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Thursday, May 9, 2019

How do we determine the refrigeration or cooling capacity experimentally ?

Any refrigeration device's performance is measured in terms of its cooling capacity or refrigeration capacity in kW or Ton. There are many terms available to call capacity of refrigeration system such as cooling capacity, refrigeration capacity, refrigeration power or cooling power or refrigeration effect.

What is cooling capacity or refrigeration capacity or refrigeration power? 

Any refrigeration device removes the heat from low temperature body or space to high temperature body or space by using external power or work (or compressor electric input) as per the Clausius statement of second law of thermodynamics. The amount of heat (J/s) absorbed or removed from the low temperature body or space or object to be cooled (for example, freezer, inside part of domestic refrigerator) is called the refrigeration capacity or refrigeration power or refrigeration effect.

The cooling capacity is termed in J/s or W or in Ton capacity. 1 Ton = 3.5 kW that means a device of 1 Ton removes the 3.5 kW of energy or heat from the space to be cooled. 

If the refrigerator works on vapor compression refrigeration cycle, the heat Qa is absorbed at evaporator (low temperature space) by taking work input (Win) and rejects the heat of Qa + Win amount to the condenser via heat exchange with the air. 

How to obtain refrigeration effect experimentally? 

COP of a refrigeration device is the ratio of Refrigeration effect to work input. Thus in order to determine the COP experimentally, one needs to obtain refrigeration power experimentally. 
When a domestic refrigerator is turned ON, initially all the parts of the refrigerator are at room temperature i.e. 30 ℃. As the cycle continues or compressor runs, the heat is getting removed at the evaporator till the low temperature around -5 ℃ is reached. This temperature can be anything around 0 ℃ depending on the design and capacity of the refrigerator. It takes around 5 minutes to reach low temperature. Once the low temperature is reached, no further temperature reduction is possible because the system reaches at steady state condition. 

Now further heat load in the evaporator of refrigerator starts pumping the heat and temperature of evaporator rises depending on the load. Again the system reaches at steady state temperature if the load is steady. This steady load is called the refrigeration capacity at given steady state temperature. 

For example, a domestic refrigerator is started from room temperature at 09:00 am and the temperature reduction starts. At 09:05 am, the low temperature of -5 ℃ is reached. This condition is called steady state condition because, even if the compressor/refrigerator keep on running, the temperature will not drop. If a heating coil of 5 W capacity is started in evaporator, it will add 5 J of heating load every second. This extra heat load need to be removed and thus, compressor again starts pumping heat. Because of 5 W load, the new steady state temperature is somewhat higher than -5 ℃. Suppose it is 3 ℃. This 3 ℃ will not change if the load remains 5 W. If the load changes, the steady state temperature changes. Thus, 5 W of refrigeration capacity is obtained at 3℃. This is how cooling capacity or refrigeration power is obtained. 

Thursday, March 1, 2018

Which type of industry is best suitable for an internship in mechanical engineering?

Undergraduate studies in mechanical engineering contain the internship as a part of the curriculum. The sole purpose of this internship is to get an experience of witnessing the real-life applications of the theories being taught in each semester. When it comes to deciding the best suitable industry for an internship when you are having more than one options. 

Area of Interest:

Try to select the industry which is very relevant to your area of interest. This will give you more insight into your existing knowledge. 

Wednesday, November 8, 2017

What is the importance of setting drawing Limits in AutoCAD ?

AutoCAD is a drafting software and requires dimensions to be specified on the drawing which has its overall size depend on the how big or small the drawing is. 

AutoCAD has unlimited space in which one can draw the drawing but in real life, one has to either print it or get it into the physical world so, the one has to prefix the size of the drawing. 

What is LIMITS command?

Friday, November 3, 2017

Is it necessary to learn AutoCAD for any Mechanical Engineer?

Any software is a tool for making a task easy in a computer. If you are an engineer, there are plenty of software prepared for the special task. Out of them, AutoCAD is also a very important software.

AutoCAD is all about CAD (Computer Aided Design). If you are a mechanical engineer, you have to design or manufacture a product or component of any machine or mechanism. 

In industry, work is continuously done and one has to rely on the computer instead of a manual task. The same is true for drawing of any product. There are plenty of chances to have an error or many errors in handmade drawing and this will cost a lot for any company. So, design department of any company has AutoCAD in their PCs. They have special persons to do this task.

Monday, October 30, 2017

M.E. or M. Tech. dissertation topics for Design specialization

This article gives dissertation topics for machine design specialization in masters of engineering or master of technology.

  • Mechanical design optimization using advanced techniques
  • Shape optimization of engineering product using FEM
  • Vibration and fatigue analysis

Sunday, October 29, 2017

M.E. or M. Tech. dissertation topics for Thermal specialization

  • Influence of operating parameters on performance and emissions of engine using ethanol
  • Energy efficiency in industrial utilities
  • Efficiency improvement in pump used for saltwater conversion into potable water