GW heat lecture

An Introduction to HEAT

Introduction to Biophysical Ecology

Lesson Objectives

 _{Define heat and the 4 primary} methods of heat transfer

 _{Define heat flux}

Defining Heat:

The first law of thermodynamics: Energy can not be created or destroyed.

U = Q + W

Defining Heat:

Heat

The fundamental interaction of biophysical ecology is energy transfer (Campbell and

Defining Heat:

The first law of thermodynamics: Energy can not be created or destroyed.

U = Q + W

Defining Heat Transfer:

Four PRIMARY modes of heat transfer are: 1) Radiation (feeling the hot sun)

2) Conduction (feeling a cold desk) 3) Convection (getting cold in a river)

Defining Heat Transfer:

What determines Q?

Four PRIMARY modes of heat transfer are:

1) Radiation: Electromagnetic energy transfer

• _{Infrared, Visible, and Ultra-violet}

(Low energy High energy)

Long-wave: IR,  > 700 m

Defining Heat Transfer:

What determines Q?

Four PRIMARY modes of heat transfer are:

Defining Heat Transfer:

What determines Q?

Four PRIMARY modes of heat transfer are:

2) Conduction: transport by direct contact

Defining Heat Transfer:

What determines Q?

Four PRIMARY modes of heat transfer are:

Defining Heat Transfer:

What determines Q?

Four PRIMARY modes of heat transfer are:

3) Convection: transport by fluid motion in presence of a kinetic energy gradient

Defining Heat Transfer:

What determines Q?

Four PRIMARY modes of heat transfer are:

Defining Heat Transfer:

What determines Q?

Four PRIMARY modes of heat transfer are:

4) Latent heat loss: heat loss due to phase

Defining Heat Transfer:

What determines Q?

Four PRIMARY modes of heat transfer are:

Describing heat transfer pathways:

Flux (Joules/sec or Watt)

Flux Density (watts/area)

Describing heat transfer pathways:

Radiant Flux Density

We will be talking about heat transfer in the units of HEAT per AREA x TIME – the area over which a heat transfer takes place and how long a body is exposed to a set of conditions is VERY

important!!!

Joules

Describing heat transfer pathways:

Heat Flux Density Equations

H = g_hc_p(T_o – T_f)

H = heat flux g_h = conductance

c_f = specific heat of fluid T_o = temp of organism

Describing heat transfer pathways:

Heat Flux Density Equations H = g_hc_p(T_o – T_f)

H = heat flux g_h = conductance

c_f = specific heat of fluid T_o = temp of organism

T_f = temp of fluid

How well it’s connected

Energy required to change temp

Describing heat transfer pathways:

Conditions that control heat transfer by CONDUCTION:

1) Temperature Difference 2) Surface area

Describing heat transfer pathways:

Conditions that control heat transfer by CONVECTION:

1) Temperature Difference 2) Fluid velocity (at surface)

Describing heat transfer pathways:

Conditions that control heat transfer by Radiation:

1) Temperature Difference 2) distance

Describing heat transfer pathways:

There are three primary equations, but the same principles apply to all:

F_m = g_j(C_js-C_ja) (Fick’s law)

H = g_hc_p(T_o – T_f) (Fourier’s law)

Describing heat transfer pathways:

There are three primary equations, but the same principles apply to all:

Transport is driven by “conductance” and the “gradient”, or difference

Describing heat transfer pathways:

Conductance Concepts:

Distance conductance

Barriers in series conductance