A porous metal evaporator liquid supply control method based on thermal load feedforward and phase state feedback

Abstract

The application discloses a kind of based on heat load feedforward and phase state feedback's porous metal evaporator liquid supply control method.Acquire evaporator heat load, according to working fluid vaporization latent heat calculation theory evaporation mass flow, and with target liquid supply ratio form target liquid supply mass flow;According to the calibration relationship of pump driving quantity and flow, feedforward driving quantity is generated.Actual liquid supply flow, vapor absolute pressure, vapor temperature or installation surface temperature and excess liquid flow or liquid level are collected, and saturation temperature is determined by absolute pressure and forms pressure correction temperature difference or vapor superheat degree.Controller identifies normal, excess liquid supply, local dry risk, sensor abnormality or branch abnormality state according to the foregoing feedback quantity, limited amplitude correction is carried out to feedforward driving quantity, and when dry risk or branch abnormality, increase liquid supply, reduce heat load or isolate branch.

Description

Technical Field

[0001] This invention relates to the field of liquid supply control in pump-driven two-phase thermal control systems, specifically to a liquid supply control method and control system for porous metal evaporators with independent liquid inlets, residual liquid outlets, and vapor outlets, employing a combination of heat load feedforward and absolute pressure correction phase feedback. Background Technology

[0002] The porous metal evaporator supplies liquid to the evaporation interface through a porous capillary structure. The liquid working fluid absorbs heat and transforms into vapor. A mechanical pump provides the main driving force for the loop. The liquid supply flow rate must cover the theoretical evaporation consumption and also reserve a margin to maintain liquid continuity and discharge excess liquid. Insufficient liquid supply may lead to local evaporation interface shrinkage, increased mounting surface temperature, or vapor overheating; excessive liquid supply will increase pump work and return flow rate, and may occupy the vapor discharge space.

[0003] Feedback control that uses only the mounting surface temperature as the controlled variable has at least three limitations. First, the heating unit, mounting interface, and evaporator base have thermal inertia, and temperature changes usually lag behind changes in heat load. Second, the saturation temperature of the working fluid varies with the absolute pressure of the loop, and using the same absolute temperature threshold at different pressures can confuse normal pressure drift with heat transfer deterioration. Third, anomalies in a single temperature signal, changes in local contact thermal resistance, or sensor detachment can also manifest as temperature rises, and a single threshold cannot reliably distinguish between the risk of drying out and sensor failure.

[0004] While conventional flow rate setpoint control can maintain the pump outlet flow rate, it cannot automatically adjust theoretical evaporation consumption according to changes in heat load and latent heat of vaporization. Conventional temperature proportional-integral-derivative control mainly relies on feedback errors and may not utilize the residual liquid continuity information provided by the independent residual liquid outlet. Therefore, a control method is needed that predicts evaporation demand based on heat load, corrects the temperature reference with absolute pressure, and identifies the operating status by combining actual flow rate, residual liquid state, and vapor state. Summary of the Invention

[0005] The technical problem to be solved by this invention is: how to first give the liquid supply feedforward based on energy conservation when the heat load changes, and then use multi-parameter phase state information to make limited amplitude correction to the feedforward under the conditions of loop pressure change, residual liquid fluctuation and sensor abnormality, so that the liquid supply control does not depend on a single fixed temperature threshold.

[0006] For the i-th porous metal evaporator, the theoretical evaporation mass flow rate is: Qi represents the effective heat load input to the i-th evaporator, hvaporization, and i represents the latent heat of vaporization of the working fluid under the corresponding pressure and state. For N evaporators, the target total liquid supply mass flow rate can be expressed as: α is the target liquid supply ratio. For multi-stage systems with series liquid circuits, the target flow rate can be calculated step by step based on the minimum liquid supply ratio of the final stage and the evaporation consumption of each upstream stage; for fully parallel systems, it can be allocated according to the theoretical evaporation of each branch, the target liquid supply ratio, and the branch priority.

[0007] The actual liquid supply ratio can be expressed as: When controlling only one evaporator, the summation term degenerates into the theoretical evaporation mass flow rate of that evaporator. Different target liquid supply ratios can be used during startup, load increase, normal operation, load decrease, and shutdown. To reduce command abrupt changes, upper and lower limits, slope limits, or first-order filters are set for the α and m targets.

[0008] The liquid supply controller 380 obtains the absolute pressure input of vapor 383 and, according to the pressure-saturation temperature relationship of the selected working fluid, obtains: The pressure-corrected temperature difference at the mounting surface is: The steam superheat is: Using absolute pressure allows for the differentiation between the saturation temperature shift caused by changes in loop pressure and the temperature rise of the mounting surface relative to saturation. Property relationships can be stored as lookup table data, piecewise polynomials, or property program interfaces. During formal implementation, pressure units and temperature scales should be standardized, and extrapolation should be prohibited or conservative mode should be entered when property data exceeds the specified range.

[0009] Non-condensable gases may cause the measured total pressure to no longer equal the partial pressure of the working fluid. Therefore, the controller can compare the vapor temperature with the corresponding saturation temperature, pressure at different locations, pressure change rate, and vacuum or venting status. When these signals are inconsistent, the pressure correction is marked as low confidence and is not used alone to reduce the fluid supply.

[0010] like Figures 2 to 4 As shown, the heat load input 381 first enters the evaporation calculation module. The calculated target flow rate is converted into pump speed, drive voltage, current, or frequency through pump calibration relationships, forming a feedforward drive quantity. Pump calibration relationships can be established separately for different inlet pressure, temperature, or working fluid viscosity ranges.

[0011] The mass flow input of 382 constitutes the inner loop of the actual flow rate. The inner loop only compensates for pump calibration deviations and loop resistance changes, and its output is limited by the permissible drive range and rate of change of the mechanical pump. The phase feedback is located in the outer layer, which corrects for temperature difference, vapor superheat, residual liquid state, and slow or graded temperature rise rate adjustments based on pressure. This avoids high-frequency pump operation directly caused by temperature noise from the outer layer.

[0012] The controller must identify at least the following five states: 1) Normal state: The actual liquid supply flow rate is within the target range, the residual liquid is continuous or meets the set conditions, and the pressure-corrected temperature difference and steam superheat are within the allowable range of the corresponding heat load. 2) Excessive liquid supply state: The residual liquid flow rate or liquid level is continuously higher than the upper limit, and the pressure-corrected temperature difference and steam superheat do not indicate insufficient liquid supply. 3) Local dry-out risk state: The pressure-corrected temperature difference, steam superheat, or local temperature dispersion of the mounting surface increases, and at least one of the following conditions is met: residual liquid decreases, actual liquid supply ratio is low, or steam pressure fluctuations. 4) Sensor abnormal state: The signal exceeds the range, the rate of change is unreasonable, redundant sensors are inconsistent, or there is a significant contradiction with the energy conservation relationship. 5) Branch abnormal state: One branch of multiple evaporators exhibits continuous deviations in flow rate, pressure, temperature, or residual liquid under the same control command.

[0013] The status determination employs persistence conditions, hysteresis, and risk levels to avoid frequent switching caused by instantaneous signal exceeding limits. Thresholds can be set according to the working fluid, evaporator structure, heat load range, and sensor uncertainty; this invention does not require a fixed response time.

[0014] When the risk of localized drying is low, the target liquid supply ratio can be slightly increased; when the risk continues to increase, the liquid supply within the upper limit of the pump drive should be increased and the corresponding heat source load should be reduced; when the risk reaches the isolation level or the branch pressure drop is abnormal, the abnormal branch should be isolated and the system should be derated.

[0015] Under excessive liquid supply conditions, the target liquid supply ratio is reduced at a limited rate. If the pressure signal is invalid but the residual liquid signal is still valid, a conservative liquid supply can be maintained. If the flow sensor is invalid, the pump can be operated temporarily based on the pump calibration value and the residual liquid status; if there is no alternative signal from the temperature or pressure sensor, rapid action to reduce liquid supply is prohibited, and the heat load can be reduced. Beneficial effects

[0016] The heat load feedforward directly changes the theoretical evaporation demand when the power of the heating unit changes, reducing the reliance on adjusting the liquid supply only after the installation surface temperature deviates significantly.

[0017] Using the saturation temperature corresponding to the absolute pressure as a dynamic reference, the risk quantity of the same phase state can adapt to changes in loop pressure, reducing the possibility of mistaking pressure drift as a change in heat transfer state when the fixed temperature threshold is used.

[0018] The residual liquid status provides information on the liquid supply margin beyond evaporation consumption. When combined with pressure-corrected temperature difference, steam superheat, and actual liquid supply ratio, it can distinguish between excessive liquid supply, insufficient liquid supply, and some sensor malfunctions.

[0019] Sensor effectiveness checks, conservative modes, heat source unloading, and branch isolation constitute a layered handling path, preventing the control system from treating increasing pump flow as the only action for all anomalies. Attached Figure Description

[0020] Figure 1 This is a flowchart of the overall liquid supply control method of the present invention.

[0021] Figure 2 This is a control block diagram combining heat load feedforward and phase feedback.

[0022] Figure 3 The flowchart shows the calculation process for the theoretical evaporation mass flow rate and the target liquid supply mass flow rate.

[0023] Figure 4 A diagram showing the connection relationships between pump flow calibration, feedforward drive, and the inner loop of actual flow.

[0024] Figure 5 This is a graph showing the calculated relationship between absolute steam pressure, saturation temperature, pressure-corrected temperature difference, and steam superheat.

[0025] Figure 6 The state machine diagram represents five states: normal, excessive liquid supply, risk of localized drying, sensor malfunction, and branch malfunction.

[0026] Figure 7 This is a logic diagram for jointly determining the risk of localized drying out using multiple parameters.

[0027] Figure 8 Flowchart for sensor fault identification and conservative operation mode.

[0028] Figure 9 Diagram showing coordinated liquid supply, isolation of abnormal branches, and load redistribution for multiple evaporators.

[0029] Figure 10 This is a schematic diagram of the dimensionless trend of the feedforward target and feedback correction under a step heat load condition.

[0030] 300—Multi-evaporator pump-driven two-phase system; 310—Mechanical pump; 360—Evaporator stage; 372—Liquid supply continuity detection element; 380—Liquid supply controller; 381—Heat load input; 382—Mass flow rate input; 383—Steam absolute pressure input; 384—Steam or mounting surface temperature input; 385—Residual liquid status input; 386—Pump drive output; 387—Heat source unloading output; 388—Branch isolation output. Detailed Implementation

[0031] The following implementation is used to illustrate the control relationship. The state threshold, sampling period, filter parameters, target liquid supply ratio, and action amplitude should be tuned according to the specific working fluid, evaporator, sensor, and loop volume. Parameters without original test records are not considered valid control performance. Example 1: Liquid supply control for a single evaporator

[0032] The liquid supply controller 380 obtains the power command of the heating unit through the heat load input 381. If not all the power of the heating unit is transmitted to the evaporator, the effective heat load Qi can be obtained through a heat loss model or a heat flow sensor. The controller also reads the absolute vapor pressure input 383 and obtains hvaporization, i, and Tsaturation from the property relationships.

[0033] Assuming an effective heat load of 1 kW for a design condition, and an example latent heat of vaporization of 1.10 × 10⁻⁶ kW. 6 If the target liquid-to-energy ratio is 1.25, then the theoretical evaporation mass flow rate is approximately 0.909 g / s. If the target liquid-to-energy ratio is 1.25, then the target liquid-to-energy mass flow rate is approximately 1.136 g / s. The above values ​​are for illustrative purposes only; the latent heat of vaporization should be re-obtained after changes in the working fluid and absolute pressure.

[0034] The controller retrieves the initial drive quantity corresponding to 1.136 g / s from the pump calibration table. After the mass flow sensor measures the actual flow rate, the inner loop compensates for individual pump differences and loop resistance. The outer phase feedback makes limited adjustments to the target supply ratio based on ΔT correction, ΔT overheating, and residual liquid status. Example 2: Start-up, Loading and Unloading

[0035] During startup, the liquid chamber and interstage piping are pre-charged with a startup supply ratio that establishes liquid continuity, and heating is permitted only after the absolute vapor pressure, residual liquid status, and flow rate signals are valid. During load increase, heat load feedforward causes the target supply flow rate to increase with Qi / h vaporization; phase state feedback then checks the actual residual liquid and pressure-corrected temperature difference.

[0036] During load reduction, the target liquid supply flow rate does not need to decrease significantly simultaneously with the heat load command. The controller can be set to a smaller rate of decrease, allowing the heat release inside the evaporator and the working fluid state to complete the transition before reducing the liquid supply. During the shutdown phase, a short-term circulation can be maintained or liquid drainage can be performed, the specific process of which is determined by the system task requirements. Example 3: Joint Desiccation Risk Assessment

[0037] like Figure 7 As shown, the controller collects at least four types of parameters: multi-point temperature of the mounting surface and its rate of change, absolute steam pressure and steam temperature, residual liquid flow rate or liquid level, and actual liquid supply flow rate. First, the signal range, timestamp, rate of change, and redundancy consistency are checked, and then the pressure-corrected temperature difference, steam superheat, and actual liquid supply ratio are calculated.

[0038] When the pressure-corrected temperature difference increases but the residual liquid remains stable and the steam superheat does not increase, the cause can be tentatively attributed to changes in contact thermal resistance or a local temperature sensor malfunction. When both the pressure-corrected temperature difference and the steam superheat increase simultaneously, the residual liquid decreases, and the actual liquid supply ratio is low, the risk level of localized drying out should be increased. Increased temperature dispersion at multiple points on the mounting surface can be used to indicate local rather than overall changes in condition.

[0039] Risk assessment employs parameters from at least three independent sources, with validity and persistence conditions set. Specific thresholds are obtained through subsequent system calibration; the manual does not limit this method to unverified fixed thresholds. Example 4: Over-supply Identification

[0040] When the residual liquid flow rate consistently exceeds expectations, the actual liquid supply ratio exceeds the target range, and both the pressure correction temperature difference and steam superheat are within the normal range, the controller enters an over-supply state. First, slightly reduce the target α flow rate instead of directly and drastically reducing the pump speed. If the residual liquid level remains high, the target flow rate can be gradually reduced over multiple control cycles.

[0041] When the pressure correction temperature difference or steam superheat increases after the liquid supply is reduced, the controller stops reducing the liquid supply and maintains the previous safe target value. This hysteresis relationship reduces the back-and-forth switching between excessive liquid supply and localized dryness risk states. Example 5: Pressure Signals and Non-condensable Gas Risk

[0042] If the saturation temperature corresponding to the absolute pressure of the vapor is significantly higher than the vapor temperature, or if there are deviations between multiple pressure measurement points that cannot be explained by the flow pressure drop, the reliability of the pressure signal can be reduced. Possible causes include sensor zero-point offset, liquid column within the measurement point, local condensation, or non-condensable gas.

[0043] When the pressure signal reliability is low, the controller retains the thermal load feedforward and the actual flow rate inner loop, but does not rapidly reduce the liquid supply based on the pressure calculation result. The system can perform venting, vacuuming, switching redundant pressure sensors, or reducing the thermal load. Example 6: Sensor Abnormal Safety Mode

[0044] When a flow sensor exceeds its range, the pump's calibrated flow rate can be used as a substitute within a limited time, while limiting the heat load based on the residual liquid status and temperature risk. If a mounting surface temperature sensor malfunctions, the median of adjacent measuring points or the spatial distribution of other measuring points can be used as a substitute. If a residual liquid flow sensor malfunctions, a level switch or the temperature change of the residual liquid pipe can be used as a low-resolution substitute.

[0045] If all critical phase signals are unavailable, the controller enters conservative mode: maintaining or moderately increasing the liquid supply ratio, limiting the pump drive descent rate, reducing the heat source load, and outputting maintenance or task management requests. Upon recovery, the controller first verifies that the signals are continuously valid within a reasonable range before gradually exiting conservative mode. Example 7: Multi-evaporator coordination

[0046] For multiple evaporators with parallel liquid supply, the controller calculates the target flow rate for each branch separately. The total target flow rate is constrained by pump capacity and condenser capacity. When the total demand exceeds the available capacity, the flow rate and heat load are allocated according to the priority of the heating unit, thermal inertia, and phase risk.

[0047] For systems with series liquid flow and parallel gas flow, the controller calculates the target flow rate of the first stage backward from the lowest liquid supply ratio of the final stage, while simultaneously monitoring the residual liquid, pressure, and temperature of each stage. The control method of P09 does not require this series topology and can also be applied to single evaporators, fully parallel systems, or systems that can switch between series and parallel connections.

[0048] When an anomaly occurs in a branch circuit, the branch circuit isolation output 388 drives the isolation valve, and the heat source unloading output 387 reduces the corresponding heat source power. The target liquid supply and heat load of the remaining branches are recalculated. Example 8: Control Trend Diagram

[0049] Figure 10 The control timing after a heat load step change is expressed as a dimensionless quantity. After the heat load command changes, the feedforward target flow rate changes first according to the theoretical evaporation demand; the actual flow rate follows the target in the inner loop; and the phase feedback performs amplitude-limited correction after obtaining pressure, temperature, and residual liquid information. The curves in the figure are used to illustrate the sequential relationship and control structure, and do not represent the response time, overshoot, or measurement results of a specific device.

Claims

1. A liquid supply control method for a porous metal evaporator based on heat load feedforward and phase state feedback, applied to a pump-driven two-phase fluid circuit including a mechanical pump and at least one porous metal evaporator, wherein the porous metal evaporator has a liquid inlet, a residual liquid outlet, and a vapor outlet, characterized in that, include: Obtain the heat load Qi of the i-th porous metal evaporator, and determine the latent heat of vaporization hvaporization,i of the working fluid under the operating conditions of the i-th porous metal evaporator; Calculate the theoretical evaporation mass flow rate mvapor,i of the i-th porous metal evaporator according to mvapor,i = Qi / hvaporization,i; determine the target liquid supply mass flow rate mtarget based on the theoretical evaporation mass flow rate of one or more porous metal evaporators and the target liquid supply ratio α; determine the feedforward drive quantity corresponding to the target liquid supply mass flow rate based on the calibration relationship between the drive quantity of the mechanical pump and the liquid supply mass flow rate; collect the actual liquid supply mass flow rate, absolute steam pressure, steam temperature or mounting surface temperature, and residual liquid flow rate or residual liquid level; determine the saturation temperature based on the relationship between the absolute steam pressure and the saturation properties of the working fluid, and form a pressure-corrected temperature difference based on the saturation temperature and the mounting surface temperature, or form a steam superheat based on the saturation temperature and the steam temperature; identify the normal state, excessive liquid supply state, local dryness risk state, sensor abnormal state, or branch abnormal state based on the actual liquid supply mass flow rate, the pressure-corrected temperature difference or the steam superheat, and the residual liquid flow rate or residual liquid level. And perform limited-amplitude feedback correction on the feedforward drive quantity according to the identified state, and perform at least one of the following actions in the state of local dryness risk or branch abnormality: increase the liquid supply mass flow rate, reduce the corresponding heat load, and isolate the abnormal branch.

2. The liquid supply control method according to claim 1, characterized in that, The heat load Qi is obtained from at least one of the following: heater power, heating unit operating power, heat flow sensor measurement value, host computer task instruction, or heat load model based on the heating unit's operating status; the latent heat of vaporization hvaporization,i is determined based on at least one of the following: working fluid type, vapor absolute pressure, and physical property database, physical property correlation formula, or lookup table data.

3. The liquid supply control method according to claim 1, characterized in that, The target liquid supply ratio α is set with different values ​​for at least two of the following stages: startup stage, normal stage, heat load increase stage, heat load decrease stage, and shutdown and liquid drainage stage; upper limit, lower limit, and unit time change limit are imposed on the target liquid supply ratio α or the target liquid supply mass flow rate m, and the lower limit is not less than the design liquid supply ratio that maintains the preset residual liquid continuity.

4. The liquid supply control method according to claim 1, characterized in that, The calibration relationship includes at least one correspondence between pump speed, pump drive voltage, pump drive current or pump stroke frequency and the mass flow rate of the supplied liquid; the feedforward drive quantity obtained according to the calibration relationship is input into the mechanical pump, and a flow inner loop correction quantity is formed according to the deviation between the actual mass flow rate of the supplied liquid and the target mass flow rate of the supplied liquid. The flow inner loop correction quantity is limited by the upper and lower limits of the mechanical pump drive and the rate of change.

5. The liquid supply control method according to claim 1, characterized in that, Before determining the saturation temperature based on the absolute vapor pressure, the measured absolute vapor pressure is compared with at least one of other pressure measurements in the loop, the rate of change of pressure, or the vapor temperature. If the comparison result does not meet the preset consistency condition, the corresponding pressure signal is marked as invalid or identified as a risk of non-condensable gas accumulation, and the reduction of the liquid supply mass flow rate is prohibited based solely on the pressure signal.

6. The liquid supply control method according to claim 1, characterized in that, When the residual liquid flow rate or residual liquid level is continuously higher than the upper limit corresponding to the target liquid supply ratio, and neither the pressure correction temperature difference nor the steam superheat indicates a risk of local drying, it is identified as an oversupply state. In the state of excessive liquid supply, the target liquid supply ratio or feedforward drive amount is reduced at a limited rate of change until the remaining liquid state returns to the preset range.

7. The liquid supply control method according to claim 1, characterized in that, The localized dry-out risk status is determined by at least three of the following parameters: pressure-corrected temperature difference, rate of change of pressure-corrected temperature difference, steam superheat, dispersion of temperature at multiple points on the mounting surface, residual liquid flow rate or residual liquid level, actual liquid supply ratio, and steam pressure fluctuation; the dry-out risk level is increased only when the signal validity condition and the persistence condition are met.

8. The liquid supply control method according to claim 1, characterized in that, When any sensor signal from the actual liquid supply mass flow rate, vapor absolute pressure, vapor temperature, mounting surface temperature, or residual liquid status is identified as abnormal, at least one of the following is adopted: redundant sensor, adjacent evaporator signal, or alternative value calculated from other valid signals; if no alternative value is available, the previous effective control value is maintained, the target liquid supply ratio is adjusted to a conservative value, or the corresponding heat load is reduced, and the mechanical pump drive is restricted from changing in the direction of reducing liquid supply.

9. The liquid supply control method according to claim 1, characterized in that, When the pump-driven two-phase fluid circuit includes multiple porous metal evaporators, calculate the theoretical evaporation mass flow rate and phase risk of each porous metal evaporator, and allocate the total liquid supply flow rate according to the heat load, priority and risk level of each porous metal evaporator. When an evaporator branch malfunctions, that branch is isolated and the available liquid supply capacity or available heat load is redistributed to the remaining evaporator branches.

10. A liquid supply control system for a porous metal evaporator, characterized in that, include: Heat load input interface; The device comprises at least one of the following: a mass flow sensor, a vapor absolute pressure sensor, a vapor temperature sensor or a mounting surface temperature sensor, and a residual liquid flow sensor or a residual liquid level sensor; a pump drive interface connected to a mechanical pump; a heat source unloading interface connected to a heating unit and a branch isolation interface connected to an evaporator branch isolation component; and a liquid supply controller, the liquid supply controller including a processor and a memory, the memory storing a calibration relationship between the pump drive quantity and the liquid supply mass flow rate and a pressure-saturation temperature relationship of the working fluid, the processor being configured to: calculate the theoretical evaporation mass flow rate based on the heat load and latent heat of vaporization, generate a target liquid supply mass flow rate and a feedforward drive quantity based on the target liquid supply ratio, form a pressure-corrected temperature difference or vapor superheat based on the vapor absolute pressure, identify the operating status in conjunction with the actual liquid supply mass flow rate and residual liquid status, and output a restricted pump drive signal, a heat source unloading signal or a branch isolation signal.

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