Distributed measurement method and device for thermodynamic parameters of hydrocarbon fuel

Abstract

The invention discloses a hydrocarbon fuel thermodynamic parameter-oriented distributed measurement method, which comprises the following steps: storing a target substance in a thermostatic bath, maintaining the temperature at 298 K, pumping the target substance into a test tube, raising the temperature to an initial cracking temperature, and raising the temperature from the initial cracking temperature to a temperature at which the target substance is deeply cracked to cause coke to block a pipeline; according to the parameters monitored in real time, on-line measuring the heat flux density of heat transfer between the on-way calorimetric infinitesimal element of the test tube and the target substance in the infinitesimal element based on the calorimetric model; adjusting the pressure, and continuing to execute the steps to obtain the heat flux density of heat transfer between the on-way calorimetric infinitesimal of the test tube and the target substance in the infinitesimal under different pressure conditions; carrying out distributed measurement on the thermodynamic parameters of the target substance to obtain a function of the thermodynamic parameters of the target substance changing along with position, temperature and pressure. The invention further discloses a measuring device adopting the method. By means of the method and device, distributed measurement of the four thermodynamic parameters including the temperature, the heat sink, the isobaric specific heat and the isobaric entropy change is achieved.

Description

Technical Field

[0001] The invention relates to the fields of thermochemistry, thermodynamics and calorimetry of hydrocarbon fuels, and in particular to a distributed measurement method and device for thermodynamic parameters of hydrocarbon fuels. Background Art

[0002] Endothermic hydrocarbon fuel is a new type of fuel developed to meet the "miniaturization, high speed and long-range" requirements of future aircraft and missile weapons. It has excellent volume properties and meets the requirements of aircraft integrated design. Due to the high temperature and high pressure working environment, the fuel has great particularity and complexity in the flow heat transfer, cracking and combustion processes. The fuel is in a supercritical state of high temperature and high pressure in the cooling channel of the aircraft, and it is accompanied by drastic changes in thermodynamic parameters near the quasi-critical temperature. As the fuel temperature increases, the fuel undergoes a cracking reaction and gradually deepens, and the fuel components undergo profound changes, often containing hundreds of components such as alkanes, cycloalkanes and aromatic hydrocarbons, which further increases the difficulty of calculating its thermodynamic parameters.

[0003] The distributed calculation method of thermodynamic parameters covers thermodynamic parameters such as heat transfer of hydrocarbon fuel flow under supercritical state, temperature, isobaric specific heat, isobaric enthalpy change, isobaric entropy change, isothermal and isobaric Gibbs free energy during thermochemical reactions.

[0004] In the traditional thermodynamic parameter measurement method, for example, the patent with application number CN201010590586.3 discloses a transient measurement method and device for thermophysical properties, which is used to measure the thermal conductivity, thermal diffusivity, isobaric specific heat and density of materials. The device satisfies the law that the thermophysical properties of materials change with temperature near room temperature. However, the application conditions of hydrocarbon fuels in hypersonic aircraft are high temperature, high pressure and high flow rate, which do not conform to the actual application scenario of the patent. Patents with application numbers CN201822011875.8 and CN201510154541.4 disclose measurement devices for isobaric specific heat of gas and liquid respectively. When hydrocarbon fuel acts in the active cooling system of hypersonic aircraft, its own phase will be transformed from liquid to gas-like and liquid-like supercritical state; the above patents only carry out constant pressure specific heat measurement for single-phase fluids, and the actual application scenario does not conform to the application scenario of hydrocarbon fuels. The patent application number CN201911177444.1 discloses a test method for an endothermic hydrocarbon fuel heat sink. The patent uses the UI heating model and the law of conservation of energy to measure the fuel heat sink. However, the contact resistance between the heating electrode and the heating pipe in the UI heating model is still unclear; secondly, the heat dissipation of the heating plate is not considered separately in the energy balance model.

[0005] Developing methods to measure the thermodynamic parameters of hydrocarbon fuels and revealing the inherent laws of hydrocarbon fuel flow heat transfer, cracking and combustion processes are currently hot topics in this field. Since hydrocarbon fuels are in an extreme environment of high temperature and pressure in the engine, the fuel components are constantly changing with time and space, so online measurement methods can be closer to actual working conditions. Summary of the invention

[0006] The purpose of the present invention is to provide a distributed measurement method and device for thermodynamic parameters of hydrocarbon fuels, which realizes the distributed measurement of four thermodynamic parameters: temperature, heat sink, isobaric specific heat and isobaric entropy change.

[0007] The present invention provides the following technical solutions:

[0008] A distributed measurement method for thermodynamic parameters of hydrocarbon fuels, the method comprising:

[0009] (1) Storing the target substance in a fuel thermostatic tank and maintaining the temperature at 298K;

[0010] (2) pumping the target substance into the test tube and heating it to the initial cracking temperature to cause a cracking reaction, and then heating the target substance from the initial cracking temperature to the target substance deep cracking temperature, where the target substance deep cracking temperature is the temperature at which coke blocks the pipe;

[0011] (3) Real-time monitoring of the inlet and outlet temperature changes of the target material, the temperature development trend of the wall surface along the test pipe, the system pressure at both ends of the test pipe, the resistance of the test pipe, and the current and voltage at both ends of the test pipe;

[0012] (4) according to the parameters monitored in real time in step (3), the energy transferred between the calorimetric microelement along the test tube and the target substance in the microelement is obtained by online measurement based on the calorimetric model;

[0013] (5) When the test tube is cooled to room temperature, the pressure is adjusted and the above steps (1) to (4) are continued to be performed to obtain the heat flux density of heat transfer between the calorimetric micro-element along the test tube and the target material in the micro-element under different pressures;

[0014] (6) The industrial computer conducts distributed measurement of the thermodynamic parameters of the target material based on the heat flux density of the heat transfer between the calorimetric micro-element along the test tube and the target material in the micro-element under different pressures, and obtains the function of the thermodynamic parameters of the target material changing with position and temperature.

[0015] In order to solve the problem of the difficulty of traditional fluid thermodynamic parameter measurement methods in obtaining thermodynamic parameters of the distribution of thermodynamic parameters of hydrocarbon fuels along the test tube and the thermal cracking reaction of hydrocarbon fuels under high temperature and high pressure conditions, the present invention proposes a new thermodynamic parameter measurement method based on distributed flow calorimetry, which aims to accurately measure the thermodynamic parameters of hydrocarbon fuels along the test tube and the relevant parameters of the thermal cracking reaction of hydrocarbon fuels under high temperature and high pressure conditions. The thermodynamic parameters measured by the present invention include the temperature, heat sink, isobaric specific heat and isobaric entropy change of hydrocarbon fuels. The accurate measurement of these key thermodynamic parameters is an important basis for studying the heat transfer law of fuel flow and investigating the chemical reaction of fuels. Therefore, the present invention is of great significance to the basic research of hydrocarbon fuels.

[0016] The technical concept of the present invention is as follows: based on the calorimetric model, the present invention measures the heat flux density of heat transfer between the calorimetric microelement along the test tube and the target material in the microelement, obtains the temperature, heat sink, isobaric specific heat and isobaric entropy change distribution of the target material along the test tube, and studies the changes of the heat sink, isobaric specific heat and isobaric entropy change of the target material with temperature; by adjusting the back pressure valve to change the pressure of the test system, the temperature, heat sink, isobaric specific heat and isobaric entropy change distribution of the target material along the test tube under different pressures are obtained, and studies the changes of the heat sink, isobaric specific heat and isobaric entropy change of the target material with temperature under different pressure conditions.

[0017] The measurement method provided by the present invention is distributed flow calorimetry.

[0018] In step (1), the target substance is selected from one or a combination of at least two of alkanes, olefins, cycloalkanes, cycloolefins or aromatic hydrocarbons.

[0019] Furthermore, in step (2), the target substance is pumped into the test tube at a flow rate of 0.1-10 g / s or 1-1000 ml / s, the initial cracking temperature is 773-823 K, the deep cracking temperature of the target substance is 1023-1123 K, and the heating rate is 5-25 K / min.

[0020] For the deep cracking temperature of the target material, fuel cracking will produce a large amount of coke to block the pipeline. The general temperature upper limit during the experiment is 1123K.

[0021] Furthermore, in step (2), the cracking reaction of the target substance includes a primary thermal cracking reaction and a multi-stage thermal cracking reaction; the primary thermal cracking reaction is the thermal cracking of the target substance itself; and the multi-stage thermal cracking reaction is a multi-step thermal cracking of the primary thermal cracking product of the target substance.

[0022] Furthermore, in step (4), the calorimetric model is used to calculate the energy required for the target substance to heat up, including the heat flux density (qtotal,x ), heat flux density (q loss,x ), heat flux density of heat conduction between micro-elements of the test tube (q cond,x ), the heat flux density (q end,x ), the heat flux density (q fluid,x );

[0023] The test tube microelement is a test tube with a length of L meters, which is evenly divided into n test tube sections with a length of ΔL during calculation, and the microelement at the inlet end of the pipe is x=1, and the microelement at the outlet end of the pipe is x=n; the heat flux density of the test tube input by the DC constant voltage power supply is obtained by the following method: the function of the test tube resistivity changing with temperature is pre-calibrated by a four-wire measurement method, and the test tube resistance is corrected in real time in combination with the current value and voltage value applied by the DC constant voltage power supply to both ends of the test tube; further, the resistance distribution along the test tube is obtained by the temperature distribution of the wall surface along the test tube; the heat flux density of the test tube microelement input by the DC constant voltage power supply is calculated according to the current value, resistance value and microelement surface area of ​​the test tube microelement, that is, q total,x ;

[0024] The heat flux density of the heat transfer from the test tube microelement to the environment is obtained by pre-calibrating the function of the heat flux density of the heat convection and heat radiation of the test tube microelement wall surface with the temperature of the test tube wall surface, that is, q loss,x ;

[0025] The heat flux density of heat conduction between the micro-elements of the test tube is obtained by pre-calibrating the function of the thermal conductivity of the test tube changing with temperature, combining the temperature distribution of the wall surface along the test tube to obtain the thermal conductivity distribution along the test tube and the first-order derivative function of the wall surface temperature along the test tube, and further obtaining the heat flux density of heat conduction between the micro-elements of the test tube, that is, q cond,x ;

[0026] The heat flux density of heat conduction from both ends of the test tube to the cold end is obtained by presetting the cold end temperature at the inlet of the pipe to 298K, and the cold end temperature at the outlet of the pipe to the fluid outlet temperature, and combining the temperature distribution of the wall along the test tube to obtain the thermal conductivity of heat conduction from both ends of the test tube to the cold end and the first-order derivative value of the wall temperature, and further obtain the heat flux density of heat conduction from both ends of the test tube to the cold end, that is, q end,x ;

[0027] The heat flux density of the heat transfer from the test tube microelement to the target material in the microelement is obtained by establishing an energy conservation equation, namely (q total,x -q loss,x )·A out =(Δq cond,x +q end,x / n)·S+q fluid,x ·Ain ; Among them A out A is the surface area of ​​the microelement of the test tube; in is the surface area of ​​the test tube microelement; S is the cross section of the test tube microelement; n is the number of test tube microelement; x is the serial number of the test tube microelement; q fluid,x is the heat flux density of heat transfer from the test tube microelement to the target material inside the microelement.

[0028] Furthermore, in step (6), the thermodynamic parameters include the temperature, heat sink, isobaric specific heat and isobaric entropy change distribution of the target substance along the test tube.

[0029] Furthermore, in step (6), the function of the target substance thermodynamic parameters changing with position, temperature, and pressure includes the temperature, heat sink, isobaric specific heat, and isobaric entropy change distribution of the target substance along the test tube at different pressures, which are T x , H x , C p,x , S x ; The heat sink, isobaric specific heat, and isobaric entropy change of the target substance at different pressures are functions of temperature, which are H(T), C p (T), S(T).

[0030] Furthermore, in step (6), the function of the target substance thermodynamic parameter changing with position, temperature and pressure is: Since the test tube microelement sequence number x and the target substance temperature in the test tube microelement have a one-to-one correspondence,

[0031] The heat sink distribution along the test tube is: H x =q fluid,x ·A in / m;

[0032] The function of the heat sink changing with temperature is: H(T)=-H inlet +∑q fluid,x ·A in / m; where H inlet is the heat sink of the target substance at 298K;

[0033] The temperature distribution of the test tube along the process is: T x =H -1 (T) = H -1 [-H inlet +∑q fluid,x ·A in / m];

[0034] The isobaric specific heat distribution of the test tube along the way is: C p,x =q fluid,x ·A in / (m·ΔT f,x );

[0035] The function of the isobaric specific heat changing with temperature is: C p (T) = q fluid,x ·A in / (m·ΔT f,x );

[0036] The isobaric entropy change distribution along the test tube is: S x =∫m C p (T)·(M0T) -1 ·dT; where C p (T) is the function of isobaric specific heat changing with temperature;

[0037] The function of the isobaric entropy change with temperature is: S(T)=-S inlet +∫m C p (T)·(M0T) -1 ·dT; where S inlet is the entropy of the target substance at 298K;

[0038] Where m is the mass of the target substance in the microelement, ΔT f,x is the temperature difference between the two ends of the test tube microelement, and M0 is the relative molecular weight of the target substance.

[0039] The present invention also provides a distributed measurement device for thermodynamic parameters of the above method, the measurement device comprising:

[0040] A high-pressure constant-flow pump is used to stably pump the target substance into the test tube;

[0041] Liquid gear flowmeters are used to monitor fluid mass flow in real time;

[0042] The DC regulated power supply is used to input stable energy to the test tube and monitor the voltage and current at both ends of the test tube in real time;

[0043] The test tube is used for energy balance;

[0044] Thermocouples are used to monitor the fluid outlet temperature in real time;

[0045] Infrared thermal imager is used to monitor the temperature of the test tube wall in real time;

[0046] The pressure sensor is used to monitor the system pressure in real time;

[0047] The back pressure valve is used to provide a stable system pressure;

[0048] The gas-liquid separation tank is used to separate the cracking gas and cracking liquid of the target substance;

[0049] The waste gas and waste liquid recovery device is used to recover the cracking gas and cracking liquid of the target substance;

[0050] The industrial computer is used to execute steps (4) and (6).

[0051] The beneficial effects of the present invention are:

[0052] The distributed measurement method provided by the present invention focuses on the changes in thermodynamic parameters of hydrocarbon fuels under high temperature, high pressure, multi-component and variable composition conditions: hydrocarbon fuels are pumped into the test pipe under constant conditions, and heated under certain heat flux conditions, thereby undergoing thermochemical reactions; after a stable temperature field is formed between the fuel, the test pipe and the environment, the temperature changes of the fuel inlet and outlet and the development trend of the wall temperature along the test pipe are measured online using a temperature measuring component; the industrial computer performs distributed calculations of thermodynamic parameters based on a calorimetric model and thermodynamic laws. The thermodynamic parameters measured by the present invention include the temperature, heat sink, isobaric specific heat and isobaric entropy change of the fuel.

[0053] Based on the distributed flow calorimetry and axial differential ideas, the present invention creatively proposes a distributed measurement method for the thermodynamic parameters of hydrocarbon fuels. This method takes the fuel and test pipeline micro-elements as research objects, deeply considers the phenomenon that the components in the fuel thermochemical process are constantly replaced with time and space changes, constructs a mapping relationship between position-pressure-temperature-thermodynamic parameters, and realizes the monitoring of the changing trend of thermodynamic parameters in the fuel thermochemical process. This provides data support for clarifying the fuel flow heat transfer mechanism and chemical thermodynamic mechanism, and provides a testing and evaluation method for the development of new fuels. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 A flow chart of the steps for measuring thermodynamic parameters of hydrocarbon fuels;

[0055] Figure 2 It is a structural schematic diagram of a device for measuring thermodynamic parameters of hydrocarbon fuels;

[0056] Figure 3 It is a schematic diagram of heat transfer between the environment, the test pipeline microelement and the fuel;

[0057] Figure 4 is the variation trend of heat flux density transferred from the test tube microelement to the environment with the test tube temperature;

[0058] Figure 5 is the heat flux density distribution along the test tube microelement input by the DC regulated power supply (toluene, 5MPa, 1g / s);

[0059] Figure 6 is the heat flux density distribution along the test tube microelement to the environment (toluene, 5MPa, 1g / s);

[0060] Figure 7 is the heat flux density distribution along the heat conduction between micro-elements of the test tube (toluene, 5MPa, 1g / s);

[0061] Figure 8 The heat flux density distribution along the test tube microelement transferred to the fuel (toluene, 5MPa, 1g / s);

[0062] Fig. 9 The heat sink distribution of toluene along the way (5MPa, 1g / s);

[0063] Fig.10 is the growth trend of toluene heat sink along the test tube (5MPa, 1g / s);

[0064] Fig.11 is the variation trend of toluene heat sink with temperature (5MPa, 1g / s);

[0065] Fig.12 is the growth trend of toluene temperature along the test tube (5MPa, 1g / s);

[0066] Fig.13 is the isobaric specific heat distribution of toluene along the process (5MPa, 1g / s);

[0067] Fig.14 is the variation trend of isobaric specific heat of toluene with temperature (5MPa, 1g / s);

[0068] Fig.15 is the isobaric entropy change distribution of toluene along the process (5MPa, 1g / s);

[0069] Fig.16 is the trend of isobaric entropy change of toluene with temperature (5MPa, 1g / s);

[0070] Fig.17 is the growth trend of n-decane heat sink along the test tube (1g / s);

[0071] Fig.18 is the growth trend of n-decane temperature along the test tube (1g / s);

[0072] Fig.19 is the growth trend of the isobaric specific heat of n-decane along the test tube (1g / s);

[0073] Fig. 20 is the variation trend of isobaric entropy change of n-decane with temperature (1g / s). DETAILED DESCRIPTION

[0074] The following examples can enable professionals to more fully understand the present invention, but do not limit the present invention in any way.

[0075] The process of a distributed measurement method for thermodynamic parameters of hydrocarbon fuels provided by the present invention is as follows: Figure 1 The structural diagram of the measuring device is shown in Figure 2 The principle of distributed measurement of thermodynamic parameters is shown in Figure 3 shown.

[0076] The method for performing distributed measurement of thermodynamic parameters of hydrocarbon fuels using the measuring device provided by the present invention includes:

[0077] (1) Storing the target substance in a fuel thermostatic tank and maintaining the temperature at 298K;

[0078] (2) pumping the target substance into the test tube and heating it to the initial cracking temperature to cause a cracking reaction, and then heating the target substance from the initial cracking temperature to a temperature at which the target substance is deeply cracked to produce coke to block the tube;

[0079] (3) Real-time monitoring of the inlet and outlet temperature changes of the target material, the temperature development trend of the wall surface along the test pipe, the system pressure at both ends of the test pipe, the resistance of the test pipe, and the current and voltage at both ends of the test pipe;

[0080] (4) Based on the parameters monitored in real time in step (2), the heat flux density of heat transfer between the calorimetric micro-element along the test tube and the target material in the micro-element is measured online based on the calorimetric model;

[0081] (5) When the test tube cools down to room temperature, the pressure is adjusted and the above steps (1) to (3) are continued to be performed to obtain the heat flux density of heat transfer between the calorimetric micro-element along the test tube and the target material in the micro-element under different pressure conditions;

[0082] (6) The industrial computer conducts distributed measurement of the thermodynamic parameters of the target material based on the energy transferred between the calorimetric micro-element along the test tube and the target material in the micro-element under different pressures, and obtains the function of the thermodynamic parameters of the target material changing with position, temperature and pressure.

[0083] Example 1

[0084] In this embodiment, the heat flux density of the heat transfer from the test tube microelement to the environment needs to be calibrated in advance; the energy conservation equation is established by heating the test tube without fluid.

[0085] q loss, x = [h x (T surface,x )·A x ·(T surface,x -T amb )+ε rad ·σ·(T surface,x 4 -T amb 4 )]·A x -1 (1-1)

[0086] Among them, q loss,x h is the heat flux density of heat transfer loss on the microelement surface of the tube; x (T) is the function of the convection heat transfer coefficient of the pipe microelement surface changing with the pipe body temperature; A x is the surface area of ​​the pipeline element; T surface,x is the surface temperature of the pipe element; T amb is the natural environment temperature; rad is the surface emissivity of the pipeline microelement; σ is the Stefan-Boltzmann constant.

[0087] Taking the ambient temperature of 288K as an example, the empirical formula fitted by the experimental data is:

[0088] q x,loss =[-12064.52+63.35×T-0.11×T 2 +8.82×10 -5 ×T 3 -3.39×10 -8 ×T 4 ] / n(1-2)

[0089] Where T is the wall temperature of the test pipe, and n is the number of test pipe elements.

[0090] This embodiment establishes the heat flux density of the test tube microelement to the environment when the ambient temperature is 288K to 308K, such as Figure 4 shown.

[0091] Furthermore, in the present embodiment, taking toluene as an example, toluene is transported to the test tube through a high-pressure constant current pump under the working conditions of 5MPa and 1g / s; a DC regulated power supply applies heat flux to the test tube, and the temperature of toluene in the test tube is gradually increased from 298K to 1073K; a thermocouple monitors the inlet and outlet temperature changes of the test tube in real time; an infrared thermal imager monitors the wall temperature changes of the test tube in real time, and a pressure sensor monitors the system pressure in real time; the industrial computer stores the fluid mass flow rate, input heat flux data, test tube wall temperature data, fluid inlet and outlet temperatures, and system pressure, and then carries out thermodynamic parameter measurement based on the calorimetric model.

[0092] Using a DC regulated power supply to apply different amounts of energy to the test tube, the industrial computer obtains the change of input heat flux density with wall temperature based on the calorimetric model:

[0093] q heater, x (x) = I 2 ·ρ(T)·S x -2 ·dx (1-3)

[0094] Among them, q heater,xis the heat flux density of heat transfer between the micro-element of the tube body; I is the current applied by the DC motor to the micro-element of the tube body; ρ(T) is the function of the change of resistivity with the temperature of the tube body; dx is the actual length of the micro-element of the tube body; S x is the cross-sectional area of ​​the tube element.

[0095] like Figure 5 The figure shows the heat flux density distribution along the test tube input by the DC regulated power supply when the toluene outlet temperature is 473-773K.

[0096] Further, according to Figure 4 The relationship between the heat flux density of the test tube microelement to the environment and the ambient temperature and the test tube wall temperature is obtained, and the distribution of the heat flux density of the test tube microelement to the environment when the toluene outlet temperature is 473-773K is obtained, as shown in Figure 6 shown.

[0097] Furthermore, the heat flux density of heat transfer between the micro-elements of the test pipeline due to the temperature difference is as follows: Figure 7 As shown in the figure, the heat conduction inside the pipe microelement is calculated when the fluid temperature is 473, 573, 673, and 773 K. The calculation formula is:

[0098]

[0099] Among them, q cond,x is the heat flux density of heat transfer between the micro-element of the tube, in J·s -1 ·m -2 ; tube (T) is the thermal conductivity of the tube element W·m -1 ·k -1 ; is the partial derivative of temperature between the infinitesimal elements of the tube.

[0100] Furthermore, the heat flux density of the heat transfer from the test tube microelement to the toluene inside the microelement is obtained by the following energy conservation equation:

[0101] (q total, x -q loss, x )·A out = (Δq cond, x + q end, x / n)·S + q fluid, x ·A in (1-5) The energy conservation equation for heat transfer from the pipeline microelement to toluene is:

[0102] P heat sink,x = q fluid, x ·A in = (q total, x -q loss, x )·A out - (Δq cond, x +q end, x / n)·S x (1-6)

[0103] Among them A out A is the surface area of ​​the microelement of the test tube; in is the surface area of ​​the test tube microelement; S is the cross section of the test tube microelement;

[0104] The heat flux density distribution along the test tube microelement transferred to the fuel is obtained as follows: Figure 8 shown.

[0105] Furthermore, a constraint condition is set at the fuel inlet end. The constraint condition is that when the fuel temperature is 25°C, the fuel heat sink is 0 MJ·kg -1 ; Based on the laws of thermodynamics, P heat sink,x Converted into heat sink of toluene along the way, the heat sink of toluene at xm in the test tube is obtained by the following energy equation:

[0106]

[0107] The heat sink distribution of toluene along the test tube is as follows: Fig. 9 and 10 shown.

[0108] Furthermore, based on the above steps, the toluene temperature-heat sink function relationship is calibrated, taking 5MPa, 1g / s working condition as an example, as follows: Fig.11 As shown; the established functional relationship is:

[0109] 298.15 K≤T<685 K, H(T) = -172.16-0.24×T +0.0028×T 2 (1-8)

[0110] 685 K≤T<870 K, H(T) = -20081.31+62.26×T-0.046×T 2 (1-9)

[0111] 870 K≤T≤1023.15 K, H(T) = -1014.76+3.11×T -1.65×T 2(1-10)

[0112] Where T is the toluene temperature;

[0113] Combined with the NIST standard database, it can be seen that the measurement error of toluene heat sink is less than 2%.

[0114] By inverting the H(T) function, the average temperature of toluene at any position along the test tube is obtained, as follows: Fig.12 shown.

[0115] Further, the P obtained in the above steps heat sink,x Defined as the fuel energy change Q at the outlet and inlet of the pipeline microelement fuel,x , obtain the temperature difference ΔT between the inlet and outlet of the microelement through the toluene temperature distribution along the way fuel,x ; The isobaric specific heat calculation formula is:

[0116] C p, fuel, x = Q fuel, x ΔT fuel, x -1 (1-11)

[0117] Through this calculation formula, the isobaric specific heat distribution of toluene along the process is solved, as follows: Fig.13 shown.

[0118] Furthermore, the temperature distribution of toluene along the path is correlated with the isobaric specific heat distribution of toluene along the path, and the variation trend of the isobaric specific heat of toluene with temperature is obtained, such as Fig.14 shown.

[0119] Combined with the NIST standard database, it can be seen that the measurement error of toluene isobaric specific heat is less than 3%.

[0120] Furthermore, the isobaric entropy change distribution of toluene along the path is obtained based on the isobaric specific heat distribution of toluene along the path and the temperature distribution of toluene along the path; the isobaric entropy change calculation formula is:

[0121] dS p, fuel, x = n C p, fuel ,x ·T -1 ·dT (1-5)

[0122] Through this calculation formula, the isobaric entropy change distribution of toluene along the process is solved, as follows: Fig.15 shown.

[0123] Furthermore, the temperature distribution of toluene along the path is correlated with the isobaric entropy change distribution of toluene along the path, and the variation trend of the isobaric entropy change of toluene with temperature is obtained, as shown in Fig.16 As shown in Figure 2, combined with the NIST standard database, it can be seen that the measurement error of toluene isobaric entropy change is less than 2%.

[0124] Furthermore, in this embodiment, taking n-decane as an example, the experimental conditions are: maintaining the system pressure at 2 MPa and 4 MPa, the mass flow rate at 1 g / s, and the outlet temperature at 373-1023 K. The distributed thermodynamic parameters of n-decane under high temperature and high pressure and thermochemical reaction conditions are measured.

[0125] According to the above steps, the heat sink change and temperature change of n-decane along the test tube are obtained, such as Fig.17 and 18 shown.

[0126] The isobaric specific heat change of n-decane along the test tube is obtained by the isobaric specific heat calculation formula, such as Fig.19 shown.

[0127] By correlating the temperature distribution of n-decane along the process with the isobaric specific heat distribution of n-decane along the process, the variation trend of the isobaric specific heat of toluene with temperature is obtained, as shown in Fig. 20 shown.

[0128] In summary, the present invention solves the difficulty of traditional fluid thermodynamic parameter measurement methods in obtaining thermodynamic parameters of the distribution of thermodynamic parameters of hydrocarbon fuels along the test tube and the thermal cracking reaction of hydrocarbon fuels under high temperature and high pressure conditions, and proposes a new thermodynamic parameter measurement method based on distributed flow calorimetry, thereby measuring the thermodynamic parameters of hydrocarbon fuels along the test tube and the relevant parameters of the thermal cracking reaction of hydrocarbon fuels under high temperature and high pressure conditions.

Claims

1. A distributed measurement method for thermodynamic parameters of hydrocarbon fuels, characterized in that: The method comprises: (1) Storing the target substance in a fuel thermostatic tank and maintaining the temperature at 298K; (2) pumping the target substance into the test tube and heating it to the initial cracking temperature to cause a cracking reaction, and then heating the target substance from the initial cracking temperature to the target substance deep cracking temperature, where the target substance deep cracking temperature is the temperature at which coke blocks the pipe; (3) Real-time monitoring of the inlet and outlet temperature changes of the target material, the temperature development trend of the wall surface along the test pipe, the system pressure at both ends of the test pipe, the resistance of the test pipe, and the current and voltage at both ends of the test pipe; (4) Based on the parameters monitored in real time in step (3), the heat flux density of heat transfer between the calorimetric micro-element along the test tube and the target material in the micro-element is measured online based on the calorimetric model; (5) When the test tube is cooled to room temperature, the pressure is adjusted and the above steps (1) to (4) are continued to be performed to obtain the heat flux density of heat transfer between the calorimetric micro-element along the test tube and the target material in the micro-element under different pressure conditions; (6) The industrial computer conducts distributed measurement of the thermodynamic parameters of the target material based on the energy transferred between the calorimetric micro-element along the test tube and the target material in the micro-element under different pressures, and obtains the function of the thermodynamic parameters of the target material changing with position, temperature and pressure.

2. The distributed measurement method for thermodynamic parameters of hydrocarbon fuels according to claim 1, characterized in that: In step (1), the target substance is selected from one or a combination of at least two of alkanes, olefins, cycloalkanes, cycloolefins or aromatic hydrocarbons.

3. The distributed measurement method for thermodynamic parameters of hydrocarbon fuels according to claim 1, characterized in that: In step (2), the target substance is pumped into the test tube at a flow rate of 0.1-10 g / s or 1-1000 ml / s, the initial cracking temperature is 773-823 K, the deep cracking temperature of the target substance is 1023-1123 K, and the heating rate is 5-25 K / min; in step (4), the system pressure is set to 0.1-12 MPa, and the increase step is 0.05-1 MPa.

4. The distributed measurement method for thermodynamic parameters of hydrocarbon fuels according to claim 1, characterized in that: In step (2), the cracking reaction of the target substance includes a primary thermal cracking reaction and a multi-stage thermal cracking reaction; the primary thermal cracking reaction is the thermal cracking of the target substance itself; and the multi-stage thermal cracking reaction is the multi-step thermal cracking of the primary thermal cracking product of the target substance.

5. The distributed measurement method for thermodynamic parameters of hydrocarbon fuels according to claim 1, characterized in that: In step (4), the calorimetric model is used to calculate the energy required to heat the target substance, including the heat flux density q of the DC constant voltage power supply input to the test tube. total,x , heat flux density q of heat transfer from the test tube microelement to the environment loss,x , the heat flux density q of heat conduction between the micro-elements of the test tube cond,x , the heat flux density q of heat conduction from both ends of the test tube to the cold end end,x , the heat flux density q of the heat transfer from the test tube microelement to the target material in the microelement fluid,x ; The experimental tube microelement is a test tube with a length of L meters, which is evenly divided into n test tube segments with a length of ΔL during calculation. The microelement at the inlet end of the pipe is x=1, and the microelement at the outlet end of the pipe is x=n. The heat flux density of the test tube input by the DC constant voltage power supply is obtained in the following manner: the function of the test tube resistivity changing with temperature is pre-calibrated by a four-wire measurement method, and the test tube resistance is corrected in real time in combination with the current value and voltage value applied by the DC constant voltage power supply to both ends of the test tube; further, the resistance distribution along the test tube is obtained by the temperature distribution of the wall surface along the test tube; the heat flux density of the test tube microelement input by the DC constant voltage power supply is calculated according to the microelement current value, resistance value and microelement surface area of ​​the test tube, that is, q total,x ; The heat flux density of heat transfer from the test tube microelement to the environment is obtained by the following method: pre-calibrating the function of heat convection and heat radiation heat flux density of the test tube microelement wall surface with the temperature of the test pipe wall surface; combining the temperature distribution of the test pipe wall surface along the test pipe to obtain the heat flux density of heat transfer from the test tube microelement to the environment, that is, q loss,x ; The heat flux density of heat conduction between the micro-elements of the test tube is obtained by pre-calibrating the function of the thermal conductivity of the test tube changing with temperature, obtaining the thermal conductivity distribution along the test tube and the first-order derivative function of the wall temperature along the test tube according to the wall temperature distribution along the test tube, and further obtaining the heat flux density of heat conduction between the micro-elements of the test tube, that is, q cond,x ; The heat flux density of heat conduction from both ends of the test tube to the cold end is obtained by the following method: presetting the cold end temperature at the pipe inlet to 298K, the cold end temperature at the pipe outlet to the fluid outlet temperature, and obtaining the thermal conductivity of heat conduction from both ends of the test tube to the cold end and the first-order derivative value of the wall temperature according to the wall temperature distribution along the test tube, and further obtaining the heat flux density of heat conduction from both ends of the test tube to the cold end, that is, q end,x ; The heat flux density of the heat transfer from the test tube microelement to the target material in the microelement is obtained by establishing an energy conservation equation, namely (q total,x -q loss,x )·A out =(Δq cond,x +q end,x / n)·S+q fluid,x ·A in ; Among them A out A is the surface area of ​​the microelement of the test tube; in is the inner surface area of ​​the test tube microelement; S is the cross section of the test tube microelement; n is the number of test tube microelement; x is the serial number of the test tube microelement; q fluid,x is the heat flux density of heat transfer from the test tube microelement to the target material inside the microelement.

6. The distributed measurement method for thermodynamic parameters of hydrocarbon fuels according to claim 1, characterized in that: In step (6), the distributed measurement of thermodynamic parameters includes the distribution of target material temperature, heat sink, isobaric specific heat and isobaric entropy change along the test tube.

7. The distributed measurement method for thermodynamic parameters of hydrocarbon fuels according to claim 1, characterized in that: In step (6), the function of the target material thermodynamic parameters changing with position, temperature, and pressure includes the distribution of temperature, heat sink, isobaric specific heat, and isobaric entropy change of the target material along the test tube at different pressures, which are T x , H x , C p,x , S x ; The functional relationship between the heat sink, isobaric specific heat and isobaric entropy change of the target substance at different pressures and temperature is H(T), C p (T), S(T).

8. The distributed measurement method for thermodynamic parameters of hydrocarbon fuels according to claim 7, characterized in that: The function of the target substance thermodynamic parameters changing with position, temperature and pressure is: Since the test tube microelement number x corresponds to the temperature of the target substance in the test tube microelement, The heat sink distribution along the test tube is: H x =q x,fluid ·A in / m; The function of the heat sink changing with temperature is: H(T)=-H inlet +∑q fluid,x ·A in / m; where H inlet is the heat sink of the target substance at 298K; The temperature distribution of the test tube along the process is: T x =H -1 (T) = H -1 [-H inlet +∑q fluid,x ·A in / m]; The isobaric specific heat distribution of the test tube along the way is: C p,x =q fluid,x ·A in / (m·ΔT f,x ); The function of the isobaric specific heat changing with temperature is: C p (T) = q fluid,x ·A in / (m·ΔT f,x ); The isobaric entropy change distribution along the test tube is: S x =∫m C p (T)·(M0T) -1 ·dT; where C p (T) is the function of isobaric specific heat changing with temperature; The function of the isobaric entropy change with temperature is: S(T)=-S inlet +∫m C p (T)·(M0T) -1 ·dT; where S inlet is the entropy of the target substance at 298K; Where m is the mass of the target substance in the microelement, ΔT f,x is the temperature difference between the two ends of the test tube microelement, and M0 is the relative molecular weight of the target substance.

9. A distributed measurement device for thermodynamic parameters using the method according to any one of claims 1 to 8, characterized in that: The measuring device comprises: A high-pressure constant-current pump is used to stably pump the target substance to the test tube; a liquid gear flowmeter is used to monitor the fluid mass flow in real time; a DC voltage-stabilized power supply is used to input stable energy into the test tube and to monitor the voltage and current at both ends of the test tube in real time; the test tube is used for energy balance; a thermocouple is used to monitor the fluid outlet temperature in real time; an infrared thermal imager is used to monitor the wall temperature of the test tube in real time; a pressure sensor is used to monitor the system pressure in real time; a back pressure valve is used to provide a stable system pressure; a gas-liquid separation tank is used to separate the cracked gas and cracked liquid of the target substance; a waste gas and waste liquid recovery device is used to recover the cracked gas and cracked liquid of the target substance; The industrial computer is used to execute steps (4) and (6).

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