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• Last Updated : 28 Apr, 2022

The heat load is the amount of heat energy that is expected to be injected into a specific space in order to keep the temperature within an acceptable range. The heat load is equal to the product of mass flow rate, specific heat constant and change in temperature. It is denoted by the symbol Q. Its standard unit of measurement is watt (W). Its dimensional formula is given by [M1L2T-3]. It has two categories, internal heat load and external load. The former works on a conditional area while the latter is based on the heat supplied to the air after it exits a location.

Formula

Q = m Ã— Cp Ã— Î”t

where,

Q is the heat load value.

m is the mass flow rate,

Cp is the value of specific heat,

Î”t is the change in temperature.

### Sample Problems

Problem 1. Calculate the heat load for a heating device if the mass flow rate is 3.67, Cp is 950 and initial and final temperatures are 15.6 and 25.7 respectively.

Solution:

We have,

m = 3.67

Cp = 950

t1 = 15.6

t2 = 25.7

Using the formula we get,

Q = m Ã— Cp Ã— Î”t

= 3.67 (950) (25.7 – 15.6)

= 3.67 (950) (25.7 – 15.6)

= 35213.65 W

Problem 2. Calculate the heat load for a heating device if the mass flow rate is 1.56, Cp is 587 and initial and final temperatures are 23.2 and 35.6 respectively.

Solution:

We have,

m = 1.56

Cp = 587

t1 = 23.2

t2 = 35.6

Using the formula we get,

Q = m Ã— Cp Ã— Î”t

= 1.56 (587) (35.6 – 23.2)

= 3.67 (950) (25.7 – 15.6)

= 43232.60 W

Problem 3. Calculate the mass flow rate for a heating device if the head load is 51265.78 W, Cp is 651 and initial and final temperatures are 23.7 and 30.9 respectively.

Solution:

We have,

Q = 51265.78

Cp = 651

t1 = 23.7

t2 = 30.9

Using the formula we get,

Q = m Ã— Cp Ã— Î”t

=> 51265.78 = m (651) (30.9 – 23.7)

=> 4687.2 m = 51265.78

=> m = 10.93 kg/s

Problem 4. Calculate the mass flow rate for a heating device if the head load is 31562.54 W, Cp is 1000 and initial and final temperatures are 33.2 and 40.67 respectively.

Solution:

We have,

Q = 31562.54

Cp = 1000

t1 = 33.2

t2 = 40.67

Using the formula we get,

Q = m Ã— Cp Ã— Î”t

=> 31562.54 = m (1000) (40.67 – 33.2)

=> 7470 m = 31562.54

=> m = 4.22 kg/s

Problem 5. Calculate the value of specific heat for a heating device if the head load is 21981.87 W, the mass flow rate is 6.7 and initial and final temperatures are 41.72 and 34.61 respectively.

Solution:

We have,

Q = 21981.87

m = 6.7

t1 = 41.72

t2 = 34.61

Using the formula we get,

Q = m Ã— Cp Ã— Î”t

=> 21981.87 = (6.7) (Cp) (41.72 – 34.61)

=> 47.637Cp = 21981.87

=> Cp = 461.44

Problem 6. Calculate the value of specific heat for a heating device if the head load is 28176.32 W, the mass flow rate is 8.5 and initial and final temperatures are 30 and 40 respectively.

Solution:

We have,

Q = 28176.32

m = 8.5

t1 = 30

t2 = 40

Using the formula we get,

Q = m Ã— Cp Ã— Î”t

=> 28176.32 = (8.5) (Cp) (40 – 30)

=> 85 Cp = 28176.32

=> Cp = 331.48

Problem 7. Calculate the final temperature for a heating device if the head load is 42432.51 W, the mass flow rate is 5, Cp is 750 and initial temperature is 25.

Solution:

We have,

Q = 42432.51

Cp = 750

m = 5

t1 = 25

Using the formula we get,

Q = m Ã— Cp Ã— Î”t

=> 42432.51 = (5) (750) (t2 – 25)

=> t2 – 25 = 11.31

=> t2 = 36.31o C

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