KR20230020112A - Method for improving effectiveness of mobile cooling unit using ice thermal energy storage based on direct contact technology - Google Patents

Abstract

The present invention relates to a method for improving cooling efficiency, which is able to load ice on a mobile cooling unit detachably arranged on a transport apparatus performing cold chain distribution by optimizing the shape and weight of the ice, be environmentally friendly, minimize the generation of noise, and achieve the temperature conditions generally required for the cold chain distribution process. According to the present invention, the method is low-priced and environmentally friendly since water, which is not hazardous and is stable, is a refrigerant. In addition, the method uses a mobile cooling unit detachable from a transport apparatus, and does not use a vapor compression cooling system driven by a conventional diesel engine, so that no greenhouse gas is emitted and the generation of noise can be reduced. Furthermore, the method is able to optimize the shape and weight of individual ice cubes, so that the generally required temperature conditions for the cold chain distribution process (under 8℃) can be efficiently achieved.

Description

Method for increasing the cooling efficiency of a mobile cooling unit using an ice storage tank based on direct contact technology

The present invention relates to a method for increasing cooling efficiency using a mobile cooling unit, and more specifically, by optimizing the shape and weight of ice and loading it into a transport device that performs cold chain distribution and a mobile cooling unit that is detachably disposed, thereby providing an eco-friendly and It relates to a method of increasing cooling efficiency capable of achieving temperature conditions generally required in a cold chain distribution process while minimizing noise generation.

Keeping fresh food in a refrigerated state when it is distributed is called the cold chain. As the demand for high-quality food increases, the demand for cooling trucks for cold chain systems is rapidly increasing worldwide. In addition, fresh food e-commerce logistics have further increased this demand. Conventional refrigerated trucks typically use a vapor compression refrigeration system powered by a relatively expensive and noisy diesel engine. These diesel engines emit greenhouse gases and are only 35-40% efficient. Therefore, in order to replace the existing cooling system, several studies using cold thermal energy storage (CTES) have been conducted.

Cold thermal energy storage can reduce equipment capacity and operating costs because it transfers the cooling load from on-peak periods to off-peak periods, and thus can be used in a variety of applications, especially in buildings. It is widely used in coordination. In the conventional studies, since the cooling energy storage tank is fixedly installed in the cooling vehicle, there is a disadvantage in that cold thermal energy can be supplied only when the truck is connected to the cooling device. Therefore, a new cooling system that can store cooling energy in an energy storage tank throughout the day and deliver the stored cooling energy directly to a cooling truck as needed appropriately utilizes the benefits of a cold heat energy storage tank, and is a cold chain for fresh food. In this case, it will be possible to replace the cooling system using the existing diesel engine.

Among cold thermal energy storage tanks, ice thermal energy storage (ITES) uses water as an energy storage medium, so it has the characteristics of showing a high heat of fusion (334 kJ/kg) and can be considered inexpensive, environmentally friendly, non-toxic, and chemically stable. can In addition, the melting/freezing point of water (0 °C) meets the general temperature requirements (below 8 °C) for cold chain distribution of fresh food. However, cold energy storage tanks, including ice thermal storage tanks, have low thermal conductivity due to storage media (usually phase change The heat transfer efficiency between the phase change material (PCM) and the heat-transfer fluid (HTF) is poor.

In this context, the heat transfer rate of thermal energy storage devices has been studied extensively and it has been shown that it can be improved with fins, encapsulation and direct contact technologies. Although the direct contact technology increases the heat transfer efficiency, much research is required before it is applied to the actual field.

Accordingly, it is necessary to develop an efficient cold chain system for the distribution of fresh foods by developing a cooling system that optimizes heat transfer efficiency by developing direct contact technology.

Accordingly, the present inventors have tried to devise a method capable of increasing the cooling efficiency of a cooling system using a direct contact method of ice.

As a result, the cooling efficiency of the cooling system is improved by optimizing various conditions such as the speed of inflow of internal air using the fan in the cooling unit of the cooling system, the shape of ice loaded in the cooling unit, the mass of individual ice, and the total amount of ice. It was confirmed that it can be maximized.

Accordingly, an object of the present invention is to provide a method for increasing cooling efficiency.

The present invention relates to a method for increasing cooling efficiency using a mobile cooling unit, and more specifically, by optimizing the shape and weight of ice and loading it into a transport device that performs cold chain distribution and a mobile cooling unit that is detachably disposed, thereby providing an eco-friendly and It relates to a method of increasing cooling efficiency capable of achieving temperature conditions generally required in a cold chain distribution process while minimizing noise generation.

Hereinafter, the present invention will be described in more detail.

One example of the present invention relates to a method for increasing cooling efficiency comprising the following steps:

A mobile cooling unit preparation step of determining a total weight of refrigerant to be loaded into a cooling unit of the mobile cooling unit, considering a cooling holding time in the transport device for performing cold chain distribution, a cooling target temperature, and a loading amount of the transport device;

a suction step of inhaling air at a constant speed through a transfer unit disposed on one side of the mobile cooling unit by using an air intake unit of the mobile cooling unit;

a cooling step of bringing air into contact with the refrigerant loaded in the cooling unit; and

A discharge step of moving the air in contact with the refrigerant through the discharge unit.

In the present invention, the mobile cooling unit preparation step is to determine the total weight of the refrigerant to be loaded in the cooling unit in consideration of the cooling holding time in the transport device for cold chain distribution, the cooling target temperature, and the loading amount of the transport device. can

In the present invention, the transportation device for performing cold chain distribution may refer to a device for transporting an object requiring refrigerated storage during distribution, and may mean, for example, a transportation device such as a truck, but is limited thereto it is not going to be

In the present invention, the object may mean fresh food, but is not particularly limited thereto, and may mean vegetables, vegetables, grains, other processed foods, etc., as long as they are intended to maintain freshness for cold chain distribution.

In the present invention, the cooling holding time is the time during which the transport device performs cold chain distribution, for example, the time the transport device moves from the first point to the second point, or the first point through the second point. It may mean the total time to move to 3 points, but is not limited thereto.

In one embodiment of the present invention, a branch may mean a distribution center, but is not particularly limited thereto, and may mean any place, structure, system, or the like that requires cold chain distribution.

In the present invention, the cooling target temperature may mean an appropriate temperature required for storage of an object or the like in a transport device.

In the present invention, the total weight of the refrigerant to be loaded in the cooling unit may be determined in consideration of the maximum loading amount of the transport device and the amount of objects to be loaded in the transport device.

In the present invention, the movable cooling unit includes an air intake unit for sucking ambient air by driving a fan; a cooling unit communicating with the air intake unit so that the intake air is movable; and a discharge unit communicating with the cooling unit so as to discharge the air moved through the cooling unit, but is not limited thereto.

In one embodiment of the present invention, the air suction unit may include a fan to suck air.

In one embodiment of the present invention, the movable cooling unit may be one in which an air intake unit equipped with a fan sucks air inside the transport device, transfers it to a cooling unit, and then cools the sucked air in the cooling unit. In addition, the sucked and cooled air can be discharged through the discharge part communicating with the cooling part, and as a result, the temperature of the air inside the transport device can be lowered.

In one embodiment of the present invention, the air intake unit may further include a temperature sensor on one side.

In one embodiment of the present invention, the movable cooling unit may generate temperature information by measuring the temperature of the internal air when the transport device sucks in the internal air through a temperature sensor provided on one side of the air intake unit.

In one embodiment of the present invention, the movable cooling unit may generate control information for controlling the fan of the air intake unit by using the temperature information generated by the temperature sensor, and the temperature sensor may transmit the generated control information from the controller. can be sent

In one embodiment of the present invention, the air intake unit may further include a controller unit for adjusting the operating speed of the fan.

In one embodiment of the present invention, the movable cooling unit may control the operating speed of the fan provided on one side of the air intake unit by receiving control information from the controller unit.

In the present invention, the cooling unit may include a refrigerant, but is not limited thereto.

In the present invention, the refrigerant may be a phase change material (PCM), and at least one selected from the group consisting of a solid-gas phase change material, a solid-liquid phase change material, and a solid-solid phase change material. It may be, for example, a solid-liquid phase change material, but is not limited thereto.

In one embodiment of the present invention, the solid-liquid phase change material may be ice.

In the present invention, the shape of the solid phase refrigerant may be a hexahedron, but is not limited thereto.

In one embodiment of the present invention, the solid phase refrigerant may have a width of 23.3 mm, a length of 21.7 mm and a height of 20.6 mm.

In the present invention, the solid refrigerant may be one side of which is depressed inward to form a space having a shape of any one of trapezoidal, square and triangular, for example, a space having a trapezoidal shape may be formed, but is limited thereto It is not.

In the present invention, the solid phase individual weight of the refrigerant is 6.0 to 10.0 g, 6.0 to 9.0 g, 6.0 to 8.0 g, 6.0 to 7.0 g, 6.4 to 10.0 g, 6.4 to 9.0 g, 6.4 to 8.0 g, 6.4 to 7.0 g, It may be 6.8 to 10.0 g, 6.8 to 9.0 g, 6.8 to 8.0 g, or 6.8 to 7.0 g, for example, 6.8 to 7.0 g, but is not limited thereto.

In the present invention, the shape of the solid refrigerant, the shape of a space formed by one side being recessed, and the individual weight of the refrigerant may be determined in consideration of power consumption required for preparing the refrigerant in the solid phase.

In the present invention, the total weight of the solid refrigerant is 2.00 to 12.00 kg, 2.00 to 11.00 kg, 3.00 to 12.00 kg, 3.00 to 11.00 kg, 4.00 to 12.00 kg, 4.00 to 11.00 kg, 5.00 to 12.00 kg, 5.00 to 11.00 kg, It may be 6.00 to 12.00 kg, 6.00 to 11.00 kg, 7.00 to 12.00 kg, 7.00 to 11.00 kg, 8.00 to 12.00 kg, or 8.00 to 11.00 kg, for example, it may be 8.00 to 11.00 kg, but is not limited thereto. Instead, it may be determined in consideration of the maximum loading amount of the transport device and the amount of objects to be loaded on the transport device.

In the present invention, the intake step may be to use the air intake unit of the mobile cooling unit to intake air in the transportation device for performing the cold chain distribution at a constant speed.

In the present invention, the speed at which the air intake unit sucks air is 0.43 to 2.00 m/s, 0.43 to 1.90 m/s, 0.43 to 1.80 m/s, 0.43 to 1.70 m/s, 0.60 to 2.00 m/s, and 0.60 to 1.80 m/s. 1.90 m/s, 0.60 to 1.80 m/s, 0.60 to 1.70 m/s, 0.85 to 2.00 m/s, 0.85 to 1.90 m/s, 0.85 to 1.80 m/s, 0.85 to 1.70 m/s, 1.00 to 2.00 m/s, 1.00 to 1.90 m/s, 1.00 to 1.80 m/s, 1.00 to 1.70 m/s, 1.28 to 2.00 m/s, 1.28 to 1.90 m/s, 1.28 to 1.80 m/s or 1.28 to 1.70 m / s, for example, 1.28 to 1.70 m / s, but is not limited thereto.

In the present invention, the movable cooling unit may additionally include a temperature sensor on one side of the air intake, but is not limited thereto.

In the present invention, the intake step may further include a temperature measurement step of generating temperature information by measuring the temperature of the air sucked by the air intake unit.

In one embodiment of the present invention, the step of measuring the temperature may be to measure the temperature of the air in the transportation device that the mobile cooling unit takes in using a temperature sensor to generate temperature information.

In one embodiment of the present invention, the temperature measurement step may further include a history management step of generating temperature history data using the measured air temperature information and time information.

In one embodiment of the present invention, the temperature history data may include object information and state information of the object.

In one embodiment of the present invention, the history management step may further include a server transmission step of transmitting the generated temperature history data to a history management server.

In the present invention, the history management server may mean a private or state-certified server that manages the cold chain distribution process, and specifically, by sharing the temperature history data of the object with the distribution center or retail store, the distribution center or retail store can refer to the object on the cold chain. It may mean a server that can check the distribution history of, but is not limited thereto.

In one embodiment of the present invention, the temperature measurement step may further include an air intake rate control step.

In one embodiment of the present invention, the step of controlling the air intake speed may be that the temperature sensor transmits control information to the controller to control the speed at which the air intake unit sucks in air.

In the present invention, the movable cooling unit may additionally include a humidity sensor on one side of the air intake unit, but is not limited thereto.

In the present invention, the cooling step may be contacting the air whose temperature is measured with the refrigerant loaded in the cooling unit.

In the present invention, the speed at which the temperature-measured air contacts the refrigerant may be the same as the speed at which the air suction unit sucks air.

In the present invention, the cooling step may further include a water discharge step of discharging water generated from the refrigerant after contacting air with the refrigerant.

In the present invention, the discharging step may be to move air in contact with the refrigerant through the discharge unit.

In the present invention, the movable cooling unit may be detachably connected to the transportation device.

In the present invention, the mobile cooling unit can be detached from the transport device to charge the cooling unit with the refrigerant, and after charging the cooling unit with the refrigerant, it is mounted on the transport device to cool the air in the transport device. can (discharging)

The present invention relates to a method for increasing cooling efficiency using a mobile cooling unit. The method of the present invention is inexpensive and environmentally friendly by using water, which is a non-toxic and stable material, as a refrigerant.

In addition, by using a removable cooling unit that can be detached from the transportation device, a vapor compression cooling system driven by a conventional diesel engine is not used, so greenhouse gases are not emitted, noise generation can be reduced, and convenience can be increased.

Furthermore, by optimizing the shape and weight of individual ice cubes, the temperature conditions normally required for cold chain distribution processes (below 8 °C) can be efficiently achieved.

1 is a schematic diagram showing an ice-making unit (IMU) for charging and a mobile cooling unit (MCU) for discharging according to the present invention.
2 is a schematic diagram showing a cross-section of the shape of a space formed in an ice cube according to the mass of an individual ice cube.
3 shows evaporation, condensation and refrigerant temperatures (ac) at the evaporator outlet in the IMU for 7,200 seconds according to an experimental example of the present invention, and power consumption (df) in each case.
Figure 4 shows the duration per cycle of ice-making and defrosting, the ratio of defrosting time to the total, average power consumption, and the average coefficient of performance due to the change in mass of ice cubes during a cycle of up to about 13,500 seconds according to an experimental example of the present invention. it's a graph
5 is an operating time (t) of the MCU according to an experimental example of the present invention and an ice-free surface air speed (V _{f, woi} ) under the condition of 0.43 to 1.28 m / s, the ice surface air speed (face It is a graph showing changes in air velocity, V _f,wi ), air temperature gradient (ΔT _air ) and cooling capacity (Q _c ) at the inlet and outlet of the cooling unit. The temperature gradient means a temperature difference between the temperature of the air sucked in by the fan and the temperature of the cooled air discharged through the discharge part.
6 is an air velocity (V _f,wi ), an air temperature gradient (ΔT _air ) at the inlet and outlet of the cooling unit, and cooling according to an operating time (t) according to an experimental example of the present invention. In the change in capacity (Q _c ), it is a graph showing the change according to the amount of ice (2.00 to 6.00 kg, m _ice,am ).
7 shows, according to an experimental example of the present invention, when the ice-free surface air velocity (V _f,woi ) is 0.43 to 1.70 m/s, the amount of ice (m ice,am ) of 2.00 to 6.00 kg and the air velocity (m _ice,am ) of 6.8 to 6.8 kg It is a graph showing the changing average cooling capacity (Q _c,avg ) under the condition of 10.0 g of ice cube mass (m _ice,cb ).
8 is 6.00 according to an experimental example of the present invention, under the condition that the ice-free surface air velocity (V _f,woi ) is 0.85 or 1.70 m/s and the air temperature (T _air,in ) is 10 to 30 °C. or 10.00 kg of ice (m _ice,am ), 6.8 to 10.0 g of ice cube mass (m _ice,cb ) is a graph showing the average cooling capacity (Q _c,avg ).
9 shows the mass of ice cubes of 6.8 g or 10.0 g, the ice-free surface air velocity of 0.85 m/s or 1.70 m/s, and the target average cooling capacity (Q It is a graph showing the relationship between total COP (COP _tot ) and power consumption (R _w,mcu , which means total fan power consumption), which varies according to _c,abg,tg ).

Hereinafter, the present invention will be described in more detail through the drawings. These examples are only for explaining the present invention in more detail, and it will be apparent to those skilled in the art that the scope of the present invention is not limited by these examples according to the gist of the present invention. .

1 is a schematic diagram showing an ice-making unit (IMU) for charging and a mobile cooling unit (MCU) for discharging.

Referring to FIG. 1, the heat transfer rate in the cold chain truck is improved by direct contact discharging using an ice making energy storage (ITES) in the cold chain truck, and the cooling energy is stored throughout the day. You can see the mobile cooling system that allows you to store

The mobile cooling system may include an ice-making unit (IMU) for charging and a mobile cooling unit (MCU) for discharge.

The ice making unit prepares ice with cooling energy stored in a distribution center, and at this time, the ice may be produced in a cube shape so as to perform heat exchange directly with air without encapsulation. In the filling process, direct type can be selected to make ice directly on the evaporator surface of the ice making unit. In the case of a truck entering a distribution center, the mobile cooling unit may be guided to an ice storage tank for filling the ice (charging process) and to the truck's refrigerated space for space cooling. (discharging process, discharging)

Referring to FIG. 1, a laboratory-scale test facility was built to verify the efficiency of a mobile cooling system composed of a mobile ice-making unit for filling and a mobile cooling unit for discharge.

Commercial ice-making equipment tested included a reciprocating compressor, condenser (CON), capillary tube for expansion device, evaporator (EVA) and solenoid valve (SV). has been used

Here, the reciprocating compressor used R-134a refrigerant, the displacement of the reciprocating compressor was 8.8 cm ³ /rev, and the power consumption was 1/3 HP. The condenser was a fin-tube heat exchanger with a depth of 45 mm, a height of 150 mm and a width of 420 mm, and the evaporator was a cross-flow type heat exchanger with a depth of 18 mm, a height of 117 mm and a width of 207 mm. The length of the capillary was 1,113 mm.

As can be seen in the ice making unit of FIG. 1 , the refrigerant discharged from the compressor flows into the condenser, discharges heat, is condensed, and enters the evaporator through the capillary tube. The refrigerant evaporates in the evaporator and flows back into the compressor. In addition, the water supplied to the ice making unit was continuously recirculated to the surface of the evaporator using a water pump. At sub-zero temperatures, water begins to freeze on the surface of the evaporator, and over time the ice thickens. After a period of time, the solenoid valve diverts the hot refrigerant from the compressor to the evaporator, which transfers heat to remove ice from the evaporator surface.

Next, the mobile cooling unit may include a fan and insulated ducts with a cooling section. Ice was moved from the ice making unit to the cooling zone of the mobile cooling unit. The air discharged from the fan can be cooled across the ice layer deposited in the cooling section.

Here, the cooling zone may have a square cross section with one side of 0.2 m.

Table 1 shows the detailed conditions of the test to confirm the efficiency of the mobile cooling system.

Parameters Values Amount of ice (kg) 2.00, 4.00, 6.00, 10.00 Mass of an ice cube (g) 6.8, 8.4, 10.0 Face air velocity without ice in the cooling zone (m/s) 0.43, 0.85, 1.28, 1.70 Air temperature at the cooling zone inlet (℃) 10, 20, 30 Relative humidity at the cooling zone inlet (%) 50 Ambient air temperature (℃) 27

As can be seen in Table 1, each ice cube mass was prepared from 6.8 to 10.0 g. The properties of the ice making unit were measured by varying the mass of each ice cube. In addition, the characteristics of the mobile cooling unit were measured by varying the total amount of ice from 2.00 to 10.00 kg, and by changing the face air velocity of the ice-free cooling unit from 0.43 to 1.70 m/s. In addition, the air temperature at the inlet of the cooling unit was prepared at 10 to 30 °C.

The average coefficient of performance (COP) of the ice making unit was calculated by Equation 1 below.

[Equation 1]

Here, total amount of m _ice is the total amount of ice, heat of fusion is heat of fusion, t is time, and W _ice-making is ice-making power consumption.

The cooling capacity of the mobile cooling unit is derived from the air flow rate and the air enthalpy gradient throughout the cooling unit as shown in Equation 2 below.

[Equation 2]

_air는 냉각부를 통과하는 공기의 유량 (m³/s), v는 부피 (m³/kg), h는 엔탈피 (kJ/kg)를 의미한다.here,

_air is the flow rate of air passing through the cooling unit (m ³ /s), v is the volume (m ³ /kg), and h is the enthalpy (kJ/kg).

The power consumption ratio of the fan of the mobile cooling unit to the power consumption of the entire test facility can be calculated by Equation 3.

[Equation 3]

Here, R is a ratio, W is power consumption, mcu is a mobile cooling unit, imu is an ice-making unit, and t is time.

Using this, the coefficient of performance (COP _tot ) of the entire test facility can be calculated by Equation 4.

[Equation 4]

2 is a schematic diagram showing a cross-section of the shape of a space formed in an ice cube according to the mass of an individual ice cube.

Referring to FIG. 2 , an approximate shape of a cross section according to the mass of each ice cube can be confirmed. All ice cubes were 23.3 mm wide, 21.7 mm long and 20.6 mm high. Each ice cube formed on the surface of the evaporator thickened as the mass of the ice increased. The shape of the outer surface of each ice cube is the same in the shape of a hexahedron, but the space formed by sinking one side into the inside of the ice cube differs according to the mass of the ice cube.

Experimental Example 1. Change in temperature and power consumption according to ice making cycle

The evaporating, condensing and refrigerant temperatures (a-c) and power consumption (d-f) in each case at the evaporator outlet in the ice making unit are shown in FIG. 3 for an operating time of 7,200 seconds.

The ice making cycle consists of frosting and defrosting.

As can be seen in FIG. 3 (a-c), the evaporating temperature decreased while the condensing temperature increased during the ice making process. The refrigerant temperature at the evaporator outlet decreased over time because the thick ice accumulated in the evaporator caused heat resistance and reduced the efficiency of heat transfer between the ice and the evaporator. Thereafter, the refrigerant discharged from the compressor is directly introduced into the evaporator, and the defrosting process is started by the solenoid valve. Accordingly, the temperature of the refrigerant at the outlet of the evaporator rises during the defrosting process.

The time required to make ice increased with the mass of each ice. As the mass of ice increased, the heat capacity of ice increased and the defrosting time also increased.

As can be seen in FIG. 3 (d-f), power consumption decreased during the ice-making process and increased during the defrosting process. Since the refrigerant does not pass through the expansion unit (capillary) and the enthalpy gradient between the inlet and outlet of the compressor increases, power consumption in the defrost process increases rapidly. In addition, as the mass of the ice cube increases, the heat capacity of the ice in the evaporator increases, and the heat transfer rate from the ice to the evaporator increases, so the temperature and enthalpy of the refrigerant at the inlet of the compressor decrease. As a result, the decrease in enthalpy reduced the peak power consumption value of the compressor.

Experimental Example 2. Change in average coefficient of performance according to ice cube mass

The duration per cycle of ice making and defrosting, the ratio of the defrosting time to the total time, the average amount of power consumption, and the average coefficient of performance (COP _avg ) varying for a cycle corresponding to about 13,500 seconds according to the mass of the ice cube are shown in FIG. 4 and Table 4. 2.

M _{ice, cb} (g) t _cc (s) _Rdf W _avg (kW) COP _avg (-) 6.8 643 0.149 0.262 0.61 8.4 851 0.115 0.259 0.57 10.0 1266 0.083 0.251 0.47

As can be seen in FIG. 4 (a) and Table 2, the duration per cycle (t _cc ) increased as the mass (m _ice,cb ) of each ice cube increased. The defrost time increased slightly as the mass of each ice cube increased, but the ratio of defrost time to total time decreased as the ice-making time became longer than the defrost time.

As can be seen in FIG. 4 (b) and Table 2, since the ratio of the defrosting time to the total time decreased and the average power consumption of the defrosting process was higher than that of the ice making process, the average power consumption as the mass of each ice cube increased. (W _avg ) decreased.

The average power consumption of the defrosting process for 6.8 g or 10.0 g ice cubes was measured to be 163.6% and 127.7%, respectively, compared to the ice-making process. In addition, as the mass of each ice cube increased, the amount of ice produced per cycle increased, but the heat resistance of the evaporator increased and the duration per cycle increased, thereby reducing the ice production efficiency. That is, the production rate of 10.0 g ice cubes was calculated to be 74.6% of the production rate of 6.8 g ice cubes.

Ice production decreased as the average power consumption decreased, and the average performance coefficient decreased as the ice cube mass increased. The average coefficient of performance for small ice cubes (6.8 g) was 28.5% higher than that for large ice cubes (10.0 g). Therefore, even though the average power consumption decreases as the mass of the ice cube increases, it is desirable to select ice cubes with a lower mass because the average performance coefficient is larger in terms of charging performance.

Experimental Example 3. Change according to the operation of the mobile cooling unit

Under the condition that the operating time (t) of the mobile cooling unit and the face air velocity without ice (V _f,woi ) are 0.43 to 1.28 m/s, the face air velocity with ice, V _f,wi ), air temperature gradient (ΔT _air ) and cooling capacity (Q _c ) changes at the inlet and outlet of the cooling unit are shown in FIG. 5 .

Here, the ice-free side air velocity means the speed at which the fan of the cooling unit constantly sucks in air, and the ice-side air velocity means the air speed when the sucked air passes through the cooling unit filled with ice. do.

Referring to FIG. 5, the operating time and air velocity of the ice-free surface are 0.43 to 1.28 m/s, the total amount of ice in the cooling section is 4 kg, and the individual mass of the ice cube is 8.4 g, the air velocity of the ice-free surface under the conditions. , the air temperature gradient and cooling capacity change at the inlet and outlet of the cooling unit can be checked.

The ice stacked on the cooling part acted as a porous material. As the ice layer blocks the path of the air flow, the pressure drop due to the ice layer increases and the air velocity decreases with the ice layer. Over time, as the ice layer melted, the pressure drop across the ice layer decreased and the air velocity over the ice surface increased. An increase in the ice-side air velocity increased the heat transfer rate in the cooling section, and accordingly, the ice melted faster and the ice-side air velocity increased rapidly.

In addition, the temperature gradient initially reached a maximum value and then decreased over time. Over time, the temperature gradient decreased significantly due to the increase in the ice-side air velocity. As a result, the cooling capacity initially reached a maximum value and then decreased over time. This is because the rate at which the temperature gradient decreases is greater than the rate at which the air velocity increases in the presence of ice.

When the ice melted in the cooling section, the pressure drop, face air velocity, and cooling capacity fluctuated as the ice cubes rearranged. In addition, the air velocity on the ice-free side increased due to the increase in the air speed on the ice-free side, but there was no significant difference in the maximum temperature gradient in the case of the air velocity on the ice-free side. Since the difference in air velocity on the ice-free side is greater than the temperature gradient, it was confirmed that the higher the air velocity on the ice-free side, the higher the cooling capacity.

Experimental Example 4. Changes according to the operation of the mobile cooling unit

Under the condition that the ice-free surface air velocity (V _f,woi ) is constant at 0.85 m/s, ice is produced according to the operating time (t) of the mobile cooling unit and the amount of ice (2.00 to 6.00 kg, m _ice,am ). Changes in air velocity (V _f,wi ), air temperature gradient at the inlet and outlet of the cooling unit (ΔT _air ), and cooling capacity (Q _c ) are shown in FIG. 6 .

Referring to FIG. 6 , as the amount of ice increases, the width of the pressure drop increases, so that the air velocity on the surface of the ice decreases. The temperature gradient widened as the ice increased because the heat exchange area between air and ice increased. As a result, the cooling capacity decreased rapidly after reaching the peak.

When the amount of ice compared to the air velocity on the ice side was above a certain value, the ice melted and the air velocity on the ice side increased, but the initial temperature gradient did not significantly decrease due to the large heat exchange area. Therefore, the cooling capacity at this time temporarily increased, because the rate of increase in the air velocity on the ice side was higher than the rate of decrease in the temperature gradient.

However, since ice melts quickly over time, the increase in air velocity over the icy side accelerated the decrease in the temperature gradient. Since the rate of decrease of the temperature gradient was higher than the rate of increase of surface air velocity due to ice, the cooling capacity decreased rapidly after reaching the peak.

The maximum cooling capacity of 2 kg of ice was lower than that of 4 kg or 6 kg of ice. This is because the amount of ice is small and the air temperature at the outlet of the cooling section is much higher than 0 °C. In contrast, when the amount of ice is 4 kg than when it is 6 kg, the maximum cooling capacities are higher for the 4 kg and 6 kg cases because the air velocity on the ice side is faster and the temperature gradient is smaller. did not show a significant difference in

Experimental Example 5. Change in Average Cooling Capacity ①

Under conditions of 2.00 to 6.00 kg of ice amount (m _ice,am ) and 6.8 to 10.0 g of ice cube mass (m _ice,cb ), the ice-free surface air velocity (V _f,woi ) is 0.43 to 1.70 m/s When changing to , the change in average cooling capacity (Q _c,avg ) is shown in FIG. 7 and Table 3. Here, the average cooling capacity was measured and calculated under the condition that the temperature difference between the inlet and outlet of the cooling zone is greater than 15 °C, which is half of the maximum temperature difference.

Q _c,avg (kW) m _{ice, cb} (g) m _{ice, am} (kg) V _f,woi 0.43 m/s 0.85m/s 1.28m/s 1.70m/s 6.8 2.00 0.564 1.096 1.543 1.827 4.00 0.605 1.179 1.758 2.163 6.00 0.563 1.153 1.784 2.276 8.4 2.00 0.534826 1.04752 1.507482 1.777 4.00 0.612234 1.146694 1.748489 2.081 6.00 0.594564 1.16703 1.762091 2.29 10.0 2.00 0.536102 0.935201 1.344015 1.421 4.00 0.640575 1.168822 1.646934 2.025 6.00 0.640419 1.206616 1.825085 2.267

As can be seen in FIG. 7 and Table 3, the increase in the ice-free surface air velocity (V _f,woi ) increased the average cooling capacity (Q _c,avg ), and the mass flow rate for heat transfer increased. By increasing it, stored energy could be utilized in a short period of time. Moreover, as the ice was deposited, the heat exchange area was enlarged, and the air velocity on the side with ice was reduced. Therefore, the average cooling capacity was determined by contrasting the decreasing face air velocity with the enlarged heat exchange area.

When the temperature of the air passing through the ice layer reached 0 °C, the ice layer did not affect the cooling of the air, only the pressure drop. At this point, the effect of air temperature on the average cooling capacity decreased. Therefore, the average cooling capacity did not show a significant difference according to the ice cube type of 6.8 g or 8.4 g, or the total weight of ice of 4 kg or 6 kg, for ice-free surface air velocity of less than 1.2 m/s.

However, in the case of 2 kg of ice, the air temperature did not reach 0 °C, and the average cooling capacity was lower than that of 4 kg and 6 kg of ice. Similarly, for an ice-free side air velocity of 1.70 m/s, the average cooling capacity was lower with less ice. Also, as the mass of the ice cube increased, the pressure drop decreased and the surface air velocity increased.

The heat transfer area had a significant effect on the average cooling capacity. Since the air temperature did not reach 0 °C, the average cooling capacity decreased as the amount of ice increased at 2 kg and 4 kg. For 6 kg of ice, the effect of the amount of ice cubes on the heat transfer area and surface air velocity is complex and the trend is unclear. The change in average cooling capacity with the amount of ice increased with the mass of the ice cube.

Experimental Example 6. Change in Average Cooling Capacity ②

The ice-free surface air velocity (V _f,woi ) is 0.85 or 1.70 m/s, the ice amount (m _ice,am ) is 6.00 or 10.00 kg, and the ice cube mass (m _ice,cb ) is 6.8 to 10.0 g 8 and Table 4 show changes in average cooling capacity (Q _c,avg ) when the air temperature (T _air,in ) varies from 10 to 30 °C under the condition of phosphorus.

The average cooling capacity was measured and calculated under conditions where the ambient air temperature was 10, 20, or 30 °C, and the temperature gradient between the inlet and outlet of the cooling unit was greater than 5 °C, 10 °C, or 15 °C, respectively.

Q _c,avg (kW) m _{ice, am} (kg) Vf _,woi (m/s) m _{ice, cb} (g) T _{air, in} (℃) 10 20 30 6.00 0.85 6.8 0.202 0.619 1.228 10.0 0.41 1.167 2.238 1.70 6.8 0.222 0.631 1.207 10.0 0.417 1.182 2.267 10.00 0.85 6.8 0.201 0.568 0.952 10.0 0.37 1.055 1.814 1.70 6.8 0.24 0.641 1.126 10.0 0.434 1.173 2.006

As can be seen in FIG. 8 and Table 4, the average cooling capacity increased as the temperature gradient between the inlet and outlet increased and as the inlet air temperature increased.

When the total amount of ice was 6.00 kg, the average cooling capacity hardly changed even if the mass of each ice cube was different. This is because as the mass of the ice cube increases, the decrease in temperature gradient offsets the increase in surface air velocity. As the mass of the ice cube increased from 6.8 g to 10.0 g, the average surface air velocity with ice increased by +14.9% on average, and the enthalpy difference between the inlet and outlet decreased by -13.1% on average.

When the total amount of ice was 10.00 kg, the average cooling capacity increased with the ice-free side air velocity and the mass of the ice cube. Similarly, as the mass of the ice cube increased from 6.8 g to 10.0 g, the average surface air velocity with ice increased by +21.2%, and the enthalpy difference between the inlet and outlet decreased on average by -6.8%.

Therefore, the average cooling capacity was higher for heavy ice cubes (10.0 g) than for light ice cubes (6.8 g).

As the total amount of ice increased from 6.00 kg to 10.00 kg, the surface air velocity with ice decreased, so the average cooling capacity also decreased. In addition, when the amount of ice was 10.00 kg, it was confirmed that the average cooling capacity of the 10.0 g ice cube was 13.0% higher than that of the 6.8 g ice cube.

As a result, to achieve high cooling capacity, the ice cube mass must be increased for large amounts of ice relative to the surface air velocity, while the ice cube mass must be decreased for small amounts of ice. Heavy ice cubes can improve the cooling capacity, since a large amount of ice must be used, considering that cooling trucks generally require several hours of cooling.

Experimental Example 7. Performance Evaluation of Mobile Cooling System for Cold Chain Distribution

In the ice making unit, the coefficient of performance and ice production rate of 6.8 g ice cubes were found to be higher than those of 10.0 g ice cubes. In contrast, the average cooling performance of the mobile cooling unit was found to be good for 10.0 g ice cubes based on moderately large amounts of ice. This can reduce the amount of power consumed by the fan for the same target average cooling capacity. Since the mobile cooling system consists of an ice making unit and a mobile cooling unit, the conflicting results of the two devices must be discussed and integrated.

Under the condition of ice amount of 10.0 kg and air temperature of 10 °C, mass of ice cubes of 6.8 g or 10.0 g, ice-free side air velocity of 0.85 m/s or 1.70 m/s, and target averages of 0.20 kW and 0.37 kW Depending on the cooling capacity (Q _c,abg,tg ), the relationship between the varying total coefficient of performance (COP _tot ) and power consumption (R _w,mcu , which means the amount of power consumed by the fan of the cooling unit for the entire system) It is shown in Figure 9 and Table 5.

The target average cooling capacity was selected based on the cooling capacity for a 6.8 g ice cube. The fan speed of the mobile cooling unit was adjusted to achieve the target average cooling capacity. The total power consumption of the entire mobile cooling system includes the power consumed by the ice making unit during the filling process and the power consumed by the fan of the mobile cooling unit.

Referring to FIG. 9 and Table 5, overall, fan power consumption decreased as the amount of ice increased, which reduced the power consumption ratio. Since the filling power for the same total amount of ice is constant, the fan power consumption decreases as the mass of the ice cube increases, which in turn reduces the total power consumption.

However, the total coefficient of performance (COP _tot ) was higher when the mass of the ice cube was smaller, because the power consumption for filling the ice making unit was significantly higher than the fan power consumption of the mobile cooling unit. Moreover, as the ice-free surface air velocity increased from 0.85 m/s to 1.70 m/s, the proportion of fan power consumption increased and the total performance coefficient decreased.

m _{ice, cb} (g) Q _c,avg,tg =0.20kW Q _c,avg,tg =0.37kW R _w,mcu (-) COP _tot (-) R _w,mcu (-) COP _tot (-) 6.8 0.17 0.51 0.21 0.48 10.0 0.12 0.42 0.15 0.40

Claims (9)

A mobile cooling unit preparation step of determining a total weight of refrigerant to be loaded into a cooling unit of the mobile cooling unit, considering a cooling holding time in the transport device for performing cold chain distribution, a cooling target temperature, and a loading amount of the transport device;
a suction step of inhaling air at a constant speed through a transfer unit disposed on one side of the mobile cooling unit by using an air intake unit of the mobile cooling unit;
a cooling step of bringing air into contact with the refrigerant loaded in the cooling unit; and
A discharge step of moving air in contact with the refrigerant through the discharge unit; includes,
The method of increasing cooling efficiency, wherein the movable cooling unit is detachably connected to the transportation device. The method of claim 1, wherein the refrigerant is at least one selected from the group consisting of a solid-gas phase change material, a solid-liquid phase change material, and a solid-solid phase change material. The method of claim 2, wherein the solid phase weight of the refrigerant is 6.0 to 10.0 g. The method of claim 1, wherein the intake step further comprises a temperature measurement step of generating temperature information by measuring the temperature of the air sucked in by the air intake unit. The method of claim 4, wherein the temperature measuring step further comprises a history management step,
Wherein the history management step is to generate temperature history data using air temperature information and time information. The method of claim 5, wherein the history management step further comprises a server transmission step,
Wherein the server transmission step transmits the temperature history data to a history management server. The method of claim 4, wherein the temperature measurement step further comprises an air intake rate control step,
Wherein the air intake rate control step is to transmit control information to a controller unit by a temperature sensor so as to control a speed at which the air intake unit sucks in air. The method of claim 1, wherein the cooling step further comprises a water discharging step,
In the step of discharging water, after contacting air with the refrigerant, water generated from the refrigerant is discharged. According to claim 1, The speed at which the air suction unit sucks air is 0.43 to 2.00 m / s, the cooling efficiency increasing method.

Images