Anti-Heat Source Fluctuation Heat Exchange System Based on Active Flow Regulation and Control Method Thereof

This application claims priority of Chinese Patent Application No. 202410448628.1, filed on Apr. 15, 2024, the entire contents of which are incorporated herein by reference.

The present disclosure relates to the technical field of heat exchanger, in particular to an anti-heat source fluctuation heat exchange system with based on active flow control and a control method thereof.

The highly applicable, flexible and efficient organic Rankine cycle technology plays a crucial role in low-temperature waste-heat power generation systems. However, in such systems, due to changes in parameters, equipment operation discontinuities, or environmental factors during industrial production process, the waste heat source is often non-stationary and fluctuating, manifested as flow and temperature fluctuations. Severe heat source fluctuations not only affect the operational efficiency of the system, but also pose serious challenges to the stable operation of the system. Therefore, effectively reducing or controlling heat source fluctuations is of great significance for improving the efficient application of organic Rankine cycles.

At present, common methods for mitigating heat source fluctuations primarily include setting a bypass valve or a thermal storage tank to regulate or store thermal energy. However, these approaches often suffer from disadvantages such as large space requirements and limited effectiveness in addressing heat source fluctuations. In addition, integrating phase change thermal storage materials into a heat exchanger can also weaken heat source fluctuations. However, this technology adjusts heat source fluctuations through the heat storage of phase change materials. On the one hand, the properties of phase change materials affect the efficiency of heat storage and release, and on the other hand, the phase change time of materials also affects the system response time, which is not conducive to the dynamic response characteristics of the system.

Based on this, in order to ensure that the constant total heat exchange quality required for the working fluid and the inlet and outlet flow rates and temperatures of the working fluid are not affected by heat source fluctuations, and also maintaining the safety and stability of the system, the present disclosure provides an anti-heat source fluctuation heat exchange system based on active flow control and a control method thereof. The invention improves upon the traditional single-loop heat source configuration for a single-loop working fluid by introducing a parallel heat exchange system mode. In this mode, multiple sub-loop heat sources correspond to multiple sub-loop working fluids. The system adjusts the flow distribution ratio of the heat source entering the different sub-loops to address the technical challenges of low heat exchange efficiency and slow response time associated with heat source fluctuations.

In order to solve the above technical problems, the present disclosure designs an anti-heat source fluctuation heat exchange system and its corresponding control method based on active flow control. Through this system, on the one hand, it can effectively ensure that the constant total heat exchange quality of the system remains constant under the condition of heat source fluctuation and constant inlet flow rate and inlet temperature of the working fluid; on the other hand, it can effectively reduce the flow resistance of the heat source and comprehensively improve the operating efficiency of the heat exchange system without the fluctuation of the heat source.

In order to achieve the above technical effects, on the one hand, the present disclosure provides an anti-heat source fluctuation heat exchange system based on active flow control, which includes a heat source circuit, a working fluid circuit, a control circuit, a first sub heat exchanger, a second sub heat exchanger, and an electronic control unit.

The heat source circuit comprises a main heat source circuit, a first sub heat source circuit, and a second sub heat source circuit; the first sub heat source circuit is connected to the first sub heat exchanger, and the second sub heat source circuit is connected to the second sub heat exchanger; the main heat source circuit is equipped with a first heat source flow sensor and a first heat source temperature sensor, the first sub heat source circuit is equipped with a second heat source flow sensor and a second heat source temperature sensor, and the second sub heat source circuit is equipped with a third heat source flow sensor and a third heat source temperature sensor; the working fluid circuit comprises a main working fluid circuit, a first sub working fluid circuit, a second sub working fluid circuit, a working fluid collection circuit; the first sub working fluid circuit is connected to the first sub heat exchanger, and the second sub working fluid circuit is connected to the second sub heat exchanger; the main working fluid circuit is equipped with a first working fluid flow sensor and a first working fluid temperature sensor, the first sub working fluid circuit is equipped with a second working fluid flow sensor, and the second sub working fluid circuit is equipped with a third working fluid flow sensor; the main heat source circuit, the first sub heat source circuit, and the second sub heat source circuit are connected through a heat source electronic control three-way valve, and the main working fluid circuit, the first sub working fluid circuit, and the second sub working fluid circuit are connected through a working fluid electronic control three-way valve; the electronic control unit is respectively connected to the heat source electronic control three-way valve, the second heat source flow sensor, and the third heat source flow sensor.

Further, the first sub heat exchanger is the same as the second sub heat exchanger, but heat exchange coefficients of heat source fluid in the first sub heat exchanger and the second sub heat exchanger are different.

Further, the first sub heat exchanger and the second sub heat exchanger are a combination of shell-and-tube exchangers; the heat source is located on a shell side of the first sub heat exchanger and flows around working fluid in the outer tube side, while the heat source is located on a tube side of the second sub heat exchanger and flows around the working fluid in the shell side.

On the other hand, the present disclosure provides a control method for an anti-heat source fluctuation heat exchange system based on active flow control, which includes the following steps:

in the formula, m, mare respectively the mass flow rates at the inlets of the sub heat source circuits and the sub working fluid circuits, kg/s; Q is the heat exchange capacity, J; Uis the heat exchange coefficient, W/(mK); εis the heat exchange efficiency; Tand Tare respectively the inlet temperature and the outlet temperature of the heat source, K; A is the heat exchange area, m; cand care the constant pressure specific heat of the heat source and the constant pressure specific heat of the working fluid, KJ/(kg·K); Dand Dare the density of the heat source and the density of the working fluid, respectively, kg/m; μand μare the dynamic viscosity of the heat source and the dynamic viscosity of the working fluid, Pa·s; and Prand Prare the Prandtl number of the heat source and the Prandtl number of the working fluid.

Further, in S3, the working fluid is introduced into the working fluid collection circuit after completing heat exchange with the heat source in both the first and second sub-heat exchangers, maintaining the constant total heat exchange quality from the heat source to the working fluid at a constant value, effectively mitigating the negative impact of heat source fluctuations on the heat exchange.

Further, the working fluid in S3 is introduced into the first and second sub heat exchangers at the same inlet flow ratio, thereby achieving anti-heat source fluctuation without the need to adjust the working fluid flow ratio.

Further, the working fluid in S3 is introduced into the first and second sub heat exchangers at different flow ratios to achieve stable heat exchange output over a broader range of heat source fluctuations.

Further, the flow areas of the heat source in the two sub heat exchangers are different, thus, the flow resistances of the heat source in the two sub heat exchangers are different. When the heat source is stable, the inlet flow distribution ratio of the sub heat exchanger with a larger heat source flow area is increased to allow more heat source to exchange heat with the working fluid, effectively reducing the flow resistance on the heat source side while maintaining constant heat exchange.

Further, the heat source is located in the shell side of the first sub heat exchanger and undergoes countercurrent heat exchange with the working fluid in the tube side, and the heat source is located in the tube side of the second sub heat exchanger and undergoes countercurrent heat exchange with the working fluid in the shell side.

Further, when there is heat source fluctuation, the inlet flow distribution ratio of the heat source between the first sub heat source circuit and the second sub heat source circuit is adjusted to maintain a constant total heat exchange quality from the heat source to the working fluid unchanged; when the heat source is stable, the inlet flow distribution ratio of the heat source in the first sub heat source circuit and the second sub heat source circuit is adjusted to effectively reduce the flow resistance of the heat source, while maintaining constant heat exchange.

The advantageous effects of the present disclosure are as following:

In the attached figures, the list of components represented by each label is as follows:

The present disclosure provides an anti-heat source fluctuation heat exchange system based on active flow control, which includes: a heat source circuit, a working fluid circuit, a control circuit, a first sub heat exchanger, a second sub heat exchanger, and an electronic control unit.

The heat source circuit includes a main heat source circuit, a first sub heat source circuit, and a second sub heat source circuit, wherein the first sub heat source circuit is connected to the first sub heat exchanger, and the second sub heat source circuit is connected to the second sub heat exchanger; the main heat source circuit is equipped with a first heat source flow sensor and a first heat source temperature sensor, the first sub heat source circuit is equipped with a second heat source flow sensor and a second heat source temperature sensor, and the second sub heat source circuit is equipped with a third heat source flow sensor and a third heat source temperature sensor. The working fluid circuit includes a main working fluid circuit, a first sub working fluid circuit, a second sub working fluid circuit, a working fluid collection circuit, wherein the first sub working fluid circuit is connected to the first sub heat exchanger, and the second sub working fluid circuit is connected to the second sub heat exchanger; the main working fluid circuit is equipped with a first working fluid flow sensor and a first working fluid temperature sensor, the first sub working fluid circuit is equipped with a second working fluid flow sensor, and the second sub working fluid circuit is equipped with a third working fluid flow sensor; the main heat source circuit, the first sub heat source circuit, and the second sub heat source circuit are connected through a heat source electronic control three-way valve, and the main working fluid circuit, the first sub working fluid circuit, and the second sub working fluid circuit are connected through a working fluid electronic control three-way valve. The electronic control unit is respectively connected to the heat source electronic control three-way valve, the second heat source flow sensor, and the third heat source flow sensor. The specific structural relationship is shown in, specifically, the first sub heat exchanger and the second sub heat exchanger are a combination of shell-and-tube exchangers, the heat source is located in a shell side of the first sub heat exchanger and undergoes countercurrent heat exchange with the working fluid in the tube side, and the heat source is located in the tube side of the second sub heat exchanger and undergoes countercurrent heat exchange with the working fluid in the shell side. The flow area of the heat source in the first sub heat exchanger is larger than the flow area of the heat source in the second sub heat exchanger, thus, the flow resistances of the heat source in the two sub heat exchangers are different. When the heat source is stable, reduce the inlet flow distribution ratio of the second sub heat exchanger, and increase the inlet flow distribution ratio of the first sub heat exchanger, to allow more heat source to exchange heat with the working fluid in the first sub heat exchanger, effectively reducing the flow resistance on the heat source under constant heat exchange. When there is heat source fluctuation, the inlet flow distribution ratio of the heat source in the first sub heat source circuit and the second sub heat source circuit is adjusted to maintain the constant total heat exchange quality from the heat source to the working fluid unchanged. When the heat source is stable, the inlet flow distribution ratio of the heat source in the first sub heat source circuit and the second sub heat source circuit is adjusted to effectively reduce the flow resistance of the heat source under constant heat exchange.

In this embodiment, during the operation of the heat exchange system as described in embodiment 1, the heat source is introduced into the first sub heat source circuitand the second sub heat source circuitthrough the main heat source circuit. The first heat source flow sensorand the first heat source temperature sensorrespectively measure the flow and temperature of the main heat source circuit; the second heat source flow sensorand the second heat source temperature sensorrespectively measure the flow and temperature of the first sub heat source circuit; and the third heat source flow sensorand the third heat source temperature sensorrespectively measure the flow and temperature of the second sub heat source circuit. The electronic control unitadjusts the heat source electronic control three-way valvebased on the flow signal provided by the first heat source flow sensor; the electronic control unitmonitors and adjusts the flow rate of the first sub heat source circuitin real time based on the flow signal from the second heat source flow sensor; and the electronic control unitmonitors and adjusts the flow rate of the second sub heat source circuitin real time based on the flow signal provided by the third heat source flow sensor, so that the heat source from the main heat source circuit to be controllably distributed between the first sub heat source circuitand the second sub heat source circuitin any flow ratio. The working fluid is introduced into the first sub working fluid circuitand the second sub working fluid circuitthrough the main working fluid circuit, after completing the heat exchange, it flows out through the working fluid collection circuit. The first working fluid flow sensorand the first working fluid temperature sensorrespectively measure the flow and temperature of the main working fluid circuit; the second working fluid flow sensorcollects the flow signal of the first sub working fluid circuit, and the third working fluid flow sensorcollects the flow signal of the second sub working fluid circuit. When there is a fluctuation in the heat source, the heat source exchanges heat with the working fluid simultaneously or separately in the first sub heat exchangerand the second sub heat exchangerto ensure that the flow rate and/or temperature of the heat source and the working fluid are within a coordinated range, further maintaining the total heat transfer from the heat source to the working fluid unchanged, so as to effectively cope with the negative impact of heat source fluctuations on heat exchange. The magnitude of heat source fluctuations during system operation is determined by the heat source flow sensors, mis the flow signals collected from the main heat source circuit, mis the flow signal collected from the first sub heat source circuit, mh,2 is the flow signal collected from the second sub heat source circuit, and the flow ratio of the heat source entering the two sub circuits is determined by real-time control of m/m. Specifically, based on the total required heat exchange Qand the total flow rate mof the working fluid, the flow ratio m/mof the heat source fluid is determined and controlled in real-time by the following set of equations (the specific form of functions f, g depends on the specific structure and flow arrangement of the sub heat exchanger):

In the formula, m, mare respectively the mass flow rates at the inlets of the sub heat source circuits and the sub working fluid circuits, kg/s; Q is the heat exchange capacity, J; Uis the heat exchange coefficient, W/(mK); εis the heat exchange efficiency; Tand Tare respectively the inlet temperature and the outlet temperature of the heat source, K; A is the heat exchange area, m; cand care the constant pressure specific heat of the heat source and the constant pressure specific heat of the working fluid, kJ/(kg·K); Dand Dare the density of the heat source and the density of the working fluid, respectively, kg/m; μand μare the dynamic viscosity of the heat source and the dynamic viscosity of the working fluid, Pa·s; and Prand Prare the Prandtl number of the heat source and the Prandtl number of the working fluid.

In this embodiment, the first sub heat exchangerand the second sub heat exchangerare a combination of a double-tube heat exchanger and a double-tube heat exchanger. The two sub tube heat exchangers have the same size, with a shell side diameter of 0.1 mm and a tube side diameter of 0.06 mm. The heat source is flue gas, with an inlet temperature of 623.15K, a working fluid of R245fa, and an inlet flow rate is 0.5 kg/s. The heat source is located on the shell side of the first sub heat exchangerand undergoes countercurrent heat exchange with the working fluid on the tube side of the first sub heat exchanger. The heat source is located on the tube side of the second sub heat exchangerand undergoes countercurrent heat exchange with the working fluid on the shell side of the second sub heat exchanger. Furthermore, according to the design method of the ε-NTU heat exchanger, the specific form of the function f in the control system is determined as shown in equation (6):

Functions gand gare used to calculate the heat exchange coefficients of fluids on the tube side and shell side, respectively, and are expanded and calculated using equations (7) and (8):

Based on the above calculation process, the variation of heat exchange under the condition of heat source fluctuation is shown in. The shaded area in the figure represents the design area, which is the achievable heat exchange range when the inlet mass flow rate of the heat source is between 0.25 and 0.75 kg/s. Taking the constant total heat exchange quality of 40,000 kJ as the benchmark, when the inlet mass flow rate of the heat source fluctuates within the range of 0.45-0.75 kg/s, it is only necessary to adjust the heat source flow ratio to achieve the required constant total heat exchange quality without adjusting the working fluid flow ratio. If 0.6 kg/s is taken as the benchmark, it can be concluded that the anti-heat source fluctuation parallel heat exchange system based on active flow control can maintain the heat exchange unchanged under ±25% heat source flow fluctuation. Within the same flow fluctuation range, if the flow ratio of the heat exchanger is not adjusted, the fluctuation of the constant total heat exchange quality can reach −50% to 20%.

In this embodiment, as shown in, the first sub heat exchangerand the second sub heat exchangerare a combination of a double tube heat exchanger and a double tube heat exchanger. The two sub tube heat exchangers have the same size, with a shell side diameter of 0.114 mm and a tube side diameter of 0.089 mm. The heat source is flue gas, the inlet temperature is 623.15K, the working fluid is R245fa, the inlet flow rate is 0.5 kg/s, and the inlet temperature is 406.35K. The heat source is located on the shell side of the first sub heat exchangerand undergoes countercurrent heat exchange with the working fluid located on the tube side of the first sub heat exchanger, and the heat source is located on the tube side of the second sub heat exchangerand undergoes countercurrent heat exchange with the working fluid located on the shell side of the second sub heat exchanger. The shaded area in the figure represents the design area, which is the achievable heat exchange range when the inlet mass flow rate of the heat source is between 0.25 and 0.75 kg/s. Taking the constant total heat exchange quality of 40,000 kJ as the benchmark, when the inlet mass flow rate of the heat source fluctuates within the range of 0.32-0.75 kg/s, it is only necessary to adjust the heat source flow ratio to achieve the required constant total heat exchange quality without adjusting the working fluid flow ratio. If 0.535 kg/s is taken as the benchmark, it can be concluded that the anti-heat source fluctuation parallel heat exchange system based on active flow control can maintain the heat exchange unchanged under ±40% heat source flow fluctuation. Within the same flow fluctuation range, if the flow ratio of the heat exchanger is not adjusted, the fluctuation of the constant total heat exchange quality can reach −45% to 40%.

In Embodiment 3 of the present disclosure, as shown in, the first sub heat exchangerand the second sub heat exchangerare a combination of a double-tube heat exchanger and a double-tube heat exchanger. The two sub tube heat exchangers have the same size, with a shell side diameter of 0.1 mm and a tube side diameter of 0.06 mm. The heat source is flue gas, the working fluid is R245fa, the inlet flow rate is 0.5 kg/s, and the inlet temperature of the working fluid is 406.35K. The heat source is located on the shell side of the first sub heat exchangerand undergoes countercurrent heat exchange with the working fluid located on the tube side of the first sub heat exchanger. The heat source is located on the tube side of the second sub heat exchangerand undergoes countercurrent heat exchange with the working fluid located on the shell side of the second sub heat exchanger. The shaded area in the figure represents the design area, which shows the achievable range of heat exchange can be achieved when the inlet mass flow rate of the heat source is between 0.4 and 0.6 kg/s. Taking the constant total heat exchange quality of 40,000 kJ as the benchmark, when the inlet mass flow rate of the heat source is 0.48-0.60 kg/s, the inlet temperature fluctuates within the range of 480-720K, and the required constant total heat exchange quality can be achieved under the condition that the inlet flow rate and inlet temperature of the working fluid remain unchanged. Taking the flow rate of 0.535 kg/s as the benchmark, it can be concluded that the anti-heat source fluctuation parallel heat exchange system based on active flow control can maintain heat exchange unchanged under ±11% coupling fluctuations of heat source flow rate and temperature. Within the same flow fluctuation range, if the flow ratio of the heat exchanger is not adjusted, the fluctuation of the constant total heat exchange quality can reach −75% to 80%.

Through the above embodiments, it can be effectively demonstrated that when there is a fluctuation in the heat source, the present disclosure actively regulates the inlet flow distribution ratio of the heat source in the first sub heat source circuit and the second sub heat source circuit, in order to maintain the constant total heat exchange quality from the heat source to the working fluid constant under the condition of changing the inlet flow rate of the working fluid and keeping the inlet temperature unchanged. That is, the present disclosure can effectively cope with the negative impact of heat source fluctuations on heat exchange efficiency.

The preferred embodiments of the present disclosure disclosed above are only for the purpose of illustrating the present disclosure. The preferred embodiments do not describe all the details in detail, nor do they limit the disclosure to only the specific embodiments described.