A. Definitions
Hygroscopic Materials – are substances which are variable in the moisture content they can h old at different times. Bone-dry weight (BDW) – is the final constant weight attained by any hygroscopic substance after being dried out or no trace of moisture left. Regain – the hygroscopic moisture content of a substance expressed as the ratio of the moisture weight to the bone dry weight. Gross weight – expressed as the sum of the moisture weight and bone-dry weight.
Gross weight = Moisture weight + Bone-dry weight
Moisture content – expressed as the ratio of the moisture weight to the gross weight.
Moisture content = Moisture weight / Gross weight B. Computations and Formulas :
Dryer Diagram
Gross Weight = Bone-dry Weight + Moisture Weight
GW = BDW + MW
BDW of entering material = BDW of leaving material
GW A – MW A = GW B – MW B
Moisture removed from materials, m R
mR = MW A – MW B
Moisture removed by air = moisture removed from materials m A(H4 – H3) = mR = MW A – MW B
m A = MW A – MW B (H 4 – H 3) where: MW A = total moisture content at A, kg wv/s w v/s MW B = total moisture content at B, kg wv/s H4 = moisture content of air leaving dryer, kg wv/kg da H3 = moisture content of air entering dryer, kg wv/kg da m A = air mass flow rate, kg dar/s da= dry air wv= water vapor
Considering the air preheater and m s = steam mass flow rate Heat gained by the air = heat lost by the steam m A( h2-h1)= mshfg ms=m A(h2-h1) hfg
C. Three Methods of drying based on heat transfer
Direct of convection drying Indirect drying Infrared or radiant heat drying
D. Types of dryers based on movement of materials
Continuous dryer Batch dryer
E. Types of dryers based on heat source
Steam heated Oil fired, coal fired Electric
F. Classification Classification of Dryers
Rotary Dryer – most commonly used dryer which consists of a rotating cylinder inside which the materials flow while getting in contact with the hot gases; the cylinder is tilted at a slight angle and fitted with lifting flights; used for copra, sand, wood chips.
Rotary Dryer Tower Dryer – consist of a vertical shaft in which the wet feed is introduced at the top and falls downward over baffles while coming in contact with the hot air which rises and exhausts at the top; used for palay, wheat, grains.
Tower Dryer
Hearth Dryer – a type of dryer in which the material to be dried is supported on a floor through which the hot gases pass; used for copra, coal, enamel wares.
Hearth Dryer
Centrifugal Dryer – consists of centrifuge revolving at high speeds causing the separation, by centrifugal force, of the water from the material; used for drying fertilizer, salt, sugar.
Centrifugal Dryer
Tray Dryer – consists of trays, carrying the materials to be dried, placed in compartment or moving conveyor; used for ipil-ipil leaves, grains.
Tray Dryer
Infrared Ray Dryer – consists of infrared lamps in which the rays are directed to the articles to be dried; use for during painted articles like cars.
G. Example problems:
1. A copra drying plant is designed to dry 1000 kg/hr of fresh coconut meat containing 30% water. The raw copra from the dryer contains 5% water. Fresh air at 27C and 40%RH enter the dryer at 98Kpa. The air is heated at 110C before entering the adiabatic drying chamber and leaves the dryer at a temperature of 75C with wi th a humidity ratio of 0.02285 Kgwv/Kgda. Assuming 100% heat transfer efficiency in the air pre-heater, find the amount of steam required by the dryer when condensing saturated steam to saturated liquid at 150Kpa. Express answer in kg/hr. 2. A rotary dryer is to deliver 1.5 Mtons per hour of copra with moisture content not to exceed 3%. The wet feed contains 40% moisture. The air enters the dyer with a humidity ratio of 0.016 kg/kg dry air and leaves at 60 °C and 100% RH. If the dyer operates at atmospheric pressure, determine the amount of wet feed in Mtons per hour.
H. Problem Set:
1. A grain dryer consist of a vertical hopper which hot air is blown. The air enters the base at 1.38 bar, 65C, 50%RH. At the top, saturated air is discharged into the atmospheric at 1.035 bar, 60C. Estimate the moisture pickup by 1 kg of dry air, and the total enthalpy change between the entering and leaving streams expressed per unit mass of dry air. Ans. 0.0864 KJ/Kg air, 220 KJ/Kg air 2. Saturated air at 21C is passed through a drier so that its final RH is 20%. The dryer uses silica gel adsorbent. The air is then passed through a cooler until its final temperature is 21C without a change in specific humidity. Find out (a) the temperature of air at the end of the drying process, (b) the heat rejected in KJ/Kg da during the cooling process, (c) the relative humidity at the end of the cooling process, (d) the dew d ew point temperature at the end of the drying process, and (e) the moisture removed during the drying process in Kg wv/ Kg da.
I. DESIGN OF MECHANICAL DRYER
Design a mechanical dryer to dry either fish or grain.
Capacity of the dryer ranges from 4 kg for fish or 5 sacks of palay.
The dryer must be naturally draft and solar heated.
The design must follow the format stated below.
FANS AND BLOWERS A. Definitions
Fan – is a machine used to apply power to a gas to increase its energy content
thereby causing it to flow or move. Blower – is a fan used to force air under pressure p ressure which means resistance to gas
flow is imposed upon discharge. Exhauster – is a fan used u sed to withdraw air under pressure which means resistance
to
gas
flow
is
imposed
upon
suction
B. Common Uses of Fans
Ventilation, air conditioning, force and induced draft service for boilers, dust
collection, drying and cooling of materials, cooling towers, heating, mine and tunnel ventilation, pneumatic conveying and other industrial process work.
C. Basic Differences According to the ASME .
Pump – a machine which adds energy to a liquid.
Fan – a machine which adds energy to a fluid at a pressure rise equal to or below 1 psig.
Blower – a machine which add energy to a fluid at a pressure rise between 50 and 1 psig.
Compressor – a machine which add energy to a fluid at a pressure rise above 50 psig.
D. Basic Element of Fan Design.
a.
Wheel or impeller – the rotating member.
b.
Housing – stationary member provided with an intake opening (inlet) and discharge opening (outlet).
E. Types of Fan.
Propeller Fan
Tube Axial Fan
Vane Axial Fan
Centrifugal Fan
F. Types of blades and performance curves used on centrifugal fans
G. Functions of Fans.
To move air or gases through distribution systems and apparatus required for conditioning of buildings. For drying and cooling. For pneumatic conveying. For duct collection, separation and exhaust. For mine and tunnel ventilation. For forced and induced draft of steam-generating units.
H. Factors Affecting Fan Selection.
Quantity of gas (air) to be moved per unit time. Estimated resistance and expected variations. Amount of noise permitted. Space available for the fan. Economic implications.
I. Fan Performance and Design.
1.
Fan capacity, Q – volume handled by a fan expressed in cubic meter per sec at fan outlet conditions. Q = AV where: Q = volume flow-rate measured at outlet, m ³/s
2.
A = fan outlet area, m ² V = velocity at outlet, m/s Fan static pressure head, hs – the total pressure diminished by the fan
where: hs = static pressure head, meters of air hw = manometer reading, meters of water ρw = density of water = 9.81 kN/m ³ or 1000 kg/m³ or 62.4 lb/ft³. ρa = density of air at standard conditions = 1.2 kg/m ³
Standard condition: 101.325 kPa (29.92 in Hg) and 21.1 C (70 F). 3.
Fan velocity pressure head, hv – corresponds to the average velocity determination from the volume of air flow at the fan outlet area.
where: hv = velocity head, meters of air V o = velocity at outlet, m/s g = acceleration due to gravity, 9.81 m/s ²
4.
Total pressure head , htotal – the rise of the pressure head from fan inlet to fan outlet. htotal =h =hs + hv
5.
Power output – is the power output of a fan developed based on total pressure. Power Output = ρa Qhtotal
6.
Static air power – air horsepower calculated from static pressure. Static Air Power = ρa Qhs
7.
Static efficiency Ꞃs – static air power divided by the shaft power.
8.
Mechanical efficiency Ꞃm – power output divided by the shaft power.
J. Bernoulli’s Equation Applied to Fans.
Basic Assumptions: a. Considering inlet and discharge static pressure. b. Considering inlet and discharge velocities. c. Constant temperature. Total head = static pressure head + velocity head
P1 and hw1 is negative if below atmospheric pressure. Where: P1 and hw1 = inlet static pressure reading. P2 and hw2 = discharge pressure reading.
ρw = density of water (10000 kg/m ³). ρa = density of air (1.2 kg/m³ at 101.325 kPa and 21.11 C). V 1 = inlet velocity, m/s. V 2 = outlet velocity, m/s. g = acceleration due to gravity
K. Fan Characteristics and Fan Laws
Fan characteristics – is the term for the variation in fan capacity or volume pressure, power requirement, and fan efficiency, with degree of restriction or resistance to gas flow, at constant speed. Fan Laws - three basic relationships between fan size, fan speed, and gas density which are the bases for predicting full-size fan performance.
1. Variable fan speed – constant fan size, constant density
2. Variable fan size – geometrically similar fans, constant density
3. Variable gas or air density – constant fan size and speed, constant system or point of rating
L. Fan Combinations
Fans in series – used to increase head with the same discharge.
Fans in parallel – used to increase discharge with the same head.
M. Example Problems
1. Find the air horsepower of an industrial that delivers 25.98 m ³/s of air through a 0.915m X 1.22m outlet. Static pressure is 127 mm of water. Air temperature is 21°C and the barometric pressure is 700 mm Hg. 2. A forced draft fan is used to provide the combustion air requirements of a boiler that burns coal at the rate of 10 metric tons per hour. The air requirements are 100,000 m³/hr, air is being provided under 150mm water gage by a fan which has a mechanical efficiency of 60%. Assume fan to deliver at a total pressure of 150mm water gage. Find the size of the driving motor.
N. Problem Set
1. At 101.325 Kpa and 21°C, an industrial indu strial fan develops a brake power of 100KW and head of 120mm water gage. What will be the power if this fan is operated at 98 Kpa and 32°C at the same speed? 2. Air enters through a duct of a fan with a velocity of 4 m/s and an inlet pressure of 2cm of water less than atmospheric pressure. The air leaves the fan through a duct at a velocity of 12 m/s and a discharge static pressure of 8cm of water above atmospheric pressure. If the specific weight of air is 1.2 kg/m ³ and the fan delivers 12 m³/sec, what is the fan input power to the motor if the fan has a mechanical efficiency of 70% and motor efficiency of 80%. 3. A fan delivers 5 m³/s at a static pressure of 6 cm of water when operating at a speed of 300 rpm. The power input required is 3.5 KW. If 9 m ³/s are desired in the same fan and installation, find the pressure in cm of water.
O. Design of Fans and Blowers
Select one function/laboratory room in BPSU Compute the ventilation requirements or any necessary data that can be used for the design Recommend fans/blowers size and capacity Suggest plans for layout and procedure for installation
PUMPS A. Purpose of Pump
The purpose of a pump is to transfer a fluid from a region of low pressure to another region at the same or higher pressure. A pump is a machine that imparts energy into a liquid to lift the liquid to a higher level, to transport the liquid from one place to another, to pressurize the liquid for some useful purpose, or to circulate the liquid in a piping system by overcoming the frictional resistance of the piping system.
B. Classification of Pumps
1.
Reciprocating a. Direct-acting b. Indirect-acting
Reciprocating Pump
2.
Rotary
Rotary pump 3.
Jet
Jet Pump 4.
Centrifugal
Centrifugal Pump
C. Definitions
Total dynamic head or dynamic head – is the sum of the pressure and velocity heads at a given section stated in units of feet of the fluid flowing. Total dynamic suction lift – is applied to pumps handling cold water and is the reading of a manometer or vacuum gage (converted to feet of the fluid flowing). Net positive suction head (NPSH) – is the difference between the absolute dynamic pressure of the liquid measured at the center line of a pump and the saturation pressure corresponding to the temperature of the liquid at the same point, all expressed in terms of feet head of the fluid flowing. NPSH may also be defined as the pressure at the pump suction flange, corrected to the pump center line, that prevents vaporization of the water.
Developed head (DH) – is the difference between the sum of the absolute pressure head and velocity head (or absolute dynamic head) at the outlet of the pump and the sum of the absolute pressure head and velocity head (or absolute dynamic head) at the inlet, both corrected to the center line of the pump and expressed in feet head of the fluid. Static head – is the height of the surface of water above the gauge point. Pressure head – is the static head plus gauge pressure on the water surface plus friction head.
Velocity head – is the head required to produce a flow of the water. Suction lift – the vertical distance in feet (meters) from the liquid supply level to the pump center line with the pump physically located above the liquid level supply. Suction head - the vertical distance in feet (meters) from the liquid supply level to the pump center line with the pump physically located below the liquid level supply. Static discharge head – the vertical distance in feet (meters) between the pump center line and the point of free discharge on the surface of the liquid in the discharge tank. Total static head – the vertical distance in feet (meters) between the liquid level of the supply and the point of free discharge on the surface of the liquid in the discharge tank. Friction head - the head required to overcome the resistance to flow in the pipe and fittings. Total dynamic suction lift – is the static suction lift plus the velocity head at the pump suction flange plus the total friction head in the suction pipeline.
Total dynamic suction head - is the static suction head minus the velocity head at the pump suction flange minus the total friction head in the suction pipeline. Total dynamic discharge head – is the static discharge head plus the velocity head at the pump discharge flange plus the total friction head in the discharge line. Capacity – is the rate of flow of fluid measure per unit time, usually gallons per minute (gpm) or liters per minute (lpm). Centrifugal pump – a pump in which the pressure is developed principally by the action of centrifugal force. End suction pump – a single suction pump having its suction nozzle on the opposite side of the casing from the stuffing box and having the face of the suction nozzle perpendicular to the longitudinal axis of the shaft.
In Line pump – a centrifugal pump whose drive unit is supported by the pump having its suction and discharge flanges on approximately the same center. Horizontal pump – a pump with the shaft normally in a horizontal position. Vertical shaft turbine pump – a centrifugal pump with one or more impellers discharging into one or more bowls and a vertical educator or column pipe used to connect the bowls b owls to the discharge head on which the pump driver is mounted. Horizontal split-case pump – a centrifugal pump characterized by a housing which is split parallel to the shaft. Booster pump – is a pump that takes suction from a public service main or private use water system for the purpose of increasing the effective water pressure. Submersible pump – is a vertical turbine pump with the pump and motor closed coupled and designed to be installed underground, as in the case of a deepwell pump Static water level – the level, with respect to the pump, of the body of water from which it takes suction when the pump is not in operation. Pumping water level – the level, with respect to the pump, of the body of water from which it takes suction when the pump is in operation. Draw-down – the vertical difference between the pumping water level and the static water level.
D. Typical Pumping Installation
E. Head and Power Calculation
1. Continuity equation Q= AV = constant d Q = As V s = Ad V V d
2. Developed Head (DH) Developed head (DH) = static head + pressure head + velocity head + friction head
Where: zs is negative if the source is below pump center-line and ps is negative if it is a vacuum. 3. Friction head Darcy Equation
4. Water power
5. Brake power (BP) and Pump efficiency ( Ꞃ p).
Where: PL = power required to overcome leakage PDF = power required to overcome disk friction PHL = power required to overcome hydraulic losses PML = power required to overcome mechanical losses
F. Characteristics of Reciprocating Pumps.
1. Piston displacement, V D. Piston rod neglected
Piston rod considered
where: D = inside diameter or bore. d = piston rod diameter. L = piston displacement or length of stroke. S = strokes per minute. N = number of cylinders. 2. Volumetric Efficiency, E v Volumetric efficiency – is the ratio of actual volume to the piston displacement.
3. Slip Slip – is one minus the volumetric efficiency. Slip=1-Ev 4. Actual discharge.
G. Characteristics of Centrifugal Pumps.
3. Specific speed – is defined as the speed in revolutions per minute at which a geometrically similar impeller would operate to develop 1 ft of head when displacing 1 gpm.
where: Ns = specific speed, rpm N = speed, rpm Q = discharge, gpm H = head, ft 4. Impeller Contours a. Radial or conventional b. Francis c. Mixed flow d. Axial flow 5. Range of Specific Speeds
Radial impellers have specific speeds up to about 3000 rpm, while Francis wheels go up to 4500 rpm. Mixed flow impellers range from the specific speed of the Francis wheels to about 10,000; for Propeller types the range is from 10,000 to 14,000 rpm. 6. Similar Pumps
Where: D is the impeller diameter. 7. Affinity Law Affinity laws – these laws express the mathematical relationship and illustrate the effect of changes in pump operating conditions or pump performance variables such as pump head, flow, speed, horsepower, and pump impeller diameters at nearly constant efficiency.
Constant impeller diameter, variable speed
Constant speed, variable impeller diameter
8. Centrifugal Pumps in Parallel and Series Operations. a. Parallel pumps – performance is obtained by adding the capacities at the same head.
b. Series pumps – performance is obtained by adding the heads at the same capacity.
H. Cavitation
Cavitation – is a two-stage phenomenon consisting of the formation of vapor cavities resulting from low pressure and their collapse as they move out of the low-pressure into higher pressure regions. The higher pressure region causing the vapor cavity to collapse can be immediately following the formation of the vapor cavity or some distance downstream from the impeller inlet, depending on the downstream pressure conditions and the quantity of vapor formed. Net positive suction head (NPSH) – is the term used by the pump industry for describing pump cavitation characteristics. NPSH is defined as the pressure (head) in excess of the saturation pressure of the fluid being pumped. NPSH is expressed as NPSH A (available) and NPSHR (required). NPSHA is the NPSH available or existing at the pump installed in the system.
NPSHR is a performance characteristic of a pump and is established through closed loop or valve suppression tests conducted by the pump manufacturer. Causes of Cavitation: a. Low suction pressure b. Low atmospheric pressure c. High liquid temperature d. High velocity e. Rough surfaces and edges f. Sharp bends Bad effects of Cavitation: a. Drop in capacity and efficiency b. Noise and vibration c. Corrosion and pitting
Types of Pumps
I. Example Problems
1. A centrifugal pump delivers 227 m³/hr of water from a source 4 meters below the pump to a pressure tank whose pressure is 2.8kg/cm ². Friction loss estimate are 2 meters in the suction line and 1 meter in the discharge line. The diameter of the suction pipe is 250mm and the discharge pipe is 200mm. Find the kw rating of the driving motor if the pump efficiency is 70%. 2. A pump is to deliver 80GPM of water at 60 °C with a discharge pressure of 1000kPag. Suction pressure indicates 50mm of mercury vacuum. The diameter of the suction and discharge pipes are 5 inches and 4 inches, respectively. If the pump has an efficiency of 70%, determine the brake horsepower of the pump. 3. An acceptance test was conducted on a centrifugal pump having a suction pipe 25.4cm in diameter and discharge pipe 12.7cm in diameter. Flow was 186m ³/hr of clear cold water. Pressure at suction was 114.3mmHg vac and discharge pressure was 107kPag at a point 91cm above the point where the suction pressure gage was measured. Input to the pump was 15hp. If the pump runs at 1750 rpm, what new hp brake hp would be developed and required if the pump speed were increased to 3500 rpm? Assume constant efficiency? 4. A motor driven pump, draws water from an open reservoir A and lifts to an open reservoir B. Suction and discharge pipes are 150mm and 100mm in inside diameter, respectively. The loss of head in the suction line 3 times the velocity head in the 150mm pipe and the loss of head in the discharge line 20 times the velocity head in the 100mm pipeline. Water level at reservoir A is at elevation 6m and that of reservoir B at elevation 75m. Pump centreline is at elevation 2m. Overall efficiency of the system is 73%. Determine the power input of the motor. 5. In problem No.4 determine the reading of the pressure gages installed just at the outlet and inlet of the pump.
J. Set Problems
1. A plant has installed a single suction centrifugal pump with a discharge of 68m ³/hr under 60m head and running at 1200rpm. It is proposed to install another pump with double suction but of the same type to operate at 30m head and deliver 90m ³/hr. What must be the impeller diameter of the proposed pump if the diameter of the existing pump is 150mm? 2. A 4m³/hr pump deliver water to a pressure tank. At the start, the gage reads 138KPa until it reads 276KPa and then the pump was shut off. The volume of the tank is 160liters. At 276KPa the water occupied 2/3 of the tank volume. Determine the volume of water that can be taken out until the gage reads 138KPa. 3. The power output is 30HP to a centrifugal pump that is discharging 900GPM and which operates at 1800rpm against a head, H = 120ft, 220 volt, 3 – phase, 60 hertz. If the pump is modified to operates 1200rpm, assuming its efficiency remains constant, determine the theoretical head. 4. A boiler feed pump receives 45 liters per second of the water 90 °C and enthalpy of 839.33 KJ/kg. It operates against a head of 952m with an efficiency of 70%. Calculate the enthalpy leaving the pump in KJ/kg. 5. Water from a reservoir is pumped over a hill through a pipe 450mm in diameter and a pressure of 1:0 kg/cm ² is maintained at the summit. Water discharge is 30m above the reservoir. The quantity pumped is 0.5m³/sec. Frictional losses in the discharge and suction pipe of the pump is equivalent to 1.5m head loss. The speed of the pump is 800 rpm, what amount of energy must be furnished by the pump in kw?
K. Design of Pumps
Select a building/house/establishment building/house/establishment where pump is to be installed Determine the total head requirements and friction head Identify appropriate pump based on: Flow-rate requirements Head Losses (static and friction) Pump Curve (volume discharge vs. total head) Recommend plans and installation
