A stream of ammonia is cooled from 100oC to 20oC at a rate of 180 kg/hr in the tube side of a double-pipe counter-flow heat exchanger. Water enters the heat exchanger at 10oC at a rate of 250 kg/hr. The outside diameter of the inner tube is 3 cm and the length of the pipe is 7m. Using the log-mean temperature difference, calculate the overall heat transfer coefficient (U) for the heat exchanger. Determine the heat transfer rate between the two fluids. Determine the outlet temperature of the water. Determine the heat transfer surface area. Determine the log-mean temperature difference. Determine the heat transfer coefficient for the heat exchanger.   Cp for ammonia is 5234J/kgK and cp for water is 4180J/kgK.

Liquid food is heated in a tubular heat exchanger. The inner pipe wall temperature is 110 ° C. The internal diameter of the pipe is 40 mm. Product flows at 0.7 kg / s. If the initial temperature of the product is 7 ° C, calculate the convective heat transfer coefficient. The thermal properties of the product are as follows: specific heat = 3.7 kJ / (kg ° C), thermal conductivity = 0.6 W / (m ° C), product viscosity = 500 x 10-6 Pa s, density = 1000 kg / m³ , the product viscosity at 110 ° C = 410 x 10-6 Pa s. a. Find the Reynold number = Answer. b. Find the number Prantl = Answer. c. Find the Nuselt = Answer number d. Convection coefficient = AnswerW / m² ° C.

(4) Determine the steady-state surface temperature of an electric cable 25 cm in diameter and 300 cm in length, which is suspended horizontally in still air in which heat is dissipated by the cable at a rate 26 W per meter of length. The air temperature is A °C. [Hints: (i) Use Churchill & Chu horizontal cylinder equation for the prediction of natural convection heat transfer coefficient. (ii) Initial guess of surface temperature = 35 °C]. State your assumptions, if any. Your parameter value for (A) will be based on the last digit of your student number. e.g. If your metric card number is A0185796Y, please take the (A) value from parameter set (6) below. A similar rule is applied to other cases. (0) A = 20 (4) A = 24 (8) A = 28 (1) A = 21 (5) A = 25 (9) A = 30 (2) A = 22 (6) A = 26 (3) A = 23 (7) A = 27

Hot oil is to be cooled in a double- tube counter- flow heat exchanger. The copper inner tubes have a diameter of 2 cm and negligible thickness. The inner diameter of the outer tube (the shell) is 3 cm. Water flows through the tube at a rate of 0.5 kg/ s, and the oil through the shell at a rate of 0.8 kg/ s. Taking the average temperatures of the water and the oll to be 45°C and 80°C, respectively, determine the overall heat transfer coefficient of this heat exchanger. Use the Table 1 if needed. The properties of water at 45 °C are as follows: Pr = 3.91 m2/s Kinematic viscosity, v = 0.602 x 10-6 p= 990.1 kg/m3 The properties of oil at 80 °C are as follows: Kinematic viscosity, v = 3.794 x 10-5 k = 0.637 W/m.K Pr = 499.3 m2/s k = 0.138 W/m.K Table 1: p= 852 kg/m3 Nusselt Number for fully developed laminar flow in a circular annulus with one surface insulated and the other isothermal Di/Do Nu Nu. 0.00 0.00 3.66 0.05 17.46 4.06 0.10 11.56 4.11 0.25 7.37 4.23 0.50 5.74 4.43 1.00 4.86 4.56