Heat transfer 1 Conduction Heat transfer One dimensional

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1. Conduction Heat transfer • One dimensional conduction heat transfer �������� – – ������������������������

1. Conduction Heat transfer • Heat flux, Q (watt/m 2)

3. Radiation Heat transfer – = ������� -������ stefan -Boltzmann constant (5. 669 x 10 -8 W/m 2 K 4) – = ������� emissivity – T A= ����������� (K)

���� • Calculate the rate of heat energy emitted by 100 m 2 of a polished iron surface (emissivity = 0. 06) the temperature of the surface is 37 o. C

Heat transfer through Composite walls ������������� T 1 T 2 q T 3 ka kb xa xb kc xc q T 4

Heat transfer through Composite walls

Heat transfer through Composite walls ������������ x q 1 q q 2 q 3 T 1 A 1 k 1 A 2 k 2 A 3 k 3 q 1 q 2 q 3 T 2 q

Heat transfer through Composite walls

Heat transfer through the walls of pipes r 0 Ti ri To - Area inside : A =2 r. L

Heat transfer through the walls of pipes r 3 b r 2 a T 3 T 2 T 1 r 1

R 3 b R 2 a T 3 T 2 R 1 = 0. 013 m T 1 Stainless ฉนวน q = 399. 20 หา q และ T 2

Thermal Conductivity of Food Products • the rate of heat that will be conducted through a unit thickness of the material if a unit temperature gradient exists across that thickness type K (W/mo. C) metal 50 -400 alloys 10 -120 water 0. 597 (at 20 o. C) air 0. 0251 (at 20 o. C) Insulating materials 0. 035 -0. 173

Thermal Conductivity of Food Products • For fruits and vegetables with water content greater than 60%: Where W is water content (%) • For meats, temperature 0 -60 o. C, water content 60 -80%, wet basis • For solids and liquid foods:

Example : Thermal Conductivity of Food Products • Predict thermal conductivity of beef roll that contain 60. 1% moisture. • Soln For meats, temperature 0 -60 o. C, water content 60 -80%, wet basis

���������� ����� OVERALL HEAT TRANSFER COEFFICIENT (U) OBJECTIVES • To calculate overall heat transfer coefficient • To develop a mathematical equation useful in designing a heat exchange

• Heat transfer through individual layers q = hi. A(Ta - T 1) q = ho. A(T 2 - Tb)

Conv. Cond. Conv.

Adding above three equations From (1) ������� U ������� )Plane wall)

OVERALL HEAT TRANSFER COEFFICIENT (U) ������� r 2 Ri Tb Ta Ra Ro r 1 RT = Rconv 1 + Rcond + Rconv 2

Heat Exchanger By. . Onuma W.

Heat Exchanger • • tubular heat exchanger triple-tube heat exchanger plate heat exchanger shell and tube heat exchanger scraped-surface heat exchanger steam infusion heat exchanger) Five stage plate pasteurizer Juice pasteurization process