Engineering thermodynamics teaching experiment device

Abstract

The utility model discloses an engineering thermodynamics teaching experiment device, which takes a water tank wrapped with fireproof heat insulation materials as a main body, the water tank is filled with water and is provided with two temperature sensors, the upper part of the water tank is provided with a top cover, and the lower part of the water tank is provided with a thermal resistance type heating chassis and a strain type weighing sensor. The input front end of the thermal resistance type heating chassis is connected in series with a power meter; and the top cover is provided with a gas channel for water vapor to escape and a stirrer for improving the heating uniformity of the water tank. The teaching experiment device can be specially used for completing calculation experiments of related concepts of the second law of thermodynamics and entropy, and can also be used for completing measurement experiments of saturated vapor pressure and boiling point of water through the closed water tank.

Description

TECHNICAL FIELD

[0001] The utility model relates to engineering thermodynamics experimental equipment, concretely relates to the comprehensive teaching experimental device of the calculation and experimental demonstration of the second law of thermodynamics and the related concept of entropy can be completed by the structure of water heating and weighing. BACKGROUND

[0002] The essence of a plurality of engineering technical problems widely involved in energy utilization, energy saving and environmental protection, and new energy development and utilization can be attributed to the effective utilization and transmission of energy. Engineering thermodynamics is a science that studies the effective utilization of thermal energy and the conversion law of thermal energy and other forms of energy (such as mechanical energy), aiming to explore ways to improve the efficiency of thermal conversion by studying the laws of thermal energy conversion and heat transfer, thereby improving the effective utilization of energy. Engineering thermodynamics experiment, as the main link between theory and practice, is an important way to deepen understanding and consolidate the theoretical knowledge of engineering thermodynamics, and is also a useful supplement to related knowledge.

[0003] The engineering thermodynamics experimental equipment used in teaching mainly focuses on completing more than 30 experimental projects such as gas specific heat measurement at constant pressure, saturated steam P-T relationship measurement, carbon dioxide P-V-T relationship measurement, and nozzle flow characteristics. Although engineering thermodynamics teaching experimental devices have basically realized electrification and automation upgrade in recent years, and some have realized virtual simulation experiment, the experimental projects integrated by these devices are highly homogeneous, and the experimental content is old, and there are few experimental projects directly related to the second law of thermodynamics.

[0004] The application of water in heat engines laid the foundation for the establishment of thermodynamics. Using water as the main medium of experimental equipment, conducting engineering thermodynamics experiments not only helps to deepen the understanding of the thermodynamic properties of water and its important role in production and life, but also helps to think about the thermodynamic phenomena related to water in daily production and learning, thereby providing new ideas or ways to solve related engineering technical problems. For example, the second law experiment device for engineering thermodynamics teaching in CN210627617U can intuitively reflect the heat loss of water in heat transfer by controlling the heating temperature of the water tank and using different bases of the built-in coil, but the experimental device cannot demonstrate the calculation of the related concept of entropy in the law.

[0005] In addition, in order to meet the needs of practical engineering applications, the parameters of some products related to thermal conversion are also detected. However, due to the complexity of the actual engineering application process, it may also involve material exchange, so the equipment used in these detections often has a single function. For example, the water vapor production detection device in CN108956369A mainly measures the weight of water vapor produced under different conditions (measured after condensation into water) and calculates the difference to determine the efficiency of the water vapor production functional element (specifically, a heating appliance that converts chemical energy into heat energy) in the product to be detected. SUMMARY

[0006] The utility model discloses an engineering thermodynamics teaching experiment device.

[0007] In order to achieve the above object, the utility model adopts the following technical scheme:

[0008] The engineering thermodynamics teaching experiment device comprises a power meter, a heat-insulated container that can be weighed, a gas temperature sensor, a water body temperature sensor and a gas passage for water vapor escape provided on the heat-insulated container, and an electric heater (for example, a resistance type) for inputting heat energy into the heat-insulated container, wherein the electric heater is connected with the power meter.

[0009] Preferably, the gas passage is closable, and the heat-insulated container becomes airtight by closing the gas passage.

[0010] Preferably, the heat-insulated container comprises a water tank and a heat-insulating layer (for reducing heat transfer with the environment) provided on the water tank, the upper part (for example, the open end of the top of the water tank) of both the heat-insulating layer and the water tank is provided with a replaceable top cover (specifically, the top cover with the gas passage is replaced by the top cover without the gas passage, and the replacement of the top cover is equivalent to closing the gas passage), and the electric heater is arranged at the lower part (for example, embedded in the closed end of the bottom of the water tank) of the water tank.

[0011] Preferably, the water tank is cylindrical, and a heat-insulating layer made of fireproof and heat-insulating material is arranged on the outer surface of the side wall of the water tank.

[0012] Preferably, a quartz observation window is further arranged on one side of the water tank to observe the boiling phenomenon of the water in the water tank.

[0013] Preferably, temperature sensors are arranged on one side (for example, the other side opposite to the above-mentioned one side) of the water tank near the upper part and the lower part, respectively (wherein the temperature sensor near the upper part is the above-mentioned gas temperature sensor, and the temperature sensor near the lower part is the above-mentioned water body temperature sensor, that is, the water surface after the water tank is filled with water is between the two temperature sensors); and the signal output end of the temperature sensor extends outwards from the water tank and penetrates through the heat-insulating layer.

[0014] Preferably, the electric heater is a heating base of a thermal resistance type.

[0015] Preferably, the first type of top cover of the heat-insulated container is provided with the gas passage (i.e. the gas passage is arranged on the top cover), and the top cover is further provided with a water tank stirrer (which is particularly used for stirring the water body part after the water tank is filled with water and starts to be heated).

[0016] Preferably, the second type of top cover of the heat-insulated container is not provided with the gas passage, so that it can seal the heat-insulated container (particularly the sealed water tank), and the top cover is provided with a water tank pressure gauge (which is particularly used for measuring the pressure inside the sealed water tank).

[0017] Preferably, the second type of top cover is further provided with a safety pressure relief valve.

[0018] Preferably, the heat-insulated container further comprises an anti-splashing screen arranged in the water tank.

[0019] Preferably, the heat-insulated container further comprises a strain device (which is particularly used for weighing the water body part in the water tank), and the water tank is arranged on the strain device (e.g. a strain type weighing sensor).

[0020] Preferably, the engineering thermodynamics teaching experimental device further comprises a control instrument, and the above-mentioned gas temperature sensor, water body temperature sensor, heating base of a thermal resistance type, strain type weighing sensor, power meter (and water tank pressure gauge or water tank stirrer) are connected to the control instrument through cables.

[0021] Preferably, the control instrument is provided with a temperature and pressure display screen, a mass (water body weighing result) display screen and a power and timing display screen.

[0022] Preferably, the water tank is supported on the control instrument through the strain device.

[0023] The beneficial effects of the utility model lie in:

[0024] The engineering thermodynamics teaching experimental device can carry out experiments on heat energy conversion and heat transfer with water as a working medium, can obtain the mass (and temperature) of the water body at different stages in the heating process while measuring the electric power for water heating by using a power meter, and provides a basis for calculating the input heat energy (i.e. electric energy for heating) and the energy required for water temperature rise and phase change, so as to complete the calculation experiment and experimental demonstration of the second law of thermodynamics and the related concepts of entropy.

[0025] Further, the engineering thermodynamics teaching experiment device can complete the determination experiment and experimental demonstration of the saturated vapor pressure, boiling point and dilute solution colligative property (specifically related to the saturated vapor P-T relationship) of water (or dilute solution) by using the stable gas pressure (measured by the water tank pressure gauge) and the water temperature (or gas temperature) at the corresponding moment under the closed condition (the closed condition can be realized by replacing the top cover without gas channel). BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 It is a principle schematic view of the comprehensive engineering thermodynamics teaching experiment device in the embodiment (the top cover can be replaced, the water tank can be weighed and heated);

[0027] Figure 2 It is a principle schematic view of the comprehensive engineering thermodynamics teaching experiment device in the embodiment (the top cover can be replaced, the water tank can be weighed and heated); Figure 1 It is a structure schematic view of the teaching experiment device shown in the figure (1# top cover is used);

[0028] Figure 3 It is a structure schematic view of the teaching experiment device shown in the figure (1# top cover is used); Figure 1 It is a structure schematic view of the teaching experiment device shown in the figure (1# top cover is used);

[0029] In the figure, 1 is a gas temperature sensor, 2 is a water temperature sensor, 3 is a temperature and pressure display screen, 4 is a mass display screen, 5 is a control instrument, 6 is a power and timing display screen, 7 is a strain type weighing sensor, 8 is a heating bottom plate of thermal resistance type, 9 is a stirrer, 10 is an observation window, 11 is a heat insulation layer, 12 is a screen, 13 is a gas channel, 14 is a 1# top cover, 15 is a pressure gauge, 16 is a safety pressure relief valve, 17 is a 2# top cover, 18 is a buckle, and 19 is a water tank. DETAILED DESCRIPTION

[0030] The utility model will be further explained in detail in combination with the drawings and embodiments. The embodiments are only used for explaining the utility model, and are not limited to the protection scope of the utility model.

[0031] (I) Structure design of the comprehensive engineering thermodynamics teaching experiment device

[0032] Referring to Figure 1This utility model's comprehensive engineering thermodynamics teaching experimental device uses a water tank 19, externally wrapped with a heat insulation layer, as its main body. Two temperature sensors (a gas temperature sensor 1 and a water temperature sensor 2) are installed inside the main body. A replaceable top cover is installed on the upper part of the main body, and a heating base (for heating the water in the tank 19) and a strain gauge for weighing are installed on the lower part. The heating base contains an electric heater, and a power meter (for measuring the electrical power used by the electric heater for heating the water) is connected in series at the input end of the electric heater (i.e., installed on the power line of the electric heater). The measurement of data such as gas and water temperatures, water mass, heating power, and heating time in the entire experimental device is controlled by a controller and displayed in real time (the time data is measured by a timer built into the controller).

[0033] The teaching experimental apparatus is equipped with two types of top covers with different functions. When the top cover with a gas channel is installed on the upper part of the main body, water vapor can escape through the gas channel during the water heating process (by setting up the gas channel, the entire experimental apparatus and its surrounding environment are integrated), which can be used to perform calculations of the second law of thermodynamics and system entropy. When the top cover without a corresponding gas channel is installed on the upper part of the main body, it can be used to determine the saturated vapor pressure of water, the boiling point under different pressures, and the colligative properties of dilute solutions (specifically involving the saturated vapor pressure-to-temperature (PT) relationship).

[0034] See Figure 2 Top cover 14 is the aforementioned top cover with a gas passage. The water tank adjacent to the lower side of this top cover is made of stainless steel and is long and cylindrical. The side wall of the water tank is wrapped with fireproof and heat-insulating material as a heat insulation layer 11. To reduce heat loss during water heating, the heat insulation layer 11 should cover the entire outer side of the water tank as much as possible; one side of the water tank ( Figure 2 A rectangular quartz observation window 10 is located on the right side of the water tank to observe the boiling process. A water temperature sensor 2 is installed on one side of the water tank. Figure 2 The lower part (left side) of the middle section is used to measure the temperature during the water heating process (heating or boiling) by inserting it into the water body; the gas temperature sensor 1 is installed on one side of the water tank. Figure 2The temperature sensor on the upper part of the left side (No. 1) does not contact the water and can measure the temperature of the water vapor rising after heating. Both temperature sensors penetrate the heat insulation layer 11 and the side wall of the water tank and are sealed. The measured temperature data are displayed on the temperature and pressure display screen 3 of the control instrument 5. The water in the water tank is heated by the embedded heating resistance type heating bottom plate 8 at the bottom of the water tank. The heating power can be adjusted (for example, the heating current can be reduced or increased) on the control instrument 5. At the same time, the heating power is measured by a power meter (provided in the control instrument 5), and the measured data are displayed on the power and timing display screen 6. Combined with the timer (measuring data on the power and timing display screen 6), the heating time is recorded, and the required electric energy for heating can be calculated. The strain type weighing sensor 7 is embedded and installed on the control instrument 5. The lower part of the water tank is supported on the upper part of the control instrument 5 through the strain type weighing sensor 7. The measured data are displayed on the mass display screen 4. After setting the measurement zero point on the control instrument 5, the initial mass of the water added to the water tank, the remaining mass of the water consumed by evaporation, or the remaining mass of the water consumed by boiling can be measured in the experiment. Using the initial mass of the water and the temperature change of the water during heating (or using the mass of the water consumed during boiling), the energy required for the water to heat up (or for the water to undergo gasification phase change) can be calculated, and the change in the entropy of the water can be calculated using the energy.

[0035] The stirrer 9 is further provided on the No. 1 top cover 14. The stirring rod of the stirrer 9 penetrates the water tank through the long rod-shaped stirring shaft at the central position between the two gas channels 13 (channel number is two) on the No. 1 top cover 14, and can stir the water at a certain frequency (rotational speed) to make the water heat evenly, thereby reducing the measurement error of the water temperature. In addition, in order to block the splashing of liquid droplets when the water boils and prevent the loss of water mass caused by the flying of liquid droplets, a metal screen 12 slightly higher than the water surface is installed in the water tank, and the stirring shaft of the stirrer 9 penetrates the screen and does not interfere with each other.

[0036] Referring to Figure 3 The No. 2 top cover 17 belongs to the above-mentioned another type of top cover without corresponding gas channels. Similar to the No. 1 top cover 14, the No. 2 top cover 17 is also tightly connected with the water tank wrapped with the heat insulation layer 11 by the buckle 18. The pressure gauge 15 is installed on the No. 2 top cover 17 to measure the pressure in the water tank in a sealed state (the actual measured is the pressure of the gas in the upper part of the water tank). The measured pressure data are displayed on the temperature and pressure display screen 3 of the control instrument 5. In addition, in order to prevent accidents caused by excessive pressure, the safety pressure relief valve 16 is further installed on the No. 2 top cover 17.

[0037] In the aforementioned comprehensive engineering thermodynamics teaching experimental device, the gas temperature sensor 1, water temperature sensor 2, strain gauge load cell 7, resistance temperature detector (RTD) heating base 8, and power meter are all connected to the controller 5 via cables (e.g., signal lines, electrical control harnesses). Once connected, the cable connections generally do not require further adjustment. The stirrer 9 or pressure gauge 15 is connected to the controller 5 via cables (e.g., signal lines, electrical control harnesses) after the corresponding top cover is replaced during the experiment. The controller 5 can also control the power supply of the RTD heating base 8 and stirrer 9 (i.e., provide power and control their on / off states). When selecting components for the teaching experimental device, the ranges of the gas temperature sensor 1 and water temperature sensor 2 are both 0~200℃, the range of the strain gauge load cell 7 is 0~2 kg, the power of the RTD heating base 8 is ≥1 kW, the speed range of the stirrer 9 is 0~500 rpm, and the range of the pressure gauge 15 is 0~300 kPa. The dimensions of the water tank are: diameter 20 cm and height 30 cm.

[0038] (II) Application of Comprehensive Engineering Thermodynamics Teaching Experiment Device

[0039] 2.1 The Second Law of Thermodynamics and Calculation of System Entropy

[0040] The experiment requires the use of top cover 14. Before the experiment, add a certain amount of water to the water tank (ensure that the water surface is above the water temperature sensor 2, but does not contact the gas temperature sensor 1). Then, install the top cover on the water tank covered with the heat insulation layer 11 and connect the electrical control harness of the stirrer 9 to the controller 5.

[0041] Demonstration Case 1

[0042] Record the mass m1 and initial temperature t1 of the system (water in the tank) after water is added. Turn on the resistance heating plate 8 and stirrer 9 to heat and stir the water. Record the time t required to heat the water to the set temperature t2 (before the water boils). v Given the system mass m2, and the average power consumption P of the resistance heating chassis 8 during heating (for example, recording 10 power meter measurements at one-minute intervals and then taking the average), then:

[0043] (1) Calculate the electricity consumption Q using the following formula:

[0044] Q = P × t v

[0045] (2) Assuming that the evaporation during the water heating process is negligible, calculate the energy input E required for water heating using the following formula. v :

[0046] E v =m1×(t2-t1)×specific heat capacity of water

[0047] (3) Calculate the change in system entropy ΔS using the following formula:

[0048] ΔS = ∫(dE v / t)

[0049] Where t is temperature.

[0050] Demonstration Case 2

[0051] For a system with a certain mass and initial temperature after water is added (referring to the water in the tank), turn on the resistance heating plate 8 and the stirrer 9 to heat and stir the water. Record the water temperature and mass m1 when the water boils (determined by the quartz observation window 10), and continue heating to maintain the water at boiling point t. b Record the system mass m2 at the specified time (e.g., minutes), and obtain the average power consumption P of the resistance heating base 8 during the heating and boiling period. Note that during the heating and boiling period, the water evaporation should not be reduced to below the installation height of the water temperature sensor 2.

[0052] (1) Calculate the electricity consumption Q using the following formula:

[0053] Q = P × t b

[0054] (2) Calculate the energy input E required for water to boil using the following formula. b :

[0055] E b = (m1-m2) × latent heat of vaporization of water

[0056] (3) Calculate the change in system entropy ΔS using the following formula:

[0057] ΔS = ∫(dE b / t)

[0058] Where t is temperature.

[0059] Test results show that the calculated electricity consumption Q in the above demonstration case is greater than the energy input E required for the corresponding water to heat up (or undergo a gasification phase change). v (or E) b In other words, the aforementioned comprehensive engineering thermodynamics teaching experimental device can demonstrate the content of the second law of thermodynamics and be used for trend analysis. Even when the entire experimental device cannot provide an adiabatic environment (it will still generate weak heat dissipation), it can achieve the teaching experimental objectives relatively accurately.

[0060] 2.2 Calculation of PT Relationship for Saturated Vapor

[0061] The experiment needs to use the No. 2 cover 17, and a certain amount of water is added to the water tank before the experiment (to ensure that the water surface is higher than the water temperature sensor 2, but will not contact the gas temperature sensor 1) After that, the cover is installed on the water tank wrapped with thermal insulation layer 11, the signal line of pressure gauge 15 is connected to control instrument 5, and the safety pressure relief valve 16 is checked for normal operation.

[0062] Demonstration case 3

[0063] For the system with a certain mass and initial temperature after adding water (referring to the water in the water tank), turn on the heating resistance heating base 8 to heat the water. Observe and record the reading of the pressure gauge 15, and when the pressure reaches a certain value (referring to a value before boiling), reduce the heating current of the heating resistance heating base 8 to keep the system warm, and when the pressure and temperature (measured by the water temperature sensor 2, with the gas temperature sensor 1 as the reference) are stable, record the pressure and temperature; Repeat the above steps, and before boiling, heat (increase pressure) and measure the stable pressure and temperature to obtain multiple measurement points. Then continue to heat the water to boiling, and continue to record the corresponding boiling point (measured by the water temperature sensor 2) as the pressure changes. According to all the data points, draw the saturated vapor P-T relationship diagram.

[0064] Demonstration case 4

[0065] Determine the mass m1 of the system after adding water (referring to the water in the water tank), open the buckle 18 on the No. 2 cover 17, and according to the water mass (i.e. m1), a small amount of salt (NaCl) is added to the water tank, and the No. 2 cover 17 is tightly connected to the water tank wrapped with thermal insulation layer 11. Calculate the NaCl concentration in the obtained dilute solution and record it, and then repeat the above demonstration case 3 saturated vapor P-T relationship (figure) determination steps.

[0066] In combination with the above demonstration case 3, compare the saturated vapor pressures of dilute solutions with different concentrations and pure water (i.e. without NaCl), and analyze the effect of solutes in the solution on the saturated vapor pressure of water, thereby revealing the colligative properties of dilute solutions.

Claims

1. An experimental apparatus for teaching engineering thermodynamics, characterized by: The device comprises a power meter, a weighable heat-insulated container, a water temperature sensor (2) and a gas passage (13) for water vapor escape arranged on the heat-insulated container, and an electric heater for inputting heat energy into the heat-insulated container, wherein the electric heater is connected with the power meter.

2. The teaching experimental apparatus for engineering thermodynamics of claim 1, wherein: The gas passage (13) can be closed.

3. The teaching experimental apparatus for engineering thermodynamics of claim 1, wherein: The heat-insulated container comprises a water tank (19) and a heat-insulated layer (11) and a top cover arranged on the water tank (19), and the gas passage (13) is arranged on the top cover.

4. The teaching experimental apparatus for engineering thermodynamics of claim 3, wherein: The top cover is further provided with a water tank stirrer (9).

5. The teaching experimental apparatus for engineering thermodynamics of claim 1, wherein: The heat-insulated container comprises a water tank (19) and a heat-insulated layer (11) and a top cover arranged on the water tank (19), and the top cover is provided with a water tank pressure gauge (15).

6. The teaching experimental apparatus for engineering thermodynamics of claim 5, wherein: The top cover is further provided with a safety pressure relief valve (16).

7. The teaching experimental apparatus for engineering thermodynamics of claim 3 or 5, wherein: The water tank (19) is further provided with an observation window (10).

8. The teaching experimental apparatus for engineering thermodynamics of claim 3 or 5, wherein: The heat-insulated container further comprises an anti-splashing screen (12) arranged in the water tank (19).

9. The teaching experimental apparatus for engineering thermodynamics of claim 3 or 5, wherein: The heat-insulated container further comprises a strain device for weighing, and the water tank (19) is arranged on the strain device.

10. The teaching experimental apparatus for engineering thermodynamics of claim 9, wherein: The water tank (19) is supported on a control instrument (5) through the strain device, and the strain device, the electric heater, the water tank pressure gauge (15), the water temperature sensor (2) and the power meter are connected with the control instrument (5) through cables.

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