Review of Heat Transfer Theory and Practice

-Manufactured and Distributed by-Kevin Dilley, Kaiwen Jiang, Zachary Landau, Aashish Parekh,

and Natalie Wittick

What Is Heat Transfer?

Heat transfer introduction

Basic Rules of Heat Transfer

● Energy, Thermal included, cannot be created nor destroyed

● Thermal energy is naturally transferred down a temperature

gradient○ Always from a warmer to cooler substance

● Heat is either transferred by Conduction, Convection, or

Radiation

Heat Transfer Mediums

Conduction - Transfer of thermal energy by direct contact or within a substance

● Ex. Electric Stove or Cooling a coke drink with ice

Convection - Transfer of thermal energy by bulk fluid movement

● Ex. Water in bottom of pot transferring energy throughout

Radiation - Transfer of thermal energy by electromagnetic waves (no direct contact!)

● Ex. Roasting marshmallows with a campfire

Heat Transfer Equations for different Coordinate Systems

Example: Heat Exchangers

Heat Exchanger Fundamentals

● General Function: A device whose primary purpose is the transfer of energy between two

fluids

● Three categories of classification:

○ Regenerators

○ open-type exchanger

○ closed-type exchangers or recuperators.

● Heat exchangers are typically classified according to flow arrangement and type of

construction

Types of Heat Exchangers

● Single Pass (parallel and crossflow)

○ Fluid flows in similar and opposite directions

● Shell and tube

○ Finned/Unfinned tubular HX

● Compact HX

○ Plate and Frame HX

Single Pass Heat Exchangers

https://www.quora.com/Why-is-a-counter-flow-heat-exchanger-better-than-a-parallel-flow-heat-exchanger

HEX Theory

Stream Energy Balance:

Total rate of heat transfer:

Heat transfer coefficient:

10

Heat Transfer Equations for Heat Ex

Graphical Analysis

Unsteady State Conduction

Finite Biot Number

Both surface and internal resistance are measurable

http://homepages.wmich.edu/~leehs/ME431/ch05_supp_heisler.pdf

Fig. : Centerline Temp as a function of time for a cylinder

Lumped Parameter Analysis

Used when Biot is very small (≤0.1)

Negligible internal resistance; spatially uniform

Negligible Surface Resistance

Bi >> 0.1

Surface temperature is constant and essentially equal to the temperature of the surroundings

Heat Transfer in Multiple Directions

For a rectangular slab:

For a cube:

For a cylinder:

Continue with same process as shown through an iterative method (one direction at a time)

until error is minimized

Semi-Infinite Wall

Shallow penetration temperature

Short application time

Undefined characteristic length

Convection

Convective heat transfer--heat transfer between a surface and surrounding fluid

Uses dimensionless numbers and analysis

Convective Problems

Source: Dr. Goldberg

Special Circumstances and Exceptions

Thank for listening

Questions?

Citations Welty, J. R., Rorrer, G. L., & Foster, D. G. (2019). Fundamentals of momentum, heat, and mass transfer. Hoboken, NJ: Wiley.

Bird, R. Byron, et al. Transport Phenomena. Wiley India Pvt. Ltd., 2014.