Heat exchanger temperature change rate control

Abstract

A closure bar adapted for use in a heat exchanger core includes a center void region configured to be partially filled with a phase-changing material and sealed, thereby containing the phase-changing material. The phase-changing material is configured to change phase in a forward direction as the flow of hot fluid over the closure bar begins, thereby slowing a rate of a temperature increase by absorbing a latent heat as the phase-changing material changes phase in the forward direction, and change phase in a reverse direction as the flow of hot fluid over the closure bar ceases, thereby slowing a rate of a temperature decrease by liberating the latent heat as the phase-changing material changes phase in the reverse direction. A method of producing and using the closure bar is also disclosed.

1 . A closure bar adapted for use in a heat exchanger core, the closure bar comprising a center void region configured to be partially filled with a phase-changing material and sealed, thereby containing the phase-changing material. 
     
     
         2 . The closure bar of  claim 1 , wherein:
 the center void region defines a center void region volume;   the center void region is filled with the phase-changing material; and   the phase-changing material fills between 20-95% of the center void region volume at an ambient temperature, thereby defining a residual void volume.   
     
     
         3 . The closure bar of  claim 2 , wherein the residual void volume contains a vacuum. 
     
     
         4 . The closure bar of  claim 2 , wherein the residual void volume is filled with a gas that includes argon, helium, nitrogen, air, or mixtures thereof. 
     
     
         5 . The closure bar of  claim 2 , wherein:
 the closure bar is configured to be subjected to a flow of a hot fluid having a hot fluid operating temperature;   the phase-changing material has a boiling point that is between an initial temperature and the hot fluid operating temperature; and   the phase-changing material is configured to:
 boil as the flow of hot fluid over the closure bar begins, thereby slowing a rate of temperature increase by absorbing a latent heat of vaporization as the phase-changing material boils; and 
 condense as the flow of hot fluid over the closure bar ceases, thereby slowing a rate of temperature decrease by liberating the latent heat of vaporization as the phase-changing material condenses. 
   
     
     
         6 . The closure bar of  claim 2 , wherein:
 the closure bar is configured to be subjected to a flow of a hot fluid having a hot fluid operating temperature;   the phase-changing material has a melting point that is between an initial temperature and the hot fluid operating temperature; and   the phase-changing material is configured to:
 melt as the flow of hot fluid over the closure bar begins, thereby slowing a rate of temperature increase by absorbing a latent heat of fusion as the phase-changing material melts; and 
 solidify as the flow of hot fluid over the closure bar ceases, thereby slowing a rate of temperature decrease by liberating the latent heat of fusion as the phase-changing material solidifies. 
   
     
     
         7 . The heat exchanger core of  claim 6 , wherein the phase-changing material is selected from the group consisting of: sodium, potassium, cesium, lithium, and salts thereof. 
     
     
         8 . The heat exchanger core of  claim 6 , wherein:
 the phase-changing material additionally has a boiling point that is between the melting point and the hot fluid operating temperature; and   the phase-changing material is configured to:
 boil as the flow of hot fluid over the closure bar continues, thereby further slowing the rate of temperature increase by absorbing a latent heat of vaporization as the phase-changing material boils; and 
 condense as the flow of hot fluid over the closure bar ceases, thereby further slowing the rate of temperature decrease by liberating the latent heat of vaporization as the phase-changing material condenses. 
   
     
     
         9 . The closure bar of  claim 1 , wherein the phase-changing material is selected from the group consisting of water, acetone, methanol, titanium tetrachloride, and mixtures thereof. 
     
     
         10 . The closure bar of  claim 1 , comprising one or more materials selected from the group consisting of nickel, aluminum, titanium, copper, iron, cobalt, and alloys thereof. 
     
     
         11 . The closure bar of  claim 1 , wherein each center void region is configured to be sealed by a method selected from the group consisting of: brazing, welding, sealing with an interference-fitted plug, and sealing with a threaded fitting. 
     
     
         12 . The closure bar of  claim 1 , wherein:
 the center void region defines an interior surface; and   the interior surface is coated with a material that is configured to prevent the phase-changing material from reacting with the first cold closure bars.   
     
     
         13 . A heat exchanger core comprising:
 a bottom end sheet;   a plurality of alternately stacked individual hot and cold layers, the cold layers defining a hot layer inlet region and a hot layer outlet region; and   a top end sheet;   wherein:
 each individual hot layer includes:
 a hot fin element forming a plurality of parallel open-ended hot channels adapted to pass a fluid therethrough; 
 a parting sheet separating each individual hot layer from the adjacent individual cold layer; and 
 two hot closure bars positioned on opposite sides of the fin element, parallel to the open-ended hot channels and extending the length of the open-ended hot channels; 
 
 each individual cold layer includes:
 a cold fin element forming a plurality of parallel open-ended cold channels adapted to pass a fluid therethrough; 
 a parting sheet separating each individual cold layer from the adjacent individual hot layer; 
 a first cold closure bar, positioned on a first side of the cold fin element proximate the hot layer inlet region, parallel to the open-ended cold channels and extending the length of the open-ended cold channels; and 
 a second cold closure bar, positioned on a second side of the cold fin element proximate to the hot layer outlet region and opposite the first cold closure bar, parallel to the open-ended cold channels and extending the length of the open-ended cold channels; 
 wherein the second cold closure bar is the closure bar of  claim 1 . 
 
   
     
     
         14 . The heat exchanger core of  claim 13 , wherein:
 each individual hot layer comprises two hot closure bars, each defining a hot closure height between 0.64-25 mm (0.025-1 inch); and   each individual cold layer comprises two cold closure bars, each defining a cold closure height between 0.64-25 mm (0.025-1 inch).   
     
     
         15 . The heat exchanger core of  claim 13 , wherein the heat exchanger core is manufactured by one or more processes selected from the group consisting of: additive manufacturing, hybrid additive manufacturing, subtractive manufacturing, and hybrid additive subtractive manufacturing. 
     
     
         16 . A method of producing a closure bar adapted for use in a heat exchanger core, the method comprising:
 forming a closure bar, the closure bar defining a center void region;   partially filling the center void region with a phase-changing material; and   sealing the closure bar, thereby containing the phase-changing material within the center void region.   
     
     
         17 . The method of  claim 16 , wherein:
 the center void region is configured to be sealed by a method selected from the group consisting of: brazing, welding, sealing with an interference-fitted plug, and sealing with a threaded fitting; and   the closure bar comprises one or more materials selected from the group consisting of nickel, aluminum, titanium, copper, iron, cobalt, and alloys thereof.   
     
     
         18 . The method of  claim 16 , wherein:
 the closure bar is configured to be subjected to a flow of a hot fluid having a hot fluid operating temperature;   the phase-changing material has at least one phase-changing point that is between an initial temperature and the hot fluid operating temperature;
 wherein the at least one phase-changing point is selected from the group consisting of: melting and boiling; 
   the phase-changing material is configured to:
 change phase in a forward direction as the flow of hot fluid over the closure bar begins, thereby slowing a rate of temperature increase by absorbing a latent heat as the phase-changing material changes phase in the forward direction; and 
 change phase in a reverse direction as the flow of hot fluid over the closure bar ceases, thereby slowing a rate of temperature decrease by liberating the latent heat as the phase-changing material changes phase in the reverse direction; 
 wherein the forward-reverse directions are selected from the group consisting of: boiling-condensing and melting-solidifying. 
   
     
     
         19 . A method of operating a heat exchanger core to reduce a rate of change of temperature in at least one portion thereof, wherein the heat exchanger core includes a closure bar having a center void region partially filled with a phase-changing material and sealed, the phase-changing material has at least one phase-changing point that is between an initial temperature and a hot fluid operating temperature, and the closure bar is disposed in a region of the heat exchanger core that is configured to receive a hot fluid having a hot fluid operating temperature, the method comprising:
 initiating a flow of the hot fluid to the heat exchanger core;   slowing a rate of temperature increase by absorbing a latent heat as the phase-changing material changes phase in a forward direction;   ceasing the flow of the hot fluid to the heat exchanger core; and   slowing a rate of temperature decrease by liberating a latent heat as the phase-changing material changes phase in a reverse direction;   wherein:
 the phase-changing material has at least one phase-changing point that is between an initial temperature and the hot fluid operating temperature;
 wherein the at least one phase-changing point is selected from the group consisting of: melting and boiling; 
 
 the phase-changing material is configured to:
 change phase in the forward direction as the flow of hot fluid over the closure bar begins, thereby slowing a rate of temperature increase by absorbing a latent heat as the phase-changing material changes phase in the forward direction; and 
 change phase in the reverse direction as the flow of hot fluid over the closure bar ceases, thereby slowing a rate of temperature decrease by liberating the latent heat as the phase-changing material changes phase in the reverse direction; and 
 
 the forward-reverse directions are selected from the group consisting of:
 boiling-condensing and melting-solidifying. 
 
   
     
     
         20 . The method of  claim 19 , wherein:
 the center void region is configured to be sealed by a method selected from the group consisting of: brazing, welding, sealing with an interference-fitted plug, and sealing with a threaded fitting; and   the closure bar comprises one or more materials selected from the group consisting of nickel, aluminum, titanium, copper, iron, cobalt, and alloys thereof.