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Heat Transfer

This homework assignment contains 5 questions related to heat exchangers and evaporators. Question 1 asks about the exit temperatures of two streams in a parallel flow heat exchanger compared to a counter-current flow heat exchanger. Question 2 involves calculating the required heat exchanger area to heat mineral oil using counter-current flow. Question 3 requires estimating the wall temperature in a copper condenser by including and excluding pipe wall resistance. Question 4 involves sizing a shell and tube heat exchanger to heat crude oil using gas oil, including calculating heat transfer coefficients. Question 5 involves sizing a triple effect evaporator to concentrate a solution and calculating steam consumption.

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67 views1 page

Heat Transfer

This homework assignment contains 5 questions related to heat exchangers and evaporators. Question 1 asks about the exit temperatures of two streams in a parallel flow heat exchanger compared to a counter-current flow heat exchanger. Question 2 involves calculating the required heat exchanger area to heat mineral oil using counter-current flow. Question 3 requires estimating the wall temperature in a copper condenser by including and excluding pipe wall resistance. Question 4 involves sizing a shell and tube heat exchanger to heat crude oil using gas oil, including calculating heat transfer coefficients. Question 5 involves sizing a triple effect evaporator to concentrate a solution and calculating steam consumption.

Uploaded by

jackson
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© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Homework-5 (Due on 7th Apr, 2020)

1. In a counter-current flow heat exchanger the hot stream is cooled from 120 to 30 oC while the
cold stream is being heated from 20 to 60 oC. If the same exchanger were operated with parallel
flow, what would be the exit temperatures of the two streams? It may be assumed that properties
are not sensitive to temperature.

2. Obtain the area required to heat mineral oil from 20 to 50 oC at a rate of 0.6 L/min in a double
pipe exchanger. The inner pipe has a diameter of 1 cm and the outer pipe has diameter 2 cm.
Pressurized water at 100 oC is available as heating fluid. The mineral oil has the following
properties which are reasonably constant over the temperature range mentioned: Cp=2000 J/Kg.
K; k=0.147 W/m. K and the viscosity may be obtained from any reliable source. Use
countercurrent flow.

3. Toluene is being condensed at 230 oF on the outside of a ¾ in OD 16 BWG copper condenser


tubes through which cooling water is flowing at an average temperature of 80 oF. Individual heat
transfer coefficients are 3970 (water side) and 2840 W/m2 K (toluene) respectively. Estimate the
wall temperature by including and excluding the pipe wall resistance.

4. Gas oil (Cp=0.625 Btu/lb oF, µ=0.7 cp, k=0.069 Btu/(hr. ft2 (oF/ft)) at 480 oF is available to heat
midcontinent crude (Cp=0.55 Btu/lb oF) at 150,000 lb/hr from 170 oF to 285 oF. This will be
achieved by using a 1-2 exchanger where the gas oil will be fed to the shell side and the crude in
the tube side. The gas oil should be cooled to 300 oF. The exchanger has the following details:
Shell ID: 25 inches, Tube Bundle: 252 nos 1 inch OD BWG tubes 16 ft long and arranged in on
1.25 inch square pitch. Bafffles are spaced 10 inch apart. Assume properties are not sensitive to
temperature. Viscosity correction due to wall temperature difference is not required.
a. Calculate the shell side equivalent diameter and mass velocity.
b. Estimate the shell side heat transfer coefficient
c. If the tube side heat transfer coefficient is 160 Btu/hr ft 2 oF, determine the overall heat
transfer coefficient.
d. Determine if the exchanger is suitable for the purpose.

5. A triple effect standard evaporator, each effect of which has 140 m 2 of heating surface, is to be
used to concentrate a solution from 4% solids to 35% solid. The solution has negligible boiling
point elevation. Forward feed is to be used. Steam is available at 120 oC and the vacuum in the
last effect corresponds to a boiling temperature of 40 oC. The overall coefficients (in W/m2 oC)
are: 2950 in I, 2670 in II and 1360 in III. All specific heats may be taken as 4200 J/kg K.
Radiation and other heat losses are negligible. Condensate leave as saturated liquid. The feed
enters at 90 oC. Calculate a) The kgs of 4% liquor that can be concentrated per hour and b) The
steam consumption in kg/hr.

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