Tuesday, January 9, 2018

Rain by humidification above the ocean.

Above shark nets, about 20 m above the ocean, have thick pipes with thousands of holes in that water streams out. Water can be pumped into the pipes using wind turbines. If the wind is blowing at 10 km per hour and the pipes are 1 km long, then the volume of air humidified in an hour is 1 km x 10 km x 0.02 km = 0.2 cubic kilometres.
In a day this is 4.8 cubic km of air. Nights are warmer with more humid air and I am going to use this as an example: RH=65% and Tair=20 deg C before humidification. RH=80% and Tair=22 deg C after humidification (the air will be blowing back and forth with land and sea breezes). Before humidification the water vapour content of the air is 11.2 grams/cubic metre and after humidification it is 15.5 grams/cubic metre. This is an increase of 38%. This relies on the fact that more humid air will keep in heat from the ocean when air is colder than the ocean. See 
http://www.asterism.org/tutorials/tut37%20Radiative%20Cooling.pdf

The heat from the ocean will help humidify. Air is usually colder than the ocean at night. During the day any mist will absorb solar energy and heat up and evaporation will occur. 

Thursday, January 4, 2018

Easy wet bulb temperature determination

People have been searching on the Internet for an easy way to calculate wet bulb temperature (and so have I). Experts give various long calculations and I wanted an accurate value easily calculated. I had a lot of trouble searching on various forums and eventually found a site that uses an equation that can be solved numerically that gives me an accurate answer, but the formula did not work unless I changed the P units from hectopascals to atmospheres. So instead of 1000 hPa I use 1000/1013.25. I solve numerically using a computer program I wrote to get Tw (wet bulb temperature). The formula is at
and I notice that P is included in one equation and left out in the next equation. However if you use atm it should work well with P included in both. The formula gives RH, but you can find Tw numerically. Say you are trying to find the wet bulb temperature for Td=45 deg C and RH=67%. Then let RHS=formula given and start with Tw=45 (represents RH=100%) and decrease Tw iteratively until RHS<=67. Find Tw at that point.

You can use a wet bulb calculator to check how accurate the above formula is (pretty good).
Your inputs into the program will be Td, RH and P. (P in atm). (Td is dry bulb T and Tw is wet bulb T.)

Code in Pascal:
Tw:=Td;
repeat
Tw:=Tw-0.001;
A:=611.2*exp(17.502*Tw/(240.97+Tw))-66.8745*(1+0.00115*Tw)*P*(Td-Tw);
B:=6.112*exp(17.502*Td/(240.97+Td));
RHS:=A/B;
until (RHS<=rh);

{Now print Tw}