Improvement Research On Partial Structure Of Chest Freezer

The operating temperature of normal chest freezer is very low,usually it can be-10to-30?.The low temperature thermodynamic characteristics may lead to certain troubles,such as “condensation on the outer surface”,“hard opening of the lid due to negative pressure caused by low temperature”,“cabinet deformation by thermal expansion and contraction”,“frost accumulating on inner surface” and other issues.These troubles shall bring inconvenience to users.This thesis tries to conduct a theoretical calculation and experimental study on two issues: condensation on the outer bottom surface of the chest freezer and vacuum trouble by negative pressure to the lid opening,explores the improvements of partial structure for chest freezer thermal characteristics,reduces user annoyance or improves the operation quality,provides useful ideas for the freezer designers.The bottom area of chest freezer is large and closed relatively.Effected by the heat transfer coefficient and environmental humidity,the temperature of bottom surface is lower than other normal areas.The traditional method for checking condensation possibility on refrigerator surface is not suitable for bottom surface of chest freezer,for it only checks the minimum thickness with no condensation with general thermodynamic theory and experience while does not consider the different structural characteristics of chest freezer.In this paper,the calculation model is established by collecting the history test data of the enterprise the writer works in,comparing the calculated data with the measured data,which verifies the availability of the model.This paper also studies the possibility of condensation under different heat transfer conditions and relative humidity,analysis effects of the foot height,ventilation,material and thickness of the insulationlayer etc.,which as main factors to condensation issue,has worked out the advantages and shortcomes of different measures and tried to provide good reference for designers.During the operation of the chest freezer,hot air enters into the cabinet when an user open the lid to get out or put in or check and arrange the articles in the cabinet;when the door closed,the temperature of hot air inside the cabinet drops accompanying with air pressure decrease,resulting in internal pressure is lower than the external atmospheric pressure,which called relative vacuum(negative pressure).At this point,it is difficult for the user to open the door lid.In this paper,by analyzing the relationship between the time and the change of the air pressure,it is found out that strong seal between the gasket and top frame of the chest freezer is the directly reason to the hard opening of the lid at the moment when the lid just closed.Therefore,in addition to the common measurement to release the vacuum pressure by air balance holes,an important means to solve this problem is to change surface characteristics of the gasket and/or the top frame.To find out the relationship between chest freezer vacuum pressure and time is more complex,in this paper a simplified alternative calculation is adopted.Through it,several time parameters shall be worked out,such as the time span when hard opening by vacuum pressure occurs after lid closed.A time remarks the hot air enters,a time shows the release of the air pressure through the air balance holes etc.Through the experimental verification of comprehensive measures for solving the negative pressure problem caused by the thermodynamic characteristics of chest freezer,mechanical structure improvement scheme shall be obtained.The significance of this subject is to work on thermodynamic mechanical structure characteristics of chest freezer which is rarely involved in public studies and articles.The study and research includes theory analysis on normal thermal characteristic troubles,studies the improvement scheme of the relative mechanical structure,and develops its theoretical foundation and solutions.In this paper,theoretic analysis shall be verified through history test data and new experiments,and then,the effective optimized solutions shall be determined.From these works,to develop ideas for structure design of chestfreezer can be widen.Although this paper only discusses two thermodynamic characteristics of the structure design of the chest freezer,the study method is common,other problems can also refer to a similar method to be analyzed and solved.