Q1: What type of HX does the one shown here belong to? What fluid(s) is(are) unmixed?
Q2: Circle the figure that most accurately represents the fluid temperatures for a counter-flow exchanger with Cc = Ch.
Q3: cont... T=T=20C. What is Tim?
Q4: According to the following table, what would be the fouling resistance R on the cold fluid side (seawater below 50C is used) in an HX if the cold side total surface area is 4 m?
TABLE 11.1 Representative Fouling Factors [1]
Fluid Seawater and treated boiler feedwater (below 50C) Seawater and treated boiler feedwater (above 50C) River water (below 50C) Fuel oil Refrigerating liquids Steam (non-oil bearing)
R(m2K/W)
0.0001 0.0002 0.0002 0.001 0.0009 0.0002 10000
LMTD method
Counterflow heat exchanger with 9-UADTm C=8.4 Tc,i=40C, K Thi=90C. mdot,hot = 2 kg/s, Th=90C m23/ C=42k mdot,cold =3 kg/s, 40r cp,hot = 4.2 kJ/kgK, cp,cold =1.8 kJ/kgK C=(3)(10)W A = 4.3 m2, =1800W/mC.
Determine: Tco ANS:72.6 C Tho ANS:69.05 C LMTD ANS:22.74 C Q ANS:176 kW
Oil(hot)
cetd)
You may use the answers above in the following calculations. O5: Plot a figure that represents both cold and hot fluid temperatures along the HX
Q6: Compute Tim
Q7: List the 3 equations that calculate the HX heat transfer rate q.
Q8: If the inner tube diameter Di = 2.5cm, and outer annulus Do = 4.5cm. Both tubes have a very thin wall (see figure above). What would be the length L of the HX? (L will be quite large so the concentric HX is not practical for this application, a different type of HX must be sought.)
Q9: What would be the convection coefficient at the inner surface of the outer tube? Explain.
Q10: If the hot oil has hn = 3000 W/m2K, find the cold water hc.
Q11: If the fouling factor on the oil side of the inner tube is 0.0002 K.m2/W after one year of service, what would be U?
Q12: Show that the hydrodynamic diameter Dp = Do - Di for the annulus.
Q13: Write out an equation to compute the Reynolds number of the hot oil flow in terms of m, Di, Do, and oil viscosity. (Last two questions are Fluid Mechanics questions)
