High-viscosity fluid pulsating flow UHT sterilization system and sterilization method

Abstract

The invention relates to a high-viscosity fluid pulsating flow UHT sterilization system and method, the system belongs to an active enhanced heat transfer technology, parameters of a frequency converter are set through a control unit, and the frequency converter controls a material centrifugal pump to apply pulsating flow to materials. A large number of vortexes are generated on the wall face through pulsation of fluid, a viscous bottom layer is damaged, the turbulence degree of mainstream fluid is increased, a thermal boundary layer is damaged, the effect of enhancing heat exchange is achieved, and a heating unit of a high-viscosity UHT system is optimized. A proper pulsation frequency is matched under different viscosities and flows of materials, the turbulence level of high-viscosity fluid is increased under the action of pulsating flow, the materials are indirectly heated in the plate heat exchanger, sterilization lasts for 2-8 seconds in the sterilization pipe, and the materials are collected through the material recovery tank after being cooled.

Description

Technical Field

[0001] The present invention relates to the technical field of enhancing heat transfer of high-viscosity fluids, and particularly relates to a pulsating flow UHT sterilization system and a sterilization method for high-viscosity fluids. Background Art

[0002] Ultra-high temperature instantaneous sterilization technology (UHT) is a new sterilization method in current food sterilization treatment. Its principle is to set the heating temperature to 135 - 150 °C, heat for 2 - 8 s, and quickly reduce the temperature to 30 - 40 °C, so as to achieve the purpose of sterilizing food. This technology is generally applied to the sterilization treatment of foods such as mineral water, milk, and beverages, and can thoroughly kill bacteria in liquid food materials. UHT technology is regarded by the United States as the most important achievement in food science in the past 50 years and was first invented by the United Kingdom in 1956. UHT equipment was first developed by the Dutch company Stork in the 1950s. Currently, the Tetra Pak UHT sterilization equipment abroad is suitable for a maximum particle size of up to 25 mm, with a sterilization temperature range of 90 - 140 °C and a production capacity range from 2 t / h to 20 t / h.

[0003] High-viscosity UHT liquid foods are ubiquitous in life, such as the sterilization treatment of dairy products and banana puree, etc.; high-viscosity fluids themselves have large internal frictional forces, high viscosity, are less affected by disturbances in the flow direction, and have a slow flow velocity. Therefore, the fluid is more likely to form a laminar flow state, seriously affecting the heat transfer efficiency and sterilization effect.

[0004] For the current design of UHT systems, only the optimization of the material cooling part and the design of the cleaning structure are carried out, and no optimization design is carried out for high-viscosity fluids. For example, the patent with the publication number CN201911421398.5 discloses a UHT system for enhancing CIP cleaning; the patent with the publication number CN201621128647.3 discloses a UHT high-temperature sterilization circulating cooling system for improving the circulating cooling effect. However, the current UHT technology does not consider how to enhance the heat transfer efficiency, and has the disadvantages of low sterilization efficiency, insufficient processing capacity, and high energy consumption.

[0005] As a branch of active heat transfer enhancement technology, pulsating flow heat transfer enhancement has received increasing attention. Pulsating flow refers to a fluid in which parameters such as the flow rate, velocity, and pressure of the fluid change periodically due to artificial forced action or system self-reason.

[0006] The formula expression of pulsating flow is as follows:

[0007]

[0008] The main reasons for enhanced heat transfer by fluid pulsation are as follows: 1) Fluid pulsation generates a large number of vortices at the wall surface; 2) Pulsating flow can thin the viscous sublayer of the wall surface, thereby increasing the turbulence intensity of the mainstream fluid; 3) It strengthens the degree of mutual mixing between fluids, thus destroying the boundary layer and leading to an increase in the heat transfer area, and therefore can achieve the effect of enhanced heat transfer.

[0009] In summary, aiming at the problems of low sterilization efficiency, high energy consumption, and insufficient engineering design of existing high-viscosity materials, developing a hygienic and efficient sterilization device suitable for high-viscosity liquids has become a research direction in the field of UHT sterilization. At the same time, based on the significant advantages of pulsating flow in increasing the mainstream turbulence intensity and destroying the thermal boundary layer, its application in the field of UHT sterilization of high-viscosity liquid foods is an excellent choice. Summary of the Invention

[0010] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a UHT sterilization system for high-viscosity fluid pulsating flow, which has the advantages of high fluid turbulence intensity, strong heat transfer effect, and better sterilization effect.

[0011] The present invention also provides a sterilization method for a UHT sterilization system of high-viscosity fluid pulsating flow, which has the advantages of convenient operation, high efficiency, and energy saving.

[0012] The present invention solves its technical problems through the following technical solutions:

[0013] A UHT sterilization system for high-viscosity fluid pulsating flow includes a heating system, a pulsating flow conveying system, a sterilization system, and a cooling system;

[0014] The heating system includes a hot water tank, a hot water pump, and an electric heater connected in sequence through a hot water pipeline, and the hot water pipeline is connected to the sterilization system;

[0015] The pulsating flow conveying system includes a material tank, a material centrifugal pump, an electromagnetic flowmeter, and a pulsating flow inlet valve; the high-viscosity material outlet of the material tank is connected to the material centrifugal pump through a material pipeline, and the high-viscosity material flows through the sterilization system via the material centrifugal pump. The material centrifugal pump is connected with an inverter and an electromagnetic flowmeter, and the material pipeline is provided with a pulsating flow inlet valve. Both the inverter and the electromagnetic flowmeter are connected to the control unit;

[0016] The sterilization system includes a sterilization pipe and the heating section and heat retention section of a plate heat exchanger. The high-viscosity material flows through the heat retention section and heating section of the plate heat exchanger in sequence via the material centrifugal pump. The heating section and heat retention section of the plate heat exchanger are connected to the sterilization pipe through a sterilization pipeline. A thermocouple is installed in the sterilization pipeline, and the hot water pipeline of the heating system is connected to the heating section of the plate heat exchanger;

[0017] The cooling system includes a first cooling section of a plate heat exchanger; the outlet of the sterilization pipe is connected to the first cooling section of the plate heat exchanger through a return pipeline, and the first cooling section is connected to a recovery tank through a material recovery pipeline;

[0018] After the high-viscosity material generates pulsation through the pulsating flow conveying system, it flows through the heat retention section and the heating section of the plate heat exchanger in sequence. After the heating section of the plate heat exchanger exchanges heat with ultra-high temperature water, it enters the sterilization pipe for sterilization, and is collected in the recovery tank after being cooled down by the first cooling section of the plate heat exchanger.

[0019] Further, the cooling system further includes a second cooling section of the plate heat exchanger. The outlet of the sterilization pipe is connected to the second cooling section through a return pipeline. The second cooling section is connected to the material tank of the pulsating flow conveying system. A first cold water valve is provided in the cooling water pipeline of the first cooling section, and a second cold water valve is provided in the cooling water pipeline of the second cooling section.

[0020] Further, the frequency regulation range of the frequency converter is 0 - 50 Hz.

[0021] A sterilization method for a high-viscosity fluid pulsating flow UHT sterilization system includes the following steps:

[0022] S1 Equipment pre-sterilization:

[0023] Open the hot water inlet valve of the heating system to inject water, turn on the electric heater, turn on the hot water pump, the first cold water valve and the second cold water valve, close the return valve, open the inlet valve of the material tank to inject water. After flowing through the heat retention section and the heating section of the plate heat exchanger by the material centrifugal pump, the heating section of the plate heat exchanger exchanges heat with ultra-high temperature water and then enters the sterilization pipe for sterilization. The outlet of the sterilization pipe is connected to the second cooling section through a return pipeline. The second cooling section is connected to the material tank of the pulsating flow conveying system and circulates for 15 to 20 minutes for pre-sterilization. Then open the return valve to drain the hot water into the recovery tank;

[0024] S2 Material pre-sterilization:

[0025] After the equipment pre-sterilization is completed, conduct material pre-sterilization. Open the return valve, set the temperature of the electric heater, pour the prepared high-viscosity material into the material tank. After the high-viscosity material flows through the heat retention section and the heating section of the plate heat exchanger by the material centrifugal pump, the heating section of the plate heat exchanger exchanges heat with ultra-high temperature water and then enters the sterilization pipe for sterilization. Set the frequency converter through the control unit. The frequency converter controls the output flow of the material centrifugal pump, and the pulsation frequency is 0.07 to 0.17 Hz. Adjust the temperature of the electric heater to 130 °C, and the material is heated by ultra-high temperature water and then enters the sterilization pipe for sterilization;

[0026] S3 Material UHT sterilization:

[0027] After the material is heated, it enters the sterilization tube and stays for several seconds for sterilization. The temperature of the reflux valve is set at 120°C. When the material undergoes primary sterilization and passes through the reflux valve, if the material does not reach 120°C, the reflux valve closes, and the material enters the material tank for circulating heating after passing through the second cooling section of the plate heat exchanger. When the material reaches 120°C, the reflux valve opens, and the material stops circulating heating;

[0028] S4 Material collection:

[0029] After the UHT sterilization of the material is completed, the reflux valve opens, and the material flows through the heat retention section and the first cooling section of the plate heat exchanger, and then is collected by the recovery tank after cooling.

[0030] Furthermore, in S2, the pulsation frequencies are preferably 0.07Hz, 0.08Hz, 0.1Hz, 0.13Hz, and 0.17Hz.

[0031] The advantages and positive effects of the present invention are:

[0032] 1. In the high-viscosity fluid pulsating flow UHT sterilization system of the present invention, the frequency converter is connected to the material centrifugal pump, and the frequency output of the frequency converter is controlled by the control unit to achieve the pulsating flow of the high-viscosity fluid. The frequency adjustment range of the frequency converter is 0 - 50Hz. It belongs to the indirect heating sterilization method, and the hot water is recycled, which is more efficient and energy-saving.

[0033] 2. The high-viscosity fluid pulsating flow UHT sterilization system of the present invention has a liquid continuous sterilization mode and a liquid circulating sterilization mode, which can be selected according to the sterilization process requirements of the material to be processed, and has wide applicability.

[0034] 3. In the high-viscosity fluid pulsating flow UHT sterilization system of the present invention, the material realizes the pulsating flow mode through the frequency converter and the centrifugal pump, which enhances the turbulence of the fluid, destroys the laminar flow and the thermal boundary layer, strengthens the heat transfer process and the sterilization efficiency, and at the same time, the used system can be cleaned in place in time by CIP cleaning.

[0035] 4. Compared with other UHT equipment, the high-viscosity fluid pulsating flow UHT sterilization system of the present invention has the advantages of high fluid turbulence, strong heat transfer effect, and better sterilization effect in processing high-viscosity fluids. Description of the Drawings

[0036] Figure 1 It is a schematic diagram of the high-viscosity fluid pulsating flow UHT sterilization system of the present invention;

[0037] Figure 2(a) is a graph showing the variation of the overall heat transfer coefficient K with Re at different pulsation frequencies for syrup sterilization in the present invention;

[0038] Figure 2(b) is a graph showing the variation of the heat transfer enhancement factor with Re at different pulsation frequencies for syrup sterilization in the present invention;

[0039] Figure 3(a) is a graph showing the variation of the overall heat transfer coefficient K with Re at different pulsating amplitudes during the sterilization of syrup by the present invention;

[0040] Figure 3(b) is a graph showing the variation of the heat transfer enhancement factor with Re at different pulsating amplitudes during the sterilization of syrup by the present invention;

[0041] Figure 4 is a graph showing the variation of the sterilization rate with time during the sterilization of syrup by the present invention;

[0042] Figure 5 are the overall heat transfer coefficient and Reynolds number corresponding to different pulsating frequencies of the present invention;

[0043] Figure 6 is a pulsation parameter calculation diagram for the flow rate data recorded by the data acquisition card during the sterilization of syrup by the present invention;

[0044] Description of reference numerals:

[0045] 1 - material tank, 2 - feed valve, 3 - frequency converter, 4 - material centrifugal pump, 5 - electromagnetic flowmeter, 6 - pulsating flow feed valve, 7 - cold water valve 1, 8 - cold water valve 2, 9 - thermocouple, 10 - sterilization tube, 11 - plate heat exchanger, 12 - reflux valve, 13 - pressure sensor, 14 - hot water tank, 15 - hot water feed valve, 16 - drain valve, 17 - hot water pump, 18 - electric heater, 19 - recovery tank, 20 - data acquisition card, 21 - computer. Detailed implementation manners

[0046] The present invention will be further described in detail below through specific embodiments. The following embodiments are only descriptive and not restrictive, and the protection scope of the present invention cannot be limited thereby.

[0047] As Figure 1 shown, a pulsating flow UHT sterilization system for high-viscosity fluids includes a heating system, a pulsating flow conveying system, a sterilization system, and a cooling system; the heating system includes a hot water tank 14, a hot water pump 17, and an electric heater 18 connected in sequence through a hot water pipeline. The hot water tank 14 is equipped with a pressure sensor 13, and the hot water pipeline is connected to the sterilization system.

[0048] The pulsating flow conveying system includes a material tank 1, a material centrifugal pump 4, an electromagnetic flowmeter 5, and a pulsating flow feed valve 6; the high-viscosity material outlet of the material tank 1 is connected to the material centrifugal pump 4 through a material pipeline. The high-viscosity material flows through the sterilization system via the material centrifugal pump 4. The material centrifugal pump 4 is connected with a frequency converter 3 and an electromagnetic flowmeter 5. The material pipeline is provided with a pulsating flow feed valve 6. The frequency converter 3 and the electromagnetic flowmeter 5 are both connected to the control unit, and the frequency adjustment range of the frequency converter 3 is 0 - 50 Hz;

[0049] There are 4 plates inside the plate heat exchanger 11, which are the heating section, the heat preservation section, the first cooling section and the second cooling section in sequence from left to right. The sterilization system includes the sterilization tube 10 and the heating section and the heat preservation section of the plate heat exchanger 11. The high-viscosity material flows through the heat preservation section and the heating section of the plate heat exchanger 11 in sequence via the material centrifugal pump 4. The heating section and the heat preservation section of the plate heat exchanger 11 are connected to the sterilization tube 10 through the sterilization pipeline, and a thermocouple 9 is installed in the sterilization pipeline. The hot water pipeline of the heating system is connected to the heating section of the plate heat exchanger;

[0050] The cooling system includes the first cooling section of the plate heat exchanger 11; the outlet of the sterilization tube 10 is connected to the first cooling section of the plate heat exchanger 11 through the return pipeline, and the first cooling section is connected to the recovery tank 19 through the material recovery pipeline; it belongs to the indirect heating sterilization method, and the hot water is recycled, which is more energy-efficient.

[0051] After the high-viscosity material generates pulsation through the pulsating flow conveying system and enters the heating section of the plate heat exchanger 11 to exchange heat with the ultra-high temperature water, it enters the sterilization tube 10 for sterilization, and is cooled and lowered in temperature through the first cooling section of the plate heat exchanger 11 and then collected through the recovery tank 19.

[0052] The cooling system also includes the second cooling section of the plate heat exchanger 11. The outlet of the sterilization tube 10 is connected to the second cooling section through the return pipeline, and the second cooling section is connected to the material tank 1 of the pulsating flow conveying system. A cold water valve 7 is provided in the cooling water pipeline of the first cooling section, and a cold water valve 8 is provided in the cooling water pipeline of the second cooling section.

[0053] The control unit is used to adjust the frequency output of the material pump, so that the material centrifugal pump 4 outputs repeatedly according to two set frequencies, realizing the pulsating flow of the material flow. Adjust the values of the two set frequencies to change the magnitude of the material flow; adjust the difference between the two set frequencies to realize the adjustment of the pulsation amplitude of the material flow; adjust the interval time of the cycle of the two set frequencies to change the pulsation period of the material flow, and then adjust the pulsation frequency.

[0054] The data acquisition card 20 records the data of the electromagnetic flowmeter every 1 second. The material flow curve is analyzed and calculated in the upper computer software to obtain the pulsation amplitude and pulsation frequency of the material.

[0055] A sterilization method for a high-viscosity fluid pulsating flow UHT sterilization system includes the following steps:

[0056] S1 Equipment pre-sterilization:

[0057] Open the hot water feed valve 15 of the heating system to fill it with water. Turn on the electric heater 18, open the hot water pump 17, cold water valve 1 7 and cold water valve 2 8, close the reflux valve 12, open the feed valve 2 of the material tank 1 to fill it with water. After flowing through the heat retention section and heating section of the plate heat exchanger 11 by the material centrifugal pump 4, after the heating section of the plate heat exchanger 11 exchanges heat with ultra-high temperature water, it enters the sterilization tube 10 for sterilization. The outlet of the sterilization tube 10 is connected to the second cooling section through a reflux pipeline, and the second cooling section is connected to the material tank 1 of the pulsating flow conveying system to circulate for 15 min to 20 min for pre-sterilization. Open the reflux valve 12 and drain the hot water into the recovery tank 19;

[0058] S2 Material pre-sterilization:

[0059] After the equipment pre-sterilization is completed, carry out material pre-sterilization. Open the reflux valve 12, set the temperature of the electric heater 18, pour the prepared high-viscosity material into the material tank 1. After the high-viscosity material flows through the heat retention section and heating section of the plate heat exchanger 11 by the material centrifugal pump 4, after the heating section of the plate heat exchanger 11 exchanges heat with ultra-high temperature water, it enters the sterilization tube 10 for sterilization. Set the frequency converter 3 through the control unit, and the frequency converter 3 controls the output flow of the material centrifugal pump 4. The pulsation frequency is 0.07 to 0.17 Hz, preferably 0.07 Hz, 0.08 Hz, 0.1 Hz, 0.13 Hz, 0.17 Hz, and adjust the temperature of the electric heater 18 to 130 °C. After the material is heated by ultra-high temperature water, it enters the sterilization tube 10 for sterilization;

[0060] S3 Material UHT sterilization:

[0061] After the material is heated, it enters the sterilization tube 10 and stays for several seconds for sterilization. Set the temperature of the reflux valve 12 to 120 °C. When the material is sterilized for the first time and passes through the reflux valve 12, when the material does not reach 120 °C, the reflux valve 12 is closed. After the material passes through the second cooling section of the plate heat exchanger 11, it enters the material tank 1 for circulating heating. When the material reaches 120 °C, the reflux valve 12 is opened and the material stops circulating heating;

[0062] S4 Material collection:

[0063] After the material UHT sterilization is completed, the reflux valve 12 is opened. The material flows through the heat retention section and the first cooling section of the plate heat exchanger 11 to cool down and is collected by the recovery tank 19. After the hot water cools down, drain the water in the hot water tank 14 through the drain valve 16.

[0064] Set the parameters of the frequency converter 2 through the control unit. The control unit includes a computer 21, a data acquisition card 20, and a PLC pulsation program. Control the frequency converter 2 through the PLC pulsation program. The frequency converter 2 controls the output flow of the material centrifugal pump, controls the pulsation frequency and pulsation amplitude of the high-viscosity fluid, so as to realize the pulsating flow of the high-viscosity fluid, enhance the turbulence of the fluid, and break the thermal boundary layer. The data acquisition card records the parameters of the electromagnetic flowmeter 5 and the thermocouple 9 and feeds them back to the computer 21 to monitor the data in real time.

[0065] Since a high-viscosity fluid pulsating flow UHT sterilization system proposed by the present invention, the electric heater 18, the plate heat exchanger 11, and the material tank 1 form a circulating heating system, which is more energy-efficient. It has a liquid continuous sterilization mode and a circulating sterilization mode, and has wide applicability. The pulsating flow of the high-viscosity fluid is realized through the frequency converter 3 and the material centrifugal pump 4, which strengthens the heat transfer and sterilization effects and reduces the heating time and energy consumption.

[0066] The present invention conducts a sterilization experiment on high-viscosity syrup as follows:

[0067] As Figure 1 shown, pre-sterilize the equipment, open the hot water inlet valve 15 of the heating system to inject water, turn on the electric heater 18, turn on the hot water pump 17, the cold water valve 1 7 and the cold water valve 2 8, close the reflux valve 12, open the feed valve 2 of the material tank 1 to inject water. After flowing through the heat retention section and the heating section of the plate heat exchanger 11 by the material centrifugal pump 4, the heating section of the plate heat exchanger 11 exchanges heat with the ultra-high temperature water and then enters the sterilization tube 10 for sterilization. The outlet of the sterilization tube 10 is connected to the second cooling section through the reflux pipeline. The second cooling section is connected to the material tank 1 of the pulsating flow conveying system, and circulates for 15 min to 20 min for pre-sterilization. Then open the reflux valve 12 to drain the hot water into the recovery tank 19.

[0068] After the pre-sterilization of the equipment is completed, conduct the pre-sterilization of the high-viscosity syrup. Open the reflux valve 12, set the temperature of the electric heater 18, pour the prepared high-viscosity syrup into the material tank 1. After the high-viscosity syrup flows through the heat retention section and the heating section of the plate heat exchanger 11 by the material centrifugal pump 4, the heating section of the plate heat exchanger 11 exchanges heat with the ultra-high temperature water and then enters the sterilization tube 10 for sterilization. Set the frequency converter 3 through the control unit. The frequency converter 3 controls the output flow of the material centrifugal pump 4. The pulsation frequency of the syrup is 0.07 to 0.17 Hz, preferably 0.07 Hz, 0.08 Hz, 0.1 Hz, 0.13 Hz, 0.17 Hz. Adjust the temperature of the electric heater 18 to 130 °C. The high-viscosity syrup is heated by the ultra-high temperature water and then enters the sterilization tube 10 for sterilization;

[0069] UHT sterilization of high-viscosity syrup. After the high-viscosity syrup is heated, it enters the sterilization tube 10 and is kept for several seconds for sterilization. The temperature of the reflux valve 12 is set at 120 °C. When the high-viscosity syrup undergoes primary sterilization and passes through the reflux valve 12, if the high-viscosity syrup does not reach 120 °C, the reflux valve 12 closes. The high-viscosity syrup enters the material tank 1 for circulating heating after passing through the second cooling section of the plate heat exchanger 11. When the high-viscosity syrup reaches 120 °C, the reflux valve 12 opens and the high-viscosity syrup stops circulating heating.

[0070] After the UHT sterilization of the high-viscosity syrup is completed, the reflux valve 12 opens. The high-viscosity syrup is cooled by passing through the heat retention section and the first cooling section of the plate heat exchanger 11 and then collected by the recovery tank 19. After the hot water is cooled, the water in the hot water tank 14 is drained through the drain valve 16.

[0071] The parameters of the frequency converter 2 are set through the control unit. The control unit includes a computer 21, a data acquisition card 20, and a PLC pulsation program. The frequency converter 2 is controlled through the PLC pulsation program. The frequency converter 2 controls the output flow of the material centrifugal pump, controls the pulsation frequency and pulsation amplitude of the high-viscosity fluid, thereby realizing the pulsating flow of the high-viscosity fluid, enhancing the turbulence degree of the fluid, and breaking the thermal boundary layer. The data acquisition card records the parameters of the electromagnetic flowmeter 5 and the thermocouple 9 and feeds them back to the computer 21 for real-time monitoring of the data.

[0072] Experimental analysis:

[0073] 1. Calculation of the overall heat transfer coefficient K

[0074] The overall heat transfer coefficient K is the heat transfer coefficient in the heat transfer process between the hot and cold media of the plate heat exchanger.

[0075] The heat exchange amount on the hot water side is: Q2 = q m2 c 2 Δt 2 ; In the formula: q m2 is the mass flow rate of hot water, c 2 is the specific heat capacity of hot water, Δt 2 is the temperature difference between the inlet and outlet of hot water.

[0076] The heat exchange amount of the material is: Q1 = q m1 c 1 Δt 1 ; In the formula: q m1 is the mass flow rate of syrup, c 1 is the specific heat capacity of syrup, Δt 1 is the temperature difference between the inlet and outlet of syrup.

[0077] The mass flow rate of syrup under pulsating flow is:

[0078]

[0079] In the formula: A *is the cross-sectional area of the output pipe diameter of the centrifugal pump, and T is the pulsation period.

[0080] The total heat transfer quantity Q is:

[0081]

[0082] In the formula: Δt m is the logarithmic mean temperature difference of the heat exchanger, and A is the heat transfer area of the heat exchanger plates.

[0083] Reynolds number Re:

[0084]

[0085] The overall heat transfer coefficient K is:

[0086]

[0087] 2. Calculation of heat transfer enhancement factor

[0088] To express the effect of pulsating flow on heat transfer enhancement, a comparison is made between the heat transfer capacity under pulsating flow and that under steady flow, and the heat transfer enhancement factor is defined as:

[0089]

[0090] In the formula: K P is the overall heat transfer coefficient under pulsating flow, and K S is the overall heat transfer coefficient under steady flow.

[0091] 3. Evaluation of sterilization effect

[0092] The plate count method is used to evaluate the sterilization effect, and the sterilization rate = (1 - the amount of bacteria after treatment / the initial amount of bacteria) × 100%.

[0093] 4. Result analysis of the UHT effect: As shown in Figure 2(a), Figure 2(b), Figure 3(a), Figure 3(b), Figure 4 , Figure 5 and Figure 6 shown:

[0094] As can be seen from Fig. 2(a), under steady-state conditions, the heat exchange amount between high-viscosity syrup and ultra-high temperature hot water increases with the increase of the Reynolds number, and thus the heat transfer coefficient of the pulsating flow UHT experimental system also increases. Under pulsating conditions, the overall heat transfer coefficient of the plate heat exchanger generally increases with the increase of the Reynolds number. When conducting the UHT pulsation experiment on high-viscosity syrup, when the Reynolds number is less than 480, the overall heat transfer coefficient at each frequency is lower than that under steady-state flow. After the Reynolds number is greater than 550, when the pulsation frequency decreases from 0.17 Hz to 0.1 Hz, the growth rate of the overall heat transfer coefficient increases. When the pulsation frequency decreases from 0.1 Hz to 0.07 Hz, the growth rate of the overall heat transfer coefficient decreases again. It can be seen that there is an optimal pulsation frequency in the experiment, and when f = 0.1 Hz, the heat exchange effect between high-viscosity syrup and ultra-high temperature water is the most ideal. As can be seen from Fig. 2(b), the heat transfer enhancement factor of high-viscosity syrup under pulsating flow is less than 1 when the Reynolds number is less than 500, greater than 1 when the Reynolds number is greater than 500, and can reach 1.1 when Re is 600. With the increase of the pulsation frequency, the growth rate of the heat transfer enhancement factor first increases and then decreases, and the growth rate is the largest when f = 0.1 Hz. This indicates that under large Reynolds numbers, pulsating flow can better destroy the thermal boundary layer, increase the turbulence intensity of the mainstream fluid, and enhance the heat exchange effect.

[0095] As can be seen from Fig. 3(a), under different pulsation amplitude conditions, the overall heat transfer coefficient of the plate heat exchanger generally increases with the increase of the Reynolds number. When the Reynolds number is less than 500, the pulsating heat transfer coefficient is less than the steady-state heat transfer coefficient because the flow velocity of the high-viscosity syrup is too small at this time, and the pulsating flow does not generate an ideal vortex street, which hinders the heat transfer. After the Reynolds number is greater than 500, as the pulsation amplitude increases from 0.19 m / s to 0.3 m / s, the growth rate of the overall heat transfer coefficient increases rapidly. When the pulsation amplitude increases from 0.3 m / s to 0.47 m / s, the growth rate of the overall heat transfer coefficient changes little and almost tends to be stable, which indicates that there is a limit to the influence of the pulsation amplitude on heat transfer, and there is an optimal pulsation amplitude value that enables the vortex street to fully develop, decompose and diffuse, and the velocity gradient at the interface between the mainstream and the vortex street reaches the maximum. With a pulsation amplitude of 0.3 m / s, the variation relationship of the heat transfer enhancement factor of the heat exchanger under different pulsation frequencies and Reynolds numbers is shown in Fig. 3(b). The heat transfer enhancement factor Em of the high-viscosity syrup under pulsating flow is less than 1 when the Reynolds number Re is less than 500, and greater than 1 when the Reynolds number is greater than 500. When the Reynolds number Re is 600, the heat transfer enhancement factor Em can reach a maximum of 1.1. As the pulsation frequency increases, the growth rate of the heat transfer enhancement factor Em first increases and then decreases, and the growth rate is the largest when f = 0.1 Hz. This is consistent with the analysis of the law of the influence of the pulsation frequency on the overall heat transfer coefficient. When the pulsation frequency is 0.1 Hz, the pulsation amplitude is 0.3 m / s, and the Reynolds number is 600, the heat energy loss can be saved by up to 10%, and the heat transfer efficiency can be improved.

[0096] As can be seen from Figure 4 Fig. 3(b), when the frequency is 0.1 Hz and the pulsation amplitude is 0.3 m / s, the UHT sterilization experiment of high-viscosity syrup is carried out. As the sterilization time increases, the sterilization rate shows a slight upward trend, and the sterilization rates at different sterilization times all exceed 95%, showing a good sterilization effect.

[0097] Although the embodiments and drawings of the present invention are disclosed for illustrative purposes, those skilled in the art can understand that various substitutions, changes and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the scope of the present invention is not limited to the content disclosed in the embodiments and drawings.

Claims

1. A high viscosity fluid pulsating flow UHT sterilization system, characterized by: Including heating system, pulsating flow conveying system, sterilization system and cooling system; The heating system comprises a hot water tank (14), a hot water pump (17) and an electric heater (18) which are connected in sequence via a hot water pipeline, and the hot water pipeline is connected to the sterilization system; The pulsating flow conveying system comprises a material tank (1), a material centrifugal pump (4), an electromagnetic flowmeter (5) and a pulsating flow feed valve (6); the high-viscosity material outlet of the material tank (1) is connected to the material centrifugal pump (4) via a material pipeline, the high-viscosity material flows through the sterilization system via the material centrifugal pump (4), the material centrifugal pump (4) is connected to a frequency converter (3) and an electromagnetic flowmeter (5), the material pipeline is provided with a pulsating flow feed valve (6), and the frequency converter (3) and the electromagnetic flowmeter (5) are both connected to a control unit; The sterilization system comprises a sterilization pipe (10) and a heating section and a heat-maintaining section of a plate heat exchanger (11); the high-viscosity material flows sequentially through the heat-maintaining section and the heating section of the plate heat exchanger (11) via a material centrifugal pump (4); the heating section and the heat-maintaining section of the plate heat exchanger (11) are connected to the sterilization pipe (10) via a sterilization pipe; a thermocouple (9) is installed in the sterilization pipe; and a hot water pipe of the heating system is connected to the heating section of the plate heat exchanger; The cooling system comprises a cooling section 1 of a plate heat exchanger (11); the outlet of the sterilization pipe (10) is connected to the cooling section 1 of the plate heat exchanger (11) via a reflux pipeline, and the cooling section 1 is connected to a recovery tank (19) via a material recovery pipeline; The high-viscosity material is pulsated by the pulsating flow conveying system and then flows through the heat retention section and the heating section of the plate heat exchanger 11 in sequence. After the heating section of the plate heat exchanger (11) exchanges heat with ultra-high temperature water, it enters the sterilization pipe (10) for sterilization. After being cooled in the cooling section of the plate heat exchanger (11), it is collected through the recovery tank (19).

2. The high viscosity fluid pulsating flow UHT sterilization system according to claim 1, characterized in that: The cooling system also includes a cooling section 2 of the plate heat exchanger (11), the outlet of the sterilization pipe (10) is connected to the cooling section 2 via a reflux pipeline, the cooling section 2 is connected to the material tank (1) of the pulsating flow conveying system, the cooling water pipeline of the cooling section 1 is provided with a cold water valve 1 (7), and the cooling water pipeline of the cooling section 2 is provided with a cold water valve 2 (8).

3. The high viscosity fluid pulsating flow UHT sterilization system according to claim 1, characterized in that: The frequency adjustment range of the frequency converter (3) is 0-50 Hz.

4. The sterilization method of the high viscosity fluid pulsating flow UHT sterilization system according to claim 1 or 2, characterized in that: The following steps are involved: S1 equipment pre-sterilization: Open the hot water feed valve (15) of the heating system to inject water, turn on the electric heater (18), turn on the hot water pump (17) and the cold water valve one (7) and the cold water valve two (8), close the reflux valve (12), open the feed valve (2) of the material tank (1) to inject water, and after the material centrifugal pump (4) flows through the heat retention section and the heating section of the plate heat exchanger (11), the heating section of the plate heat exchanger (11) exchanges heat with the ultra-high temperature water, and then enters the sterilization pipe (10) for sterilization, the outlet of the sterilization pipe (10) is connected to the cooling section two through the reflux pipeline, and the cooling section two is connected to the material tank (1) of the pulsating flow conveying system to circulate for 15 minutes to 20 minutes for pre-sterilization, open the reflux valve (12), and discharge the hot water into the recovery tank (19); S2 material pre-sterilization: After the equipment is pre-sterilized, the material is pre-sterilized. The reflux valve (12) is opened, the temperature of the electric heater (18) is set, and the prepared high-viscosity material is poured into the material tank (1). The high-viscosity material flows through the heat retention section and the heating section of the plate heat exchanger (11) through the material centrifugal pump (4). The heating section of the plate heat exchanger (11) exchanges heat with ultra-high temperature water, and then enters the sterilization pipe (10) for sterilization. The frequency converter (3) is set by the control unit. The frequency converter (3) controls the output flow of the material centrifugal pump (4), and the pulsation frequency is 0.07 to 0.17 Hz. The temperature of the electric heater (18) is adjusted to 130° C. After the material is heated by the ultra-high temperature water, it enters the sterilization pipe (10) for sterilization. S3 material UHT sterilization: After the material is heated, it enters the sterilization pipe (10) and is kept for a few seconds for sterilization. The temperature of the reflux valve (12) is set to 120°C. The material is sterilized once and passes through the reflux valve (12). When the material does not reach 120°C, the reflux valve (12) is closed. The material passes through the second cooling section of the plate heat exchanger (11) and then enters the material tank (1) for cyclic heating. When the material reaches 120°C, the reflux valve (12) is opened and the cyclic heating of the material stops. S4 material collection: After the UHT sterilization of the material is completed, the reflux valve (12) is opened, and the material flows through the heat retention section and the cooling section of the plate heat exchanger (11) and is collected by the recovery tank (19) after the temperature is reduced.

5. The sterilization method of the high viscosity fluid pulsating flow UHT sterilization system according to claim 4, characterized in that: The pulsation frequency in S2 is preferably 0.07 Hz, 0.08 Hz, 0.1 Hz, 0.13 Hz, or 0.17 Hz.

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