Tang Yue rummaged through the cabinets and pulled out several large sheets of polyethylene plastic. These sheets were originally used to pack food, but now they were no longer needed.
He then picked up the plexiglass water tank on the workbench, put on the Bright Light Armour, and waved goodbye to Mai Dong before leaving Kunlun Station.
Old Cat was standing at the edge of the pit, leaning on a long shovel. His body was covered in dust and sand, and he looked into the distance with a weary expression.
The pit had been dug. It was about one meter in diameter and half a meter deep. The sand and gravel that had been dug out were piled up at the side — Old Cat was indeed an Old Cat, an expert at digging pits.
"Speak," Old Cat pointed at the pit by his feet. "How exactly do you use this pit to collect water?"
Based on Tang Yue's answer, it would decide whether to bury him in the pit.
"Condense."
Tang Yue placed the plastic sheet and water tank on the ground. He slowly bent down and grabbed a handful of soil from the pit. The soil was still very dry, mixed with hard siliceous and layered rocks.
Tang Yue picked up the shovel and began to repair the pit. He widened the bottom of the pit, removed the sharp gravel, and smoothed the walls and bottom of the pit.
"What's the temperature now?" Tang Yue asked.
Old Cat looked at the sun in the sky. "It's -13 degrees Celsius. It's almost noon, so the temperature is a little higher."
Tang Yue nodded.
"Come on, help me unfold this plastic sheet."
Tang Yue and Old Cat unfolded the smooth plastic sheet, and then placed it on the bottom of the pit. They carefully flattened the plastic sheet, and it fit the entire pit perfectly. The LDPE plastic sheet was very soft and had good plasticity. Next, Tang Yue placed the water tank in the center of the pit.
"Is this water tank used to collect water?" Old Cat asked.
"Yes," Tang Yue pulled the rubber tube that was used to transport fuel over and inserted the glass Y-shaped tube at the end into the pit.
Tang Yue and Old Cat unfolded the second plastic sheet. They stretched the plastic sheet taut and covered the pit completely. After confirming that there were no gaps and that there would be no air leakage, they pressed the edges of the plastic sheet with soil and stones.
Next, Tang Yue picked up a stone and gently placed it in the center of the plastic sheet at the pit.
The force of gravity caused the plastic film to sink slightly.
"It's done," Tang Yue clapped his hands. "This is a condensing device, much faster than the condensing tube.."
Tomcat circled the pit and understood Tang Yue's intentions.
This was indeed a condensing device. As long as they ignited the methane, the water vapor produced would rise and come into contact with the cold plastic sheet. The ambient temperature of Mars was very low, which would keep the plastic sheet at the pit's mouth cold. Once the water vapor cooled down, it would condense into water droplets. Then, under the effect of gravity, the water droplets would gather along the inclined surface of the plastic sheet to the lowest point in the center of the plastic sheet.
All the water droplets would gather here and finally drip into the water tank at the bottom of the pit.
The first plastic sheet at the bottom of the pit was to prevent water droplets from falling into the soil. This condensing device was almost a completely enclosed structure. The water vapor would not leak out. All the water would either fall into the water tank or be intercepted by the plastic sheet at the bottom of the pit.
"The entire plastic sheet is a condensing device. The bigger the pit, the more water it can collect," Tang Yue said.
Old Cat pondered for a moment. "But it can't be too big. Otherwise, the water will freeze on the film. After all, the heat generated by the combustion of methane is limited."
Tang Yue was stunned for a moment. After thinking about it carefully, it did make sense.
Old Cat turned around and climbed onto the roof of the Mars Wanderer. He opened the valve of the relief valve.
Tang Yue crouched down and carefully lifted a corner of the plastic sheet. He reached in and adjusted the height of the glass tube. He could not let the methane flame get too close to the plastic sheet. After all, polyethylene was not heat-resistant and would melt as soon as it was baked. Then, Tang Yue ignited the methane with an electric arc lighter.
Old Cat and Tang Yue surrounded the edge of the pit and stared intently at the plastic sheet.
The LDPE film was transparent. Through it, Tang Yue could see the pale yellow flame burning in the pit.
He was a little nervous. No one knew if this method would really work, but fresh water was really a precious resource. If this method failed, they would have to find other ways to collect fresh water.
Five seconds later.
The transparent plastic sheet was covered with a layer of blurry mist. The water gathered at an extremely fast speed. Soon, large droplets of water appeared and slowly flowed along the plastic sheet.
Tang Yue and Old Cat both sat down on the sand and let out a long sigh.
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Tang Yue and Old Cat calculated that they should be able to collect three to five liters of water per hour on average. This depended on the combustion rate of the propellant. If Old Cat increased the amount of methane and liquid oxygen, then more water vapor would be produced.
Of course, this increase could not be unlimited. If they increased the amount of methane, the flame would burn through the plastic sheet.
After an hour and a half, the water tank was full. Old Cat carried the water tank out of the pit and immediately returned to Kunlun Station. However, the water in the water tank began to freeze as soon as it was exposed to the air. When Old Cat closed the hatch of the airlock, a thick layer of ice was floating on the surface of the water tank.
They fumbled around, trying to find a more suitable collection rate.
As usual, Old Cat drove Tang Yue back to avoid wasting the power of the Bright Light Armour. It sat alone on the edge of the pit to look after the condenser.
Tang Yue maintained the OGS system and the water circulation collection system in Kunlun Station.
"Three cubic centimeters of water flow is too slow, and the temperature of the flame is not high enough."
Old Cat's voice came from the earpiece. "The water at the edge of the film has completely frozen. I think the temperature in the pit should be maintained between zero and five degrees Celsius... I should get a thermometer."
"Then increase the amount of methane."
Tang Yue opened the lid of the OGS cabinet and held a wrench in his hand. "Increase it to five centimeters."
"Well... it has been increased to five centimeters. The freshwater collection rate is twice as fast as before, but the water at the edge of the film still shows signs of freezing."
Old Cat's voice rang out. "The temperature at the bottom of the pit is... one degree Celsius above zero. The temperature of the pit walls is still below zero."
"The temperature in the pit is not uniform?"
"Yes, it is not uniform."
Old Cat said, "After all, the only heat source is the methane flame. The hot air flow is rising, so the air in the upper layer of the pit is heating faster than the surrounding and bottom layer. We'd better increase the temperature."
"Then increase it even more."
Tang Yue closed the lid of the OGS system cabinet, patted the old man, and turned his head to look out.
He saw Old Cat climbing down from the Mars Wanderer in the distance. His movements were very nimble, and he must have just twisted open the pressure relief valve of the propellant.
The cat lay on the ground with his butt up, opened the plastic film, and ignited the methane.
One second later.
"Bang!" There was a loud noise, and the flames exploded.