Heat exchangers (LMTD) worksheet with answers

Free printable Heat exchangers (LMTD) worksheet: 6 problems from easy to exam level, with an answer key. Print it or save it as a PDF.

New worksheetPractise online with hints

For teachers: free to print, copy and use in class. Every new worksheet has new values and its own answer key. A link to ExamProblems on your course page is appreciated.

Name: ____________________   Date: ____________

1.Easy
lengthT105 °C70 °C20 °C65 °CΔT₁ΔT₂parallel flow

In a parallel-flow heat exchanger the hot fluid cools from 105 to 70 °C while the cold fluid heats from 20 to 65 °C. Find the log-mean temperature difference ΔTlm.

Th: 105 → 70 °CTc: 20 → 65 °C
ΔTlm = K
2.Easy
lengthT120 °C105 °C20 °C60 °CΔT₁ΔT₂parallel flow

In a parallel-flow heat exchanger the hot fluid cools from 120 to 105 °C while the cold fluid heats from 20 to 60 °C. Find the log-mean temperature difference ΔTlm.

Th: 120 → 105 °CTc: 20 → 60 °C
ΔTlm = K
3.Medium
lengthT100 °C25 °C45 °CΔT₁ΔT₂condensing steam

In a condenser, steam condenses at a constant 100 °C on the outside of the tubes. Cooling water (3 kg/s, cp = 4.18 kJ/(kg·K)) flows through the tubes and heats from 25 to 45 °C. The overall heat transfer coefficient is 2000 W/(m²·K). Find the heat transfer area A needed.

Ts = 100 °Cṁ = 3 kg/scp = 4.18 kJ/(kg·K)Tc: 25 → 45 °CU = 2000 W/(m²·K)
A = m²
4.Medium
lengthT95 °C40 °C10 °C30 °CΔT₁ΔT₂parallel flow

A parallel-flow heat exchanger transfers 140 kW. Its heat transfer area is 15 m². The hot fluid cools from 95 to 40 °C and the cold fluid heats from 10 to 30 °C. Find the overall heat transfer coefficient U.

Q̇ = 140 kWA = 15 m²Th: 95 → 40 °CTc: 10 → 30 °C
U = W/(m²·K)
5.Hard
lengthT120 °C30 °C?ΔT₁ΔT₂condensing steam

Steam condenses at a constant 120 °C on the outside of the tubes of a condenser with a heat transfer area of 8 m² and U = 3000 W/(m²·K). Cooling water (3 kg/s, cp = 4.18 kJ/(kg·K)) enters the tubes at 30 °C. Find the water outlet temperature Tc,out.

Ts = 120 °CA = 8 m²U = 3000 W/(m²·K)ṁ = 3 kg/scp = 4.18 kJ/(kg·K)Tc,in = 30 °C
Tc,out = °C
6.Hard
lengthT110 °C25 °C?ΔT₁ΔT₂condensing steam

Steam condenses at a constant 110 °C on the outside of the tubes of a condenser with a heat transfer area of 2 m² and U = 2000 W/(m²·K). Cooling water (3 kg/s, cp = 4.18 kJ/(kg·K)) enters the tubes at 25 °C. Find the water outlet temperature Tc,out.

Ts = 110 °CA = 2 m²U = 2000 W/(m²·K)ṁ = 3 kg/scp = 4.18 kJ/(kg·K)Tc,in = 25 °C
Tc,out = °C

Answer key

  1. 1. ΔTlm = 28.24 K
  2. 2. ΔTlm = 68.88 K
  3. 3. A = 1.945 m²
  4. 4. U = 266.3 W/(m²·K)
  5. 5. Tc,out = 106.7 °C
  6. 6. Tc,out = 48.21 °C

Full step-by-step solutions: practise this topic on examproblems.com.