Heat Transfer Formula

Heat is a type of energy that moves from a hot to a cold thing. When we contact something cold, heat from our bodies is transferred to the cold item. Heat is transferred between objects of differing temperatures. The passage of heat ceases when the two objects reach the same temperature.

Heat Transfer

Heat transfer occurs when energy from a higher-temperature body transfers to a lower-temperature body. Heat is the term for the energy in transit. Our palms feel cold when we hold an ice cube in our hands. This occurs as a result of heat transmission from our bodies to the ice cube. The temperature of our hands drops as a result of the loss of heat from our bodies, making us feel chilly. The faster heat transfer happens between two items, the greater the temperature differential between them.

Heat Transfer Formula

Q = C×m×ΔT

Where,

Q = heat

c = specific heat

m = mass of the body

ΔT = temperature difference

Sample Problems

Question 1: What is Heat?

Answer

The vibrations of molecules or atoms increase as the temperature of a body rises. These vibrations are then passed from one body part to the next. The amount of energy used to vibrate the molecules in a system is referred to as heat.

It is denoted by Q.

Problem 2: Determine the heat needed to raise a 1 kg of iron from 250° C to 600° C?

Solution

Mass, m = 1 Kg,

Specific heat of iron, C = 0.45 Jg⁻¹°C

Also, temperature difference,

ΔT=700°C–250°C

ΔT=450°C

Now applying the heat formula,

c=Q/mΔT

rearranging the formula

Q=mcΔT

Q=1×0.45×103×450

= 20.25 J

Problem 3:  Determine how much heat energy is lost if 50 Kg water is cooled from 600\degree C to 200\degree C. Specific heat of water is given as C=4.2×103JKg⁻¹°C.

Solution

Mass of water, m = 50 Kg,

Specific heat of water, C = 4.2×103JKg−1°

Temperature difference,

ΔT=–40°

Heat energy by formula is,

Q = mcΔT

Q = 50×4.2×103×(−400)

Q= – 840 J

Question 4: What is the convection mode of heat transfer?

Answer

In liquids and gases, heat is transferred through convection. The particles of a liquid or gas move from one location to another to transfer heat in the convection mechanism of heat transmission.

Problem 5: A system weighing 5 Kgs is heated from its initial temperature of 30ᵒC to its final temperature of 60ᵒC. Calculated the total heat gained by the system. (Specific heat of the system = 0.45 kJ/Kg K)

Solution

The Initial temperature of the system, T_i = 30ᵒC

The Final temperature of the system, T_f = 60ᵒC

Mass of the system, m = 5 kg

The total heat gained by the system can be calculated by using the formula for heat transfer as mentioned above,

Q= c x m x ΔT

Q=5×0.45×30

Q=67.5 J

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