A method and system for calculating heat exchange performance of a medium-deep underground heat exchanger

Abstract

The present invention relates to the technical field of heat exchange performance calculation, and specifically to a method and system for calculating the heat exchange performance of a medium-deep underground heat exchanger. The method obtains the heat conversion efficiency at the sampling moment through the heat exchange of the outer pipe at different temperature sampling positions at the sampling moment under different water flow rates, as well as the thermal conductivity of the rock mass, combined with the deviation of the outlet temperature and the bottom temperature of the pipe; based on the distribution of changes in the heat conversion efficiency in the time sequence of different thermal response test experiments, the stable sampling moment is screened, and the ideal flow rate is determined through the proportion of unstable sampling moments and the distribution of heat conversion efficiency at the stable sampling moment; based on the ideal flow rate and the current operating flow rate, the heat exchange performance index is obtained. The present invention performs heat conversion analysis at multiple positions under multiple water flow rates, and combines the changes in the heat conversion efficiency in the time sequence to evaluate the heat exchange performance from the perspective of the operating water flow rate, combining the heat exchange effect and the water flow energy situation, thereby improving the reliability and accuracy of the heat exchange performance evaluation.

Description

Technical Field

[0001] The present invention relates to the technical field of heat exchange performance calculation, and in particular to a heat exchange performance calculation method and system for a medium-deep underground heat exchanger. Background Art

[0002] With the increasing demand for low-carbon and environmentally friendly heating solutions, the technical innovation and research and development of medium-deep underground coaxial heat exchangers as an efficient way to utilize geothermal energy have received more attention. Heat transfer performance is one of the key factors that determine whether the installation quality of medium-deep underground heat exchangers meets the standards, so the calculation requirements for the heat transfer performance of medium-deep underground heat exchangers are becoming more and more stringent.

[0003] Thermal response test experiments are usually used to test the heat transfer performance of medium-deep underground heat exchangers. Through thermal response tests, underground thermal parameters can be analyzed and whether the operation of the heat exchanger meets the requirements can be verified. However, the judgment of heat transfer performance is usually too simple. The inlet and outlet temperature difference when the heat exchanger is working is often used to judge the heat transfer of the heat exchanger. However, in thermal response test experiments, the thermal conductivity of different rock layers is different. Therefore, there are many changes in the overall heat conversion during heat transfer analysis. When the analysis data of the experimental situation is considered single, the reliability of the heat transfer efficiency analysis is reduced, affecting the accuracy of the heat transfer performance evaluation. Summary of the invention

[0004] In order to solve the technical problem that the single heat exchange efficiency analysis in the prior art affects the accuracy of heat exchange performance evaluation, the purpose of the present invention is to provide a heat exchange performance calculation method and system for a medium-deep underground heat exchanger. The technical solution adopted is as follows:

[0005] The present invention provides a method for calculating the heat exchange performance of a medium-deep underground heat exchanger, the method comprising:

[0006] Conduct thermal response test experiments on the heat exchanger based on different preset water flow rates, obtain the outlet temperature and tube bottom temperature of the heat exchanger at each sampling time under each preset water flow rate, and the internal temperature of the outer tube at each temperature sampling position; and obtain the thermal conductivity and detection temperature of the rock mass at each temperature sampling position;

[0007] In each thermal response test experiment, the heat absorption degree of the outer tube at each temperature sampling position is obtained according to the difference between the detected temperature of the rock mass at each temperature sampling position at each sampling time and the internal temperature of the outer tube, combined with the thermal conductivity of the rock mass; the heat conversion efficiency at each sampling time is obtained according to the deviation between the outlet temperature of the heat exchanger and the bottom temperature of the tube at each sampling time, combined with the heat absorption degree of the outer tube at all temperature sampling positions;

[0008] In the thermal response test experiment of each preset water flow rate, the stable sampling time is selected according to the distribution change of the heat conversion efficiency in the time series; according to the distribution of the heat conversion efficiency corresponding to the stable sampling time under each preset water flow rate and the proportion of the unstable sampling time, the ideal flow rate is determined from the preset water flow rate;

[0009] According to the deviation between the water flow rate of the heat exchanger and the ideal flow rate during the current operation of the heat exchanger and the size of the ideal flow rate, the current heat exchange performance index of the heat exchanger is obtained.

[0010] Furthermore, the method for obtaining the heat absorption degree of the outer tube includes:

[0011] For any sampling time in the thermal response test experiment, the product of the detected temperature and thermal conductivity of the rock mass at each temperature sampling position at the sampling time is normalized to obtain the heat reserve degree of each temperature sampling position at the sampling time;

[0012] The difference between the internal temperature of the outer tube at each temperature sampling position at the sampling time and the detected temperature of the rock mass is taken as the internal and external temperature difference of the outer tube at each temperature sampling position at the sampling time;

[0013] The heat absorption degree of the outer tube at each temperature sampling position at the sampling moment is obtained by combining the heat reserve degree at each temperature sampling position at the sampling moment and the temperature difference between the inside and outside of the outer tube.

[0014] Further, the heat reserve degree of each temperature sampling position at the sampling moment and the temperature difference between the inside and outside of the outer tube are combined to obtain the heat absorption degree of the outer tube at each sampling position at the sampling moment, including:

[0015] The product of the value of the negative correlation mapping of the temperature difference between the inside and outside of the outer tube at each temperature sampling position at the sampling moment and the heat reserve degree is used as the heat absorption degree of the outer tube at each temperature sampling position.

[0016] Furthermore, the method for obtaining the heat conversion efficiency includes:

[0017] For any sampling time in the thermal response test experiment, the difference between the outlet temperature and the bottom temperature of the heat exchanger at the sampling time is taken as the heat loss degree at the sampling time;

[0018] Calculate the average of the outer tube heat absorption at all temperature sampling positions at the sampling moment to obtain the heat absorption at the sampling moment;

[0019] The heat conversion efficiency at the sampling moment is obtained by combining the heat loss degree and the heat absorption degree at the sampling moment.

[0020] Furthermore, the method for obtaining the stable sampling time includes:

[0021] For any thermal response test experiment of a preset water flow, the heat conversion efficiencies at all sampling moments in the thermal response test experiment are sorted in chronological order and curve fitting is performed to obtain the efficiency curve of the thermal response test experiment;

[0022] Get the slope of each sampling moment on the efficiency curve;

[0023] For any sampling moment on the efficiency curve, two sampling moments adjacent to the sampling moment in time sequence are regarded as adjacent moments of the sampling moment;

[0024] Calculate the difference in slope between the sampling moment and each adjacent moment to obtain the change difference between the sampling moment and each adjacent moment; take the ratio of each change difference to the slope of the sampling moment as the change rate between the sampling moment and each adjacent moment;

[0025] When all the change rates corresponding to the sampling moment are less than the preset change threshold, the sampling moment is regarded as the stable sampling moment.

[0026] Furthermore, the method of determining the ideal flow rate from the preset water flow rate according to the distribution of the heat conversion efficiency corresponding to the stable sampling moment under each preset water flow rate and the proportion of the unstable sampling moment includes:

[0027] For any thermal response test experiment under a preset water flow rate, the average value of the heat conversion efficiency corresponding to all stable sampling moments in the thermal response test experiment is used as the stable efficiency distribution index of the thermal response test experiment;

[0028] The ratio of the number of all unstable sampling moments in the thermal response test experiment to the total number of all sampling moments is used as a stable rate index of the thermal response test experiment;

[0029] Combining the stable efficiency distribution index and the stable rate index of the thermal response test experiment, the heat transfer performance index of the thermal response test experiment is obtained;

[0030] The ideal flow rate is determined based on the heat transfer performance indicators corresponding to all preset water flow rates.

[0031] Furthermore, the step of determining the ideal flow rate based on the heat exchange performance index corresponding to all preset water flow rates includes:

[0032] The preset water flow rate corresponding to the maximum heat exchange performance index among all preset water flow rates is taken as the ideal flow rate.

[0033] Furthermore, the method for obtaining the heat exchange performance index includes:

[0034] The difference between the water flow rate of the heat exchanger during current operation and the ideal flow rate is taken as the water flow deviation;

[0035] The product of the water flow deviation and the ideal flow rate is negatively correlated and normalized to obtain the heat transfer performance index of the current heat exchanger.

[0036] Furthermore, after obtaining the heat exchange performance index of the current heat exchanger, the step further includes:

[0037] When the heat exchange performance index is greater than or equal to the preset first quality threshold, the current heat exchanger operation quality is recorded as excellent;

[0038] When the heat exchange performance index is less than the preset first quality threshold and greater than the preset second quality threshold, the current heat exchanger operation quality is recorded as qualified;

[0039] When the heat exchange performance index is less than or equal to the preset second quality threshold, the current heat exchanger operation quality is recorded as poor;

[0040] The preset first quality threshold is greater than the preset second quality threshold.

[0041] The present invention also provides a heat exchange performance calculation system for a medium-deep downhole heat exchanger, including a memory and a processor, wherein the processor executes a calculation program stored in the memory to implement a heat exchange performance calculation method for a medium-deep downhole heat exchanger as described above.

[0042] The present invention has the following beneficial effects:

[0043] In the thermal response test experiment under different preset water flow rates of the present invention, the heat exchange with the rock mass at different temperature sampling positions at each sampling moment is combined with the adjustment of the thermal conductivity of the rock mass to obtain the heat absorption of the outer tube, reflecting the heat conversion at different positions, and further combined with the deviation of the outlet temperature and the bottom temperature of the tube to reflect the heat loss of the inner tube, and the heat conversion efficiency at each sampling moment is comprehensively obtained, so that the overall heat conversion analysis is more comprehensive and accurate. Then, according to each thermal response test experiment, the change distribution of the heat conversion efficiency in the time sequence is analyzed, the stable sampling moment is screened, and the proportion of the unstable sampling moment and the heat conversion efficiency distribution at the stable sampling moment are determined from the stable rate of the thermal response test experiment and the efficiency value after stabilization. From multiple preset water flow rates, the ideal flow rate is determined, and the quantitative heat conversion performance can further reflect the use of water flow energy from the flow rate, and the optimal water flow situation that characterizes the effect of heat conversion is obtained. Based on the ideal flow rate and the current running flow rate, the heat exchange performance index is obtained by combining heat conversion and energy operation. The present invention performs heat conversion analysis at multiple positions under multiple water flow rates, and combines the changes in heat conversion efficiency over time to comprehensively evaluate the heat exchange performance from the perspective of operating water flow rate by combining the heat exchange effect and water flow energy conditions, thereby improving the reliability and accuracy of the heat exchange performance evaluation. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] In order to more clearly illustrate the technical solutions and advantages in the embodiments of the present invention or the prior art, the drawings required for use in the embodiments or the prior art descriptions are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0045] Figure 1 A flow chart of a method for calculating heat exchange performance of a medium-deep downhole heat exchanger provided by one embodiment of the present invention;

[0046] Figure 2 A schematic diagram of the working process of a mid-deep underground coaxial heat exchanger provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0047] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the following is a detailed description of the heat exchange performance calculation method and system of a medium-deep downhole heat exchanger proposed by the present invention, its specific implementation method, structure, features and effects, in combination with the accompanying drawings and preferred embodiments. In the following description, different "one embodiment" or "another embodiment" does not necessarily refer to the same embodiment. In addition, specific features, structures or characteristics in one or more embodiments may be combined in any suitable form.

[0048] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

[0049] The following is a detailed description of a method and system for calculating the heat exchange performance of a medium-deep downhole heat exchanger provided by the present invention in conjunction with the accompanying drawings.

[0050] This embodiment mainly analyzes the heat exchange performance through the thermal response test experiment of the medium-deep underground heat exchanger. The medium-deep underground heat exchanger uses geothermal heat pump technology to extract heat energy from deep underground. It is often used for heating buildings or enterprises. It is a clean renewable energy utilization method. The coaxial nested heat exchanger is a common medium-deep underground heat exchanger. Its working process can be found in Figure 2 , which shows a schematic diagram of the working process of a mid-deep underground coaxial heat exchanger provided by an embodiment of the present invention.

[0051] The deep-hole coaxial heat exchanger of the embodiment of the present invention adopts a nested inner and outer double-tube structure. The heat exchanger is installed in a designated hole. When the heat exchanger is working, cold water to be heated is injected into the inlet of the outer tube, and then transmitted to the bottom of the rock layer through the outer tube annular pipeline. In this process, the cold water absorbs the heat of the rock layer and becomes hot water. The hot water is then pumped out of the heat exchanger by a water pump in the inner tube of the heat exchanger for subsequent use, thereby making full use of the thermal energy of the underground rock layer.

[0052] Since the heat exchange efficiency of the heat exchanger is affected by changes in the installation conditions or operating environment, it is necessary to test the heat exchange performance to provide data support for the maintenance or improvement of the heat exchanger. The water flow rate parameter of the heat exchanger is an important operating parameter of the heat exchanger. If the water flow rate is too low, the heat exchange capacity of the heat exchanger is too small to meet the demand. If the water flow rate is too high, although the total heat exchange capacity increases, the cost is high and the heat exchange efficiency is not high. Therefore, the embodiment of the present invention analyzes the heat exchange performance of the heat exchanger through the optimal water flow performance under the thermal response test experiment.

[0053] In the thermal response test experiment of the embodiment of the present invention, the heat exchanger is placed in a hole used for the experiment, and the outer pipe water inlet and the inner pipe water outlet outside the heat exchanger on the ground are connected through a transmission pipeline to form a circulating water body, and a condenser is set in the external transmission pipeline, so that the water injected into the outer pipe of the heat exchanger in the thermal response test experiment is low-temperature water, and the heat exchanger is continuously input with low-temperature water. The low-temperature water is transmitted to the underground through the internal pipe of the heat exchanger. During the water transmission process, the heat exchanger is used as an intermediary, and the water absorbs heat from the external rock layer, and then the hot water is discharged to the heat exchanger outlet by the heat exchanger's pipeline transmission system and water pump. Each thermal response test experiment needs to end after the outlet temperature stabilizes for a period of time, and data is collected at a fixed sampling frequency during the duration to analyze the heat exchange performance.

[0054] See also Figure 1 , which shows a flow chart of a method for calculating the heat exchange performance of a medium-deep downhole heat exchanger provided by an embodiment of the present invention, the method comprising the following steps:

[0055] S1: Conduct a thermal response test experiment on the heat exchanger based on different preset water flow rates, obtain the outlet temperature and tube bottom temperature of the heat exchanger at each sampling time under each preset water flow rate, and the internal temperature of the outer tube at each temperature sampling position; and obtain the thermal conductivity and detection temperature of the rock mass at each sampling position.

[0056] In the embodiment of the present invention, different water flow rates are used to carry out thermal response test experiments, and the performance of heat conversion under different water flow rates is reflected through data analysis during the different thermal response test experiments.

[0057] In a specific implementation method in an embodiment of the present invention, temperature sensors are arranged at the water outlet, the bottom of the pipe and the inside of the coaxial heat exchanger in a medium-deep well, wherein a temperature sensor is arranged at the water outlet and the bottom of the pipe respectively, and every 100m inside the heat exchanger is used as a temperature sampling position, and a temperature sensor is arranged at each temperature sampling position to detect the flowing water temperature at each position of the heat exchanger during operation, and then a temperature sensor is arranged on the external rock mass at each temperature sampling position in the hole where the heat exchanger is placed to detect the temperature of the rock mass, and the thermal conductivity of the rock mass at each temperature sampling position is obtained through geothermal property testing.

[0058] Cold water is injected from the water inlet of the heat exchanger. In each thermal response test experiment, the outlet temperature and the bottom temperature of the tube at each sampling moment, as well as the internal temperature of the outer tube and the detection temperature of the rock mass at each temperature sampling position are obtained through the preset sampling frequency.

[0059] In a specific implementation method of an embodiment of the present invention, the values ​​of different preset water flow rate settings include: 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 and 1.0, the unit is meters per second, the sampling frequency is set to 30 minutes, and sampling is performed every 30 minutes. The duration of the thermal response test experiment under different preset water flow rates is 48 hours.

[0060] S2: In each thermal response test experiment, the heat absorption degree of the outer tube at each temperature sampling position is obtained according to the difference between the detected temperature of the rock mass at each temperature sampling position at each sampling time and the internal temperature of the outer tube, combined with the thermal conductivity of the rock mass; the heat conversion efficiency at each sampling time is obtained according to the deviation between the outlet temperature of the heat exchanger and the bottom temperature of the tube at each sampling time, combined with the heat absorption degree of the outer tube at all temperature sampling positions.

[0061] After completing the test of the thermal conductivity of the rock mass, the heat exchange efficiency of the heat exchanger is analyzed by changing the water flow rate. Under different water flow rates, the heat exchange rate between the fluid and the rock mass will change, thereby affecting the heat exchange efficiency of the heat exchanger. Since the heat exchanger mainly relies on the outer tube to exchange heat with the rock layer and relies on the inner tube to store and transmit hot water, the heat conversion efficiency of the heat exchanger can be obtained first based on the heat absorption capacity of the outer tube of the heat exchanger and the heat loss degree of the inner tube.

[0062] The heat absorption capacity of the outer tube is mainly reflected by the temperature difference between the inner wall of the outer tube of the heat exchanger and the rock layer at the same depth. Although the overall temperature of the holes generally shows a trend of higher depth as the depth increases, the distribution of underground rock layers is relatively random, resulting in the local rock temperature not meeting the depth and temperature trend characteristics. If the thermal physical property detection temperature of the rock at a certain depth is high and the thermal conductivity is good, it means that the rock at this location is more likely to provide more heat. Therefore, at each sampling moment, combined with the adjustment of the thermal conductivity of the rock at the temperature sampling position, the heat absorption degree of the outer tube is obtained according to the difference between the rock detection temperature and the internal temperature of the outer tube.

[0063] Preferably, in an embodiment of the present invention, the method for obtaining the heat absorption degree of the outer tube includes:

[0064] First, for any sampling moment in the thermal response test experiment, the product of the detected temperature and thermal conductivity of the rock mass at each temperature sampling position at the sampling moment is normalized to obtain the heat reserve degree of each temperature sampling position at the sampling moment. The higher the rock mass detection temperature and the rock mass thermal conductivity, the higher the heat reserve of the rock mass at this position of the hole, which can provide more energy.

[0065] The difference between the internal temperature of the outer tube at each temperature sampling position at the sampling moment and the detected temperature of the rock mass is further taken as the temperature difference between the inside and outside of the outer tube at each temperature sampling position at the sampling moment. The smaller the temperature difference is, the stronger the heat absorption capacity of the outer tube of the heat exchanger is.

[0066] Finally, the heat reserve degree of each temperature sampling position at the sampling moment and the temperature difference between the inside and outside of the outer tube are combined to obtain the heat absorption degree of the outer tube at each temperature sampling position at the sampling moment. The higher the heat reserve degree at the sampling position in the hole, the more important the heat exchange performance analysis of the heat exchanger at this position. Therefore, the heat reserve degree can be used as a weight to adjust the temperature difference analysis.

[0067] In an embodiment of the present invention, the product of the value of the negative correlation mapping of the temperature difference between the inside and outside of the outer tube at each temperature sampling position at the sampling moment and the heat reserve degree is used as the heat absorption degree of the outer tube at each temperature sampling position. The smaller the difference, the better the absorption degree of the outer tube. At the same time, the higher the heat reserve degree, the higher the importance of the corresponding temperature sampling position in the absorption analysis.

[0068] It should be noted that negative correlation mapping and normalization processing are both technical means well known to those skilled in the art. Negative correlation mapping can be in the form of inverse proportion or negative exponential idempotence, and normalization processing can be in the form of linear normalization, etc., without limitation here.

[0069] The degree of heat loss in the inner tube is that the cold water is heated by the outer tube of the heat exchanger and then transported through the inner tube insulation. Since there may be a certain amount of heat loss in the inner tube due to the tube wall material, there will be a certain loss in the water temperature when the water flows out of the outlet. Therefore, the deviation between the outlet temperature and the bottom temperature of the tube at each sampling moment can reflect the heat loss in the inner tube.

[0070] The heat conversion efficiency at each sampling moment is obtained by combining the inner tube loss with the outer tube heat absorption at multiple temperature sampling positions. Preferably, in an embodiment of the present invention, the method for obtaining the heat conversion efficiency includes:

[0071] First, for any sampling moment in the thermal response test experiment, the difference between the outlet temperature of the heat exchanger and the bottom temperature of the tube at the sampling moment is taken as the heat loss degree at the sampling moment. The smaller the temperature difference, the smaller the heat loss.

[0072] Furthermore, the average of the outer tube heat absorption at all temperature sampling positions at the sampling moment is calculated to obtain the heat absorption at the sampling moment, which, combined with the absorption capacity at all temperature sampling positions, reflects the overall absorption capacity of the heat exchanger at this sampling moment.

[0073] The heat conversion efficiency at the sampling moment is obtained by combining the heat loss degree and the heat absorption degree at the sampling moment. The stronger the heat absorption capacity of the overall outer tube of the heat exchanger is and the smaller the heat consumption is, the higher the heat conversion efficiency of the heat exchanger is. In an embodiment of the present invention, the heat loss degree at the sampling moment is negatively correlated and mapped and normalized, and the product of the value and the heat absorption degree is normalized to obtain the heat conversion efficiency at the sampling moment.

[0074] At this point, the analysis of the heat exchange efficiency at each sampling moment is completed.

[0075] S3: In the thermal response test experiment of each preset water flow rate, the stable sampling time is selected according to the distribution change of the heat conversion efficiency in time series; according to the distribution of the heat conversion efficiency corresponding to the stable sampling time under each preset water flow rate and the proportion of the unstable sampling time, the ideal flow rate is determined from the preset water flow rate.

[0076] In general, heat exchange performance analysis is performed after the test data reaches stability. If the heat exchanger takes a long time to reach stability after starting to work, even if the stable heat conversion value is high, a lot of energy has been consumed and the overall heat conversion performance is not good. Therefore, in the timing of the thermal response test experiment of the heat exchanger, the faster the heat conversion efficiency can enter a stable state and the higher the value distribution after stabilization, the better the heat exchange performance of the thermal response test experiment and the better the corresponding water flow rate.

[0077] In the thermal response test experiment under each preset water flow rate, the relatively stable sampling moments are first screened through the changes in the heat conversion efficiency. When the degree of change in the heat conversion efficiency between the sampling moment and the adjacent sampling moments in the time sequence is not much different, it means that the heat conversion efficiency has entered a relatively stable change process, and the sampling moment is a stable sampling moment.

[0078] Preferably, in an embodiment of the present invention, the method for acquiring a stable sampling moment includes:

[0079] For any thermal response test experiment of a preset water flow, the heat conversion efficiency at all sampling moments in the thermal response test experiment is sorted in chronological order and curve fitting is performed to obtain the efficiency curve of the thermal response test experiment. The change of the heat conversion efficiency is reflected by a two-dimensional spatial curve. In the embodiment of the present invention, the horizontal axis of the efficiency curve is time, and the vertical axis is the heat conversion efficiency. The curve fitting can adopt a polynomial fitting algorithm. Curve fitting is a technical means well known to those skilled in the art. The curve fitting can also adopt the least squares method, etc., which will not be elaborated here.

[0080] The slope of each sampling moment on the efficiency curve is further obtained, and the slope is used to reflect the change of the heat conversion efficiency at each sampling moment. For any sampling moment on the efficiency curve, the two sampling moments adjacent to the sampling moment in time sequence are taken as the adjacent moments of the sampling moment, and the adjacent moments are determined for each sampling moment. In the embodiment of the present invention, for non-first and last sampling moments, the two sampling moments adjacent in time sequence are the two sampling moments closest to the left and right of the sampling moment, and for the first and last sampling moments, the two sampling moments adjacent in time sequence are the two consecutive closest sampling moments on one side of the sampling moment in time sequence.

[0081] The difference in slope between the sampling moment and each adjacent moment is further calculated to obtain the change difference between the sampling moment and each adjacent moment, and the degree of change deviation is reflected by the slope difference. The ratio of each change difference to the slope at the sampling moment is used as the change rate between the sampling moment and each adjacent moment, and the proportion of the slope change difference is reflected by the ratio of the change deviation to the slope of the sampling moment itself.

[0082] When all the change rates corresponding to the sampling moment are less than the preset change threshold, it means that the slope has a small deviation and is basically a stable change. The sampling moment is taken as a stable sampling moment. In the embodiment of the present invention, the preset change threshold is set to 0.05, that is, when the change rate does not exceed 5%, it can be regarded as a relatively stable change. The specific value can be adjusted by the implementer according to the specific implementation situation, and is not limited here.

[0083] After screening out the stable sampling moment for each thermal response test experiment, the overall size of the heat conversion efficiency after stabilization and the duration of the unstable moment reflect the degree of heat conversion characterization of the thermal response test experiment, and then determine the optimal water flow rate.

[0084] Preferably, in some possible implementations of the embodiments of the present invention, the method for determining the ideal flow rate includes:

[0085] First, for any thermal response test experiment under a preset water flow rate, the mean value of the heat conversion efficiency corresponding to all stable sampling moments in the thermal response test experiment is used as the stable efficiency distribution index of the thermal response test experiment. The distribution degree of the overall heat conversion efficiency under the stable state reflects the heat exchange performance under stable conditions. The greater the heat conversion efficiency, the better the heat exchange performance.

[0086] Secondly, the ratio of the number of all unstable sampling moments in the thermal response test experiment to the total number of all sampling moments is used as the stability rate indicator of the thermal response test experiment. The proportion of the number of unstable sampling moments reflects the duration of the unstable state. The more unstable moments there are, that is, the longer the unstable state lasts, it means that there is more energy consumption in the heat exchange and the heat exchange performance is poor.

[0087] Finally, the heat exchange performance index of the thermal response test experiment is obtained by combining the stable efficiency distribution index and the stable rate index of the thermal response test experiment. The higher the overall heat conversion efficiency after stabilization, that is, the larger the stable efficiency distribution index, the better the conversion situation. The shorter the duration of the unstable moment, that is, the smaller the stable rate index, the faster the heat conversion tends to stabilize, and the better the overall performance of the heat exchanger. In an embodiment of the present invention, the product of the value of the stable rate index of the thermal response test experiment after negative correlation mapping and the stable efficiency distribution index is used as the heat exchange performance index of the thermal response test experiment.

[0088] The ideal flow rate is determined based on the heat transfer performance index corresponding to all preset water flow rates. The larger the heat transfer performance index, the better the heat transfer performance in the corresponding thermal response test experiment, and the closer the corresponding water flow rate is to the optimal situation.

[0089] In an embodiment of the present invention, the preset water flow rate corresponding to the maximum heat exchange performance index among all preset water flow rates is taken as the ideal flow rate, and the optimal flow rate parameters are obtained by quantifying the heat exchange efficiency and comparing the heat exchange performance under different flow rates.

[0090] S4: According to the deviation between the water flow rate of the heat exchanger and the ideal flow rate during the current operation of the heat exchanger and the size of the ideal flow rate, the current heat exchange performance index of the heat exchanger is obtained.

[0091] Usually, the actual operation of the heat exchanger needs to meet the heat demand. When the deviation between the actual water flow rate of the heat exchanger and the ideal flow rate of the test result increases, it means that the actual operation of the heat exchanger is poor in heat exchange performance. For the ideal flow rate, when the heat exchange performance is the best, the lower the water flow rate, the better the energy saving effect and the better the heat exchange performance of the heat exchanger. Therefore, the heat exchange performance index is obtained by combining the actual deviation of the heat exchanger and the size of the ideal flow rate.

[0092] Preferably, in an embodiment of the present invention, the method for obtaining the heat exchange performance index includes:

[0093] The difference between the water flow rate of the heat exchanger during current operation and the ideal flow rate is taken as the water flow deviation. The larger the water flow deviation is, the greater the difference between the heat exchange performance under current operation and the optimal situation is.

[0094] Combined with the test size of the ideal flow rate, the ideal flow rate parameter can reflect the degree of optimization of the heat exchanger design. The smaller the ideal flow rate, the better the water energy saving effect under the optimal heat exchange performance. Therefore, the product of the water flow deviation and the ideal flow rate is negatively correlated and normalized to obtain the heat exchange performance index of the current heat exchanger. The larger the heat exchange performance index, the better the heat exchange performance of the heat exchanger.

[0095] After the heat exchange performance of the heat exchanger is analyzed, the current operation quality of the heat exchanger can be further analyzed through the size of the heat exchange performance index. When the operation index is poor, the staff can be notified to readjust the design of the heat exchanger. Therefore, after obtaining the heat exchange performance index, it also includes:

[0096] When the heat exchange performance index is greater than or equal to the preset first quality threshold, it means that the heat exchange performance at this time is better, and the current heat exchanger operation quality is recorded as excellent, and it can continue to be used. When the heat exchange performance index is less than the preset first quality threshold and greater than the preset second quality threshold, it means that the heat exchange performance of the heat exchanger at this time is average, and the current heat exchanger operation quality is recorded as qualified. You can notify the operator to optimize the maintenance of the heat exchanger and re-monitor the heat exchange performance. When the heat exchange performance index is less than or equal to the preset second quality threshold, it means that the heat exchange performance of the heat exchanger is poor, and the current heat exchanger operation quality is recorded as poor. The heat exchange effect of the heat exchanger can no longer meet this environment, and the heat exchanger needs to be replaced or repaired and the heat exchange performance needs to be re-tested.

[0097] In the embodiment of the present invention, since the larger the heat exchange performance index is, the better the heat exchange effect is, the preset first quality threshold must be greater than the preset second quality threshold. The preset first quality threshold can be set to 0.8, and the preset second quality threshold can be set to 0.6. The specific numerical values ​​can be adjusted by the implementer according to the specific implementation scenario, and are not limited here.

[0098] In summary, in the thermal response test experiment under different preset water flow rates of the present invention, the heat exchange with the rock mass at different temperature sampling positions at each sampling moment is combined with the adjustment of the thermal conductivity of the rock mass to obtain the heat absorption of the outer tube, reflecting the heat conversion at different positions, and further combined with the deviation of the outlet temperature and the bottom temperature of the tube to reflect the heat loss of the inner tube, and the heat conversion efficiency at each sampling moment is comprehensively obtained, so that the overall heat conversion analysis is more comprehensive and accurate. Then, according to each thermal response test experiment, the change distribution of the heat conversion efficiency in the time sequence is analyzed, the stable sampling moment is screened, and the proportion of the unstable sampling moment and the heat conversion efficiency distribution at the stable sampling moment are determined from the stable rate of the thermal response test experiment and the efficiency value after stabilization. From multiple preset water flow rates, the ideal flow rate is determined, and the quantitative heat conversion performance can further reflect the use of water flow energy from the flow rate, and the optimal water flow situation that characterizes the effect of heat conversion is obtained. Based on the ideal flow rate and the current running flow rate, the heat conversion and energy operation are combined to obtain the heat exchange performance index. The present invention performs heat conversion analysis at multiple positions under multiple water flow rates, and combines the changes in heat conversion efficiency over time to comprehensively evaluate the heat exchange performance from the perspective of operating water flow rate by combining the heat exchange effect and water flow energy conditions, thereby improving the reliability and accuracy of the heat exchange performance evaluation.

[0099] The present invention also provides a heat exchange performance calculation system for a medium-deep downhole heat exchanger, including a memory and a processor, wherein the processor executes a calculation program stored in the memory to implement a heat exchange performance calculation method for a medium-deep downhole heat exchanger as described above.

[0100] It should be noted that the sequence of the above embodiments of the present invention is for description only and does not represent the advantages and disadvantages of the embodiments. The processes depicted in the accompanying drawings do not necessarily require the specific order or continuous order shown to achieve the desired results. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0101] The various embodiments in this specification are described in a progressive manner, and the same or similar parts between the various embodiments can be referenced to each other, and each embodiment focuses on the differences from other embodiments.

Claims

1. A method for calculating the heat exchange performance of a medium-deep underground heat exchanger, characterized in that: The method comprises: Conduct thermal response test experiments on the heat exchanger based on different preset water flow rates, obtain the outlet temperature and tube bottom temperature of the heat exchanger at each sampling time under each preset water flow rate, and the internal temperature of the outer tube at each temperature sampling position; and obtain the thermal conductivity and detection temperature of the rock mass at each temperature sampling position; In each thermal response test experiment, the heat absorption degree of the outer tube at each temperature sampling position is obtained according to the difference between the detected temperature of the rock mass at each temperature sampling position at each sampling time and the internal temperature of the outer tube, combined with the thermal conductivity of the rock mass; the heat conversion efficiency at each sampling time is obtained according to the deviation between the outlet temperature of the heat exchanger and the bottom temperature of the tube at each sampling time, combined with the heat absorption degree of the outer tube at all temperature sampling positions; In the thermal response test experiment of each preset water flow rate, the stable sampling time is selected according to the distribution change of the heat conversion efficiency in the time series; according to the distribution of the heat conversion efficiency corresponding to the stable sampling time under each preset water flow rate and the proportion of the unstable sampling time, the ideal flow rate is determined from the preset water flow rate; According to the deviation between the water flow rate of the heat exchanger and the ideal flow rate during the current operation of the heat exchanger and the size of the ideal flow rate, the current heat exchange performance index of the heat exchanger is obtained.

2. The method for calculating the heat exchange performance of a medium-deep downhole heat exchanger according to claim 1 is characterized in that: The method for obtaining the heat absorption degree of the outer tube includes: For any sampling time in the thermal response test experiment, the product of the detected temperature and thermal conductivity of the rock mass at each temperature sampling position at the sampling time is normalized to obtain the heat reserve degree of each temperature sampling position at the sampling time; The difference between the internal temperature of the outer tube at each temperature sampling position at the sampling time and the detected temperature of the rock mass is taken as the internal and external temperature difference of the outer tube at each temperature sampling position at the sampling time; The heat absorption degree of the outer tube at each temperature sampling position at the sampling moment is obtained by combining the heat reserve degree at each temperature sampling position at the sampling moment and the temperature difference between the inside and outside of the outer tube.

3. The method for calculating the heat exchange performance of a medium-deep downhole heat exchanger according to claim 2 is characterized in that: The step of combining the heat reserve degree of each temperature sampling position at the sampling moment and the temperature difference between the inside and outside of the outer tube to obtain the heat absorption degree of the outer tube at each sampling position at the sampling moment includes: The product of the value of the negative correlation mapping of the temperature difference between the inside and outside of the outer tube at each temperature sampling position at the sampling moment and the heat reserve degree is used as the heat absorption degree of the outer tube at each temperature sampling position.

4. The method for calculating the heat exchange performance of a medium-deep downhole heat exchanger according to claim 1 is characterized in that: The method for obtaining the heat conversion efficiency includes: For any sampling time in the thermal response test experiment, the difference between the outlet temperature and the bottom temperature of the heat exchanger at the sampling time is taken as the heat loss degree at the sampling time; Calculate the average of the outer tube heat absorption at all temperature sampling positions at the sampling moment to obtain the heat absorption at the sampling moment; The heat conversion efficiency at the sampling moment is obtained by combining the heat loss degree and the heat absorption degree at the sampling moment.

5. The method for calculating the heat exchange performance of a medium-deep downhole heat exchanger according to claim 1 is characterized in that: The method for obtaining the stable sampling time comprises: For any thermal response test experiment of a preset water flow, the heat conversion efficiencies at all sampling moments in the thermal response test experiment are sorted in chronological order and curve fitting is performed to obtain the efficiency curve of the thermal response test experiment; Get the slope of each sampling moment on the efficiency curve; For any sampling moment on the efficiency curve, two sampling moments adjacent to the sampling moment in time sequence are regarded as adjacent moments of the sampling moment; Calculate the difference in slope between the sampling moment and each adjacent moment to obtain the change difference between the sampling moment and each adjacent moment; take the ratio of each change difference to the slope of the sampling moment as the change rate between the sampling moment and each adjacent moment; When all the change rates corresponding to the sampling moment are less than the preset change threshold, the sampling moment is regarded as the stable sampling moment.

6. The method for calculating the heat exchange performance of a medium-deep downhole heat exchanger according to claim 1 is characterized in that: The method of determining the ideal flow rate from the preset water flow rate according to the distribution of the heat conversion efficiency corresponding to the stable sampling moment under each preset water flow rate and the proportion of the unstable sampling moment includes: For any thermal response test experiment under a preset water flow rate, the average value of the heat conversion efficiency corresponding to all stable sampling moments in the thermal response test experiment is used as the stable efficiency distribution index of the thermal response test experiment; The ratio of the number of all unstable sampling moments in the thermal response test experiment to the total number of all sampling moments is used as a stable rate index of the thermal response test experiment; Combining the stable efficiency distribution index and the stable rate index of the thermal response test experiment, the heat transfer performance index of the thermal response test experiment is obtained; The ideal flow rate is determined based on the heat transfer performance indicators corresponding to all preset water flow rates.

7. The method for calculating the heat exchange performance of a medium-deep downhole heat exchanger according to claim 6 is characterized in that: The step of determining the ideal flow rate based on the heat exchange performance index corresponding to all preset water flow rates includes: The preset water flow rate corresponding to the maximum heat exchange performance index among all preset water flow rates is taken as the ideal flow rate.

8. The method for calculating the heat exchange performance of a medium-deep downhole heat exchanger according to claim 1 is characterized in that: The method for obtaining the heat exchange performance index includes: The difference between the water flow rate of the heat exchanger during current operation and the ideal flow rate is taken as the water flow deviation; The product of the water flow deviation and the ideal flow rate is negatively correlated and normalized to obtain the heat transfer performance index of the current heat exchanger.

9. The method for calculating the heat exchange performance of a medium-deep downhole heat exchanger according to claim 8, characterized in that: The step of obtaining the heat exchange performance index of the current heat exchanger further includes: When the heat exchange performance index is greater than or equal to the preset first quality threshold, the current heat exchanger operation quality is recorded as excellent; When the heat exchange performance index is less than the preset first quality threshold and greater than the preset second quality threshold, the current heat exchanger operation quality is recorded as qualified; When the heat exchange performance index is less than or equal to the preset second quality threshold, the current heat exchanger operation quality is recorded as poor; The preset first quality threshold is greater than the preset second quality threshold.

10. A heat exchange performance calculation system for a medium-deep underground heat exchanger, comprising a memory and a processor, characterized in that: The processor executes the calculation program stored in the memory to implement a method for calculating the heat exchange performance of a mid-depth downhole heat exchanger as described in any one of claims 1-9.

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