Principle of Heat Flow

Question 1

Range

Answer 1

Tch- Tcc

Question 2

Approach

Answer 2

DelT1, delT2

Question 3

Point temperature difference

Answer 3

Temperature difference at any point inside the heat exchanger

Question 4

Average or mixing cup temperature

Answer 4

Since the temperature the fluid is not uniform inside the system ( hotter near the hot surface and colder close to atmosphere for example) the temperature curves drawn are using the temperature that the fluid would have if mixed perfectly at adiabatic conditions

Question 5

Important assumptions for fluid flow in a heat exachanger derivation

Answer 5

U is constant and independent of temperature

Cp is constant - reason for linear relationship between delT and q

Steady state conditions

Heat transfer with ambient conditions is negligible

Question 6

Overall heat transfer coefficient

Answer 6

May depend upon the area used inside or outside

It does not matter which one we use but we should clearly mention it

Question 7

Types of flow in heat exchanger

Answer 7

Counter current

Parallel

Cross flow

Question 8

Counter current

Answer 8

Most commonly preferred

Constant delT hence almost constant heat transfer throughout

Less heat transfer are compared to other flows

Question 9

Cross flows

Answer 9

Not commonly used

Used in car radiators

Cooling of refrigerator compressor

Question 10

Parallel flow

Answer 10

Not commonly used

High heat transfer area

Usually used when high amount of heat has to be transferred in a short amount of time

Like quenching of hot metal rod

Question 11

Heat balance

Answer 11

All the other energies are neglible

Only heat transfer due to enthalpy transfer is dominant