I think the idea to create clouds over the oceans by these scientists is an excellent idea, but I do not agree that they should necessarily be brighter. It is a good idea because about 93% of the heat gain is gain into oceans. Creating mist clouds will reflect the light, but clouds are good absorbers of infrared (very roughly 50% of solar energy is infrared), so the clouds will evaporate. These clouds will prevent a lot of solar radiation entering water, because water is a good absorber of just about all solar radiation. Having mist clouds would be fairly natural and evaporation of these would increase relative humidity, which is good for drought areas and for making more clouds, which would reflect sunlight. If ordinary mist clouds are made rather than very white ones I think absorption of solar radiation and more cloud formation will result. However they aim to get other data and information from the creation of the very fine droplets, so perhaps this is a very necessary part of the experiment.
What I think will happen with the generation of the clouds is that the air will cool rapidly because the droplets are to be fine (the air could cool to near wet bulb temperatures - see mist cooling) and they will need some method of getting the cloud to rise (they say they will spray it high into the atmosphere). I think if they generate hot steamy air around their cloud generator the droplets might not evaporate and could rise high. Perhaps they have ideas on how to get the spray to move high up. Possibly they could have hot steamy droplets (heat the water before making the spray).
Again I mention my Rain Enhancement steam generator as a means of producing hot humid air- see below:
But if your air parcel is at, say, 21 deg C and the surrounding air is at 20 deg C, you can expect immediate acceleration upwards of about 0.03 m/s^2. If your air parcel is saturated you might find that this parcel eventually moves upwards (the moist adiabatic lapse rate situation) at about 5 m/s. Evaporation and heating by solar energy absorption would, in my opinion, be very difficult to control.
If the parcel of air with fine droplets in is colder, it will sink. It seems that when it reaches the sea and becomes fairly stationary, you could use a terminal settling velocity formula depending on the size and density of droplets, etc, to calculate the velocity of descending droplets. If the top of the cloud is not flat, parts will be differently heated by the sun.