The overall goal of this experiment is to study the refrigeration performance of a solar adsorption system with a solar collector trough. This method can help answer key questions in the solar adsorption cooling field, such as how to improve the coefficient for performance and the specific cooling of the power of the system. We first had an idea for this method a few years ago, when we considered how to reduce the cooling environment by making use of solar energy.
This is the solar adsorption refrigeration system on the campus of Beijing University of Technology. A principle component is an adsorption bed at the focus of a solar trough collector, with a solar tracking device. The bed is connected to a condenser and an evaporator.
The evaporator is seated on a water tank that will be cooled by the system. A circulating water loop can cool the adsorption bed. The connections among these elements are in this schematic.
The adsorption bed is connected to the evaporator and condenser by tubing. A pressure gage monitors the pressure in the adsorption bed tube. A valve can isolate the adsorption bed.
To release water vapor from the adsorption bed, open this valve and the one at the condenser. Close the condenser valve and open the evaporator valve when it is time for the adsorption bed to take in water vapor. A pump establishes a vacuum in the tubing, connecting the bed evaporator and condenser.
When necessary, the circulating water loop cools the adsorption bed. Details of the adsorption bed are in this schematic. There is an outer glass tube.
It is concentric with the solar-adsorbing tube. Between the two is a vacuum. Inside the solar-adsorbing tube is a concentric copper tube for the water cooling system.
This cross-section reveals that there is a mass-transfer channel off the central axis. The region between the solar-adsorbing tube and the interior tubes is packed with adsorbent material with water as the refrigerant. There are temperature probes in the adsorbent material at different points in the system.
Two are 140 millimeters from one end of the system. Five are arrayed at the middle of the system. Two more are 140 millimeters from the other end of the system.
To begin the cycle that results in refrigeration, start with the solar trough aligned to track the sun. Manually adjust the trough to maximize its exposure to the sun, then move to isolate the adsorption bed and ensure the pressure of the bed and the tube is below 800 pascals. Do this by shutting off the valve connected to it.
Ensure that all valves are closed and that no cooling water circulates, then start the controller for the solar tracking system. Over time, the system tracks the sun, which heats the water-saturated adsorption bed under closed conditions. As the trough moves, monitor the bed pressure with the pressure gauge.
Wait for a pressure above the value for the condensation temperature of the environment. At an appropriate pressure, start the desorption process. Open the valves that allow a connection between the bed and the condenser.
As the water vapor flows, maintain solar heating to the adsorption bed. When the bed and condenser pressures are the same, turn off the valves between the bed and condenser. Next, obtain an aluminum foil sheet, enough to cover the adsorption bed.
Use it to shield the tube from solar radiation, in order to start the adsorption process. Open the circulating water loop to cool the adsorbent material. Monitor the bed pressure to identify when it is below the evaporator's saturated vapor pressure.
At that point, open the valves between the bed and the evaporator. Let the water vapor rush into the bed. Continue the adsorption process and record the change in bed temperature and bed pressure.
When the bed and the evaporator have equal pressures, close the valves connecting the two. Then, stop the flow in the water loop. Finally, remove the aluminum foil block from over the adsorption tube to start the desorption process.
These data are from the nine temperature sensors over the course of the adsorption process, using SAPO-34 zeolite. The plots are for sensors nearest to the evaporator, at the center of the rod, and furthest from the evaporator. Plotted together, the data demonstrates that adsorption at different sections starts at almost the same time.
This suggests the mass-transfer ability of SAPO-34 is good. The water cooling system prevented temperatures from rising after about 400 to 600 seconds of adsorption, expect for at the far end of the tube. Different adsorption materials have different heat transfer properties.
These data-compared temperatures of SAPO-34 zeolite in blue and ZSM-5 zeolite in red during desorption. Solar intensity data for the two different trials do not suggest a great difference in heating. Despite this, the temperature increase in the ZSM-5 zeolite was 32 degrees Celsius, while that in the SAPO-34 zeolite was 17 degrees Celsius.
The ZSM-5 has better heat transfer characteristics in comparison with SAPO-34. Measurement of the evaporator chilled water tank temperature reveals the different adsorption materials have a performance difference. With the SAPO-34 zeolite, the temperature declined quickly and then slowed down.
The temperature change with the ZSM-5 zeolite was relatively smooth throughout. The advantage of this technique is that maleficent coolant is chilled through the enhance of the transfer in the solar adsorption bed. So, this method provides insight into the solar adsorption techniques.
It can also be a light into other systems, such as air conditioning. A master of this technique can be done into yours if it is performed properly. After you watch this video, you should have a good understanding of how to realize refrigeration, using only solar energy as the process.
Don't forget that working with the adsorption bed at high temperatures can be extremely higher death and the precautions, such as maintaining your distance from the bed, should always be taken while performing the procedure.
