Patent Publication Number: US-10760826-B2

Title: Double acting alpha Stirling refrigerator

Description:
CROSS REFERENCE TO THE RELATED APPLICATIONS 
     This application is the national phase entry of International Application No. PCT/CN2018/083455, filed on Apr. 18, 2018, which is based upon and claims priority to Chinese Patent Application No. 201710347418.3, filed on May 17, 2017, the entire contents of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to refrigerator technology, and in particularly to a double acting alpha Stirling refrigerator. 
     BACKGROUND 
     For a long time, refrigeration has always been achieved by using a refrigerant through a compressor. Stirling refrigerators, which have a wide range of refrigeration temperature and a highest theoretical efficiency, are merely used in some deep cryogenic refrigeration. Specifically, the free piston Stirling refrigerator has high stability, but the actual efficiency is low and the cost is relatively high, thus its popularization is difficult. The alpha Stirling refrigerator has a simple structure and a relatively high efficiency, but has a relatively short service life because the piston thereof is sealed by an oil-free dynamic seal and the working medium gets easily leaked and cause pollution. 
     SUMMARY 
     Technical Problem 
     In view of the above technical problems, the present invention provides a double acting Stirling refrigerator, solving the defects of easy leakage of the working medium and the pollution caused, and the issue of relatively short service life of the traditional alpha Stirling refrigerator. Moreover, single action is turned to be double action, improving mechanical efficiency. 
     Technical Solution 
     The technical solution of the present invention is: 
     A double acting alpha Stirling refrigerator includes a piston cylinder and a piston, the piston is provided in the piston cylinder, upper and lower ends of the piston cylinder are closed, and a cylinder air vent is provided at each closed position of the upper and lower ends of the piston cylinder. The piston is in a clearance fit with an inner wall of the piston cylinder, a closed cavity is formed inside the piston. 
     A pressure relief pipe is provided in the cavity of the piston, and through holes corresponding to outlets of the pressure relief pipe are provided on upper and lower surfaces of the piston, and middle parts of side walls of the piston, respectively. 
     The outlets of the pressure relief pipe are respectively provided in the through holes and matched with each other in size, so that an interior of the pressure relief pipe is connected to an inner cavity of the piston cylinder outside the piston. 
     An air outlet for connecting the cavity of the piston to the inner cavity of the piston cylinder is further provided on the side wall of the piston. A gap-sealed and gas-lubricated piston is used to replace an original structure with the piston and a piston ring. 
     A traction frame capable of moving relative to the piston cylinder is provided outside the piston cylinder, and a movement of the piston is controlled by a movement of the traction frame. 
     One-way air outlet valves and one-way air intake valves are further provided. 
     Specifically, the one-way air outlet valves are provided on an upper part and a lower part of the pressure relief pipes corresponding to the upper and lower surfaces of the piston, so that the air flow can only flow along a middle part of the pressure relief pipe toward upper and lower end faces of the piston and flow into the inner cavity of the piston cylinder. 
     The one-way air intake valves are provided on side walls of the pressure relief pipes outside the one-way air outlet valves or on the upper and lower end faces of the piston, so that the inner cavity of the piston cylinder is connected to the interior of the cavity of the piston. The one-way air intake valves allow gas to enter the cavity of the piston only from the inner cavity of the piston cylinder. 
     A guiding groove is provided on an outer side wall of the piston, and the guiding groove surrounds the piston, and the outlets of the pressure relief pipe on the side wall of the piston are intercommunicated. The guiding groove facilitates the collection of the gas flowing out of the air outlets and allows the gas to flow into the pressure relief pipe. 
     A piston magnet is provided at a bottom of the piston, a traction magnet is provided on the traction frame, the traction magnet is provided corresponding to the piston magnet, and the two magnets move simultaneously by a magnetic force. Except for the magnets, other components are not magnetically conductive. 
     The piston magnet is a disk-shaped strong magnet with a hole in the middle, the traction magnet is a ring-shaped strong magnet; the two magnets have a same thickness. 
     Different magnetic poles of the two magnets are configured oppositely on a same height, so that the piston magnet is stabilized at a center of the traction magnet. Permalloy sheets or silicon steel sheets having a same shape may be added to two poles of the magnet to collect magnetism to obtain a larger force. Magnetism gathering is performed on both ends of the strong magnet with a ferromagnetic material to enhance the force between the magnets, thereby reducing the number of magnets required. 
     A crank-connecting rod mechanism is further included. The above-mentioned traction frame is hinged to one end of a connecting rod of the crank-connecting rod mechanism. 
     Each two groups of piston cylinders and pistons form a set. The air vents at the upper parts of two piston cylinders are connected to each other, the air vents at the lower parts of the two piston cylinders are connected to each other, and a regenerator and a heat exchanger are provided on a pipeline at a connecting position. Traction frames of the two piston cylinders are respectively connected to the same crank-connecting rod mechanism. 
     A maximum pressure intensity difference between the two systems is reduced by appropriately increasing a phase difference, and a volume ratio of a cold cylinder to a hot cylinder is configured to be equal to a ratio of a preset low temperature to a preset high temperature. 
     Operating principle: gas applies work externally through expansion to lower the temperature, and gas is compressed to apply work to increase the temperature. The system expands the gas at low temperatures, and absorbs heat from the environment to be cooled; compresses the gas at high temperatures, and releases heat to the outside environment. 
     The beneficial effects of the invention are: 
     In the present invention, the traditional single acting alpha Stirling refrigerator is turned into a double acting alpha Stirling refrigerator, which improves the mechanical efficiency and makes the working medium remain in a completely internal circulation without causing leakage and pollution. Using the ferromagnetic material to carry out magnetism gathering at both ends of the strong magnet can enhance the force between the magnets, thereby reducing the number of magnets required. Compared with the gas bearing in the free piston Stirling refrigerator, the piston uses a new self-lubricating gas bearing support technology, which can make the air outlets at both ends work at states 1-4 in the embodiments, and the gas film stiffness is stable, so that no friction occurs in the non-stop operation, and the overall structure of machine is simple, stable, efficient and has long service life. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view showing a structure of the present invention; 
         FIG. 2  is a schematic view showing a flow of airflow when a pressure intensity above a piston is high; 
         FIG. 3  is a schematic view showing a flow of airflow when pressure intensities of upper and lower end faces of a piston are both lower than an internal pressure intensity of the piston; 
         FIG. 4  is a schematic view showing a flow of airflow when a pressure intensity below a piston is high; 
         FIG. 5  is a schematic view of an operation of the present invention; 
         FIG. 6  is a process view of an operation state of a refrigeration system; and 
         FIG. 7  is a schematic diagram showing a change of an operating pressure intensity of a system. 
     
    
    
     Where,  1 —piston cylinder,  2 —piston,  3 —one-way air outlet valve,  4 —side wall air outlet,  5 —pressure relief pipe,  6 —piston magnet,  7 —traction magnet,  8 —traction frame,  9 —cylinder air vent,  10 —one-way air intake valve,  11 —guiding groove,  12 —heat exchanger,  13 —regenerator, and  14 —crank-connecting rod mechanism. 
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     The contents of the present invention are described in detail below: 
     The gas flow direction of the gas storage chamber of the piston in each state is as follows: 
     As shown in  FIGS. 1-2 , when the pressure intensity above a piston  2  is higher than the pressure intensity of the cavity of the piston, the gas enters the cavity of the piston from a one-way air intake valve  10  located at an upper part of the piston, and a one-way outlet valve  3  at the upper part is closed. The pressure intensity in the cavity of the piston is relatively high, and the gas coming out from a side wall air outlet  4  in the upper part of the piston  2  can only move downward due to the high pressure intensity of the upper part, and then flows into a pressure relief pipe  5  located at a middle part. At this time, a one-way outlet valve  3  at a lower part is opened, a one-way air intake valve  10  is closed, and the gas flows to a low pressure chamber at the lower part. The gas from the side wall air outlet  4  in the lower portion of the piston  2  flows up and down, on one hand, flows through the pressure relief pipe  5  into the low pressure chamber at the lower part, and on the other hand, flows directly from a gap between the piston  2  and the piston cylinder  1  into the low pressure chamber at the lower part. 
     When the pressure intensities of the upper and lower end faces of the piston  2  are both lower than a pressure intensity inside the piston, the one-way air intake valves  10  are completely closed. Only the one-way air outlet valve  3  at one end of the piston  2  having a lower pressure intensity is opened, and the one-way air outlet valve  3  at the other end is closed. At this time, the gas flows into the inner cavity of the piston cylinder  1  through the gap between the piston  2  and the piston cylinder  1 , and the pressure relief pipe  5 . As shown in  FIG. 3 , the pressure intensity at the upper end of the piston  2  is lower at this time. 
     As shown in  FIG. 4 , when the pressure intensity of a lower part of the piston  2  is higher than the pressure intensity of the cavity of the piston, the gas enters the cavity of the piston from the one-way air intake valve  10  at the lower part. At this time, the one-way air outlet valve  3  at the lower part is closed, and the pressure intensity in the cavity of the piston is relatively high. The gas coming out from the side wall air outlet  4  of the piston  2  can only flow upward due to the high pressure intensity at the lower portion, and then flow to the low pressure chamber at the upper part through the pressure relief pipe  5  at the middle. The gas from the side wall air outlet  4  of the piston  2  at the upper part flows up and down, on one hand, flows through the pressure relief pipe  5  into the low pressure chamber at the upper part, and on the other hand, directly flows from the gap between the piston  2  and the piston cylinder  1  into the low pressure chamber at the upper part. 
     In summary: when the equipment is in operation, the pressure will be changing all the time, the side wall air outlet  4  of the piston  2  will have gas flowing out at states 1-4, and the piston  2  can operate without friction as long as the gas is still discharged. 
     As shown in  FIGS. 5-6 : 
     Operation Process: 
     Each two groups of piston cylinders and pistons form a set of refrigeration system. The air vents at the upper parts of two piston cylinders are connected to each other, the air vents at the lower parts of the two piston cylinders are connected to each other, and a regenerator and a heat exchanger are provided on the pipeline at connecting position. Traction frames of the two piston cylinders are respectively connected to the same crank-connecting rod mechanism. 
     Taking the flywheel clockwise rotation as an example, the upper cavity of the first cylinder and the upper cavity of the second cylinder constitute the system A. The lower cavity of the first cylinder and the lower cavity of the second cylinder constitute the system B. It is defined that the cylinder at the left side is the first cylinder, and the cylinder at the right side is the second cylinder. 
     The piston of the first cylinder at the uppermost part is set as the initial state, from state 1 to state 2, the flywheel rotates 90 degrees clockwise, which is the gas removal process. When passing through the heat exchanger  12 , the gas in the lower cavity of the first cylinder absorbs heat from the system to be cooled; when passing through the regenerator  13 , the cold energy is left in the regenerator  13 ; when passing through the heat exchanger at a high temperature, no heat exchange occurs; and finally the gas enters the lower chamber of the second cylinder. The gas in the upper chamber of the second cylinder passes through the heat exchanger  12 , dissipating the heat in the environment. The gas is cooled to the temperature of the system when passing through the regenerator  13 , and no heat exchange occurs when the gas passes through the heat exchanger  12  at a low temperature. 
     From state 2 to state 3, the flywheel rotates from 90 degree to 180 degrees. System A is subjected to an expansion and cooling process, mainly occurring in the first cylinder, which causes the gas in the upper chamber of the first cylinder to be cooled down and have a temperature lower than the system temperature. System B is subjected to a compression and heating process, mainly occurring in the second cylinder, which causes the temperature of the gas in the lower chamber of the second cylinder to be increased and higher than the temperature of the environment. 
     From state 3 to state 4, the flywheel rotates 180 degree to 270 degrees. It is subjected to the air moving process. When passing through the heat exchanger  12 , the gas in the upper cavity of the first cylinder absorbs heat from the system to be cooled; when passing through the regenerator  13 , the cold energy is left in the regenerator  13 ; when passing through the heat exchanger at a high temperature, no heat exchange occurs, and finally the gas enters the upper chamber of the second cylinder. The gas in the lower chamber of the second cylinder passes through the heat exchanger  12 , dissipating heat in the environment. The gas is cooled to the temperature of the system when passing through the regenerator  13 . No heat exchange occurs when the gas passes through the heat exchanger  12  at a low temperature. 
     From state 4 to state 1, the flywheel rotates from 270 degree to 360 degrees. System A is subjected to a compression and heating process, mainly occurring in the second cylinder, which causes the temperature of the gas in the upper chamber of the second cylinder to be increased and higher than the temperature of the environment. System B is subjected to the expansion and cooling process, mainly occurring in the first cylinder, which causes the gas in the lower chamber of the first cylinder to be cooled down and have a temperature lower than the temperature of the system. 
     In the whole process, the first cylinder is a cold cylinder, which is mainly subjected to expansion. The second cylinder is a hot cylinder, which is mainly subjected to compression. 
       FIG. 7  is a diagram showing the pressure intensity change of the refrigeration system and the piston cavity based on that the volume ratio of the cold cylinder to the hot cylinder is equal to the ratio of the low temperature T to the high temperature T. The piston of the first cylinder at the uppermost part is set as the initial state, P 0  is the pressure intensity change in the cavity of the piston, 
     P 1  is the pressure intensity change in the A system, 
     P 2  is the pressure intensity change in the B system.