Materi Pindah Panas 13 Februari 2019.pptx

Materi Kuliah pindah panas

1. Heat Transfer 1st Week – 13 Feb 2019 Redika A. Kusuma (FTP UGM)

2. U ntil a concept is conceptually grasped , a mathematical treatment is often not really helpful It might be right , but it doesn’t help ..

3. What is heat transfer ? What is thermal energy ? It represents the cumulative effect of microscopic activities ( translation, rotation, vibration and electronic states of the atoms /molecules) and is directly linked to the temperature of matter. It’ s thermal energy in transit due to a temperature difference .

4. Quantity Meaning Symbol Units Thermal Energy + Energy associated with microscopic behavior of matter Temperature A means of indirectly assessing the amount of thermal energy stored in matter Heat Transfer Thermal energy transport due to temperature gradients Heat Amount of thermal energy transferred over time interval  t  0 Heat Rate Thermal energy transfer per unit time Heat Flux Thermal energy transfer per unit time and surface area DO NOT confuse or interchange the meanings of Thermal Energy , Temperature and Heat Transfer

5. in a solid or a stationary fluid (gas or liquid) due to the random motion of its molecule due to the combined influence of bulk and random motion for fluid flow over a surface. Energy that is emitted by matter due to changes in the electron c onfig of its molecules . transported as electromagnetic Modes of Heat Transfer

6. Energy transfer across a system boundary due to a temperature difference by the mechanism of inter-molecular interactions Needs Matter Doesn’t require matter bulk motion Conduction

7. A B C 3.8 W/m² 38 W/m² 0 W/m²

8. q” = - k . Δ T/ Δ x (W/m 2 ) ΔT is the temperature difference, Δx is the thickness of the wall , k is the conductivity (the property of the material) Heat Flux (heat rate transfer per unit Area)

9. K vs Cp? kemampuan menghantar panas kemampuan menyimpan panas

10. K tembaga = 370 W/m o C

11. Energy transfer across a system boundary due to a temperature difference by the combined mechanism of inter-molecular interactions and bulk transport Needs Fluid Matter Convection

12. Akibat beda densitas oleh variasi suhu fluida

13. Fluid velocity at the plate is zero (conduction) Velocity far away From the plate

14. Ts > T ∞ q

15. q” = h (Ts – T∞) q” is the heat flux in W/m², h is the convection coefficient ( W/m² K) ≠ thermodynamic property of material Newton’s Law of Cooling ** ** mengalirkan udara dingin melewati plat panas

16. h depends on a number of fluid properties: - density - viscosity - thermal conductivity - specific heat capacity And also on: - surface geometry - flow conditions

17. T ransfer of heat by electromagnetic radiation that arises due to the temperature of the body. Doesn’t need Matter Radiation

18. E max = σ T absolut 4  E = εσ T absolut 4 E is the emissive power ( gross energy emitted from an ideal surface per unit area, time ) , T is the absolute temp in kelvin , σ is the stefan bolzman constan (5,67x10 -8 W/m 2 K 4 ), ε is the emissivity Radiation (from surface) * E = total energi meninggalkan permukaan (tanpa perlu melihat arah dan waktunya)

19. Saat dua permukaan saling berdekatan, kedua permukaan saling memancarkan radiasi (karena suhunya > -273 o C) mengikuti persamaan Stefan Boltzman. Heat flux (q”) dihitung sebagai aliran radiasi antar keduanya: