim 24  wherein the heating means comprises at least one electrical heating element positioned within the tank.  
   
   
       26 . Apparatus according to  claim 25  wherein the or each electrical heating element located within the tank is positioned in the upper half of the tank.  
   
   
       27 . Apparatus according to  claim 16  wherein the tank is adapted to enable deposits that have broken away from the internal surfaces to be removed.  
   
   
       28 . Apparatus according to  claim 27  wherein the tank is provided with a removable sump at the bottom that can be detached for disposal of deposits collected therein and the sump re-attached for continued use of the water heater.  
   
   
       29 . Apparatus according to  claim 27  wherein the tank is provided with an openable drain at the bottom through which deposits settling on the bottom of the tank can be flushed.  
   
   
       30 . Apparatus according to  claim 16  wherein the tank has an inlet for connection to a water supply and an outlet from which water can be discharged from the tank.  
   
   
       31 . Apparatus according to  claim 30  wherein the inlet and/or outlet have low adhesion internal surfaces.  
   
   
       32 . A water purifier comprising apparatus according to  claim 16 .  
   
   
       33 . A beverage dispenser including apparatus according to  claim 16 .  
   
   
       34 . A beverage dispenser according to  claim 33  wherein the heating means is operable to maintain the water at an elevated temperature in a stand-by mode of operation.  
   
   
       35 . A method according to  claim 7  wherein the surfaces are alternately heated and cooled in any order.  
   
   
       36 . A method according to  claim 8  wherein one or both steps of heating and cooling the surfaces is repeated.  
   
   
       37 . A method according to  claim 36  wherein deposits that break away from the internal surfaces are collected and periodically removed.  
   
   
       38 . A method according to  claim 10  wherein the internal surfaces are low friction surfaces.  
   
   
       39 . A method according to  claim 11  wherein the internal surfaces are subjected to a change in temperature during the heat shock treatment producing forces that exceed the forces experienced during normal operation of the apparatus.  
   
   
       40 . Apparatus according to  claim 19  wherein the lining is pre-formed for insertion in the tank.  
   
   
       41 . Apparatus according to  claim 19  wherein the internal surfaces of the tank are coated with material to form the lining.  
   
   
       42 . Apparatus according to  claim 21  wherein the tank has a base wall and side walls upstanding from the base wall of which at least the side walls have low adhesion internal surfaces.  
   
   
       43 . Apparatus according to  claim 23  wherein the heating means is positioned internally or externally of the tank.  
   
   
       44 . Apparatus according to  claim 26  wherein the tank is adapted to enable deposits that have broken away from the internal surfaces to be removed.  
   
   
       45 . Apparatus according to  claim 29  wherein the tank has an inlet for connection to a water supply and an outlet from which water can be discharged from the tank.  
   
   
       46 . A water purifier comprising apparatus according to  claim 31 .  
   
   
       47 . A beverage dispenser including apparatus according to  claim 31 .  
   
   
       48 . A beverage dispenser according to  claim 31  wherein the heating means is operable to maintain the water at an elevated temperature in a stand-by mode of operation.