Evaporative cooling in mammals and machines

Jonathan Toomimjtoomim@jtoomim.org

Witnesses of ClimatologyAugust, 2019

Science vs freedom units

How EC doesn’t work

How EC actually works

Latent heat of vaporization

Substance Specific latent heat of vaporization (kJ/kg)Helium (He) 21Oxygen (O2) 213

Refrigerant R134a 216Toluene (C7H8) 351

Hydrogen (H2) 455

Ethyl alcohol (C2H5OH) 855

Lead (Pb) 871Ammonia (NH3) 1369

Water (H2O) 2265

H2O’s LHV in context

Action Specific heat (kJ/kg)Melting ice 334Heating water from 0°C to 100°C 418Evaporating water 2265Burning methane (CH4) in O2 10,028

Burning H2 in O2 16,823

The evaporation of water is pretty cool.

The evaporation of water is pretty cool.

[Audience groans]

Most biomass does not use EC for thermoregulation

EC in humans

● We are mostly hairless apes● Humans perspire more than any

other mammal● Hairlessness/sweat and bipedalism

may be adaptations for low-speed persistence hunting

● Low body temperature (37°C)● Uses a lot of water, maladaptive in

deserts

EC in canidae● Sweating only on palms and nose; low effect● Most EC happens in mouth, lungs● Panting is the primary cooling mechanism● Arteries bound for the brain pass through the

nose as a dedicated brain cooling system● High blood flow and salivation in mouth and

tongue● Good persistence hunters at moderate

speeds (e.g. African wild dogs)● Moderate body temp (39°C)

EC in other mammals● Kangaroos wet their limbs with licking● Cows pant through their noses, but are

extra susceptible to heat stress from fermentation heat

● Sheep, goats, and horses sweat● “Sweating like a pig” is a lie● Desert-adapted animals prefer dry

cooling (e.g. large ears, burrowing)● Typically moderate body temp (39°C)

EC in birds

● Birds cool with EC via respiratory system

● Gular fluttering forces air through the throat and mouth

● Bathing also common when possible

● Birds have high body temps (41°C typical, up to 44.5°C in hummingbirds)

Modern EC machines

Persian EC construction dates back 1000 years

Psychrometric chart(Relative humidity is the devil’s spawn)

Temperature (°C)

Abs

olut

e hu

mid

ity(k

g H

2O/k

g dr

y ai

r)

Dry bulb temperature and dew point

Temperature (°C)

Abs

olut

e hu

mid

ity(k

g H

2O/k

g dr

y ai

r)

Dry bulb temperature (30°C)

Dew point (10.8°C) 30°C at 30% RH

Direct evaporative cooling

Temperature (°C)

Abs

olut

e hu

mid

ity(k

g H

2O/k

g dr

y ai

r)

Wet bulb temperature

Temperature (°C)

Abs

olut

e hu

mid

ity(k

g H

2O/k

g dr

y ai

r)

30°C at 30% RH

Wet

bulb

tempe

ratur

e (18

°C)

Wet vs dry vs dew

Temperature (°C)

Abs

olut

e hu

mid

ity(k

g H

2O/k

g dr

y ai

r)

30°C at 30% RHDew point (10.8°C)

Dry bulb temperature (30°C)

Wet

bulb

tempe

ratur

e (18

°C)

Direct vs Indirect EC

Temperature (°C)

Abs

olut

e hu

mid

ity(k

g H

2O/k

g dr

y ai

r)

30°C at 30% RHDew point (10.8°C)

Multi-stage indirect EC

Temperature (°C)

Abs

olut

e hu

mid

ity(k

g H

2O/k

g dr

y ai

r)

30°C at 30% RHDew point (10.8°C)

Saturation efficiency

Temperature (°C)

Abs

olut

e hu

mid

ity(k

g H

2O/k

g dr

y ai

r)

30°C at 30% RHDew point (10.8°C)

Typical EC systems have saturation efficiencies in the 60%-90% range. If the wet bulb temp is 10°C lower than the dry bulb temp, an 80%efficient system can reduce temp by 8°C.

Athens, Greece

Las Vegas, NV

London, UK

Hong Kong, HK

Hong Kong, HK

Global warming moves everything UP and to the right

Hong Kong, HKDanger zone (30°C) Death zone (35°C)

Limits of human survival

With a wet bulb temperature of >35°C, if you– Are young and otherwise healthy,– well-hydrated,– resting,– in the shade,– and completely naked...

... you’re still going to die.● Non-human homeothermic animals have higher body temperatures,

but less area for evaporative cooling. A single day with a WBT of 35°C would likely cause mass extinctions.

Currently close to RCP8.5 (2.6°C to 4.8°C expected warming by 2100)

https://twitter.com/peters_glen/status/1107923815508701184

... but hopefully that will change soon, as RCP8.5’s emissions assumptions are more extreme and somewhat unlikely over the long term

Peak annual wet bulb temperature (today)

Peak annual wet bulb temperature (10°C increase)

Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Slide 32Slide 33Slide 34