Write short notes, not exceeding 150 words each, on any Four of the following: (1) Radiator Pressure cap (2) Starting aids used in diesel tractors (3) Paddy drum seeder (4) Savonius wind rotor (5) Solar photo-voltanic cellsby Madan Mohan
1. Radiator Pressure Cap:
The pressure cap is similar to the safety valve found on a kitchen pressure cooker. The pressure cap seals the operating cooling system forcing the hot pressurized coolant to carry approximately 50 more degrees of heat than the normal (212) boiling point of water. When seepage or leaks have reduced the quantity of coolant, the temperature rises, forcing open the pressure valve, causing even more coolant to escape. The pressure valve also operates under normal conditions. When the cooling system pressure exceeds the rated pressure of the cap, the hot coolant escapes and overflows under the pressure valve and bottom seal of the cap and into the coolant reservoir tank. After the engine is shut down and begins to cool, the temperature, and therefore the pressure, drops to a point of slight partial vacuum equal to the task of siphoning the overflow coolant back from the reservoir tank, through the vacuum valve of the radiator cap, thereby continually maintaining the radiator at full capacity. The desired siphoning action will only take place if the entire cooling system is free of all leaks and seepage.
2. Starting aids used in Diesel Tractors:
Starting diesel engines during cold weather can be frustrating if engines are not properly prepared for lower temperatures. Batteries that are weak may not crank the starter motor fast enough or long enough to start a cold engine. As the temperature goes down, so does battery capacity. A battery that has all of its power available at 80 degrees F will have only about 46% available power at 0 degrees F. Plus, the engine will be 2.5 times harder to start at 0 degrees due to thicker oil and resistance to movement of internal moving parts. In effect, an engine is about five times harder to start at 0 degrees F than at 80 degrees F. Test weak or suspicious batteries under load before cold weather to help eliminate potential problems during busy times. If batteries need replacement, always replace with a battery equal to or more powerful than the original battery. Accessories such as radios, air conditioners, heaters and other high amperage devices put extra strain on batteries. Turn all of these devices off while the starter motor is in use. Use glow plugs or block heaters on the engine for cold weather starts. Glow plugs heat the internal combustion chamber area to suitable temperatures for combustion. Otherwise, cold fuel sprayed into the chamber and onto the glow plugs can gel and adhere to these parts. Hard starting and inefficient combustion occur with potential for damage to plugs and cylinder heads. Use Number 1 diesel fuel in cold weather. It is more volatile than Number 2 fuel and ignites more readily under cold conditions. Keep the fuel tank full to prevent condensation inside the tank. Water from condensation can freeze and plug fuel lines from the tank to the engine. Add winter diesel fuel additive to the fuel to lower the possibility of gelling and improve starting. Store tractors inside tool sheds, barns, garages or other suitable locations that are heated or warmer than outside temperatures. Only a few degrees warmer temperature can make starting faster and easier. The warmer the battery is, the more power it can provide to the starter motor to crank the engine. The warmer the engine oil is, the thinner it will be and have less resistance to moving engine parts. Make sure you are using the proper viscosity oil recommended for your engine for cold temperatures. If you cannot store engines inside or in a heated area, install a block heater on the engine. To save time and electricity, put the block heater on an electrical timer set to come on a couple of hours before you plan to start the engine. If you suspect fuel has gelled from cold temperatures, change the fuel filter and warm the fuel (wait for the outside temperature to rise, use a block heater or put the tractor inside a heated area) before attempting to start the engine. Gelled fuel in the filter can block the flow of fuel from the tank to the injector pump. After starting the engine on a cold day, allow the engine to warm up a few minutes before putting the tractor under load. Proper engine operation temperatures assure more efficient fuel combustion and may prevent damage to cold engine parts. Engine oil flows more readily at operating temperatures and allows proper lubrication of upper engine parts and areas.
3. Paddy Drum Seeder
The paddy drum seeder is used for sowing pre-germinated paddy seeds directly on well puddle and levelled fields. The seeder consists of a seed drum, baffles, main shaft, ground wheel, floats, and handle. Joining the smaller ends of frustum of cones makes the seed drum. The seed drum is hyperboloid shaped with 20 cm diameter. There are eight numbers of seeding metering holes of 9 mm diameter. Baffles in the drum maintain the uniformity in seed rate. Nine numbers of seed metering holes of 10 mm diameter are provided along the circumference of the drum at the both ends for a row torow spacing of 200 mm. Flat spikes of 12 mm wide and 25 mm long are joined on the plastic ground wheel parallel to its axis of rotation. The slope of the cone facilitates the free flow of seeds towards the metering holes. Two floats are provided on either side to prevent the shrinkage and to facilitate easy pulling of the seeder.
4. Savonius Wind Rotor
Figure shows the basic parameters needed to calculate power and rotational speed of a Savonius wind rotor.
d – diameter of plastic pipe [m]
D – wing spread of rotor [m]
e – pipe spacing [m]
h – height of blades / tubes [m]
v – wind speed [m/s]
F – diameter of end plates [m]
The maximum power of the rotor is estimated according to Betz’s law
?ѕ = ½ ?∙?∙?³∙??=0.36∙ℎ∙?∙?³. [W] ……………
? =1.2 kg/m³ is the air density, ?=ℎ∙? the sweep area of the rotor blade and Cp=0.593 the Betz coefficient. However, there are aerodynamic and mechanical losses in the order of 50%. Our rotor shaft power equation then becomes
??=0.18∙ ℎ∙ ?∙?³. [W] …………………………………
The rotational speed is defined as
?= (60/2?) ∙?, [rpm] …………………………………
Where ?=?∙?/? is the angular velocity in units of radians per second, ?=?/2 the radius of the rotor and λ = 1 the tip-speed ratio. Furthermore, the torque at the rotor shaft is given as
??=??/?. [Nm] ………………………………………….
It is now possible to calculate key parameters of the rotor using the above equations.
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