A method for calculating the pressure and temperature of a CO2 storage tank

Abstract

The present invention discloses a method for calculating the pressure and temperature of a CO2 storage tank, establishing the CO2 mass conservation and energy conservation equations under two states before and after the tank exhausts gas, assuming that the temperature and pressure of the exhausted CO2 remain unchanged during the exhaust process, and solving for the temperature, pressure, and remaining mass of the CO2 in the storage tank after exhaust; through cyclic iteration, the variation curves of the temperature and pressure of the CO2 in the storage tank with time under different mass flow conditions are obtained. The present invention can obtain the variation curves of the temperature and pressure of the CO2 in the storage tank with time under different mass flow conditions.

Description

Technical Field

[0001] The present invention relates to the technical field of combined engine system performance design, and particularly relates to a method for calculating the pressure and temperature of a CO2 storage tank. Background Art

[0002] The combined engine uses CO2 as a cooling medium to actively cool the combustion chamber wall surface and broaden the engine operating speed range. The CO2 supply system in such engines is an important part of the engine. Due to the limited size and space of the engine, it is necessary to accurately design the size of the on-board CO2 storage tank. The volume of the CO2 storage tank is related to the CO2 mass flow rate.

[0003] With the change of different CO2 supply flow rates, whether CO2 can be continuously supplied at a certain temperature and pressure is a decisive factor for the success or failure of the scheme. Due to the limited size and weight of the on-board space, it is impossible to leave enough margin for the CO2 storage tank. It is necessary to accurately calculate the changes in the temperature and pressure inside the storage tank when CO2 flows out of the storage tank and is heated by the external environment during the design. Summary of the Invention

[0004] In view of this, the present invention provides a method for calculating the pressure and temperature of a CO2 storage tank, which can obtain the change curves of the temperature and pressure of CO2 in the storage tank with time under different mass flow rate conditions.

[0005] The technical solution adopted by the present invention is as follows:

[0006] A method for calculating the pressure and temperature of a CO2 storage tank establishes the CO2 mass conservation and energy conservation equations for two states before and after the storage tank exhausts gas. Assuming that the temperature and pressure of the exhausted CO2 remain unchanged during the exhaust process, the temperature, pressure, and remaining mass of the CO2 in the storage tank after exhaust are solved; through iterative cycles, the change curves of the temperature and pressure of CO2 in the storage tank with time under different mass flow rate conditions are obtained.

[0007] Further, the establishment process of the CO2 mass conservation and energy conservation equations is as follows:

[0008] Step 1, determine the total volume V1 of the storage tank in the initial state, the volume V of the liquid CO2 in the storage tank 1L , the initial temperature T1 of the CO2 in the storage tank, and the total calculation time;

[0009] Step 2, determine the densities and specific enthalpies of the gaseous CO2 and liquid CO2 corresponding to the initial temperature T1, and then calculate the total mass M1 and total enthalpy value h1 of the CO2 in the initial state;

[0010] Step 3, given the mass flow rate of the CO2 flowing out of the storage tank within the microelement time dt, assume that the volume of the liquid CO2 in the storage tank after dt time is V 2L, at a temperature of T2, the densities and specific enthalpies of gaseous CO2 and liquid CO2 corresponding to the temperature T2 are obtained. Assuming that the temperature of the CO2 flowing out of the storage tank remains unchanged at T1, calculate the total mass M2 and total enthalpy value h2 of the CO2 including that flowing out of the storage tank after dt time;

[0011] Step 4, according to the mass conservation and energy conservation of the states before and after dt time, the state equations M1 = M2 and h1 = h2 are obtained.

[0012] Furthermore, the total mass M2 is the sum of the total mass of CO2 in the storage tank and the mass of CO2 flowing out of the storage tank after dt time; the total enthalpy value h2 is the sum of the enthalpy value of CO2 in the storage tank, the enthalpy value of the flowing-out part of CO2, and the enthalpy value input through environmental heat conduction.

[0013] Furthermore, the Newton method or the least squares method is used to iteratively solve the CO2 mass conservation and energy conservation equations to obtain the volume V of liquid CO2 after dt time 2L and temperature T2.

[0014] Furthermore, the cyclic iteration method is as follows:

[0015] Assign the obtained V 2L and T2 to V 1L and T1, and use this as the new initial state, repeat Step 3 and Step 4 above, calculate the volume and temperature of liquid CO2 in the storage tank after the next dt time, and obtain the storage tank pressure;

[0016] Judge whether the sum of the iterated times has reached the set total calculation time. If not, continue the cyclic iteration; if the total calculation time is reached, the iteration stops.

[0017] Beneficial effects:

[0018] The present invention can calculate the temperature, pressure, and phase state of CO2 in the storage tank at different times in real time, obtain the changes in the temperature and pressure in the storage tank under the conditions of CO2 flowing out of the storage tank and being heated by the external environment, and is applicable to the performance design of the combined engine system with limited space on the missile. Description of the drawings

[0019] Figure 1 is a schematic flow chart of the calculation method of the present invention;

[0020] Figure 2 is a schematic structural diagram of the CO2 storage tank;

[0021] Among them, 1 - gaseous CO2, 2 - liquid CO2. Specific embodiments

[0022] The present invention will be described in detail below with reference to the accompanying drawings and by way of examples.

[0023] This embodiment provides a method for calculating the pressure and temperature of a CO2 storage tank. Mass conservation and energy conservation equations of CO2 are established for two states before and after the tank exhaust. Assuming that the temperature and pressure of the exhausted CO2 remain unchanged during the exhaust process, the temperature, pressure, and remaining mass of CO2 in the storage tank after exhaust are solved. Through cyclic iteration, the variation curves of the temperature and pressure of CO2 in the storage tank with time under different mass flow conditions are obtained.

[0024] As Figure 1 shown, the specific steps of the calculation method are as follows:

[0025] Step 1, as Figure 2 shown, determine the total volume V1 of the storage tank in the initial state, the volume V 1L of liquid CO22 in the storage tank, the initial temperature T1 of CO2 in the storage tank, the ambient temperature, the thickness of the storage tank, the thermal conductivity of the storage tank, the thickness of the external insulation layer of the storage tank, the thermal conductivity of the insulation layer, and the total calculation time t.

[0026] Step 2, determine the density and specific enthalpy of gaseous CO21 and liquid CO22 corresponding to the initial temperature T1 by querying the physical property software, and then calculate the total mass M1 and total enthalpy value h1 of CO2 in the initial state;

[0027] Step 3, given the mass flow rate of CO2 flowing out of the storage tank within the microelement time dt, assume that the volume of liquid CO22 in the storage tank after dt time is V 2L and the temperature is T2. Obtain the density and specific enthalpy of gaseous CO21 and liquid CO22 corresponding to the temperature T2 by querying the physical property software. Assume that the temperature of the exhausted CO2 remains unchanged at T1. Calculate the total mass M2 and total enthalpy value h2 of CO2 including the exhausted CO2 after dt time. The total mass M2 is the sum of the total mass of CO2 in the storage tank and the mass of CO2 flowing out of the storage tank after dt time. The total enthalpy value h2 is the sum of the enthalpy value of CO2 in the storage tank, the enthalpy value of the exhausted part of CO2, and the enthalpy value input through environmental heat conduction. The enthalpy value input through environmental heat conduction is calculated based on the ambient temperature, the thickness of the storage tank, the thermal conductivity of the storage tank, the thickness of the external insulation layer of the storage tank, and the thermal conductivity of the insulation layer.

[0028] Step 4, according to the mass conservation and energy conservation of the states before and after dt time, obtain the state equations M1 = M2, h1 = h2. This state equation is an implicit nonlinear algebraic equation system. Use the Newton method or the least squares method to iteratively solve the mass conservation and energy conservation equations of CO2 to obtain the volume V 2L of liquid CO22 and the temperature T2 after dt time.

[0029] Step 5, assign the solved V 2L and T2 to V 1LAnd T1, taking this as the new initial state, repeat the above Step Three and Step Four to calculate the volume and temperature of the liquid CO2 in the storage tank after the next dt time, and obtain the storage tank pressure by querying the physical property software;

[0030] Step Six, determine whether the sum of the iteration times has reached the set total calculation time t. If not, continue the loop iteration; if the total calculation time t is reached, the iteration stops.

[0031] The mass flow rate of CO2 flowing out of the storage tank within the micro-element time dt can be changed at any time in Step Three, or the mass flow rate of CO2 flowing out of the storage tank within the micro-element time dt can be re-specified during the next iteration, thereby obtaining the curves of the temperature and pressure of CO2 in the storage tank changing with time under different mass flow rate conditions.

[0032] In summary, the above are only the preferred embodiments of the present invention and are not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for calculating the pressure and temperature of a CO2 storage tank, characterized in that, Establish the CO2 mass conservation and energy conservation equations for two states before and after the exhaust of the storage tank. Assume that the temperature and pressure of the exhausted CO2 remain unchanged during the exhaust process, and solve the temperature, pressure, and remaining mass of CO2 in the storage tank after the exhaust; through cyclic iteration, obtain the curves of the temperature and pressure of CO2 in the storage tank changing with time under different mass flow conditions; The establishment process of the CO2 mass conservation and energy conservation equations is as follows: Step 1, determine the total volume V1 of the storage tank in the initial state, the volume V of the liquid CO2 in the storage tank 1L , the initial temperature T1 of the CO2 in the storage tank, and the total calculation time; In step two, determine the densities and specific enthalpies of gaseous CO2 and liquid CO2 corresponding to the initial temperature T1, and then calculate the total mass M1 and total enthalpy value h1 of CO2 in the initial state; Step 3: Given the mass flow rate of CO2 flowing out of the storage tank within the differential time dt, assume that the volume of liquid CO2 in the storage tank after time dt is V 2L , and the temperature is T2, obtain the densities and specific enthalpies of gaseous CO2 and liquid CO2 corresponding to temperature T2. Assume that the temperature of the CO2 flowing out of the storage tank remains unchanged at T1, and calculate the total mass M2 and total enthalpy value h2 of the CO2 including that flowing out of the storage tank after time dt; In step four, according to the mass conservation and energy conservation of the states before and after the dt time, obtain the state equations M1 = M2 and h1 = h2; The cyclic iteration method is as follows: Assign the obtained V 2L and T2 to V 1L and T1, and take this as the new initial state, repeat the above Step 3 and Step 4 to calculate the volume and temperature of the liquid CO2 in the storage tank after the next dt time, and obtain the storage tank pressure; Judge whether the sum of the iterated times has reached the set total calculation time. If not, continue the cyclic iteration; If the total calculation time is reached, the iteration stops.

2. The method for calculating the pressure and temperature of a CO2 storage tank according to claim 1, wherein, The total mass M2 is the sum of the total mass of CO2 in the storage tank after the dt time and the mass of CO2 flowing out of the storage tank; the total enthalpy value h2 is the sum of the enthalpy value of CO2 in the storage tank, the enthalpy value of the part flowing out, and the enthalpy value input through environmental heat conduction.

3. The method for calculating the pressure and temperature of a CO2 storage tank according to claim 1, wherein, The Newton method or the least squares method is used to iteratively solve the CO2 mass conservation and energy conservation equations to obtain the volume V of liquid CO2 after a time dt 2L , and the temperature T2.

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