Write down the physical illeanings and the units of the sy~nbols appeared in this equation: D,, , Go

1. Following Ergun equation has been widely employed for describing packed columns

Write down the physical illeanings and the units of the sy~nbols appeared in this equation: D,, , Go

L , Po

PI. ,

,

,and

. Please follow the order shown above.(l6%)

2. Consider the turbulent flow of air at 30

1 s , 1 c/fnl and 20 "C over a flat plate 1 nz long, with the air containing a low concentration of water vapor. Find the mass transfer coefficieilt h,,

Asstune

1.18

lo-.' 1 cin' ,

p

I

0. 157cn12 I s , D,,

0.220cn12 I s , and SIi

0.036 ~ e ~ ' ~ S c " ' . (1 5%)

3. There is an electric wire of circular cross section with radius R and the rate of heat production per unit volume is S < , . We assume here that the steady state is applicable and the thermal conduction as well as the heat source resulting from electrical dissipation need be considered. The surface of the wire is maintained at temperature To. Please derive the radial temperature distribution expression within the wire. T

T ( r ) , starting froin shell energy balance.

Uniform heat production by eleclrical

I I heating

I I I I

I I Heat in by I I Heat out by I l conduction l I conduction

I I

I I

4. The duct from a heater has an inside diameter of 114.3 mm with ceramic walls 6.4 mm thick. The average k=1.52 W1m.K. Outside this wall, an insulation of rock wool 102 mm thick is installed. The thermal conductivity of the rock wool is k=0.046+1.56~10-~ TPC (W1m.K). The inside surface temperature of the ceramic is Tl=588.7 K, and the outside surface temperature of the insulation is T3=3 11 K. Please estimate the heat loss for 1.5 m o f duct and the interface temperature T2 between the ceramic and the insulation. (20%)

5. Consider a capillary flowmeter as shown in the following figure. Please determine (a) average velocity; (b) the volume flow rate. (1 5%)

Density of flow fluid: pl

Density of fluid in flowmeter: p2

6. An open tank travels along x-direction at a velocity v,. A jet of area Ai exhausts fluid of density p at a velocity vj relative to the car. At the same time, the tank collects fluid from an overhead sprinkler which directs fluid downward with velocity v,. Assume that the sprinkler flow is uniform over an area, A,. Please determine the net force of the fluid on the tank car.

(1 5%)