Calculation method for evaluating energy efficiency of electromagnetic heater

Abstract

The invention discloses a calculation method for evaluating the energy efficiency of an electromagnetic heater, and the method comprises the steps: adding the influence of the heat absorbed by a medium, a stray magnetic field in a system, environment heat dissipation, a control system outside the system, and the cooling electric energy consumption of a machine room on the efficiency of the electromagnetic heater; according to the method, an ANSYS simulation calculation result is compared with the outer surface temperature and the heat dissipation loss rate of an electromagnetic heater model obtained through an experiment, and the surface temperature of a heat preservation layer obtained through simulation calculation and the outer surface temperature of a steel pipe with the exposed top are basically completely matched with the temperature measured through the experiment; the result provides a basis for calculating the accuracy of the heat flux density of the outer surface, and also verifies the reliability of the electromagnetic heater energy efficiency evaluation model, so that the energy efficiency evaluation result is more accurate.

Description

Technical Field

[0001] This invention relates to the field of energy efficiency calculation technology, and in particular to a calculation method for evaluating the energy efficiency of an electromagnetic heater. Background Technology

[0002] Under the constraints of the energy crisis and environmental limitations, the efficient use of energy has become a hot topic of discussion in academia and industry in recent years. Oil and gas field enterprises are both major energy producers and consumers. Conventional energy-saving monitoring and technological upgrades mainly target energy conversion equipment such as boilers, heating furnaces, compressors, and pumps. As the work progresses, the energy-saving potential of these devices has been largely exhausted. According to the principle of diminishing marginal returns, continuing to invest resources in upgrading these devices will not yield significant benefits.

[0003] For process systems, thermal systems engineering reveals that the main energy dissipation of the system is not caused by conventional energy supply and conversion equipment, but is determined by the performance of process equipment such as mass transfer and heat transfer. Therefore, energy-saving monitoring and evaluation of shell-and-tube heat exchangers, which are unconventional energy-consuming equipment, is the basis of system optimization, one of the development trends of energy conservation and consumption reduction, and also the main research goal under the "dual carbon" policy in recent years.

[0004] Energy efficiency is short for energy utilization efficiency. The Energy Efficiency Index (EEI) is used to monitor and calculate the energy utilization efficiency of energy-consuming equipment or the energy consumption of energy-consuming equipment over a certain period of time.

[0005] Electromagnetic heaters, as a highly efficient and energy-saving emerging heating technology, are increasingly being used in industrial production and civilian applications. However, due to the lack of precise energy efficiency monitoring and evaluation methods, oil and gas field workers find it difficult to accurately grasp the actual operating efficiency of these devices, thus failing to effectively take targeted energy-saving measures, which undoubtedly exacerbates energy waste. Summary of the Invention

[0006] This invention relates to a calculation method for evaluating the energy efficiency of electromagnetic heaters, providing important theoretical basis and practical guidance for optimizing the energy efficiency of electromagnetic heaters and rational energy use.

[0007] The technical solution adopted in this invention is as follows: A calculation method for evaluating the energy efficiency of an electromagnetic heater is proposed. This method incorporates the effects of heat absorbed by the medium, stray magnetic field within the system, environmental heat dissipation, and external factors such as the power consumption of the control system and computer room cooling on the efficiency of the electromagnetic heater. The energy efficiency evaluation calculation method is constructed as follows: In the formula, Correction factors are added to account for the power consumption of the control system, voltage drop, and computer room cooling in practical applications. The heat gained by the electromagnetic heater, i.e. the heat absorbed by the medium, is expressed in kJ / h. t1 is the electrical energy consumed by the electromagnetic heater, kJ / h; G is the mass flow rate, kg / h; C is the average specific heat capacity of the heating medium between t1 and t2, k / (kg·℃); t1 is the inlet temperature of the heating medium, ℃; t2 is the outlet temperature of the heating medium, ℃. It represents the electrical energy consumed, in kilowatt-hours (kWh).

[0008] Given that existing energy efficiency evaluation technologies for electromagnetic heaters are currently lacking both domestically and internationally, this invention offers the following advantages: Firstly, most electromagnetic heaters use energy utilization rate as their energy efficiency evaluation indicator. While their energy efficiency monitoring methods are relatively simple and easy to implement, their evaluation models are not comprehensive. The relevant technologies for energy efficiency monitoring and evaluation of electromagnetic heaters used in oil and gas fields are still lacking. In our study of energy loss in electromagnetic heaters, based on energy utilization rate, we investigated the impact of stray magnetic fields within the system, environmental heat dissipation, and the energy consumed by external control systems and machine room cooling on the efficiency of electromagnetic heaters.

[0009] Secondly, this invention, starting from the first and second laws of thermodynamics, comprehensively analyzes the "quality" and "quantity" of energy, calculates the energy loss caused by the irreversibility of the electromagnetic heater during operation and the total destination of energy, and concludes that the thermal efficiency in the second law of thermodynamics is low. Therefore, the thermal efficiency in the first law of thermodynamics is directly applied to evaluate and analyze its energy efficiency.

[0010] Finally, this invention compares the outer surface temperature and heat loss rate of the electromagnetic heater model obtained by ANSYS simulation calculation with those obtained by experiments. The simulation calculation results show that the surface temperature of the insulation layer and the outer surface temperature of the exposed steel pipe at the top are basically in complete agreement with the temperature measured in the experiment. This result provides a basis for the accuracy of calculating the heat flux density of the outer surface and also verifies the reliability of the electromagnetic heater energy efficiency evaluation model, making the energy efficiency evaluation results more accurate. Attached Figure Description

[0011] Figure 1 This is a schematic diagram of the energy consumption test points of the present invention; Figure 2 The present invention is 35Nm 3 Trend diagram of positive and negative equilibrium thermal efficiency at / h volumetric flow rate; Figure 3 This invention illustrates the variation trend of evaporation efficiency with outlet temperature under different volumetric flow rates. Figure 4This invention illustrates the trend of thermal efficiency with outlet temperature under different volumetric flow rates. Figure 5 This is a simulation model diagram of the electromagnetic heater of the present invention; Figure 6 This refers to the temperature field on the outer surface of the electromagnetic heater of the present invention. Figure 7 The present invention is 56Nm 3 The trend of heat loss rate changes under forward and reverse balance and simulation results at / h. Detailed Implementation

[0012] The present invention will be further described in detail below with reference to the accompanying drawings and experimental and simulation verification processes.

[0013] A calculation method for evaluating the energy efficiency of an electromagnetic heater is proposed. Firstly, through preliminary research and literature review, this invention identifies the energy consumption factors of the electromagnetic heater as: heat absorbed by the medium, stray magnetic field within the system, environmental heat dissipation, and energy consumption by the external control system and computer room cooling. Under these conditions, the following energy efficiency evaluation calculation method is constructed: In the formula, Correction factors are used to account for the power consumption of the control system, voltage drop, and computer room cooling in practical applications; (since there is no computer room cooling in the laboratory, only the power consumption of the control system is considered, and the measured value in the laboratory is in the range of 0.85 to 0.95). The heat gained by the electromagnetic heater, i.e. the heat absorbed by the medium, is expressed in kJ / h. t1 is the electrical energy consumed by the electromagnetic heater, kJ / h; G is the mass flow rate, kg / h; C is the average specific heat capacity of the heating medium between t1 and t2, k / (kg·℃); t1 is the inlet temperature of the heating medium, ℃; t2 is the outlet temperature of the heating medium, ℃. It represents the electrical energy consumed, in kilowatt-hours (kWh).

[0014] Experimental testing and simulation verification of the present invention: Experimental tests collected data on flow rate, temperature, pressure, and power consumption related to thermal efficiency. Thermal efficiency, heat loss, and energy efficiency were calculated, trend lines were plotted, and data analysis was performed. Thermal efficiency and energy efficiency were analyzed based on the first and second laws of thermodynamics, respectively, examining the "quality" and "quantity" of energy. The irreversible energy loss caused by the electromagnetic heater's operation and the total energy loss occurred. Analysis of the experimental data showed that the energy efficiency under the second law of thermodynamics was relatively low; therefore, the thermal efficiency under the first law of thermodynamics was directly applied for energy efficiency evaluation and analysis.

[0015] The calculation of the energy efficiency value of the electromagnetic heater was based on experimental data analysis and software simulation data comparison using air as the medium.

[0016] 1. Energy efficiency evaluation experiment of electromagnetic heater The electromagnetic heater used in this invention experiment is model ZRQD-5.

[0017] (1) Experimental conditions Assume the medium is air; the operating temperature is 0~300℃ (adjustable); the operating voltage is AC 380V / 50Hz three-phase four-wire.

[0018] Make thorough preparations before the experiment to ensure that the circuits and water systems are safe and usable.

[0019] Conduct the experiment according to the experimental procedure. After the experiment, close all steam valves and disconnect all power.

[0020] Figure 1 The detection indicators and detection instruments set for each test point are shown in the table below.

[0021] Table 1. Basic Parameter Test Results for Electromagnetic Heater Energy Consumption (2) Experimental testing and data analysis The inlet temperature of the electromagnetic heater was controlled at 22℃, and the outlet temperatures of the resistance heater were controlled at 60℃, 70℃, 80℃, 90℃, 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, and 160℃. The volumetric flow rate of the electromagnetic heater was measured at 25 Nm³. 3 / h, 35Nm 3 / h、56Nm 3 Under the condition of [flow rate] / h, the electrical work consumed by the electromagnetic heater, heat loss, thermal efficiency, and efficiency are calculated when the medium reaches a certain temperature. 33 sets of positive balance experimental test data and 33 sets of negative balance experimental test data are shown in Table 2. Based on the experimental data, taking a volumetric flow rate of 35 Nm³ / h as the analysis object, the thermal efficiency of positive and negative balance is analyzed and studied. 3 The trend of positive and negative equilibrium thermal efficiency under / h volumetric flow rate is as follows: Figure 2 As shown, observing the trend, as the outlet temperature increases, the thermal efficiency of the positive and negative equilibrium approaches and then decreases. (Using 25 Nm³ / h) 3 / h, 35Nm 3 / h、56Nm 3 Using the / h volumetric flow rate as the analysis object, the efficiency of the forward and reverse equilibrium is analyzed and studied. The changing trends of the efficiency under different volumetric flow rates are as follows: Figure 3 As shown, observing the trend, the efficiency gradually increases with the rise in outlet temperature, and the change range and value of efficiency are basically the same under different volumetric flow rates.

[0022] The experimental data shows that the thermal efficiency of the positive and negative balance electromagnetic heaters is similar, with little difference in heat dissipation loss and an error rate within a certain range. The efficiency is within 0.3%. Therefore, both the forward and reverse balance methods can be used to calculate the thermal efficiency of the electromagnetic heater. It can also be seen that the efficiency is relatively low when the outlet temperature of the electromagnetic heater varies from 60℃ to 160℃, reaching a maximum of 17.639%. Utilizing high-quality electrical energy for heating the medium is itself a form of low-quality energy utilization, making efficiency a significant factor in evaluating the energy efficiency of the electromagnetic heater. Therefore, the forward balance method should be used directly to evaluate its energy efficiency. The variation of thermal efficiency with outlet temperature for different volumetric flow rates of the electromagnetic heater is shown below. Figure 4 As shown.

[0023] Table 2 Experimental data of electromagnetic heaters using the positive and negative balance methods. 2. ANSYS Simulation. The outer surface temperature and heat loss rate of the electromagnetic heater model obtained from the experiment are compared with the simulation calculation results to verify the reliability of the numerical values ​​obtained from the experimental test.

[0024] The electromagnetic heater used in the simulation is the same as the experimental electromagnetic heater. Based on the experimental test environment, temperature measuring points for averaging temperature were arranged at the upper outlet of the heater. A polyhedral unstructured mesh was used, and mesh refinement was applied to complex structural components. The electromagnetic heater parameters are shown in the longitudinal cross-sectional view of the mesh. The simulation model medium is air, and the numerical simulation employs unsteady-state simulation using ANSYS FLUENT combined with a steady-state thermal model. The physical electromagnetic heater and the simulation model are shown below. Figure 5 As shown.

[0025] Based on the temperature of the measuring point located at the center of the outlet pipe, heating power is supplied by the heating pipe to allow for a continuous steady-state flow of air. When the medium flow rate is 56 Nm³ / h and the outlet temperature is 100℃, the temperature field on the outer surface of the insulation layer is simulated. The temperature field changes of the air inside the electromagnetic heater before and after a single heating cycle in the simulation are as follows: Figure 6 As shown.

[0026] From simulation data and Figure 6 It can be seen that, under the laboratory testing environment, the surface temperature of the insulation layer and the outer surface temperature of the exposed steel pipe obtained by simulation calculation are not much different from the average temperature of the experimental test, with an error rate of less than 10%, which is basically a perfect match. This result verifies the reliability of the simulation model and provides a certain foundation for the accuracy of ANSYS FLUENT simulation calculation of heat loss on the outer surface. Figure 7 It is 56Nm3 Tables and trend graphs of heat loss rate obtained from forward and reverse balancing and simulation at a mass flow rate of / h.

[0027] Preliminary simulation results indicate that when the air outlet temperature is below 100℃, the relative errors between the heat loss rates calculated using positive balance, negative balance, and simulation are small. This suggests that the simulation-calculated heat loss rate is highly accurate at lower outlet temperatures. However, as the air outlet temperature continues to rise, the error in the simulation-calculated heat loss rate will increase. This conclusion suggests that when the heating medium outlet temperature is below 100℃, the simulation results can be used to preliminarily determine the thermal efficiency and energy consumption of the designed electromagnetic heater.

[0028] This invention analyzes the energy efficiency of electromagnetic heaters from two perspectives: the "quantity" of thermal efficiency and the "quality" of thermal efficiency. The working principle of an electromagnetic heater is primarily based on electromagnetic induction, which induces eddy currents within the heater's columnar structure, thereby converting electrical energy into heat for the object being heated. The device first converts electrical energy into electromagnetic energy, then converts the electromagnetic energy back into heat energy, generating heat within the metal workpiece and achieving the metal heating process. Regardless of whether the thermal efficiency is calculated using the positive balance method or the negative balance method, when the outlet temperature of the electromagnetic heater varies from 60℃ to 160℃, the heat loss due to the thermal resistance of the steel pipe and insulation layer is within 17%. This indicates that almost all electrical energy is converted into electromagnetic energy, and then all electromagnetic energy is converted into heat energy (with a conversion rate exceeding 95%). The main energy loss of the electromagnetic heater is heat dissipation from the heater surface.

[0029] The thermal efficiency of the electromagnetic heater measured in the experimental platform was relatively low, reaching a maximum of 17.639%. Using high-quality electrical energy to heat the medium is essentially a waste of high-quality energy, making thermal efficiency a practically meaningless factor in evaluating the energy efficiency of the electromagnetic heater. Therefore, the thermal efficiency calculation formula is directly used in the energy efficiency balance equation and energy efficiency evaluation index of the electromagnetic heater.

Claims

1. A calculation method for evaluating the energy efficiency of an electromagnetic heater, characterized in that, This method incorporates the effects of heat absorbed by the medium, stray magnetic field within the system, environmental heat dissipation, and external factors such as the control system and the electrical energy consumed by the computer room for cooling on the efficiency of the electromagnetic heater, and constructs the following energy efficiency evaluation calculation method: In the formula, To account for the power consumption of the control system, voltage drop, and computer room cooling in practical applications; The heat gained by the electromagnetic heater, i.e. the heat absorbed by the medium, is expressed in kJ / h. t1 is the electrical energy consumed by the electromagnetic heater, kJ / h; G is the mass flow rate, kg / h; C is the average specific heat capacity of the heating medium between t1 and t2, k / (kg·℃); t1 is the inlet temperature of the heating medium, ℃; t2 is the outlet temperature of the heating medium, ℃. It represents the electrical energy consumed, in kilowatt-hours (kWh).

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