Ht 035 Solution

CHEMICAL ENGINEERING SERIES: HEAT TRANSFER SOLVED PROBLEMS

Prior to the processing of a vegetable oil in a plant, it has to be heated to a certain temperature. At the Cebu plant, 5,000 kg of vegetable oil at 20°C is charged to an agitated vessel with heating coil with a heat transfer area of 30 m 2. The over-all heat transfer coefficient is 900 kcal/h·m 2·°C and the thermal fluid is flowing at the rate of 10,000 kg/h inside the heating coil. The inlet temperature of the thermal fluid is 350°C and its specific heat is 0.8 kcal/kg·°C. Assume the specific heat of the vegetable oil is 0.9 kcal/kg·°C. how many minutes will it take to heat the vegetable oil to an average bulk temperature of 250°C? .

Source: CHE BP May 1986 SOLUTION: For coil in tank: non-isothermal heating medium, using equation 11-35b CHE HB 8th edition:

ln

T 1−t 1 WC K 1−1 = θ T 1−t 2 Mc K 1

(

)

K 1=e UA /WC

K 1=exp

[

(900 h∙ mkcal∙ ° C ) (30 m ) 2

2

(

kg kcal 10,000 0.8 h kg ∙° C

)(

)

]

=29.2243

350−20 ( 350−250 ) θ= (10,000 kgh )( 0.8 kgkcal∙° C ) 29.2243−1 kg kcal ( 29.2243 ) 5,000 0.9 ( h )( kg ∙° C ) ln

θ=0.6954 h

ENGR. RONNIE V. FLORES

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