Calorimetric method and instrument for measuring activity of water
A calorimetry and moisture technology, applied in the direction of material moisture content, etc., can solve the problems of destroying the sensor, interfering with the temperature field, large measurement error, etc., to achieve the effect of simple measurement principle, easy engineering, and easy miniaturization
Inactive Publication Date: 2012-05-23
QINGDAO UNIV
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Problems solved by technology
[0004] The literature (Zheng Yihua et al. Measurement of water activity in food. Modern Instruments, 2006, 12(2): 11-14) analyzed the significance of food water activity, gave a comprehensive measurement method, and listed commonly used The instrument points out the existing water activity measurement method and the problems to be solved by the instrument: ①The equilibration time between the sample and the surrounding air is long, resulting in a long measurement time (several hours)
③ There are lags (sensors, etc.) and interference (temperature changes, etc.) in various links in the actual application of various methods, resulting in actual measurement errors
④ When the food contains more volatile matter or some components, it will cause a large measurement error
and will destroy the sensor
⑤ Various methods have certain limitations, and there will be large differences in the results in different measurement ranges and applicable occasions
Since the measurement of material surface temperature and airflow temperature is an intrusive measurement, it will interfere with the temperature field and affect the accuracy
Moreover, the adjustment of air humidity is poor in operability, difficult to control, and susceptible to external interference
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[0020] Such as figure 2 As shown, the valve 12 is adjusted, the filter 13 removes impurities, the flow meter 14 indicates the flow rate, and the carrier gas 11 is introduced at a constant pressure and a constant flow rate under a constant temperature state. Then enter the calorimetry module 16, its structure is as image 3 As shown, it consists of a sample detection pool 1 , an empty detection pool 2 , a pure water detection pool 3 , a thermal sensor 4 and a constant temperature calorimetric block 5 . The three detection pools adopt a twin structure, and the structural parameters are exactly the same. Among them, the sample detection pool 1 is placed with samples, the empty detection pool 2 is empty, and the pure water detection pool 3 is placed with a fixed volume of pure water. Both the sample detection cell 1 and the pure water detection cell 3 use the empty detection cell 2 as a reference. By employing twin structures and reference methods, interferences can be effectiv...
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The invention relates to a calorimetric method and an instrument for measuring activity of water of the solid or liquid material. A sample detection pool, an empty detection pool and a pure water detection pool of twinborn structures are arranged in a constant-temperature environment, a carrier gas with constant pressure and flux is used for passing the pure water detection pool, the empty detection pool and the sample detection pool uniformly and simultaneously, the water wherein is evaporated at a continuously stable rate; therefore, a compensation heat flow exists among the sample detectionpool, the empty detection pool and the pure water detection pool and the external constant-temperature environment, and the heat flow size needed to be compensated is directly proportional to the partial pressure of the steam of the sample. By respectively measuring the calorimetric signals of the compensation heat flows of the sample detection pool, the empty detection pool and the pure water detection pool and subsequently comparing and computing the sample detection pool and the pure water detection pool with the calorimetric signals of the empty detection pool, the value of the water activity of the material is obtained. The method can consider the measurement precision and consumption time simultaneously and the water activity measurement instrument adopting the method has compact structure and simple and convenient operation.
Description
technical field [0001] The invention relates to a calorimetric method and an instrument for measuring water activity, which can accurately and rapidly measure the water activity of solid or liquid materials. Background technique [0002] Moisture is the main component of materials such as food, medicine, aquatic products and solutions, and its existing state directly affects the biochemical process of the material itself and the reproduction status of surrounding microorganisms. Water activity indicates the state of water in the substance and the degree of combination with other components, and is an important indicator of stability and safety. Seeking a convenient, reliable, accurate and fast water activity measurement method is an urgent requirement for the development of related industries and has important practical significance. [0003] Under low pressure and low temperature conditions, water activity can be obtained by measuring the partial pressure of gas vapor in e...
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IPC IPC(8): G01N25/60
Inventor 郑艺华刘君马永志
Owner QINGDAO UNIV