Ht 030 Solution

CHEMICAL ENGINEERING SERIES: HEAT TRANSFER SOLVED PROBLEMS

A newly hired chemical engineer was assigned to assess the performance of a coconut oil (CNO) counter-current cooler in an oil mill. From the cooler’s design book, he obtained thye following data: Coconut Oil (CNO): Flow rate : 30 MT/day Inlet temperature : 70°C Outlet temperature : 30°C Specific heat : 0.65 kcal/kg·°C Cooling water: Inlet temperature : 25°C Outlet temperature : 40°C From a series of test runs, the chemical engineer conducted, he established that with the flow rates and inlet temperature of the two media maintained at design conditions, the average outlet temperatures of CNO is 45°C. a) Calculate the resulting outlet temperature of the cooling water in °C. b) Calculate the % reduction in the OHTC of the system from the design value, assuming no reduction in the heat transfer area. (Source: CHE BP May 1989) SOLUTION: For the design conditions (1)

q c qh mC P ∆ T c mC P ∆ T h

mc

m CP ∆ Th ⟶ eqn 1 CP ∆ T c

To find the outlet temperature of the cooling water during the test run (2), assume all conditions the same excluding the CNO outlet temperature, from equation

1

mc1mc 2 mC P ∆ T h mC P ∆ T h C P ∆ T c 1 C P ∆T c 2

ENGR. RONNIE V. FLORES

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CHEMICAL ENGINEERING SERIES: HEAT TRANSFER SOLVED PROBLEMS

∆ T h 1 ∆T h 2 ∆ Tc 1 ∆ Tc 2 3070 4570 4025 T co225 T co234.375° C ANSWER

OHTC reduction

U 1U 2 x 100 U1

qUA ∆T lm Assume one pass tube heat exchanger; since no change in heat transfer area and heat transfer rate

q q A1A 2 U 1 ∆ T lm 1U 2 ∆ T lm 2

U 2U 1

∆T lm 1 ∆T lm 2 ∆ T lm 1 ∆ T lm 2 x 100 U1

U1U 1 OHTC reduction

OHTC reduction100 1

∆ T lm1

∆ T lm 1 ∆ T lm 2

T hi T coT hoT ci 70403025 13.9528° C T hi T co 7040 ln ln 3025 T ho T ci

ENGR. RONNIE V. FLORES

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CHEMICAL ENGINEERING SERIES: HEAT TRANSFER SOLVED PROBLEMS

∆ T lm2

T hi T coT hoT ci 7034.3754525 27.0649° C T hi T co 7034.375 ln ln 4525 T ho T ci

OHTC reduction100 1

13.9528 27.0649

OHTC reduction 48.47 ANSWER B

ENGR. RONNIE V. FLORES

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