The document discusses optimum design parameters and provides examples of determining optimum values that minimize costs. Question 1 finds the optimum insulation thickness. Question 2 determines optimum temperature and pressure values that minimize total cost. Question 3 calculates the daily profit at the production rate giving minimum cost per unit and maximum daily profit. Question 4 involves determining the batch cycle time that gives the minimum total annual cost of producing 1 million kg of chemical product.
5. QUESTION 1
Find the optimum thickness to achieve minimum total cost knowing that the fixed
cost of the insulation is 3x+20 egp where x is the insulation in cm, and the cost of
heat lost is 20/x +50.
Solution
Total Cost = fixed + variable = 3x+20 + 20/x +50.
dcost/ dx = 3-20/x2 x= 2.58 cm
D2cost/dx2= 40/x3 at x = 2.58 the value will be positive
6. QUESTION 2
if you know that the temperature and pressure are two variables affecting the
industry, on the other hand both of them contribute in the total cost if you know
that the effect of temperature is 2.33T + (3000/PT) +3 and the effect of pressure
is 5P+ (5000/PT) +5
1- Determine the optimum values for P and T which gives you the minimum cost
knowing that T in C and P in Psi.
2- Determine the total cost at the optimum conditions
7. QUESTION 2
Total cost = 2.33T + 3000/PT +3 + 5P+ 5000/PT +5 =2.33T+8000/PT +5P+ 8
Derivative w.r.t T = 2.33 8000/PT2 = 0
Derivative w.r.t P = 5 8000/TP2 = 0
Solving both equations
P = 9 psi and T = 19.5 C
Second derivatives are:
2*8000/PT3 and 2*8000/TP3 and both of them has + values after substitution
The total cost at optimum conditions is 144 EGP
8. QUESTION 3
A plant produces at a rate of P units per day. The variable costs per unit was 30
+ 0.1P, The total daily fixed charges are 1000, and all other expenses are constant
at 7000 per month. If the selling price per unit is 100 determine:
(a)The daily profit at production giving the minimum cost per unit.
(b)The daily profit at production giving the maximum daily profit.
9. QUESTION 3 CONTINUE (A)
a) Total Cost per unit = 30+0.1P + 1000/P + (7000/30)/P = 30 + 0.1 P + 1233.33/P
d(cost)/P = 0.1 -1233.33/P2 P= 111 Unit
Second derivative of the previous equation is 2* 1233.33/P3 (+ve at all cases)
Daily profit is = selling revenue per day total cost per day
Total cost per unit at p =111 = 52.2 $
Total cost per day = 52.2 * 111 = 5794.2$
Selling revenue per day = 100*111 = 11100$
Daily profit is 5305.8 $
10. QUESTION 3 CONTINUE (B)
B) daily profit = selling price per unit * no. of units per day - Total cost per unit * no. of units
per day
daily profit = 100P [30 + 0.1 P + 1233.33/P]P
d profit/dP = 100-30 - 0.2P P = 350 unit
Second derivative = - 0.2 always negative which indicates a maximum value
Daily profit at a production giving the maximum daily profit = 11016.67 $
11. QUESTION 4
An organic chemical is being produced by a batch operation. Each cycle consists of
the operating time necessary to complete the reaction plus a discharging time of 0.7
hour and charging time of 0.3 hour. The operating time per cycle is equal to 2P0.5 h,
where P is the kilograms of product produced per batch. The operating costs during
the operating period are $20 per hour, and the costs during the discharge-charge
period are $10 per hour. The annual fixed costs for the equipment vary with the size of
the batch as the fixed cost is equal to 300P1.2 dollars per year. the plant can be
operated 24 h per day for 300 days per year. The annual production is 1 million kg of
product. At this capacity, the other costs rather than those already mentioned is
$200,000 per year. Determine the cycle time for conditions of minimum total cost per
year.
12. QUESTION 4 SOLUTION
Givens:
P production per cycle (kg)
discharging time of 0.7 hour/cycle
charging time of 0.3 hour/cycle
operating time per cycle = 2P0.5 h
operating costs
during the operating= $20/h
during the discharge-charge are
$10/h
fixed cost= 300P1.2 $/year
Operation time
24 h per day for 300 days per year
annual production is 106 kg of
product
other costs= 200000$/year
Determine the cycle time for conditions of minimum total cost
per year.
Total cost/year = fixed cost/year + variable cost/year
Cycle time= operating + charge + discharge = 2P0.5+1
Total cost/year = 300P1.2 + 200000 + variable cost/year
Variable cost /year =
p
$
*
. $
. 巨$
=
$
$
=
106
p
$
= cost of operation + cost of charge and discharge
=
20
* time of operation +
10 $
* time of charge and Discharge
13. QUESTION 4 SOLUTION
Givens:
P production per cycle (kg)
discharging time of 0.7 hour/cycle
charging time of 0.3 hour/cycle
operating time per cycle = 2P0.5 h
operating costs
during the operating= $20/h
during the discharge-charge are
$10/h
fixed cost= 300P1.2 $/year
Operation time
24 h per day for 300 days per year
annual production is 106 kg of
product
other costs= 200000$/year
p
$
= cost of operation + cost of charge and discharge
=
20
* time of operation +
10 $
* time of charge and Discharge
=
20
* 2P0.5+
10 $
* (0.7+0.3)
Total cost/year = 300P1.2 + 200000 +[
20
* 2P0.5+
10 $
* (0.7+0.3)]*
106
From dTotal annual Cost/d(p)= zero get = 625 kg/bath
Substitute in Cycle time= 2P0.5+1 get the minimum time