Isotope thermo-photoelectric power supply for deep space exploration and design method thereof

Abstract

The invention discloses an isotope thermoelectric power supply for deep space exploration and a design method thereof, belongs to the technical field of deep space exploration nuclear power supplies, and aims to solve the problems of low power supply conversion efficiency and insufficient power density of a traditional radioactive isotope thermoelectric battery. The power supply is sequentially provided with an isotope heat source, a selective radiator, a spectrum filter and a GaSb type PV photocell array module from inside to outside; a heat source is made into PuO2 ceramic by 238Pu and is coated with a tungsten coating, a radiator adopts a tungsten material to emit spectrum below 2 microns at 1400-1500K, a filter adopts a one-dimensional Si / SiO2 photonic crystal to realize spectrum selective transmission, and a PV photocell completes photoelectric conversion by utilizing near-infrared band high quantum efficiency. The design method comprises the four steps of parameter type selection, model establishment, simulation optimization and structure determination. The energy conversion efficiency reaches 22.2%, and the long-period and high-power energy requirements of deep space exploration are met.

Description

Technical Field

[0001] This invention relates to the field of nuclear power technology for deep space exploration, and in particular to an isotope thermo-photoelectric power supply and its physical design method. Background Technology

[0002] Deep space exploration missions face challenges such as extremely weak sunlight, long flight cycles, and extremely harsh space environments. Solar cell arrays cannot meet energy supply requirements, making nuclear power systems the preferred solution.

[0003] Among existing technologies, radioisotope thermoelectric cells (RTGs) are the most successful nuclear power source, but their energy conversion efficiency is only 4%–8%, and their power density is low. To improve the performance of nuclear power sources, NASA has proposed three alternatives: alkali metal thermoelectric transducers (AMTECs), Stirling cycle generators (SECs), and radioisotope thermoelectric power generation. Among these, the AMTEC system is susceptible to instability due to extreme high and low temperatures, and the SEC system has high structural complexity. In contrast, the radioisotope thermoelectric power generation system possesses advantages such as light weight, high specific power, and high energy conversion efficiency, making it the preferred technology for nuclear power sources in deep space exploration.

[0004] my country's nuclear battery research started late, and the isotope batteries developed independently have low power density and low conversion efficiency. Moreover, isotope thermoelectric technology is still a blank in the domestic research field, which cannot meet the energy system requirements of deep space exploration missions. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides an isotope thermoelectric power supply for deep space exploration and its design method, aiming to solve the problems of low conversion efficiency and insufficient power density of traditional RTG power supplies, and meet the energy supply requirements of deep space exploration missions.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] An isotope thermo-photovoltaic power supply includes, from the inside out, an isotope heat source module, a selective radiator module, a spectral filter module, and a GaSb-type PV photovoltaic cell array module.

[0008] (1) Isotope heat source module: 238 Pu is a pyrogen nuclide, made into PuO2 ceramic form, with a smooth tungsten coating on the outside to provide stable heat energy output; 238 Pu has a half-life of 87.7 years, releases 5.48 MeV in decay, and has a power-to-weight ratio of 0.55 W / g.

[0009] (2) Selective radiator module: Using tungsten as the surface material, it can emit a spectrum with most wavelengths below 2μm under high temperature conditions of 1400K-1500K, so as to achieve spectral matching with the back-end GaSb type PV photovoltaic cell.

[0010] (3) Spectral filter module: One-dimensional Si / SiO2 photonic crystal (PHC) is used as the surface material. It has the characteristics of high transmission of wavelengths below 2μm and high reflection of wavelengths above 2μm. It reflects long-wavelength photons back to the heat source for heating, reducing the waste heat input of PV photovoltaic cells.

[0011] (4) GaSb type PV photovoltaic cell array module: The array is composed of GaSb type semiconductor cells, which have high quantum efficiency in the near-infrared band and are used to convert the energy of short-wavelength photons that pass through the filter into electrical energy.

[0012] A design method for an isotope thermoelectric power supply includes the following steps:

[0013] (1) Determine the core parameters of the system and select materials.

[0014] 1. Based on the power requirements and mission duration of the deep space exploration mission, select... 238 Pu was used as an isotopic heat source nuclide and was made into a PuO2 ceramic structure to ensure that the heat source half-life matched the mission cycle and met the requirement of specific power of 0.55W / g.

[0015] 2. Tungsten was selected as the surface material for the selective radiator, so that its emission spectrum was concentrated in the band below 2 μm at a temperature of 1400K-1500K;

[0016] 3. Using one-dimensional Si / SiO2 photonic crystals as spectral filter materials, the spectral modulation function of high transmission for short wavelengths below 2μm and high reflection for long wavelengths above 2μm is achieved;

[0017] 4. A PV photovoltaic array is constructed using GaSb-type semiconductor cells, utilizing their high quantum efficiency in the near-infrared band to achieve photoelectric conversion.

[0018] (2) Establish a system energy calculation model

[0019] 1. Calculate the spectral beam flux of the radiator:

[0020] For a planar heat source, the flux of the spectral beam emitted outward from the radiator [ It can be represented as:

[0021] ;

[0022] in: These are Planck's constant and Boltzmann's constant, respectively. The speed of light; The surface temperature of the radiator; wavelength The corresponding radiator spectral emissivity; wavelength The corresponding radiator spectral reflectance coefficient; This represents the spectral beam flux reflected from the filter surface.

[0023] 2. Calculate the spectral heat flux of the filter:

[0024] band The light emitted by the radiator reaches the filter surface and is reflected as a heat flux beam. for:

[0025] ;

[0026] Then band The heat flux of light passing through the filter at that location for:

[0027] ;

[0028] in: wavelength The corresponding filter spectral emission coefficient; wavelength The corresponding filter spectral reflectance coefficient; The wavelength emitted by the radiator surface Spectral beam flux; This refers to the surface temperature of the filter.

[0029] because In formula (3), the second term can be ignored.

[0030] ;

[0031] Integrating over each wavelength segment yields the net radiative heat flux through the filter across the entire spectral band. for:

[0032] ;

[0033] 3. Calculate the photoelectric conversion parameters of the PV photovoltaic array:

[0034] The light flux reaching the GaSb wafer array is absorbed in the form of photons, in the following wavelength range. Photon beam flux obtained from absorption for:

[0035] ;

[0036] in: It is an effective conversion factor;

[0037] Due to the quantum properties of photoelectric conversion, PV photovoltaic cells can convert wavelengths... The absorbed photons are converted into electric current. :

[0038]

[0039] in: To correspond to the quantum efficiency of different wavebands.

[0040] The total short-circuit current density across the entire band is obtained. :

[0041]

[0042] in: It represents the electron charge.

[0043] Open-circuit voltage of each PV cell It can be obtained from the following formula:

[0044]

[0045]

[0046]

[0047] in: This represents the saturation current density of a single GaSb cell. The energy band gap of GaSb material.

[0048] Calculate the output power of a single PV cell for:

[0049]

[0050]

[0051] in: The power utilization efficiency is called the fill factor, which gives the corresponding energy conversion efficiency. for:

[0052] .

[0053] (3) System simulation and parameter optimization based on Matlab

[0054] 1. Build a physical model of the isotope thermo-photovoltaic power source and simulate the effects of radiator temperature, PV cell temperature, and net radiative heat flux on the system output power and conversion efficiency with and without filters.

[0055] 2. Optimize system parameters based on simulation results: control the surface temperature of the radiator to 1200℃ and the operating temperature of the PV photovoltaic array to 25℃, and improve the system's energy conversion efficiency by utilizing the selective reflection and transmission performance of the filter.

[0056] (4) Determine the overall system structure and performance indicators

[0057] The overall structure of the isotope thermophotovoltaic power supply is designed, with GaSb-type PV photovoltaic cell arrays arranged on six faces around the heat source. Each face is composed of several GaSb cells, and each cell has a specific area. When the surface temperature of the radiator is 1200℃ and the operating temperature of the PV photovoltaic cell is 25℃, the system receives a net heat power of 495W and outputs a power of 110W, achieving an energy conversion efficiency of 22.2%.

[0058] The beneficial effects of this invention are:

[0059] (1) The isotope thermo-photovoltaic power supply of the present invention adopts a hierarchical structure of “isotope heat source - selective radiator - spectral filter - GaSb type PV photovoltaic cell”, and achieves efficient conversion of thermal energy to electrical energy through spectral modulation. The energy conversion efficiency reaches 22.2%, which is much higher than that of traditional RTG power supply (4%~8%), and greatly improves the energy utilization efficiency of nuclear power supply.

[0060] (2) The present invention selects 238 Pu, as a heat source nuclide, has a half-life of up to 87.7 years, which can meet the energy supply requirements of long-term deep space exploration missions. Moreover, it adopts the characteristics of alpha heat source, requiring less radiation shielding weight and reducing the overall mass of the power supply.

[0061] (3) The design method of this invention, through the establishment of an accurate energy calculation model and Matlab simulation optimization, clarifies the influence of radiator temperature, PV cell temperature and filter performance on the system, providing a reliable theoretical basis and parameter guidance for the engineering development of isotope thermo-photovoltaic power supplies. Attached Figure Description

[0062] Figure 1 This is a schematic diagram of an isotope thermoelectric power supply.

[0063] Figure 2 Spectral emissivity of different radiator materials;

[0064] Figure 3 The spectral transmittance of the filter in the horizontal direction;

[0065] Figure 4 Quantum efficiency of GaSb-type PV cells;

[0066] Figure 5 A physical model of a first-generation isotope thermo-photovoltaic monolayer battery;

[0067] Figure 6 Factors affecting isotope thermoelectric systems without filters;

[0068] Figure 7 Optimized physical model of isotope thermophotovoltaic cell;

[0069] Figure 8 Factors affecting isotope thermoelectric systems with filters;

[0070] Figure 9 Schematic diagram of the isotope thermoelectric power supply system;

[0071] Figure 10 Overall performance parameters of the isotope thermo-photoelectric power supply system. Detailed Implementation

[0072] To make the above-mentioned objectives, features, and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to examples. The following content is merely an example and illustration of the concept of the present invention. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to replace them, as long as they do not deviate from the concept of the invention, they should all fall within the protection scope of the present invention.

[0073] The preparation method of the present invention will be described below through specific embodiments.

[0074] Example

[0075] Isotope thermoelectric system adopts 238 Pu serves as a radioactive isotope heat source, encased in a smooth tungsten-coated container. This tungsten coating acts as an emitter, maximizing the emission intensity of usable light wavelengths below 2 micrometers. Light wavelengths above 2 micrometers are highly reflected by a spectral filter before being heated by the heat source. Light wavelengths below 2 micrometers exhibit high transmittance, reaching the surface of the GaSb-type PV cell, achieving optimal matching with the cell's quantum efficiency. Figure 1 This is a schematic diagram of an isotope thermoelectric power supply. Through the coordinated operation of various physical modules, energy conversion efficiency is significantly improved, achieving maximum power output. The following sections will introduce each calculation module in detail.

[0076] Isotope heat source: selection 238 Pu is a pyrogen nuclide. 238Pu has a half-life of 87.7 years, releases 5.48 MeV of energy during decay, and has a power-to-weight ratio of 0.55 W / g.

[0077] Radiator: The advantage of a selective radiator is that the majority of the light emitted at high temperatures (1400K-1500K) has wavelengths below 2 micrometers, which can be utilized by conventional GaSb cells. On the other hand, the proportion of light above 2 micrometers emitted by the radiator is relatively small, thus reducing the impact of excess waste heat on the photovoltaic cell temperature, which leads to a decrease in conversion efficiency. Figure 2 As shown, tungsten, which is relatively inexpensive and has good performance parameters, was selected as the surface material of the radiator in the simulation calculation.

[0078] Filter: In the simulation, a one-dimensional Si / SiO2 photonic crystal (PHC) is used as the filter surface material to prevent long-wavelength photons from passing through the filter, while increasing the transmittance of short-wavelength photons and thus increasing the photovoltaic cell conversion efficiency. Specific performance parameters are as follows: Figure 3 As shown.

[0079] PV cell array: GaSb semiconductor cells are selected as the energy conversion unit. Their advantage lies in the high quantum properties of this cell in the near-infrared band. Specific performance parameters are as follows: Figure 4 As shown.

[0080] Physical Model and Results

[0081] We first built a physical model and used the Matlab programming language to simulate and calculate the factors affecting the performance of the isotope thermophotovoltaic power supply with and without filters under the same physical conditions. Based on this, we gave the specific dimensions of the heat source radiator and the PV photovoltaic array, and studied the output characteristics of the entire isotope thermophotovoltaic system.

[0082] Simulation results of a first-generation isotope thermophotovoltaic monolayer: A radioactive isotope heat source heats the radiator, raising the temperature to 1100℃. The radiator emits a spectrum of light, and the energy of the emitted photons reaches the GaSb-type photoelectric conversion unit. Most of the energy is converted into electrical power output, with a small amount of waste heat being discharged from the system via a heat sink. The PV cell temperature remains around 80℃. The system physical model is as follows: Figure 5 As shown.

[0083] Ignoring the physical effects of filters, simulation calculations are used to illustrate the influence of net radiative heat flux, heat source temperature, and PV cell temperature on the output power and energy conversion efficiency of the isotope thermophotovoltaic system. Figure 6 As shown.

[0084] As shown in the figure, the unit heat flux reaching the GaSb-type PV photovoltaic cell is positively correlated with the isotopic heat source temperature, while the cell's ability to convert the received heat flux into output electrical power is negatively correlated with the cell surface temperature. According to the figure, when the radiator surface temperature is 1100... o C, the battery surface is 80 o At C, the thermo-photovoltaic energy conversion efficiency of a single GaSb cell reaches about 6.5%, possessing the excellent performance of mature RTG technology.

[0085] Optimized simulation results of isotope thermophotovoltaic cells, based on a first-generation isotope thermophotovoltaic physical model, show that a spectral filter is added to the front end of a GaSb-type PV cell. The special microstructure on the filter surface allows most of the short-wavelength spectrum to pass through the filter and reach the photovoltaic cell, while the remaining long-wavelength spectrum is reflected by the filter surface to the heat source for heating, raising the temperature to 1200°C. o C. On the other hand, compared to the case without a filter, the photovoltaic cell receives less long-wavelength spectrum, and the surface temperature of the cell drops significantly. After reaching equilibrium, the temperature can reach 25°C. o C. System physical model as follows Figure 7 As shown.

[0086] The simulation calculations consider the selective filtration performance of the filter. The simulation results reveal the factors affecting the unit output power and energy conversion of the isotope thermoelectric system, such as... Figure 8 As shown.

[0087] As shown in the figure, under the same net radiative heat flux conditions, compared with the first-generation isotope thermophotovoltaic system, the addition of a spectral filter significantly improves the output power of a single GaSb photovoltaic cell, and the thermophotovoltaic energy conversion efficiency can be increased by about 15%. Because the filter has selective reflection and transmission capabilities for the spectrum, when the surface temperature of the radiator is maintained at 1200°C... o C, PV photovoltaic cell operating temperature 25 o At time C, according to the formula, the energy conversion efficiency of a single GaSb photovoltaic cell is about 22%, which increases the efficiency of the isotope thermophotovoltaic power supply to three times the original efficiency.

[0088] Overall performance of isotope thermo-photoelectric power supply system

[0089] To provide a reference for engineering design, we present a schematic diagram of the isotope thermoelectric power supply system, such as... Figure 9 As shown. A selective filter is added to the system, where the size of the thermal radiator is... Isotope thermoelectric power supply housing dimensions A GaSb-type PV cell array with six faces surrounding the heat source receives a photon flux beam passing through a filter. Each face is composed of... Composed of GaSb wafers, each GaSb cell has an area of ​​[area missing]. .

[0090] Using the Matlab language for precise programming calculations, the simulation is performed. 238 The emission spectrum from the external radiator of the Pu isotope thermoelectric source is received by the photoelectric conversion device after passing through the spectrum modulation module and converted into electrical power output. The thermoelectric conversion efficiency is obtained, and the simulation results are as follows: Figure 10 As shown.

[0091] Through reasonable physical design, rigorous simulation calculations, and close cooperation of multiple modules, an isotope thermophotovoltaic power supply system with a compact structure, small size, long lifespan, high output power, and high energy conversion efficiency can be designed. As shown in the figure, when the surface temperature of the thermal radiator is controlled at 1200... o C, Photoelectric conversion device temperature 25 o At time C, it can be seen that the net heat power received by the PV photovoltaic array is 495W, and the output power of the isotope thermo-photovoltaic power system is 110W. The calculated thermoelectric conversion efficiency of the entire device reaches 22.2%.

Claims

1. An isotope thermoelectric power supply for deep space exploration, characterized in that, From the inside out, the module consists of an isotope heat source module, a selective radiator module, a spectral filter module, and a GaSb-type PV photovoltaic cell array module. The isotope heat source module 238 Pu is a pyrogen nuclide and is made into PuO2 ceramic form, with a smooth tungsten coating on the outside; The selective radiator module uses tungsten as the surface material, and the spectral wavelengths emitted at temperatures of 1400K-1500K are mostly concentrated below 2μm. The spectral filter module uses a one-dimensional Si / SiO2 photonic crystal as the surface material, achieving high transmission for spectra below 2μm and high reflection for spectra above 2μm. The GaSb-type PV photovoltaic cell array module is composed of GaSb-type semiconductor cells and has high quantum efficiency in the near-infrared band.

2. The isotope thermoelectric power supply according to claim 1, characterized in that, The 238 Pu has a half-life of 87.7 years, decays to release 5.48 MeV, and has a power-to-weight ratio of 0.55 W / g.

3. The isotope thermoelectric power supply according to claim 1, characterized in that, The spectral filter module transmits the reflected long-wavelength photons back to the isotope heat source module, thereby heating the heat source.

4. The isotope thermoelectric power supply according to claim 1, characterized in that, The GaSb-type PV photovoltaic cell array module is arranged on six surfaces surrounding the isotope heat source module, and each surface is composed of several GaSb crystals.

5. The isotope thermoelectric power supply according to claim 4, characterized in that, When the surface temperature of the selective radiator module is controlled at 1200℃ and the operating temperature of the GaSb PV photovoltaic array module is controlled at 25℃, the system receives a net heat power of 495W, outputs a power of 110W, and achieves an energy conversion efficiency of 22.2%.

6. A design method for an isotope thermoelectric power supply for deep space exploration, characterized in that, Includes the following steps: (1) Determine the core system parameters and material selection: Based on the power requirements and mission cycle of the deep space exploration mission, select... 238 Pu was used as an isotopic heat source nuclide and fabricated into a PuO2 ceramic structure to ensure that the heat source half-life matches the mission cycle; tungsten was selected as the surface material of the selective radiator. One-dimensional Si / SiO2 photonic crystals were used as the spectral filter material. A PV photovoltaic array is constructed using GaSb-type semiconductor cells. (2) Establish a system energy calculation model: calculate the spectral beam flux of the radiator, the spectral heat flux of the filter, and the photoelectric conversion parameters of the PV photovoltaic array in sequence; (3) System simulation and parameter optimization based on Matlab: A physical model of the isotope thermo-photovoltaic power supply was built to simulate the effects of radiator temperature, PV cell temperature and net radiative heat flux on system output power and conversion efficiency with and without filters, and the system parameters were optimized based on the simulation results. (4) Determine the overall structure and performance indicators of the system: Design the overall structure of the power supply, arrange the GaSb type PV photovoltaic cell array and clarify the performance parameters.

7. The design method according to claim 6, characterized in that, The formula for calculating the spectral beam flux of the radiator in step (2) is: ； in: These are Planck's constant and Boltzmann's constant, respectively. The speed of light; The surface temperature of the radiator; wavelength The corresponding radiator spectral emissivity; wavelength The corresponding radiator spectral reflectance coefficient; This represents the spectral beam flux reflected from the filter surface.

8. The design method according to claim 6, characterized in that, In step (2), when calculating the spectral heat flux of the filter, the band... The formula for the heat flux through the filter is: ； Then band The heat flux of light passing through the filter at that location for: ； in: wavelength The corresponding filter spectral emission coefficient; wavelength The corresponding filter spectral reflectance coefficient; The wavelength emitted by the radiator surface Spectral beam flux; The surface temperature of the filter; because The second term in the formula can be ignored. ； Integrating over each wavelength segment yields the net radiative heat flux through the filter across the entire spectral band. for: 。 9. The design method according to claim 6, characterized in that, In step (2), when calculating the photoelectric conversion parameters of the PV photovoltaic array, the wavelength band... The formula for the photon beam flux obtained from absorption is: ； in: It is an effective conversion factor; Due to the quantum properties of photoelectric conversion, PV photovoltaic cells can convert wavelengths... The absorbed photons are converted into electric current. : in: To correspond to the quantum efficiency of different wavebands. The total short-circuit current density across the entire band is obtained. : in: It represents the electron charge. Open-circuit voltage of each PV cell It can be obtained from the following formula: in: This represents the saturation current density of a single GaSb cell. The energy band gap of GaSb material; Calculate the output power of a single PV cell for: in: The power utilization efficiency is called the fill factor, which gives the corresponding energy conversion efficiency. for: 。 10. The design method according to claim 6, characterized in that, The optimized system parameters in step (3) are: the surface temperature of the radiator is controlled at 1200℃, and the operating temperature of the PV photovoltaic array is controlled at 25℃.

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