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
Heaterglycol mix · 40 °C70 °CQ = ?

A stream of glycol mix flowing at 1 kg/s is heated from 40 °C to 70 °C. Find the heat duty Q.

ṁ = 1 kg/scp = 3.6 kJ/(kg·K)Tin = 40 °CTout = 70 °C
Q = kW
2.Easy
Heaterethanol · 25 °C75 °CQ = ?

A stream of ethanol flowing at 5 kg/s is heated from 25 °C to 75 °C. Find the heat duty Q.

ṁ = 5 kg/scp = 2.44 kJ/(kg·K)Tin = 25 °CTout = 75 °C
Q = kW
3.Medium
hot sidecold sideglycol mix · 150 °C90 °Cwater · 15 °Ct = ? °C

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

ṁh = 3 kg/scp,h = 3.6 kJ/(kg·K)Th: 150 → 90 °Cṁc = 3 kg/scp,c = 4.18 kJ/(kg·K)tin = 15 °C
tout = °C
4.Medium
hot sidecold sidelight oil · 160 °C90 °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 = 2.5 kg/scp,h = 2.1 kJ/(kg·K)Th: 160 → 90 °Cṁc = 1 kg/scp,c = 4.18 kJ/(kg·K)tin = 25 °C
tout = °C
5.Hard
hot sidecold sideethanol · 120 °C80 °Cwater · 15 °C90 °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 = 2.5 kg/scp,h = 2.44 kJ/(kg·K)Th: 120 → 80 °Ct: 15 → 90 °Ccp,c = 4.18 kJ/(kg·K)loss = 15 %
ṁc = kg/s
6.Hard
hot sidecold sideglycol mix · 140 °C60 °Cwater · 30 °C50 °C · ṁ = ?5% lost

Hot glycol mix heats water in an exchanger that loses 5% of the heat released by the hot stream to the surroundings. Find the water flow rate ṁc needed.

ṁh = 1 kg/scp,h = 3.6 kJ/(kg·K)Th: 140 → 60 °Ct: 30 → 50 °Ccp,c = 4.18 kJ/(kg·K)loss = 5 %
ṁc = kg/s

Answer key

  1. 1. Q = 108 kW
  2. 2. Q = 610 kW
  3. 3. tout = 66.67 °C
  4. 4. tout = 112.9 °C
  5. 5. ṁc = 0.6616 kg/s
  6. 6. ṁc = 3.273 kg/s

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