Patent Publication Number: US-2019170407-A1

Title: Magnetic cooling systems

Description:
Embodiments of the present disclosure generally relate to magnetic cooling systems such as magnetocaloric refrigeration systems for cooling. More particularly, embodiments of the present disclosure relate to magnetocaloric refrigeration systems for cooling gas turbine inlet air. 
     BACKGROUND 
     A gas turbine engine combusts a mixture of fuel and air to drive one or more turbine stages. The gas turbine engine generally intakes ambient air into a compressor, which compresses the air to a suitable pressure for optimal combustion of the fuel in a combustor. Unfortunately, the temperature and humidity of the ambient air can vary significantly due to geographic location, seasons, and so forth. A temperature variation of the ambient air may lead to reduced performance of the gas turbine engine. For example, an increase of 50 degrees in temperature may causes more than 25 percent loss of power. 
     One approach for avoiding the power degradation caused by high temperature of the ambient air is cooling the inlet air before compressing it in the compressor. Such inlet air cooling causes the air to have a higher density so as to create a higher mass flow rate into the compressor. The higher mass flow rate of the air in a compressor allows more air to be compressed so as to allow the gas turbine engine to produce more power output. 
     Various refrigeration techniques have been proposed such as vapor compression refrigeration, absorption cooling, and evaporative cooling. Disadvantages of such techniques are high cost and energy consumption, utilization of environmentally hazardous fluids (for example, HCFCs) and unreliability of the cooling capacity due to the dependency upon vagaries of weather. 
     Magnetic refrigeration uses a magnetocaloric material to provide cooling in some refrigeration systems. However, the amount of cooling from conventional magnetic refrigeration systems may not be sufficient for the cooling of inlet air of the gas turbine engines. 
     BRIEF DESCRIPTION 
     An improved magnetic cooling system suitable for cooling of inlet air of gas turbine engines, for example, is disclosed herein. In one aspect, the magnetic cooling system includes at least one magnetic assembly, at least one magnetic regenerator including a magnetocaloric material movably arranged in a closed loop to cyclically pass through the at least one magnetic assembly and a fluid supply device in fluid communication with the at least one magnetic assembly to supply a cooling fluid to the at least one magnetic assembly. 
     In another aspect, a turbine assembly includes a magnetic cooling system disposed in a path of an inlet air to a turbine system. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       These and other features and aspects of embodiments of the present disclosure will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters in each individual figure, represent like parts throughout the drawings, wherein: 
         FIG. 1  is a block diagram of a magnetic cooling system, in accordance with some embodiments of the present disclosure. 
         FIG. 2  is a schematic of a magnetic cooling system, in accordance with some embodiments of the present disclosure. 
         FIG. 3  is a block diagram of a magnetic cooling system, in accordance with some other embodiments of the present disclosure. 
         FIG. 4  is a block diagram of a magnetic cooling system, in accordance with yet some other embodiments of the present disclosure. 
         FIG. 5  is a schematic of a magnetic cooling system, in accordance with some embodiments of the present disclosure. 
         FIG. 6  is a schematic of a turbine assembly including a magnetic cooling system, in accordance with some embodiments of the present disclosure. 
     
    
    
     DESCRIPTION 
     Provided herein are magnetic cooling systems. In particular, embodiments of the present disclosure provide magnetic cooling systems employing magnetocaloric materials. The magnetic cooling systems provides improved cooling, and can be used for various applications such as, for example, cooling inlet air of gas turbines, cooling homes, and cooling offices. 
     In the following specification and the claims, singular forms “a”, “an” and “the” include plural referents unless the context clearly dictates otherwise. As used herein, the term “or” is not meant to be exclusive and refers to at least one of the referenced components being present and includes instances in which a combination of the referenced components may be present, unless the context clearly dictates otherwise. 
     Approximating language, as used herein throughout the specification and claims, may be applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term such as “about” or “substantially” is not limited to the precise value specified. 
     In some embodiments, a magnetic cooling system includes at least one magnetic assembly, at least one magnetic regenerator movably arranged in a closed loop to cyclically pass through the at least one magnetic assembly, and a fluid supply device in fluid communication with the at least one magnetic assembly to supply a cooling fluid. The at least one magnetic regenerator includes a magnetocaloric material. In some embodiments, the at least one magnetic regenerator is arranged on a conveyor that passes through the at least one magnetic assembly and forms the closed loop. The at least one magnetic assembly may include a pair of N pole and S pole magnets or a coil. 
     As used herein, the term “magnetocaloric material” refers to materials that exhibit magnetocaloric effect. In general, the magnetocaloric effect refers to a process of entropic change upon application or withdrawal of an external magnetic field. On application or increase of an external magnetic field, the magnetic moments of a magnetocaloric material become more ordered and cause the magnetocaloric material to generate heat. Conversely, withdrawing or decreasing the external magnetic field allows the magnetic moments of the magnetocaloric material to become more disordered and cause the material to absorb heat. Some magnetocaloric materials exhibit the opposite behavior i.e. generating heat when the magnetic field is removed (which are sometimes referred to as para-magneto caloric materials but both types are referred to collectively herein as magneto caloric materials). The theoretical Carnot cycle efficiency of a refrigeration cycle based on an magnetocaloric material can be significantly higher than for a comparable refrigeration cycle based on a fluid refrigerant. Generally, magnetocaloric materials have pores having high permeability for flow of the heat transfer fluid, and have high capacity to absorb and dissipate heat. Suitable examples of the magnetocaloric materials include, but are not limited to, gadolinium (Gd), manganese iron compound (MnFe), lanthanum iron compounds (LaFe), or a combination thereof. 
     Examples of the cooling fluids include, but are not limited to, water, alcohols, antifreezes such as ethylene glycol, helium gas, or a combination thereof. 
       FIGS. 1 and 2  show a block diagram and a perspective view of a magnetic cooling system  100 , in some embodiments. The magnetic cooling system  100  includes a magnetic assembly  102 , a magnetic regenerator  104  and a fluid supply device  106  in fluid communication with the magnetic assembly  102 . The magnetic cooling system  100  may have a tubular shape having a length “L” ( FIG. 2 ) along an axis  105 . The magnetic cooling system  100  may have a cross-section of any shape such as a circle, square, rectangle or oval. 
     As illustrated, the magnetic assembly  102  is disposed at a portion  108  of the magnetic cooling system  100 . In some embodiments, the magnetic assembly  102  is disposed in a casing  112 . The casing  112  may have an inlet port  114  allowing the magnetic assembly  102  to be in fluid communication with the fluid supply device  106  and an outlet port  116  allowing the magnetic assembly  102  to be in fluid communication with an outside environment. In some embodiments, the fluid supply device  106  is configured to supply a cooling fluid to the magnetic assembly  102 . During operation, the cooling fluid enters to the casing  112  through the inlet port  114 , flows through the magnetic assembly  102  and exits from the outlet port  116 . In some embodiments, the casing  112  may have a plurality of inlet ports  114  and a plurality of outlet ports  116 , as shown in  FIG. 2 . 
     The magnetic regenerator  104  is movably arranged in a closed loop  101  to cyclically pass through the magnetic assembly  102 . In some embodiments, as illustrated in  FIGS. 1 and 2 , the magnetic regenerator  104  is arranged on a conveyor  118  that is configured to move in the closed loop  101  and passes through the magnetic assembly  102 . The conveyor  118  may be a belt, chain, or rope made of metal, plastic or rubber, for example. The conveyor  118  may be arranged at any place along the length L of magnetic cooling system  100 . As illustrated in  FIG. 2 , the conveyor  118  is arranged/located at opposing ends  120 ,  122  of the magnetic cooling system  100  with the magnetic regenerator  104  being held therebetween. 
     The magnetic regenerator  104  may be in form of a plate, a sheet, a foil, a strip or a combination thereof having a length. In some embodiments, as illustrated in  FIG. 2 , the magnetic regenerator  104  is in form of a thin strip (for example, about 1-5 millimeters thick) including the magnetocaloric material, that extends along the length L of the magnetic assembly  102 . The dimensions of the thin strips (for example, width and thickness) may be suitable to desirably limit a resistance and pressure differential on a fluid (to be cooled) that flows across the closed loop and the magnetic cooling system  100 . In addition, the thin strip may provide high surface area to maximize heat transfer between the fluid and the magnetic regenerator  104 . 
     The magnetic regenerator  104  is arranged on the conveyor  118 . The conveyor  118  may be arranged at any location along the length L of the magnetic regenerator  104 . The magnetic regenerator  104  may be mechanically coupled to the conveyor  118 . As illustrated in  FIG. 2 , the magnetic regenerator  104  is arranged on the conveyor  118  such that one end of the magnetic regenerator  104  is coupled to the conveyor  118 . In some embodiments, the magnetic cooling system  100  may include an additional conveyor (not shown in figures) at other end  122  of the magnetic cooling system  100  to support the magnetic regenerator  104  along the length L. 
     Further, the magnetic cooling system  100  is configured to allow a fluid that has to be cooled (the fluid may also be referred to as ‘to-be cooled fluid’) to flow across the closed loop  101  through an inlet and an outlet. In some embodiments, as illustrated in  FIGS. 1 and 2 , the inlet and the outlet are the two sides of the magnetic cooling system  100  opposing to each other i.e., an inlet side  124  and an outlet side  126 . The inlet side  124  and the outlet side  126  provide a path for the to-be cooled fluid to flow across the closed loop  101  in a direction  135  as shown by an arrow in  FIGS. 1 and 2 . The inlet side  124  and the outlet side  126  allow the to-be cooled fluid to enter and exit the magnetic cooling system  100  across the closed loop  101 . In some other embodiments, a housing (not shown in figures) may surround the closed loop  101  and the magnetic assembly  102 . The housing may have an inlet opening and an outlet opening on the inlet side  124  and the outlet side  126 , respectively, to provide a path for the to-be-cooled fluid in the direction  135  through the housing. During operation, the to-be cooled fluid may come in contact to the magnetic regenerator  104  that is arranged to move in the closed loop  101 , while flowing from the inlet side  124  to the outlet side  126 . In some embodiments, a blower (not shown in figures) can be disposed at the inlet side  124  to direct the to-be cooled fluid through the magnetic cooling system  100 . 
     In the magnetic cooling system  100 , during operation, the magnetic regenerator  104  moves cyclically in the closed loop  101  to alternately enter and leave the magnetic field generated by the magnetic assembly  102 . While in the magnetic assembly  102 , the magnetic regenerator  104  becomes cooler. When the to-be cooled fluid flows through the magnetic cooling system  100  across the closed loop  101 , heat transfer occurs between the to-be-cooled fluid and the magnetic regenerator  104 . One complete cycle of the closed loop  101  performed by the magnetic regenerator  104  may be referred to as a cooling cycle. The process of heat transfer in one cooling cycle, in some embodiments, is described below. 
     Referring to  FIG. 1 , a to-be-cooled fluid enters through the inlet side  124  to the magnetic cooling system  100 . The to-be cooled fluid has a temperature higher than the curie temperature (Tcurie) of the magnetocaloric material of the magnetic regenerator  104 . At a point ‘a’ in the closed loop  101 , the magnetic regenerator  104  is at a temperature (T a ) less than the temperature of the to-be cooled fluid. As the to-be cooled fluid comes in contact with the magnetic regenerator  104  at point ‘a’, the heat transfer occurs and the magnetic regenerator  104  takes heat from the to-be cooled fluid. The temperature of the magnetic regenerator  104  increases and the temperature of the to-be cooled fluid decreases. At point ‘b’, the temperature (T b ) of magnetic regenerator is higher than T a  and less than Tcurie (i.e., T b &lt;Tcurie). As the magnetic regenerator  104  moves towards the magnetic assembly  102  (towards point ‘c’), the magnetic regenerator  104  becomes hotter due to magnetization as it enters the magnetic field generated by the magnetic assembly  102 . The temperature of the magnetic regenerator  104  increases and is higher than the Tcurie (Tc&gt;&gt;Tcurie) at point ‘c’. As the magnetic regenerator  104  moves through the magnetic assembly  102 , a cooling fluid supplied by the fluid supply device  106  to the magnetic assembly  102 , takes heat from the magnetic regenerator  104 . The cooling fluid helps to control and reduce the temperature of the magnetic regenerator  104  inside the casing  112  in the magnetic field generated by the magnetic assembly  102 . As the magnetic regenerator  104  leaves the magnetic field, the temperature of the magnetic regenerator  104  drops below Tcurie at point ‘d’ (T d &lt;Tcurie). The cooled magnetic regenerator  104  comes in contact with the to-be-cooled fluid) again at location “e” as the fluid exits from the outlet side  126 . The heat transfer occurs, and the magnetic regenerator  104  takes heat from the to-be cooled fluid flowing in the direction  135 . Due to the heat transfer, the to-be cooled fluid exiting the magnetic cooling system  100  has lower temperature as compared to the temperature of the to-be cooled fluid before contacting the magnetic regenerator  104  (or after contacting the magnetic regenerator first time near the opening at the inlet side  124 ). The temperature of the magnetic regenerator  104  increases after the interaction of the magnetic regenerator  104  and the to-be cooled fluid at point e′. The temperature of the magnetic regenerator at a point ‘f’ is higher than the temperature at point ‘d.’ and less than the curie temperature T d &lt;T f &lt;Tcurie. The magnetic regenerator  104  moves in the closed loop  101 , and reaches the point ‘a’ to complete one cooling cycle. As the magnetic regenerator moves from point ‘f’ to ‘a’, the temperature of the magnetic regenerator  104  is less the temperature of the to-be cooled fluid entering the magnetic cooling system  100 . In some embodiments, the magnetic regenerator  104  repeats this cooling cycle multiple times to continue reducing the temperature of the to-be cooled fluid supplied to the magnetic cooling system  100  and providing a cooled fluid for continuous cooling. 
     In some embodiments, a magnetic cooling system may include a plurality of magnetic assemblies, a plurality of magnetic regenerators or a combination thereof. The level of cooling may depend on the number of cooling cycles encountered by a fluid to be cooled (i.e., to-be cooled fluid), the number of magnetic assemblies, the number of magnetic regenerators, and their combinations arranged in a closed loop of a magnetic cooling system as described above. The number of cooling cycles may further depend, in part, on the number of magnetic regenerators arranged to move in the closed loop, the speed of a conveyor and/or the speed of the to-be-cooled fluid flow. The number of magnetic assemblies, the number of magnetic regenerators or both and the movement of the magnetic regenerators may depend on the desired temperature for the end use application. As an example, for cooling a to-be cooled fluid to a temperature in a range from 15 degrees Celsius to about 22 degrees Celsius such as for home or office cooling, the magnetic cooling system may include one magnetic assembly and a few magnetic regenerators depending on the magnetocaloric material(s) used. In another example, cooling to a much lower temperature for example, lower than 10 degrees Celsius, a plurality of magnetic regenerators and a plurality of magnetic assemblies may be required. 
     In embodiments where a magnetic cooling system includes a plurality of magnetic assemblies, a plurality of magnetic regenerators or a combination thereof, the plurality of magnetic assemblies may be disposed substantially apart.  FIG. 3  illustrates a block diagram of a magnetic cooling system  200  that includes a pair of magnetic assemblies: a first magnetic assembly  102  and a second magnetic assembly  103  disposed substantially opposite to each other in the closed loop  101 . The first and second magnetic assemblies ( 102 ,  103 ) are individually disposed in separate casings  112 . In these embodiments, the fluid supply device  106  is configured to supply the cooling fluid to the first magnetic assembly  102  and the second magnetic assembly  103  during operation. In some embodiments, an additional fluid supply device may be used for supplying the cooling fluid to the second magnetic assembly  103 . The magnetic regenerator  104  is movably arranged in the closed loop  101  to cyclically pass through both the first magnetic assembly  102  and the second magnetic assembly  103 . 
     In the magnetic cooling system  200  of  FIG. 3 , as the magnetic regenerator  104  moves towards the second magnetic assembly  103  after crossing the point ‘e’ (i.e., from e to g), the magnetic regenerator  104  becomes hotter due to magnetization as it enters the magnetic field generated by the second magnetic assembly  103 . As the magnetic regenerator  104  passes through the second magnetic assembly  103 , the heat is transferred to the cooling fluid supplied by the fluid supply device (for example,  106 ) to the second magnetic assembly  103 . As the magnetic regenerator  104  leaves the magnetic field, the temperature of the magnetic regenerator  104  drops below Tcurie at point “h” (T h &lt;Tcurie). The temperature T h  is lower than the temperature of the to-be cooled fluid that enters the magnetic cooling system  200  at point ‘a’. The cooled magnetic regenerator  104  comes in contact with the to-be cooled fluid again at location “a” near the inlet side  124 , and completes one cooling cycle. The heat transfer occurs, and the magnetic regenerator  104  takes heat from the to-be cooled fluid flowing in the direction  135 . The magnetic regenerator  104  becomes hotter i.e., the temperature of the magnetic regenerator  104  at point ‘b’ is again higher than that of point ‘a’ (T b &gt;T a ). In some embodiments, the magnetic regenerator  104  moves in the closed loop  101  multiple time to carry out multiple cooling cycle to cool the to-be cooled fluid that is continuously supplied to the magnetic cooling system  200 . 
       FIG. 4  illustrates a block diagram of a magnetic cooling system  300  including a pair of magnetic assemblies ( 102 ,  103 ) and a plurality of magnetic regenerators  104 .  FIG. 5  shows a schematic of the magnetic cooling system  300 . Each magnetic regenerator of the plurality of magnetic regenerators  104  is moveably arranged on the conveyor  118 . The magnetic regenerators of the plurality of magnetic regenerators  104  are arranged separately from each other with gaps between adjacent magnetic regenerators. Each magnetic regenerator  104  takes heat from the to-be cooled fluid as it comes in contact with while moving successively in the closed loop  101 . The continuous and successive interaction of the plurality of magnetic regenerators  104  with the to-be cooled fluid flowing in the direction  135 , enables continuous heat transfer from the to-be cooled fluid to the plurality of magnetic regenerators  104 . 
     One embodiment is directed to a turbine assembly that includes a magnetic cooling system (as described hereinabove) for cooling inlet air provided to a turbine system for example, a gas turbine system. The turbine assembly includes the magnetic cooling system disposed in a path of an inlet air to the turbine system.  FIG. 6  illustrates a turbine assembly  400  that includes a magnetic cooling system  410  disposed at an inlet  402  that supplies an inlet air to a turbine system  420 . The inlet air is supplied to an inlet of the magnetic cooling system  410  (similar to the inlet side  124  of the magnetic cooling system  300  as shown in  FIGS. 4 and 5 ) to flow across the closed loop  101  and exit from an outlet of the magnetic cooling system  410  (similar to the outlet side  126  of the magnetic cooling system  300  as shown in  FIGS. 4 and 5 ). The magnetic cooling system  410  may include a plurality of magnetic assemblies and a plurality of magnetic regenerators similar to as described in embodiments shown in  FIGS. 4 and 5 . As illustrated, the magnetic cooling system  410  reduces the temperature of the inlet air prior to entering to the turbine system  420  to provide the cooled inlet air to the turbine system  420 . In some embodiments, the temperature of the cooled inlet air is in a range from about 5 degrees Celsius to about 15 degrees Celsius. 
     The magnetic cooling systems, as disclosed in above embodiments, are advantageously capable of reducing the temperature to a desirable level with some alterations in the configuration. The configuration of the magnetic cooling systems may be tailored by varying the number and size of magnetic regenerators and magnetic assemblies to achieve a desired level of cooling. These magnetic cooling systems are suitable for use in the gas turbine systems for cooling the inlet air (for example, to a temperature up to 5 degrees Celsius) and providing high performance. In a gas turbine system, these magnetic cooling systems provide many advantages over conventional refrigeration or cooling techniques. Unlike, the conventional vapor compression refrigeration, the magnetic cooling system uses no refrigerants that may have environmental concerns and no compressor that may cause large parasitic losses. Further, unlike evaporation cooling techniques, the lowest temperature provided is not limited. In addition, the magnetic cooling systems are compact and have smaller footprint as compared to conventional refrigeration techniques. Their designs also provide cheaper and simpler integration with a gas turbine systems. 
     While only certain features of the disclosure have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the disclosure.