Method of coating a part of a heat exchanger and heat exchanger

Abstract

A method of coating an internal surface of an assembled heat exchanger is provided. The heat exchanger comprising a first passage for a first heat exchange fluid, and a second passage for a second heat exchange fluid. The first and second passages are separated by at least one heat transfer element. The heat transfer element has a first surface facing the first passage. The method comprises; pre-treating the first surface by circulating at least one pre-treatment liquid through the first passage of the heat exchanger and a pre-treatment liquid storage separate from the heat exchanger, and electroless nickel plating the first surface by circulating a solution comprising nickel ions through the first passage of the heat exchanger and a solution container separate from the heat exchanger. A heat exchanger comprising a nickel plating is also disclosed.

1 . A method of coating an internal surface of a heat exchanger, the heat exchanger comprising a first passage for a first heat exchange fluid, and a second passage for a second heat exchange fluid, the first and second passages being separated by at least one heat transfer element, the heat transfer element having a first surface facing the first passage and a second surface facing the second passage, wherein the method comprises;
 pre-treating the first surface by circulating at least one pre-treatment liquid through the first passage of the heat exchanger and a pre-treatment liquid storage separate from the heat exchanger, and   electroless nickel plating the first surface by circulating a solution comprising nickel ions through the first passage of the heat exchanger and a solution container separate from the heat exchanger, wherein the circulating of the at least one pre-treatment liquid and the circulating of the solution is effected by at least one pump forming part of a conduit system that is configured to convey the at least one pre-treatment liquid respectively the solution to the heat exchanger.   
     
     
         2 . The method according to  claim 1 , wherein the pre-treating comprises;
 circulating one of a pre-treatment liquid in the form of water, a solvent, an acid, or a liquid comprising solid particles through the first passage.   
     
     
         3 . The method according to  claim 1 , wherein the pre-treating comprises;
 circulating water through the first passage and a water container, or by directing water from a water source through the first passage, and   cleaning the first surface by circulating a solvent, or a liquid which comprises solid particles, through the first passage and through a container for the solvent, or through a container for the liquid which contains solid particles.   
     
     
         4 . The method according to  claim 1 , wherein pre-treating comprises;
 a surface activating step for activating the first surface before the electroless nickel plating by circulating an activating liquid through the first passage and a container for the activating liquid.   
     
     
         5 . The method according to  claim 1 , wherein circulating the pre-treatment liquid and circulating the solution is performed by one or more pumps forming part of a conduit system, the conduit system further comprising a releasable connection to the heat exchanger, the pre-treatment liquid storage, the solution container, and a valve arrangement for directing either the pre-treatment liquid, or the solution, through the pump and the heat exchanger. 
     
     
         6 . The method according to  claim 1 , wherein the solution is an aqueous solution comprising nickel ions, a chemical reducing agent, and a catalyst. 
     
     
         7 . The method according to  claim 1 , wherein the method comprises heating the solution in the solution container by means of a heating element. 
     
     
         8 . The method according to  claim 1 , wherein the method comprises heating the pre-treatment liquid in the pre-treatment liquid storage by means of a heating element. 
     
     
         9 . The method according to  claim 1 , wherein the method comprises stirring the solution in the solution container by means of a stirring element. 
     
     
         10 . The method according to  claim 1 , wherein the method comprises stirring the pre-treatment liquid in the pre-treatment liquid storage by means of a stirring element. 
     
     
         11 . The method according to  claim 1 , wherein the method comprises;
 removing any nickel plating layer present on the first surface by circulating a removing liquid through the first passage of the heat exchanger and a container for the removing liquid, before the pre-treating is performed.   
     
     
         12 . The method according to  claim 1 , wherein the heat exchanger comprises at least two permanently joined heat transfer elements, the first and second passages being separated by at least a first heat transfer element of the at least two permanently joined heat transfer elements. 
     
     
         13 . The method according to  claim 1 , wherein the heat exchanger is a spiral heat exchanger and the at least one heat transfer element comprises a first spiral shaped sheet metal piece extending in a spiral in a first plane, the first plane extending perpendicularly to the first spiral shaped sheet metal piece. 
     
     
         14 . The method according to  claim 13 , wherein circulating the pre-treatment liquid comprises the pre-treatment liquid flowing through the first passage at least partially in a main direction and circulating the solution comprises the solution flowing through the first passage at least partially in the main direction, the main direction extending substantially perpendicularly to the first plane. 
     
     
         15 . The method according to  claim 14 , wherein the first passage is closed by means of at least one closing portion at one side of the first spiral shaped sheet metal piece, in a plane substantially parallel to the first plane, and wherein the closing portion is provided with a number of openings, which openings are flowed through by the pre-treatment liquid during circulating the pre-treatment liquid and which openings are flowed through by the solution during circulating the solution. 
     
     
         16 . The method according to  claim 15 , wherein the method comprises sealing the openings after coating the internal surface. 
     
     
         17 . The method according to  claim 14 , wherein the method comprises arranging the spiral heat exchanger with the first plane extending in a substantially horizontal direction and the main direction extending in a substantially vertical direction during circulating the pre-treatment liquid and during circulating the solution. 
     
     
         18 . The method according to  claim 13 , wherein the method comprises circulating the pre-treatment liquid and circulating the solution through the first passage having a width of between 5-40 mm. 
     
     
         19 . The method according to  claim 13 , wherein the first spiral shaped sheet metal piece has a thickness of between 2-6 mm. 
     
     
         20 . The method according to  claim 13 , wherein the heat exchanger comprises a second heat transfer element ( 4 ,  24 ) comprising a second spiral shaped sheet metal piece extending in a spiral in the first plane substantially concentrically with the first spiral shaped sheet metal piece and wherein studs extend in the first passage between the first and second spiral shaped sheet metal pieces the studs being arranged at a density of 280-780 studs per square metre. 
     
     
         21 . The method according to  claim 13 , wherein the method provides a Nickel/Boron coating or a Nickel/Diamond coating. 
     
     
         22 . A heat exchanger comprising a first passage for a first heat exchange fluid, and a second passage for a second heat exchange fluid, the first and second passages being separated by at least one heat transfer element, the heat transfer element having a first surface facing the first passage, the first surface having a nickel plating applied in accordance with the method according to  claim 1 . 
     
     
         23 . The heat exchanger according to  claim 13 , wherein the heat transfer element is welded to a further heat transfer element having a first surface facing the first passage, at least part of the first passage being formed between the heat transfer element and the further heat transfer element. 
     
     
         24 . The heat exchanger according to  claim 13 , wherein the heat transfer element is brazed to a further heat transfer element having a first surface facing the first passage, at least part of the first passage being formed between the heat transfer element and the further heat transfer element. 
     
     
         25 . The heat exchanger according to  claim 22 , wherein the heat exchanger is a spiral heat exchanger and the at least one heat transfer element comprises a first spiral shaped sheet metal piece extending in a spiral in a first plane, the first plane extending perpendicularly to the first spiral shaped sheet metal piece, and wherein the first passage is closed by means of at least one closing portion at one side of the first spiral shaped sheet metal piece, in a plane substantially parallel to the first plane, and wherein the closing portion is provided with a number of openings, which openings are sealed.