Question 1: A concentric tube heat exchanger is comprised of a thin wall inner tube of 25.4 mm diameter and an outer tube of 47 mm diameter. The heat exchanger is used for cooling lubricating oil. The exchanger operates in counterflow, the inner tube carrying water and the outer tube carrying the oil with an overall heat transfer coefficient of 65 W/m2K.
a) If the oil outlet temperature is 55oC, determine the total heat transfer and the water outlet temperature.
b) Determine the length required for the tube heat exchanger.
Question 2: A concentric tube heat exchanger, counterflow arrangement was designed to heat water from 20oC to 80oC using hot oil that is supplied to the annulus at 160oC and discharged at 140oC. The thin-walled inner tube has a 20 mm diameter. The overall heat transfer coefficient if 527 W/m2 K. The designed condition requested a total heat transfer rate of 3700 W.
a) What is the length of this heat exchanger?
b) After 3 years of operation, the heat exchanger performance is degradated by fouling on the water side, and the water outlet temperature is 57oC for the same flow rate and inlet temperatures. What are the corresponding values of the heat transfer rate, the oil outlet temperature, the overall heat transfer coefficient, and the water side fouling factor, R”f,c?
Question 3: A Shell-and-tube Heat Exchanger (1 shell pass, 2 tube passes) is to be used to condensate 3.21 kg/s of saturated steam at 350K. Condensation occurs on the outer tube surfaces, and the corresponding convection coefficient is 10,215 W/m2K. The temperature of the cooling water entering the tubes is 15oC. Thin-walled tubes of 20mm diameter are specified, and the mean velocity of water flow through the tubes is to be maintained at 0.45 m/s.
a) What is the minimum number of tubes that should be used?
b) What is the corresponding tube length per pass?
c) To reduced the size of the heat exchanger, it is proposed to increase the water side convection coefficient by inserting a wire mesh in the tubes. If the mesh increases the convection coefficient by 2, what is the required tube length per pass?
Question 4: A customer requested the design of a Heat Exchanger and provided the following information to the Engineering Department. In his factory, as part of the process upgrade, there is a need to heat 97.2 m3/hr of cold water from 32oC to 60oC. The heat is available from 100.8 m3/hr of hot water at 90oC. The customer does not know of any other information that could lead to a final configuration of heat exchanger type. In this initial stage, he requires a preliminary design that can be evaluated to determine what additional requirements should be considered.
In a meeting conducted at the Engineering Department, it was decided to:
a) Design the Heat Exchanger with the information provided. In this stage, all assumptions must be listed and explained for customer evaluation and review.
b) Prepare Heat Exchanger drawings of the proposed solution/s.
c) At the same time, the design must be evaluated to identify features and configurations that could be discussed with the customer with the aim of developing more complete specifications.
d) Cost analysis in not required.