Heat Copy by Convection

 Heat Transfer by Convection Essay

Heat Transfer by Convection

Ch. E. 324 Depending on the notes from a class of Prof. Alberto Laurito

Learning Objectives

At the end from the discussion you should be able to: • differentiate convection from conduction • determine whether a high temperature transfer simply by convection is usually forced or natural • solve person film coefficients(h) and total heat transfer coefficients(U) in a double water pipe heat exchanger.


- heat is usually transferred due to a combining process between cold and hot portions of a liquid. Two Types of Convection 1 . Forced convection - mixing up is due to mechanised means including pumps, air compressors, agitators. installment payments on your Natural convection - combining is due to denseness difference as a result of temperature lean.


APPLICATIONS: 1 . Dual pipe warmth exchanger* installment payments on your Shell and tube heat exchanger several. Bank of tubes 5. Film type condensation

Film Concept

Steel wall


Cold fluid Tb To Ta Popular fluid

• When a rapidly moving fluid comes in contact with a stationary phase, a thin film is formed.


Inner film

•The slender film acts as a boundary part between the going fluid and the wall. •The thin film contributes one more resistance to high temperature flow.

exterior film

Temperatures profile intended for heat transfer by

convection from one substance to another

Film Concept

Metallic wall Atmosphere 25oC Frosty fluid


Cold liquid Tb To Ta Warm fluid

100oC Water

Warm fluid


Inner film

outer film

Temperature profile for heat transfer by simply

convection from one fluid to another

Heat Transfer Equation

Immunities in Series: q = qi = qw = qo

Metallic wall Ti Cold substance

RT = Ri + Rw & Ro

Hot fluid



Internal film:


Ti Tag Ri

Tag Tb Rw Tb To Ro


xi kiAi xw kwAw xo koAo



Metal wall membrane: q t


exterior film

Internal film

o – outside the house i – inside

watts – material wall

Exterior film: qo


Person Heat copy Coefficient (h)

• times i and xo are certainly not measurable

by k

one particular h

xi ki

1 hi

xo ko

one particular ho

hello there - inside film agent or high temperature transfer coefficient

ho -- outside film coefficient or heat-transfer pourcentage


Ri R t R to

Ri 1 hi A i Rw xw kwAw


1 ho A o

Convection Conduction Convection


you hi A i

xw kwAw

you ho A o

Person Heat transfer Coefficient (h)

Recall: Fourier's Law

Big t q kA x

or perhaps: q

Big t A xk

x nevertheless: k

Tb To

one particular h

Ti Ta

Capital t therefore: queen A 1h finally: queen hA Big t

Inner film: qi

hi Ai Ti



Ti Konstruera

outer film

outer film: qo = ho A o О”To overall:

Tb To

Internal film

queen UA Tlm

Overall Warmth Transfer Agent (U)



Tlm RT


q User interface A i Tlm q Uo A o Tlm

Note: The values of hi, ho are dependent upon the houses of the fluid and the kind of flow.

1 RT sama dengan UA

one particular 1 sama dengan = User interface A we Uo A o

Overall Heat Transfer Coefficient (U)

RT one particular UA 1 Ui A i one particular Uo A o

but: R To

1 hi A i actually

xw kwAw

1 ho A um

1 Urinary incontinence A my spouse and i

1 Urinary incontinence A my spouse and i 1 User interface 1 hi A i 1 hello there

1 Uo A o

xw kwAw

1 hello there A i actually

xw kwAw

1 Uo A u 1 Uo


1 ho A o

1 hi A i Ao hi A i

Ao hi A i

one particular ho A o Aje ho A o

xw kwAw xw Ao kwAw

1 xw Ao kwAw

1 ho A to 1 ho

1 ho

x watts Ai kwAw


one particular hi

1 xw Ai kwAw

Aje ho A o

Heat Transfer Areas (Ao & Ai)

For the single tube:


Ao and Ai are horizontal surface area of the pipe.






A w Am

LDlm (mean part of cylindrica l sec tion)

Heat Transfer Areas (Ao & Ai)

1 Aje 1 howdy x watts Ai kwAw Ai ho A to 1 Uo Ao hi A i actually xw Ao kwAw you ho RE: LDlm

Substituting in the above formulas: A i

Exactly where:




Di = product inner diameter of internal tube.

Do = outside the house diameter of tube.

one particular Ui

you hi

x w DiL k t LDlm

DiL ho DoL

1 Uo

DoL hi DiL

back button w DoL k watts LDlm

one particular ho

one particular Ui

you hi

back button wDi k wDlm

Dalam hoDo

1 Uo

Perform hiDi

x w Carry out k wDlm

1 ho

Heat Copy Coefficient (hi and ho)

MAIN PROBLEM: Getting h (hi and ho) • hello there and ho are necessary to find User interface or Uo • hi - heat transfer agent of the internal film. •...


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