A rapid and low-energy consumption precooling device for boxed fruits and vegetables and its control method

Abstract

A rapid and low-energy pre-cooling device for boxed fruits and vegetables and its control method. An air suction device is arranged in a cold storage. A fan is installed on the air suction device. The boxed fruits and vegetables are closely arranged on the air suction side of the air suction device. Ventilation holes are evenly distributed on the side surface of the box. The upper and end surfaces of the boxed fruits and vegetables are covered with felt cloth to form a closed space in the middle of the box. The method of the present invention is applicable to pre-cooling boxed fresh fruits and vegetables in a cold storage. The negative pressure air suction method of a mobile air suction device is adopted to accelerate the pre-cooling effect. By using a variable-power cooling fan and temperature probes placed outside and inside the box, only by setting the cold storage temperature within the appropriate pre-cooling temperature range of the fruits and vegetables, the automatic control of the operation of the air suction fan can be realized, so as to achieve the rapid and precise pre-cooling of the boxed fresh fruits and vegetables, ensure the freshness and moisture retention of the fresh fruits and vegetables, and cause no damage to the fruits and vegetables.

Description

Technical Field

[0001] The present invention relates to the technical field of food refrigeration and preservation, and specifically relates to a rapid and low-consumption precooling device for boxed fruits and vegetables and its control method. Background Technique

[0002] Precooling of fruits and vegetables is an important precondition for fruit and vegetable preservation. The commonly used precooling method is to put the fruits and vegetables in boxes / baskets and then place them in a cold storage, relying on the natural convection of cold air in the cold storage to cool down. This method has a slow cooling rate and cannot achieve the effect of rapid precooling. To accelerate the precooling rate of boxed fruits and vegetables in the cold storage, an improved method of cold storage + forced air exchange by a fan is currently often used. Although the precooling speed is increased, there are still the following disadvantages: 1. The outer packaging of boxed fruits is a corrugated cardboard box, which has good heat insulation ability. Even in the state of forced air supply, the cold air in the cold storage can only slowly enter the box through the holes on the box body to exchange heat with the fruits and vegetables, and cannot achieve the effect of rapid cooling. Therefore, the boxed fruits and vegetables cannot be rapidly precooled, which has a certain impact on the freshness of the fruits and vegetables. 2. Since the heat in the fruits is slowly released into the cold storage, in a certain period of time when the fruits and vegetables first enter, the cold storage will repeatedly reach the upper limit temperature and the lower limit temperature, and the refrigeration compressor will repeatedly start and stop, which greatly increases the energy consumption of the cold storage and also aggravates the equipment loss of the cold storage. 3. After the fan for forced air supply approaches or reaches the specified temperature during precooling of the fruits and vegetables, it cannot automatically stop or reduce the wind speed, which easily causes the water loss on the surface of the fruits and vegetables to accelerate. The high-speed operation of the air supply fan generates a large amount of heat, and the cold storage starts and stops frequently, increasing the power consumption. 4. At present, some devices insert probes into the interior of the fruits and vegetables and realize the start and stop of the fan by setting the internal temperature nodes, which is likely to cause damage to the fruits and vegetables. At the same time, the operating temperatures of the cold storage and the precooling device need to be set, and the operation is cumbersome.

[0003] The following relevant public literatures on fruit and vegetable precooling are retrieved: 1. A movable air duct type mixed-flow variable-frequency fruit and vegetable precooling machine and its application; CN201510291092.8; A movable air duct type mixed-flow variable-frequency fruit and vegetable precooling machine and its application, which includes: a mixed-flow fan, an air distribution air duct, an air duct end face sealing baffle, a temperature control variable-frequency control cabinet, a fruit and vegetable temperature measuring probe, a covering cloth, a universal wheel with a chassis, and non-uniform openings; non-uniform openings are designed on the air distribution air duct, one end is connected to the suction port of the mixed-flow fan, the other end is closed, and it is parallelly arranged in a tunnel surrounded by fruit and vegetable packaging boxes and a covering cloth. The air duct end face sealing baffle is installed on the mixed-flow fan. The fruit and vegetable temperature measuring probe uses a probe type PT100 thermal resistor and is inserted into the interior of the fruits and vegetables to sense the decrease in the temperature of the fruits and vegetables. The temperature signal transmission line is connected to the temperature control variable-frequency control cabinet. The movable air duct type mixed-flow variable-frequency fruit and vegetable precooling machine of the present invention uses a temperature control variable-frequency control cabinet to realize the adjustment of the air flow rate in different temperature sections of the precooled fruit and vegetable products, achieving the purpose of reducing power consumption and saving energy.

[0004] Although there are relevant literature records on such negative pressure precooling devices in the prior art, how to precisely control and adjust the fan power in the device has not been involved. In the state of negative pressure precooling in the comparative document, if the air suction time is not accurately controlled, the dry cold air is likely to take away the moisture on the surface of fruits and vegetables, ultimately resulting in serious water loss of fruits and vegetables, shriveled appearance of fruits and vegetables, and dull color. Therefore, how to ensure the water content of fruits and vegetables while achieving rapid heat exchange is also a technical problem that needs to be solved by those skilled in the art. In particular, as mentioned in the existing literature, "set the starting temperature of the frequency change of the temperature control variable frequency control cabinet to 10°C, and the deceleration operating frequency to 35HZ", which shows that in the prior art, for when to reduce the air suction power and when to stop air suction, it can only be detected by the temperature measuring instrument embedded inside the fruits and vegetables, causing damage to the fruits and vegetables and economic losses. Summary of the Invention

[0005] The purpose of the present invention is to provide a precooling device and method for boxed fruits, which is applicable to precooling boxed fresh fruits and vegetables in a cold storage. The method uses a mobile air suction device with negative pressure air suction to accelerate the precooling effect, and utilizes a cooling fan with variable power and temperature probes placed outside and inside the box. Only by setting the cold storage temperature within the suitable precooling temperature range of the fruits and vegetables, the automatic control of the operation of the air suction fan can be achieved, so as to achieve rapid and precise precooling of boxed fresh fruits and vegetables, ensuring the freshness and moisture retention of fresh fruits and vegetables; and causing no damage to the fruits and vegetables.

[0006] In order to achieve the purpose of the present invention, the technical solutions adopted are as follows:

[0007] A rapid and low-consumption precooling method for boxed fruits and vegetables. An air suction device is arranged in the cold storage, and a fan is installed on the air suction device. The boxed fruits and vegetables are closely arranged on the air suction side of the air suction device, and ventilation holes are evenly distributed on the side surface of the box. The upper and end surfaces of the boxed fruits and vegetables are covered with felt cloth, so as to enclose a closed space in the middle of the box; a number of temperature probes are respectively arranged in the cold storage and the boxed fruits and vegetables. The temperature measured by the probe in the boxed fruits and vegetables is T1, and the temperature measured by the cold storage probe is T2. The signals of the probes inside the box and the external probes are transmitted to the single-chip microcomputer, and the single-chip microcomputer controls the working power of the fan to supply air by comparing the temperatures of T1 and T2.

[0008] The specific steps of temperature control include:

[0009] A. After the precooling program starts, the fan operates at the maximum wind speed;

[0010] B. After the initial time Tc, the high temperature value of the curve fluctuation measured by the cold storage probe is T2g; the high temperature value of the T1 curve fluctuation measured by the in-box probe is T1g; and the temperature T1 is taken at intervals of the time frequency t, and the difference ΔT1 between two adjacent times T1 within the T1 frequency t interval is calculated, ΔT1 = the temperature value at the later time - the temperature value at the previous time, and ΔT1 takes a positive value; the calculated ΔT1 represents the trend of the temperature rise in the box.

[0011] C. If T2g - T1g < 0, the single-chip microcomputer controls the cooling fan to operate at the maximum power.

[0012] D. If T2g - T1g ≥ 0, then look at the slope of ΔT1: K1 = ΔT1 / t. If K1 ≥ 0.2, the fan operates at the maximum power; if 0.1 < K1 < 0.2, the cooling fan is turned on at partial power; if K1 ≤ 0.1, the cooling fan stops and the pre-cooling ends.

[0013] The initial time Tc can take a fixed value, or its end time point is set to T2g - T1g ≥ 0.

[0014] The setting range of the time frequency t is 10s - 60s.

[0015] The fan is a stepless variable-frequency speed-regulating fan, and the power P is continuously adjusted according to the change of the K1 value: P = Pe * (K1 - 0.1) * 10; where Pe is the maximum rated power of the fan. That is, if the single-chip microcomputer calculates that the slope K1 = 0.15 and the maximum rated power Pe of the fan is 200W, then the real-time power P of the fan = Pe * (K1 - 0.1) * 10 = 200 * (0.15 - 0.1) * 10 = 100W. That is, when the slope K1 = 0.15, the real-time power P of the fan is 100W. That is, the slope of the temperature rise in the box is positively correlated with the operating power of the fan.

[0016] The air suction device includes an inverted T-shaped frame. A fixed plate is installed in the middle of the vertical part of the frame, and a fan is installed on the fixed plate.

[0017] Walking wheels are installed at the bottom of the frame. The walking wheels can facilitate its movement in the cold storage. After the packed fruits and vegetables are placed and arranged, the pushing device pushes the U-shaped spacer against the side of the box, and after covering the felt cloth, air suction is carried out.

[0018] A U-shaped spacer is fixedly installed at the front end of the frame. The flexible U-shaped spacer abuts against the side of the box, will not damage the box, and is more fitted to the box, and the air suction effect is better.

[0019] The temperature measurement method of changing the working power of the fan by comparing the temperature difference at the high temperature points of T1 and T2 is applied in other precooling forms. For example, in a cold storage, when changing the suction air to forced air cooling form, the detection method and calculation method of the present invention can still be adopted, and the accurate grasp of the moment of air supply change can still be achieved.

[0020] The control principle based on the present invention is as follows:

[0021] In a cold storage, the temperature drop of fresh fruit and vegetable tissues is roughly divided into three stages: rapid cooling, slow cooling, and the end of the stable stage. During the period when the temperature T1 in the packaging box is higher than the cold storage temperature T2, it is the rapid cooling stage. When the temperature T1 in the fruit and vegetable box is equal to or lower than the cold storage temperature T2, it means that the external tissue temperature of 30-50% of the fruits and vegetables has been basically stable, and the cooling of the central part depends on the conduction from the external tissue to the internal center. At this time, the cooling process is slow; when the temperature of the central part is basically the same as that of the external tissue, it means that the precooling is over.

[0022] Since the cold storage is generally set with a working temperature range, when the cold storage temperature reaches the upper limit of the high temperature, the refrigeration starts, the temperature drops, and when it reaches the lower limit, the machine stops and the temperature rises. Therefore, the temperature curve of the cold storage presents a regular zigzag shape. During the period when the cold storage is stopped, if the surface temperature of the fruits and vegetables is high, the time for T1 to recover from the low temperature to the high temperature is short, and the curve slope is large. When the internal temperature of the fruits and vegetables is basically the same as that of the cold storage, the time for T1 to recover to the high temperature is longer, and the slope is small. Therefore, the slope of the temperature change in the box can be detected to judge the precooling stage of the fruits and vegetables, and then the power of the fan can be adjusted to determine the precooling end point.

[0023] The advantages of the present invention are as follows:

[0024] 1. The present invention changes the way of precooling fruits and vegetables by forced circulation air in the cold storage, and adopts the method of negative pressure forced suction to precool the packed fruits and vegetables, which greatly speeds up the precooling efficiency of the packed fruits and vegetables in the cold storage, maintains the freshness of the fruits and vegetables, and improves the quality of the fruits and vegetables.

[0025] 2. Compared with the existing literature 1, the present invention controls the power of the suction fan by combining the temperature measurement probe in the cold storage and the temperature measurement probe in the fruit and vegetable box, which can effectively avoid the errors of manual control and the disadvantages of inaccurate control of the precooling temperature of fruits and vegetables. The fruits and vegetables can be precooled at the fastest and most economical speed, ensuring the freshness of the fruits and vegetables; and there is no need to adopt a pulp-inserted temperature measurement device, avoiding the damage of the pulp and causing losses.

[0026] 3. Since the power of the suction fan can be dynamically adjusted in the later stage of the present invention, heat dissipation is effectively reduced, and the frequent start of the cold storage refrigeration unit is avoided, thereby reducing the power consumption of the cold storage refrigeration equipment, saving electric energy, and reducing the loss of the compressor. At the same time, since the total output power of the fan decreases, the heat dissipated into the cold storage is reduced, and the overall power consumption of the equipment and the number of starts and stops of the compressor are also reduced.

[0027] 4. Since the present invention realizes precise suction control and the total suction air volume time is controlled, it can effectively avoid the disadvantage that excessive water loss on the surface of fruits and vegetables affects the quality of fruits and vegetables due to too long suction time.

[0028] 5. The present invention can achieve accurate precooling only by setting the cold storage temperature within the suitable range for fruits and vegetables, without setting the temperature of the precooling device. The operation is simple, reducing the possibility of setting errors and also reducing the probability that the buttons of traditional temperature control equipment are prone to failure due to repeated adjustment of temperature settings.

[0029] 6. The precooling technology of the present invention does not require excessive equipment costs. The suction device is simple and reliable, and can be achieved by adding a temperature probe inside the box and changing the control program of the single-chip microcomputer. The transformation cost is low. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Schematic diagram of the decomposed structure of each part of the present invention;

[0031] Figure 2 Schematic diagram of the vertical structure in the working state of the present invention;

[0032] Figure 3 Schematic diagram of the external structure of the air supply device from another angle;

[0033] Figure 4 Schematic diagram of the connection of the structure machine and the temperature measuring device of the air supply device in the cold storage;

[0034] Figure 5 Temperature curve diagram of Embodiment 1;

[0035] Figure 6 Temperature curve diagram in the comparative experiment;

[0036] The names of the components marked in the figure are: 1 - frame; 2 - fan; 3 - gantry spacer; 4 - walking wheel; 5 - fixing plate; 6 - boxed fruits and vegetables; 7 - felt cloth. EMBODIMENT

[0037] EXAMPLE <l

[0038] Taking the fruit banana as an example, the cold storage volume is 50 cubic meters, the set temperature range of the cold storage is 13 - 16°C, the cold storage is equipped with a built-in circulation fan, the weight of each box of bananas is 15 kg, there are 40 boxes in total, the external dimensions of the box are approximately 500*350*220 mm, several ventilation holes are provided on the sides of the box, the boxes are arranged in two columns, a passage about 500 mm wide is left in the middle, a felt cloth is covered on the top, the power of the suction device fan is 200 W, the spacer is closely attached to the end face of the box to form a closed negative pressure space; an NTC temperature probe is respectively set inside the cold storage and the packaging box, the temperature value measured by the probe inside the box is T1, the temperature value measured by the probe outside the box is T2, and the signals of the internal probe and the external probe are transmitted to the external single-chip microcomputer through signal cables, the model of the single-chip microcomputer is PIC16C72, and the single-chip microcomputer controls the working power of the cooling fan for air supply by calculating the temperatures of T1 and T2;

[0039] Two temperature test probes G1 and G2 are also inserted into the pulp of the banana fruit for verification and detection, where G1 is placed in the outer banana pulp and G2 is placed in the inner banana pulp to verify the pre-cooling situation inside the banana pulp.

[0040] The specific steps of temperature control include:

[0041] A. After the pre-cooling program starts, the fan runs at the maximum wind speed;

[0042] B. After the initial time Tc, the high temperature value of the curve measured by the cold storage probe is T2g; the high temperature value of the T1 curve measured by the probe inside the box is T1g; and the temperature T1 is taken at intervals of the time frequency t, and the difference ΔT1 between two adjacent times T1 within the T1 frequency t interval is calculated, ΔT1 = the temperature value of the later time - the temperature value of the previous time, and ΔT1 takes a positive value;

[0043] C. If T2g - T1g < 0, the single-chip microcomputer controls the cooling fan to run at the maximum power;

[0044] D. If T2g - T1g ≥ 0, then look at the slope of ΔT1: K1 = ΔT1 / t. If K1 ≥ 0.2, the fan runs at the maximum power; if 0.1 < K1 < 0.2, the power P is continuously adjusted according to the change of the K1 value: P = Pe * (K1 - 0.1) * 10; if K1 ≤ 0.1, the cooling fan stops and the pre-cooling ends.

[0045] The total time required to finally complete the pre-cooling is: 1035 min; (in the attached figure, the value 1 on the abscissa is equal to 3 min)

[0046] During the pre-cooling period, the electricity consumption of the cold storage is measured to be 23 KWh;

[0047] During the pre-cooling period, the start-stop times of the cold storage compressor are 54 times;

[0048] During the pre-cooling period, the measured temperature curve is as shown in the appendix Figure 2 As shown, it can be seen that the descending curves of G1 and G2 almost coincide, proving that the pre-cooling effect of the bananas is good and the pre-cooling effect of the fruits and vegetables at each position in the box is balanced.

[0049] Comparative experiment 1:

[0050] Bananas were pre-cooled using the same cold storage and packing environment. The temperature of the 400 kg packed bananas when entering the warehouse was about 25°C, and the cold storage was set at 16 - 18°C. Comparative example 1 relied on the self-cooling environment of the cold storage and the circulating fan for pre-cooling; it was compared with the pre-cooling control method in Example 1; the core temperature of the fruits in the boxes in the middle of the stack was continuously measured. Two temperature test probes G1 and G2 were still inserted into the pulp of the bananas for verification and detection. Calculations were carried out when the core temperatures of G1 and G2 reached 18°C.

[0051] The total time required to finally complete pre-cooling was: 850 min;

[0052] The core temperatures of G1 and G2 of the control method of this patent were 18.8 and 18.3 degrees respectively, while the temperature of the traditional cooling method was still as high as 22 degrees.

[0053] Comparative experiment 2:

[0054] Using the same cold storage with the cold storage temperature set at 13 - 15°C, the same batch of banana products were pre-cooled separately. The 40 cases of packed bananas, a total of 600 kg, had a temperature of 30°C when entering the warehouse. The pre-cooling control method of Example 1 was compared with Comparative example 2; Comparative example 2 used the single-point temperature control method, and the fan ran at full power until the core temperature was lower than 15°C, then the fan stopped. Then, a water content measuring instrument was used to test the surface water content of the bananas by the two pre-cooling methods. The measuring instrument used was the Japan Sanliang MA110 water content measuring instrument;

[0055] The total time required for this invention to complete pre-cooling was 1205 min; the number of starts and stops of the cold storage compressor was 66 times

[0056] The time required for the single-point temperature control method to complete pre-cooling was 1156 min; the number of starts and stops of the cold storage compressor was 75 times;

[0057]

[0058]

[0059] As can be seen from the above, compared with Comparative example 2, for the pre-cooling control method using the method of this invention: to achieve the same pre-cooling effect, although the time of the control method of this invention is slightly longer than the single-point temperature control method of Comparative example 2, however:

[0060] 1. The average moisture content of the banana peel decreased by 2.66% (F was greater than Fcrit, and the difference between the two reached the significant standard). At the same time, the number of compressor starts and stops increased by 12%, indicating that the present invention can reduce the moisture loss of fruits and vegetables during the precooling process.

[0061] 2. In the comparative example, due to the long-term operation of the maximum power of the fan, the motor itself generated heat, resulting in an increase in the temperature in the cold storage. The refrigeration compressor needed to increase its power for refrigeration, leading to an increase in the number of starts and stops. Due to the timely reduction of power in the control method of the present invention, the heat generated by the motor decreased, and both the energy consumption and the number of compressor starts and stops decreased significantly.

Claims

1. A method for controlling the rapid and low-consumption pre-cooling of boxed fruits and vegetables, characterized in that: A suction device is provided in the cold storage, and a fan (2) is installed on the suction device. The boxed fruits and vegetables (6) are closely arranged on the suction side of the suction device. Ventilation holes are evenly distributed on the side of the box body. The upper and end surfaces of the boxed fruits and vegetables (6) are covered with felt cloth (7), so that a closed space is formed in the middle of the box body. A plurality of temperature probes are respectively provided in the cold storage and the boxed fruits and vegetables (6). The temperature measured by the probe in the boxed fruits and vegetables (6) is T1, and the temperature measured by the probe in the cold storage is T2. The signals of the probe in the box and the external probe are transmitted to the single chip microcomputer. The single chip microcomputer changes the working power of the fan (2) to supply air by comparing the temperatures of T1 and T2. No need to use pulp insertion temperature measuring device, thus avoiding damage to the pulp and loss; The specific steps of temperature control include: A. After the pre-cooling process starts, the fan runs at the maximum wind speed; B. After the initial time Tc, the high temperature value of the curve fluctuation measured by the cold storage probe is T2g; the high temperature value of the curve fluctuation measured by the probe inside the box is T1g; and the temperature T1 is taken at intervals of time frequency t, and the temperature difference ΔT1 between two adjacent times T1 is calculated, ΔT1 = the temperature value of the latter time - the temperature value of the previous time, and ΔT1 is a positive value; C. If T2g-T1g < 0, the single chip microcomputer controls the cooling fan to operate at maximum power; D. If T2g-T1g≥0, then look at the slope of ΔT1: K1=ΔT1 / t. If K1≥0.2, the fan will run at maximum power; if 0.1<K1<0.2, the cooling fan will be turned on at partial power; if K1≤0.1, the cooling fan will stop and pre-cooling will end. The fan (2) is a stepless variable speed fan, and the power P is continuously adjusted according to the change of K1 value: P = Pe*(K1-0.1)*10; wherein Pe is the maximum rated power of the fan.

2. The method for controlling the rapid and low-consumption pre-cooling of boxed fruits and vegetables according to claim 1, characterized in that: The initial time Tc may be a fixed value, or its end time point may be set to T2g-T1g≥0.

3. The method for controlling the rapid and low-consumption pre-cooling of boxed fruits and vegetables according to claim 2, characterized in that: The setting range of the time frequency t is 10s-60s.

4. The method for controlling the rapid and low-consumption pre-cooling of boxed fruits and vegetables according to claim 1, characterized in that: The air suction device comprises an inverted T-shaped frame (1), a fixing plate (5) is installed in the middle of the vertical portion of the frame (1), and a fan (2) is installed on the fixing plate.

5. The method for controlling the rapid and low-consumption pre-cooling of boxed fruits and vegetables according to claim 4, characterized in that: Travel wheels (4) are installed at the bottom of the frame (1).

6. The method for controlling the rapid and low-consumption pre-cooling of boxed fruits and vegetables according to claim 4, characterized in that: A door-shaped spacer (3) is fixedly mounted on the front end of the frame (1).

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