slide1 n.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
CONDUCTION Heat transport - short distance 1. No mass movement PowerPoint Presentation
Download Presentation
CONDUCTION Heat transport - short distance 1. No mass movement

Loading in 2 Seconds...

play fullscreen
1 / 14

CONDUCTION Heat transport - short distance 1. No mass movement - PowerPoint PPT Presentation


  • 108 Views
  • Uploaded on

CONDUCTION Heat transport - short distance 1. No mass movement 2. Interaction adjacent molecules Magnitude - heat transfer Determined by: 1. thermal conductivity - material a. Metals high b. Gases low 2. Contact surface

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'CONDUCTION Heat transport - short distance 1. No mass movement' - aadi


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
slide1

CONDUCTION

Heat transport - short distance

1. No mass movement

2. Interaction adjacent molecules

Magnitude - heat transfer

Determined by:

1. thermal conductivity - material

a. Metals high

b. Gases low

2. Contact surface

a. lying down vs. standing up

slide2

Resting human or standing animal -

Heat exchange via conduction - usually small

Often neglected - heat balance studies

Air layer against skin = pathway for conduction

BUT - air has low thermal conductivity

Therefore - small role - total transfer

Heat transfer feet >> ground = small contact area

Hoofed animal - distance between blood vessels & surface much greater than in feet

slide3

Conductive heat transfer increases with animal lying on

  • cool/wet surfaces
  • Greater import. under these conditions
  • 1. substrate thermal conductance
  • 2. temperature gradient
  • 3. area of contact relative to total surface area
  • Sheep - lying on cold, poorly insulated ground -
  • dissipates up to 30% minimum heat production by
  • conduction.
  • If temperature of substrate is greater than body temperature
  • gradient is reversed - heat inflow via conduction and
  • increases heat load.
slide4

Floor material - important for animals such as pigs

(~20% - pig’s surface - may be in contact with floor)

Thermal capacity - floor material - very important

Density of material x specific heat = thermal capacity

Different materialsaffect instantaneous fall in temperature

Feeling of warmth - related to instantaneous temperature

drop

Assumed that floor would not feel very cold if:

Instantaneous drop did not exceed 1.6F at Ta = 64.5 F

(wood floor)

slide5

40 kg animal - LCT = 11.5 - 13.0 C straw

(thermal insulation + decreases heat flow > floor)

= 14.0 - 15.0 C asphalt

= 19.0 - 20.0 C concrete

Newborn pig at Ta = 10 C - Moving animal from bare concrete >> straw has same thermal effect on

metabolism as increasing Ta > 18 C.

slide6

Heat Transfer - warming food or drink -

usually insignificant.

If a 20 kg pig drinks 2.5 L/day and water temp. = 20 C

Pig puts 200 kJ into water to raise it to deep body

Temperature

MR = 6700 kJ / day

Therefore - a 3% shift (same found for sheep).

_________________________________________

slide7

What is tissue insulation?

Resistance offered to heat flow between heat-producing

tissues and skin surface.

Dependent on:

1. Thickness - subcutaneous fat

2. Vasomotor changes - blood flow

Internal thermal conductance = combination - 2 heat

transfer channels

1. Conduction - heat through muscle and fat layers

2. Convection - heat transfer via blood

slide8

Tissue Insulation (°C x m2 x W-1)

________________________________________________

Calf 0.09 0.04

(vasoconstriction) (vasodilation)

Adult Steer 0.14 0.04

________________________________________________

• Cold Ta conductance - not greatly affected by Ta

In theory - fully vasoconstricted at LCT

Minimal peripheral blood flow

Likewise - after vasodilation - little additional increase

in peripheral blood flow

slide9

External Insulation

(Animal Coat or Clothing Insuln.) + (Air - Ambient Insuln.)

(Air - Ambient Insuln.) = region between surface of coat

or bare skin and environment

Hair Coat Insulation (°C x m2 x W-1)

________________________________________________

Calf 0.11 0.16

(unerected) (erected)

________________________________________________

1. Hair coat insulation increases with coat dept

2. Air trapped between fibers

3. Wind velocity decreases amount of trapped air

slide10

(mW x m-1 x °C-1)

______________________________________________

Thermal conductivity still air (20°C) 25

Coats - artic mammals 55

________________________________________________

COAT TYPE - IMPORTANT

Decrease in thermal insulation with less still air

Insulation of dead fat - greater than for live fat –

WHY

slide11

INSULATION DENSITY

Barnett - used isolated mouse skin

Insulation = 0.069°C/m2/W-1 for a unit hair density

(1 mg/cm-2)

Insulation of mouse coat - using these units = 4 times

that of pig hair of same density and 10 times that of calf

WHY GREATER INSULATION VALUE OF MOUSE FUR?

Possibly - greater # - fine hairs (wt for wt) & more

effective layer - trapped air

Measurement of density as number hairs / unit area may

be more useful comparison - than meas. - density as

weight of hair / unit area

slide12

Coat Density - very important

Thick coat - husky dog - so dense - it can sleep

comfortably on snow - with no melting on tips of hairs

• Wind - less effect on dense coats than sparse coats

Dividing line - sparse and dense = 1,000 hairs/cm2

Coat also important - preventing heat gain - hot

environments

slide13

External Insulation - Birds

  • Plumage = effective barrier - heat loss
  • 1. Down feathers - traps air >> little convection
  • Contour feathers - distal parts >> windproof cover
  • • Chicks without contours - have a problem
  • Water Problem -
  • 1. thin layer oil - preen gland
  • 2. + spaces between finest divisions feather
  • structure - extremely small
  • • Both factors >> plumage with high resistance - wetting
slide14

Thermal insulation - greater in larger birds

  • 1. Able to carry heavier load feathers than small birds
  • Because of radial distribution of feathers - smaller
  • objects (torso, extremities) have less compact
  • insulation
  • Definite benefit during cold exposure
  • Some birds elevate feathers during expsoure -
  • solar radiation
  • Permits better circulation - air through plumage & incr.
  • heat loss
  • Acclimation - warm Ta > decr. plumage - domestic fowl
  • Some birds - winter plumage may be 30% greater
  • than summer