Development of experimental apparatus for measuring heat transfer coefficient of steam condensation surface under natural convection
[Objective]The surface heat-transfer coefficient represents the heat transfer per unit time per unit heat transfer area under a unit temperature difference,which can be used to measure the difference in the performance of various convective heat transfer processes.Measurement of the surface heat transfer co-efficient is crucial.Several experimental devices for measuring the heat transfer coefficients of steam condensation surfaces under natural convection have been developed for undergraduate experimental teaching to enable students to systematically study the main factors affecting the heat transfer process and master the essence of the convective heat transfer process.[Methods]To determine the heat transfer coefficient of the steam condensation surface under natural convection,water vapor was passed through a set of pipes with different surface states.The pipe was cooled naturally over a large space.As the material,geometry,contact mode,and airflow outside the pipe affect the heat transfer effect to different degrees,the factors affecting the heat transfer process can be methodically and systematically analyzed by measuring the heat transfer coefficient of each pipe.This experiment is a required part of the engineering heat transfer experiment course.The contents of this course include experimental research on the influence of pipe material on the heat transfer coefficient,experimental research on the influence of different finned structures on the heat transfer coefficient,experimental research on the influence of pipe cross-section geometry on the heat transfer coefficient,and experimental research on the influence of pipe insulation material on the heat transfer coefficient.[Results]The following results were obtained from the experimental data.① Under the condition that the steam flow rate,geometry,diameter,wall thickness,and length of the heat exchange tube are the same,the comprehensive heat transfer performance of each heat exchange pipe with different materials is ordered from highest to lowest:copper tube>aluminum alloy tube>stainless steel tube>titanium alloy tube.② Under the condition that the steam flow rate,base tube material,geometry,diameter,wall thickness,and length of the heat exchange tube are the same,the comprehensive heat transfer performance of each heat exchange pipe with different fin structures is ordered from highest to lowest:large annular ribbed tube>spiral ring ribbed tube>straight ribbed tube>needle ribbed tube.③ Under the condition that the steam flow rate,base tube material,equivalent diameter,wall thickness,and length of the heat exchange tube are the same,the comprehensive heat transfer performance of each heat exchange pipe with different cross-sections is ordered from highest to lowest:square tube>rectangular tube>circular tube>oval tube.④Under the condition that the steam flow rate,base tube material,diameter,wall thickness,and length of the heat exchange tube were the same,the thickness and length of the insulation material were the same.The comprehensive heat transfer performance of each heat exchange pipe with different insulation materials was ordered from highest to lowest:perlite insulation tube>sawdust insulation tube>ceramic fiber insulation tube>glass fiber insulation tube.⑤ The error between the experimental and theoretical calculation values of the heat transfer coefficient of the steam condensation surface in the horizontal tube was approximately 15%,indicating that the test accuracy of the developed experimental device was high.[Conclusions]The developed experimental device provided strong support for undergraduate teaching.Application practice shows that the content of this experiment is comprehensive,which greatly improves students'enthusiasm in class and has a good teaching effect.
steam condensationheat transfer coefficientexperimental projectteaching effect
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