تعيين برخي خواص فيزيكي، مكانيكي و حرارتي دانه هاي جو (ارقام نصرت و كوير)

Determination of physical, mechanical and thermal properties of barley grains (vars. Nosrat and Kavir)

جو يكي از غلات مهم در ايران بوده و دانستن خصوصيات آن از جمله خواص فيزيكي، مكانيكي و حرارتي، داراي اهميت زيادي در بسياري از توليدات صنعتي، فرآوري و ذخيره آن مي باشد. هدف از اين تحقيق اندازه گيري برخي خواص دو واريته جو (نصرت و كوير) بود. براي اين منظور، اثر رطوبت در چهار سطح 3/7، 1/12، 8/16 و 6/21 درصد بر پايه خشك، براي رقم نصرت و چهار سطح 7/6، 6/11، 4/15 و 2/21 درصد بر پايه خشك، براي رقم كوير مورد بررسي قرار گرفت. اثر رطوبت، جهت بارگذاري و نوع واريته روي خواص مكانيكي، نيرو و انرژي شكست، تعيين شد. بعلاوه، خواص حرارتي واريته هاي جو، گرماي ويژه، هدايت گرمايي و ضريب پخش گرمايي، در رطوبت اوليه ي آنها و در دماي 25 درجه سانتيگراد، اندازه گيري شد. نتايج نشان داد كه با افزايش رطوبت، ابعاد، قطر ميانگين حسابي و هندسي، كرويت، وزن هزار دانه، زاويه استقرار و ضريب اصطكاك روي صفحات مختلف براي هر دو واريته افزايش داشت. چگالي ظاهري و واقعي هر دو واريته با افزايش رطوبت، كاهش يافت. اثر رطوبت روي تخلخل دانه هاي جو معني دار نبود. نيروي شكست براي هر دو واريته با افزايش رطوبت، كاهش و انرژي شكست افزايش يافت. همچنين نيرو و انرژي شكست براي هر دو واريته تحت بارگذاري افقي بيشتر از بارگذاري عمودي بود. نيروي لازم براي شكست واريته نصرت(28/104نيوتن)بيشتر از واريته كوير(76/71 نيوتن) بود. ميانگين انرژي شكست واريته نصرت 38/54 ميلي ژول بدست آمد، در حالي كه براي واريته كوير 65/60 ميلي ژول بود. تفاوت معني داري بين خواص حرارتي واريته هاي نصرت و كوير وجود نداشت.

Barley is an ancient and important cereal grain crop in iran. Complete knowledge of properties of barley grains such as physical, mechanical and thermal properties has a decisive importance for the realization of many technological processes, especially for monitoring of their qualities and health harmlessness during their production and storage. The aim of this study was to measuring of Physical, Mechanical and Thermal Properties of two varieties of persian barely grain, Nosrat and Kavir. For this purpose, effect of moisture content at four levels of 7.3, 12.1, 16.8, and 21.6% d.b. for Nosrat variety, and four levels of 6.7, 11.6, 15.4, and 21.2% d.b. for Kavir variety, on some physical properties of barley grain was studied. Effects of moisture content, grain orientation, and variety on mechanical properties namely, rupture force Strain energy density were determined. In addition, thermal properties of barley grain varieties such as specific heat, thermal conductivity, and thermal diffusivity at initial moisture contents of the grains and temperature of 25°C, were measured.The results showed that, with increasing moisture content, length, width, thickness, arithmetic mean diameter, geometric mean diameter, sphericity, surface area, thousand grains mass, angle of repose, and static coefficient of friction on various surfaces, for both varieties increased. Bulk density and true density of the two varieties increased as moisture content increased. The effect of moisture content on porosity of the two varieties of barley grain was not significant. With increasing moisture content, the rupture force for both varieties decreased, while the rupture energy of the varieties increased. In addition, rupture force and Strain energy density for both varieties under horizontal orientation was higher than vertical orientation The average value of the rupture force for Nosrat variety was obtained as 104.28 N, varying from 53.11 to 172.39 N, while the value for Kavir variety was 71.76 N, varying from 40.88 to 111.72 N. The mean value of the rupture energy for Nosrat variety was calculated as 54.38 mJ, ranging from 29.10 to 78.24 mJ, while the value for Kavir variety was 60.65 mJ, in the range of 40.33 to 77.43 mJ. There is not any significant difference between the two varieties in the case of thermal properties.