Mass transfer coefficients inside pipes

Consider a circular pipe of inner diameter D = 0.015 m whose inner surface is I covered with a layer of liquid water as a result of condensation (Fig. 14-49). In I order to dry the pipe, air at 300 K and 1 atm is forced to flov/ through if with an average velocity of 1.2 m/s. Using the analogy between heat and mass transfer, determine the mass transfer coefficient inside the pipe for fully developed flov/. 

Air flows in a 4-cm-diameter wet pipe at 20 C and 1 atm with an average velocity of 4 m/s in order to dry the surface. The Nussell number in this case can be determined from Nu = 0.023Re Pi"- where Ke = 10,550 and Pr = 0.731. Also, the diffusion coefficient of water vapor in air is 2.42 X 10 mVs. Using the analogy between heal and mass transfer, the mass transfer coefficient inside the pipe for fully developed flow becomes... 

Let us consider, as an example, the mass transfer of component A from the inside surface of a pipe to the bulk of a liquid flowing through the pipe. The liquid-phase mass transfer coefficient for this case, kp, is defined by... 

We consider, a case of convective mass transfer where a fluid is flowing by forced convection in a pipe and mass transfer is occurring from the wall to the fluid. The fluid flows at a velocity v inside a pipe of diameter D and we wish to relate the mass-transfer coefficient /c to the variables D, p, p, v, and D g. The total number of variables is < = 6. The fundamental units or dimensions are u = 3 and are mass M, length L, and time f. The units of the variables are... 

Experimental data have come from so-called weft H-walLtowers (Fig. 3.11) and flow of liquids through soluble pipes. In Fig. 3.11, a volatile pure liquid is permitted to flow down the inside surface of a circular pipe while a gas is blown upward or downward through the central core. Measurement of the rate of evaporation of the liquid into the gas stream over the known surface permits calculation of the mass-transfer coefficients for the gas phase. Use of different gases and liquids provides variation of Sc. In this way, Sherwood and Gilliland... 

Figure 10-50C. Tube-side (inside tubes) liquid film heat transfer coefficient for Dowtherm . A fluid inside pipes/tubes, turbulent flow only. Note h= average film coefficient, Btu/hr-ft -°F d = inside tube diameter, in. G = mass velocity, Ib/sec/ft v = fluid velocity, ft/sec k = thermal conductivity, Btu/hr (ft )(°F/ft) n, = viscosity, lb/(hr)(ft) Cp = specific heat, Btu/(lb)(°F). (Used by permission Engineering Manual for Dowtherm Heat Transfer Fluids, 1991. The Dow Chemical Co.)...

An air stream at approximately atmospheric temperature and pressure and containing a low concentration of carbon disulphide vapour is flowing at 38 m/s through a series of 50 mm diameter tubes. The inside of the tubes is covered with a thin film of liquid and both heat and mass transfer are taking place between the gas stream and the liquid film. The film heat transfer coefficient is found to be 100 W/mzK. Using a pipe friction chan and assuming the tubes to behave as smooth surfaces, calculate ... 

Correlation coefficient in the direction normal to the airflow in a pipe of 4-in inside diameter at various velocities. [From T. K. Sherwood, Heat transfer, mass transfer and fluid friction relationships in turbulent flow, Ind. Eng. Chem 42 2077 (1950). Reproduced by piermission of the publisher.]... 

A double-pipe heat exchanger (inside tube diameter of 0.5 m cools engine oil from 160°C to 60°C. Water at 25°C is used as a coolant. Mass flow rates are 2 kg/sec for both fluids. Estimate the length of the exchanger if the overall heat transfer coefficient is 250 W/m °K. 

Compressed air at 0.505 MPa and 300 K flows in the inner tube of a straight concentric-tube exchanger with a mass flow rate of 0.04 kg/s. The inside diameter of the pipe is 12 mm. If the gas exits at a temperature of 160 K and the average pipe temperature is 220 K, what is the heat transfer coefficient based on the inside surface area ... 

A standby air liquefaction plant uses a cold carbon dioxide gas to countercurrently precool a 20.2-MPa air stream from 300 to 260 K in an insulated concentric tube heat exchanger. The cold carbon dioxide gas enters the outer annulus at 220 K and exits at 280 K. The mass flow rate of the carbon dioxide gas is 1 kg/s. The outside diameter of the inner pipe is 80 mm, while the inside diameter of the outer pipe is 155 mm. Assuming comparable resistances to heat transfer through the carbon dioxide and air films, evaluate the heat transfer coefficient for the carbon dioxide side of the heat exchanger. At a mean film temperature of 257 K, carbon dioxide gas has the following properties /i= 1.28 x 10 kg/m s Cp = 795.7 J/kg K p = 2.11 kg/ml... 

In the previous problem if the mass flow rate of the high-pressure air stream is also 1 kg/s and the inside diameter of the inner pipe is 75 mm, determine the heat transfer coefficient for the high-pressure air stream side of the exchanger. Also determine the overall heat transfer coefficient for the heat exchanger. Was the assumption of comparable heat transfer resistances made in the previous problem a reasonable one If not, what must be done to correctly evaluate the overall heat transfer coefficient ... 

T = Temperature on the shell (outer) side r = Temperature on the tube (inner) side Ui = Overall heat transfer coefficient based on D, D = Inside diameter of the inner pipe (tube side) m = Mass flow rate on the shell side m = Mass flow rate on the tube side... 

A condenser consists of 30 rows of parallel pipes of outer diameter 230 mm and thickness 1.3 mm with 40 pipes, each 2 m long in each row. Water, at an inlet temperature of 283 K, flows through the pipes at 1 m/s and steam at 372 K condenses on the outside of the pipes. There is a layer of scale 0.25 mm thick of thermal conductivity 2.1 W/m K on the inside of the pipes. Taking the coefficients of heat transfer on the water side as 4.0 and on the steam side as 8.5 kW/m2 K, calculate the water outlet temperature and the total mass flow of steam condensed. The latent heat of steam at 372 K is 2250 kJ/kg. The density of water is 1000 kg/m3. 

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