kg/ an inlet temperature of e heat exchanger at a rate of 8.0 kg/s wit ata gave the following equation for the ow 600/(1/mº³ + 2/m08), where m, and m, ar respectively.

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2 3 IN41 5 6 .7.1 819 10 11 12. 13 I 14. 15. 16 .
17 118 I 19
A counterflow double-pipe heat exchanger with A, = 9m² is used for cooling a liquid
stream (c, = 3.15 kJ/kg. K) at a rate of 10.0 kg/s with an inlet temperature of 90°C. The
coolant (c, = 4.2 kJ/kg. K) enters the heat exchanger at a rate of 8.0 kg/s with an inlet
temperature of 10°C. The plant data gave the following equation for the overall heat
transfer coefficient in W/m . K:U = 600/(1/m + 2/m), where m, and m, are the cold-
and hot-stream flow rates in kg/s, respectively.
a) Calculate the rate of heat transfer and the outlet stream temperatures for this
unit.
b) The existing unit is to be replaced. A vendor is offering a very attractive discount
on two identical heat exchangers that are presently stocked in its warehouse,
each with A, = 5m. Because the tube diameters in the existing and new units
are the same, the above heat transfer coefficient equation is expected to be valid
for the new units as well. The vendor is proposing that the two new units could
be operated in parallel, such that each unit would process exactly one-half the
flow rate of each of the hot and cold streams in a counterflow manner; hence,
they together would meet (or exceed) the present plant heat duty. Give your
recommendation, with supporting calculations, on this replacement proposal.
19°C
Transcribed Image Text:AaBbCc AaBbCc · AaBbC AaBbCcC AaB AABBCCC AoBbr の.. 1 Normal 1 No Spac.. Heading 1 Heading 2 Title Subtitle Subtle sepe Font Paragraph Styles 2 3 IN41 5 6 .7.1 819 10 11 12. 13 I 14. 15. 16 . 17 118 I 19 A counterflow double-pipe heat exchanger with A, = 9m² is used for cooling a liquid stream (c, = 3.15 kJ/kg. K) at a rate of 10.0 kg/s with an inlet temperature of 90°C. The coolant (c, = 4.2 kJ/kg. K) enters the heat exchanger at a rate of 8.0 kg/s with an inlet temperature of 10°C. The plant data gave the following equation for the overall heat transfer coefficient in W/m . K:U = 600/(1/m + 2/m), where m, and m, are the cold- and hot-stream flow rates in kg/s, respectively. a) Calculate the rate of heat transfer and the outlet stream temperatures for this unit. b) The existing unit is to be replaced. A vendor is offering a very attractive discount on two identical heat exchangers that are presently stocked in its warehouse, each with A, = 5m. Because the tube diameters in the existing and new units are the same, the above heat transfer coefficient equation is expected to be valid for the new units as well. The vendor is proposing that the two new units could be operated in parallel, such that each unit would process exactly one-half the flow rate of each of the hot and cold streams in a counterflow manner; hence, they together would meet (or exceed) the present plant heat duty. Give your recommendation, with supporting calculations, on this replacement proposal. 19°C
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