A kind of parabolic trough solar collector efficiency dynamic testing device and method

Abstract

This invention discloses a dynamic testing device and method for the efficiency of a parabolic molten salt trough solar collector, specifically relating to the field of dynamic efficiency testing technology for solar collectors. The device includes a molten salt circulation section, a measuring instrument section, a cooling circulation section, and an oil-salt heat exchanger. By adjusting the first regulating valve in the molten salt circulation section, the third regulating valve in the cooling circulation section, and the frequency of the silicone oil pump, this invention can flexibly adapt to the flow regulation requirements and temperature rise conditions at the commissioning site. It can achieve dynamic testing of thermal efficiency under complex actual operating conditions without changing the original operating logic, and the test results more accurately reflect the true operating performance of the solar collector.

Description

Technical Field

[0001] This invention relates to the field of dynamic testing technology for solar collector efficiency, and more specifically, to a device and method for dynamic testing of the efficiency of a parabolic molten salt tank solar collector. Background Technology

[0002] Parabolic trough solar collectors, as one of the most commercially mature concentrating solar collectors, are widely used in solar power generation, industrial heating, and building heating due to their high efficiency in concentrating solar energy. Their core principle is to focus dispersed solar radiation onto a vacuum collector tube using parabolic mirrors, heating the molten salt, heat transfer oil, and other heat transfer media flowing inside the tube, thus converting solar energy into thermal energy. This allows them to replace traditional fossil fuels, playing a crucial role in reducing carbon emissions and promoting the clean energy transition.

[0003] Thermal efficiency is a core indicator for evaluating the performance of parabolic trough solar collectors. Accurately determining their thermal efficiency during actual operation is a crucial prerequisite for assessing the operating status of the solar collector system, optimizing system design, and improving energy utilization efficiency. With the continued expansion of the parabolic trough solar energy application market, the need for convenient and accurate dynamic thermal efficiency testing at actual operational sites is becoming increasingly urgent.

[0004] However, the standard testing system has stringent requirements for testing conditions, and in order to maintain a stable outlet temperature of the heat collector field, the flow rate of the heat transfer medium needs to be frequently adjusted at the commissioning site, making it difficult to meet the test requirement of volumetric flow rate change ≤2%. On the other hand, there are actual heating needs and complex operating conditions at the commissioning site, which makes it difficult for the inlet temperature rise rate of the heat transfer medium to meet the standard range of heating rate ≤2.5℃ / min. Summary of the Invention

[0005] In order to overcome the above-mentioned defects of the prior art, the present invention provides a dynamic testing device and method for the efficiency of a parabolic molten salt tank collector, which aims to solve the problems mentioned in the background art.

[0006] This invention provides the following technical solution: a dynamic testing device for the thermal efficiency of a parabolic molten salt trough solar collector, comprising a molten salt circulation section, a measuring instrument section, a cooling circulation section, and an oil-salt heat exchanger; The molten salt circulation section is used to realize the circulation flow of molten salt, including a cold salt tank, a cold salt pump, a first regulating valve, a trough collector, a hot salt tank, a hot salt pump, a second regulating valve, and several valves and circulation pipelines. The cold salt pump is installed in the cold salt tank, and the outlet of the cold salt pump is connected to the first regulating valve through a pipeline. The other side of the first regulating valve is connected to the inlet pipeline of the trough collector. The outlet pipeline of the trough collector is connected to the cold salt tank and the hot salt tank respectively. The hot salt pump is installed in the hot salt tank, and the outlet of the hot salt pump is connected to the second regulating valve through a pipeline. The other side of the second regulating valve is connected to the shell-side pipeline of the oil-salt heat exchanger. The outlet pipeline of the oil-salt heat exchanger is connected to the inlet of the cold salt tank and the inlet of the hot salt tank respectively. The cooling circulation section is used for heat dissipation and includes a nitrogen cylinder, a nitrogen breather valve, a thermal oil expansion tank, a silicone oil pump, a silicone oil electric heater, an air cooler, and several valves and circulation pipelines. One end of the nitrogen breather valve is connected to the top pipeline of the thermal oil expansion tank, and the other end is connected to the nitrogen cylinder pipeline. The bottom of the thermal oil expansion tank is connected to the silicone oil pump through a pipeline. The other side of the silicone oil pump is connected to the tube side of the oil-salt heat exchanger through a pipeline. The outlet pipeline of the oil-salt heat exchanger is connected to the silicone oil electric heater and the air cooler respectively. The outlet pipelines of the silicone oil electric heater and the air cooler are both connected to the bottom of the thermal oil expansion tank, and the inlet and outlet of the bottom of the thermal oil expansion tank are connected through pipelines. The inlet and outlet of the oil-salt heat exchanger are connected through pipelines. The measuring instruments are used to collect test parameters, including a flow meter, a temperature sensor, an environmental monitor, and an anemometer. The flow meter is installed in the inlet pipe of the parabolic trough collector. The temperature sensor is installed in the pipe near the flow meter, the inlet pipe of the parabolic trough collector, and the outlet pipe. The environmental monitor and the anemometer are both installed on the parabolic trough collector. The parabolic trough collector achieves solar tracking through hydraulic drive.

[0007] Optionally, in one possible implementation, several valves in the molten salt circulation section include a first shut-off valve assembly; Specifically, the first shut-off valve assembly includes a first shut-off valve, a second shut-off valve, a third shut-off valve, a fourth shut-off valve, and a fifth shut-off valve. The outlet pipe of the trough collector is connected to the first shut-off valve. The other side of the first shut-off valve is connected to the second shut-off valve and the third shut-off valve through pipes. The second shut-off valve is connected to the cold salt tank pipe, and the third shut-off valve is connected to the hot salt tank pipe. The outlet pipe of the oil-salt heat exchanger is connected to the fourth shut-off valve and the fifth shut-off valve. The fourth shut-off valve is connected to the cold salt tank inlet pipe, and the fifth shut-off valve is connected to the hot salt tank inlet pipe. Optionally, in one possible implementation, several valves in the cooling cycle section include a second shut-off valve assembly; The second shut-off valve assembly specifically includes the sixth shut-off valve, the seventh shut-off valve, the eighth shut-off valve, the ninth shut-off valve, the tenth shut-off valve, the eleventh shut-off valve, the twelfth shut-off valve, the thirteenth shut-off valve, the fourteenth shut-off valve, the fifteenth shut-off valve, and the sixteenth shut-off valve. The bottom of the thermal oil expansion tank is connected to the sixth shut-off valve via a pipeline. The other side of the sixth shut-off valve is connected to the silicone oil pump pipeline. The other side of the silicone oil pump is connected to the seventh shut-off valve and the third regulating valve via pipelines. The other side of the third regulating valve is connected to the eighth shut-off valve pipeline. The eighth shut-off valve is connected to the tube-side pipeline of the oil-salt heat exchanger. The outlet pipeline of the oil-salt heat exchanger is connected to the ninth shut-off valve. The other side of the ninth shut-off valve is connected to the tenth shut-off valve and the eleventh shut-off valve. The tenth shut-off valve is connected to the silicone oil electric heater pipeline. The outlet pipeline of the silicone oil electric heater is connected to the twelfth shut-off valve. The eleventh shut-off valve is connected to the air cooler pipeline. The outlet pipeline of the air cooler is connected to the thirteenth shut-off valve. The other side of the twelfth and thirteenth shut-off valves is connected to the fourteenth shut-off valve pipeline. The fourteenth shut-off valve is connected to the bottom pipeline of the thermal oil expansion tank. The fifteenth shut-off valve is connected to the bottom inlet and outlet pipelines of the thermal oil expansion tank. The sixteenth shut-off valve is connected to the inlet and outlet pipelines of the oil-salt heat exchanger. Optionally, in one possible implementation, the flow meter is an ultrasonic flow meter, and the temperature sensor includes at least three, namely a first temperature sensor, a second temperature sensor, and a third temperature sensor. The first temperature sensor is installed in the pipeline near the flow meter, the second temperature sensor is installed in the inlet pipeline of the parabolic trough collector, and the third temperature sensor is installed in the outlet pipeline of the parabolic trough collector. A method for dynamic testing of collector thermal efficiency, using the aforementioned parabolic molten salt trough type solar collector thermal efficiency dynamic testing device, specifically includes the following steps; S1: Before testing, confirm that the measuring instrument is working properly and that the measured values ​​are accurate; S2: Using molten salt as the working fluid, start the molten salt pump, open the valves required for the molten salt circulation section, and adjust the opening of the first regulating valve to control the molten salt flow rate; S3: Preheat the heat transfer oil, start the silicone oil pump, turn on the silicone oil electric heater, and open the valve corresponding to the heat transfer oil preheating. The heat transfer oil flows through the oil-salt heat exchanger connecting pipe and the silicone oil electric heater and then returns to the silicone oil pump. It does not flow through the oil-salt heat exchanger until the heat transfer oil reaches the set temperature. S4: Activate the trough collector tracking system to preheat the molten salt by circulating it from the cold salt tank and the trough collector to the cold salt tank. The flow rate is controlled by adjusting the opening of the first regulating valve through the automatic temperature control program so that the molten salt in the cold salt tank reaches the set temperature. At the same time, the molten salt in the hot salt tank circulates from the hot salt tank and the oil-salt heat exchanger to the hot salt tank. S5: When the molten salt in the cold salt tank reaches the set temperature, switch the molten salt circulation path to the cold salt tank, trough collector, hot salt tank, oil-salt heat exchanger to the cold salt tank. Before switching, start the silicone oil circulation cooling in advance, close the silicone oil electric heater and the corresponding pipeline valves, open the inlet and outlet valves of the air cooler, so that the silicone oil flows through the oil-salt heat exchanger and the air cooler and returns to the silicone oil pump. Adjust the silicone oil pump frequency and the opening of the third regulating valve according to the cooling requirements. S6: Collect test parameters through measuring instruments. The test parameters include molten salt volumetric flow rate, molten salt inlet temperature, molten salt outlet temperature, ambient air temperature, solar normal direct irradiance, and wind speed. S7: The solar collector operates in normal mode. After stopping tracking and reverting to its previous state, the data is exported. The solar normal direct irradiance is selected to be ≥700W / m². 2 The time intervals of continuous measurement data shall be used as valid test data, the time interval between continuous measurement data shall be ≤5s, and the total valid test time shall be ≥4h. S8: Based on the test parameters collected in step S6, calculate the solar incidence angle, and combine this with the collector end loss to calculate the collector's dynamic thermal efficiency. The technical effects and advantages of this invention are as follows: 1. This invention, through the first regulating valve of the molten salt circulation section, the third regulating valve of the cooling circulation section, and the frequency regulation of the silicone oil pump, can flexibly adapt to the flow regulation requirements and heating conditions at the commissioning site. It can achieve dynamic testing of thermal efficiency under complex actual conditions without changing the original operating logic at the site, and the test results can better reflect the true operating performance of the solar collector. 2. The molten salt circulation section of this invention adopts a customized circulation pipeline and multiple sets of shut-off valve assemblies to achieve flexible switching and stable control of the molten salt circulation path, effectively avoiding risks such as molten salt solidification and leakage; the cooling circulation section uses a nitrogen protection system to prevent the oxidation of the heat transfer oil, and works in conjunction with the coordinated regulation of the silicone oil electric heater and the air cooler to ensure system temperature balance. 3. The measuring instrument part of this invention uses a high-precision ultrasonic flow meter and a K-type thermocouple, combined with an integrated environmental monitoring instrument and an anemometer, to achieve real-time and accurate acquisition of molten salt parameters and environmental parameters. Moreover, it selects only the effective data of solar normal direct irradiance, further improving the accuracy of the test results. 4. This invention simulates operating conditions under different irradiance, wind speed, and ambient temperature by adjusting parameters such as molten salt flow rate and cooling capacity. It is not only suitable for thermal efficiency testing of parabolic molten salt trough collectors, but also provides data support for the optimized design and fault diagnosis of heat collection systems. It can be widely used in various commissioning sites such as solar power plants and industrial heating systems, and has significant practical value and promotion prospects. Attached Figure Description

[0008] To more clearly illustrate the technical solutions in this disclosure, the accompanying drawings used in some embodiments will be briefly described below. Obviously, the drawings described below are only drawings of some embodiments of this disclosure, and those skilled in the art can obtain other drawings based on these drawings. In addition, the drawings described below can be regarded as schematic diagrams and are not intended to limit the actual size of the product, the actual flow of the method, the actual timing of the signals, etc. involved in the embodiments of this disclosure.

[0009] Figure 1 This is a flowchart of the dynamic efficiency test of the parabolic molten salt trough solar collector of the present invention. Detailed Implementation

[0010] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0011] Example 1 This embodiment provides a dynamic efficiency testing device for parabolic molten salt trough solar collectors, which can accurately and stably perform dynamic testing of the thermal efficiency of parabolic molten salt trough solar collectors at the commissioning site. Its specific structure is as follows: The testing device mainly consists of a molten salt circulation section, a cooling circulation section, a measuring instrument section, and an oil-salt heat exchanger. Each part is sealed together through customized circulation pipelines and valve assemblies to ensure the stability of fluid transmission and the safety of the testing environment.

[0012] Molten salt circulation section The core function of the molten salt circulation section is to achieve closed-loop circulation of molten salt, providing a stable heat transfer medium loop for collector thermal efficiency testing. Its specific composition and connection relationships are as follows: Includes a cold salt tank (material can be 347H stainless steel, with insulation layer design), a cold salt pump (model IHF50-32-160), a first regulating valve (electric three-way regulating valve), a trough-type solar collector, a hot salt tank equipped with an electric heat tracing device to prevent molten salt from solidifying, and a hot salt pump (model IHF65-50-125). The second regulating valve has the same structure and parameters as the first regulating valve.

[0013] Valve assembly: The first shut-off valve assembly, including the first to fifth shut-off valves, are all manually operated shut-off valves.

[0014] The inlet of the cold salt pump is sealed to the outlet of the cold salt tank via a flange. A further cold salt pump can be mounted on top of the cold salt tank via a bracket. The outlet of the cold salt pump is connected to the inlet of the first regulating valve via a seamless steel pipe. The outlet of the first regulating valve is connected to the inlet flange of the trough solar collector via a seamless steel pipe of the same specification. The outlet pipe of the trough solar collector is connected to the inlet of the first shut-off valve via a seamless steel pipe. The outlet of the first shut-off valve is connected to the inlet of the second and third shut-off valves via a tee pipe. The outlet of the second shut-off valve is connected to the return port at the top of the cold salt tank via a pipeline, forming a bypass loop for molten salt circulation. The outlet of the third shut-off valve is connected to the feed inlet at the top of the hot salt tank via a pipeline. The inlet of the hot salt pump is connected to the outlet at the bottom of the hot salt tank via a flange. The outlet of the hot salt pump is connected to the inlet of the second regulating valve via a seamless steel pipe. The outlet of the second regulating valve is connected to the shell-side inlet flange of the oil-salt heat exchanger via a seamless steel pipe. The shell-side outlet flange of the oil-salt heat exchanger is connected to the inlet of the fourth and fifth shut-off valves via seamless steel pipes. The outlet of the fourth shut-off valve is connected to the inlet pipeline of the cold salt tank, and the outlet of the fifth shut-off valve is connected to the inlet pipeline of the hot salt tank, thereby realizing the circulation and recirculation of molten salt or its replenishment.

[0015] In the above steps, the shut-off valve assembly can be replaced with an electric shut-off valve and PLC automatic control. With the help of flow and temperature feedback signals, the automatic switching of the molten salt circulation path can be realized, such as from the preheating circuit to the test circuit, reducing human operation errors and improving the timeliness and accuracy of operating condition switching.

[0016] Temperature stratification monitoring modules are added to the cold and hot salt tanks, with multiple sets of temperature sensors arranged longitudinally to monitor the uniformity of molten salt temperature in the tank in real time, avoiding inlet temperature fluctuations caused by molten salt stratification and further stabilizing the test conditions.

[0017] Cooling circulation section The cooling circulation section absorbs the heat transferred by the molten salt and maintains the temperature balance of the test system. Its specific components and connections are as follows: Includes a nitrogen cylinder equipped with a pressure reducing valve and pressure gauge, a nitrogen breather valve (model QHF-25), a thermal oil expansion tank equipped with a level gauge and temperature gauge, a silicone oil pump (model GR65-160), a silicone oil electric heater, and an air cooler (model GL-100), with air as the cooling medium.

[0018] Valve assembly: The second shut-off valve assembly includes the sixth to sixteenth shut-off valves, all of which are manual shut-off valves, and the third regulating valve, which is an electric regulating valve.

[0019] One end of the nitrogen breather valve is connected to the interface flange at the top of the heat transfer oil expansion tank via a seamless steel pipe, and the other end is connected to the outlet of the pressure reducing valve of the nitrogen cylinder via a steel pipe of the same specification. This is used to maintain a slightly positive pressure environment inside the expansion tank and prevent oxidation of the heat transfer oil. The outlet at the bottom of the heat transfer oil expansion tank is connected to the inlet end of the sixth shut-off valve via a seamless steel pipe. The outlet end of the sixth shut-off valve is connected to the inlet flange of the silicone oil pump. The outlet end of the silicone oil pump is connected to the inlet ends of the seventh shut-off valve and the third regulating valve in sequence via seamless steel pipes. The outlet end of the third regulating valve is connected to the inlet end of the eighth shut-off valve via a seamless steel pipe. The outlet end of the eighth shut-off valve is connected to the tube-side inlet flange of the oil-salt heat exchanger. The tube-side outlet flange of the oil-salt heat exchanger is connected to the inlet of the ninth shut-off valve via a seamless steel pipe. The outlet of the ninth shut-off valve is connected to the inlet of the tenth and eleventh shut-off valves via a tee pipe. The outlet of the tenth shut-off valve is connected to the inlet pipe of the silicone oil electric heater, and the outlet pipe of the silicone oil electric heater is connected to the inlet of the twelfth shut-off valve. The outlet of the eleventh shut-off valve is connected to the inlet pipe of the air cooler, and the outlet pipe of the air cooler is connected to the inlet of the thirteenth shut-off valve. The outlets of the twelfth and thirteenth shut-off valves are connected together to the inlet of the fourteenth shut-off valve via a seamless steel pipe. The outlet of the fourteenth shut-off valve is connected to the return port at the bottom of the heat transfer oil expansion tank, forming the main cooling circulation loop. Furthermore, the fifteenth shut-off valve is connected in parallel to the inlet and outlet pipes at the bottom of the heat transfer oil expansion tank as a bypass valve for the expansion tank; the sixteenth shut-off valve is connected in parallel to the tube-side inlet and outlet pipes of the oil-salt heat exchanger as a bypass valve for the oil-salt heat exchanger, facilitating equipment maintenance and operating condition adjustment.

[0020] Measuring Instruments Section The measuring instrument section is used to collect various key parameters in real time during the test process, providing accurate data support for thermal efficiency calculation. Its specific configuration and installation location are as follows: Flow meter: An ultrasonic flow meter, model TDS-100H, is used. It is installed on the pipeline at the inlet of the trough collector to ensure that the pipeline in the measurement area is straight and without bends, thereby reducing the impact of fluid disturbance on measurement accuracy.

[0021] Temperature sensors: Three sensors are installed, all using type K thermocouples, namely the first temperature sensor, the second temperature sensor, and the third temperature sensor. The first temperature sensor is installed on the pipeline near the flow meter to measure the temperature of the molten salt near the flow meter; the second temperature sensor is installed on the inlet pipeline of the trough collector to measure the actual inlet temperature of the molten salt when it enters the collector; the third temperature sensor is installed on the outlet pipeline of the trough collector to measure the outlet temperature of the molten salt after it has been heated by the collector.

[0022] Environmental monitoring instrument: The integrated environmental monitoring station, model BYQL-6, can measure solar irradiance, ambient temperature, and ambient humidity. The solar irradiance measurement range is 5m away from the surface of the solar collector reflector. It is installed on the side of the trough solar collector, ensuring that the photosensitive surface of the monitoring instrument is aligned with the concentrating surface of the solar collector.

[0023] Anemometer: A cup anemometer, model FC-6, is used and installed on the top bracket of the environmental monitoring instrument. The height of the cup anemometer is higher than the surface of the solar collector reflector. It is used to measure the real-time wind speed at the test site to correct for the influence of ambient wind on the solar collector efficiency.

[0024] Oil-salt heat exchanger The oil-salt heat exchanger adopts a shell-and-tube heat exchanger, with its shell side connected to the molten salt circulation section and its tube side connected to the cooling circulation section. Heat transfer between the molten salt and the heat transfer oil is achieved through the tube wall, ensuring that the molten salt temperature remains stable within the required range for testing. In the above steps, multiple temperature sensors and heat flow meters can be arranged on the surface of the collector to measure the surface heat loss, providing data support for optimizing the collector structure, such as shortening the end length and improving the performance of the reflector coating.

[0025] By expanding the molten salt circulation branch and measurement channel, the thermal efficiency of multiple collectors can be tested simultaneously, which is suitable for batch acceptance of solar thermal fields, such as spot checks of collector performance during the construction of power plants.

[0026] After the test is completed, the system automatically compares the actual thermal efficiency with the benchmark value and analyzes the reasons for the difference, such as insufficient irradiance, improper flow regulation, and equipment aging, providing direction for operation and maintenance optimization.

[0027] Example 2 Based on Example 1, the trough solar collector is equipped with a hydraulically driven solar tracking system, including a hydraulic pump, a hydraulic cylinder, an angle sensor, and a control system. The control system receives solar position information collected by an environmental monitoring instrument, drives the hydraulic pump to work, and then controls the extension and retraction of the hydraulic cylinder, causing the solar collector to rotate around a single axis to achieve solar tracking and ensure that the solar collector is always in the optimal concentrating state.

[0028] The specific working principle is as follows: During the system preheating stage, firstly, the fifteenth and sixteenth shut-off valves are opened, and the silicone oil pump is started, allowing the heat transfer oil in the cooling circulation system to circulate through the bypass circuit. Simultaneously, the silicone oil electric heater is started to heat the heat transfer oil. The operating temperature of the molten salt is 290-550℃. To avoid thermal shock to the silicone oil from the introduction of high-temperature molten salt during heat exchange, the silicone oil preheating temperature can be increased to approximately 250℃ to remove moisture and air from the system. Subsequently, the fifteenth and sixteenth shut-off valves are closed, and the third regulating valve is adjusted to allow the heat transfer oil to enter the tube side of the oil-salt heat exchanger, establishing a stable cooling cycle.

[0029] Molten salt circulation start-up phase: Open the second and fourth shut-off valves, start the cold salt pump, and adjust the first regulating valve to allow the molten salt in the cold salt tank to circulate through the bypass loop, preheating the molten salt circulation pipeline; after the pipeline temperature stabilizes, close the second and fourth shut-off valves, open the third and fifth shut-off valves, and adjust the first and second regulating valves to allow the molten salt to flow sequentially through the cold salt pump, the first regulating valve, the trough collector, the third shut-off valve, the hot salt tank, the hot salt pump, the second regulating valve, the shell side of the oil-salt heat exchanger, and the fifth shut-off valve, returning to the hot salt tank, establishing the main molten salt circulation loop, and achieving heat exchange between the molten salt and the heat transfer oil through the oil-salt heat exchanger to maintain a stable molten salt temperature.

[0030] The solar tracking system is activated, enabling the trough solar collector to begin tracking the sun. Simultaneously, the measuring instruments are activated: the ultrasonic flow meter collects the volumetric flow rate of the molten salt in real time; three temperature sensors collect the initial temperature of the molten salt, the inlet temperature of the solar collector, and the outlet temperature, respectively; the environmental monitoring instrument collects solar irradiance, ambient temperature, and humidity; and the anemometer collects real-time wind speed. All collected data is transmitted to the computer for storage and processing via the data acquisition module.

[0031] According to the test requirements, the volumetric flow rate of molten salt is changed by adjusting the first and second regulating valves. The power of the air cooler can be adjusted by controlling the number of fans in operation. The power changes the heat dissipation capacity of the cooling circulation system, thereby adjusting the inlet temperature rise rate of the molten salt, simulating different operating conditions at the commissioning site.

[0032] After the test is completed, first turn off the silicone oil electric heater, adjust the first and second regulating valves to reduce the circulation flow of molten salt; at the same time, adjust the third regulating valve to increase the heat dissipation capacity of the cooling circulation system, so that the temperature of molten salt gradually drops to about 290℃. Then turn off the cold salt pump and hot salt pump, close all shut-off valves, and finally turn off the silicone oil pump and measuring equipment such as environmental monitoring instrument and anemometer to complete the system shutdown.

[0033] Example 3: Dynamic Testing Method for the Efficiency of Parabolic Molten Salt Tube Solar Collector This embodiment, based on the testing device of Embodiment 2, provides a dynamic testing method for the efficiency of a parabolic molten salt trough solar collector. The specific steps are as follows: S1: Before testing, confirm that the measuring instrument is working properly and that the measured values ​​are accurate; S2: Using molten salt as the working fluid, start the molten salt pump, open the valves required for the molten salt circulation section, and adjust the opening of the first regulating valve to control the molten salt flow rate; S3: Preheat the heat transfer oil, start the silicone oil pump, turn on the silicone oil electric heater, and open the valve corresponding to the heat transfer oil preheating. The heat transfer oil flows through the oil-salt heat exchanger connecting pipe and the silicone oil electric heater and then returns to the silicone oil pump. It does not flow through the oil-salt heat exchanger until the heat transfer oil reaches the set temperature. S4: Activate the trough collector tracking system to preheat the molten salt by circulating it from the cold salt tank and the trough collector to the cold salt tank. The flow rate is controlled by adjusting the opening of the first regulating valve through the automatic temperature control program so that the molten salt in the cold salt tank reaches the set temperature. At the same time, the molten salt in the hot salt tank circulates from the hot salt tank and the oil-salt heat exchanger to the hot salt tank. S5: When the molten salt in the cold salt tank reaches the set temperature, switch the molten salt circulation path to the cold salt tank, trough collector, hot salt tank, oil-salt heat exchanger to the cold salt tank. Before switching, start the silicone oil circulation cooling in advance, close the silicone oil electric heater and the corresponding pipeline valves, open the inlet and outlet valves of the air cooler, so that the silicone oil flows through the oil-salt heat exchanger and the air cooler and returns to the silicone oil pump. Adjust the silicone oil pump frequency and the opening of the third regulating valve according to the cooling requirements. S6: Collect test parameters through measuring instruments. Test parameters include molten salt volumetric flow rate, molten salt inlet temperature, molten salt outlet temperature, ambient air temperature, solar normal direct irradiance, and wind speed. S7: The solar collector operates in normal mode. After stopping tracking and reverting to its previous state, the data is exported. The solar normal direct irradiance is selected to be ≥700W / m². 2 The time intervals of continuous measurement data shall be used as valid test data, the time interval between continuous measurement data shall be ≤5s, and the total valid test time shall be ≥4h. S8: Based on the test parameters collected in step S6, calculate the solar incidence angle and, combined with the collector end loss, calculate the collector dynamic thermal efficiency.

[0034] In the above steps, the physical quantities used to calculate the dynamic thermal efficiency of the trough solar collector at the commissioning site are as follows:

[0035] In the formula: GDN is the measured solar normal direct irradiance, W / m2; θ is the incident angle, that is, the angle formed between the direct sunlight and the normal of the collector's light-collecting plane, °.

[0036] Taking into account the losses at the ends of the collector, we have:

[0037] In the formula: f is the focal length of the parabolic surface of the solar collector, in meters; L is the length of the solar collector, in meters.

[0038] The active power output of the solar collector at the test data point is:

[0039] In the formula: ρ is the density of the heat transfer fluid, kg / m3; V is the volumetric flow rate of the heat transfer fluid, m3 / h; he is the outlet enthalpy of the heat transfer fluid, kJ / kg; and hi is the inlet enthalpy of the heat transfer fluid, kJ / kg.

[0040] he and hi are obtained by substituting the corresponding temperatures, te and ti, into the formula. Since the inlet temperature ti and outlet temperature te of the heat transfer fluid measured simultaneously do not correspond to these two parameters in Formula 3 in terms of time, the corresponding functional relationship of these two parameters is corrected as follows:

[0041] In the formula: τi is the time for measuring and recording the inlet temperature of the heat transfer fluid, in seconds; τp is the flow time of the heat transfer fluid from the inlet to the outlet of the collector, in seconds. τp is calculated using the following formula:

[0042] In the formula: V is the mass flow rate of the heat transfer fluid, calculated from the volumetric flow rate and the corresponding density of the molten salt near the flow meter, kg / s; ρ is the density of the heat transfer fluid at the average temperature at the inlet and outlet of the collector, kg / m3; and A is the cross-sectional area inside the collector tube, m2.

[0043] In summary, considering end losses, the dynamic thermal efficiency of the parabolic trough solar collector is:

[0044] In the formula: Aa is the light-collecting area of ​​the trough solar collector, m2; τ is time, s.

[0045] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A dynamic testing device for the thermal efficiency of a parabolic molten salt trough solar collector, characterized in that: It includes the molten salt circulation section, the measuring instrument section, the cooling circulation section, and the oil-salt heat exchanger; The molten salt circulation section is used to realize the circulation flow of molten salt, including a cold salt tank, a cold salt pump, a first regulating valve, a trough collector, a hot salt tank, a hot salt pump, a second regulating valve, and several valves and circulation pipelines. The cold salt pump is installed in the cold salt tank, and the outlet of the cold salt pump is connected to the first regulating valve through a pipeline. The other side of the first regulating valve is connected to the inlet pipeline of the trough collector. The outlet pipeline of the trough collector is connected to the cold salt tank and the hot salt tank respectively. The hot salt pump is installed in the hot salt tank, and the outlet of the hot salt pump is connected to the second regulating valve through a pipeline. The other side of the second regulating valve is connected to the shell-side pipeline of the oil-salt heat exchanger. The outlet pipeline of the oil-salt heat exchanger is connected to the inlet of the cold salt tank and the inlet of the hot salt tank respectively. The cooling circulation section is used for heat dissipation and includes a nitrogen cylinder, a nitrogen breather valve, a thermal oil expansion tank, a silicone oil pump, a silicone oil electric heater, an air cooler, and several valves and circulation pipelines. One end of the nitrogen breather valve is connected to the top pipeline of the thermal oil expansion tank, and the other end is connected to the nitrogen cylinder pipeline. The bottom of the thermal oil expansion tank is connected to the silicone oil pump through a pipeline. The other side of the silicone oil pump is connected to the tube side of the oil-salt heat exchanger through a pipeline. The outlet pipeline of the oil-salt heat exchanger is connected to the silicone oil electric heater and the air cooler respectively. The outlet pipelines of the silicone oil electric heater and the air cooler are both connected to the bottom of the thermal oil expansion tank, and the inlet and outlet of the bottom of the thermal oil expansion tank are connected through pipelines. The inlet and outlet of the oil-salt heat exchanger are connected through pipelines. The measuring instruments are used to collect test parameters, including a flow meter, a temperature sensor, an environmental monitor, and an anemometer. The flow meter is installed in the inlet pipe of the parabolic trough collector. The temperature sensor is installed in the pipe near the flow meter, the inlet pipe of the parabolic trough collector, and the outlet pipe. The environmental monitor and the anemometer are both installed on the parabolic trough collector. The parabolic trough collector achieves solar tracking through hydraulic drive.

2. The dynamic testing device for the thermal efficiency of a parabolic molten salt trough solar collector according to claim 1, characterized in that: The valves of the molten salt circulation section include a first shut-off valve assembly; Specifically, the first shut-off valve assembly includes a first shut-off valve, a second shut-off valve, a third shut-off valve, a fourth shut-off valve, and a fifth shut-off valve. The outlet pipe of the trough collector is connected to the first shut-off valve. The other side of the first shut-off valve is connected to the second shut-off valve and the third shut-off valve through pipes. The second shut-off valve is connected to the cold salt tank pipe, and the third shut-off valve is connected to the hot salt tank pipe. The outlet pipe of the oil-salt heat exchanger is connected to the fourth shut-off valve and the fifth shut-off valve. The fourth shut-off valve is connected to the cold salt tank inlet pipe, and the fifth shut-off valve is connected to the hot salt tank inlet pipe.

3. The dynamic testing device for the thermal efficiency of a parabolic molten salt trough solar collector according to claim 2, characterized in that: Several valves in the cooling circulation section include a second shut-off valve assembly; The second shut-off valve assembly specifically includes the sixth shut-off valve, the seventh shut-off valve, the eighth shut-off valve, the ninth shut-off valve, the tenth shut-off valve, the eleventh shut-off valve, the twelfth shut-off valve, the thirteenth shut-off valve, the fourteenth shut-off valve, the fifteenth shut-off valve, and the sixteenth shut-off valve. The bottom of the thermal oil expansion tank is connected to a sixth shut-off valve via a pipeline. The other side of the sixth shut-off valve is connected to a silicone oil pump pipeline. The other side of the silicone oil pump is connected to a seventh shut-off valve and a third regulating valve via pipelines. The other side of the third regulating valve is connected to an eighth shut-off valve pipeline. The eighth shut-off valve is connected to the tube-side pipeline of the oil-salt heat exchanger. The outlet pipeline of the oil-salt heat exchanger is connected to a ninth shut-off valve. The other side of the ninth shut-off valve is connected to a tenth shut-off valve and an eleventh shut-off valve. The tenth shut-off valve is connected to a silicone oil electric heater pipeline. The outlet pipeline of the silicone oil electric heater is connected to a twelfth shut-off valve. The eleventh shut-off valve is connected to an air cooler pipeline. The outlet pipeline of the air cooler is connected to a thirteenth shut-off valve. The other side of both the twelfth and thirteenth shut-off valves is connected to a fourteenth shut-off valve pipeline. The fourteenth shut-off valve is connected to the bottom pipeline of the thermal oil expansion tank. The fifteenth shut-off valve is connected to the inlet and outlet pipelines at the bottom of the thermal oil expansion tank. The sixteenth shut-off valve is connected to the inlet and outlet pipelines of the oil-salt heat exchanger.

4. The dynamic testing device for the thermal efficiency of a parabolic molten salt trough solar collector according to claim 3, characterized in that: The flow meter is an ultrasonic flow meter.

5. The dynamic testing device for the thermal efficiency of a parabolic molten salt trough solar collector according to claim 4, characterized in that: The temperature sensor includes at least three sensors: a first temperature sensor, a second temperature sensor, and a third temperature sensor. The first temperature sensor is installed in the pipeline near the flow meter, the second temperature sensor is installed in the inlet pipeline of the parabolic trough collector, and the third temperature sensor is installed in the outlet pipeline of the parabolic trough collector.

6. A method for dynamically testing the thermal efficiency of a solar collector, using the dynamic testing device for the thermal efficiency of a parabolic molten salt trough solar collector as described in claims 1-5, characterized in that: Specifically, it includes the following steps; S1: Before testing, confirm that the measuring instrument is working properly and that the measured values ​​are accurate; S2: Using molten salt as the working fluid, start the molten salt pump, open the valves required for the molten salt circulation section, and adjust the opening of the first regulating valve to control the molten salt flow rate; S3: Preheat the heat transfer oil, start the silicone oil pump, turn on the silicone oil electric heater, and open the valve corresponding to the heat transfer oil preheating. The heat transfer oil flows through the oil-salt heat exchanger connecting pipe and the silicone oil electric heater and then returns to the silicone oil pump. It does not flow through the oil-salt heat exchanger until the heat transfer oil reaches the set temperature. S4: Activate the trough collector tracking system to preheat the molten salt by circulating it from the cold salt tank and the trough collector to the cold salt tank. The flow rate is controlled by adjusting the opening of the first regulating valve through the automatic temperature control program so that the molten salt in the cold salt tank reaches the set temperature. At the same time, the molten salt in the hot salt tank circulates from the hot salt tank and the oil-salt heat exchanger to the hot salt tank. S5: When the molten salt in the cold salt tank reaches the set temperature, switch the molten salt circulation path to the cold salt tank, trough collector, hot salt tank, oil-salt heat exchanger to the cold salt tank. Before switching, start the silicone oil circulation cooling in advance, close the silicone oil electric heater and the corresponding pipeline valves, open the inlet and outlet valves of the air cooler, so that the silicone oil flows through the oil-salt heat exchanger and the air cooler and returns to the silicone oil pump. Adjust the silicone oil pump frequency and the opening of the third regulating valve according to the cooling requirements. S6: Collect test parameters through measuring instruments. The test parameters include molten salt volumetric flow rate, molten salt inlet temperature, molten salt outlet temperature, ambient air temperature, solar normal direct irradiance, and wind speed. S7: The solar collector operates in normal mode. After stopping tracking and reverting to its previous state, the data is exported. The solar normal direct irradiance is selected to be ≥700W / m². 2 The time intervals of continuous measurement data shall be used as valid test data, the time interval between continuous measurement data shall be ≤5s, and the total valid test time shall be ≥4h. S8: Based on the test parameters collected in step S6, calculate the solar incidence angle and, combined with the collector end loss, calculate the collector dynamic thermal efficiency.

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