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Engineering Principles for

Agro-Industry

คาํอธิบายรายวิชา

• มิติและหน่วยทางวศิวกรรม สมบติัทางเทอร์โมไดนามิกส์ กฎการอนุรักษม์วลสารและพลงังาน ระบบและสถานะของระบบ กฎขอ้ที0สองของเทอร์โมไดนามิกส์ กลศาสตร์ของไหล การถ่ายเทความร้อนและมวลสาร

การแบ่งคะแนน• สอบกลางภาค 30 %• สอบปลายภาค 30 %• ปฏิบติัการ 30 %• จิตพิสยั 10 %

หนงัสืออ่านประกอบ

• Introduction to Food Engineering– Singh and Heldman 2nd ed., 3rd ed.

• Food Engineering– Heldman and Singh

• Web : www.rpaulsingh.com

หน่วยที0 1 บทนาํ

• Food Engineering

• Quantitative examination of interaction of physical and energy transfer operations with food.

มิติ Dimensions

• Time, t• Length, L• Mass, M• Force, F• Energy, E

ค่าของมิติ แสดงไดห้ลายรูปแบบ แต่ละแบบ เรียกว่า หน่วย (Unit)

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Dimensions

• Primary Dimension– Length, time, temperature, mass, force

• Secondary Dimension– Combination of primary dimension– Volume = L3

– ความเร่ง = ความเร็ว/เวลา = L.t-1/t = L.t-2

• แรง = มวล . ความเร่ง = m.L.t-2

• ความดนั = แรง/พืhนที0

= mLt-2/L2 = mL-2t-2

• งาน = แรง . ระยะทาง

= mLt-2.L

= mL2t-2

หน่วย Unit

1. Length, meter (m)

2. Mass, kilogram (kg)

3. Time, second (s)

4. Electric Current, Ampere (A)

5. Thermodynamic temperature, Kelvin (K)

6. Amount of substance, mole (mol)

7. Luminous intensity, candela (cd)

8. Force, Newton (N) = kg.m.s-2

CHAPTER I INTRODUCTION

1. Dimensions

2. Engineering Units

1. Base Units

2. Derived Units

3. Supplementary

Units

Measurable attribute of phenomena or matter

Name Symbol

Length meter m

Mass kilogram

kg

Time second s

Electric current ampere A

Thermodynamic temperature

Kelvin K

Amount of substance mole mol

Luminous intensity candela cd

TABLE 1.1 SI Base Units

TABLE 1.2 Examples of SI Derived Units

Expressed in Terms of Base Units

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3. System

System

• Closed system – closed to mass flow

• Open system – heat and mass flow in/out

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4. Properties

1. Intensive Properties– Do not depend on mass of system : temp,

pressure, density

2. Extensive Properties– Depends on size of system : mass, length,

vol, Energy

5. Area Length2 : m2

densitySolid

densityBulk - 1 Porosity =

6. Density

(1.1)

density Particle

densityBulk - 1 Porosity cleInterparti = (1.2)

Mass/Length3 : kg/m3

Inversion of density

= specific volume (m3/kg)

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7. Concentration

BA

AA nn

n X

+= (1.4)

BA

AA

M1000

M

M X

+′

′= (1.5)

Amount per unit volume

w/w, w/v

Mole fraction

sample moist of mass

waterof mass MCwb =

8. Moisture Content

(1.6)

solidsdry of mass

waterof mass MC db = (1.7)

Wet basis, MCwb

Dry basis, MCdb May be > 100 %

sample moist of mass

waterof mass MC wb = (1.8)

solidsdry of mass water of mass

waterof mass MC wb += (1.9)

1 solidsdry of mass water / of mass

solidsdry of mass water / of mass MC wb += (1.10)

1MC

MC MC

db

dbwb +=

wb

wbdb MC1

MC MC−

=

(1.11)

(1.12)

9. Equation of State and Perfect Gas Law

ATR VP =′ (1.13)

ATR P ρ= (1.14)

A0A0A T nR T(m/M)R TmR PV === (1.15)

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10. Phase Diagram of Water

sublimation

• Saturated liquid : at satn temp & pressure

• Subcooled liquid :

• Saturated vapor : at satn temp & pressure

• Superheated vapor : higher temp

At satn pressure but lower temp

kPa01.3251 bar 1.01325 lb/in. 14.696 atm l 2 ===

11. Pressure, force to area

Pressure of fluid – height or head

P = ρgh

Absolute pressure for perfect vacuum = 0 Pa

Absolute pressure = gauge pressure + atm P

12.Enthalpy

H = U + PV (1.18)

14.Conservation of Mass

material input through the system boundary

material output through the system boundary

material generation within the system boundary

material consumption within the system boundary

Material accumulation within the system boundary

(1.19)

Extensive property

Enthalpy value is always given relative to a reference state

material input through the system boundary

material output through the system boundary

material accumulation within the system boundary

(1.20)

material input through the system boundary

(1.21)material output through the system boundary

If no generation or consumption

At steady state, no accumulation

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15. Energy

12PE mgh - mgh E =∆ (1.22)

υυ=∆

1

2 -

2

2m

2

1 E KE

(1.23)

Potential energy

Kinetic energy

PEKE E E U Eenergey in change Total ∆+∆+∆=∆

Internal energy ∆U

Heat, Q

Energy transferred due to temp difference

Q +ve when heat is entering system

Q –ve when heat is leaving system

16.Work

Fig. 1.16 Schematic illustration of the expansion of a gas in a cylinder

Action on system

PEE - W ∆= (1.28)

KEE - W ∆= (1.30)

Object moved

Increased velocity

17. Conservation of Energy

Energy input through the system boundary

Energy output through the system boundary

Energy accumulation within the system boundary

(1.37)

W -Q E =∆ (1.38)

W -Q E E U PEKE =∆+∆+∆ (1.39)

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For Heating Processes

• Constant pressure

• No friction

QH =∆

TmcH p∆=∆

18. Power

Rate or doing work

1 hp = 0.7457 kW