Number of transfer units (NTU) height of a transfer unit(hTu) VY2 X2 H H OG OK.a Y,Ⅹ, dh y1 dy OG Y2Y一Y VYI L XI Kya: overall volumetric mass transfer coefficient based on gas componentNumber of transfer units (NTU) & Height of a transfer unit(HTU) V, Y2 L, X2 V, Y1 L, X1 Y, X, dH H * 1 2 Y Y dY N K a V H Y Y OG Y OG − =  =  KYa: overall volumetric mass transfer coefficient based on gas component