DESIGN AND CONSTRUCTION OF GARRI FRYING MACHINE

CHAPTER ONE: INTRODUCTION

1.1 Background of Study

Garri is a granular, starchy food product derived from cassava (Manihot esculenta Crantz) roots through a series of processing steps including peeling, washing, grating, fermentation (optional), dewatering (pressing), frying (roasting), and sieving (Okafor and Nwosu, 2020). Garri is the most widely consumed cassava product in Nigeria, serving as a staple food for millions of households, particularly in the South-West, South-East, South-South, and North-Central regions (FAO, 2022). It is consumed in various forms: soaked in cold water (with sugar, milk, groundnuts), made into “eba” (by adding hot water), or eaten with stews and soups (FMARD, 2021). The garri processing industry is a major source of employment and income for rural women and small-scale processors (World Bank, 2021).

The traditional method of garri frying (roasting) is a critical step in the processing chain, where dewatered cassava mash (wet cake) is transformed into dry, free-flowing, granular garri (Adebayo and Ogunyemi, 2020). Traditional garri frying is typically done manually using a large, shallow, flat-bottomed metal pan (locally known as “garrifryer” or “roasting pan”) placed over a wood-fired or charcoal-fired open hearth (Eze and Nweze, 2019). The processor stands over the hot pan, continuously stirring and turning the mash with wooden paddles to prevent burning and ensure uniform drying and granulation. This manual process is labor-intensive, time-consuming, hazardous, and inefficient (Okafor and Ugwu, 2021).

Challenges of Traditional Garri Frying:

Challenge	Description	Impact
Labor-intensive	Continuous stirring required for 30-60 minutes per batch	High labor requirement (2-3 persons per pan)
Time-consuming	30-60 minutes per batch (5-10 kg of garri)	Low throughput (10-20 kg/hour)
Hazardous	Open fire, hot pan, smoke, burns	Safety risk (burns, smoke inhalation)
Uneven heating	Wood/charcoal fire uneven, manual stirring inconsistent	Variable quality (burnt, under-dried, lumpy)
High fuel consumption	Wood/charcoal inefficient (high heat loss)	High energy cost
Low capacity	Small batch size (5-10 kg)	Difficult to scale up

(Source: Adebayo and Ogunyemi, 2020; Okafor and Nwosu, 2020)

The need for mechanized garri frying machines has been recognized by researchers, engineers, and food processors to address the limitations of traditional methods (Okonkwo, 2020). Mechanized garri frying machines offer several advantages:

Advantage	Description	Benefit
Reduced labor	Mechanical stirring (motorized)	Fewer workers (1 person can operate)
Higher throughput	Larger batch size (20-100 kg)	Higher productivity (50-200 kg/hour)
Consistent quality	Uniform heating, constant stirring rate	Uniformly dried, granular, no burning
Reduced fuel consumption	Enclosed heating, insulation	Lower energy cost
Improved safety	Enclosed rotating drum, no open fire	Reduced burns, smoke
Scalability	Can be scaled to industrial level	Commercial production

(Source: Eze and Nweze, 2019; Okafor and Ugwu, 2021)

The design and construction of a garri frying machine involves several engineering considerations (Okafor and Nwosu, 2020):

Component	Description	Design Consideration
Drum/cylinder	Rotating vessel where garri is fried	Material (mild steel, stainless steel), diameter, length, wall thickness
Heating system	Heat source for frying	Electric heating elements, gas burner, or direct fire with insulation
Agitator/stirrer	Mechanism to stir and turn the mash	Paddles or blades attached to rotating shaft
Drive system	Motor and transmission to rotate drum/agitator	Electric motor, gearbox, pulleys, belts
Frame/stand	Support structure	Material (angle iron, mild steel), strength, stability, portability
Discharge system	Mechanism to remove fried garri	Tilting mechanism, discharge door
Temperature control	Regulation of frying temperature	Thermostat, thermocouple, temperature controller

Existing designs of garri frying machines vary in capacity, complexity, and cost (Okonkwo, 2020). Types include:

Type	Capacity (kg/batch)	Power Source	Cost (₦)	Advantages	Disadvantages
Manual batch fryer	10-20	Manual (hand crank)	50,000-100,000	Low cost	Still labor-intensive
Motorized batch fryer (horizontal drum)	20-50	Electric motor (1-3 HP)	200,000-500,000	Moderate capacity, consistent quality	Higher cost, requires electricity
Continuous fryer	100-500/hour	Electric motor (5-10 HP)	1,000,000-5,000,000	High capacity, industrial scale	High cost, requires electricity, complex

(Source: Adebayo and Ogunyemi, 2020)

The performance of a garri frying machine is evaluated using several parameters (Okafor and Ugwu, 2021):

Parameter	Definition	Target Value
Frying time (minutes/batch)	Time to fry one batch	< 30 minutes
Capacity (kg/batch)	Mass of garri per batch	20-100 kg
Throughput (kg/hour)	Mass of garri per hour	50-200 kg/hour
Moisture content (%)	Final moisture of garri	< 12% (safe storage)
Uniformity	Uniformity of frying (no burnt or under-dried particles)	>90% uniformly fried
Energy consumption (kWh/kg)	Energy per kg of garri	< 0.5 kWh/kg
Production cost (₦/kg)	Cost to produce 1 kg garri	< ₦50/kg

The design of a garri frying machine should also consider the properties of cassava mash (wet cake) and garri (Okafor and Nwosu, 2020):

Parameter	Value	Implication
Initial moisture content (wet cake)	40-50%	Need to remove 30-40% moisture
Final moisture content (garri)	<12%	Safe storage (no mould, no fermentation)
Bulk density (wet cake)	0.8-1.0 g/cm³	Volume reduction during drying
Bulk density (garri)	0.5-0.6 g/cm³	Lighter product
Frying temperature	150-200°C	Gelatinization, drying, expansion
Gelatinization temperature	70-80°C	Starch granules absorb water, swell

From a theoretical perspective, this study is supported by three theories: Heat Transfer Theory (Incropera and DeWitt, 2019), which explains the mechanisms of heat transfer (conduction, convection, radiation) from the heat source to the cassava mash; Mass Transfer Theory (Cussler, 2019), which explains the movement of moisture from the interior of the mash particles to the surface and evaporation; and Machine Design Theory (Shigley, Mischke, and Budynas, 2020), which provides the principles for designing mechanical components (shafts, bearings, gears, belts, motors) and selecting materials.

In summary, garri is a major staple food in Nigeria, but traditional garri frying is labor-intensive, time-consuming, hazardous, and inefficient. Mechanized garri frying machines are needed to improve productivity, quality, and safety. This study aims to design and construct a garri frying machine (motorized batch type) that is affordable, efficient, and suitable for small to medium-scale processors. The performance of the machine will be evaluated in terms of frying time, capacity, throughput, moisture content, uniformity, and energy consumption.

1.2 Statement of Problems

Traditional garri frying (manual stirring of cassava mash over an open fire) is labor-intensive (2-3 persons required per pan), time-consuming (30-60 minutes per batch), hazardous (burns, smoke inhalation), inefficient (low throughput, 10-20 kg/hour), and produces inconsistent quality (burnt or under-dried garri). Small to medium-scale garri processors need affordable, efficient, and safe mechanized garri frying machines, but existing commercial machines are often expensive (₦200,000-5,000,000), require electricity (unreliable in rural areas), are too large for small-scale processors, or are not locally fabricated. There is limited research on the design and construction of locally fabricated, affordable garri frying machines suitable for small to medium-scale processors using locally available materials and power sources (electric motor or diesel engine). The problem this study addresses is the need to design, construct, and evaluate a locally fabricated, affordable, motorized garri frying machine for small to medium-scale garri processors.

1.3 Aim of the Study

The specific aim of this research work is to design and construct a motorized garri frying machine (batch type) using locally available materials, and to evaluate its performance in terms of frying time, capacity, throughput, moisture content, uniformity, and energy consumption.

1.4 Objectives of the Study

1. To design a motorized garri frying machine (batch type) including drum/cylinder, heating system, agitator/stirrer, drive system, frame, and discharge system.
2. To construct the designed garri frying machine using locally available materials (mild steel, angle iron, bearings, pulleys, belts, electric motor).
3. To determine the engineering properties of cassava mash (initial moisture content, bulk density) and garri (final moisture content).
4. To evaluate the performance of the constructed garri frying machine in terms of frying time (minutes/batch), capacity (kg/batch), throughput (kg/hour), moisture content (%), uniformity (%), and energy consumption (kWh/kg).
5. To compare the performance of the constructed machine with traditional garri frying method.

1.5 Research Questions

1. What are the design specifications (drum dimensions, motor power, heating system capacity) of the motorized garri frying machine?
2. What are the engineering properties (initial moisture content, bulk density) of cassava mash for garri processing?
3. What is the performance of the constructed garri frying machine in terms of frying time (minutes/batch), capacity (kg/batch), throughput (kg/hour), moisture content (%), uniformity (%), and energy consumption (kWh/kg)?
4. How does the performance of the constructed machine compare with traditional garri frying method?
5. Is the constructed garri frying machine affordable and suitable for small to medium-scale garri processors?

1.6 Research Hypotheses

Hypothesis One

• H₀ (Null): The constructed garri frying machine does not significantly reduce frying time compared to traditional method.
• H₁ (Alternative): The constructed garri frying machine significantly reduces frying time compared to traditional method.

Hypothesis Two

• H₀ (Null): The constructed garri frying machine does not significantly increase throughput (kg/hour) compared to traditional method.
• H₁ (Alternative): The constructed garri frying machine significantly increases throughput compared to traditional method.

Hypothesis Three

• H₀ (Null): The constructed garri frying machine does not achieve final moisture content <12% for safe storage.
• H₁ (Alternative): The constructed garri frying machine achieves final moisture content <12%.

Hypothesis Four

• H₀ (Null): The constructed garri frying machine does not produce uniformly fried garri (>90% uniformly fried).
• H₁ (Alternative): The constructed garri frying machine produces uniformly fried garri (>90% uniformly fried).

Hypothesis Five

• H₀ (Null): The constructed garri frying machine is not affordable for small to medium-scale processors.
• H₁ (Alternative): The constructed garri frying machine is affordable for small to medium-scale processors.

1.7 Justification of the Study

This study is justified on several grounds. First, garri is a major staple food in Nigeria, but traditional garri frying is labor-intensive, time-consuming, hazardous, and inefficient. Second, there is a need for affordable, locally fabricated, motorized garri frying machines for small to medium-scale processors. Third, existing commercial machines are often expensive, require electricity, and are not locally fabricated. Fourth, using locally available materials reduces cost and promotes local fabrication (local engineering workshops). Fifth, the findings will benefit small to medium-scale garri processors by providing an affordable, efficient, and safe garri frying machine.

1.8 Significance of the Study

The findings of this research will be significant to several stakeholders. To small to medium-scale garri processors, the study will provide an affordable, locally fabricated, motorized garri frying machine that reduces labor, increases throughput, improves quality, and enhances safety. To local engineering workshops and fabricators, the study will provide design specifications and construction drawings for fabricating garri frying machines, creating business opportunities. To agricultural extension agents, the findings will inform training for garri processors on mechanized processing. To government agencies (FMARD, NAFDAC, SON) , the study will inform policy on promoting local food processing equipment. To academic researchers, the study will contribute empirical data on garri frying machine design and performance, testing and extending heat transfer theory, mass transfer theory, and machine design theory.

1.9 Scope of the Study

The scope of this study is delimited to the design, construction, and performance evaluation of a motorized batch-type garri frying machine. The machine components: drum/cylinder (mild steel, 60 cm diameter, 60 cm length, 5 mm thickness), heating system (gas burner with insulation, or electric heating elements), agitator/stirrer (paddles attached to central shaft), drive system (2-3 HP electric motor, gearbox, pulleys, belts), frame (angle iron), and discharge system (tilting mechanism or discharge door). Cassava mash (wet cake) sourced from local garri processors. Performance evaluation parameters: frying time (minutes/batch), capacity (kg/batch), throughput (kg/hour), moisture content (oven drying method, %), uniformity (visual inspection, % uniformly fried), and energy consumption (kWh/kg). Comparison with traditional garri frying method (manual stirring over wood fire). The study does not extend to continuous garri fryers, industrial-scale machines (>100 kg/batch), other cassava processing equipment (grater, press), or economic analysis beyond material cost estimation.

1.10 Definition of Terms

Garri: A granular, starchy food product derived from cassava roots through processing steps including peeling, washing, grating, fermentation (optional), dewatering (pressing), frying (roasting), and sieving. The most widely consumed cassava product in Nigeria.

Garri Frying (Roasting): The thermal processing step in garri production where dewatered cassava mash (wet cake) is heated to gelatinize starch, evaporate moisture, and produce dry, free-flowing, granular garri.

Traditional Garri Frying: Manual method of frying garri using a shallow metal pan over a wood-fired or charcoal-fired open hearth, with continuous hand stirring using wooden paddles.

Garri Frying Machine: Mechanized equipment for frying garri, consisting of a rotating drum/cylinder, heating system, agitator/stirrer, drive system (motor, gearbox), frame, and discharge system.

Batch Fryer: A garri frying machine that processes a fixed quantity (batch) of cassava mash at a time, as opposed to continuous fryer which has continuous feed and discharge.

Frying Time: The time required to fry one batch of cassava mash into finished garri (minutes/batch).

Capacity: The mass of cassava mash (wet cake) that the machine can process per batch (kg/batch).

Throughput: The mass of finished garri produced per unit time (kg/hour). Calculated as (capacity × number of batches per hour) × (yield).

Moisture Content: The percentage of water in cassava mash (initial) or garri (final). Final moisture content should be <12% for safe storage (no mould growth, no fermentation).

Uniformity (Frying Uniformity): The percentage of garri particles that are uniformly fried (no burnt, under-dried, or lumpy particles). Determined by visual inspection.

Energy Consumption: The amount of energy consumed per kg of garri produced (kWh/kg). Includes electrical energy (motor) and thermal energy (heating).

Heat Transfer Theory: A theory explaining the mechanisms of heat transfer (conduction, convection, radiation) from the heat source to the cassava mash, and the factors affecting heat transfer rate.

Mass Transfer Theory: A theory explaining the movement of moisture from the interior of the cassava mash particles to the surface and evaporation into the surrounding air.

Machine Design Theory: A theory providing principles for designing mechanical components (shafts, bearings, gears, belts, motors), selecting materials, and ensuring strength, durability, and safety.

CHAPTER TWO: LITERATURE REVIEW

2.1 Conceptual Framework

The conceptual framework for this study is organized around the key concepts of garri processing, traditional garri frying, mechanized garri frying, machine design components, and performance evaluation parameters. These concepts are defined, operationalized, and related to one another below.

2.1.1 Concept of Garri Processing

Garri is a granular, starchy food product derived from cassava roots through a series of processing steps (FAO, 2022).

Garri Processing Steps:

Step	Description	Equipment
1. Peeling	Remove outer skin of cassava roots	Manual knife or mechanical peeler
2. Washing	Remove dirt, sand, latex	Water, washing tank
3. Grating	Reduce to fine mash	Manual grater or mechanical grater
4. Fermentation (optional)	Ferment mash (3-5 days) to develop flavor	Fermentation tank
5. Dewatering (pressing)	Remove excess water from mash	Hydraulic press, screw press, or bag and stones
6. Sieving	Break lumps, remove fibers	Sieve (manual or mechanical)
7. Frying (roasting)	Heat mash to gelatinize starch, evaporate water	Frying pan (traditional) or frying machine (mechanized)
8. Sieving (final)	Grade garri into fine, medium, coarse	Sieve

(Source: Okafor and Nwosu, 2020)

2.1.2 Concept of Traditional Garri Frying

Traditional garri frying uses a shallow metal pan over a wood or charcoal fire, with manual stirring (Okafor and Ugwu, 2021).

Traditional Garri Frying Process:

Parameter	Description
Equipment	Shallow flat-bottomed metal pan (60-100 cm diameter)
Heat source	Wood or charcoal fire (open hearth)
Batch size	5-10 kg cassava mash
Frying time	30-60 minutes per batch
Stirring	Continuous manual stirring with wooden paddles (2-3 persons)
Temperature	Inconsistent (flames vary, hot spots)
Quality	Variable (burnt, under-dried, lumpy)
Labour	2-3 persons per pan
Throughput	10-20 kg/hour

(Source: Adebayo and Ogunyemi, 2020)

2.1.3 Concept of Mechanized Garri Frying

Mechanized garri frying uses a machine with rotating drum and mechanical stirring (Eze and Nweze, 2019).

Components of a Garri Frying Machine:

Component	Function	Material
Drum/cylinder	Holds cassava mash during frying	Mild steel, stainless steel (food-grade)
Heating system	Provides heat for frying	Gas burners, electric heating elements, insulated firebox
Agitator/stirrer	Mixes and turns mash to prevent burning	Paddles/blades attached to rotating shaft
Drive system	Rotates agitator/drum	Electric motor, gearbox, pulleys, belts
Frame/stand	Supports all components	Angle iron, mild steel
Discharge system	Removes fried garri from machine	Tilting mechanism, discharge door
Temperature control	Regulates frying temperature	Thermostat, thermocouple, controller

(Source: Okonkwo, 2020)

Types of Garri Frying Machines:

Type	Capacity (kg/batch)	Power Source	Cost (₦)	Suitability
Manual batch fryer (hand-crank)	10-20	Manual	50,000-100,000	Very low cost, still labor-intensive
Motorized batch fryer (horizontal drum)	20-50	Electric motor (1-3 HP)	200,000-500,000	Small to medium-scale
Motorized batch fryer (vertical drum)	30-60	Electric motor (2-5 HP)	300,000-700,000	Medium-scale
Continuous fryer	100-500/hour	Electric motor (5-10 HP)	1,000,000-5,000,000	Industrial-scale

(Source: Okafor and Nwosu, 2020)

2.1.4 Engineering Properties of Cassava Mash and Garri

Property	Cassava Mash (Wet Cake)	Garri (Final Product)	Importance for Design
Initial moisture content	40-50%	8-12%	Determines drying requirement
Bulk density	0.8-1.0 g/cm³	0.5-0.6 g/cm³	Affects volume of drum
Angle of repose	30-40°	25-35°	Affects discharge design
Specific heat capacity	2.5-3.5 kJ/kg·K	1.5-2.0 kJ/kg·K	Affects heat requirement
Thermal conductivity	0.3-0.5 W/m·K	0.1-0.2 W/m·K	Affects heat transfer rate
Gelatinization temperature	70-80°C	–	Minimum frying temperature

(Source: Okafor and Ugwu, 2021)

2.1.5 Performance Evaluation Parameters for Garri Frying Machine

Parameter	Definition	Formula	Target
Frying time	Time to fry one batch (minutes)	Direct measurement	<30 min
Capacity	Mass of cassava mash per batch (kg)	Direct measurement	20-50 kg
Throughput	Mass of garri per hour (kg/h)	(Capacity × batches/h) × yield	>50 kg/h
Moisture content (final)	Water content of finished garri (%)	(Wet weight – Dry weight)/Wet weight × 100	<12%
Uniformity	% uniformly fried (no burnt/under-dried)	Visual inspection	>90%
Energy consumption (electrical)	Electrical energy per kg garri (kWh/kg)	Motor power (kW) × time (h) / mass (kg)	<0.5 kWh/kg
Energy consumption (thermal)	Thermal energy per kg garri (MJ/kg)	Fuel consumption × calorific value / mass	Optimize
Production cost	Cost per kg garri (₦/kg)	Total cost (labour, energy, depreciation)/mass	<₦50/kg

(Source: Adebayo and Ogunyemi, 2020)

2.1.6 Design Considerations for Garri Frying Machine

Design Parameter	Consideration	Recommended Value
Drum diameter	Affects capacity, heat transfer	50-80 cm
Drum length	Affects capacity, stirring efficiency	50-100 cm
Drum wall thickness	Affects durability, heat transfer	3-5 mm (mild steel)
Agitator speed	Affects mixing, prevents burning	20-50 rpm
Motor power	Depends on capacity and agitator speed	1-5 HP (0.75-3.7 kW)
Heating system capacity	Depends on heat required to evaporate water	5-20 kW
Frying temperature	Gelatinization temperature + margin	150-200°C
Material (food contact)	Must be food-grade, non-toxic	Stainless steel (preferred) or mild steel

(Source: Okafor and Nwosu, 2020)

2.1.7 Material Selection for Garri Frying Machine Components

Component	Material Options	Selected	Reason
Drum/cylinder	Mild steel, stainless steel	Mild steel (or stainless steel if affordable)	Cost, availability, ease of fabrication
Agitator/paddles	Mild steel, stainless steel	Mild steel (or stainless steel if affordable)	Cost, ease of fabrication
Shaft	Solid mild steel rod	30-50 mm diameter	Strength, durability
Bearings	Ball bearings (pillow block)	Pillow block bearings	Easy to mount, low cost
Pulleys	Cast iron, mild steel	Cast iron	Durability
Belts	V-belts	A, B, or C section	Standard, available
Frame	Angle iron (50×50×5 mm)	Angle iron	Strength, rigidity
Heating elements	Gas burners, electric heaters	Gas burners (or electric if available)	Cost, availability

(Source: Shigley, Mischke, and Budynas, 2020)

2.1.8 Conceptual Framework Diagram (Described in Text)

The conceptual framework can be visualized as follows:

Input (Design and Materials) → Machine Components → Output (Garri) → Performance Parameters

Input (Independent Variables):

• Machine design specifications (drum dimensions, motor power, agitator speed, heating system capacity)
• Material selection (mild steel, angle iron, bearings, pulleys, belts)

↓ Machine Components (Construction):

• Drum/cylinder
• Heating system
• Agitator/stirrer
• Drive system (motor, gearbox, pulleys, belts)
• Frame/stand
• Discharge system
• Temperature control

↓ Output (Dependent Variables – Performance):

• Frying time (minutes/batch)
• Capacity (kg/batch)
• Throughput (kg/hour)
• Moisture content (%)
• Uniformity (%)
• Energy consumption (kWh/kg)
• Production cost (₦/kg)

Comparison:

• Traditional garri frying method (manual stirring over open fire)

The framework posits that machine design and materials (independent variables) determine machine components, which in turn determine performance parameters (dependent variables). The performance of the constructed machine is compared with traditional garri frying.

2.2 Theoretical Framework

This study is anchored on three supporting theories that provide a comprehensive theoretical foundation for the design and construction of a garri frying machine. These theories are Heat Transfer Theory, Mass Transfer Theory, and Machine Design Theory.

2.2.1 Heat Transfer Theory

Heat Transfer Theory, developed by Fourier (1822) and extended by Incropera and DeWitt (2019), explains the mechanisms of heat transfer (conduction, convection, radiation) and the factors affecting heat transfer rate (Incropera and DeWitt, 2019).

Core Propositions:

1. Conduction: Heat transfer through solid materials (drum wall, cassava mash). Fourier’s law: , where  is heat flux,  is thermal conductivity,  is temperature gradient.
2. Convection: Heat transfer between a solid surface and a fluid (air, steam). Newton’s law of cooling: , where  is convective heat transfer coefficient,  is surface temperature,  is fluid temperature.
3. Radiation: Heat transfer via electromagnetic waves. Stefan-Boltzmann law: , where  is emissivity,  is Stefan-Boltzmann constant.
4. Heat required for frying: Heat required to raise temperature of cassava mash to frying temperature and evaporate water: , where  is mass,  is specific heat,  is temperature rise,  is mass of water evaporated,  is latent heat of vaporization.

Application to Garri Frying Machine Design

Heat Transfer Theory predicts:

• The drum wall should have high thermal conductivity to transfer heat efficiently from the heat source to the cassava mash.
• The frying temperature should be 150-200°C to achieve gelatinization and drying without burning.
• Insulation around the drum reduces heat loss, improving energy efficiency.
• The heat requirement for frying 20 kg of cassava mash (initial moisture 45% to final 10%) is approximately 5-10 MJ per batch.

2.2.2 Mass Transfer Theory

Mass Transfer Theory, developed by Fick (1855) and extended by Cussler (2019), explains the movement of moisture from the interior of the mash particles to the surface and evaporation into the surrounding air (Cussler, 2019).

Core Propositions:

1. Diffusion: Moisture movement within the cassava mash occurs by diffusion. Fick’s law: , where  is mass flux,  is diffusion coefficient,  is concentration gradient.
2. Evaporation: Moisture at the surface evaporates into the surrounding air. Evaporation rate depends on temperature, humidity, and air velocity.
3. Drying rate: Drying occurs in three stages:
   • Constant rate period: Surface moisture evaporates (high rate)
   • First falling rate period: Moisture front moves into particle (decreasing rate)
   • Second falling rate period: Bound water removal (slow rate)
4. Moisture content target: Final moisture content should be <12% for safe storage (no mould, no fermentation).

Application to Garri Frying Machine Design

Mass Transfer Theory predicts:

• Agitation (stirring) continuously exposes new surfaces, increasing evaporation rate and reducing frying time.
• Higher temperature increases evaporation rate (reduces frying time).
• The machine should remove water vapor (ventilation) to prevent condensation.
• Initial moisture content (40-50%) must be reduced to <12%, requiring removal of 28-38% of the mass as water.

2.2.3 Machine Design Theory

Machine Design Theory, developed by Shigley, Mischke, and Budynas (2020), provides the principles for designing mechanical components (shafts, bearings, gears, belts, motors) and selecting materials (Shigley, Mischke, and Budynas, 2020).

Core Propositions:

1. Factor of safety: Design components to withstand loads greater than expected (factor of safety = ultimate strength / allowable stress). Typical factor of safety: 2-4 for agricultural machinery.
2. Shaft design: Shaft diameter is determined by torque and bending moment: , where  is bending moment,  is torque,  is allowable shear stress.
3. Bearing selection: Bearings are selected based on radial and axial loads, speed, and desired life ( life, hours).
4. Belt drive design: Belt length and tension are calculated from center distance, pulley diameters, and power transmitted.
5. Motor selection: Motor power is determined by torque and speed: , where  is angular speed (rad/s). Add safety factor (1.5-2.0) for starting torque.
6. Material selection: Materials are selected based on strength, stiffness, durability, corrosion resistance, cost, and availability.

Application to Garri Frying Machine Design

Machine Design Theory predicts:

• The agitator shaft must be designed to withstand the torque from stirring (viscous resistance of cassava mash).
• Bearings must support the shaft and withstand radial loads.
• The motor power must be sufficient to drive the agitator (1-5 HP depending on capacity).
• The frame must be rigid and stable (angle iron 50×50×5 mm).
• Materials in contact with food (drum, agitator) should be food-grade (stainless steel preferred, or clean mild steel).

Integration of the Three Theories

The three theories are complementary and collectively provide a robust theoretical framework for this study:

Theory	Focus	Contribution to Study
Heat Transfer Theory	Heat transfer from source to cassava mash	Determines heating system design, insulation requirements, frying temperature
Mass Transfer Theory	Moisture movement and evaporation	Determines frying time, agitation requirements, moisture content target
Machine Design Theory	Mechanical components (shafts, bearings, motor, frame)	Determines agitator design, motor power, bearing selection, material selection

Together, these theories support the design and construction of a garri frying machine, recognizing that: (1) heat transfer determines the heating system (Heat Transfer); (2) mass transfer determines frying time and agitation (Mass Transfer); and (3) machine design principles ensure structural integrity and proper component selection (Machine Design).

2.3 Review of Related Empirical Studies

This section reviews empirical studies relevant to the design and construction of garri frying machines.

2.3.1 Studies on Traditional Garri Frying (Nigeria)

Adebayo and Ogunyemi (2020) studied traditional garri frying in Oyo State. Using surveys and direct observation, they documented: batch size (5-10 kg), frying time (30-60 minutes), labour (2-3 persons per pan), throughput (10-20 kg/hour), and challenges (burning, smoke, inconsistent quality). The study recommended mechanized garri frying.

2.3.2 Studies on Mechanized Garri Frying Machines (Nigeria)

Eze and Nweze (2019) designed and constructed a motorized garri frying machine in Enugu State. Specifications: drum (60 cm diameter, 50 cm length), agitator (4 paddles), motor (2 HP, 1440 rpm, gear reduction to 30 rpm), capacity (30 kg/batch), frying time (25 minutes), throughput (50 kg/hour). The machine produced uniformly fried garri with moisture content <10%. The study recommended the machine for small-scale processors.

Okafor and Nwosu (2020) evaluated three types of garri frying machines in Edo State: manual batch fryer, motorized batch fryer, and continuous fryer. The motorized batch fryer had capacity 40 kg/batch, frying time 20 minutes, throughput 80 kg/hour, moisture content 9%. The continuous fryer had capacity 200 kg/hour, moisture content 10%, but cost ₦2.5 million. The study recommended the motorized batch fryer for small to medium-scale processors.

Okonkwo (2020) designed and constructed a gas-fired garri roasting machine in Cross River State. Specifications: drum (50 cm diameter, 60 cm length), gas burner (2 burners), motor (3 HP), capacity (50 kg/batch), frying time (30 minutes), throughput (60 kg/hour). The machine cost ₦350,000 (fabrication cost). The study recommended gas-fired machines for areas with unreliable electricity.

2.3.3 Studies on Performance Evaluation Parameters

Okafor and Ugwu (2021) evaluated the performance of motorized garri frying machines in Anambra State. Parameters measured: frying time (15-25 minutes), capacity (20-50 kg/batch), throughput (40-100 kg/hour), moisture content (8-12%), uniformity (85-95%), energy consumption (0.4-0.6 kWh/kg). The study concluded that motorized garri frying machines are effective and efficient.

2.3.4 Studies on Material Selection and Fabrication

Okafor and Nwosu (2020) compared mild steel and stainless steel drums for garri frying. Mild steel drums cost 60% less than stainless steel but require food-grade coating to prevent rust. The study recommended mild steel with food-grade coating for affordability.

2.3.5 Summary of Empirical Findings

The empirical literature reveals consistent findings: (1) traditional garri frying is labor-intensive, time-consuming, and inefficient; (2) motorized garri frying machines reduce frying time by 50-70% and increase throughput by 200-400%; (3) capacity ranges from 20-50 kg/batch for small to medium-scale machines; (4) frying time 20-30 minutes; (5) throughput 50-100 kg/hour; (6) moisture content 8-12%; (7) uniformity 85-95%; (8) material cost is a major constraint (mild steel with coating is more affordable). This study designs and constructs a machine based on these findings.

2.4 Summary of Literature Review

The table below summarizes key theoretical and empirical literature relevant to the design and construction of a garri frying machine.

S/N	Author(s) and Year	Focus of Study	Strength	Weakness	Limitation	Gap Identified
1	Incropera and DeWitt (2019)	Heat Transfer Theory	Explains conduction, convection, radiation	Complex mathematics	General theory	Application to garri frying needed
2	Cussler (2019)	Mass Transfer Theory	Explains diffusion, evaporation, drying stages	Complex mathematics	General theory	Application to garri drying needed
3	Shigley, Mischke and Budynas (2020)	Machine Design Theory	Principles for shaft, bearing, motor selection	General; not food-specific	General theory	Application to food processing equipment needed
4	Adebayo and Ogunyemi (2020)	Traditional garri frying (Oyo)	Documented challenges	No machine design	No design	Design study needed
5	Eze and Nweze (2019)	Motorized garri frying machine (Enugu)	Designed and constructed; capacity 30 kg/batch	Single design	Limited design variations	Alternative designs needed
6	Okafor and Nwosu (2020)	Evaluation of three machine types (Edo)	Compared manual, motorized, continuous	Single state	Geographic gap	Multi-state design needed
7	Okonkwo (2020)	Gas-fired garri roasting machine (Cross River)	Gas-fired design	Single state; gas only	Geographic and energy source gaps	Electric and diesel options needed
8	Okafor and Ugwu (2021)	Performance evaluation (Anambra)	Quantified performance parameters	Single state	Geographic gap	Multi-state evaluation needed
9	Okafor and Nwosu (2020)	Material comparison (mild steel vs. stainless steel)	Cost comparison	Single state	Geographic gap	Material selection guidance needed
10	FAO (2022)	Cassava processing (global)	Overview	Not Nigeria-specific	Geographic gap	Nigeria-specific design needed
11	FMARD (2021)	Agricultural sector report	Official data	Not engineering-specific	No design data	Engineering study needed

Summary of Identified Gaps from the Table:

Design Variation Gap: Existing designs vary; no standardized design for small to medium-scale processors.

Material Cost Gap: Stainless steel is expensive; alternative materials (mild steel with coating) need evaluation.

Energy Source Gap: Electric motors require reliable electricity (not available in rural areas); gas or diesel options needed.

Affordability Gap: Existing machines cost ₦200,000-500,000; more affordable designs needed.

Locally Fabricated Gap: Few designs use locally available materials and standard components.

This study is designed to address these identified gaps by: (1) developing a standardized design; (2) evaluating mild steel with food-grade coating as an affordable alternative; (3) designing for electric motor (with option for diesel engine); (4) targeting a fabrication cost of <₦200,000; and (5) using locally available materials (mild steel, angle iron, bearings, pulleys, belts).