CN102437280A - Optimization method of structure of minitype thermoelectric cell - Google Patents

Abstract

The invention discloses an optimization method of a structure of a minitype thermoelectric cell. According to the method, real details of a thermoelectric cell are better considered; a hot point conversion efficiency of the thermoelectric cell as well as correlated property parameters of various materials in the thermoelectric cell are linked; and further optimization is carried out, so that a corresponded numerical value of a structural parameter of the thermoelectric cell is obtained on the condition that the hot point conversion efficiency of the thermoelectric cell is optimal. According to the invention, the method has good accuracy; and a great reference value and guiding significance are provided for the design of a structure of a thermoelectric cell.

Description

A kind of optimization method of miniature thermoelectric cell structure

Technical field

The present invention relates to the thermoelectric cell field, more particularly, relate to a kind of optimization method of miniature thermoelectric cell structure.

Background technology

Thermoelectric cell is a kind of solid-state energy conversion, utilizes the Seebeck effect of thermoelectric material can thermal power transfer be become electric energy.Thermoelectric cell has advantages such as the high stability, life-span length, Maintenance free of high degree of adaptability to operational environment, performance, pollution-free, shockproof and noiselessness; Its range of application mainly is the recycling to used heat at present; And as the aspects such as independent current source of some equipment, but low conversion efficiency of thermoelectric has become a bottleneck that limits its application.

The conversion efficiency of thermoelectric of thermoelectric cell mainly receives two aspect factor affecting, is the thermoelectricity capability of thermoelectric material on the one hand, is the thermoelectric cell structure Design on the other hand.All the time, more to the research of thermoelectric material, and reached certain level, the performance of material unlikely has a distinct increment in a short time, and the thermoelectric cell structure optimization design is just being received increasing concern.Traditional one-dimensional model optimization method has been ignored more actual conditions; Optimization result and actual effect differ bigger; And the finite element method of bibliographical information is a kind of technology preferably of optimizing the thermoelectric cell structure at present; But the foundation of this method model and the follow-up equal more complicated of analysis use time and effort consuming.

Summary of the invention

The objective of the invention is to overcome the deficiency of prior art, a kind of optimization method of miniature thermoelectric cell structure is provided.This method combines the actual detail of miniature thermoelectric cell more, sets up the One dimensional Mathematical Model of expressing miniature thermoelectric cell performance, through calculating under the battery performance optimal situation dependency structure parameter of thermoelectric cell.This method simply is easy to grasp, and accuracy is better, and the structural design of thermoelectric cell is had bigger reference value.

Optimization method of the present invention carries out to the thermoelectric cell with Fig. 1 construction unit.This thermoelectric cell is made up of outer package layer 1, conduction articulamentum 2, packing material 3, p type thermoelectric leg 4 and n type thermoelectric leg 5.P type thermoelectric leg 4 in the thermoelectric cell is arranged in parallel with n type thermoelectric leg 5, and conduction articulamentum 2 is used to realize the electricity series connection between p type thermoelectric leg 4 and the n type thermoelectric leg 5 that outer package layer 1 and packing material 3 are used to protect the internal structure of thermoelectric cell.

The object of the invention is achieved through following technical proposals:

The first step, confirm the character and the residing operational environment of thermoelectric cell material therefor:

(1) the Seebeck coefficient α of n type thermoelectric material _n, the electricalresistivity _n, thermal conductivity λ _n, n type thermoelectric material and the contact resistivity ρ of conduction between articulamentum _N-contact

(2) the Seebeck coefficient α of p type thermoelectric material _p, the electricalresistivity _p, thermal conductivity λ _p, p type thermoelectric material and the contact resistivity ρ of conduction between articulamentum _P-contact

(3) the thermal conductivity λ ' of packing material

(4) the thermal conductivity λ of outer package layer material on the cold and hot end face of thermoelectric cell ₀And thickness h ₀

(5) the temperature difference T between between the cold junction of thermoelectric cell hot junction

(6) temperature T in thermoelectric cell hot junction _Hot

(7) resistance value of thermoelectric cell external load is R _L0With rated power be P ₀

Second step, the structural parameters of setting thermoelectric cell:

Set the span and the stepping amount of height h of section radius b and thermoelectric leg of section radius a, the p type thermoelectric leg of n type thermoelectric leg, and carry out progressively iterative computation, until the maximum η of the conversion efficiency of thermoelectric that obtains thermoelectric cell according to following formula _Max, this moment, corresponding a, b, h was the final optimization pass structural parameters

${\mathrm{\ΔT}}_0=\frac{2\sqrt{P_0/R_{L0}}(\frac{{\mathrm{h\ρ}}_n-{2\mathrm{\ρ}}_{n-\mathrm{contact}}}{a^2}+\frac{{\mathrm{h\ρ}}_p-{2\mathrm{\ρ}}_{p-\mathrm{contact}}}{b^2})}{{\mathrm{\π\α}}_{p,n}}$

$A_T/N=\frac{\mathrm{\&pi;}({\mathrm{\&lambda;}}_n-{\mathrm{\&lambda;}}^{\&prime;})a^2+\mathrm{\&pi;}({\mathrm{\&lambda;}}_p-{\mathrm{\&lambda;}}^{\&prime;}){\mathrm{<figure-callout\; id="2"\; label="b"\; filenames="HDA0000121873160000011.png"\; state="\{\{state\}\}">b</figure-callout>}}^2}{\frac{{\mathrm{\&lambda;}}_{0}h(\mathrm{\&Delta;T}-{\mathrm{\&Delta;T}}_0)}{2h_0{\mathrm{\&Delta;T}}_0}-{\mathrm{\&lambda;}}^{\&prime;}}$

$Q=\frac{\mathrm{\&pi;}{R}_{L0}{\mathrm{\&alpha;}}_{p,n}{T}_{\mathrm{hot}}\sqrt{P_0/R_{L0}}}{\frac{{\mathrm{h\&rho;}}_n+{2\mathrm{\&rho;}}_{n-\mathrm{contact}}}{a^2}+\frac{{\mathrm{h\&rho;}}_p+{2\mathrm{\&rho;}}_{p-\mathrm{<figure-callout\; id="2"\; label="contact\; b"\; filenames="HDA0000121873160000011.png"\; state="\{\{state\}\}">contact</figure-callout>}}}{b^{}}}$

$+\frac{2\sqrt{P_0{R}_{L0}}(\mathrm{\&pi;}({\mathrm{\&lambda;}}_n-{\mathrm{\&lambda;}}^{\&prime;})a^2+\mathrm{\&pi;}({\mathrm{\&lambda;}}_p-{\mathrm{\&lambda;}}^{\&prime;}){\mathrm{<figure-callout\; id="2"\; label="b"\; filenames="HDA0000121873160000011.png"\; state="\{\{state\}\}">b</figure-callout>}}^2+{\mathrm{\&lambda;}}^{\&prime;}{A}_T/N)}{{\mathrm{\&alpha;}}_{p,n}h}-\frac{P_0}{2}$

$\mathrm{\&eta;}=\frac{P}{Q}$

The optimization method of the thermoelectric cell structure that the present invention proposes; Relevant nature parameter with the conversion efficiency of thermoelectric and the various materials in the thermoelectric cell of thermoelectric cell; The hot junction of thermoelectric cell and cold junction temperature; The structural parameters of thermoelectric cell, and the relevant parameter of the load that is connected with thermoelectric cell connects.Above-mentioned relevant nature parameter comprises the n type thermoelectric material that thermoelectric cell adopts and Seebeck coefficient, thermal conductivity, resistivity and the contact resistivity data of p type thermoelectric material; The thermal conductivity data of the packing material in the thermoelectric cell between each thermoelectric leg; And the thermal conductivity data of employed outer package layer on thermoelectric cell cold junction and the hot junction; The present invention optimizes the structural parameters of thermoelectric cell with above-mentioned parameter, i.e. the sectional area (being radius) of n type thermoelectric leg and p type thermoelectric leg and height.This optimization method that the present invention proposes has more been considered the actual conditions of thermoelectric cell, comprising:

(1) sectional area of n type thermoelectric leg 5 and p type thermoelectric leg 4 is identical or different;

(2) all there is contact resistance between n type thermoelectric leg 5 and p type thermoelectric leg 4 and the conduction articulamentum 2;

(3) heat (comprise p type thermoelectric leg 4, n type thermoelectric leg 5) from the hot junction along the thermoelectric leg and the thermoelectric leg between 3 two kinds of channels of packing material be delivered to cold junction;

(4) temperature difference between the upper and lower end face of thermoelectric leg, the temperature difference that equals between thermoelectric cell hot junction and the cold junction deducts the temperature difference of consumption on upper and lower outer package layer;

This optimization method that the present invention proposes connects the structural parameters of conversion efficiency of thermoelectric and thermoelectric cell, is optimization objects with the conversion efficiency of thermoelectric, obtains the structural parameters of the thermoelectric cell of correspondence when most effective.This methodological science is reasonable, and the result of calculation accuracy is better, and this is for the structure of optimizing thermoelectric cell, and the performance that promotes thermoelectric cell has bigger directive significance.

Description of drawings

The cross-sectional view of the thermoelectric unit that constitutes by a n type thermoelectric leg and p type thermoelectric leg in Fig. 1 thermoelectric cell.The numbering explanation: 1 is outer package layer, and 2 are the conduction articulamentum, and 3 is packing material, and 4 is p type thermoelectric leg, and 5 is n type thermoelectric leg.

Fig. 2 optimization method sketch map of the present invention.

Embodiment

Further specify technical scheme of the present invention below in conjunction with specific embodiment.

The temperature difference structural optimization method that the present invention adopts, the actual conditions below having taken all factors into consideration: the sectional area of (1) n type thermoelectric leg 5 and p type thermoelectric leg 4 is identical or different; (2) all there is contact resistance between n type thermoelectric leg 5 and p type thermoelectric leg 4 and the conduction articulamentum 2; (3) heat (comprise p type thermoelectric leg 4, n type thermoelectric leg 5) from the hot junction along the thermoelectric leg and the thermoelectric leg between 3 two kinds of channels of packing material be delivered to cold junction; (4) temperature difference that equals between the cold junction of thermoelectric cell hot junction of the temperature difference between the upper and lower end face of thermoelectric leg deducts the temperature difference of consumption on upper and lower outer package layer.

Concrete optimization method is following: the first step, the gross area of supposing thermoelectric cell is A _T, wherein contain N to the thermoelectric unit, and thermoelectric leg 4 or 5 is cylinder (the thermoelectric leg is similar for the situation of other shape), with reference to accompanying drawing 1, be research object with a pair of thermoelectric unit area, then its resistance can use [1] formula to represent as follows:

$R=R_n+R_p+R_{\mathrm{contact}}={\mathrm{\&rho;}}_n\frac{h}{\mathrm{\&pi;}{\mathrm{<figure-callout\; id="2"\; label="a"\; filenames="HDA0000121873160000011.png"\; state="\{\{state\}\}">a</figure-callout>}}^2}+{\mathrm{\&rho;}}_p\frac{h}{\mathrm{\&pi;}{\mathrm{<figure-callout\; id="2"\; label="b"\; filenames="HDA0000121873160000011.png"\; state="\{\{state\}\}">b</figure-callout>}}^2}+\frac{{2\mathrm{\&rho;}}_{n-\mathrm{contact}}}{{\mathrm{\&pi;<figure-callout\; id="2"\; label="a"\; filenames="HDA0000121873160000011.png"\; state="\{\{state\}\}">a</figure-callout>}}^2}+\frac{{2\mathrm{\&rho;}}_{p-\mathrm{contact}}}{\mathrm{\&pi;}{b}^2}---\left[1\right]$

Wherein: R, R _n, R _p, R _ContactRepresent the all-in resistance of a pair of thermoelectric leg, the resistance of n type thermoelectric leg 5, the resistance of p type thermoelectric leg 4 respectively, and the contact resistance between n type thermoelectric leg and p type thermoelectric leg and the conduction articulamentum 2, ρ _n, ρ _p, ρ _N-contact, ρ _P-contactThe resistivity of the p type thermoelectric material of the resistivity of the n type thermoelectric material of the n of expression formation respectively type thermoelectric leg 5, formation p type thermoelectric leg 4; And the contact resistivity of 2 of n type thermoelectric leg 5 and p type thermoelectric leg 4 and conduction articulamentums, a, b, h represent the section radius of n type thermoelectric leg 5, the section radius of p type thermoelectric leg 4 and the height of thermoelectric leg respectively.

The overall thermal conductance K of a pair of thermoelectric unit can use [2] formula to represent as follows:

$K=K_n+K_p+K^{\&prime;}={\mathrm{\&lambda;}}_n\frac{{\mathrm{\&pi;a}}^2}{h}+{\mathrm{\&lambda;}}_p\frac{{\mathrm{\&pi;b}}^2}{h}+{\mathrm{\&lambda;}}^{\&prime;}\frac{A_T/N-{\mathrm{\&pi;a}}^2-{\mathrm{\&pi;b}}^2}{h}---\left[2\right]$

Wherein: K _n, K _p, K ' representes the thermal conductance of packing material 3 between thermal conductance and the thermoelectric leg of thermal conductance, p type thermoelectric leg 4 of n type thermoelectric leg 5, λ respectively _n, λ _p, λ ' represent respectively to constitute the n type thermoelectric material of n type thermoelectric leg 5 thermal conductivity, constitute the thermal conductivity of the p type thermoelectric material of p type thermoelectric leg 4 and the thermal conductivity of packing material 3.

The temperature difference between the upper and lower end face of thermoelectric leg can use [3] formula to represent as follows:

${\mathrm{\&Delta;T}}_0=\frac{\mathrm{\&Delta;<figure-callout\; id="1"\; label="T"\; filenames="HDA0000121873160000011.png"\; state="\{\{state\}\}">T</figure-callout>}}{1+2K/K_0};$ $K_0={\mathrm{\&lambda;}}_0\frac{A_T/N}{h_0}$

${\mathrm{\&Delta;T}}_0=\mathrm{\&Delta;T}/\{1+\frac{{2h}_0}{h}[\frac{\mathrm{\&pi;}{\mathrm{Na}}^2({\mathrm{\&lambda;}}_n-{\mathrm{\&lambda;}}^{\&prime;})}{{\mathrm{\&lambda;}}_0{A}_T}+\frac{\mathrm{\&pi;}{\mathrm{Nb}}^2({\mathrm{\&lambda;}}_p-{\mathrm{\&lambda;}}^{\&prime;})}{{\mathrm{\&lambda;}}_0{A}_T}+\frac{{\mathrm{\&lambda;}}^{\&prime;}}{{\mathrm{\&lambda;}}_0}\left]\right\}---\left[3\right]$

Wherein: Δ T, Δ T ₀Represent the temperature difference and the temperature difference between the thermoelectric leg upper and lower end face between the cold junction of thermoelectric cell hot junction respectively, K ₀, λ ₀, h ₀The thermal conductance of representing outer package layer 1 on the cold and hot end face respectively, thermal conductivity and thickness thereof.(then can think Δ T like no outer package layer ₀=Δ T)

Simultaneously, because

$I=\frac{{\mathrm{N\&alpha;}}_{p,n}{\mathrm{\&Delta;T}}_0}{\mathrm{NR}+R_L}---\left[4\right]$

$P=I^2{R}_L=\frac{{\mathrm{<figure-callout\; id="2"\; label="N"\; filenames="HDA0000121873160000011.png"\; state="\{\{state\}\}">N</figure-callout>}}^2{\mathrm{\&alpha;}}_{p,\mathrm{<figure-callout\; id="2"\; label="n"\; filenames="HDA0000121873160000011.png"\; state="\{\{state\}\}">n</figure-callout>}}^2{\mathrm{\&Delta;T}}_0^2{R}_L}{{(\mathrm{NR}+R_L)}^2}---\left[5\right]$

Q＝N?(Iα _p，nT _hot+KΔT ₀-I ²R/2) [6]

$\mathrm{\&eta;}=\frac{P}{Q}---\left[7\right]$

Wherein: I, P, Q, η represent that respectively the output current of thermoelectric cell, power output (are the rated power P of load ₀), import the hot-fluid of thermoelectric cell and the conversion efficiency of thermoelectric of thermoelectric cell, α into from the thermoelectric cell hot junction _{P, n}Represent the relative Seebeck coefficient (α of p type and n type thermoelectric material _{P, n}=α _p-α _n, α wherein _p, α _nBe respectively the Seebeck coefficient of p type thermoelectric material, the Seebeck coefficient of n type thermoelectric material), R _LRepresent the resistance value of load, T _HotRepresent the temperature in thermoelectric cell hot junction.

In second step, the resistance value of the electrical appliance of supposing to be connected with thermoelectric cell (load) is R _L0, rated power is P ₀, and think that thermoelectric cell just in time satisfies the plant capacity requirement in Maximum Power Output, promptly work as NR=R _L0The time, the battery power output is P ₀

Then can get following expression formula through series of iterations:

$N=R_{L0}/R=\mathrm{\&pi;}{R}_{L0}/(\frac{{\mathrm{h\&rho;}}_n+{2\mathrm{\&rho;}}_{n-\mathrm{contact}}}{a^2}+\frac{{\mathrm{h\&rho;}}_p+{2\mathrm{\&rho;}}_{p-\mathrm{contact}}}{b^2})---\left[8\right]$

${\mathrm{\&Delta;T}}_0=\frac{2\sqrt{P_0/R_{L0}}(\frac{{\mathrm{h\&rho;}}_n+{2\mathrm{\&rho;}}_{n-\mathrm{contact}}}{a^2}+\frac{{\mathrm{h\&rho;}}_p-{2\mathrm{\&rho;}}_{p-\mathrm{contact}}}{b^2})}{\mathrm{\&pi;}{\mathrm{\&alpha;}}_{p,n}}---\left[9\right]$

$A_T/N=\frac{\mathrm{\&pi;}({\mathrm{\&lambda;}}_n-{\mathrm{\&lambda;}}^{\&prime;})a^2+\mathrm{\&pi;}({\mathrm{\&lambda;}}_p-{\mathrm{\&lambda;}}^{\&prime;}){\mathrm{<figure-callout\; id="2"\; label="b"\; filenames="HDA0000121873160000011.png"\; state="\{\{state\}\}">b</figure-callout>}}^2}{\frac{{\mathrm{\&lambda;}}_{0}h(\mathrm{\&Delta;T}-{\mathrm{\&Delta;T}}_0)}{2h_0{\mathrm{\&Delta;T}}_0}-{\mathrm{\&lambda;}}^{\&prime;}}---\left[10\right]$

$Q=\frac{\mathrm{\&pi;}{R}_{L0}{\mathrm{\&alpha;}}_{p,n}{T}_{\mathrm{hot}}\sqrt{P_0/R_{L0}}}{\frac{{\mathrm{h\&rho;}}_n+{2\mathrm{\&rho;}}_{n-\mathrm{contact}}}{a^2}+\frac{{\mathrm{h\&rho;}}_p+{2\mathrm{\&rho;}}_{p-\mathrm{<figure-callout\; id="2"\; label="contact\; b"\; filenames="HDA0000121873160000011.png"\; state="\{\{state\}\}">contact</figure-callout>}}}{b^{}}}$

$+\frac{2\sqrt{P_0{R}_{L0}}(\mathrm{\&pi;}({\mathrm{\&lambda;}}_n-{\mathrm{\&lambda;}}^{\&prime;})a^2+\mathrm{\&pi;}({\mathrm{\&lambda;}}_p-{\mathrm{\&lambda;}}^{\&prime;}){\mathrm{<figure-callout\; id="2"\; label="b"\; filenames="HDA0000121873160000011.png"\; state="\{\{state\}\}">b</figure-callout>}}^2+{\mathrm{\&lambda;}}^{\&prime;}{A}_T/N)}{{\mathrm{\&alpha;}}_{p,n}h}-\frac{P_0}{2}---\left[11\right]$

So, formula [9] is updated in the formula [10], formula [10] being updated to is in [11] again, at last with in formula [11] the substitution formula [7]; (a, b h), remove a in the formula can to obtain the expression formula of conversion efficiency of thermoelectric: η=η; B, other outer parameter of h all can record concrete numerical value or the artificial numerical value of setting through pertinent instruments, as long as set independent variable a, b so; The span of h, a, b, the h of correspondence in the time of just can obtaining the η maximum, and, obtain N and A with their substitution formulas [8] and formula [10] _TValue, promptly reached the purpose of optimizing battery structure through said method like this.

According to above-mentioned optimization method, at first measure and confirmed that the character of thermoelectric cell material therefor and residing operational environment are following:

1.α _p＝1.2×10 ^-4V/K，ρ _p＝2×10 ^-5Ω·m，λ _p＝1.22W/(m·K)，ρ _p-contact＝3×10 ^-9Ω·m ²

2.α _n＝-1.4×10 ^-4V/K，ρ _n＝1.1×10 ^-5Ω·m，λ _n＝1.85W/(m·K)，

ρ _n-contact＝1×10 ^-9Ω·m ²

3.λ′＝0.306W/(m·K)，λ ₀＝100W/(m·K)，h ₀＝5×10 ^-5m

4.ΔT＝20K，T _hot＝318.15K

5.R _L0＝100Ω，P ₀＝1×10 ^-3W

Set the span and the stepping amount of height h of section radius b and thermoelectric leg of section radius a, the p type thermoelectric leg of the structural parameters n type thermoelectric leg of thermoelectric cell then respectively, as follows:

1.a (5 μ m, 1mm), the stepping amount is 10 μ m to ∈

2.b (5 μ m, 1mm), the stepping amount is 10 μ m to ∈

3.h (5 μ m, 2mm), the stepping amount is 10 μ m to ∈

When above-mentioned parameter substitution formula is carried out calculation optimization, at first calculate Δ T according to formula [9] ₀, bring formula [10] then into and calculate A _T/ N can obtain Q with operation result substitution formula [11] again, at last with the conversion efficiency of thermoelectric η that can obtain thermoelectric cell in the substitution formula as a result [7].So carrying out iterative computation according to the stepping amount, is the iteration terminal point to obtain maximum efficiency eta, and this moment, corresponding a, b, h was the structure of optimizing the back thermoelectric cell.Final calculation result shows below: η _Max=0.00269, this moment h=875 μ m, a=95 μ m, b=135 μ m, N=121.8, A _T=10.59mm ²

Result according to above-mentioned computation optimization; According to actual conditions N is chosen as 122; H is chosen as 875 μ m, and a is chosen as 95 μ m, and b is chosen as 135 μ m; Produced a thermoelectric cell, and utilize thermoelectric cell the conversion efficiency of thermoelectric test system and test conversion efficiency of thermoelectric of this battery when above-mentioned operational environment be 0.00267.

The optimization method of miniature thermoelectric cell structure of the present invention has been considered actual conditions more; With respect to traditional optimization methods; Optimizing structure of the thermoelectric cell that the method obtains more approaches actual result, for the conversion efficiency of thermoelectric that improves thermoelectric cell through Optimal Structure Designing bigger using value arranged.During practical operation, the N round numbers, the scope of a, b, h can give different assignment of above-mentioned parameter or scope according to actual conditions, to obtain the optimization structure of corresponding thermoelectric cell.

More than the present invention has been done exemplary description; Should be noted that; Under the situation that does not break away from core of the present invention, the replacement that is equal to that any simple distortion, modification or other those skilled in the art can not spend creative work all falls into protection scope of the present invention.

Claims (1)

1. the optimization method of a miniature thermoelectric cell structure is characterized in that,

At first, confirm the character and the residing operational environment of thermoelectric cell material therefor:

(1) the Seebeck coefficient α of n type thermoelectric material _n, the electricalresistivity _n, thermal conductivity λ _n, n type thermoelectric material and the contact resistivity ρ of conduction between articulamentum _N-contact

(2) the Seebeck coefficient α of p type thermoelectric material _p, the electricalresistivity _p, thermal conductivity λ _p, p type thermoelectric material and the contact resistivity ρ of conduction between articulamentum _P-contcat

(3) the thermal conductivity λ ' of packing material

(4) the thermal conductivity λ of outer package layer on the cold and hot end face of thermoelectric cell ₀And thickness h ₀

(5) the temperature difference T between the cold junction of thermoelectric cell hot junction

(6) temperature T in thermoelectric cell hot junction _Hot

(7) resistance of thermoelectric cell external load is R _L0With rated power be P ₀

Set the structural parameters of thermoelectric cell then respectively; The span and the stepping amount of height h of section radius b and thermoelectric leg that comprises section radius a, the p type thermoelectric leg of n type thermoelectric leg; And carry out progressively iterative computation according to following formula, until the maximum η of the conversion efficiency of thermoelectric that obtains thermoelectric cell _Max, this moment, corresponding a, b, h was the final optimization pass structural parameters

To optimize structure parameter a, b, h obtain the gross area A of final optimization pass structural parameters thermoelectric cell again in the substitution following formula _TAnd the thermoelectric element number N that contains in the thermoelectric cell

。

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