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.

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1.Easy

A stream of glycol mix flowing at 0.2 kg/s is heated from 35 °C to 95 °C. Find the heat duty Q.

ṁ = 0.2 kg/sc_p = 3.6 kJ/(kg·K)T_in = 35 °CT_out = 95 °C

Q = kW

2.Easy

A stream of glycol mix flowing at 0.8 kg/s is heated from 35 °C to 90 °C. Find the heat duty Q.

ṁ = 0.8 kg/sc_p = 3.6 kJ/(kg·K)T_in = 35 °CT_out = 90 °C

Q = kW

3.Medium

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

ṁ_h = 0.5 kg/sc_p,h = 3.6 kJ/(kg·K)T_h: 120 → 80 °Cṁ_c = 3 kg/sc_p,c = 4.18 kJ/(kg·K)t_in = 25 °C

t_out = °C

4.Medium

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

ṁ_h = 1.5 kg/sc_p,h = 2.44 kJ/(kg·K)T_h: 130 → 90 °Cṁ_c = 1 kg/sc_p,c = 4.18 kJ/(kg·K)t_in = 25 °C

t_out = °C

5.Hard

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 ṁ_c needed.

ṁ_h = 2.5 kg/sc_p,h = 2.44 kJ/(kg·K)T_h: 150 → 90 °Ct: 25 → 70 °Cc_p,c = 4.18 kJ/(kg·K)loss = 15 %

ṁ_c = kg/s

6.Hard

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

ṁ_h = 2.5 kg/sc_p,h = 3.6 kJ/(kg·K)T_h: 130 → 100 °Ct: 10 → 50 °Cc_p,c = 4.18 kJ/(kg·K)loss = 15 %

ṁ_c = kg/s

Answer key

1. Q = 43.2 kW
2. Q = 158.4 kW
3. t_out = 30.74 °C
4. t_out = 60.02 °C
5. ṁ_c = 1.654 kg/s
6. ṁ_c = 1.373 kg/s

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