Question

Air flows over a solid slab of frozen carbon dioxide formed in dry ice with an exposed cross- sectional area of 1.0x109 m². The carbon dioxide sublimes into the 2.0 m/s flowing stream at a total of mass flux rate is 2.29x107 mol/s and partial pressure is 4.7410Pa. The air is at ambient conditions of 293 K and 1.01310% Pa pressure. At this ambient condition, the diffusivity of carbon dioxide in air is 1.5x10-6 m²/s. At ambient conditions (293 K and 1.013*10Pa), the density and viscosity of air is 1.123 kg/m² and 1.8*10kg/m.s, respectively. The gas constant, R is 8.314 Pa.m/mol.K. a) What is the significant of Sherwood number for calculation of convective mass transfer coefficient? (3 Marks) b) Determine the value of convective mass transfer coefficient of carbon dioxide subliming into the flowing air at the ambient condition of the experiment. State any assumptions used. (7 Marks) c) If the flowing stream and temperature are increased to 4.0 m/s and 313K, respectively, calculate the new convective mass transfer coefficient for that experiment. (15 Marks)

Answer 1

Answer 1

The Sherwood number (Sh) (also called the mass transfer Nusselt number) is a dimensionless number used in mass-transfer operation. It represents the the ratio between mass transfer by convection (β) and mass transfer by diffusion (δ/L) represent the effectiveness of heat and mass convection at the surface and is useful in mass transfer coefficient.

And is given as

sh = K_c D / D_ab

<sub>solution Part (6) assumphins : at Can ( incarnation Term) is zero by applying equation." NA = Ke ACA NA 2 ke Cias -CAR) ka NA CAS- CARO [t-ANqs w ). NA z Wy hate. ka wa A Area. ACCAS - CAN) at 293'ki and 1013x105 Pai Casa PAA 4.748103 - RY a 194 molim 3. 8.314 X 293 If he ansine at Caso = = 6 9.29 x1024. .. Kez NA ACCAP-CAno) -0.118mler | 10 x103 m²x logy Ang

Part (0) NO ho NA Кс 2 2.29*10-4 1.70x10?m?x CMS A(Car CAM) Casa Pa 4674X103 9 1.82 mollm. RT 8.314 X 313 Nowr Substfucking in eq 2.29x107 Ke= 2:29x104 TOXIOXCAS 1.10X103 x12 Ke 28 Oolly so New M.T.C.) 0.114.</sub>

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