We might circulate antifreeze through an optional 12.5"x22.5" rectangular bladder under ice-cube trays in a small freezer http://www.walmart.com/ip/Igloo-3.2-cu.-ft.-2-Door-Refrigerator-and-Freezer/15162473 in series with the U-bladder, in order to cool the cooler without adding ice.
This system has adjustable flow rate temperature control, ie we can vary the pump flow rate manually to vary the cooling. A more advanced system could have an adjustable bladder thermostat to run the pump as needed and measure the dew point of the surrounding air and limit the lower bladder temp to avoid condensation. Air at T (F) (absolute temp 460+T R) and RH% has an approximate (T+460)/(1-ln(RH/100)(T+460)/9621))-460 F dewpoint. For example, 70 F air at 50% RH has a 530/(1-ln(0.5)530/9621))-460 = 50.5 F dewpoint.
If it's humid, air movement helps. The Berkeley online comfort calculator http://www.cbe.berkeley.edu/comforttool/ says 25.4 C (77.7 F) air with a 25 C mean radiant (wall) temp and a 0.15 m/s air speed and a 50% RH and a 1.2 metabolic rate and 0.5 clo clothing is comfortable (PMV = 0.01 on a scale of -3 (very cold) to +3 (very hot)). Increasing the RH to 60% makes the PMV = 0.08 (slightly warm.) Increasing the air speed to 0.17 m/s makes things comfortable again, with PMV = -0.01. So does removing some clothing, with PMV = -0.02 at 0.45 clo. See also http://sustainabilityworkshop.autodesk.com/buildings/human-thermal-comfort and http://wikihelp.autodesk.com/Simulation_CFD/enu/2014/Help/0083-Tutorial83/0334-Tutorial334 and http://www.labeee.ufsc.br/sites/default/files/disciplinas/Thermal%20Booklet.pdf
Losing weight also helps, allometrically-speaking, ie increasing our heat-losing-surface-to-heat-generation-volume ratio. The ASHRAE Handbook of Fundamentals says a W-pound animal generates P = 6.6W^0.75 Btu/h of heat, and a W pound x H inch tall person has A = 0.108W^0.425H^0.725 ft^2 of DuBois surface area, eg P = 289 Btu/h and A = 19.6 ft^2 for a 154 lb 68" tall ASHRAE-standard human, who might be dT = P/(1.5A) = 9.8 F warmer than surrounding still air if naked, with no sweating or shivering or other adaptations. Raising W to 200 lb makes P = 351 Btu/h and A = 21.9 ft^2 and dT = 10.7 F, with H = 68". A proportional height gain to H = 12.7x200^(1/3) = 74.2" raises A to 23.3 ft^2 and lowers dT to 10.0 F.
See also: http://theoatmeal.com/comics/running
Nick
Hi Nick,
ReplyDeleteA personal cooler is a nice, low energy idea. Lots of personal heaters out there, but have not seen any personal coolers.
If you could build one from the ground up, what would a good design look like?
The one you site looks promising, but I wonder about the delivery of the coolth to only small areas. Is that going to be comfortable.
This may be more than a matter of convenience and comfort for people on a small budget and ever hotter heat waves.
Seems like a good personal cooler would be a good thing to work on.
Gary
Hi,
ReplyDeleteActually, googling around, there are a few personal cooling devices/garments out there. But, maybe some room for improvement?
Gary
Gary wrote:
ReplyDelete>If you could build one from the ground up, what would a good design look like?
Peltier devices are improving with new materials, eg skutterites... http://www.academia.edu/467388/Measurements_of_Anisotropy_Thermoelectric_Behaviour_and_multi-Fractal_aspects_of_FeSi_and_of_complex_custom_made_TE_materialsPhase change garments and head sink hats and wooden bead backrests for car seats can also help. And cat litter dehumidification?
>I wonder about the delivery of the coolth to only small areas. Is that going to be comfortable.
Maybe. We don't want to freeze flesh.
>This may be more than a matter of convenience and comfort for people on a small budget and ever hotter heat waves.
The Phila Energy Coordinating Agency cites statistics showing that more elderly low-income people die in hot weather...
Nick
More...
ReplyDeletehttp://www.nbcnews.com/id/43400428/ns/technology_and_science-innovation/#.UUQhAnBUOxI
Skutterudite thermoelectrics
Recently, skutterudite materials have sparked the interest of researchers in search of new thermoelectrics[29] These structures are of the form (Co,Ni,Fe)(P,Sb,As)
3 and are cubic with space group Im3. Unfilled, these materials contain voids into which low-coordination ions (usually rare earth elements) can be inserted in order to alter thermal conductivity by producing sources for lattice phonon scattering and decrease thermal conductivity due to the lattice without reducing electrical conductivity.[30] Such qualities make these materials exhibit PGEC behavior.
The composition of skutterudites corresponds to the chemical formula LM4X12, where L is a rare earth metal, M a transition metal and X a metalloid, a group V element or pnictogen whose properties lie between those of a metal and nonmetal such as phosphorus, antimony, or arsenic. These materials could be potential in multistage thermoelectric devices as it has been shown that they have ZT>1.0, but their properties are not well known and optimization of their structures is under way.
from https://en.wikipedia.org/wiki/Thermoelectric_materials#Skutterudite_thermoelectrics
http://virtual.clemson.edu/TMRL/Publications/pdfs/s6_ltrp.pdf