Tang Yue rummaged through the boxes and took out several large sheets of polyethylene plastic film from the packing box, which were originally used to pack and wrap food, but now they are no longer needed.

He took the plexiglass sink on the workbench in his hand, put on the Mingguang armor, and waved to Mai Dong to leave Kunlun Station.

The old cat was standing on the edge of the pit, with a long-handled shovel, covered in dust and sand, looking into the distance with a face full of vicissitudes.

The pit has been dug with a diameter of about one meter and a depth of about half a meter, and the sand and gravel that have been dug out are piled on the side - the old cat is the old cat, a good hand at digging the pit.

"Say it." The old cat pointed to the pit at his feet, "How the hell do you use this pit to collect fresh water?" ”

Based on Tang Yue's answer, it will decide whether to bury this goods in this pit.

"Condensation." Tang Yue placed the plastic film and sink on the ground, and slowly leaned down to grab a handful of dirt from the pit, which was still very dry, mixed with hard siliceous and layered rock. Tang Yue picked up the shovel and began to trim the pit, he enlarged the bottom of the pit, removed the sharp gravel, and smoothed the pit wall and the bottom of the pit.

"What's the temperature now?" Tang Yue asked.

The old cat glanced at the sun in the sky, "It's minus thirteen degrees, and it's about to be noon, so the temperature is relatively high." ”

Tang Yue nodded.

"Here, do me a favor and unfold this plastic sheet."

Tang Yue and the old cat unfolded the smooth plastic film, and then flattened it on the pit wall at the bottom of the pit, they carefully flattened the plastic film, and the whole pit was tightly together, the LDPE plastic film was very soft, the plasticity was very good, and then Tang Yue put the sink in the center of the bottom of the pit.

"Is this sink for water?" The old cat asked.

"Yes." Tang Yue pulled the rubber tube that transported the fuel over and poked the glass Y-shaped tube at the end into the pit.

Tang Yue and Lao Mao unfolded the second piece of plastic film, they straightened and tightened the plastic sheet, completely covered the mouth of the pit, confirmed that there were no gaps and no air leakage, and pressed the edge of the plastic film with soil and stones.

Next, Tang Yue picked up a stone and gently placed it in the center of the film at the mouth of the pit.

Gravity crushed the plastic film slightly.

"It's done." Tang Yue clapped his hands, "This is a condensing device, and the speed is much faster than the condenser tube. ”

The old cat circled around the pit and understood Tang Yue's intentions.

It's really a condensing device, and as soon as they ignite the methane, the resulting water vapor rises and comes into contact with the cold plastic film - the ambient temperature of Mars is very low, which keeps the plastic film at the mouth of the crater cold, and once it cools down, the water vapor condenses into water droplets, and then under the action of gravity, it converges along the sloped surface of the film to the lowest point in the center of the plastic film.

All the water droplets collect here and end up dripping into the sink at the bottom of the pit.

The first plastic film was laid on the bottom of the pit to prevent water from falling into the soil, and the condensation device was almost completely enclosed, so that water vapor would not leak out, and all the water would either fall into the sink or be intercepted by the plastic sheeting at the bottom of the pit.

"The whole plastic film is a condenser, and the bigger the pit, the more fresh water is collected." Tang Yue said.

The old cat pondered for a moment, "But it can't be too big, otherwise the water will freeze on the film, and the heat generated by methane combustion is limited after all." ”

Tang Yue was stunned for a moment, thinking about it carefully, this is indeed the truth.

The old cat turned and climbed onto the roof of the Martian stray dog and opened the valve of the pressure relief valve.

Tang Yue lay down, carefully lifted the corner of the plastic film, reached in and adjusted the height of the glass tube, he couldn't let the methane flame get too close to the plastic film, after all, the polyethylene material is not heat-resistant, and it melts as soon as it is baked, and then Tang Yue lit the methane with an arc lighter.

The old cat and Tang Yue gathered around the edge of the pit, staring intently at the plastic film.

The LDPE film is transparent, and through it, Tang Yue can see the pale yellow flames burning in the pit.

He was a little nervous, no one knew if this method would really work, but fresh water was too desperate for resources, and if this method failed, they would have to find another way to collect fresh water.

Five seconds later.

A fuzzy mist of water was applied to the transparent plastic film, and the moisture gathered at a very fast rate, and soon large droplets of water appeared, and they flowed slowly along the plastic film.

Tang Yue and the old cat both sat down on the sand and let out a sigh.

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Tang Yue and Lao Mao calculated that if they collected fresh water in this way, they should get an average of three to five liters of water per hour - it depends on the rate of burning of the propellant, and if Lao Mao increased the dose of methane and liquid oxygen, then more water vapor would be produced.

Of course, this increase cannot be unlimited, and the flame of methane will burn through the plastic film with a higher dose.

After an hour and a half, the sink was full, and the old cat took the sink out of the bottom of the pit and immediately returned to Kunlun Station, but the water in the tank began to freeze as soon as it was exposed to the air, and by the time the old cat closed the hatch of the airlock, a thick layer of ice was already floating on the surface of the tank.

They fumbled to find a suitable collection speed.

The old cat drove Tang Yue back as usual, so as not to waste the power of the Mingguang armor, and it sat on the edge of the pit to take care of the condenser.

Tang Yue maintains the OGS system and the water recycling collection system at the Kunlun station.

"The flow rate of three cubic centimeters is too slow, and the temperature of the flame is not high enough." The old cat's voice came from the headphones, "The water at the edge of the film is completely frozen, and I think the temperature inside the pit is best to maintain it between zero and five degrees...... I should go get a thermometer. ”

"Then you increase the dose of methane." Tang Yue opened the lid of the OGS cabinet and carried a wrench in his hand, "Enlarge it to five centimeters." ”

"Hmm...... It has grown to five centimeters, and the fresh water is collected twice as fast as before, but the water at the edges of the film still shows signs of freezing. The old cat's voice rang out, "The temperature at the bottom of the pit is ...... At minus 1 degree Celsius, the temperature of the pit wall is still below zero. ”

"The temperature in the pit is uneven?"

"Well, it's not even." "After all, the heat source is only methane flames, and the hot air flow is rising, so the air in the upper layer of the pit heats up faster than the surrounding and bottom, so we had better speed up the heating rate." ”

"Then increase it again."

Tang Yue closed the lid of the OGS system cabinet, patted the old guy, and turned his head to look out.

He saw in the distance that the old cat was climbing down from the Martian stray dog, and the movement was very neat, it should have just unscrewed the pressure relief valve of the propellant.

The cat pouted and lay on the ground, lifted the plastic film, and ignited the methane.

A second later.

"Bang!" There was a loud bang on the ground, and the fire flashed.