Sunday, August 27, 2017

Preventing flooding

In the tropics strong solar energy creates strong convection. So you will find that rain occurs frequently in areas near the equator and this convection and frequent rain dries out the air (the water vapour becomes rain). This results in higher level clouds - Espy’s equation says that the height of cloud bases = 125 (temperature- dewpoint temperature). To explain, the dewpoint temperature is the temperature near ground level in this equation and the temperature is the ambient temperature near ground level. The answer is in metres. Now if you had solar air heaters on every rooftop and on poles in the cities, it is my belief that you would have far greater convection and more frequent rain. This would dry the air and prevent flooding, but you would often get rain in smaller amounts. One reference that discusses this phenomenon of frequent rain and higher level clouds is “Understanding the sky” by Dennis Pagen and it can be found on the internet. To build your own solar air heater see

Thursday, August 24, 2017

Urban heat island effect and cool paints

A lot of people are asking about how the cool paint works. Looking at one photo, it appears fairly dark so the paint is absorbing some light energy. All components of sunlight, if they are absorbed, heat a surface. So untraviolet heats, visible light heats and infrared heats if they are absorbed. We cannot see the ultraviolet and we cannot see the infrared, so we do not know if they are being reflected instead of being absorbed by looking. If something is white we know it is reflecting the visible portion of sunlight (about 43% of the energy from the sun is visible energy). may help. Green vegetation does shade and also does reflect infrared, so trees are a good option. I am an advocate of using solar air heaters on poles to shade streets. By the conservation of energy, if air is heated by solar air heaters, other objects can not be heated with the same energy (can either be in air or in the other objects). My understanding of this paint is that it reflects infrared. With an urban heat island effect, the sunlight (includes infrared and ultraviolet) enters the city and gets reflected around onto walls and so on. They absorb the sunlight to some extent and heat up. The sunlight coming in has mainly short wavelength. After buildings heat up they emit radiation of a longer wavelength. Some of this longer wavelength radiation will probably be reflected by the paint and some will go out to space. The infrared of sunlight is high frequency (short wavelenth ) infrared. The heated buildings emit longer wavelength infrared radiation, mainly. With white cool roofs some sunlight is reflected onto other buildings causing heat problems. One of the big problems can be windows with sunlight entering. Window glass transmits radiation up to about 2.5 microns (the energy goes through the glass if its wavelength is less than about 2.5 microns) and about 97% of solar energy has wavelength less than 2.5 microns, so virtually all enters via a window.
Now how much of this energy escapes? Well if the walls heats up to 50 deg C, then radiation from them that is above 2.5 microns will not escape. The answer is that far less than 1% of this radiation can escape through the glass because more than 99% of the energy radiated by the 50 deg C walls is of wavelength greater than 2.5 microns (using a blackbody approximation). If a particular cool paint does reflect infrared, where is the infrared radiation going to go? Remember angle of incidence= angle of reflection. One may note that green vegetation reflects solar energy of wavelength between 0.75 to 2.4 microns significantly. Most of this could be reflected through your window into your house (glass lets in radiation of wavelength less than about 2.5 microns). This radiation would heat up objects and the radiation from the hot objects would not be able to get out through the window again (wavelength too long). About 42% of solar energy is energy of wavelength 0.75 to 2.4 microns.
Note that: 

1) Radiation of less than about 2.5 microns in wavelength can enter via ordinary glass windows. About 96.6% of sunlight (solar radiation) is energy of wavelength less than 2.5 microns.
2)  If you have black roads and they heat up in the sun, almost all of the radiation from the hot roads will NOT be able to enter through windows (wavelength too long) and so this helps cool houses regarding radiation, but hot roads do warm the air above them by conduction.
3) If you have trees, a significant amount of sunlight reflected from trees will be able to go through windows into your house (reflected radiation between 0.75 and 2.4 microns in wavelength by green vegetation is significant - see ). About 42.4% of solar radiation is radiation of wavelength 0.75 to 2.4 microns. But, because of evapotranspiration, trees also cool.
4) With the usual black roads, almost all solar energy is absorbed (this makes these roads and air immediately above it hot), but there is little reflection of solar energy into your house from the standard black roads.
5) With "cool surfaces paint" solar energy can be reflected into your house through windows.
6) Once radiation has entered your house via windows it heats objects, which then radiate energy of a wavelength that cannot exit your house via windows (except for a tiny amount).
7) We can usually make a rough approximation and treat bodies as blackbodies. Any blackbody radiates heat in mainly the infrared range, if it has a temperature of less than 100 deg C or so. Radiation from a 100 deg C blackbody "peaks" at about 7.8 microns. Light (visible) is in the 0.4 to 0.76 micron range. Infrared radiation has wavelength longer than about 0.76 microns.
8) If the "cool paint" reflects solar radiation of wavelength between 0.76 microns and 2.5 microns (which it almost certainly will, unless it is whitish and reflects the light portion), then that radiation can enter buildings through windows and the heat will generally remain trapped in the building (will not be able to come out via windows). About 41.8% of solar radiation is radiation of wavelength between 0.76 and 2.5 microns. 
9) If the cool paint is the old style white paint that reflects the light portion, then that radiation can enter buildings through glass and remain trapped as lower frequency radiation after heating objects in the house. About 43% of sunlight (solar radiation) is light energy.
10) Using a blackbody approximation, if a dark road heats up to 60 deg C, then about 39.1% of the radiation from this dark road is radiation having wavelength between 8 and 14 microns (could escape to space via the atmospheric window).
11) With reflection from smooth surfaces, angle of incidence=angle of reflection.
12 ) With dark roads that heat up a lot in the sun, the air above these roads is heated. This can result in higher than usual cloud formation and convectional rain. Cloud formation can drastically reduce the heating up of cities by shading them. The cloud itself radiates heat to space and low clouds in low latitudes cool Earth.

CONCLUSION: It there is a large area of buildings consisting of windows and the sun is not directly overhead, reflection of light and higher frequency infrared radiation into buildings could cause more problems than dark coloured surfaces. Using solar air heaters on poles to shade streets would get rid of heat. By the conservation of energy, if air is heated by solar air heaters, other objects can not be heated with the same energy (the heat can either be in the air or in other objects).

Monday, August 21, 2017

Steam solar updraft tower

Drought and fires and heat: Recently there have been reports of fires and heatwaves in Nigeria, Kuwait city, California, etc. When the ground absorbs solar radiation it heats up and heats up the air above it, making the whole area hot. If you shade the ground with solar air heaters, mirrors, and so on and transfer this heat to water or air, you can move the heat away from the ground to higher regions where it dissipates. So you could use mirrors to reflect solar energy onto a container of water and feed the steam produced into a solar updraft tower or you could heat air with solar air heaters and feed it into the tower, or do both. The process of rain making with evaporation at ground level (cooling) and condensation high up (producing heat of condensation) moves heat from the ground to higher altitude (a well known ocurrence explained in physical geography books and so on). When clouds form,  they can reflect solar energy back to space, reducing solar energy to the ground by 50% or so. People have been advocating solar updraft towers, but so far not much has been done. They can be used for energy supply and convectional rain formation. The design usually mentioned has a greenhouse at the bottom providing hot air. My concern is that air does not come into intimate contact with hot surfaces with a greenhouse, and if the hot air is not transferred quickly, there will be heat losses through the glass of the greenhouse and so on. 
Air is not heated much by radiation, but it is heated efficiently by direct contact with hot surfaces. I therefore propose that solar air heaters be used for the "base" of the solar updraft towers, rather than greenhouses. With greater efficiency one would not have to have such a large area (the greenhouse needs a huge area). Also, with solar air heaters, the heaters can be mounted vertically, saving huge space. See photo.
President Trump is trying to save oil, gas and coal jobs and so on, so it seems oil is here to stay for a while, in the US anyway. If one could use oil and gas at night to heat water and feed moist air or steam into the solar updraft tower, one could increase the chances of convectional rain. With gas and oil to heat water, the tower could become a steam method electricity generator and rain maker at night. One could heat seawater if one is close to the sea. Trees could be grown in the deserts using this method, making it fairly "green". 

I did some calculations as to ground surface temperatures with and without shade. I used the following for my calculations:
          1) Solar absorptivity of sand/soil  0.5
2) Emissivity of sand/soil 0.75
              3) Convective coefficient (calm day) 12 W/m^2.K
            4) Effective sky temperature 0 deg C
5) Air temperature 35 deg C
6) Solar radiation onto soil/sand (direct and diffuse) 900 W/m^2 without shade and only 200 W/m^2 (diffuse radiation) with shade
ANSWERS: Without shade the ground temperature is about 52 deg C and with shade the ground temperature is about 32 deg C (assuming the ground insulates fairly well).

CONCLUSION: The shading by mirrors, solar air heaters and so on will make a big difference to ground and surrounding air temperatures.
For solar heater information see

Saturday, August 5, 2017

Rain with sea temperatures higher than land temperatures

I was interested to read about "The Slow Food Movement" and about "Campesina" in an "The Conversation" article, who are helping small scale farmers. But drought can affect small scale farmers badly. UAEREP (can be found on Facebook) is working with rain enhancement methods and I have my own rain enhancement methods. I hope what I say below will help countries lessen the effects of drought:
With global warming land is heating up faster than the sea and air blowing from the sea heats up more and the relative humidity (RH) drops more when air blows from sea to land.
Consider two cases:
1) If land temperatures are higher than sea temperatures, then air blowing from land to sea is cooled by the sea, its RH increases and water can condense out and it could rain over the sea. With high RH evaporation into air is reduced and the air will not pick up much moisture. When the air blows back with sea breezes it will have very little extra moisture in (it could have less).
2) If the land temperatures are cooler than the sea, then when air blows from land to sea the sea heats up the air and RH drops and the air readily takes up moisture from the sea, so that it has more moisture than it started with and when it blows back with sea breezes it will decrease in temperature over cooler land and and rain can occur from condensation.
Solution: So here is a solution. Make more spray (mist) over the sea with floating spray pumps operated by wave motion. Solar energy will be absorbed by the spray mist and evaporation will occur as the mist heats up. Then this moist air could supply rain when it blows to land. If possible, reflect solar energy from the land onto the mist that is generated over the sea, using mirrors.  

It takes less than 1 kWh to evaporate 1 litre of water. Now in sunny areas, every day, we can get more than 8 kWh of solar energy falling on every square metre. If the mist absorbs 1/8th of this, there will be 1 kWh of solar energy every day on every square metre, to evaporate the mist and heat the air that the mist is in. It seems we could evaporate 1 litre on every square metre every day. This is a significant amount of water to put into the air, and a 1 km by 1 km square could supply 1000x1000 = 1000000 litres per day to the air. By comparison, at 25 deg C and a relative humidity of 50% a column of air with base of 1 square metre and a height of 200 m has 2.3 litres of water in (evaporated water actually). At the same temperature, but with a relative humidity of 72% this column has 3.3 litres in (1 extra litre). Humid air has two advantages I can think of: 1) Humid air is less dense than dry air at the same temperature and pressure and rises (which can result in convectional rain). 2) Humid air can be heated by infrared radiation from the ground, causing it to rise - water is a greenhouse gas and this heating is part of the greenhouse effect.

Friday, August 4, 2017

Reduce heat wave harm with solar air heaters

Humid Heat Waves Will Top Limits of Human Survivability 
Heat danger in coming years. But warm humid climates have one advantage - it might easily be possible to create convectional rain, merely by heating the air. Usually the solar energy goes into heating ground and air, but with solar air heaters the ground is prevented from heating because solar air heaters shade the ground. Most of the energy would go into heating the air, so we could have massive convection and rain. The clouds formed would reflect and radiate solar energy back to space. This is especially so with low clouds in low latitudes. See
on how to build a solar air heater. We could have huge solar air heaters on every roof.
Using Espy's equation shows that with high relative humidity, low clouds form.
H = 125 (T-Tdew), where H is the height of the base of the clouds, where T is the temperature (deg C) of the parcel at near ground level and Tdew is the dew point temperature at near ground level. With high relative humidity Tdew is close to T. The formula gives the altitude of the cloud base in metres.The heated air parcel that we are applying the above formula to is the air heated by the solar air heaters.
Example: The temperature of the air parcel heated by all the solar air heaters is 45 deg C. The dew point is 35.9 deg C.
Then H=125(45-35.9) = 125x9.1=1138 m.
The whole process of causing the rain takes heat away from near the ground and moves it higher up. It also removes water vapour from the air, dehumidifying the air (the water vapour has become water). In the tropical forests the temperature usually stays below 35 deg C or so because evaporation reduces temperatures near the ground.

The present design has a greenhouse at the bottom providing hot air. My concern is that air does not come into intimate contact with hot surfaces with a greenhouse and if the hot air is not transferred quickly, there will be heat losses through the glass of a greenhouse and so on. Air is not heated much by radiation, but it is heated efficiently by direct contact with hot surfaces. I therefore propose that solar air heaters be used for the base of the solar updraft towers, rather than greenhouses. With greater efficiency one would not have to have such a large area (the greenhouse needs a huge area). Also, with solar air heaters, the heaters can be mounted vertically saving huge space. See
Example on air pollution: Kathmandu has an air pollution problem and solar air heaters could be used to cause convection and dilute the air pollution. Kathmandu, in winter, has about 4.2 kWh of solar energy falling on every square metre in a day. Because of a fairly high altitude, the air pressure is about 87 kPa (instead of 101.325 kPa). With a temperature of 25 deg C, 4.2 kWh could heat 2954 cubic metres of this low pressure air by 5 deg C. If a one square metre solar air heater was 50% efficient, it could heat 1477 cubic metres of air by 5 deg C every day. In summer Kathmandu has about 7.6 kWh of solar energy falling on every square metre every day.
VOLUMETRIC HEAT CAPACITY OF AIR: I had a hard time finding figures for the volumetric heat capacity of air. They will be useful for calculating how many cubic metres of air at a certain temperature and pressure of 101.325 can be heated by a solar air heater, for example. I calculated the figures using Specific heat of mixture of gases=sum of (mass fraction x specific heat of each gas). I then calculated the mass of a cubic metre of air with RH=50% for various temperatures and multiplied specific heat by mass of a cubic metre of air with RH=50 and P=101.325 kPa at various temperatures. The RH makes very little difference to the volumetric heat capacity (although it does make a bigger difference to the specific heat). For instance the volumetric heat capacity of dry air at 35 deg C at P=101.325 kPa=1.154 kJ/degC.m^3 and the volumetric heat capacity for an RH=50% parcel at the same temperature and pressure is 1.159 kJ/degC.m^3.