Energy balance worksheet with answers

Free printable Energy balance 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
Heaterlight oil · 25 °C50 °CQ = ?

A stream of light oil flowing at 5 kg/s is heated from 25 °C to 50 °C. Find the heat duty Q.

ṁ = 5 kg/scp = 2.1 kJ/(kg·K)Tin = 25 °CTout = 50 °C
Q = kW
2.Easy
Heaterglycol mix · 25 °C70 °CQ = ?

A stream of glycol mix flowing at 1.5 kg/s is heated from 25 °C to 70 °C. Find the heat duty Q.

ṁ = 1.5 kg/scp = 3.6 kJ/(kg·K)Tin = 25 °CTout = 70 °C
Q = kW
3.Medium
hot sidecold sidelight oil · 170 °C130 °Cwater · 25 °Ct = ? °C

Hot light oil cools water in a counter-flow heat exchanger with no heat loss. Find the water outlet temperature tout.

ṁh = 3 kg/scp,h = 2.1 kJ/(kg·K)Th: 170 → 130 °Cṁc = 3 kg/scp,c = 4.18 kJ/(kg·K)tin = 25 °C
tout = °C
4.Medium
hot sidecold sideethanol · 150 °C110 °Cwater · 30 °Ct = ? °C

Hot ethanol cools water in a counter-flow heat exchanger with no heat loss. Find the water outlet temperature tout.

ṁh = 1 kg/scp,h = 2.44 kJ/(kg·K)Th: 150 → 110 °Cṁc = 1 kg/scp,c = 4.18 kJ/(kg·K)tin = 30 °C
tout = °C
5.Hard
hot sidecold sideethanol · 160 °C90 °Cwater · 15 °C35 °C · ṁ = ?15% lost

Hot ethanol heats water in an exchanger that loses 15% of the heat released by the hot stream to the surroundings. Find the water flow rate ṁc needed.

ṁh = 3 kg/scp,h = 2.44 kJ/(kg·K)Th: 160 → 90 °Ct: 15 → 35 °Ccp,c = 4.18 kJ/(kg·K)loss = 15 %
ṁc = kg/s
6.Hard
hot sidecold sideethanol · 160 °C130 °Cwater · 10 °C50 °C · ṁ = ?10% lost

Hot ethanol heats water in an exchanger that loses 10% of the heat released by the hot stream to the surroundings. Find the water flow rate ṁc needed.

ṁh = 0.5 kg/scp,h = 2.44 kJ/(kg·K)Th: 160 → 130 °Ct: 10 → 50 °Ccp,c = 4.18 kJ/(kg·K)loss = 10 %
ṁc = kg/s

Answer key

  1. 1. Q = 262.5 kW
  2. 2. Q = 243 kW
  3. 3. tout = 45.1 °C
  4. 4. tout = 53.35 °C
  5. 5. ṁc = 5.21 kg/s
  6. 6. ṁc = 0.197 kg/s

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