Energy balance equation and heat transfer process

Energy balance equation and heat transfer process is very important as a chemical engineering point of view. So today we will learn how to do energy balance.

This article contains what is energy balance, how to to energy balance, what is latent heat and what is sensible heat, how heat transfer take Place.

Types of heat transfer

There are two types of heat transfer, first is latent heat transfer and second is sensible heat transfer.So to do energy balance we need to calculate latent heat of vaporisation and sensible heat.

we know that there are 3 types by which heat transfer take place, conduction, convection and radiation.

Latent heat

Latent heat is nothing but heat that transfer during the phase changes take place.Latent heat of vaporisation is nothing but heat transfer take place when there is phase changes from liquid to vapor. When we heat a product up to its boiling point that is sensible heat and when after boiling point we heat that is heat is nothing but heat of vaporization.

Latent heat can be calculate by,

Latent heat transfer = mass * heat of vaporisation

Latent heat = m * lambda

lambda of water = 540 kcal/kg

lambda of methanol =264 kcal/kg

to calculate latent heat we need lambda value of that particular component. Like lamba value of methanol is 264 kcal/kg and latent heat of vaporisation for water is 540 kcal / kg.

Sensible Heat transfer

sensible heat transfer is nothing but heat transfer due to change in temperature of mass or volume.

example heat required to change the water temperature from Room temperature to 100 degree celcius is sensible heat and heat required to vaporise water is nothing but latent heat of vaporisation for water.

sensible heat transfer can be calculate using following formula.

Sensible heat = mass * specific heat * temperature difference.

Sensible heat = m x cp x deltaT

to calculate sensible heat we need specific heat of compound.

What is specific heat?

specific heat is nothing but amount of heat required to raise the temperature by 1 degree celcius.

What is specific heat of water?

specific heat of water is 1 kcal/Kg.degC.

Energy balance and material balance is far necessary for a chemical engineer.

Latent heat versus sensible heat

What is difference between latent heat and sensible heat. In interview you of chemical engineer ut is very common question ” Explain latent heat versus sensible heat or tell difference between latent heat and sensible heat.

Energy balance equation

Energy balance is nothing but doing balance in between heat transfer and heat required by process. It is simply heat transfer by hot fluid is equal to heat gain by process plus heat losses.

To energy balance we need to calculate the latent heat and sensible heat.

if there phase changes in that case we need to calculate latent heat transfer and sensible heat transfer.

if there is only sensible heat transfer then we can do energy balance by using sensible heat transfer only.

example No 1

Calculate heat transfer required to heat 1 kg water from 30 degree celcius to 50 degree celcius.

Solution :-

m is 1 kg

Specific heat of water is 1 kcal/kg.DegC

Delta The = 50 -30 = 20 DegC.

Energy balance = m cp deltaT

Required heat = 1 x 1x 20

Required heat is 20 kcal.

Conclusion

From above article we understand that to calculate energy balance we need to calculate latent heat and sensible heat as per process requirement. Latent heat transfer is result of phase change while sensible heat transfer is result of temperature changes.

Please comment your email id if you want excel spreadsheet for energy balance equation.

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