A liquid ammonia closed loop pump comprehensive performance test system

Abstract

This invention relates to the field of pump performance testing technology and provides a comprehensive performance testing system for a liquid ammonia closed-loop pump. The system includes a liquid receiver, a filter, a pump under test, a flow meter, a regulating valve, and a heat exchanger connected in sequence. The heat exchanger outlet is connected to the liquid receiver inlet, and the liquid receiver outlet is connected to the filter inlet. The liquid receiver is a bladder-type liquid receiver with a pre-filled nitrogen bladder. A pressure sensor and a temperature sensor are installed at the pump inlet, and differential pressure sensors are installed before and after the filter. A controller is connected to the aforementioned sensors, the heat exchanger, and the regulating valve to adjust the heat exchanger so that the liquid ammonia temperature at the pump inlet is lower than the corresponding saturation temperature, and to monitor the inlet pressure drop caused by filter blockage to determine whether liquid ammonia vaporization has occurred. This application can maintain the single-phase liquid stability of the liquid ammonia at the pump inlet, ensuring accurate testing and preventing cavitation.

Description

Technical Field

[0001] This application relates to the field of pump performance testing technology, and more specifically, to a comprehensive performance testing system for a liquid ammonia closed-loop pump. Background Technology

[0002] Pump performance testing is a necessary step in verifying key indicators of fluid machinery pumps, such as head, flow rate, and efficiency. Existing pump testing systems mostly employ open water tanks or rigid closed tank structures for water media. They adjust valves to change system resistance and collect pressure, temperature, flow rate, and power data to plot performance curves. However, when the working fluid is liquid ammonia, existing systems face significant technical obstacles.

[0003] The saturated vapor pressure of liquid ammonia is extremely sensitive to temperature changes. Saturated vapor pressure refers to the pressure at which liquid ammonia begins to vaporize at a specific temperature; the higher the temperature, the greater the pressure. Within the common test temperature range of 0℃ to 40℃, the saturated vapor pressure of liquid ammonia rises sharply from approximately 0.43 MPa to approximately 1.55 MPa. This means that even slight temperature fluctuations in liquid ammonia within a closed loop can cause significant volume expansion or contraction. If the loop lacks an effective volume compensation mechanism, the pressure will drift drastically, and liquid ammonia vaporization is highly likely to occur at the pump inlet, leading to distortion in flow rate and head measurements, and even causing pump cavitation damage. Cavitation refers to the vaporization of liquid ammonia in a localized area at the pump inlet when the pressure is lower than its saturated vapor pressure. This vaporization forms bubbles that are carried into the high-pressure zone within the pump and collapse, causing impeller erosion and a sudden drop in performance.

[0004] Furthermore, liquid ammonia is toxic and volatile. Existing testing systems typically require purging the entire circuit when disassembling and reassembling the pump under test for vibration comparison experiments or maintenance. This not only results in significant liquid ammonia loss and high safety risks, but also makes it difficult to restore the circuit temperature, pressure, and filling volume to their pre-disassembly states after refilling, severely impacting the consistency of operating conditions in performance comparison tests. Regarding cavitation performance testing, existing technologies mostly employ vacuuming to reduce the gas phase pressure in the storage tank. However, the volatile nature of liquid ammonia makes vacuum control difficult, resulting in low accuracy in capturing the cavitation critical point and the potential for uncontrollable gas-liquid two-phase flow in the circuit.

[0005] To address the aforementioned issues, existing technologies urgently need improvement. Summary of the Invention

[0006] The purpose of this application is to provide a comprehensive performance testing system for a liquid ammonia closed-loop pump, which has the advantages of maintaining the stability of the liquid ammonia phase at the pump inlet in the liquid ammonia closed loop, realizing rapid disassembly and retesting of the pump under test, and safely and accurately completing the full-condition performance test.

[0007] This application provides a comprehensive performance testing system for a liquid ammonia closed-loop pump, including a closed-loop circulation system. The closed-loop circulation system includes, in sequence along the liquid ammonia flow direction, a reservoir, a filter, an inlet pressure measuring section for the pump under test, the pump under test, an outlet pressure measuring section for the pump under test, a mass flow meter, a flow regulating valve, and a heat exchanger. The liquid ammonia side outlet of the heat exchanger is connected to the inlet of the reservoir, the liquid ammonia chamber outlet of the reservoir is connected to the inlet of the filter, and the filter outlet is connected to the inlet pressure measuring section of the pump under test.

[0008] The liquid storage device is a bladder-type liquid storage device, which has a pre-filled nitrogen bladder inside, and the bladder divides the interior of the liquid storage device into a gas chamber and a liquid ammonia chamber. The pressure measuring section at the inlet of the pump under test is equipped with a pressure sensor and a temperature sensor, and inlet differential pressure sensors are installed before and after the filter; the controller is connected to the pressure sensor, temperature sensor, inlet differential pressure sensor, heat exchanger, and flow regulating valve; The controller adjusts the heat exchanger according to the pressure sensor and temperature sensor so that the temperature of the liquid ammonia at the inlet of the pump under test is lower than the saturation temperature corresponding to the inlet pressure. The controller monitors the inlet pressure drop caused by filter blockage based on the inlet differential pressure sensor and the pressure sensor to determine whether liquid ammonia vaporization has occurred at the inlet of the pump under test.

[0009] Furthermore, the pre-filled nitrogen pressure of the airbag is set according to the saturated vapor pressure corresponding to the lowest operating temperature of liquid ammonia; The airbag is compressed when the liquid ammonia temperature rises and its volume expands, and expands when the liquid ammonia temperature falls and its volume contracts to compensate for the volume of liquid ammonia in the circuit.

[0010] Furthermore, when the liquid ammonia temperature rises to the maximum operating temperature, the remaining volume of the compressed airbag is not less than a set proportion of the original volume of the airbag, so as to ensure that the liquid ammonia chamber of the reservoir has sufficient space to accommodate the expansion of liquid ammonia.

[0011] Furthermore, the system also includes three-way ball valves located at the inlet and outlet of the pump under test, the three-way ball valves having an on-state and a partially isolated state; When the three-way ball valve switches to the partial isolation state, it disconnects the pump under test from its adjacent pipe section.

[0012] Furthermore, the system also includes a recovery device, a vacuum device, a nitrogen purging device, and a filling and exhaust valve; The addition and discharge valve is connected to the pump under test and its adjacent pipe section, and the addition and discharge valve is selectively connected to the recovery device, the vacuum device or the nitrogen replacement device; When the three-way ball valve switches to the partial isolation state, it cuts off the connection between the pump under test and its adjacent pipe section, and the rest of the closed circulation loop remains in a closed pressurized state.

[0013] Furthermore, the system also includes an electrical parameter acquisition unit connected to the drive end of the pump under test, and the electrical parameter acquisition unit is connected to the controller; The controller obtains the rotational speed of the pump under test and adjusts the opening of the flow regulating valve to enable the pump under test to operate under different rotational speeds and flow rates.

[0014] Furthermore, the controller controls the heat exchanger to raise the temperature of the liquid ammonia, so that the inlet liquid ammonia temperature of the pump under test approaches the saturation temperature corresponding to the inlet pressure; The airbag contracts accordingly as the liquid ammonia expands, in order to absorb the volume of liquid ammonia that expands due to the increase in temperature.

[0015] Furthermore, when conducting performance comparison tests before and after replacing the pump under test, the three-way ball valves at the inlet and outlet of the pump under test are switched to a partial isolation state, and the liquid ammonia in the pump under test and its adjacent pipe section is discharged into the recovery device through the discharge valve; After replacing the pump under test, the pump under test and its adjacent pipe sections are evacuated and purged with nitrogen through the filler and drain valves, and then filled with liquid ammonia. The liquid ammonia working medium and operating parameters of the remaining parts of the closed-loop circuit remain consistent with those before the replacement.

[0016] As can be seen from the above, this application achieves the following technical effects: (1) By binding the heat exchanger and the bladder-type liquid storage tank with specific flow direction and the dynamic volume compensation of the air bladder, and by coordinating the controller's closed-loop regulation of subcooling and filter pressure difference monitoring, the pressure drift and inlet vaporization caused by liquid ammonia temperature fluctuations can be effectively suppressed, ensuring that the liquid ammonia at the inlet of the pump under test remains in a single-phase liquid state, ensuring the accuracy of test data and preventing cavitation risks.

[0017] (2) By setting the matching relationship between the pre-filled nitrogen pressure of the airbag and the saturated vapor pressure of the liquid ammonia at the lowest working temperature, and limiting the proportion of the remaining volume of the airbag after high-temperature compression, the airbag has sufficient compression and expansion strokes in the entire temperature range, ensuring that the liquid ammonia chamber of the liquid reservoir has a stable liquid ammonia expansion capacity.

[0018] (3) By using the local isolation interface and local ammonia discharge interface of the three-way shut-off valve in conjunction with the recovery device, vacuum device and nitrogen replacement device, when replacing the pump to be tested, only the pump section is isolated and emptied, keeping the rest of the main circuit sealed and pressurized, so as to achieve rapid reassembly and retesting and maintain consistent operating conditions.

[0019] (4) By conducting point-by-point tests under full operating conditions at different speeds and flow rates, dynamically buffering the airbag during the temperature rise cavitation test, and interlocking the pump to stop and close the valve to exhaust air using the ammonia leak detector, a complete closed loop of test execution and safety protection is formed. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of the experimental platform for the comprehensive performance testing system of the liquid ammonia closed-loop pump disclosed in an embodiment of the present invention; Figure 2 This is a schematic diagram of the structure of the bladder-type liquid reservoir disclosed in an embodiment of the present invention. Detailed Implementation

[0022] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which these embodiments belong; the terminology used herein and in the specification of the application is for the purpose of describing particular embodiments only and is not intended to limit these embodiments; the terms "comprising" and "having," and any variations thereof, in the specification of these embodiments and the foregoing drawings, are intended to cover non-exclusive inclusion. The terms "first," "second," etc., in the specification of these embodiments and the foregoing drawings are used to distinguish different objects, not to describe a particular order.

[0023] The implementation details of the technical solution in this embodiment are described in detail below: This embodiment is mainly applied to the mechanical pump performance verification stage in the research of key technologies for high-efficiency pump-driven two-phase flow in space. In this type of research, the pump under test uses liquid ammonia as the working fluid, and it is necessary to accurately measure the core performance indicators such as head, flow rate, and efficiency under different speeds and flow rates, and plot the corresponding performance curves. Due to the physical properties of liquid ammonia, such as drastic changes in saturated vapor pressure with temperature, easy vaporization, toxicity, and volatility, it is essential to ensure that the liquid ammonia at the pump inlet remains in a single-phase liquid state throughout the test, and to maintain a certain temperature and pressure margin to avoid measurement distortion or pump cavitation damage caused by liquid ammonia vaporization.

[0024] Furthermore, in the aforementioned research tasks, the pumps under test typically need to undergo environmental assessments such as vibration experiments. Performance comparison tests must be conducted on the same testing system before and after vibration to evaluate the impact of vibration on pump performance. This requires the testing system to have the capability for rapid disassembly and retesting of the pump under test, while maintaining the working fluid state and operating parameters of the remaining parts of the circuit as unchanged as possible during disassembly and reassembly. This ensures consistency of operating conditions between the two tests, making the performance change assessment results reliable. Simultaneously, given the toxicity and environmental safety risks of liquid ammonia, the testing system must also be equipped with appropriate leak monitoring and ventilation facilities to prevent liquid ammonia leaks that could cause personal injury and environmental pollution.

[0025] Therefore, this application proposes a comprehensive performance testing system for liquid ammonia closed-loop pumps, such as... Figure 1 The diagram shows the experimental setup of the liquid ammonia closed-loop pump comprehensive performance testing system in this embodiment. The system, along the liquid ammonia flow direction, includes a storage tank, a filter, a pump under test, a mass flow meter, a flow control valve, and a heat exchanger. The heat exchanger outlet returns to the storage tank, forming a closed loop. The storage tank has a filler / drain valve at the top. Differential pressure sensors are connected before and after the filter. The inlet pressure measuring section of the pump under test is equipped with a pressure gauge and a temperature sensor. The pump body has a speed detection interface, and a differential pressure sensor is connected between the inlet and outlet. The outlet pressure measuring section of the pump under test is equipped with a pressure gauge and a temperature sensor. A refrigeration unit is connected to the cold side of the heat exchanger. The diagram labels the corresponding symbols for the mass flow meter, flow control valve, filter, differential pressure sensor, filler / drain valve, pressure gauge, and temperature sensor.

[0026] like Figure 1 The liquid ammonia closed-loop pump comprehensive performance testing system of this embodiment includes a closed-loop circulation system. After initial commissioning or pump section reassembly, the system requires the following preparatory steps: First, the entire closed-loop circulation system is evacuated by connecting the filler / drain valve to the vacuum pump, then purged with dry nitrogen gas, repeated several times to reduce air and moisture content within the loop. Next, liquid ammonia is injected into the loop through the liquid ammonia filling port, monitoring the pressure and temperature of the reservoir during the injection process until the liquid ammonia injection volume meets the loop circulation requirements. Finally, the water chiller and heat exchanger are started to adjust the liquid ammonia temperature to the target test temperature, and it is confirmed that the pressure and temperature of the inlet pressure measuring section of the pump under test meet the subcooling requirements. After completing the above preparations, the liquid ammonia circulates in the loop along a fixed flow direction, sequentially flowing through the reservoir, filter, inlet pressure measuring section of the pump under test, the pump under test, outlet pressure measuring section of the pump under test, mass flow meter, flow regulating valve, and heat exchanger. The liquid ammonia outlet of the heat exchanger is connected to the inlet of the storage tank, the liquid ammonia outlet of the storage tank is connected to the inlet of the filter, and the filter outlet is connected to the pressure measuring section of the inlet of the pump under test. This connection sequence ensures that after the liquid ammonia completes heat exchange in the heat exchanger, it first enters the storage tank for pressure stabilization and buffering, and then passes through the filter to enter the pump under test, thus guaranteeing that the liquid ammonia is in a stable state before entering the pump under test.

[0027] In this embodiment, the heat exchanger adopts a liquid ammonia-water countercurrent heat exchange structure. Its designed heat exchange capacity is selected based on 1.2 times the maximum input power of the pump under test, with a heat exchange area margin of no less than 20% to ensure that the heat exchanger still has sufficient heat exchange capacity when the pump under test is running at full load and the liquid ammonia temperature rise needs to be rapidly suppressed. A water chiller connected to the cold side of the heat exchanger provides circulating cooling water, and its cooling capacity is also configured according to the above 1.2 times principle. Therefore, the controller can adjust the cooling power output of the water chiller to quickly lower or slowly raise the liquid ammonia temperature, meeting the requirements of different test conditions for the liquid ammonia inlet state.

[0028] The liquid reservoir is a bladder-type reservoir, with a pre-filled nitrogen bladder inside, which divides the interior of the reservoir into a gas chamber and a liquid ammonia chamber. Figure 2 The diagram shows a schematic of the bladder-type liquid reservoir structure in this embodiment. Dry nitrogen gas is filled into the gas chamber, and the liquid ammonia chamber is connected to a closed-loop circuit. When the liquid ammonia in the circuit expands due to increased temperature, it enters the reservoir and compresses the gas chamber, reducing its volume and increasing the nitrogen pressure accordingly. This absorbs the increase in liquid ammonia volume and prevents a sharp rise in circuit pressure. When the liquid ammonia contracts in volume due to decreased temperature, the gas chamber expands under nitrogen pressure, pushing the liquid ammonia back into the circuit and compensating for the pressure drop caused by the volume contraction. The pre-filling nitrogen pressure of the gas chamber is set according to the saturated vapor pressure corresponding to the lowest operating temperature of the liquid ammonia, denoted as Ppre. Its value satisfies Ppre = k × Psatmin, where Psatmin is the saturated vapor pressure of liquid ammonia at the lowest operating temperature, and k is the pre-filling pressure coefficient, typically between 0.85 and 0.95. Saturated vapor pressure is the pressure value at which liquid ammonia begins to vaporize at a specific temperature; the higher the temperature, the greater the saturated vapor pressure.

[0029] The pressure measuring section at the inlet of the pump under test is equipped with a pressure sensor and a temperature sensor, and inlet differential pressure sensors are installed before and after the filter; the controller is connected to the pressure sensor, temperature sensor, inlet differential pressure sensor, heat exchanger, and flow regulating valve; The controller adjusts the heat exchanger according to the pressure sensor and temperature sensor so that the temperature of the liquid ammonia at the inlet of the pump under test is lower than the saturation temperature corresponding to the inlet pressure; the controller monitors the inlet pressure drop caused by filter blockage according to the inlet differential pressure sensor and pressure sensor to determine whether liquid ammonia vaporization has occurred at the inlet of the pump under test.

[0030] In this embodiment, a pressure sensor and a temperature sensor are arranged at the inlet pressure measurement section of the pump under test to measure the liquid ammonia pressure (Pin) and temperature (Tin) at that location in real time, respectively. Pressure measurement interfaces are arranged at the front and rear ends of the filter, with an inlet differential pressure sensor bridging the two interfaces to measure the pressure difference ΔPfilter before and after the liquid ammonia flows through the filter. The controller establishes signal connections with the aforementioned pressure sensor, temperature sensor, inlet differential pressure sensor, heat exchanger, and flow control valve. By collecting real-time data from each sensor, the controller adjusts the cooling power of the heat exchanger and the opening of the flow control valve.

[0031] The controller acquires the liquid ammonia pressure (Pin) and temperature (Tin) in real time using pressure and temperature sensors at the inlet of the pump under test. There is a one-to-one correspondence between the saturated vapor pressure and temperature of liquid ammonia; the saturated vapor pressure corresponding to the current temperature (Tin) is denoted as Psat. The controller internally stores data on the correspondence between the saturated vapor pressure and temperature of liquid ammonia, or calculates Psat using the thermodynamic equation of state.

[0032] The controller compares the measured pressure Pin with the saturated vapor pressure Psat. When Pin is greater than Psat, it indicates that the liquid ammonia is in a liquid state and has a certain pressure margin. This pressure margin can be characterized by the net positive suction head (NPSHa), which is the difference between the liquid ammonia pressure head and the saturated vapor pressure head at the pump inlet pressure measurement section, minus the inlet pipeline losses. For example, under the condition of 20°C inlet temperature, the saturated vapor pressure of liquid ammonia is approximately 0.857 MPa. If a 3°C subcooling is required, the inlet liquid ammonia temperature should not exceed 17°C. Based on this, the controller maintains the inlet pressure at a level not lower than the saturated vapor pressure corresponding to this subcooling temperature. Alternatively, equivalently, when maintaining an inlet temperature of 20°C, the inlet pressure should not be lower than the saturated vapor pressure of approximately 0.943 MPa corresponding to 23°C, thus ensuring that NPSHA is greater than the required NPSHr provided by the pump manufacturer, preventing cavitation damage to the pump under test. The controller adjusts the cooling power of the heat exchanger to lower or maintain the liquid ammonia temperature Tin below the saturation temperature corresponding to the current pressure Pin, thereby ensuring that the liquid ammonia at the inlet of the pump under test remains in a liquid state and does not vaporize. The saturation temperature is the temperature at which liquid ammonia begins to vaporize at the current pressure Pin; as long as the actual temperature is below this saturation temperature, the liquid ammonia will not vaporize.

[0033] During testing, impurities gradually accumulate in the filter, leading to increased flow resistance. The differential pressure ΔPfilter measured by the inlet differential pressure sensor increases accordingly, indicating increased pressure loss of liquid ammonia after passing through the filter. This, in turn, causes a decrease in the actual pressure Pin at the inlet of the pump under test. The controller continuously monitors the trends of ΔPfilter and Pin. When ΔPfilter increases to the point that Pin approaches the saturated vapor pressure Psat corresponding to the current temperature Tin, the risk of liquid ammonia vaporization at the inlet of the pump under test increases significantly. At this point, the controller determines that liquid ammonia vaporization is occurring at the inlet of the pump under test and outputs corresponding control commands, such as reducing the opening of the flow regulating valve to decrease loop resistance, or prompting the operator to replace the filter element to prevent cavitation damage to the pump under test due to liquid ammonia vaporization.

[0034] Furthermore, in this embodiment, the pre-filled nitrogen pressure of the airbag is set according to the saturated vapor pressure corresponding to the lowest operating temperature of liquid ammonia; the airbag is compressed when the liquid ammonia temperature rises and expands in volume, and expands when the liquid ammonia temperature falls and contracts in volume to compensate for the volume of liquid ammonia in the circuit.

[0035] Specifically, the pre-charge nitrogen pressure of the airbag is determined based on the saturated vapor pressure of liquid ammonia at the system's lowest operating temperature. Let the lowest operating temperature be Tmin, and the saturated vapor pressure of liquid ammonia at that temperature be Psatmin. The pre-charge nitrogen pressure Ppre of the airbag satisfies the relationship Ppre = k × Psatmin, where k is the pre-charge pressure coefficient. This coefficient is typically taken as a value between 0.85 and 0.95, ensuring that the pre-charge pressure is lower than the system's lowest operating pressure while guaranteeing sufficient expansion capacity of the airbag under cryogenic conditions. The purpose of this setting is that when the liquid ammonia temperature decreases and its volume shrinks, the nitrogen pressure inside the airbag is higher than the liquid ammonia chamber pressure, allowing the airbag to fully expand and push the liquid ammonia back into the main circuit, preventing the liquid ammonia chamber in the reservoir from emptying and causing the airbag to bottom out and lose its compensating ability.

[0036] Changes in the temperature of liquid ammonia cause changes in the total volume of liquid ammonia in the circuit, and the gasbag provides bidirectional dynamic compensation accordingly. When the temperature of liquid ammonia rises, its volume expands, and the expansion enters the liquid ammonia chamber of the reservoir, compressing the gasbag. The nitrogen gas inside the gasbag follows a polytropic compression law; as the pressure increases, the volume decreases, thus absorbing the increase in liquid ammonia volume and suppressing a sharp rise in system pressure. When the temperature of liquid ammonia decreases, its volume contracts, the pressure in the liquid ammonia chamber drops, and the gasbag expands under the pressure of the nitrogen gas, pushing the liquid ammonia back into the circuit to compensate for the contracted volume and maintain stable system pressure. Let the initial volume of the gasbag be V0, the maximum volume of the gasbag after expansion under low-temperature conditions be V1, and the minimum volume of the gasbag after compression under high-temperature conditions be V2. Then, the effective working stroke of the gasbag is the difference between V1 and V2, and this difference should not be less than the total volume expansion of liquid ammonia within the temperature change range.

[0037] Furthermore, in this embodiment, when the liquid ammonia temperature rises to the maximum operating temperature, the remaining volume of the compressed airbag is not less than a set proportion of the original volume of the airbag, so as to ensure that the liquid ammonia chamber of the reservoir has sufficient space to accommodate the expansion of liquid ammonia.

[0038] Specifically, when the liquid ammonia temperature rises to the maximum operating temperature Tmax, the volume expansion of the liquid ammonia reaches its maximum, and the gasbag is compressed to its minimum working volume V2. To ensure that the liquid ammonia chamber of the reservoir has sufficient expansion space and to prevent the gasbag from being completely compressed, leading to system pressure runaway, V2 must not be less than a set proportion of the original gasbag volume V0. That is, V2 ≥ α × V0, where α is the remaining volume proportion coefficient, typically taken as 0.2 to 0.3. This constraint means that the gasbag retains 20% to 30% of its original volume as remaining space even under maximum compression, thereby ensuring that the liquid ammonia chamber can continuously accommodate the expanding liquid ammonia while preventing the nitrogen pressure from exceeding the safe range due to over-compression.

[0039] The selection of the nominal volume of the reservoir is directly related to the total volume of liquid ammonia involved in temperature changes in the system. Let Vsys be the sum of the rigid volume of the main circuit and the minimum liquid volume held on the ammonia side of the reservoir. When liquid ammonia rises from its lowest operating temperature to its highest operating temperature, the volume expansion ΔV is approximately 0.10Vsys. Since the gasbag contains pre-filled nitrogen, the liquid ammonia expansion volume that the reservoir can absorb is related to the effective compression stroke of the gasbag. After multivariate process calculations and the introduction of a safety factor, the original gasbag volume V0 is approximately equal to the nominal volume of the gasbag reservoir. Therefore, the nominal volume of the reservoir is usually taken as 40% to 50% of the total liquid ammonia volume Vsys of the system, i.e., V0 ≈ (0.4~0.5) × Vsys. For example, when Vsys is 10L, it is recommended to use a gasbag reservoir with a nominal volume of 5L to 6L. In this case, the original gasbag volume V0 is approximately 5L to 6L to ensure that the gasbag has sufficient compression and expansion strokes throughout the entire operating temperature range.

[0040] The initial volume V0 of the airbag must satisfy both the pre-charge pressure constraint and the remaining volume constraint. Based on the volume expansion ΔV of liquid ammonia between the lowest operating temperature Tmin and the highest operating temperature Tmax, and the polytropic process equation Ppre × V1^n = Pmax × V2^n, where Pmax is the nitrogen pressure at the highest operating temperature and n is the nitrogen polytropic index (1.0 for slow temperature changes, 1.2 to 1.4 for rapid pressure fluctuations, and 1.4 for conservative calculations), the relationship between V0 and Ppre can be established. In engineering design, the expansion ΔV is first calculated based on the total liquid ammonia volume and temperature range. Then, combined with the pre-charge pressure coefficient k and the remaining volume proportionality coefficient α, a reasonable value for the initial volume V0 of the airbag is determined, ensuring that the airbag has sufficient compression and expansion stroke throughout the entire operating temperature range.

[0041] Furthermore, the system also includes three-way ball valves located at the inlet and outlet of the pump under test. The three-way ball valves have an on-state and a partial isolation state. When the three-way ball valves are switched to the partial isolation state, the connection between the pump under test and its adjacent pipe section is cut off.

[0042] Specifically, in this embodiment, a three-way ball valve is installed at both the inlet and outlet of the pump under test. This three-way ball valve has two operating states: a continuous operating state and a partial isolation state. In the continuous operating state, the three-way ball valve connects to the main pipeline of the closed-loop circulation circuit, allowing the liquid ammonia to circulate normally. In the partial isolation state, the three-way ball valve disconnects the pump under test from its adjacent upstream and downstream pipe sections.

[0043] Furthermore, the system also includes a recovery device, a vacuum device, a nitrogen purging device, and a filler / exhaust valve; the filler / exhaust valve is connected to the pump under test and its adjacent pipe sections, and the filler / exhaust valve is selectively connected to the recovery device, the vacuum device, or the nitrogen purging device; when the three-way ball valve is switched to the partial isolation state, the connection between the pump under test and its adjacent pipe sections is cut off, and the rest of the closed-loop circulation loop remains in a sealed pressurized state.

[0044] Specifically, in this embodiment, the system is equipped with a recovery device, a vacuum pumping device, a nitrogen purging device, and a purging valve as auxiliary equipment. The recovery device is a sealed pressure vessel used to receive liquid ammonia discharged from the purging valve. The vacuum pumping device is a vacuum pump unit used to evacuate the isolated pump section and adjacent short pipe sections. The nitrogen purging device is a dry nitrogen source used to fill the evacuated pump section with nitrogen to reduce the residual ammonia concentration. A purging valve is installed on the pipe section between the two three-way ball valves at the inlet and outlet of the pump under test. This purging valve has multiple external interfaces, which selectively connect to the recovery device, the vacuum pumping device, and the nitrogen purging device, respectively.

[0045] When the pump under test needs to be replaced or maintained, the operator switches the three-way ball valves at the inlet and outlet of the pump to the partial isolation state. At this time, the three-way ball valves disconnect the pump under test from its adjacent pipe sections before and after it, isolating the pump and the two short pipe sections directly connected to it, forming an independent local pipe section. Meanwhile, the rest of the closed-loop circuit—the liquid receiver, heat exchanger, filter, mass flow meter, flow control valve, and connecting pipes—remains in a sealed, pressurized state, and the internal temperature and pressure parameters of the liquid ammonia remain unchanged.

[0046] After partial isolation is completed, operators use the venting valve to guide the liquid ammonia in the isolation section into the recovery device under residual pressure. Once the liquid ammonia is drained, the venting valve is switched to connect to the vacuum device to evacuate the isolation section; then, the venting valve is switched to connect to the nitrogen purging device to fill the section with dry nitrogen. After several alternating vacuuming and nitrogen purging operations, the ammonia concentration in the isolation section drops to a safe level. The pump under test can then be disassembled for replacement or repair. After reinstalling the new or original pump, the pump section is evacuated again using the venting valve and purged with nitrogen, and finally, liquid ammonia is injected to restore operation. Throughout the entire disassembly and reassembly process, the liquid ammonia working fluid in the remaining parts of the main circuit does not need to be discharged; its temperature, pressure, and filling volume remain consistent with before isolation, thus significantly shortening the preparation time before retesting and ensuring the consistency of operating conditions for performance comparison tests before and after the vibration experiment.

[0047] Furthermore, the controller is connected to the drive end of the pump under test to obtain the rotational speed of the pump under test; the system also includes an electrical parameter acquisition unit connected to the power supply circuit of the pump under test motor, and the electrical parameter acquisition unit is connected to the controller; the controller adjusts the opening of the flow regulating valve according to the rotational speed of the pump under test, so that the pump under test can operate under different rotational speeds and different flow conditions.

[0048] Specifically, in this embodiment, the controller is connected to the drive end of the pump under test to directly obtain the actual rotational speed of the pump shaft, denoted as n. The system is equipped with an electrical parameter acquisition unit, which is connected to the motor power supply circuit of the pump under test. This unit measures the input voltage, current, and power factor of the motor, and calculates the input electrical power of the pump, denoted as Pe. The electrical parameter acquisition unit uploads the real-time data to the controller.

[0049] During pump performance testing, the controller first obtains the current speed n from the drive end of the pump under test and maintains this speed constant. Subsequently, the controller gradually adjusts the opening of the flow control valve, changing it point by point from fully open to closed, with each opening corresponding to a stable flow condition.

[0050] In this embodiment, the mass flow meter uses the Coriolis principle to directly measure the mass flow rate Q of liquid ammonia. Its range covers the entire range of the pump under test, from the minimum stable flow rate to the maximum flow rate, and its pressure resistance rating is not lower than the highest working pressure of the circuit to avoid sensor damage under high-pressure conditions of liquid ammonia. A flow regulating valve is installed downstream of the mass flow meter. Its flow coefficient is selected according to the variable pressure drop that the pump under test needs to withstand at its rated head. The valve opening range, from fully open to fully closed, can generate sufficient and continuously variable circuit resistance, thereby enabling the pump under test to operate stably at different flow rate points. At each operating point, the controller records the mass flow rate Q measured by the mass flow meter, the pressure difference ΔPpump measured by the pump inlet and outlet pressure differential sensors, and the input power Pe measured by the electrical parameter acquisition unit. Based on the liquid ammonia density ρ and the pressure difference ΔPpump, the head H is calculated using the formula H = ΔPpump / (ρ × g), where g is the acceleration due to gravity; then, the pump efficiency η is calculated using the formula η = (ρ × g × Q × H) / Pe. After completing all flow rate tests at the current speed, the controller changes the speed of the pump under test to another set value n', and repeats the process of adjusting the flow regulating valve point by point and recording the data. By obtaining the correspondence between flow rate and head, flow rate and power, and flow rate and efficiency at different speeds, a family of performance curves of the pump under test at different speeds can be plotted.

[0051] Furthermore, the controller controls the heat exchanger to raise the temperature of the liquid ammonia, so that the inlet temperature of the liquid ammonia of the pump under test approaches the saturation temperature corresponding to the inlet pressure; the airbag contracts accordingly when the liquid ammonia volume expands, so as to absorb the volume of liquid ammonia that expands due to the temperature increase.

[0052] Specifically, in this embodiment, cavitation occurs when liquid ammonia vaporizes in a localized area at the pump inlet where the pressure is lower than its saturated vapor pressure. This vaporization forms bubbles that then flow into the high-pressure zone within the pump and collapse, causing impeller erosion and a sudden drop in performance. To determine the cavitation initiation point of the pump under test, the controller reduces the cooling power of the heat exchanger or switches it to heating mode, gradually increasing the temperature of the liquid ammonia flowing through the heat exchanger. As the liquid ammonia temperature rises, the temperature Tin at the pump inlet pressure measurement section gradually approaches the saturation temperature Tsat corresponding to the pressure Pin at that point. When the difference between Tin and Tsat, i.e., the subcooling margin, decreases to a critical value, a significant drop in pump head occurs, at which point cavitation is determined to have occurred.

[0053] During the aforementioned heating process, the total volume of liquid ammonia in the circuit expands due to the increased temperature. The expanded liquid ammonia enters the liquid ammonia chamber of the reservoir, compressing the gas bladder. The gas bladder contracts accordingly, increasing the internal nitrogen pressure and absorbing the volume increase, thus preventing an abnormal rise in circuit pressure due to the expansion of liquid ammonia. This dynamic buffering effect of the gas bladder, in conjunction with the heat exchanger's temperature control, allows the system to safely and continuously regulate the inlet liquid ammonia state without additional liquid ammonia discharge, until the cavitation critical point is reached.

[0054] Furthermore, when conducting performance comparison tests before and after replacing the pump under test, the three-way ball valves at the inlet and outlet of the pump under test are switched to a partial isolation state, and the liquid ammonia in the pump under test and its adjacent pipe section is discharged into the recovery device through the discharge valve; After replacing the pump under test, the pump under test and its adjacent pipe sections are evacuated and purged with nitrogen through the filler and drain valves, and then filled with liquid ammonia. The liquid ammonia working medium and operating parameters of the remaining parts of the closed-loop circuit remain consistent with those before the replacement.

[0055] Specifically, in this embodiment, when performing performance comparison tests on the pump under test before and after replacement, the local isolation function of a three-way ball valve is used to achieve rapid disassembly and assembly of the pump section while maintaining the operating condition of the rest of the circuit. Performance comparison testing refers to measuring and comparing the performance parameters of the same pump under test before and after undergoing a specific experimental treatment to evaluate the impact of the experimental treatment on pump performance. For example, before and after a vibration test, the same pump under test needs to be installed in this system for performance testing. A set of baseline data is measured before vibration, and the changes in head, flow rate, and efficiency are remeasured and compared after vibration.

[0056] Before replacing the pump under test, switch the three-way ball valves at the inlet and outlet of the pump under test to the partial isolation state. At this time, the three-way ball valves disconnect the pump under test from the adjacent pipe sections before and after it. The pump under test and its two adjacent short pipe sections are cut off, forming an independent local pipe section. The rest of the closed-loop circuit, including the liquid receiver, filter, heat exchanger, mass flow meter, flow control valve and connecting pipelines, remains in a closed pressurized state. The internal liquid ammonia temperature is recorded as T0, the pressure as P0, and the filling volume as M0. These parameters remain unchanged before and after the isolation operation.

[0057] Liquid ammonia in the isolation section is introduced into the recovery device under residual pressure via the venting valve. After the liquid ammonia is drained, the venting valve is switched to connect to the vacuum pump to evacuate the isolation section. Then, the venting valve is switched to connect to the nitrogen purging device to purge the section with dry nitrogen. After several alternating vacuuming and nitrogen purging operations, the ammonia concentration in the isolation section is reduced to a safe level, at which point the pump under test can be disassembled. The disassembled pump is then externally treated or replaced with a new pump before being reinstalled at its original location.

[0058] After reassembly, the pump section and adjacent short pipes were evacuated and purged with nitrogen again using the venting valve to eliminate internal air and moisture. Then, liquid ammonia was injected into the isolation pipe section through the venting valve until its pressure and temperature matched the current P0 and T0 of the main circuit. Finally, the three-way ball valve was switched back to the operating state, reconnecting the pump under test to the closed-loop circuit. Because the main circuit remained in a closed, pressurized state during isolation, its liquid ammonia working fluid was not discharged, and the temperature, pressure, and injection volume remained consistent with those before replacement. Therefore, after reassembly, it was not necessary to re-evacuate, purge with nitrogen, and recharge the entire circuit. The system could quickly return to its stable operating conditions before replacement, allowing for direct performance retesting. The consistency of the operating conditions between the two tests was ensured by the closed nature of the main circuit, thus ensuring the reliability of the performance comparison data.

[0059] Furthermore, the system also includes an ammonia leak detector and an exhaust system.

[0060] Specifically, in this embodiment, the system is also equipped with a safety valve as a pressure safety boundary for the closed-loop circuit. The set pressure of the safety valve is determined based on the allowable working pressure of the weakest pressure-bearing component of the system and the maximum pressure at the pump outlet. When the circuit pressure rises to the set pressure due to abnormal operating conditions, the safety valve automatically opens to release pressure, preventing the pipeline or reservoir from rupturing due to overpressure. In addition, the system is also equipped with an ammonia leak detector and an exhaust system. The ammonia leak detector is placed in potential leakage risk areas such as the pump under test, valve interfaces, and pipeline connections within the experimental site to monitor the ammonia concentration in the ambient air in real time. The exhaust system includes two independent ventilation paths: conventional mechanical ventilation and emergency exhaust. The emergency exhaust has a greater air exchange capacity to cope with sudden leakage conditions, reduce the ammonia concentration in the experimental site, and prevent ammonia from accumulating indoors to a concentration range that endangers human health or is flammable.

[0061] The above description is merely an embodiment of this application and is not intended to limit the scope of protection of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A comprehensive performance testing system for a liquid ammonia closed-loop pump, characterized in that, The system includes a closed-loop circulation system, which sequentially comprises a reservoir, a filter, a pressure measuring section at the inlet of the pump under test, the pump under test, a pressure measuring section at the outlet of the pump under test, a mass flow meter, a flow regulating valve, and a heat exchanger along the liquid ammonia flow direction. The liquid ammonia side outlet of the heat exchanger is connected to the inlet of the reservoir, the liquid ammonia chamber outlet of the reservoir is connected to the inlet of the filter, and the filter outlet is connected to the pressure measuring section at the inlet of the pump under test. The liquid storage device is a bladder-type liquid storage device, which has a pre-filled nitrogen bladder inside, and the bladder divides the interior of the liquid storage device into a gas chamber and a liquid ammonia chamber. The pressure measuring section at the inlet of the pump under test is equipped with a pressure sensor and a temperature sensor, and inlet differential pressure sensors are installed before and after the filter; the controller is connected to the pressure sensor, temperature sensor, inlet differential pressure sensor, heat exchanger, and flow regulating valve; The controller adjusts the heat exchanger according to the pressure sensor and temperature sensor so that the temperature of the liquid ammonia at the inlet of the pump under test is lower than the saturation temperature corresponding to the inlet pressure. The controller monitors the inlet pressure drop caused by filter blockage based on the inlet differential pressure sensor and the pressure sensor to determine whether liquid ammonia vaporization has occurred at the inlet of the pump under test.

2. The comprehensive performance testing system for liquid ammonia closed-loop pumps according to claim 1, characterized in that, The pre-filled nitrogen pressure of the airbag is set according to the saturated vapor pressure corresponding to the lowest operating temperature of liquid ammonia. The airbag is compressed when the liquid ammonia temperature rises and its volume expands, and expands when the liquid ammonia temperature falls and its volume contracts to compensate for the volume of liquid ammonia in the circuit.

3. The comprehensive performance testing system for liquid ammonia closed-loop pumps according to claim 2, characterized in that, When the liquid ammonia temperature rises to the maximum operating temperature, the remaining volume of the compressed airbag is not less than a set proportion of the original volume of the airbag, so as to ensure that the liquid ammonia chamber of the reservoir has sufficient space to accommodate the expansion of liquid ammonia.

4. The comprehensive performance testing system for liquid ammonia closed-loop pumps according to claim 1, characterized in that, The system also includes three-way ball valves located at the inlet and outlet of the pump under test, the three-way ball valves having an on-state and a partially isolated state; When the three-way ball valve switches to the partial isolation state, it disconnects the pump under test from its adjacent pipe section.

5. The comprehensive performance testing system for a liquid ammonia closed-loop pump according to claim 4, characterized in that, The system also includes a recovery device, a vacuum device, a nitrogen purging device, and a filling and exhaust valve; The addition and discharge valve is connected to the pump under test and its adjacent pipe section, and the addition and discharge valve is selectively connected to the recovery device, the vacuum device or the nitrogen replacement device; When the three-way ball valve switches to the partial isolation state, it cuts off the connection between the pump under test and its adjacent pipe section, and the rest of the closed circulation loop remains in a closed pressurized state.

6. The comprehensive performance testing system for a liquid ammonia closed-loop pump according to claim 1, characterized in that, The system also includes an electrical parameter acquisition unit connected to the drive end of the pump under test, and the electrical parameter acquisition unit is connected to the controller. The controller obtains the rotational speed of the pump under test and adjusts the opening of the flow regulating valve to enable the pump under test to operate under different rotational speeds and flow rates.

7. The comprehensive performance testing system for a liquid ammonia closed-loop pump according to claim 6, characterized in that, The controller controls the heat exchanger to raise the temperature of liquid ammonia, so that the inlet liquid ammonia temperature of the pump under test approaches the saturation temperature corresponding to the inlet pressure. The airbag contracts accordingly as the liquid ammonia expands, in order to absorb the volume of liquid ammonia that expands due to the increase in temperature.

8. The comprehensive performance testing system for a liquid ammonia closed-loop pump according to claim 5, characterized in that, When performing a performance comparison test before and after replacing the pump under test, the three-way ball valves at the inlet and outlet of the pump under test are switched to a partial isolation state, and the liquid ammonia in the pump under test and its adjacent pipe section is discharged into the recovery device through the discharge valve. After replacing the pump under test, the pump under test and its adjacent pipe sections are evacuated and purged with nitrogen through the filler and drain valves, and then filled with liquid ammonia. The liquid ammonia working medium and operating parameters of the remaining parts of the closed-loop circuit remain consistent with those before the replacement.

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