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 ethanol flowing at 0.2 kg/s is heated from 20 °C to 80 °C. Find the heat duty Q.

ṁ = 0.2 kg/sc_p = 2.44 kJ/(kg·K)T_in = 20 °CT_out = 80 °C

Q = kW

2.Easy

A stream of light oil flowing at 0.8 kg/s is heated from 40 °C to 95 °C. Find the heat duty Q.

ṁ = 0.8 kg/sc_p = 2.1 kJ/(kg·K)T_in = 40 °CT_out = 95 °C

Q = kW

3.Medium

Hot light oil 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 = 2.1 kJ/(kg·K)T_h: 180 → 70 °Cṁ_c = 1 kg/sc_p,c = 4.18 kJ/(kg·K)t_in = 15 °C

t_out = °C

4.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 → 60 °Cṁ_c = 0.5 kg/sc_p,c = 4.18 kJ/(kg·K)t_in = 20 °C

t_out = °C

5.Hard

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

ṁ_h = 1 kg/sc_p,h = 2.1 kJ/(kg·K)T_h: 120 → 90 °Ct: 30 → 55 °Cc_p,c = 4.18 kJ/(kg·K)loss = 10 %

ṁ_c = kg/s

6.Hard

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

ṁ_h = 2 kg/sc_p,h = 2.44 kJ/(kg·K)T_h: 170 → 110 °Ct: 20 → 55 °Cc_p,c = 4.18 kJ/(kg·K)loss = 5 %

ṁ_c = kg/s

Answer key

1. Q = 29.28 kW
2. Q = 92.4 kW
3. t_out = 97.89 °C
4. t_out = 71.67 °C
5. ṁ_c = 0.5426 kg/s
6. ṁ_c = 1.901 kg/s

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