Thermophysical Properties of Selected Cash Crops Grown in Ghana

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In this thesis, the influence of moisture on selected physical, compressive and thermal properties of cocoa beans, shea and cashew nut and kernel were studied. Standard methodologies that have been accepted internationally and used by several researchers globally were used for the determination of the selected properties in moisture content ranges normally used for the postharvest processing of the selected crops. The results of moisture variation on physical properties of cocoa beans and cashew kernels such as 1000-bean mass, true density, porosity, emptying angle of repose and static coefficient of friction showed increasing trends with linear relationships while bulk density decreased linearly for cocoa bean and cashew kernel samples. The compressive strain and Young’s Modulus for cocoa beans decreased linearly with moisture from 0.009 to 0.0045, and 1300 to 205 MPa respectively. However the compressive stress decreased exponentially with increasing moisture content from 1.5 - 0.3 MPa while the crushing energy had more positive linear function with moisture content and increased from 0.013 - 0.2 J. For shea kernel, compressive stress, compressive strain and Young’s Modulus decreased linearly from 2.0 - 0.8 MPa, 0.0085 - 0.002 mm/mm and 2000 – 100 MPa with increasing moisture content. Crushing energy increased non-linearly from 0.005 - 0.13 mJ in the moisture content range of 5% - 24% w.b. The compressive stress, strain, and Young’s modulus for the cashew kernel increased from 0.214 - 1.214 MPa, 0.355 - 0.472 mm/mm, and 2.446 - 6.416 MPa respectively as moisture content increased from 5.0 - 9.0% wb. Thermal conductivity increased linearly for ground cocoa beans sample from 0.0243 - 0.0311 W/oCm and for ground shea kernels from 0.0165 - 0.0458 W/oCm in the moisture content range of 12.59 - 43.84%w.b. at a constant bulk density of 295 kg/m3. Specific heat, thermal conductivity and thermal diffusivity for ground cashew kernel were found to increase linearly from 1586 – 1756 J/kgº., 0.2103 - 0.2296 W/mK and 2.369×10-7 - 2.588×10-7 m2/s with increasing moisture content from 5.0 - 9.0% w.b. Keywords: Cocoa beans, shea kernel, cashew kernel, physical properties, compressive properties, thermal properties, moisture content. iii Contribution to Science and Technology From this study, the following have been established and therefore added onto the scientific knowledge on engineering properties of food materials: 1. The publication on the physical properties of cocoa beans has been cited by 96 related articles as found in google thus contributing to information on physical properties of food grains. 2. The findings on crushing energy provide useful information for food and agricultural engineers in the design of suitable cocoa beans, shea and cashew nut crackers. 3. In a bid to mechanize the various unit operations involved in the postharvest processing of shea and cashew kernel, information and data on the behaviour of these strength properties as a function of moisture is needed. These data when utilised fully will not only save energy but will promote the design and development of effective and efficient processing machines. 4. Attempts have been made to optimize the drying process and to minimize internal cracking during drying of food grains with the aid of mathematical and numerical drying models, but estimation of the thermal properties of the material being dried, is also required. Data generated on specific heat, thermal conductivity, thermal diffusivity could be used in the analysis of drying processes and storage conditions. iv Publications from Candidate’s Work 1. Bart-Plange, A., Dzisi, K. A., Addo, A., Teye, E. and Kumi, F. (2012). A comparative study of some physical properties of large and medium size Cocoa beans from Ghana. ARPN Journal of Science and Technology. 2(3): 135-141, ISSN NO.: 2225-7217. 2. Bart-Plange, A. P. Mohammed-Kamil, A. Addo and E. Teye (2012). Some Physical and Mechanical Properties of Cashew Nut and Kernel Grown in Ghana. International Journal of Science and Nature (IJSN). 3(2): 406-415, May ISSN NO.: 2229-6441. 3. Bart-Plange, A., Addo, A., Abano, E.E. and Akowuah, J.O. (2012). Compressive Properties of Cocoa Beans Considering the Effect of Moisture Content Variations. International Journal of Engineering and Technology (IJET UK). 2(5): 850-858 http:/ ISSN NO.: 2049-3444. 4. Bart-Plange, A. Addo, J. O. Akowuah and J. Ampah (2012). Some moisture dependent compressive properties of Shea Kernel (vitellaria Paradoxa L). Canadian Journal of Pure and Applied Sciences (CJPAS), 6(3): 2113-2119, ISSN NO.: 1920-3853. 5. Bart-Plange, A. Addo, F. Kumi, and A. K. Piegu (2012). Some moisture dependent thermal properties of Cashew kernel (Anarcardium occidentale L.). Australian Journal of Agricultural Engineering. AJAE 3(2): 65-69. ISSN NO.: 1836-9448. 6. Bart-Plange, A. Addo, S. K. Amponsah and J. Ampah (2012). Effect of Moisture, Bulk Density and Temperature on Thermal Conductivity of Ground Cocoa Beans and Ground Sheanut Kernels. Global Journal of Science Frontier Research (GJSFR). 12( 8). ISSN NO.: 2249-4626.
Thesis submitted to the Department of Agricultural Engineering Kwame Nkrumah University of Science and Technology in fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY PhD, Food and Postharvest Engineering