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- Item. Reducing energy consumption of air-conditioners in warm-humid climates through desiccant cooling - a CFD study(KNUST, 2019-03) BAAH,BismarkThe ambient temperature and relative humidity in hot-humid climates, particularly in most countries in sub-Saharan Africa, can get as high as 41 °C and 84%, respectively. For indoor thermal comfort for people, temperature of 20–25 °C and relative humidity of 50–55% should be maintained. Air-conditioners that operate with vapour compression cycle are used to maintain such conditions. In conventional Vapour Compression Systems (VCS), inlet air is cooled below its dew point for dehumidification and then reheated again to obtain air flow with desired temperature and humidity. This process of dehumidification and reheating is inefficient and leads to high consumption of energy. In Desiccant Cooling Systems, dehumidification of air is done by utilizing desiccant material to get desirable humidity and then the dry air is cooled by evaporation method or cooling coils down to suitable temperature. The process of using desiccant to control the air humidity before the air-conditioning process makes the system more energy efficient. In this work, a CFD study has been conducted to ascertain how desiccant can be used to reduce the relative humidity of air prior to the air-conditioning process. The CFD simulations were conducted using TRNSYS software with input data from the Typical Metrological Year (TMY) data for Kumasi. The results show that the desiccant system is able to reduce the cooling load of a selected inefficient VCS in an office in Kumasi by as much as 65%. In addition, analysis in this study has shown that there is potential electricity savings of 2406 kWh/year with the desiccant cooling system over the conventional VCS.
- ItemStrength properties of locally constructed rice bunds in the Adansi North District Of Ghana(KNUST, 2019-10) . DZANDU, Thomas KwakuThe rice industry in Ghana faces challenges of low productivity, low yield and poor grain quality, resulting in overwhelming import dependence. Rice can be cultivated all year round with bund and irrigation. Also, land originally not suitable for rice cultivation can be used when bund is considered. Successive Governments over the years launch series of flagship programs which are aimed at reducing rice imports, poverty alleviation and employment creation which many have failed. Though bunds are widely used in many countries and other parts of Ghana, the system is relatively new in the Adansi North District of the Ashanti region of Ghana. The purpose of this study is to examine the durability and soil strength properties of rice bund constructed by local farmers. Three farmer’s fields KB, FB and PB were studied to ascertain their strength properties iv and their durability. Four bunds were constructed on a research plot labeled RB1, RB2, RB3 and RB4. RB1 and RB4 where compacted while RB2 and RB3 where uncompacted. Laboratory test indicates that soils of RB1, RB2 and KB where classified as clay of intermediate plasticity which proved stronger than RB3, RB4, FB and PB which were clay of low plasticity. After 40 days of bund measurements, farmer field bunds reduced in height between 36 to 42 %. Research field measured that uncompacted bunds reduced in height by 34 and 40 % while compacted bunds reduced by 6 % or less. Bund compaction increases operational cost and reduces profit in the first season however, increases profit drastically in the second season. It is therefore concluded that uncompacted bunds erode faster than compacted bunds, compaction increases soil strength and bund strength is determined by soil type and level of compaction.
- ItemAssessing the impact of septic tanks on groundwater quality of Selected communities around knust campus(KNUST, 2019-10) TAKAL, JeremiWater is an indispensable resource to mankind and life in general. Over the world, issues of water scarcity and quality are becoming pronounced with increasing global population, industrialization and urbanization. As a result, groundwater has become an important source of water supply throughout the world. The pressure on land and its resources in the study communities as they serve as residence for students, lecturers and the business community has impacted on groundwater quality. Small pieces of land acquired for building virtually does not give room for considering the siting of septic tanks and underground water. The quality of groundwater from eight boreholes/wells from Ayeduase, Boadi and Kotei in the Oforikrom Sub-Metro of the Ashanti Region were analyzed between February and July 2017. Water samples were collected from the eight boreholes/wells within the three communities and analyzed for temperature, pH, and some selected anions NO3- , SO2 -4 and Cl and bacteriological parameters such as total coliform and faecal coliform. The GPS locations of other 54 boreholes and the closest septic tank were taken and the kriging interpolation was applied to extrapolate values of the measured parameters at these locations. The results from the analysis showed that pH of the water was slightly acidic (4.8 to 5.9). With the chemical parameters measured, all of them were within the WHO guidelines for drinking water, ranging from 11.7587 to 53.4723 mg/L, 0.00048 mg/l to 19.4753mg/l, and 4.22 to 40.32 mg/l for chlorides, sulfates and nitrates respectively. Both the total coliform and the faecal coliform levels were low, 0.07 CFU/100ml iv – 7.94 CFU/100ml for the total coliform count and 2.59 CFU/ml – 19.89 CFU/ml for the faecal coliform count. The research also measured the effect of septic tank-borehole/well distance on the variables measured. A regression analysis revealed that there was zero to weak correlation in all the parameters measured, with the “r” values as -0.02, -0.05, -0.04, 0.06, -0.09, 0.11 and -0.42 for total coliform, sulfate, pH, faecal coliform, nitrates and chlorides respectively.
- Itemmodelling and optimisation of head rice yield of two rice varieties in a two-stage drying process Performance(KNUST, 2019-11) YEBOAH,Patricia OhenewaA considerable loss of milled rice (percentage of broken kernels) is traced to inadequate and untimely drying of harvested paddy. Therefore, an effective drying process or technique is required to minimise the reduction of head rice yield during paddy processing for an improved milled rice quality. In view of that, this study sought to integrate multi-criteria analysis and response surface methodology to optimise selection and operation of a two-stage drying process to maximise head rice yield. The study applied the method of Analytical Hierarchy Process (AHP) in the selection of an appropriate two-stage drying technique and factors (influencing the unit operations involved in obtaining a proper milled rice after harvesting and cleaning) based on its level of significance on head rice yield (HRY). A fluidised bed and tunnel dryer were selected as the best two-stage drying technique. Factors selected for the experimental design were fluidised bed drying temperature, tunnel drying temperature, paddy variety and storage time. A central composite design (CCD) in conjunction with a response surface methodology (RSM) based on four factors at three levels, which included six centre points, was used to evaluate the effects of the fluidised bed drying temperature (60 °C, 80 °C and 100 °C), tunnel drying temperature (40 °C, 45 °C and 50 °C), paddy variety (Amankwatia and AGRA) and storage time (1, 2 and 3 months) on the percentage of head rice yield were determined prior to optimising the operating conditions for optimal head rice yield. A regression model(quadratic), with a p-value of 6.5E-0.6 (<0.05), R 2 of 0.995, RMSE of 1.14, AdjR2 of 0.986 indicated that the quadratic model was significant. Fluidised bed drying temperature, tunnel drying temperature and paddy variety were found to have significant effects on the head rice yield with p-values of 1.9E-0.5 (<0.05), 5.5E-0.6 (<0.05) and 2.5E-0.5 (<0.05) respectively. However, storage time had no significant effect on head rice yield with a p-value of 0.6 (>0.05). The optimal operating conditions for Amankwatia rice variety yielding 69.25 % head rice yield were as follows: fluidised bed drying temperature of 73 °C, tunnel drying temperature of 41.5 °C and storage time of three months. The optimal operating conditions for AGRA rice variety yielding 62.56 % HRY were as follows: fluidised bed drying temperature of 79 °C, tunnel drying temperature of 42 °C and storage time of three months. Keywords: AHP, two-stage drying, performance modelling, CCD, RSM, HRY, Paddy
- Item. An approach to selectively block mobile Phone communication within a mobile phone restricted area(KNUST, 2019-07) AGYARE, MichaelThe use of mobile phone jammers to discourage mobile phone usage in mobile phone restricted areas has some limitations. One major limitation is that, once the jammer is activated no mobile phone can be able to function within the restricted area. For that reason, in the case of emergencies, no mobile phone can either make or receive phone calls or perform emergency calls (police, fire and ambulance services). Works done in literature can detect and block phone calls in a certain way but depends on the mobile switching centre in order to block communication in the restricted area. Therefore, in this thesis, a selective mobile phone communication blocking system is proposed which does not depend on the mobile switching centre in order to perform blocking of communication. The proposed system seeks to allow privilege users access to communication and block non-privilege users with respect to a specific user location. Some mobile phone user locations were considered in this thesis (Hospitals, Banks and Schools). A user from a particular user location cannot enjoy the same privileges at a different location provided that user is privileged. The selective blocking nature of the system was simulated using Fuzzy Inference System (FIS) toolbox (mamdani). The inference method is based on a set of IF-THEN rules and membership functions of the input variable and output variables of the system. Users for the different locations were converted into input triangular membership functions. The output is the decision (“allow” and “not allow”) for each of the inputs. S-shape and Z-shape membership functions were used as the output decision variables. The set of IF-THEN rules were used to link the input variables to the output variables. The fuzzy inference system was able to perform selective blocking of communication services for privileged and non-privileged users. The results in this work shows that when the proposed system is implemented mobile phone communication service can be prioritised to suit privilege users in specific mobile phone restricted areas.