Name _ Spring 2008
ME 3304: Test 1
Open book and 1 review sheet allowed. No other materials permitted.
Instructor: Vick_ Nichole Rylander Chris Rylander Ekkad
Problem 1: 25%
A long wire of radius r1 = 0.25 cm and thermal conductivity kw of 25 W
ME 3433 Heat Transfer
Prof. Srinath Ekkad sekkad@vt.edu 101 Randolph Hall 231-7192
3/30/2008 Lecture 1 1
Introduction
What is the definition for Heat Transfer? - Transfer of thermal energy due to temperature difference - Examples?
- Everywhere - Par
Problem 3: 307o Water is to be heatedfrom 15oC 65oCas it flows through a 3-cm intemal diameter5-m long to tube. The tube is equippedwith an electric resistanceheaterthat provides uniform heating throughoutthe surface of the tube. The outer surfaceof
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Quiz 3 Solution
Finite Difference Example - Pin Fin (3 nodes)
& Assume uniform convection and heat generation, E g ; constant x, k, Ac;
And steady state conditions; T1=Tb=const a. Find equation for T2: First Law: qconv Tb=T1 q1 x/2 T2
& q1 + qconv
Heat Transfer Quiz 5 March 10, 2008 Name: _ Given: The coverplate for a flat-plate solar collector is at 15oC while ambient air at 10oC is in parallel flow over the plate, with u =2m/s. Length, L=1m, and width, W=2m.
W=2m
Find: Rate of convective h
Heat Transfer Quiz 6 Air is flowing through a cylindrical pipe with the following properties shown in the schematic below. The pipe experiences a uniform surface heat flux. Assume fully developed flow.
Table A.4, Air (for an assumed value of Tm,o =
ME3304 Quiz 1
An electrical heater is wrapped around the outer surface of a long cylindrical tube whose inner surface is maintained at a temperature, Ti of 5oC. The tube wall has inner and outer radii of 25 mm and 75 mm respectively, and a thermal co
Free Convection: Cylinders, Spheres, and Enclosures
Chapter 9 Section 9.6.3 through 9.8
Cylinders
The Long Horizontal Cylinder
Boundary Layer Development and Variation of the Local Nusselt Number for a Heated Cylinder:
The Average Nusselt Number
Free Convection: General Considerations and Results for Vertical and Horizontal Plates
Chapter 9 Sections 9.1 through 9.6.2, 9.9
General Considerations
General Considerations
Free convection refers to fluid motion induced by buoyancy forces. Buo
Lecture Notes 4
Dr. Srinath Ekkad
Thermal Energy Generation
Processes within the medium may cause energy to be converted to thermal energy
1. Electrical Resistance Heating Electrical energy Thermal energy = Rate of energy generated (W) = I2Re = Vol
Lecture 5
Dr. Srinath V. Ekkad
Two-Dimensional Steady-State Conduction
One coordinate direction conduction is grossly oversimplified and most times, it is very important to consider multi-dimensional effects.
Heat flow lines Isotherms
Hot surface
Lecture 5 Numerical Methods
Dr. Srinath Ekkad
Finite Difference Equations
Instead of solving the heat conduction equation exactly for the temperature at every point, we divide the region into a discrete set of points or nodes and approximate the de
Lecture 7
Dr. Srinath V. Ekkad
Transient Conduction
Methods: Lumped Capacitance Model Charts (graphic results) Numerical techniques
Finite difference Finite element BEM
Analytical
Separation of variables Fourier series Etc.
Lumped Capaci
Lecture 8
Dr. Srinath V.Ekkad
Transient Conduction Finite Difference Method
In order to include the effects of the time variable, various finite difference schemes have been devised. These include: 1. Explicit scheme - Forward differences in time 2.
Lecture 9
Dr. Srinath V. Ekkad Chapter 6 - Convection
Boundary Layer Features
Boundary Layers: Physical Features
Velocity Boundary Layer
A consequence of viscous effects associated with relative motion between a fluid and a surface.
A region of
Lecture 10 Convection (External) Flat Plate
Dr.Srinath V.Ekkad
Physical Features
Physical Features
As with all external flows, the boundary layers develop freely without constraint. Boundary layer conditions may be entirely laminar, laminar and
External Flow: Flow over Bluff Objects (Cylinders, Spheres, Packed Beds) and Impinging Jets
Dr. Srinath V. Ekkad
CYLINDER in CROSS FLOW
Photograph of flow past a circular cylinder. Visualization is by air bubbles in water. (From "An Album of Fluid
Internal Flow: General Considerations and Correlations
Lecture 12 - Chapter 8 Dr. Srinath Ekkad
Entrance Conditions
Entrance Conditions
Must distinguish between entrance and fully developed regions. Hydrodynamic Effects: Assume laminar flow with
PROBLEM 1.1 KNOWN: Heat rate, q, through one-dimensional wall of area A, thickness L, thermal
conductivity k and inner temperature, T1. FIND: The outer temperature of the wall, T2. SCHEMATIC:
ASSUMPTIONS: (1) One-dimensional conduction in the x-direction,