## Lesson 2. Design and operational parameters

In the assessment of performance of any gadget, it is important to understand the basics of their design and operational aspects.  For better understanding of the design and operational aspects, the parameters that play important role in the process and operation of the gadgets have to be understood very well.  This lecture deals with the various design and operational parameters involved with the renewable energy based gadgets and their significance.

1. Temperature

Temperature is an important parameter and has major effect in almost all the processes.  It is the measure of heat present in the substance.  It is measured using thermometers, thermocouples etc.  It can be measured either by physical contact with the substance or by noncontact such as infra red thermometers.  The units of measurement are ˚C, F, K etc

2. Pressure

It is the measure of force per unit area.  Normally it will be given in terms of atmospheric pressure by considering atmospheric pressure as 1 atm.  The other units of measurement of pressure are psi, Pascal, kgm s-1 etc.

3. Relative humidity

The degree of saturation of air is given in terms of relative humidity.  It is the ratio of actual water content of air to the moisture content of saturated air at a particular temperature.

4. Air velocity

This is the movement of air in meters per unit time.  The unit is given as m s-1.

5. Flow rate

Mass flow rate : The quantity in terms of mass of substance flowing with respect to time.  The unit is given as mass per unit time (kg min-1).

Volume flow rate : The quantity in terms of volume of substance flowing with respect to time.  The unit is given as volume per unit time (m3 s-1).

The quantity of solar radiation falling on a surface may be measured in terms of total, beam and diffused radiation.  The beam radiation is the radiation falling perpendicular to the surface.  The diffused radiation is the resultant of the scattered radiation falling on the plane.  The sum of both the radiation provides total radiation from sun falling on a surface.

7. Voltage

Voltage is the electrical potential or electromagnetic force appears across a resistance of one ohm when a current of one amphere flows through that resistance.

8. Current

Current is the rate of flow of charge.  The unit is ampere.  It is the current which produces a specified force between two parallel wires, which are 1 meter apart in a vacuum.

9. Power

It is the measure of electrical energy consumption done be any utility.  For single phase and three phase utilities, the power calculation is given as below.

10. Power factor

It is a measure of quality of power.  This is due to the inductive or capacitive effect created in the magnetic load.  This is the ratio between active power and apparent power.

11. Efficiency

The ratio between output and input is known as efficiency of any system.  This gives the performance of the system in terms of effectiveness of the conversion or process performed by the system.

Thermal Efficiency : Thermal efficiency is used to assess the performance of a system whereas the output is in terms of thermal energy.

Electrical efficiency : If the system’s output is measured in terms of electricity, electrical efficiency can be used to assess the performance of the system.

Mechanical efficiency : Mechanical efficiency is used to assess the performance of a system whereas the process of conversion of mechanical energy prevails.

12. Feed rate

The consumption of feed or raw material to any system with respect to time is given as feed rate.  This has to be optimised for better performance of the process inside the system and maximum output.

13. Heating value

This is the measure of energy content of the material otherwise called as calorific value.

Higher Heating Value (HHV) : HHV considers all vapour produced during the combustion process is fully condensed.  Hence, this value is higher than LHV.

Lower Heating Value (LHV) : Whereas LHV considers that the water vapour leaves with the combustion products without fully being condensed.

14. Viscosity

Viscosity is a measure of internal resistance to flow of fluids.  The units for viscosity is Stokes / Centistokes, Engler, Saybolt or Redwood. The measurement of viscosity is made with an instrument called Viscometer.

15. Cetane number

The Cetane Number (abbreviated CN) refers to the combustion quality of diesel fuel. It represents the time delay between the start of injection process and the the point where the fuel ignites.  This value is determined by the % volume of cetane or hexadecane (C16H34) in isocetane that provides the identical ignition delay of the measured fuel sample.

16. Octane number

Octane number is a value used to indicate the resistance of a motor fuel to knock. Octane numbers are based on a scale on which isooctane is 100 (minimal knock) and heptane is 0 (bad knock).

17. Flash point

The flash point of a fuel is the lowest temperature at which the fuel can be heated so that the vapour gives off flashes momentarily when an open flame is passed over it.

18. Pour point

The pour point of a fuel is the lowest temperature at which it will pour or flow when cooled under prescribed conditions.

19. Specific fuel consumption

This is one of the major energy consumption indicators.  This represents the quantity of energy consumed per unit specific to the product.

20. Brake thermal efficiency

It is the ratio of brake thermal horse power to the fuel input.

21. Brake Horse Power

This is the mechanical output of engine in terms of horse power.  The measure of an engine's horsepower without the loss in power caused by the gearbox, generator, differential, water pump and other auxiliaries. The actual horsepower delivered to the driving wheels is less.

22. Biological Oxygen Demand

This is the indicator of the presence of organic matter in the given sample.  Biochemical oxygen demand or B.O.D is the amount of dissolved oxygen needed by aerobic biological organisms in a body of water to break down organic material present in a given water sample at certain temperature over a specific time period.  The BOD value is most commonly expressed in milligrams of oxygen consumed per litre of sample during 5 days of incubation at 20 °C and is often used as a robust surrogate of the degree of organic pollution of water.

23. Chemical Oxygen Demand

Chemical oxygen demand (COD) is defined as the amount of a specified oxidant that reacts with the sample under controlled conditions. It is the measure of oxygen required to oxidize compounds and measures the amount of chemicals in the water that can be oxidized by oxygen.

Chemical Oxygen Demand is a test done to indirectly determine the amount of organic compounds present in a water sample. It is vital for the assessment of the quality of effluents and waste water.

24. Moisture content

The amount of moisture present in the system and can be measured by keeping the material above 100˚C in an oven till reaching a standard dry weight of material.

25. Drying rate

The rate at which the moisture removal from a substance has to be carried out to achieve the required quality of the produce.

26.  Specific heat

It is the amount of heat energy needed to raise the temperature of 1 kg of liquid by 1˚C.