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The heat exchanger was tested using nitrogen ( N2 ) on the hot-side and air on the cold-side as the working fluids .
 machine or equipment: heat exchanger; material: nitrogen; material: N2; material: as; material: fluids
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: manufacturing standard, machanical property, manufacturing process, material, engineering feature, process parameter, machine or equipment, application, process characterization, enabling technology, biomedical, concept or principle 
Text: {0} 
Answer:
 machine or equipment: heat exchanger; material: nitrogen; material: N2; material: as; material: fluids