COVENANT UNIVERSITY NIGERIA
TUTORIAL KIT OMEGA SEMESTER
PROGRAMME: CHEMICAL ENGINEERING COURSE: CHE 320
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CHE320: CHEMICAL ENGINEERING PROCESS ANALYSIS I Contributor: Dr! O"#$#%&'#n! En(r! )Mr* O+&,u-i M! E . Mr O"#%i-&+i T&-it#/o
Distinguish amongst the three types of a system.
Q2. A house is 45 ft! and has 12 ft ceilings. "or comfort# the home owner specifies .$ changes of air per hour. The outside air temperature is %&" dry bulb and '$.5& wet bulb. The air indoors is '5&" dry bulb 5( relative humidity. )hat is the amount of cooling re*uired to provide the fresh air+ Q3(i) State three reasons for studying energy balances of industrial processes. (ii)
Distinguish succinctly between extensive and intensive properties, giving two exaples in each property.
,iven the ambient temperature is '&" measured by a dry bulb thermometer and -&" measured by a wet bulb thermometer# what is the relative humidity+
Distinguish succinctly between path and point functions with illustration, and give two exaples of each function.
)hat is the heat duty for a mier that mies %.2 moles of / 20 with 1 mole of .2 mole fraction /204 if the inlet and outlet streams are all to be at 25 o+
#alculate the heat re$uired in %& to raise ' %g of nitrogen () oxide, * '+, fro 3! o# C v o
to '! # in a constantvolue vessel if the heat capacity, this teperature range is given by: C v R
4.$23 + 1.214 × 1 T − .%23 × 1 T
, of *'+ at constant volue in
-/ &0(ol 1) and T -/
1 (ii) *eon gas is to be heated in an insulated plasa deposition chaber with a volue of 2.! l by an electric resistance heater. nitially, the gas, which can be treated as an ideal gas, is at 3.! a and 3"! 1. 4he 5!oh heater draws current at 6!7 for 5! inutes. 8hat are the 9nal gas teperature and pressure at e$uilibriu 4he ass of the heater is '! g and its heat capacity is .3! &0(g 1). ;ssue that the heat transfer to the chaber fro the gas at this low pressure and in the short tie is negligible. 4he olal heat
Q<. #alculate the adiabatic =ae teperature of li$uid butane burned with 3> excess air. ?oth the air and li$uid butane enter at '!o#.
f an ideal gas at 3! 1 and '! %a is enclosed in a cylinder by a frictionless piston, and the gas slowly forces the piston up so that the volue of gas expands fro .' to .2 3, calculate the wor% done by the gas on the piston if two diAerent paths are used to go fro the initial state to the 9nal state - R<.352 &0(ol 1)/: ath : expansion occurs at constant pressure ( p '! %a). ath : expansion occurs at constant teperature ( T 3! 1). S%etch the pV diagra for both paths. (ii) ;ir is being copressed fro 5 %a and '!! 1 (where it has an enthalpy of 2<@ %&0%g) to 5 %a and '"< 1 (where it has an enthalpy of !@ %&0%g). 4he exit velocity of the air fro the copressor is "! 0s. 8hat is the power re$uired (in %8) for the copressor if the load is 5! %g0h of air 4he olecular weight of air is '<[email protected]
Q1. ethane is burned with 5( ecess air in a furnace. "ig below shows the stream compositions and those variables whose values are specified. The process occurs with each stream at 1atm. Determine if the number of degrees of freedom for the process is ero. A table is needed to ma6e the count of the variables and e*uilibrium. The 7nergy balance is assumed to reduce to Q 8 9/: replaced as a variable with p and T ;umber of variables in the process < pecies in
Total no of species is 3
7tent of reaction >2 reactions?
Q55. 4he olal heat capacity, as: C p R
, of nbutane at constant pressure is expressed
1.%$5 + $-.%15 × 1 T − 11.42 × 1 T
-/ &0(g ol 1) and
T -/ 1
#onvert this e$uation into a for so that the speci9c heat capacity can be expressed over the entire teperature range in &0(%g o#).
Q5'. 4he conversion of solid wastes to innocuous gases can be accoplished in incinerators in an environental acceptable fashion. Bowever, hot exhaust gases often ust be cooled or diluted with air. ;n econoic feasibility study indicates that solid unicipal waste can be burned to a gas of the following coposition (on a dry basis): #+': @.'>C #+: 5.!>C + ': ".3> and *': <'.>. 8hat is the enthalpy diAerence for this gas per g ol between the botto and the top of the stac% if the teperature at the botto of the stac% is 3 o# and the teperature at the top is @! o# gnore the water vapour in the gas. *eglect any energy eAects resulting fro the ixing of the gaseous coponents. ;ssue ideal gas ixture. 4he heat capacity e$uations are given in the table below. a
b × 1 2
C p = a + bT + cT
b × 1 %
saturation ixing ratio (3 g0%g). (?) 4hen you ight be able to 9gure out the ixing ratio in your head. ;ir that is 9lled to !> of its capacity could hold up to 3 g0%g. Balf of 3 is 5!, that is the ixing ratio. +r you can substitute into the relative huidity forula and solve for the ixing ratio (the details are shown above). Hinally, to deterine the dew point, we iagine cooling the air. 4he saturation ixing ratio decreases, the ixing ratio stays constant, and the relative huidity increases. n this exaple the KB reachs 5> when the air has cooled to " H. 4hat is the dew point teperature.
Noo% at the horiGontal axis to 9nd "6H. Oove a pencil up this line to eet the intersection with the exponential line for 2> relative huidity. Oove the pencil to the right to read the dew point. 4his is !H. 4he evaporator coil is warer than the dew point so it will not condense water fro the air. Q'. 4he total volue of the house is 2! x 5' !2, ftM. 8e need to change !2, x .3 56,' ftM0hour (which e$uates to '" ftM0inute or cf). Hro the psychroetric chart, the enthalpy of the incoing air is 3". ?4I0lb and the speci9c volue is 52.' ftM0lb. 4herefore the energy of the incoing air is 56,' x 3" 0 52.' 2','55 ?4I0hour. Siilarly, the enthalpy of the air indoors is 56,' x '<.5 0 53." 33,''< ?4I0hour. 4he heat diAerence is <,@<2 ?4I0h, or about ."! tons.