Question

2. (a) With sketches, distinguish between parallel and counterflow heat exchangers. Why is the counterflow heat exchanger configuration preferred over the parallel type? (8 marks) (b) Hot oil with specific heat, $C_p$ = 2200 J/kg. °C is to be cooled by water ($C_p$ = 4180 J/kg.°C) in a 2-shell pass and 12 tube pass heat exchanger as shown in Fig. Q2(b). Oil 160°C 0.2 kg/s Water 18°C 0.1 kg/s (12 tube passes) Fig. Q2(b) 2-shell passes and 12-tube passes The tubes are thin-walled and are made of copper with a diameter of 1.8cm. The length of each tube pass in the heat exchanger is 3m and the overall heat transfer coefficient is 340W/m².°C. Water flows through the tubes at a flow rate of 0.1kg/s and the oil through the shell at a rate of 0.2kg/s. The water and the oil enter at temperatures 18°C and 160°C respectively. (i) Evaluate the maximum heat transfer rate of the heat exchanger. (6 marks) (ii) What is the Number of Transfer Unit (NTU) of this heat exchanger? (4 marks)

          2.
(a) With sketches, distinguish between parallel and counterflow heat
exchangers. Why is the counterflow heat exchanger configuration
preferred over the parallel type?
(8 marks)
(b)
Hot oil with specific heat, $C_p$ = 2200 J/kg. °C is to be cooled by
water ($C_p$ = 4180 J/kg.°C) in a 2-shell pass and 12 tube pass heat
exchanger as shown in Fig. Q2(b).
Oil
160°C
0.2 kg/s
Water
18°C
0.1 kg/s
(12 tube passes)
Fig. Q2(b) 2-shell passes and 12-tube passes
The tubes are thin-walled and are made of copper with a diameter
of 1.8cm. The length of each tube pass in the heat exchanger is
3m and the overall heat transfer coefficient is 340W/m².°C. Water
flows through the tubes at a flow rate of 0.1kg/s and the oil
through the shell at a rate of 0.2kg/s. The water and the oil enter
at temperatures 18°C and 160°C respectively.
(i) Evaluate the maximum heat transfer rate of the heat
exchanger.
(6 marks)
(ii) What is the Number of Transfer Unit (NTU) of this heat
exchanger?
(4 marks)

2.
(a) With sketches, distinguish between parallel and counterflow heat
exchangers. Why is the counterflow heat exchanger configuration
preferred over the parallel type?
(8 marks)
(b)
Hot oil with specific heat, Cp = 2200 J/kg. °C is to be cooled by
water (Cp = 4180 J/kg.°C) in a 2-shell pass and 12 tube pass heat
exchanger as shown in Fig. Q2(b).
Oil
160°C
0.2 kg/s
Water
18°C
0.1 kg/s
(12 tube passes)
Fig. Q2(b) 2-shell passes and 12-tube passes
The tubes are thin-walled and are made of copper with a diameter
of 1.8cm. The length of each tube pass in the heat exchanger is
3m and the overall heat transfer coefficient is 340W/m².°C. Water
flows through the tubes at a flow rate of 0.1kg/s and the oil
through the shell at a rate of 0.2kg/s. The water and the oil enter
at temperatures 18°C and 160°C respectively.
(i) Evaluate the maximum heat transfer rate of the heat
exchanger.
(6 marks)
(ii) What is the Number of Transfer Unit (NTU) of this heat
exchanger?
(4 marks)

Added by Carrie T.

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