MIX Flashcards
Isolation
➢Direct radiation
➢Diffuse radiation
➢Reflect radiation
extratessterial radiation
Earth’s orbit around the Sun is not a perfect circle but slightly elliptical. Due to this elliptical orbit, the distance between the Earth and the Sun changes throughout the year, which causes a variation in the intensity of the solar radiation received.
Collector field
Many collector troughs placed in parallel rows
Steering problem for troughs
You have to track the sun in 2 axises but it will be hard to execute this since its required to route the water and steam to and from the focus
Solutions to parabolic trough sun tracking systems
Flexible connections of oil and water
Types ofsolar thermal
Forced circulation (Active): Uses a pump to move water from the collector to the storage tank.
Gravity circulation (Passive): Relies on natural convection, where hot water rises and cold water sinks, to circulate water through the system.
Direct: The water that is used in taps and showers circulates directly through the solar collector, where it is heated by the sun.
Indirect: A heat-transfer fluid that does not freeze or boil easily circulates through the collector and transfers heat to the water in a separate storage tank via a heat exchanger.
Open (also known as open-loop): The water in the system is open to the atmosphere; this is common in warmer climates where there is no risk of the water freezing.
Closed (also known as closed-loop): The system is sealed and pressurized, which is necessary in climates where water could freeze, damaging the system.
Adv and disadv ofactive and passive circulations
active circulation
adv: Independent location ,Large systems
Dis:need pump, control , energyconsumption
Passive
adv: no pump no control simple indpendent
disadv: Dependant location between tank and collector , large pipe are required and small systems .
Direct and indirect adv and dis
Direct
Adv:No heat exchanger , No expansipn tank, Lowtemp loss
dis: corrosion ,stagnant water , deposition on collector
Indirect
Adv:Closedloop , no corrosion , no deposition
dis:needs heat exchanger , highertemp loss, expensive
Sacrificial Anode in metal tanks.
The magnesium rod is more “active” in electrochemical terms than the steel of the tank. This means that it will corrode, or “sacrifice” itself, before the steel does.
tank design
-Size
system temprature
* Orientation. Vertical or horizontal?
* With or without heat exchanger.
* Material
* Vented or unvented
Pump sizing based on
pressure drop and volume flow rate
Total pressure drop in a solar system =
Total pressure drop in a solar system =
Pressure losses across collector array +
Pressure losses in pipe runs +
Pressure losses in fittings and other components +
Pressure losses in heat exchangers
Stagnation temprature
The stagnation temperature in a solar collector is the highest temperature that the collector can reach when there is no fluid (like water or antifreeze) moving through it to carry away the heat
ut since the heat isn’t being transferred away by the circulating fluid, the temperature inside the collector keeps rising. This temperature can get very high, potentially causing damage to the collector’s materials or reducing its performance over time.
Expansion vessel
as the water volume increases due to heat, it pushes into the expansion vessel. The gas on the other side of the diaphragm gets compressed, which absorbs the extra pressure without a significant increase in the system’s overall pressure. This helps in stagnation temperature as the vessel will accommodate for the fluid expansion and rising pressure
The drainback system
the drainback system is a safety feature in solar thermal systems that prevents water from freezing inside the collectors by allowing it to drain back into a reservoir when not in use. It also manages the expansion of water when it heats up, preventing pressure build-up that could damage the system.
