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
lengthT120 °C100 °C25 °C55 °CΔT₁ΔT₂parallel flow

In a parallel-flow heat exchanger the hot fluid cools from 120 to 100 °C while the cold fluid heats from 25 to 55 °C. Find the log-mean temperature difference ΔTlm.

Th: 120 → 100 °CTc: 25 → 55 °C
ΔTlm = K
2.Easy
lengthT100 °C45 °C85 °C25 °CΔT₁ΔT₂counter-flow

In a counter-flow heat exchanger the hot fluid cools from 100 to 45 °C while the cold fluid heats from 25 to 85 °C. Find the log-mean temperature difference ΔTlm.

Th: 100 → 45 °CTc: 25 → 85 °C
ΔTlm = K
3.Medium
lengthT145 °C30 °C65 °C10 °CΔT₁ΔT₂counter-flow

A counter-flow heat exchanger transfers 80 kW. The hot fluid cools from 145 to 30 °C and the cold fluid heats from 10 to 65 °C. The overall heat transfer coefficient is 200 W/(m²·K). Find the heat transfer area A needed.

Q̇ = 80 kWU = 200 W/(m²·K)Th: 145 → 30 °CTc: 10 → 65 °C
A = m²
4.Medium
lengthT160 °C85 °C150 °C30 °CΔT₁ΔT₂counter-flow

A counter-flow heat exchanger transfers 150 kW. The hot fluid cools from 160 to 85 °C and the cold fluid heats from 30 to 150 °C. The overall heat transfer coefficient is 500 W/(m²·K). Find the heat transfer area A needed.

Q̇ = 150 kWU = 500 W/(m²·K)Th: 160 → 85 °CTc: 30 → 150 °C
A = m²
5.Hard
lengthT125 °C??30 °CΔT₁ΔT₂counter-flow

In a counter-flow heat exchanger both streams have the same heat capacity rate, ṁ·cp = 1 kW/K. The hot stream enters at 125 °C and the cold stream at 30 °C. The exchanger has A = 1.5 m² and U = 200 W/(m²·K). Find the hot outlet temperature Th,out.

Ch = Cc = 1 kW/KTh,in = 125 °CTc,in = 30 °CA = 1.5 m²U = 200 W/(m²·K)
Th,out = °C
6.Hard
lengthT130 °C??15 °CΔT₁ΔT₂counter-flow

In a counter-flow heat exchanger both streams have the same heat capacity rate, ṁ·cp = 1 kW/K. The hot stream enters at 130 °C and the cold stream at 15 °C. The exchanger has A = 6 m² and U = 500 W/(m²·K). Find the hot outlet temperature Th,out.

Ch = Cc = 1 kW/KTh,in = 130 °CTc,in = 15 °CA = 6 m²U = 500 W/(m²·K)
Th,out = °C

Answer key

  1. 1. ΔTlm = 66.92 K
  2. 2. ΔTlm = 17.38 K
  3. 3. A = 9.242 m²
  4. 4. A = 11.36 m²
  5. 5. Th,out = 103.1 °C
  6. 6. Th,out = 43.75 °C

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