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Convection

Storyboard

The difference in atmospheric pressure leads to displacement of air masses both at surface level and at heights.

The vertical flow is called convection and is key to cloud formation, rain generation and effective energy flow between surface and atmosphere.

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ID:(552, 0)



Convection

Description

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ID:(40, 0)



Número de Rayleigh

Equation

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El inicio de convecci?n t?rmica esta descrito por el n?mero de Rayleigh

Ra=\displaystyle\frac{\rho^2 g c_p}{\eta\lambda}\displaystyle\frac{(T_e-T_t)}{T_e}h^3

Para un sistema entre dos placas con las temperaturas inferior T_b y superior T_t la convecci?n se iniciar? al alcanzar un n?mero de Rayleigh de 1708. Para el caso de dos superficies libres el valor cr?tico es 657.51. Para un sistema de un borde fijo y el otro libre 1,100.65.

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Velocidad de Ascenso

Equation

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v_c=\sqrt{\displaystyle\frac{2hg(\rho_m-\rho}{C_W\rho_m}}

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Velocidad de Ascenso en función de la Temperatura

Equation

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Como la velocidad de acenso es igual a

v(z) ^2 = 2 g \displaystyle\int_0^zds\displaystyle\frac{( \rho_m(s) - \rho(s) )}{ \rho(s) }



y en condiciones isobaricas se cumple

\rho_i T_i = \rho_f T_f



la ecuación para la velocidad se puede también escribir en función de la temperatura

v =\sqrt{2 CAPE }

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convection007

Image

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![convection007](showImage.php)

convection007

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Mixing ratio of water vapor with air

Equation

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The mixing ratio of water vapor with air is defined as the ratio of the masses of each component present in a volume:

\displaystyle\frac{M_v}{M_a}=\displaystyle\frac{n_vM_{mol,v}}{n_aM_{mol,a}}=\displaystyle\frac{p_v}{p_a}\displaystyle\frac{M_{mol,v}}{M_{mol,a}}\sim 0.01



Where M_v and M_a are the masses of water vapor and air respectively, n_v and n_a are the moles of water vapor and air, M_{mol,v} and M_{mol,a} are the molar masses of water vapor and air, p_v and p_a are the relative pressures of water vapor and air, and r is the mixing ratio. Therefore, we have

r =\displaystyle\frac{ M_v }{ M_a }

Gamma=displaystyle rac{g}{c_p}displaystyle rac{1+displaystyle rac{l_mr_s}{RT}}{1+displaystyle rac{l_m^2r_sepsilon}{c_pRT^2}}v(z)^2=2gdisplaystyleint_0^zdsdisplaystyle rac{2( ho_m(s)- ho(s))}{ ho(s)} r = M_v / M_a v =sqrt(2* CAPE ) Ra =( rho ^2* g * c_p /( eta * lambda ))*(( T_e - T_t )* h ^3 / T_e )CAPE=gdisplaystyleint_0^z dsdisplaystyle rac{(T(s)-T_m(s))}{T_m(s)}Gamma=displaystyle rac{g}{c_p}z=M_molv/M_moladisplaystyle rac{dT}{T}=-displaystyle rac{(1+r/zeta)}{(1+r)}(kappa-1)displaystyle rac{dV}{V} dQ = M_a *(1+ r )* c_p * dT delta W=-left(1+displaystyle rac{r}{zeta} ight)n_aRTdisplaystyle rac{dV}{V} dc_s = c_s * l_m * dT /( R *T ^2)delta W=-left(1+displaystyle rac{l_mr_s}{RT} ight)n_aRTdisplaystyle rac{dV}{V}delta Q = M_aleft(c_p+displaystyle rac{l_m^2r_s}{RT^2} ight)dTdisplaystyle rac{dT}{T}=-displaystyle rac{left(1+displaystyle rac{l_mr_s}{RT} ight)}{left(1+displaystyle rac{l_m^2r_s}{c_pRT^2} ight)}(kappa-1)displaystyle rac{dV}{V}displaystyle rac{n_v}{n_a}=displaystyle rac{r}{zeta}dM_s=M_sdisplaystyle rac{l_m}{RT^2}dTr_s=zeta_sdisplaystyle rac{p_0}{p_a}e^{-l_m/RT} ho vdisplaystyle rac{dv}{dx}=( ho_m- ho) gv(z)^2=2gdisplaystyleint_0^zdsdisplaystyle rac{2( ho_m(s)- ho(s))}{ ho(s)}Tkapparhogc_sc_pT_tlambdaRvetaV_a

In the specific case of water vapor in air, the mixing ratio is proportional to the relative pressures, which can be quantified using the vapor pressure of water p_v\sim 1500 Pa and the air pressure p_a\sim 10^5 Pa. By applying the ideal gas equation and the definition of molar mass, it can be determined that the mixing ratio is approximately 0.01. This means that the amount of water vapor compared to air is low under normal conditions.

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convection006

Equation

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![convection006](showImage.php)

convection006

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