JP7060787B2 - Ice making system and control method of evaporation temperature used for it - Google Patents

Description

The present disclosure relates to an ice making system suitable for producing an ice slurry and a method for controlling the evaporation temperature used therein.

For example, as an ice making system using seawater as a raw material, ice adhering to the inner peripheral surface of the inner pipe of an ice generator cooled by a refrigerant circuit is scraped off with a blade (also called a scraper) and mixed with seawater to form an ice slurry. There is something to manufacture.
According to Patent Document 1, in the above ice making system, the current value of the drive source of the blade mechanism is detected during the ice making operation, and when the current value exceeds a predetermined value, the refrigeration cycle of the evaporation compression type refrigerant circuit is reverse cycled. The method of restoring to steady operation by switching to is described.

Japanese Unexamined Patent Publication No. 2011-85388

In this type of ice making system, the phenomenon in which the ice layer adheres to the inner peripheral surface of the inner tube of the ice generator and an excessive load is applied to each part of the blade mechanism is called "ice lock".
In the method of switching the operation mode based on the current value of the drive source of the blade mechanism as in Patent Document 1, ice lock has already occurred when an increase in the current value is detected. Therefore, each time an ice lock occurs, an excessive load is applied to each part of the blade mechanism, fatigue is accumulated, and the life of the blade mechanism is shortened.

It is an object of the present disclosure to avoid the phenomenon that a load is applied to the blade mechanism at the beginning of ice formation, and to improve the reliability of the ice making system.

(1) The ice making system according to one aspect of the present disclosure controls a refrigerant circuit that performs a steam compression type refrigeration cycle, a circulation circuit of a solution to be cooled by the refrigerant circuit, and an evaporation temperature control of the refrigerant in the refrigerant circuit. It is equipped with a control device to execute.
The circulation circuit includes a solution flow path of an ice generator, a solution tank for storing a solution, and a pump for pumping a solution to the solution flow path, and the refrigerant circuit includes an evaporator of the ice generator and a compressor. , Includes a condenser and an expansion valve.

Further, the control device executes switching control for switching the target evaporation temperature used for the evaporation temperature control to a higher level than in the case of steady operation when the degree of supercooling of the solution in the ice generator is larger than a predetermined threshold value. ..

According to the ice-making system of the present disclosure, since the control device executes the above switching control, when the degree of supercooling of the solution becomes larger than a predetermined threshold value, the target evaporation temperature used for the evaporation temperature control becomes higher than that in the case of steady operation. Set higher.
For this reason, it is possible to perform an operation in which the ice making capacity is reduced in advance, triggered by an increase in the degree of supercooling, which is considered to be a sign of ice lock, and the occurrence of ice lock can be avoided in advance. Therefore, the load on the blade mechanism can be reduced and the reliability of the ice making system can be improved.

(2) In the ice making system of the present disclosure, it is preferable that the control device executes the switching control in the first period from the start of the system to the lapse of a predetermined time.
The reason is that ice making has not yet been performed at the time of system startup, so there is a high possibility that there will be a point at which ice begins to form (time at which the degree of supercooling rises) before a predetermined time elapses from the time of startup. ..

(3) In the ice making system of the present disclosure, it is preferable that the control device executes the switching control in the second period from the detection time of the operation input notifying the additional charging of the solution to the lapse of a predetermined time.
The reason is that when an additional solution is added, the solution that has not yet been ice-made flows through the circulation circuit, so the time when ice begins to form (supercooling degree) from the time of additional addition to the time when a predetermined time elapses. Is likely to exist)

(4) In the ice making system of the present disclosure, the control device stores the relational expression between the solute concentration and the theoretical freezing temperature, and the solution of the solution is based on the theoretical freezing temperature calculated by using the stored relational expression. It is preferable to calculate the degree of supercooling.
By doing so, the degree of supercooling of the solution can be calculated accurately, so that the time point at which the target evaporation temperature is switched can be appropriately determined.

(5) The control method of the present disclosure relates to the evaporation temperature control method executed in the ice making system according to (1) to (4) above.
Therefore, the control method of the present disclosure has the same effect as the ice making system described in (1) to (4) above.

According to the present disclosure, in an ice making system in which a solution is a cooling target, the reliability of the ice making system can be improved.

It is a schematic block diagram of the ice making system which concerns on embodiment of this disclosure. It is a side view which shows the structural example of an ice generator. It is a graph which shows the relationship between the salinity of seawater, the freezing point and the evaporation temperature. It is a flowchart which shows an example of evaporation temperature control based on a salt concentration. It is a graph which shows an example of the temporal change of the blade current, the seawater inlet temperature, and the seawater outlet temperature within a predetermined time including the time of occurrence of ice lock. It is a flowchart which shows an example of the mode switching control based on the degree of supercooling. It is a flowchart which shows an example of mode switching control based on a freezing temperature.

Hereinafter, the details of the embodiments of the present disclosure will be described with reference to the drawings.
[Overall configuration of ice making system]
FIG. 1 is a schematic configuration diagram of an ice making system 50 according to an embodiment of the present disclosure.
The ice making system 50 of the present embodiment is a system in which ice slurries are continuously generated by ice making machines 1U and 1L using seawater stored in the seawater tank 8 as a raw material, and the generated ice slurries are returned to the seawater tank 8.

The ice maker (hereinafter, also referred to as “ice generator”) 1U, 1L of the present embodiment includes, for example, a double-tube ice maker.
In the present embodiment, the reference code "1" is used when a plurality of (two in the figure) ice makers (ice generators) are collectively referred to, and the reference codes "1U" and "1L" are used when distinguishing them. .. The same applies to the case of the "first expansion valve".

An ice slurry is a sherbet-like ice in which fine ice is turbid in water or an aqueous solution. The ice slurry is also called ice slurry, slurry ice, slush ice, or liquid ice.
The ice making system 50 of the present embodiment can continuously generate an ice slurry based on seawater. Therefore, the ice making system 50 of the present embodiment is installed in, for example, a fishing boat or a fishing port, and the ice slurry returned to the seawater tank 8 is used for keeping fresh fish cold.

As shown in FIG. 1, the ice making system 50 circulates seawater, which is a cooling target of the refrigerant circuit 60, between the refrigerant circuit 60 that performs a steam compression type refrigeration cycle, the seawater tank 8, and the ice generators 1U and 1L. A circulation circuit 70 is provided.
The ice making system 50 further includes a control device (controller) 80 that controls the operation of each device included in the ice making system 50, and an input / output device 90 that is communicably connected to the control device 80.

The refrigerant circuit 60 includes a heat exchange section 20 (see FIG. 2) of the ice generator 1, a compressor 2, a heat source side heat exchanger 3, a four-way switching valve 4, a first expansion valve 5, a superheater 6, and a second expansion valve. 11 and a receiver 7 and the like are provided. The refrigerant circuit 60 is configured by piping each of these devices along the route shown in the figure.

The heat exchange unit 20 of the ice generator 1 functions as a heat exchanger on the user side of the refrigerant circuit 60. The compressor 2 includes an inverter compressor whose capacity is variable by inverter control.
The first expansion valve 5 is an expansion valve on the utilization side, and includes an electronic expansion valve whose opening degree can be adjusted according to a control signal. The second expansion valve 11 is an expansion valve on the heat source side, and includes an electronic expansion valve whose opening degree can be adjusted according to a control signal.

The circulation circuit 70 includes a seawater flow path 12A (see FIG. 2) of the ice generator 1, a seawater tank 8, a pump 9, and the like. The circulation circuit 70 is configured by piping each of these devices along the route shown in the figure.

The seawater channel 12A of the ice generator 1 functions as a sherbet-like ice slurry generation section in the circulation circuit 70.
The pump 9 sucks seawater from the seawater tank 8 and pumps the seawater to the seawater flow path 12A of the ice generator 1. The ice slurry generated in the seawater flow path 12A is returned to the seawater tank 8 together with the seawater by the pump pressure.

The circulation circuit 70 of the present embodiment includes a plurality of ice generators 1U and 1L. The seawater channels 12A of the ice generators 1U and 1L are connected in series.
Therefore, the seawater pumped from the pump 9 is ice-made by the ice generator 1L on the lower stage side, then supplied to the ice generator 1U on the upper stage side, and further ice-making is performed by the ice generator 1U on the upper stage side. Is returned to the seawater tank 8.

The first expansion valves 5U, 5L and the superheater 6 of the refrigerant circuit 60 are provided for each ice generator 1U, 1L. In the refrigerant circuit 60 of FIG. 1, the ice generator 1U corresponds to the first expansion valve 5U, and the ice generator 1L corresponds to the first expansion valve 5L.
The superheater 6 is composed of, for example, a double-tube heat exchanger, and a plurality of (two in the example) are provided for each of the ice generators 1U and 1L. The plurality of superheaters 6 corresponding to the ice generators 1U and 1L each include an outer tube and an inner tube.

The discharge-side pipe to which the refrigerant is supplied from the receiver 7 in the ice-making operation includes a discharge-side branch pipe that branches by the number of ice generators 1U and 1L.
The outer pipe of the superheater 6 is connected in series with the discharge side branch pipe. Of the plurality of superheaters 6 arranged in series with respect to the discharge side branch pipe, the outer pipe of the superheater 6 on the downstream side in the refrigerant traveling direction in the ice making operation leads to the first expansion valves 5U and 5L.

The return-side pipe that returns the refrigerant to the compressor 2 in the ice-making operation includes a return-side branch pipe that branches by the number of ice generators 1U and 1L.
The inner pipe of the superheater 6 is connected in series with the return side branch pipe. Of the plurality of superheaters 6 arranged in series with respect to the return-side branch pipe, the inner pipe of the superheater 6 on the upstream side in the refrigerant traveling direction in the ice making operation is the refrigerant outlet 19 of the ice generator 1 (see FIG. 2). ).

[Structure of ice generator]
FIG. 2 is a side view showing a configuration example of the ice generator 1.
As shown in FIG. 2, the ice generator 1 of the present embodiment includes a horizontal double-tube ice maker including an inner tube 12 and an outer tube 13.

The inner tube 12 is made of a metal cylindrical member whose both ends in the axial direction (left-right direction in FIG. 2) are sealed. The internal space of the inner pipe 12 constitutes a seawater flow path 12A through which seawater and ice slurry pass. A blade mechanism 15 is provided in the seawater flow path 12A of the inner pipe 12.
The blade mechanism 15 scrapes the ice particles generated on the inner peripheral surface of the inner tube 12 inward and disperses them inside the inner tube 12. A seawater inflow port 16 is provided on one end side (right end side in FIG. 2) of the inner pipe 12 in the axial direction. A seawater outlet 17 is provided on the other end side (left end side in FIG. 2) of the inner pipe 12 in the axial direction.

The outer tube 13 is made of a metal cylindrical member having a larger diameter and a shorter length than the inner tube 12. The outer pipe 13 covers the outer peripheral surface of the inner pipe 12 in a state of being coaxial with the inner pipe 12. Both ends of the outer tube 13 in the axial direction are sealed to the outer peripheral surface of the inner tube 12 by a donut-shaped sealing wall (not shown).

The annular space having a donut-shaped cross section, which is partitioned by the outer peripheral surface of the inner pipe 12 and the inner peripheral surface of the outer pipe 13, constitutes the refrigerant flow path 13A through which the refrigerant passes. The heat exchange portion 20 of the ice generator 1 is composed of a peripheral wall portion of an inner pipe 12 and an outer pipe 13 constituting the refrigerant flow path 13A.
A plurality of (three in the example) refrigerant inlets 18 are provided in the lower portion of the outer pipe 13. A plurality of (two in the figure) refrigerant outlets 19 are provided on the upper portion of the outer pipe 13.

As shown in FIG. 2, the blade mechanism 15 for scraping ice particles includes a rotating shaft 21, a support bar 22, and a blade 23.
The rotating shaft 21 is housed in the seawater flow path 12A in a state of being coaxial with the inner pipe 12. Both ends in the axial direction of the rotating shaft 21 are rotatably attached to the central portion of the sealing wall 24 that seals both ends in the axial direction of the inner pipe 12.

A motor 25 is connected to one end in the axial direction of the rotating shaft 21 (the left end in FIG. 2). The motor 25 functions as a drive unit that rotates the blade mechanism 15 in a predetermined direction.
The support bar 22 is composed of a rod-shaped member protruding radially outward from the outer peripheral surface of the rotating shaft 21. The support bars 22 are arranged at predetermined intervals in the axial direction of the rotating shaft 21. The blade 23 is fixed to the tip of each support bar 22. The blade 23 is made of, for example, a resin strip member. The front edge of the blade 23 in the rotation direction has a sharp tapered shape.

The ice generator 1 has a scraper assembly (hereinafter, abbreviated as "assembly") composed of a pair of blades 23, 23.
The pair of blades 23, 23 constituting one assembly have the same axial position and are offset by 180 degrees in the rotational direction. A plurality of sets (6 sets in the figure) are provided along the axial direction of the rotating shaft 21.

[Operation mode of ice making system]
The operation mode of the ice making system 50 of the present embodiment includes a normal ice making operation and a defrost operation performed when an abnormality occurs.
In the ice making operation, the four-way switching valve 4 is held in the state of the solid line in FIG. In this case, the high-temperature and high-pressure gas refrigerant discharged by the compressor 2 flows into the heat source-side heat exchanger 3 that functions as a condenser in the ice making operation.

The gas refrigerant flowing into the heat source side heat exchanger 3 exchanges heat with the air blown by the blower fan 10 to condense and liquefy. The refrigerant liquefied in the heat source side heat exchanger 3 flows into the first expansion valves 5U and 5L, respectively, via the second expansion valve 11 (fully open in the ice making operation), the receiver 7, and the outer pipes of the superheater 6.
The liquefied refrigerant is decompressed to a predetermined low pressure by the first expansion valves 5U, 5L, and heat exchange from the inflow port 18 of the ice generator 1 (see FIG. 2) to the ice generators 1U, 1L that function as an evaporator in the ice making operation. It flows into the part 20.

The refrigerant flowing into the heat exchange unit 20 of the ice generator 1 exchanges heat with the seawater pumped to the seawater flow path 12A of the inner pipe 12 by the pump 9 and evaporates. When seawater is cooled by evaporation of the refrigerant, ice particles are generated on the inner surface of the inner pipe 12 and its vicinity.
The generated ice particles are scraped off by the blade mechanism 15 and mixed with seawater inside the seawater flow path 12A to form an ice slurry. The ice slurry flows out from the outlet 17 of the inner pipe 12 and returns to the seawater tank 8. The refrigerant evaporated and vaporized in the heat exchange section 20 of the ice generators 1U and 1L is returned to the compressor 2 via the inner pipe of the superheater 6 and the four-way switching valve 4.

As described above, the circulation circuit 70 has two ice generators 1U and 1L in which the inner pipe 12 is connected in series. Therefore, the processing in the circulation circuit 70 is in the following order.
1) Supply of raw materials from the pump 9 to the lower ice generator 1L 2) Generation of ice slurry in the lower ice generator 1L 3) Ice slurry and seawater from the lower ice generator 1L to the upper ice generator 1U Transfer 4) Generation of ice slurry in the upper ice generator 1U 5) Return of ice slurry and seawater from the upper ice generator 1U to the seawater tank 8

If a phenomenon (ice accumulation) occurs in which ice accumulates in the inner pipe 12 of the ice generator 1 and the flow of seawater deteriorates, the ice making operation cannot be continued. Therefore, a defrost operation is performed to melt the ice accumulated in the seawater flow path 12A.
In the defrost operation, the four-way switching valve 4 is held in the state of the broken line in FIG. In this case, the high-temperature and high-pressure gas refrigerant discharged by the compressor 2 passes through the inner pipes of the four-way switching valve 4 and the superheater 6, and is the heat exchange unit of the ice generators 1U and 1L that function as a condenser in the defrost operation. It flows into 20.

The gas refrigerant flowing into the heat exchange unit 20 exchanges heat with seawater containing ice in the inner pipe 12 to condense and liquefy. As a result, the ice accumulated in the seawater channel 12A is melted. The liquefied refrigerant in the heat exchange unit 20 flows into the second expansion valve 11 via the first expansion valves 5U and 5L (fully open in the defrost operation) and the receiver 7.

The liquefied refrigerant is depressurized to a predetermined low pressure by the second expansion valve 11, and the depressurized refrigerant flows into the heat source side heat exchanger 3 which functions as an evaporator in the defrost operation. The refrigerant flowing into the heat source side heat exchanger 3 exchanges heat with air by the operation of the blower fan 10, vaporizes, and is sucked into the compressor 2.

[Control device configuration]
As shown in FIG. 1, the control device 80 includes a control unit 81 including a CPU and the like, and a storage unit 82 including a volatile memory and the like. The storage unit 82 also includes storage such as an HDD or SSD for storing a computer program.
The control unit 81 realizes various controls related to the operation of the ice making system 50 by executing the computer program read from the storage unit 82.

For example, the control unit 81 of the control device 80 performs switching operations of the four-way switching valve 4, first and first, based on measured values of pressure sensors, temperature sensors, current sensors and the like provided throughout the refrigerant circuit 60. 2 It is possible to perform opening adjustment control of the expansion valves 5 and 11 and capacity control of the compressor 2.
The control unit 81 of the control device 80 can execute the following control as the control to be executed during the ice making operation. In the following description, assuming the case of ice making operation, the "heat exchange unit 20" of the ice generator 1 is referred to as "evaporator 20".

1) Evaporation temperature control (Fig. 4)
This control is a control for adjusting the evaporation temperature of the refrigerant of the evaporator 20 during the ice making operation. In the present embodiment, control is performed to adjust the evaporation temperature of the refrigerant by using a relational expression in which stable ice making operation and desired ice making capacity are compatible even if the salt concentration changes.

2) Mode switching control based on the degree of supercooling (Fig. 6)
This control is a control for setting the control mode of the ice making operation to the reliability priority operation mode when the degree of supercooling of seawater in the ice generators 1U and 1L exceeds a predetermined value.
3) Mode switching control based on seawater temperature (Fig. 7)
This control is a control for returning the control mode of the ice making operation to the steady operation mode when the temperature of the seawater in the ice generators 1U and 1L becomes substantially equivalent to the freezing temperature.

The sensors required for the above three types of control are the following sensors 31 to 35 provided in the ice making system 50.
Suction pressure sensor 31: A pressure sensor attached to the suction pipe of the compressor 2 and measuring the pressure of the refrigerant flowing through the suction pipe. The measured value of the suction pressure sensor 31 is substantially equal to the low pressure of the refrigeration cycle performed in the refrigerant circuit 60.

First concentration sensor 32: A sensor attached to the seawater inlet pipe of the lower ice generator 1L and measuring the salt concentration of the seawater flowing through the inlet pipe.
The measured value of the first concentration sensor 32 is substantially equal to the salinity concentration of the seawater flowing into the ice generator 1L on the lower stage side.

First temperature sensor 33: A sensor attached to the seawater outlet pipe of the ice generator 1L on the lower stage side and measuring the temperature of the seawater flowing through the outlet pipe.
The measured value of the first temperature sensor 33 is substantially equal to the temperature of the seawater containing the ice slurry immediately after ice making by the ice generator 1L on the lower stage side.

Second concentration sensor 34: A sensor attached to the seawater inlet pipe of the ice generator 1U on the upper stage side and measuring the salt concentration of the seawater flowing through the inlet pipe.
The measured value of the second concentration sensor 34 is substantially equal to the salinity concentration of the seawater flowing into the ice generator 1U on the upper stage side.

Second temperature sensor 35: A sensor attached to the seawater outlet pipe of the ice generator 1U on the upper stage side and measuring the temperature of the seawater flowing through the outlet pipe.
The measured value of the second temperature sensor 35 is substantially equal to the temperature of the seawater containing the ice slurry immediately after ice making by the ice generator 1U on the upper stage side.

The storage unit 82 of the control device 80 stores the control information used for each of the above controls. The control information includes the relational expression (Ti = Ai × C) between the salinity C and the theoretical freezing temperature Ti of seawater, and the salinity C and the evaporation temperature T1. A plurality of types of relational expressions with T2 (T1 = A1 × C, T2 = A2 × C) and a threshold value Ths used for determining the degree of supercooling are included.
The above relational expressions and threshold values are recorded in the storage unit 82 when the user performs a predetermined operation input to the input / output device 90 or a user terminal communicably connected to the input / output device 90.

The input / output device 90 includes a user interface capable of communicating with the control device 80. The communication between the control device 80 and the input / output device 90 may be either wired communication or wireless communication.
The input / output device 90 may be a communication device (for example, a remote control, a notebook PC, a tablet PC, a mobile terminal, etc.) separate from the control device 80, or is housed in a single housing together with the control device 80. It may be an operation interface.

The input / output device 90 outputs a touch panel for receiving operation input, an input unit including various input buttons, a display unit such as a display for displaying information received from the control device 80 to the user, and predetermined information thereof by voice. Equipped with a speaker and the like.
The input / output device 90 includes a communication port (for example, a USB port or an RS-232 port) for communicating with a user terminal such as a notebook PC. In this case, if the user terminal is connected to the input / output device 90, communication between the user terminal and the control device 80 becomes possible.

[Specific example of control information]
FIG. 3 is a graph showing the relationship between the salinity of seawater and the freezing point and evaporation temperature.
In FIG. 3, the horizontal axis represents the salinity (% by weight) of seawater, and the vertical axis represents the temperature (° C.).
The straight line L0 in FIG. 3 is a graph representing the theoretical freezing point (° C.) of seawater.

Assuming that the salinity of seawater is C and the theoretical freezing temperature of seawater is Ti, the straight line Li representing the correlation between the two is a linear function of Ti = Ai × C. Ai is a coefficient (slope) representing the degree of freezing point depression of seawater with respect to the salinity C.
The temperature range R0 above the straight line Li indicates the temperature range R1 in which freezing from seawater is impossible. The area below the straight line L0 indicates the temperature range in which freezing from seawater is possible.

The straight line Lm in FIG. 3 is a graph defining the boundary between the temperature range R1 where stable ice making is possible and the temperature range R2 where ice lock may occur.
Assuming that the salt concentration of seawater is C and the evaporation temperature of the refrigerant is Tm, the straight line Lm is defined by a linear function of Tm = Am × C. The straight line Lm is a straight line representing the evaporation temperature Tm for each salinity concentration C when the amount of ice making is maximized. The value of the coefficient Am is determined in advance for each of the ice generators 1U and 1L by a test run or a simulation test.

The function L1 in FIG. 3 represents the relationship between the salinity concentration C and the evaporation temperature T1 used in the “steady operation mode”. The function L1 is defined by the correlation equation of T1 = A1 × C.
In the straight line L1, the coefficient A1 is set to a value larger than the coefficient Am (a value having a small absolute value) in order to avoid ice lock during the ice making operation as much as possible. The value of the coefficient A1 is determined in advance for each of the ice generators 1U and 1L by a test run or a simulation test.

The function L2 in FIG. 3 represents the relationship between the salinity concentration C and the evaporation temperature T2 used in the “reliability priority operation mode”. The function L2 is defined by, for example, a correlation equation of T2 = A2 × C.
In the straight line L2, the coefficient A2 is set to a value larger than the coefficient A1 (a value having a small absolute value) in order to avoid ice lock more reliably and in advance than in the steady operation mode. The value of the coefficient A2 is determined in advance for each of the ice generators 1U and 1L by a test run or a simulation test.

[Evaporation temperature control based on salinity]
FIG. 4 is a flowchart showing an example of evaporation temperature control based on salinity.
The control unit 81 of the control device 80 executes the evaporation temperature control shown in the flowchart of FIG. 4 every predetermined control cycle D1 (for example, 20 to 60 seconds) during the ice making operation.
Further, the control unit 81 of the control device 80 executes the evaporation temperature control shown in the flowchart of FIG. 4 for each of the ice generators 1U and 1L included in the circulation circuit 70.

As shown in FIG. 4, the control unit 81 first executes a process of measuring the salinity C of seawater at the present time (step S10).
The measured value Cd of the salt concentration C of seawater is a measured value by the first and second concentration sensors 32 and 34 of the inlet pipes of the ice generators 1U and 1L.

Next, the control unit 81 calculates the target evaporation temperature Tg from the measured value Cd of the salinity concentration C (step S11). Specifically, when the current control mode is the "steady operation mode", the control unit 81 sets the evaporation temperature T1 calculated by the following equation (1) as the target evaporation temperature Tg. Further, when the current control mode is the "reliability priority operation mode", the control unit 81 sets the evaporator temperature T2 calculated by the following equation (2) as the target evaporation temperature Tg.
Tg: T1 = A1 × Cd …… (1) In the steady operation mode Tg: T2 = A2 × Cd …… (2) In the reliability priority operation mode

Next, the control unit 81 calculates the saturation pressure (hereinafter referred to as “target saturation pressure”) Psg corresponding to the target evaporation temperature Tg, which is determined according to the physical properties of the refrigerant (step S12).
Next, the control unit 81 reads the measured value Pd of the suction pressure sensor 31 (step S13), and determines whether or not the measured value Pd is equal to the target saturation pressure Psg (step S14).

When the determination result in step S14 is positive (Pd = Psg), the control unit 81 maintains the opening degree of the first expansion valves 5U and 5L (step S15).
When the determination result in step S14 is negative (Pd ≠ Psg), the control unit 81 determines whether or not the measured value Pd of the suction pressure sensor 31 is larger than the target saturation pressure Psg (step S16).

If the determination result in step S16 is positive (Pd> Psg), the control unit 81 expands the opening degree of the first expansion valves 5U, 5L by a predetermined amount (step S17).
If the determination result in step S15 is negative (Pd <Psg), the control unit 81 reduces the opening degree of the first expansion valves 5U, 5L by a predetermined amount (step S18).

As described above, in the ice making system 50 of the present embodiment, the control unit 81 applies the measured value Cd of the salt concentration C to the relational expression (T1 = A1 × C, T2 = A2 × C) according to the current control mode. Then, the target evaporation temperature Tg is calculated, and the opening degrees of the first expansion valves 5U and 5L are adjusted so as to be the calculated target evaporation temperature Tg.
Therefore, the evaporation temperature of the evaporator 20 of the ice generators 1U and 1L can be adjusted by the target evaporation temperature Tg that is different for each type of control mode.

[Problems associated with ice lock and their solutions]
FIG. 5 is a graph showing an example of temporal changes in the blade current, the seawater inlet temperature, and the seawater outlet temperature within a predetermined time including the time of occurrence of ice lock. In FIG. 5, the horizontal axis represents time and the vertical axis represents current value or temperature.

In FIG. 5, the “blade current” is the drive current of the motor 25 of the blade mechanism 15. The "seawater inlet temperature" is the seawater temperature of the inlet pipes of the ice generators 1U and 1L. The "seawater outlet temperature" is the seawater temperature of the outlet pipes of the ice generators 1U and 1L.
The "supercooling degree" is a temperature obtained by subtracting the seawater outlet temperature of the ice generators 1U and 1L from the theoretical freezing temperature (broken line in FIG. 5) with respect to the salt concentration of the seawater supplied to the ice generators 1U and 1L.

As shown in FIG. 5, the blade current increases slightly at the beginning of ice formation and rises sharply after approximately 3 minutes in the illustrated example. The occurrence of ice lock can be detected at this rising point.
In Patent Document 1 (hereinafter referred to as "conventional example"), the above-mentioned abnormal increase in the current value is regarded as the occurrence of ice lock, and the refrigeration cycle of the refrigerant circuit is switched to the reverse cycle.

However, as in the conventional example, in the method of taking some countermeasure after the ice lock actually occurs, an excessive load is applied to each part of the blade mechanism 15 every time the ice lock occurs, and fatigue accumulates. The life of the blade mechanism 15 is shortened.
On the other hand, as shown in the graph of the seawater outlet temperature in FIG. 4, the degree of supercooling becomes 0.5 ° C. or higher at the time when ice begins to form approximately 3 minutes before the occurrence of ice lock. Further, the higher the degree of supercooling, the larger the amount of ice generated at once, so that the load on the blade 23 increases sharply.

Therefore, in the present embodiment, an increase in the degree of supercooling is estimated as a sign of ice lock, and when the degree of supercooling exceeds a predetermined threshold, the evaporation temperature of the refrigerant is raised to reduce the ice making capacity (reliability). By switching to the priority operation mode), the occurrence of ice lock can be avoided.
As described above, if the control mode for avoiding the ice lock is executed, the load on the blade mechanism 15 can be reduced and the durability of the blade mechanism 15 can be improved.

By the way, as a structural measure to protect the blade mechanism 15, the elastic force of the spring member (not shown) that presses the blade 23 against the wall surface is weakened (measure 1), and a predetermined number of holes are made in the blade 23 to obtain front-rear pressure. It may be adopted to reduce the difference (measure 2).
However, in Countermeasure 1, the blade 23 floats from the wall surface, and the ice tends to thicken immediately. Therefore, the support bar 22 of the blade 23 may come into direct contact with the ice to apply bending stress, which may cause damage.

Further, in the measure 2, the amount of ice scraped off is reduced because the ice escapes from the hole, which may cause a decrease in the ice making ability.
In this regard, if the ice making operation that avoids the ice lock itself is performed as in the present embodiment, the load applied to the blade mechanism 15 can be reduced without taking the above measures 1 or 2, so that the measures 1 or 2 are taken. You can avoid the drawbacks of adopting it.

[Mode switching control based on supercooling degree]
FIG. 6 is a flowchart showing an example of mode switching control based on the degree of supercooling.
During the ice making operation, the control unit 81 of the control device 80 performs the mode switching control shown in the flowchart of FIG. 6 with a predetermined control cycle D2 (for example, 10 to 30 seconds) shorter than the control cycle D1 of the evaporation temperature control (FIG. 4). ) Every time.
Further, the control unit 81 of the control device 80 executes the mode switching control shown in the flowchart of FIG. 5 for each of the ice generators 1U and 1L included in the circulation circuit 70.

As shown in FIG. 6, the control unit 81 executes the processes after step S21 on condition that the current time is within the predetermined determination period (Yes in step S20). The predetermined determination period includes, for example, the following first and second periods.
1st period: Period from the time when the system is started until a predetermined time (for example, 30 minutes) elapses 2nd period: A predetermined time (for example, 30 minutes) from the time when the operation input for notifying the additional input of seawater (for example, seawater at room temperature) is detected. ) Elapses

The system startup time point in the first period may be, for example, the time when the power-on of all the devices constituting the ice making system 50 is completed.
The reason for using the first period as a condition is that ice making has not yet been performed at the time of system startup, so there may be a point at which ice begins to form (time at which the degree of supercooling rises) before a predetermined time elapses from the time of startup. This is because it has a high sex.

The time of detection of the operation input in the second period may be, for example, the time when the control device 80 receives the operation input of the additional input of seawater performed by the user to the input / output device 90.
The reason for setting the second period as a condition is that when seawater is additionally added, seawater that has not yet been ice-made flows through the circulation circuit 70, so that ice will be generated from the time of additional addition until a predetermined time elapses. This is because there is a high possibility that there will be a point at which it begins to form (a point at which the degree of supercooling rises).

When the current time is within a predetermined determination period, the control unit 81 reads out the current control mode (step S21). In the present embodiment, the default control mode executed by the control unit 81 is assumed to be "steady operation mode". Therefore, the current control mode in step S21 is the "steady operation mode".
As described above, in the steady operation mode, the target evaporation temperature Tg used in the evaporation temperature control (FIG. 4) is calculated by the relational expression of Tg = T1 = A1 × Cd.

Next, the control unit 81 measures the seawater temperature Tw on the outlet side of the ice generators 1U and 1L and the salinity C on the inlet side of the ice generators 1U and 1L (step S22).
The measured value Twd of the seawater temperature Tw is a measured value by the first or second temperature sensors 33 and 35. The measured value Cd of the salinity concentration C of seawater is a measured value by the first or second concentration sensors 32 and 34.

Next, the control unit 81 calculates the theoretical freezing temperature Ti for each concentration (step S23).
Specifically, the control unit 81 uses the theoretical freezing temperature Ti obtained by the calculation formula of Ti = Ai × Cd as the freezing temperature in the ice generators 1U and 1L.
Next, the control unit 81 calculates the supercooling degree SC (step ST24).
Specifically, the control unit 81 uses the temperature obtained by the calculation formula of SC = Ti—Twd as the degree of supercooling in the ice generators 1U and 1L.

Next, the control unit 81 determines whether or not the calculated supercooling degree SC exceeds a predetermined threshold value Ths (for example, 0.5 ° C.) (step S25).
If the determination result in step 25 is positive (SC> Ths), the control unit 81 sets the control mode to the reliability priority operation mode (step S26), and ends the process. As a result, the target evaporation temperature Tg in the evaporation temperature control (FIG. 4) is calculated by the relational expression of Tg = T2 = A2 × Cd.

If the determination result in step 25 is negative (SC ≦ Ths), the control unit 81 ends the process without executing the switching of the control mode in step S26. That is, the current control mode (steady operation mode) is maintained.

As described above, according to the ice making system 50 of the present embodiment, the control unit 81 controls the ice making operation when the degree of supercooling of the seawater on the outlet side of the ice generators 1U and 1L is larger than the predetermined threshold value Ths. Switch to the reliability priority operation mode to avoid the occurrence of ice lock.
Therefore, the load on the blade mechanism 15 can be reduced, and the reliability of the ice making system 50 can be improved.

[Mode switching control based on freezing temperature]
FIG. 7 is a flowchart showing an example of mode switching control based on the freezing temperature.
During the ice making operation, the control unit 81 of the control device 80 performs the mode switching control shown in the flowchart of FIG. 7 with a predetermined control cycle D2 (for example, 10 to 30 seconds) shorter than the control cycle D1 of the evaporation temperature control (FIG. 4). ) Every time.
Further, the control unit 81 of the control device 80 executes the mode switching control shown in the flowchart of FIG. 7 for each of the ice generators 1U and 1L included in the circulation circuit 70.

As shown in FIG. 7, the control unit 81 executes the processes after step S31 on condition that the current control mode is the “reliability priority operation mode” (Yes in step S30).

When the current control mode is the reliability priority operation mode, the control unit 81 measures the seawater temperature Tw on the outlet side of the ice generators 1U and 1L and the salinity C on the inlet side of the ice generators 1U and 1L (step). S31).
The measured value Twd of the seawater temperature Tw is a measured value by the first or second temperature sensors 33 and 35. The measured value Cd of the salinity concentration C of seawater is a measured value by the first or second concentration sensors 32 and 34.

Next, the control unit 81 calculates the theoretical freezing temperature Ti for each concentration (step S32).
Specifically, the control unit 81 uses the theoretical freezing temperature Ti obtained by the calculation formula of Ti = Ai × Cd as the freezing temperature in the ice generators 1U and 1L.
Next, the control unit 81 determines whether or not the measured value Twd of the seawater temperature Tw is equivalent to the calculated freezing temperature Ti (step S33). The term "equivalent" includes the case where the difference between the two temperatures falls within a predetermined error range (for example, ± 0.02 ° C.).

If the determination result in step 33 is positive (Twd≈Ti), the control unit 81 sets the control mode to the steady operation mode (step S34), and ends the process. As a result, the target evaporation temperature Tg in the evaporation temperature control (FIG. 4) is calculated by the relational expression of Tg = T1 = A1 × Cd.

If the determination result in step 33 is negative (Twd ≠ Ti), the control unit 81 ends the process without executing the switching of the control mode in step S34. That is, the current control mode (reliability priority operation conversion mode) is maintained.

As described above, according to the ice making system 50 of the present embodiment, the control unit 81 normally sets the control mode of the ice making operation when the seawater temperature on the outlet side of the ice generators 1U and 1L becomes equal to the freezing temperature Ti. Switch to the steady operation mode of.
Therefore, even if the ice making capacity drops once due to the execution of the reliability priority operation mode, the ice making capacity can be restored by the steady operation mode that is switched after that.

[First modification]
In the above-described embodiment, the correlation between the salinity C of seawater and the evaporation temperatures T1 and T2 of the refrigerant is defined by a predetermined relational expression (T1 = A1 × C, T2 = A2 × C). The relational expression of is not limited to a linear function, but may be a quadratic function or a cubic function. Further, the correlation between the two may be defined in a reference table or in a graph format as shown in FIG.
That is, the storage unit 82 may store the correlation between the salt concentration C and the evaporation temperatures T1 and T2 in any of a relational expression, a table format, and a graph format. The same applies to the formula for calculating the theoretical freezing temperature (Ti = Ai × C).

[Other variants]
The embodiments disclosed this time are exemplary in all respects and are not restrictive. The scope of rights of this disclosure is indicated by the scope of claims and includes all modifications within the meaning and scope equivalent to the scope of claims.

In the above-described embodiment, the ice generator 1 including the "horizontal" double-tube ice maker is exemplified, but the ice generator 1 is a "vertical" or "tilted" double-tube ice maker. You may.
In the above-described embodiment, the ice making system 50 including two ice generators 1 is exemplified, but the number of ice generators 1 may be one or three or more.

In the above-described embodiment, the ice making system 50 in which the cooling target of the refrigerant circuit 60 is “seawater” is exemplified, but the cooling target of the refrigerant circuit 60 is not limited to seawater, but is a “solution” containing seawater. Can be generalized.
When the object to be cooled is generalized to a solution, "seawater" described in the above-described embodiment may be read as "solution". Further, the "salt concentration" of the seawater described in the above-described embodiment may be read as the "solute concentration" of the solution.

1 Double tube ice machine (ice generator)
1U Upper double tube ice maker (ice generator)
Double tube ice machine (ice generator) on the lower side of 1L
2 Compressor 3 Heat source side heat exchanger (condensor)
4 Four-way switching valve 5 First expansion valve 5U Upper stage side first expansion valve 5L Lower stage side first expansion valve 7 Receiver 8 Seawater tank (solution tank)
9 Pump 10 Blower fan 11 Second expansion valve 12A Seawater flow path (solution flow path)
12 Inner pipe 13 Outer pipe 13A Refrigerant flow path 15 Blade mechanism 16 Inflow port (for seawater)
17 Outlet (for seawater)
18 Inflow port (for refrigerant)
19 Outlet (for refrigerant)
20 Heat exchanger (evaporator)
20A Full liquid evaporator 21 Rotating shaft 22 Support bar 23 Blade 24 Sealing wall 25 Motor 31 Suction pressure sensor 32 First concentration sensor 33 First temperature sensor 34 Second concentration sensor 35 Second temperature sensor 50 Ice making system 60 Refrigerator circuit 70 Circulation circuit 80 Control device 81 Control unit 82 Storage unit 90 Input / output device Ths Overcooling degree threshold

Claims (6)

A refrigerant circuit (60) that performs a steam compression type refrigeration cycle, a solution circulation circuit (70) to be cooled by the refrigerant circuit (60), and a refrigerant evaporation temperature control of the refrigerant circuit (60) are executed. An ice making system (50) equipped with a control device (80).
The circulation circuit (70) is
The ice generator (1) includes a solution flow path (12A), a solution tank (8) for storing the solution, and a pump (9) for pumping the solution to the solution flow path (12A).
The refrigerant circuit (60) is
The ice generator (1) includes an evaporator (20), a compressor (2), a condenser (3), and an expansion valve (5).
The solution flow path (12A) is provided with a blade mechanism (15) for scraping ice particles generated on the inner peripheral surface of the solution flow path (12A).
The control device (80) is
It remembers the relational expression between the solute concentration and the theoretical freezing temperature.
The degree of supercooling of the solution was calculated based on the theoretical freezing temperature calculated using the above-mentioned relational expression memorized.
An ice making system (50) that executes switching control for switching the target evaporation temperature used for the evaporation temperature control to a higher value than in the case of steady operation when the calculated degree of supercooling of the solution is larger than a predetermined threshold value (Ths). The control device (80) is
The ice making system (50) according to claim 1, wherein the switching control is executed in the first period from the time when the system is started until the predetermined time elapses. The control device (80) is
The ice making system (50) according to claim 1 or 2, wherein the switching control is executed in the second period from the detection time of the operation input for notifying the additional charging of the solution to the lapse of a predetermined time. A refrigerant circuit (60) that performs a steam compression type refrigeration cycle, a solution circulation circuit (70) to be cooled by the refrigerant circuit (60), and a refrigerant evaporation temperature control of the refrigerant circuit (60) are executed. An ice making system (50) equipped with a control device (80).
The circulation circuit (70) is
The ice generator (1) includes a solution flow path (12A), a solution tank (8) for storing the solution, and a pump (9) for pumping the solution to the solution flow path (12A).
The refrigerant circuit (60) is
The ice generator (1) includes an evaporator (20), a compressor (2), a condenser (3), and an expansion valve (5).
The control device (80) is
It remembers the relational expression between the solute concentration and the theoretical freezing temperature.
Based on the theoretical freezing temperature calculated using the stored relational expression, the degree of supercooling of the solution in the ice generator (1) was calculated.
An ice making system (50) that executes switching control for switching the target evaporation temperature used for the evaporation temperature control to a higher value than in the case of steady operation when the calculated degree of supercooling of the solution is larger than a predetermined threshold value (Ths). It is a method of controlling the evaporation temperature of the evaporator (20) of the ice generator (1) included in the refrigerant circuit (60) that performs a steam compression type refrigeration cycle in which the solution is cooled.
A step of scraping ice particles generated on the inner peripheral surface of the solution flow path (12A) of the ice generator (1) by a blade mechanism (15) provided in the solution flow path (12A).
A step of calculating the degree of supercooling of the solution in the ice generator (1) based on the theoretical freezing temperature calculated by using the relational expression between the solute concentration and the theoretical freezing temperature .
A method for controlling an evaporation temperature, which comprises a step of switching a target evaporation temperature to a higher temperature than in a steady operation when the calculated degree of supercooling is larger than a predetermined threshold value (Ths). It is a method of controlling the evaporation temperature of the evaporator (20) of the ice generator (1) included in the refrigerant circuit (60) that performs a steam compression type refrigeration cycle in which the solution is cooled.
A step of calculating the degree of supercooling of the solution in the ice generator (1) based on the theoretical freezing temperature calculated by using the relational expression between the solute concentration and the theoretical freezing temperature.
A method for controlling an evaporation temperature, which comprises a step of switching a target evaporation temperature to a higher temperature than in a steady operation when the calculated degree of supercooling is larger than a predetermined threshold value (Ths).

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