Principle of Heat Flow Flashcards Preview

Heat transfer > Principle of Heat Flow > Flashcards

Flashcards in Principle of Heat Flow Deck (11):
1

Range

Tch- Tcc

2

Approach

DelT1, delT2

3

Point temperature difference

Temperature difference at any point inside the heat exchanger

4

Average or mixing cup temperature

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

5

Important assumptions for fluid flow in a heat exachanger derivation

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

6

Overall heat transfer coefficient

May depend upon the area used inside or outside

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

7

Types of flow in heat exchanger

Counter current

Parallel

Cross flow

8

Counter current

Most commonly preferred

Constant delT hence almost constant heat transfer throughout

Less heat transfer are compared to other flows

9

Cross flows

Not commonly used

Used in car radiators

Cooling of refrigerator compressor

10

Parallel flow

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

11

Heat balance

All the other energies are neglible

Only heat transfer due to enthalpy transfer is dominant