Mechanical Engineering Test - 1

Concept:

• Products are manufactured by the transformation of raw material (into finished goods). This is how production is achieved.
• Planning looks ahead anticipates possible difficulties and decides in advance as to how the production be carried out.
• The control phase makes sure that the programmed production is constantly maintained.
• A production planning and control system has many functions to perform, some before the arrival of raw materials and tools, and others while the raw material undergoes processing.
• There are four steps in the process of production planning and control:

1. Routing: Routing can be defined as the process of deciding the path (route) of work and the sequence of operations.
2. Scheduling: The scheduling function determines when an operation is to be performed, or when work is to be completed.
3. Dispatching: It is the action, doing or implementation stage. It comes after routing and scheduling. Dispatching means starting the process of production. It provides the necessary authority to start the work.
4. Expedition or follow-up: It is designed to keep track of the work effort. The aim is to ensure that what is intended and planned is being implemented. It maintains proper records of work, delays, and bottlenecks. Such records can be used in the future to control production.

Explanation:

So, finally, we can say that Routing - Scheduling - Dispatching - Follow-up is the correct sequence of operation in production planning and control.

Explanation:

Basic Processes in Conditioning of Air:

Sensible heating: 

The moisture content of air remains constant so specific humidity is constant, temperature increases as it flows over a heating coil.

Sensible cooling: 

The moisture content of air remains constant so specific humidity is constant, but its temperature decreases as it flows over a cooling coil.

Dehumidification:

• When the temperature remains constant but specific humidity decreases.
• It is represented by a vertical line.

Humidification:

• When in a process, the temperature remains constant but specific humidity increases.
• It is represented by a vertical line.

Cooling and dehumidification:

• This process involves lowering both the air temperature and specific humidity. 
• This process is commonly used in summer air conditioning in which air passes over a cooling coil. 
• When moist air is cooled below its dew point, the vapor is condensed from the air resulting in simultaneous cooling and dehumidification.

Heating and Humidification:

• During winter it is essential to heat and humidify the room air for comfort.
• It is done by first sensibly heating the air and then adding water vapor to the air stream through steam nozzles, as a result, both the temperature and humidity ratio of air increases.

Cooling & humidification:

Air temperature drops and its humidity increases. 

Heating and de-humidification:

This process can be achieved by using a hygroscopic material, which absorbs the water vapor from the moisture. If this process is thermally isolated, then the enthalpy of air remains constant, as a result, the temperature of air increases.

Additional Information

Dry Bulb Temperature: Actual temperature of gas or mixture of gases.

Wet Bulb temperature: Temperature obtained by an accurate thermometer having a wick moistened with distilled water.

Dew point temperature: Temperature at which the liquid droplets just appear when the moist air is cooled continuously.

Relative humidity along the saturation line is 100%.

Explanation:

∇⋅(∇f × ∇g) = ∇g. curl (∇f) - ∇f. (curl (∇g)

[∵ div (A̅ × B̅) = B̅. curl A̅ - A̅. curlB̅)]

And by the property Curl (grad ϕ) = 0

∴ ∇.(∇f × ∇g) = ∇g. 0 - ∇f . 0

∴ ∇.(∇f × ∇g) = 0

Concept:

Effectiveness:

• Effectiveness is defined as the ratio of actual heat transfer to the maximum possible heat transfer in the heat exchanger.
• The maximum possible heat transfer is determined by using the counter flow concept.

Effectiveness in terms of NTU and heat capacity ratio for a compact heat exchanger, When heat capacity ratio C = 1,

Additional Information

The formula of effectiveness for:

Concept:

Diesel cycle:

Explanation:

If in any process the temperature of the system decreases even after supplying the heat, then the specific heat capacity of such a process is considered as negative.

Now, in the above case:

• If Q < W, then an extra amount of energy is required to complete the work, other than the energy supplied by heat (Q).
• This extra amount of energy comes from the internal energy, hence the internal energy decreases.
• Since internal energy (U) is the function of temperature only, so the temperature of the system will also decrease.
• So in this process, we can see that even while we are supplying the heat, the temperature is decreasing, which indicates that the specific heat capacity of the process is negative.

The specific heat capacity for a polytropic process can be expressed as:

Explanation:

Temperature gradient:

• For the given direction, the temperature gradient is the rate of change in temperature with respect to the displacement.
• It means that the temperature gradient is the ratio of the temperature difference between two points to the distance between these two points.

• The temperature gradient in a flowing fluid over a flat plate is Zero at the top of the boundary layer and maximum at y = 0.

Additional Information

Thermal Boundary Layer:

• Similar to the velocity boundary layer, a thermal boundary layer develops when fluid at a specific temperature flows over a surface which is at a different temperature.

• The relative thickness of the velocity and the thermal boundary layers is described by the Prandtl number.
• For low Prandtl number fluids, i.e. liquid metals, heat diffuses much faster than momentum flow and the velocity boundary layer is fully contained within the thermal boundary layer.
• On the other hand, for high Prandtl number fluids, i.e. oils, heat diffuses much slower than the momentum and the thermal boundary layer is contained within the velocity boundary layer.

​Concept:

• In uniform pressure theory, Pressure (P = Constant)
• In uniform wear theory, (Pr = constant)

where T_UPT  = Torque transmitted in uniform pressure theory, μ = Coefficient of friction, W = Axial load, R₀ = Outer radius, R_i = Inner radius

R_eff = Effective radius, n = No. of Pairs

Case 2: Uniform Wear theory

Total torque transmitted by the clutch is given by: