1MCFC stack dynamic model of temperature distribution

Fuel cells are a new type of fuel through the electrolyte to produce electricity to power a chemical reaction approach. The principle is the use of hydrogen, carbon monoxide and other combustible gases oxidation reaction to produce electricity,dell laptop battery the reaction process by means of electrolyte transfer electrons to form the output power. Fuel cells with energy conversion efficiency (fuel resources), pollution, low noise, a variety of advantages. Molten carbonate fuel cell (MoltenCarbonateFuelCell, MCFC) is the mainstream of today's fuel cell research, it is highly efficient, low-cost, highly competitive, can be used for large central station. It is the sodium carbonate / potassium carbonate and lithium carbonate mixed melting material as the electrolyte salt, natural gas and coal gas as fuel is available,dell Latitude CPi battery, dell Inspiron 8200 battery, dell Inspiron 8000 battery, dell Inspiron 8100 battery, the working temperature of 600 ~ 700 ° C.

In this paper, the weighted residual method to the downstream-and convection-type MCFC stack temperature model for solving the spatial and temporal distribution and simulation, the temperature distribution between the two curves. On this basis, comparing the advantages and disadvantages of two different flow patterns and concluded that the flow field of MCFC design of some significance.

1MCFC stack dynamic model of temperature distribution

MCFC stack structure is shown. Stack in the middle part of the electrolyte, the electrolyte for the anode and cathode sides of the plate, up and down the partitions, partitions between the electrodes of fuel channels, there are many slots open road. Fuel flows through the electrolyte after the chemical reaction and generate electricity. For MCFC, according to the fuel gas and oxidant gas flow in different ways, successful direct communication between right angle, you can also have the fuel and air way downstream and parallel to the parallel but opposite direction of convection.

In the MCFC power generation process, due to chemical reactions and the current in the electrolyte, the electrode in the flow of heat are produced to promote the fuel cell body temperature rises. Temperature rises to promote chemical reactions speed up, but the temperature will affect the characteristics of the battery, and damage to the electrolyte, causing evaporation of the electrolyte, corrosion bipolar plates. Flow of fuel in the process of power generation,dell Latitude CPi battery, the dynamic temperature distribution was, therefore, to improve the performance of fuel cells, its effective control, the fuel cell power generation must understand the dynamic process of the temperature distribution characteristics.

Considering that each stack of cathode, anode, electrode - electrolyte plate and separator material changes in flow and energy changes in the fuel cell stack internal heat and mass transfer analysis based on the conservation of matter and energy Law, get a partial differential equations. The dimensionless coefficients of their treatment, get the following equations: a al = a1 (ea) a2 (sa) a3c ± cl = a4 (ec) a5 (sc) e = a6 (ae) a7 (ce) a8e a9 a10 (se) s = a11 (as) a12 (cs) a13 (es) (1) Where: temperature; of time; l is the length of the stack gas flow, the non-dimensional treatment can be considered in the l (0,1) interval; subscript following meaning: c is the cathode, a anode, e is the electrode - electrolyte plate, s is the partition.

Convection and downstream battery model coefficients a3 key difference is that the sign behind the contrary, it is because the downstream-and convection-type MCFC stack oxidant gas flows in the opposite. Convection-type stack of anode,dell Latitude CPi battery, dell Inspiron 8200 battery, dell Inspiron 8000 battery, dell Inspiron 8100 battery, electrolyte electrode plates and separators of the same type of energy process and the downstream, so the equations, the coefficients ai (i = 1,2,3, ..., 13) and the definition of the same type of downstream .

In addition, the battery model convection and downstream boundary conditions are different: downstream of the stack-type anode and cathode in the l = 0, the temperature is always the fuel gas and oxidant gas preheat temperature; convective stack in the l = 0, the cathode temperature changes over time, the fuel gas outlet, the oxidant gas at the entrance, the temperature is always equal to the cathode oxidant gas preheat temperature.

2MCFC dynamic temperature distribution model solution

In this paper, three orthogonal polynomials as basis functions,dell Inspiron 8200 battery, using the weighted residual method to the downstream temperature-and convection-type MCFC model solution, assuming that 1 = l, 2 = 3l-4l23 = 6l-20l2 15l3 ...

(2) is consistent with other base function symbols. Initial temperature as constant basis function, denoted by 0.

For the downstream type MCFC stack, the boundary conditions at the entrance to the anode and cathode gas preheat temperature and the temperature is always the same, namely a (t, 0) = c (t, 0) = e (t, 0) = s ( t, 0) = 600 ° C so

da (t, 0) dt = dc (t, 0) dt = de (t, 0) dt = ds (t, 0) dt = 0 (3) take the anode, cathode, electrode plates and separators of electrolyte temperature test function as follows: a (, l) = 0 Σni = 1Ai () i (l) c (, l) = 0 Σni = 1Bi () i (l) e (, l) = 0 Σni = 1Ci ( ) i (l) s (, l) = 0 Σni = 1Di () i (l) (4) where, 0 = 600 ° C.

Substituting (3) into equations (1), then use Galerkin method to basis functions i (l) for the weight function for each equation in [0,1] on the points, so that each integration is equal to zero, you get a set of ordinary differential equations. So: p = [Ai, Bi, Ci, Di] i = 1,2, ..., n, the above equations in a matrix form expression for the M × p '= Np q (5) where: M, N for the 4n × 4n matrix, n is the order of the trial function; vector q is constant. ODE boundary conditions Ai (0) = 0, Bi (0) = 0, Ci (0) = 0Di (0) = 0i = 1,2, ..., n (6) for this form of ordinary differential equation has the classic numerical method, such as the Adams method, Gear method, RungeKutta law, which in the mathematical software Mathematica, you can call the function ND-Solve solution of these equations.

For convection-type MCFC stack, the model equations such as equation (2) below, with the same type with the downstream solve this set of algorithms to partial differential equations with variable coefficients, but the flow pattern downstream model boundary conditions and type of phase greater than the difference.

To meet the boundary conditions, taking the anode, cathode, electrolyte electrode plates and separators of basis functions as follows: a (, l) = 0 Σni = 1Ai () i (l) c (, l) = B0 () Σni = 1Bi () i (l) e (, l) = [0 B0 ()] / 2 Σni = 1Ci () i (l) s (, l) = [0 B0 ()] / 2 Σni = 1Di ( ) i (l) (7) where, dell Inspiron 8000 battery, 0 = 600 ° C.

In the convective electric pile, anode inlet temperature of the fuel gas preheat temperature, the cathode inlet, the anode exit (l = 1) temperature of the gas oxidant preheat temperature. Therefore, the l = 1 the temperature conditions of 0 into (6), we obtain: B0 () = 0-Σni = 1Bi () i Substituting (8) into (7), and then substituted into equations ( 1), repeat the above Galerkin method for solving the convection model.

3 the results of model solution

Using Mathematica software solution, the results shown. Dark for the low temperature zone, light as a high temperature, a total of 30 isotherms. The results are given along the convection-type power reactor temperature versus time curve, compared the two stack temperature changes in different regions, and the stack in two categories based on the spatial distribution of temperature, dell Latitude CPi battery, dell Inspiron 8200 battery, dell Inspiron 8000 battery, dell Inspiron 8100 battery,and then gives the distribution of isotherms diagram. It can be seen, two types of temperature distribution in the stack some distinction.

4 Conclusion

(1) model of the temperature over time better convergence; (2) convective-type MCFC stack with the more downstream, the maximum temperature is almost equal (655 ° C or so), close to the speed of temperature rise; (3) Both have a greater spatial distribution of temperature differences, convection-type electrolyte plate, separator and cathode plates of high-temperature part of the plate than in the preceding (0.4X, X is the length of the plate), and downstream-oriented electrolyte plate, separator and high-temperature part of the electrode plates in a later section of plate (> 0.6X), this board will result in a different part of the corrosion in varying degrees;dell Inspiron 8100 battery, (4) convection in the electrolyte plate and separator type on the large temperature range than the downstream type more likely to cause corrosion.

The above conclusions consistent with experimental results, therefore, the results of this actual MCFC stack of flow field design reference value.