Understanding Heat Exchanger Effectiveness: Key Equations and
School
Northeastern University**We aren't endorsed by this school
Course
ME 3455
Subject
Mechanical Engineering
Date
Dec 12, 2024
Pages
18
Uploaded by GrandOxideAardvark42
Fig. 11.10 Effectiveness of a parallel-flow heat exchanger (Equation 11.28a-11.28b).FIG. 11 11 Effectiveness of a counterflow heat exchanger (Equation 11.29a-11.29b).
Fig. 11.12 Effectiveness of a shell-and-tube heat exchanger with one shell and any multiple of two tube passes (two, four, etc. tube passes) (Equation 11.30a-11.30b).FIG. 11.13 Effectiveness of a shell-and-tube heat exchanger with two shell passes and any multiple of four tube passes (four, eight, etc. tube passes) (Equation 11.31a-11.31b-11.31c-11.31d with n= 2)
FIGURE11.15Effectiveness of a single-pass, cross-flow heat exchanger with one fluid mixed and the other unmixed (Equations 11.33a-11.33b, 11.34a-11.34b).FIGURE11.14Effectiveness of a single-pass, cross-flow heat exchanger with both fluids unmixed (Equation 11.32).
11.27A counterflow, twin-tube heat exchanger is made by brazing two circular nickel tubes, each 40 m long, together as shown below. Hot water flows through the smaller tube of 10-mm diameter and air at atmospheric pressure flows through the larger tube of 30-mm diameter. Both tubes have a wall thickness of 2 mm. The thermal contact conductance per unit length of the brazed joint is 100 W/m · K. The mass flow rates of the water and air are 0.04 and 0.12 kg/s, respectively. The inlet temperatures of the water and air are 85 and 23°C, respectively. Employ the ε-NTU method to determine the outlet temperature of the air.Hint:Account for the effects of circumferential conduction in the walls of the tubes by treating them as extended surfaces.
LP=LA=LtD/2
11. 30 A cross-flow heat exchanger used in a cardiopulmonary bypass procedure cools blood flowing at 5 L/min from a body temperature of 37°C to 25°C in order to induce body hypothermia, which reduces metabolic and oxygen requirements. The coolant is ice water at 0°C, and its flow rate is adjusted to provide an outlet temperature of 15°C. The heat exchanger operates with both fluids unmixed, and the overall heat transfer coefficient is 750 W/m2· K. The density and specific heat of the blood are 1050 kg/m3and 3740 J/kg · K, respectively.(a) Determine the heat transfer rate for the exchanger.(b) Calculate the water flow rate.(c) What is the surface area of the heat exchanger?