In the increasingly escalating consumer wave, consumers' demand for personalized and differentiated dairy products is constantly increasing. Adding puree and granular jam to fermented dairy products to obtain a direct feeling of eating well and chewing is gradually favored and recognized by consumers, becoming a new driving force and direction for the growth of liquid food. At present, the addition of jam raw materials in fermented dairy products is mainly achieved through the sterile double line method. Independent tube sterilizers are used to process the base material and jam raw materials separately, and then they are mixed online aseptically to ensure the optimal sterilization efficiency of the product; Jam raw materials belong to non Newtonian fluids, and the pressure drop in the pipeline during ultra-high temperature treatment is mainly the sum of pipeline friction pressure drop, velocity pressure drop, and static pressure drop. The viscosity of the material, sterilizer flow rate, pipe diameter, elbows, and other factors have a significant impact on its system pressure. At the same time, due to significant differences in viscosity among different types of jam, In the process of product design and industrial transformation, choosing high viscosity jam is prone to causing the sterilization machine to break due to the increase in system pressure and insufficient power of the feed pump, while choosing low viscosity jam is difficult to ensure the uniformity of particles in the production process. Therefore, the matching between the pressure drop of the sterilization machine system and the viscosity of the jam material has become a key factor affecting the product launch and subsequent production costs.
Modern sterilization machines are not only designed for sterilization of a single variety of materials, but often have multiple uses, meaning that multiple products can be sterilized on the same sterilization machine. This requires a more complex sterilization process in the design of sterilization machines, taking into account multiple production varieties to meet the needs of different consumers for different flavors. Therefore, in the process of launching new products, it is often necessary to modify the tubular sterilizer to meet the production needs of jam with different viscosities. To meet the passability of high viscosity yogurt inside the tube sterilizer, according to the pressure drop calculation formula, it can be achieved by reducing the length of the pipeline or reducing the production flow rate. The adjustment of the sterilization machine pipeline and flow rate will affect the heating temperature and heating time inside the sterilization machine, thereby affecting the microbial inactivation effect in the jam. Therefore, during the renovation process of the jam tube sterilizer, the evaluation of the jam heating condition is based on ensuring product safety and reducing quality risks caused by microorganisms.
This study constructs a pressure drop and sterilization intensity calculation model for the jam tube sterilizer system based on the structure of the tube sterilizer and basic physics formulas. By detecting the dynamic viscosity of 9 different types of jam, the theoretical sterilization intensity and pressure drop were calculated using the model. Select a representative high viscosity jam, evaluate the actual operating pressure drop and sterilization strength of the jam in the tube sterilizer, and complete the suitability evaluation and modification of the tube sterilizer. This study lays the theoretical foundation and scientific basis for the matching evaluation of jam and tube sterilizer.
Instruments and equipment
Jam sterilization machine
Preparation for model construction
Select jam with different viscosities and use a UHT sterilizer for sterilization. Record the actual operating pressure, temperature, and heating time of the sterilizer during the sterilization process for model building.
Determination of dynamic viscosity of jam
The rotational rheometer measures the viscosity of jam by measuring rotational torque and speed. Due to the influence of factors such as shear rate, temperature, and pressure on the viscosity of jam, it is necessary to measure the dynamic viscosity of jam and select an appropriate viscosity regression model for analysis. After cooling the refrigerated jam to room temperature, select the CC27 measuring fixture and use the 79312 four blade anti settling paddle rotor, which is suitable for measuring samples with sedimentation tendency containing particulate matter (>0.1mm). Evenly take a jam sample, transfer it into a measuring fixture measuring cup, and add it to the internal scale line. Set pre shear for 1 minute, set the shear rate to 100s-1, and read data every 15 seconds, totaling 60 data points. Measure the dynamic viscosity curve of the jam during the process of heating from 15 ℃ to 90 ℃.
Pressure drop calculation of jam sterilization system
The system pressure drop of jam after passing through the sterilization machine pipeline consists of three parts, namely static pressure drop Δ Pa, speed pressure drop Δ PN and frictional pressure drop Δ Pf. Total pressure drop Δ P= Δ Pa+ Δ PN+ Δ The calculation method for different pressure drops of Pf is as follows:
In the equation:
Z1- Elevation of the beginning of the pipeline, m;
Z2- Terminal elevation, m;
U1- Jam flow velocity at the beginning, m/s;
U2- terminal jam flow rate, m/s;
U - Average flow velocity of jam in the pipeline, m/s;
ρ— The density of jam, kg/m3;
λ— Friction coefficient;
L - pipeline length, m;
D - Inner diameter of outer pipeline, m;
K - Resistance coefficient of pipe fittings, valves, etc.
Value of resistance coefficient for common pipeline accessories of jam tube sterilizers
Calculation of sterilization intensity of jam
During the sterilization process of the sterilizer, the jam material is continuously processed, and the jam undergoes three main processes: heating, constant temperature, and cooling in the pipeline. Data analysis and visualization
The calculation model for the pressure drop and sterilization intensity of jam sterilization was compiled using R language (version 4.2.0), and the data visualization was executed using R language Tidyverse package.
Results and Discussion
Establishment of pressure drop calculation model for jam tube sterilizer
In order to evaluate the pressure drop value of high viscosity jam in existing sterilization machines, this study constructed a pressure drop calculation model for jam tube sterilization machines. The basic pipeline information of the sterilization machine used in building the model is shown in Table 2. Compared with the pure milk ultra-high temperature sterilization machine, the structure of this sterilization machine is relatively simple, with a total of 5 pipelines, which can achieve sterilization of jam raw materials from 8 ℃ inlet to 115 ℃, and then lower to 25 ℃ outlet. In addition, the difference from pure milk sterilization machines is that all pipeline structures are sleeves, that is, there is only one inner pipe inside the outer pipe. This structure is mainly to meet the passability of granular jam inside the sterilization machine.
Basic Information of High Temperature Tubular Sterilization Machine for Jam
This study used mango oat jam to construct a pressure drop calculation model. Firstly, the dynamic viscosity of mango oat jam was tested. At 15 ℃, the viscosity of mango oat jam is 8000m Pa · s. When the jam temperature rises to 90 ℃, the viscosity decreases to around 3000m Pa · s, indicating a significant effect of temperature on the viscosity of mango jam. Based on the structure of the tubular sterilizer, the pressure drop of each pipeline section of the sterilizer was calculated and a schematic diagram of pressure drop increase was drawn. The total pressure drop inside the tubular sterilizer for mango oat jam was 58 bar. To verify the accuracy of the model calculation results, this study conducted production line tests on mango oat jam, and the total pressure of the PT10 and PT31 pressure gauges inside the sterilization machine pipeline reached 59bar. The theoretical calculation pressure and actual operating process pressure are 58 bar and 59 bar respectively, with a calculation error of 1.72%. In summary, the pressure drop calculation model constructed in this study can accurately predict the pressure drop of jam inside the tubular sterilizer.
Construction and validation of pressure drop model for jam tube sterilizer
a. Dynamic viscosity curve of mango oat jam; b. The actual operation and theory of mango oats in jam tube sterilizers; c. Calculate pressure drop; d. Comparison of theoretical and actual pressure drop
Establishment of a sterilization intensity calculation model for jam tube sterilizers
The production technology of jam used for processing fruit raw materials may be a key control point that affects the quality of the final product. The concept of food safety is that if prepared and/or consumed according to appropriate purposes, food will not cause harm to consumers. Tubular heat exchangers have a lower cost than plate heat exchangers, but the former has a lower heat exchange surface area per unit length of tubes. Therefore, the length of tube heat exchangers is a necessary condition to ensure heat transfer. The calculation of the heat treatment process depends on the inactivation of microorganisms within a specific time and temperature range. The time required to reduce the microbial population by 10 times at a constant temperature is called the D value of the process, which provides a quantitative indicator of the heat resistance of microbial cells or spores. The process of quantifying the sterilization strength of food raw materials based on the multiple of the D value under reference temperature, also known as the F value under reference conditions. We calculated the heat transfer area of the jam tube sterilizer, which reached 29 square meters. To evaluate the microbial safety of the sterilization machine during the processing of jam, this study used the sterilization intensity calculation model constructed earlier to calculate the sterilization intensity of the jam tube sterilization machine. When the sterilization temperature is 107 ℃, the reference temperature is 90 ℃, the sterilization machine flow rate is 2 cubic meters per hour, and the overall sterilization intensity is 170 minutes.
Dynamic viscosity and theoretical pressure drop evaluation of jam
The validation of a model is usually defined as the process of determining to what extent the model is an accurate representation of real data from the perspective of its intended use. To evaluate the accuracy of theoretical calculation models for pressure drop and sterilization strength, this study tested the viscosity of jam added to 9 types of liquid dairy products at room temperature. These jams can be roughly divided into two groups based on their characteristics: containing particles/not containing particles (or high viscosity/low viscosity). The correlation coefficient range between viscosity and temperature for 9 types of jam is -0.75~-1, indicating that temperature has a significant impact on the viscosity of the jam. In addition, the smoothness and correlation coefficient of the dynamic viscosity curve of jam containing particles are relatively low, due to the uneven compression force of irregular particles in the viscometer fixture during the viscosity testing process. Among them, the viscosity of 7 # passion fruit jam is the lowest, with a viscosity of less than 100m Pa · s at 20 ℃, and the highest viscosity of 4 # sample is 10000m Pa · s at 20 ℃. The significant viscosity difference between two types of jam can lead to pressure drop differences during the sterilization process. It can be seen that the theoretical pressure drop range of nine types of jam during the same time flow process inside the sterilization machine is 8.0 bar to 83.0 bar. Considering that the maximum pressure bearing capacity of the sterilization machine pipeline design does not exceed 50bar, it is necessary to reduce the viscosity of the jam or modify the jam tube sterilization machine.
Dynamic viscosity and theoretical pressure drop value of jam
(a) 9 types of jam appearance; (b) 9 types of jam dynamic viscosity; (c) Theoretical operating pressure drop for 9 types of jam
Trial production and equipment transformation of high viscosity jam
This study modified the jam tube sterilizer to reduce the pressure drop during the jam sterilization process. For the tubular sterilizer involved in this study, the static pressure drop Δ Pa mainly comes from the height difference between the inlet and outlet of the sterilization machine, which is designed to meet the connectivity of upstream and downstream equipment and does not have the feasibility of transformation. Due to the consistent flow rate at the inlet and outlet of the sterilization machine, the speed and pressure drop.
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