Browsing by Author "Gikuru, Mwithiga"
Now showing 1 - 20 of 23
Results Per Page
Sort Options
Item 5 Infrared Drying(CRC Press, 2010-07-26) Gikuru, Mwithiga; Nindo, CalebThis chapter will present the mechanism, techniques, and advantages of infrared (IR) drying for various food and agricultural products. The propagation of IR radiation from a source (considered as any material at a temperature above absolute zero Kelvin) to other materials is discussed, and emphasis is placed on the subsequent transformation of the IR radiation into thermal energy for the drying of foods. The advantages and disadvantages of IR drying are briefly reviewed, followed by a discussion of selected applications in the processing of ...Item Alternative methods of harvesting and storage of grass biomass in a semi-arid region(Academic Journals, 2012-04-12) Gikuru, Mwithiga; Mazwiduma, P.J.; Tsopito, C.M.Biomass is considered a potential feedstock for many renewable energy production systems and interest especially in grass production has increased markedly in the last two decades. The present work focuses on grass biomass in the semi arid regions of sub-Saharan Africa and includes the study of two different methods of harvesting and baling as well as two different bale storage methods. The results indicated an average dry matter yield of 22600 kg ha-1. The average harvesting rate and fuel consumption were 1.57 h ha-1 and 6.23 ℓ ha-1, respectively. The baling rate was 0.80 h ha-1 while diesel consumption during baling was 2.69 ℓ ha-1. Manual harvesting using scythes varied extensively depending on time of day and the quality of the handmade bales though acceptable could at times fall below standards. The open barn storage method and open barn plus tarpaulin cover storage method could be used to store bales for a period of up to 5 months with minimum changes in neural detergent fibre (NDF) and acid detergent fibre (ADF) of biomass. The average fuel energy required to both harvest and bale, the biomass constituted less than 1% of the energy that could be recovered from the biomass if used as a fuel.Item Analysis of Fish Fillet Drying Rates under Three Solar Energy Drying Systems(2009-02-20) Gikuru, Mwithiga; Mwangi, Samuel GathukiA small Box type solar dryer with controllable air inlet was designed and tested. The dryer had a mild steel absorber plate and a polyvinyl chloride (pvc) transparent cover and could be adjusted to allow variation in airflow rate through the drying chamber. A convectional green house covered with transparent pvc and into which a drying tray stand at a height of 90 cm above the ground was placed made up the second drying method. The rate of air flow through the green house could be controlled by adjusting the opening at either end of the tunnel. The third method of drying which also served as the control is sun drying in which case the drying trays was placed 90 cm above the ground but left unenclosed to allow free flow of ambient air. The air temperature at points just above the drying rack was monitored for all three drying systems under no load conditions from morning to late afternoon. The temperature was also monitored during drying when the trays were loaded with fish of different fillet thicknesses. The rate of loss of moisture was also monitored by weighing the fillets at regular interval until the moisture dropped to 20%, dry basis or lower. The average temperature inside the plenum chamber of the box type solar dryer was found to have a high daily value of 71.1OC although an absolute maximum value of 74.4OC was recorded. This maximum value could be reached on cloudless days between the hours of 13:00 and 1400. The green house recorded a slightly lower average temperature and its peak value occurred latter in the day. Both the green house and the box-type solar dryer had average drying chamber temperatures that were more than 30 centigrade degrees above ambient conditions. Both the box-type and green house type solar dryer could dry thin slices of fish fillet in 1-3 days as opposed to the 7-9 days normally required under sun drying conditions. The quality of the dry fillet was satisfactory and CIE LAB colour values did not change significantly during drying.Item Coffee Drying in a Rotary Conduction-Type Heating Unit(Blackwell Publishing Ltd, 2004-06-01) Gikuru, Mwithiga; Jindal, V.K.Parchment coffee (Arabica) was dried from an initial moisture content of about 90% to 10% dry basis (db) in a recirculating rotary conduction type heating unit at controlled plenum temperatures of 100, 120 and 140C or controlled product temperatures of 50, 60, and 70C. the temperature of the plenum or moving beans could be maintained at specified levels with small variations during coffee drying experiments. the color and specific gravity of coffee beans exhibited minimum changes as a result of drying operations. the susceptibility of coffee beans to breakage decreased with the lowering of moisture and attained minimum values in the moisture content range of 20 to 30% db. the breakage susceptibility increased sharply with further reduction in moisture content. A drying model, which considered product temperature-time history alone under different operating conditions, estimated the change in moisture content adequately. Such a model could be used for computer-based control of the coffee drying process.Item Comparison of a gas fired hot-air dryer with an electrically heated hot-air dryer in terms of drying process, energy consumption and quality of dried onion slices(Academic Journals, 2012-08-14) Gikuru, Mwithiga; EL-Mesery, Hany S.Onion slices were dried in either a gas-fired hot air dryer or an electrically heated hot air dryer at air temperatures of 50, 60 or 70°C, and at air flow velocities of 0.5, 1.0 or 2.0 m/s. Records of the drying rates and energy consumption were kept by using electronic weighing balances and an electric metering device. The results showed that the drying rate and final product quality in the two dryer were not significantly different at P < 0.05 level for the same setting of air flow and air temperature, and all dried products were of acceptable quality in terms of rehydration ratio and appearance. The specific energy consumption was found to decrease with increase in temperature but to increase with increase in air velocity in both dryers and for all conditions within the range of these experiments. The thermal efficiency of the gas dryer was between 54.87 to 69.52% while that of the electrically heated dryer was between 31.27 to 53.84%. The thermal efficiency of both dryers increased with increase in temperature and decreased with increase in air velocity. However, there was considerable difference in the energy consumption and efficiency of the two dryers, with the gas-fired dryer being more efficient at all settings.Item The drying kinetics of kale (Brassica oleracea) in a convective hot air dryer(Elsevier, 2005-12-31) Gikuru, Mwithiga; Olwal, Joseph OchiengThe effect of air temperature and sample thickness on the drying kinetics of kale was investigated using a convective air dryer at a fixed airflow rate of 1 m/s and drying air temperatures of 30, 40, 50 and 60 °C. The sliced kale leaves were dried in wire trays in 10, 20, 40 and 50 mm thick layers. The drying rate increased with drying air temperature but decreased with layer thickness. The effective diffusivity for 10 mm thick layers was found to increase with the drying air temperature and ranged between 14.9 and 55.9 × 10−10 m2/s. The effect of temperature on diffusivity could be expressed by an Arrhenius type relationship with a high R2 of 0.9989. The activation energy of kale was found to be 36.115 kJ/mol. When four drying models were developed using the experimental data the Modified Page model was found to be marginally better than the other models in estimating the drying curve over the experimental temperature range.Item The drying of onion slices in two types of hot-air convective dryers(Academic Journals, 2012-08-07) Gikuru, Mwithiga; El-Mesery, Hany S.Drying experiments were carried out using two types of convective hot-air dryers such that the hot air passed perpendicularly through a thin layer of onion slices in one dryer while the air passed parallel to the thin layer in the second dryer. The drying air temperatures were 50, 60 or 70°C, while air velocity was set at 0.5, 1.0 or 2.0 m/s. The drying behavior of onion slices under the aforementioned experimental parameters was fitted using Newton, Henderson and Pabis, Page and Modified Page models. The results were compared for their goodness of fit in terms of coefficient of determination (R2) and standard error (SE). The Page model was the best in describing the drying behavior of onion slices when compared to the other models. The drying time in the case of the horizontal convective hot-air dryer in comparison with vertical convective hot-air dryer was considerably less while onion slices dried at higher temperatures generally had higher rehydration ratios.Item Effect of moisture content on the physical properties of three varieties of sorghum seeds(Elsevier, 2006-08-31) Gikuru, Mwithiga; Sifuna, Mark MasikaThree sorghum varieties (Kari-mtama, Serena and Seredo) were obtained from the Kenya Agricultural Research Institute and reconditioned to moisture contents ranging from 13.64% to 21.95% db. The reconditioned grain kernels were then evaluated for dimensions, 1000 grain mass, bulk density, true density, angle of repose and hardness. The major, medium and minor diameters were found to increase with increase in moisture content for all three varieties of sorghum within the experimental moisture range. At the moisture content of 13.64% db the geometric mean diameter, sphericity, 1000 grain mass, bulk density, true density, porosity, angle of repose and kernel strength were found to be 3.94 mm, 0.737, 33.91 g, 588.4 kg/m3, 1264 kg/m3, 53.44%, 30.43° and 87.89 N for Kari-mtama, 3.33 mm, 0.733, 20.89 g, 686.33 kg/m3, 1087 kg/m3, 36.86%, 24.41° and 59.64 N for Serena, and 3.15 mm, 0.789, 19.66 g, 757.61 kg/m3, 1138 kg/m3, 33.31%, 20.11° and 48.66 N for Seredo, respectively. The geometric mean diameter increased linearly with moisture content for all three sorghum varieties while sphericity remained fairly unchanged. Both the 1000 grain mass and angle of repose increased linearly with moisture content within the experimental testing range (13.64–21.95% db) while bulk density and true density decreased linearly with increase in moisture content. When the moisture content was raised from 13.64% to 21.95% db, the porosity of Kari-mtama decreased slightly but linearly with increase in moisture content while that of Serena and Seredo increased linearly with increase in moisture content. The hardness of Kari-mtama, Serena and Seredo decreased with increase in the moisture content of the grains although a linear relationship with moisture content over the entire range of 13.64–21.95% db was not observed.Item Evaluation of the effect of ripening on the sensory quality and properties of tamarillo (Cyphomandra betaceae) fruits(Elsevier, 2007-03-31) Gikuru, Mwithiga; Mukolwe, Michael Inzoberi; Shitanda, Douglas; Karanja, Paul NyotaTamarillo (Cyphomandra betaceae) fruits were sourced from a single farmer from the Central province of Kenya soon after harvesting. The fruits were then cleaned and sorted in order to remove all immature and damaged fruits. The resulting fruits were by visual inspection divided into eleven groups or ripeness scales depending on the degree of ripening and then subjected to a sensory evaluation for taste and colour using an untrained panel of 10 people. Objective measurements of firmness, colour, juice yield, pH and total soluble solids were also done for all the eleven ripeness groups. The sensory score for both taste and colour increased with the degree of ripeness to reach a maximum at the ripeness scale of between 7 and 9, respectively, and thereafter decreased with further ripening. There was a remarkable change in the fruit pulp colour with L∗ and b∗ decreasing with increase in ripeness from 64.6 to 36.1 and 40.8 to 13.2, respectively, while a ∗ values increased from −4.3 to 8.5. Changes in fruit surface colour were well pronounced and decreased from 46.3 to 22.1 and 28.3 to 4.9 for L∗ and b∗, respectively, while a∗ increased from −4.9 to 28.3. There was progressive increase in juice yield (10.6–26.0%), total soluble solids (9.4–10.9) and pH (3.35–3.85) with increase in degree of ripeness. However, the firmness decreased from 115.5 to 71.6 N with increase in degree of ripeness. There was a linear relationship between the colour lightness coordinates for peel and pulp with an R2 value of 0.989 indicating that fruit surface L∗ values are good indicators of internal quality.Item Humidity Control System for Wine Maturation Structures(2013-12-13) Gikuru, Mwithiga; Magama, P.; Hlophe, M.Abstract. Fogging systems can be used to maintain the high humidity required in wine aging structures at acceptable levels during the day and as long as temperature inside the wine maturation store is rising. However, as soon as the temperature starts falling, fogging systems will fail to bring down the humidity resulting in condensation. Condensation is undesirable because apart from causing the development of mould on the barrels and sections of the structure it might even lead to structural failure. A device that controls the humidity and maintains it at set levels throughout the day was designed and constructed. The devise could control the humidity and maintain it within set levels inside a standard storage container and at no time did condensation occur.Item Mathematical Modelling of Thin Layer Drying Kinetics of Onion Slices Hot-air Convection, Infrared Radiation and Combined Infrared- Convection Drying(AENSI Publisher, 2014) Gikuru, Mwithiga; EL-Mesery, Hany SOnion slices were dried in convection hot-air, infrared radiation and combined infraredconvection hot air dryers. A systematic experimental design was applied to analyse drying kinetics due to the effect of type of dryer, infrared radiation intensity, drying air temperature and drying air velocity, until a final moisture content of 7 ± 1 % (wet basis) was attained. Mathematical modelling of thin layer drying kinetics under the different drying methods were studied and verified with experimental data. Eleven different mathematical drying models were compared according to three statistical parameters namely, the correlation coefficient (R2), chi-square (χ2) and modelling efficiency (EF). Drying curves obtained from the experimental data were fitted to the-thin layer drying models. The results show that, the Midilli et al. model obtained the highest (EF and R2) value and the lowest (χ2) values for both dryers. Therefore, this model is the best for describing the drying curves of onion slices under all the drying processing conditionsItem Mechanical expression of oil from grated and preheated coconut meat Botswana Journal of agricultural sciences(2015) Gikuru, Mwithiga; Fondo, Emanuel ChengoCoconut oil was extracted from grated coconut using a hydraulic pressing method after the coconut gratings were preheated at heating medium air temperature in the range of 30-90oC and heating durations ranging from zero to 45 minutes. Oil yields from the preheated copra indicated that adding distilled water to fresh grated copra in the ratio of 3:1 prior to heating the mixture in sealed plastic bags resulted in higher oil yield at all heating temperatures when compared to unheated copra. The oil yield also increased with increase in heating medium temperature up to 70oC but declined with any further rise in heating medium temperature. Lowering the moisture content by drying copra in an air oven at 40oC followed by oil extraction resulted in an increase in oil yield. It was noted that the oil yield increased with increase in the duration of preheating at all temperatures although the maximum increase was observed at heating temperatures of 50 and 60oC. Grating the coconut to flakes of approximately 1mm thickness had the effect of increasing oil yield when compared to 2mm thick flakes.Item Performance of a convective, infrared and combined infrared-convective heated conveyor-belt dryer(Springer, 2015-05) Gikuru, Mwithiga; El-Mesery, Hany S.A conveyor-belt dryer was developed using a combined infrared and hot air heating system that can be used in the drying of fruits and vegetables. The drying system having two chambers was fitted with infrared radiation heaters and through-flow hot air was provided from a convective heating system. The system was designed to operate under either infrared radiation and cold air (IR-CA) settings of 2000 W/ m2 with forced ambient air at 30 °C and air flow of 0.6 m/s or combined infrared and hot air convection (IR-HA) dryer setting with infrared intensity set at 2000 W/m2 and hot at 60 °C being blown through the dryer at a velocity of 0.6m/s or hot air convection (HA) at an air temperature of 60 °C and air flow velocity 0.6 m/s but without infrared heating. Apple slices dried under the different dryer settings were evaluated for quality and energy requirements. It was found that drying of apple (Golden Delicious) slices took place in the falling rate drying period and no constant rate period of drying was observed under any of the test conditions. The IR-HA setting was 57.5 and 39.1 % faster than IR-CA and HA setting, respectively. Specific energy consumption was lower and thermal efficiency was higher for the IR-HA setting when compared to both IR-CA and HA settings. The rehydration ratio, shrinkage and colour properties of apples dried under IR-HA conditions were better than for either IR-CA or HA.Item Performance of a convective, infrared and combined infraredconvective heated conveyor-belt dryer(Association of Food Scientists & Technologists, 2015-05) Gikuru, Mwithiga; El-Mesery, Hany SA conveyor-belt dryer was developed using a combined infrared and hot air heating system that can be used in the drying of fruits and vegetables. The drying system having two chambers was fitted with infrared radiation heaters and through-flow hot air was provided from a convective heating system. The system was designed to operate under either infrared radiation and cold air (IR-CA) settings of 2000 W/ m2 with forced ambient air at 30 °C and air flow of 0.6 m/s or combined infrared and hot air convection (IR-HA) dryer setting with infrared intensity set at 2000 W/m2 and hot at 60 °C being blown through the dryer at a velocity of 0.6m/s or hot air convection (HA) at an air temperature of 60 °C and air flow velocity 0.6 m/s but without infrared heating. Apple slices dried under the different dryer settings were evaluated for quality and energy requirements. It was found that drying of apple (Golden Delicious) slices took place in the falling rate drying period and no constant rate period of drying was observed under any of the test conditions. The IR-HA setting was 57.5 and 39.1 % faster than IR-CA and HA setting, respectively. Specific energy consumption was lower and thermal efficiency was higher for the IR-HA setting when compared to both IR-CA and HA settings. The rehydration ratio, shrinkage and colour properties of apples dried under IR-HA conditions were better than for either IR-CA or HA.Item Performance of a solar dryer with limited sun tracking capability(Elsevier, 2006-05-31) Gikuru, Mwithiga; Kigo, Stephen NjorogeA small solar dryer with limited sun tracking capabilities was designed and tested. The dryer had a mild steel absorber plate and a polyvinyl chloride (pvc) transparent cover and could be adjusted to track the sun in increments of 15°. The performance was tested by adjusting the angle the dryer made with the horizontal either once, three, five or nine times a day when either loaded with coffee beans or under no load conditions. The temperature distribution in the plenum and also the drying rate of parchment coffee were determined. The temperature inside the plenum chamber could reach a maximum of 70.4 °C and the dryer could lower the moisture content of coffee beans from 54.8% to below 13% (w.b.) in 2 days as opposed to the 5–7 days required in sun drying. Tracking the sun though allowing a faster rate of drying did not offer a significant advantage in terms of length of drying duration.Item Physical changes during coffee roasting in Rotary Conduction‐Type Heating Units(Blackwell Publishing Ltd, 2003-08-23) Gikuru, Mwithiga; Jindal, V.K.Coffee beans were roasted in a rotary conduction-type-heating unit under constant heating surface or product temperatures ranging from 200 to 240C or 170 to 210C, respectively. the roasting duration was varied from 0 to 70 min through intermittent sampling of coffee beans at selected intervals. There were marked changes in physical conditions of coffee beans during roasting. the specific gravity, bulk density, susceptibility to breakage, and color lightness index L changed from 1.2 to 0.5, 0.7 to 0.3 g/cm3, 20 to 100, and 50 to 12, respectively.Item The potential for second generation bio-ethanol production from agro-industrial waste in South Africa(Academic Journals, 2013) Gikuru, MwithigaThere has been a sustained and growing interest in the production of liquid fuel from biomass in recent years. South Africa is a large producer of sugar, maize and wheat among other agricultural products that release big quantities of biomass byproducts during postharvest processing operations. This work looks at the energy situation in South Africa and especially the liquid fuel sector and explores the possibility of producing bioethanol from biomass. A brief discussion of the different types of feedstock for bioethanol production is given. A review of possible bio-sources that can be used for bioethanol production with emphasis on those that have potential of replacing conventional fuels with little or minor modification of existing biomass production capacity and trend is presented. Data analysis indicates that the straw from maize, sorghum and wheat can produce up to 601.8 million litres of bioethanol per annum and that it is possible to produce up to 549.4 million litres of bioethanol from sugarcane. The physical ability of mass production from various crop byproducts that are produced in South Africa, as well as the immediately economic effect is also discussed.Item Potential of nightsky nocturnal radiative cooling as a fresh produce preservation method(2007-07-30) Gikuru, Mwithiga; Kirui, Anthony C.Abstract: The change in water temperature in horizontally placed pans exposed to the night-sky radiation was monitored at night between the hours of 8:00pm and 6:00am. The effect of varying the quantity of water in the pan was studied by varying the depth (1.0, 1.5, 2.0, 2.5 and 3.0mm) while effect of surface color of radiating surface was determined by placing two different coloured pans adjacent to each other. The effectiveness of this method in capturing “cold load” and the possible use of this cold energy for daytime preservation of fresh produce is analyzed and discussed. It was found that the water in the pan could be cooled to a temperature that was 9 oC below the lowest ambient dry bulb temperature. Also, the black painted surfaces cooled the water at higher rates than white surfaces and ultimately attained much lower temperatures in the long run. Within the experimental water loading depth range of 1-3 mm, the shallower depths attained lower final cold water temperature but had lower cooling efficiency in terms of total peak cold load per unit area of pan surface. The authors have shown that each square metre of pan surface can store enough “cold load” to remove the heat of respiration of a 10 kg load of vegetables or fruits that is maintained at or below the lowest ambient night dry bulb temperature. The fresh produce so maintained can therefore be about 10-15 oC below recorded daytime dry bulb temperature in the tropics which is sufficient to double the shelf life of most fresh produce commodities.Item Research trends in modeling, optimization and control of the drying operation(2007) Gikuru, MwithigaDrying food is an extremely sensitive operation that requires the proper monitoring and control of the heating medium temperature as well as the length of time that the product is exposed to this temperature. Since the different food products have different heat sensitivity the heat load tolerance during drying cannot be generalized if loss of quality is to be avoided. On the other hand the drying process is a very high energy consuming operation and energy usage must be minimized without necessarily compromising on product quality. Optimization of a drying process requires that we consider the heat and mass transfer dynamics, product quality indices and production costs. Different control strategies and objective functions must be tried because it would not make business sense to produce a very high valued product at astronomical costs to the producer and nor would a low quality product sell simply because it is produced at minimum cost or energy consumption. This Chapter reviews first the research trends on modeling of the drying process based a heat and mass transfer, cost of dying and product quality. The strategic logistics that have been used over the years in attempts to optimize the drying operation have also been reviewed. Last but not least, the performance of these dryer control strategies in the practical optimization of the drying process have been discussed since it is how well a control strategies works that can make the entire optimization process either a success or a failure.Item Specific Energy Consumption of Onion Slices During Hot-air Convection, Infrared Radiation and Combined Infrared-Convection Drying(AENSI Journals, 2014) Gikuru, Mwithiga; EL-Mesery, Hany S.Total energy requirement and specific energy consumption for drying of onion slices were evaluated using various drying methods including hot-air convection, infrared radiation and hot air convection-infrared combination drying. Onion slices with initial moisture content of 7.31 g water/g dry solids, were dried to a final moisture content of 0.07 g water/g dry solids. Energy and specific energy consumption under the different drying conditions of the onion slices were compared. In particular, the experiments were carried out in convective dryer at three air temperature levels of 50, 60 and 70 oC and three air velocity levels of 0.5, 1.0 and 2.0 m/s. Experiments in the infrared dryer were done at three air velocity of 0.5, 0.7 and 1.0 m/s. For combination of infrared and hot-air convection drying, there were three air temperature levels of 40, 50 and 60 oC and three air velocity levels 0.5, 0.7 and 1 m/s while the infrared intensity was set at 0.15, 0.20 and 0.30 W/cm2. Results of data analysis showed that the lowest and highest energy consumption levels in drying onion slices were associated with the hot air convection-infrared combination (IR-HA) and convection (HA) dryers, respectively. Specific energy consumption in the hot air dryer showed a downward trend with increasing air temperature and an upward trend with increasing air velocity. In infrared (IR) drying, it was observed that increasing the air velocity increases the drying time and consequently the amount of energy consumed. However, a reduction in energy IRHA was noted with increasing infrared intensities under combination drying relative to infrared drying alone. Therefore, IR-HA drying of onion slices proved to have the lowest specific energy consumption and therefore the most efficient.