Engineering Answers

In the Danckwerts model, it is assumed that elements of the surface have an age

distribution ranging from zero to infinity. Obtain the age distribution function for this model

and apply it to obtain the average mass transfer coefficient at the surface, given that from the

penetration theory the mass transfer coefficient for the surface of age θ is

/( ) DAB

. (4)

By what percentage would the rate of absorption be increased or decreased by increasing

the total pressure from 100 to 200 kN/m2

in absorption of ammonia from a mixture of

ammonia and air containing 10% ammonia by volume, using pure water as solvent. Assume

that all the resistance to mass transfer lies within the gas phase. The diffusivity can be

assumed to be inversely proportion to the absolute pressure.

Ammonia is diffusing through a non-diffusing gas mixture of methane and hydrogen in

volume ratio 2:1 under steady state condition. The total pressure is 1 atm. and the temperature

is 100C. The partial pressure of ammonia at two planes 2 mm apart is 13000 and 6500 N/m2

,

respectively. Calculate the flux of ammonia through the layer. Estimate also the quantity of

ammonia diffusing in kg/ day, if the area of cross section of stagnant gas film is 2 m2

.

NH 3 H 2

D  = 7.0 x 10-5 m

2

/ s at 303 K and 1 atm.

NH 3 CH 4

D  = 2.0 x 10-5 m

2

/ s at 288 K and 1.5 atm. (

the following data were recorded during the tensile test of a 14-mm diameter mild steel rod. the gauge length was 50-mm, at fracture the elongation between the gauge was 4-mm and the minimum diameter was 11.3-mm. plot a convectional stress strain curve for mild steel

A roof truss and the detail of the riveted connection at joint B, see Fig. 2. Using allowable stresses

of ߬ = 70 MPa and ߪ ௕ൌ 140 ܯ ,ܽܲhow many 22-mm diameter rivets are required to fasten

members BC and member BE to the gusset plate. What is the largest average tensile or compressive

stress in BC and BE?

Continuous cable ADB runs over a small frictionless pulley at D to support beam OABC which is

part of an entrance canopy for a building (see figure 3). A downward distributed load with peak

intensity q0 = 5 kN/m at O acts on the beam. Assume that canopy weight W = 8 kN and that cable

cross-sectional area is 100 mm2

.

a) Find cable force T and pin support reactions at O and D

b) Find the normal stress in the cable in the cable ADB

c) Determine the required diameter of pins A, B, D and O if the pins are in double shear and

the allowable shear stress is 80 MPa? Note that OA = AB = BC = 1.5m.

A continuous cable (diameter 6 mm) with tension force T is attached to a horizontal frame member

at B and C to support a sign structure, Fig. 1. The cable passes over a small pulley at D. The wire

is made of a copper alloy, and the stress-strain relationship for the wire is

(a) Find the axial normal strain in the cable and its elongation due to the load W = 6.8 kN

(b) If the forces are removed, what is the permanent set of the cable.

Hint: Start with constructing the stress-strain diagram and determine the modulus of elasticity, E

and the 0.2% offset yield stress.

01)  An inventor claims to have developed a heat engine that receives 700Kj of heat from a source at 500K and produces 300Kj of net work while rejecting the waste heat to a sink at 290K. is this reasonable claim?

01)  Refrigerant – R134a enters an adiabatic compressor as saturated vapor at 120kPa at a rate of 0.3m³/min and exits at 1MPa pressure. If the isentropic efficiency of the compressor is 80 percent, determine

a)     The temperature of the refrigerant at the exit of the compressor

b)     The power input, in kW. Also show the process on a T- s diagram with respect to the satuaration lines.

01)  Steam enters an adiabatic turbine at 8MPa and 500⁰C with a mass flow rate 3kg/s and leaves at 30kPa. The isentropic efficiency of the turbine is 0.90. neglecting the kinetic energy of the steam, determine

a)     The temperature at the turbine exit

b)     The power output of the turbine