0. HeatTransfer_web

# 0. HeatTransfer_web - ENU 4134 – Single-Phase Heat...

This preview shows pages 1–8. Sign up to view the full content.

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: ENU 4134 – Single-Phase Heat Transfer Review D. Schubring September 8, 2009 Topics I Conduction I Radiation I Convection I Application to Rod Bundles Conduction General conduction equation: ρ c p ( ~ r , T ) ∂ T ( ~ r , t ) ∂ t = ∇ · k ( ~ r , t ) ∇ T ( ~ r , t ) + q 000 ( ~ r , t ) (1) Conduction (2) Possible simplifications Steady-state – constant power in fuel: 0 = ∇ · k ( ~ r ) ∇ T ( ~ r ) + q 000 ( ~ r ) (2) and constant conductivity – can be assumed for fuel behavior under certain conditions: 0 = k ∇ 2 T ( ~ r ) + q 000 ( ~ r ) (3) and no heat generation – cladding: 0 = ∇ 2 T ( ~ r , t ) (4) Radiation q 00 out = σ T 4 (5) Must use absolute temperature! Emissivity ( ) – a value between 0 and 1 indicating how efficiently surface emits thermal radiation I In general, can be a function of wavelength, temperature, position, etc. We’ll model as a constant. Stefan-Boltzmann constant ( σ ) σ = 5 . 67 × 10- 8 W m 2 K 4 (6) Radiation Examples – = 1 Temperature of 300 K (atmosphere): q 00 out = σ T 4 = 5 . 67 × 10- 8 × 300 4 = 460 W m 2 (7) Negligible Temperature of 500 K (LWR): q 00 out = σ T 4 = 5 . 67 × 10- 8 × 500 4 = 3 , 500 W m 2 (8) Minor Temperature of 1200 K (VHTR): q 00 out = σ T 4 = 5 . 67 × 10- 8 × 1200 4 = 118 , 000 W m 2 (9) Significant Convection Combination of conduction in the fluid and mass transfer Usually phrased as a heat transfer coefficient, h (sometimes α ): h = q 00 Δ T (10) Often correlated as the dimensionless Nusselt number, Nu Nu = hL k (11) L is a length scale ( e.g. , D for round tubes, D h other geometries), and k , the thermal conductivity, is evaluated in the fluid . Laminar Flow...
View Full Document

{[ snackBarMessage ]}

### Page1 / 24

0. HeatTransfer_web - ENU 4134 – Single-Phase Heat...

This preview shows document pages 1 - 8. Sign up to view the full document.

View Full Document
Ask a homework question - tutors are online