Experimental Research On Promoting Sublimation Efficiency Of Freeze Frying Of Moisture Food Material

The main content of this paper is to search the approach to promotethe efficiency of sublimation process of freeze drying throughexperiments, the material has been used in the research is the middle partof herring, the main testing methods are overturn dystopia method andpunching guide method.The overturning dystopia method is to add an overturning processbetween the freezing stage and the sublimation stage of freeze drying.The main job of the research is to see how this method will affect theefficiency of sublimation velocity. Samples of the experiment was frozeby the layers of freeze drying machine, during the process of freezing,water would move towards the bottom of the sample so that waterdistribution inside the samples got to be uneven, the content of water washigher at the bottom of samples. But when freeze drying got to the stageof sublimation, vapor would escape from the upside of the samples, so thewater at the bottom of the sample which is the main part of the wholewater was difficult to get out, but if we add the overturn process afterfreezing, the situation has been totally changed, because most of thewater has been turned onto the top of the samples. And this is the basicprinciple of overturning dystopia method. Also influences of some otherconditions such as the initial moisture, the thickness of the sample, thefreezing velocity and the vacuum of the drying chamber have also beenconsidered. Meanwhile the experimental results reviewed that with60%initial moisture,6～8mm thickness, freeze under30℃and control thevacuum of the dry chamber at50Pa, the experiment could reach a goodeffect.Not only the inconsistency of the vapor escaping but also theeffective sublimation areas would influences the efficiency of freezedrying, so approaches which can add the effective sublimation area wereexplored and at last two different ways of doing this have been foundwhich are punching holes with different areas and preset hole area butwith different styles. So the punching guide’s method just focused on theinfluence of the surface areas and styles of holes, besides some otherconditions such as the thickness and the kind of the sample have alsobeen considered. For example herring fillets with the thickness of10mm, when the number of the holes increased from1to4, the increase of thevelocity of sublimation changed form7.25%to15.42%; meanwhile whenthe surface of the holes were controlled the same, when the number of theholes increased from1to4, he increase of the velocity of sublimationchanged form8.16%to16.38%.