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A maximum heat duty of 2.78 kW and a maximum overall heat transfer coefficient of 1000 W/m2K were achieved during the experiments .
 concept or principle: heat; concept or principle: heat transfer
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:
 concept or principle: heat; concept or principle: heat transfer