真空冷凍乾燥機 (VFD) 是一種干燥技術，其基本概念/原理涉及直接將冰變成蒸汽形式或簡稱為昇華。該過程也稱為凍乾。通過昇華，我們知道在 0.01 攝氏度的特定溫度和 611.657 帕斯卡的蒸汽分壓下，水以所有三種形式存在。這被稱為水的三相點，並使用三相圖顯示。只有當我們將溫度降低到三相點以下時，水才會進入固態，因此通過將壓力降低到 0.1 托到 0.3 托左右的非常低的值，水將在特定環境條件下恢復到最低溫度。現在將在密封室內進行傳熱概念。由於相應溫度的壓力差，固體內部水分子的運動以及來自溫度較高的腔室壁的熱量，所有三種傳熱形式即傳導，對流和輻射都會發生。所有這些都會使產品溫度從其最小值緩慢升高，當它與軸的溫度相交時，我們就可以說水的干燥完成了。這也稱為初級乾燥。在純水的情況下，我們可以說達到完全乾燥的水份，但在水果和蔬菜等含水量高的樣品的情況下，將有另一個步驟稱為二次乾燥。這將從樣品中去除小於總體積百分比的剩餘水，因為使用初級乾燥去除了大約 90%-95% 的大部分水。我們實驗室做了一系列實驗來驗證確定的終點，使用兩種方式，一種是在上面移動，另一種是通過確定室內濕度。當濕度變為 0% RH 時，表示乾燥完成。我們從我們的實驗中完全驗證了這兩種方法。已根據實驗結果和數學建模得出結論。在工藝開發之後，已經探索了食品的應用。選擇不同厚度的蘋果切片來研究其工藝和應用。真空冷凍乾燥機通過增加4個加熱器進行改造，以提高效率和節能。在不同的樣品溫度下進行實驗，最後進行感官評價以更好地了解乾製品。

Vacuum Freeze dryer (VFD) is a drying technique which works basically on the basic concept/ principle which involves directly changing ice to vapor form or in short, Sublimation. This process is also known as Lyophilization. From secondary, we know that water exist in all three forms at a particular temperature of 0.01-degree Celsius and partial vapour pressure of 611.657 pascal. This is known as triple point of water and is shown using 3 phase diagrams. There only if we reduce temperature below triple point water gets in its solid state and thus by reducing pressure to very low value of around 0.1 torr to 0.3 torr, water will get back to its minimum temperature in particular environmental condition. Now inside a sealed chamber concept of heat transfer will take place. All three form of heat transfer that are conduction, convection and radiation will take place due to pressure difference for corresponding temperature, movement of water molecules inside solid and heat from walls of chamber which is at higher temperature respectively. All this will slowly increase product temperature from its minimum value and when it will intersect with temperature of shaft then we can say that drying of water is complete. This is also known as primary drying. In case of pure water this is the point where we can say that complete dry out of water is achieved but in case of sample like fruits and vegetables which has high content of water, there will be another step called as secondary drying. This will remove remaining water from sample which is less than percent of total volume as majority of water around 90%-95% get removed using primary drying. We in our lab have done series of experiment to verify end point of determination using two ways that are one motioned above and other by determining humidity inside chamber. When humidity becomes 0% RH, it means drying is complete. We from our experiment have verified both methods altogether. Conclusions have been made based on experimental results and mathematical modelling. After process development, application has been explored with food stuffs. Different thickness of apple slices has been chosen to study the process and application. Vacuum freeze dryer is modified by adding 4 heaters for better efficiency and energy saving. Experiments are done at different sample temperature and finally sensory evaluation is performed to have better understanding of dry products.

Abstract i
Acknowledgement iii
Table of Contents iv
List of figures vi
List of tables ix
1. Introduction - 1 -
1.1. Terminologies of Vacuum Freeze drying - 2 -
1.1.1. Fundamental Theory of Vacuum: - 2 -
1.1.2. Fundamentals of Freezing: - 3 -
1.1.3. Concept of drying: - 5 -
1.1.4. Important Parameters for Vacuum Freeze dryer - 10 -
1.2. Applications of Vacuum Freeze Dryer - 13 -
1.3. Aim and Outline of thesis - 15 -
2. Literature Survey - 17 -
2.1. Classical or contemporary with time - 17 -
2.1.1. Historical perspective - 17 -
2.1.2. Can future be as it is? - 19 -
2.2. Vacuum Freeze dryer fundamentals - 19 -
2.2.1. Freeze drying chamber - 19 -
2.2.2. Refrigerated condenser - 19 -
2.2.3. Refrigeration unit - 20 -
2.2.4. Vacuum pump - 20 -
2.3. Categories of Freeze dryer - 21 -
2.4. Physics based model for Vacuum Freeze Drying - 21 -
3. Principle and Methodology of Experiment - 23 -
3.1. General operation process of vacuum freeze dryer - 23 -
3.1.1. Process Check up - 23 -
3.1.2. Operational Procedure - 26 -
3.1.3. Data storage from Vacuum Freeze dryer - 31 -
3.1.4. VFD modified with Infrared (IR) heater - 31 -
3.2. Block diagram and operating principle of VFD. - 33 -
3.3. Drying and determination of it’s end point. - 36 -
3.3.1. Primary and Secondary Drying - 37 -
3.3.2. Determination of end point for primary drying - 40 -
4. Calibration of Humidity sensor with VFD - 45 -
5. Ways of experiment - 48 -
6. Results, Analysis and Discussion - 51 -
6.1. Water experiment - 52 -
6.1.1. Experimental result and analysis with water - 52 -
6.1.2. Summary of water experiment - 72 -
6.2. Mathematical modelling and analysis of water of different volume to develop correlations - 74 -
6.2.1. Mathematical modelling and analysis - 75 -
6.2.2. Experimental results & theoretical interpretation - 79 -
6.2.3. Temperature characterization and correlation for water - 84 -
6.2.4. Humidity Characterization and Correlation for water - 87 -
6.2.5. Starting and end point determination using humidity sensor - 89 -
6.3. Experimental results and drying process with semisolid and solid - 91 -
6.3.1. Semisolid experiment with passion fruit paste - 91 -
6.3.2. Freeze drying process and prediction of drying using apple - 92 -
6.3.3. Influence of thickness and surface area on VFD of apple slices. - 97 -
6.3.4. Sensory evaluation - 99 -
6.3.5. Summary of drying apple slices - 99 -
6.4. Study the effects of drying on apple slices with IR assisted VFD - 100 -
6.4.1. IR drying at sample temperature of 200 C - 101 -
6.4.2. IR drying at sample temperature of 250 C - 102 -
6.4.3. IR drying at sample temperature of 350 C - 103 -
6.4.4. IR drying at sample temperature of 300 C - 104 -
6.4.5. Summary of IR drying - 105 -
7. Conclusion and future scope - 107 -
References........................................................................................................................- 110 - Appendix........................................................................................................................- 113 -

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