11.21 A concentric tube heat exchanger for cooling lubricating oil is comprised of a thin-walled inner tube of 25-mm diameter carrying water and an outer tube of 45-mm diameter carrying the oil. The exchanger operates in counterflow with an overall heat transfer coefficient of 60 W/m².K and the tabulated average properties. Teout Toin = 100°C Oil Water m,= 0.1 kg/s n = 0.1 kg/s Tw,in = 30°C Tw.out Properties Water Oil P (kg/m3) 1000 800 Cp (J/kg • K) 4200 1900 v (m²/s) 7x 10-7 1x 10-5 k (W/m - K) 0.64 0.134 Pr 4.7 140 (a) If the outlet temperature of the oil is 66°C, determine the total rate of heat transfer and the outlet temperature of the water. (b) Determine the length required for the heat exchanger.

A dairy farm needs to chill the milk from 39°C (extraction temperature is the same as the cow's body temperature) to at least 12°C for storage by using an existing 4-m long concentric-tube heat exchanger. The inner tube of the heat exchanger is 4 cm in diameter. The milk (density: 1035 kg/m³, specific heat: 3860 J/kg.K) flows into the heat exchanger at a rate of 270 liters per hour. On the cold side, there is a supply of water at 2°C at a rate of 0.23 kg/s. The estimated overall heat transfer coefficient of the heat exchanger is 1084.2 W/m².K. It was measured that the water comes out of the heat exchanger at 11°C. Is the milk indeed being cooled down to at least 12°C by heat exchanger as required by the farm? Looking at the temperatures obtained from your calculation, put an argument whether the heat exchanger is a parallel-flow or a counter-flow heat exchanger. Approximate specific heat of water is 4200 J/kg.K. Neglect radiation.

A shell and tube heat exchanger is designed as a counter flow type. Water (cp = 4182 J/kg.oC) enters the shell side at 30 oC with a mass flow rate of 12.5 kg/s. A mass flow rate of 19.5 kg/s of engine oil (cp = 1060 J/kg.o C), enters the tube side at 300 oC. Each tube is having an inner diameter of 36 mm and a wall thickness of 2 mm, and a length of 3 m. If the heat exchanger effectiveness is 60 %, calculate the following:1. The heat transfer rate,2. The exit temperature for each fluid,

Below data was obtained from an experimental activity for a parallel pipe heat exchanger. Arrangement: counterflow (cold fluid in annular and hot fluid in tube). Mass flow rate: - Hot fluid: 1.03 kg/s - Cold fluid: 0.91 kg/s Temperatures: - Hot fluid inlet (Th.1): 80.5 +/- 10% °C - Hot fluid outlet (Th2): 64.0 +/- 10% °C - Cold fluid inlet (Te1): 20.0 +/- 10% °C - Cold fluid outlet (Tc2): 41.0 +/- 10% °C Assume cp constant and equal to 4.2 kJ/kg-K. 1. State assumptions (at least 9 unique ones) and include references. 2. What is the log mean temperature difference in °C? 3. What is the heat transfer rate on the cold side in kW? Heat added or lost on cold side? 4. What is the heat transfer rate on the hot side in kW? Heat added or lost on hot side? 5. What is the effectiveness of the heat exchanger for the given conditions? 6. Calculate the propagation of uncertaintv in kW for part 3 (heat transfer rate on the cold side) and part 4 (heat transfer rate on the hot side).