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    Showing posts with label Technical. Show all posts
    Showing posts with label Technical. Show all posts

    Sunday, December 15, 2019

    Free e-books for mechanical engineering subjects

    This article aims at sharing free e-books for mechanical engineering subjects. You can ask for any book that is listed below.

    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 the capacity of refrigeration systems such as cooling capacity, refrigeration capacity, refrigeration power or cooling power or refrigeration effect.

    What is the 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 the 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 the 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 a refrigeration effect experimentally? 

    COP of a refrigeration device is the ratio of the 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 a low temperature. Once the low temperature is reached, no further temperature reduction is possible because the system reaches a steady-state condition. 

    Further heat load in the evaporator of the refrigerator starts pumping the heat and the temperature of the 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 a 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 keeps on running, the temperature will not drop. If a heating coil of 5 W capacity is started in the evaporator, it will add 5 J of heating load every second. This extra heat load needs to be removed and thus, the 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. 

    Friday, November 3, 2017

    Is it necessary to learn AutoCAD for any Mechanical Engineer?

    Any software is a tool for making a task easy on a computer. If you are an engineer, there are plenty of software prepared for a 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 the 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, the design department of any company has AutoCAD in their PCs. They have special persons to do this task.

    Monday, October 16, 2017

    What would happen if compressor is removed from the refrigerator?

    Simply, the refrigerator would STOP! but why?

    To answer this question, one needs to know the Second law of thermodynamics (Clausius Statement) which states "It is impossible to construct a heat pump which continuously takes away the heat from low-temperature region to high-temperature region without taking any external work". 

    Here, the heat pump is our refrigerator which keeps on throwing heat from low-temperature environment to room temperature. As per the above statement, external work is must to run the refrigerator. That external work is represented by "Compressor".

    Friday, March 17, 2017

    How to write an 'abstract' for technical report or article or paper?

    If you are an engineer and working in industry or academics, you need to submit a technical report or research papers to express the findings and work of stuff.

    An abstract is an important element of any technical report or any research paper/article. It is something that people normally prefer to read before taking a look at the whole article. The abstract must contain enough information that highlights and give the complete essence of the article. 

    Normally abstract should deliver objectives of the research, methods that one has used for research, key results obtained and a clear and concise conclusion. 

    The abstract should contain a minimum 100 to 200 words. The content of the abstract should be clear and concise. 

    Sunday, January 29, 2017

    Tips for GPSC Interview for lecturer and assistant professor

    These are the tips which can be helpful to clear the GSPC personal interview for lecturer and assistant professor
    1. Have confidence in your answer while you are asked to speak about yourself. This is normally the very first question asked by the chairman of the interview "Tell me about yourself". Make answer ready in advance. Speak your full name, age, qualification with college and university, current job.
    2. Now when you are asked about your job, give positive aspects of the job.
    3. Why do you want to do a teaching job? Why not a current job? Do not say I am not enjoying the current job but say, "I love teaching and this changes the lives of people. I want to impact the lives of many by teaching jobs. This job is a respectful job"
    4. Always ready with two or three favorite subjects
    5. Prepare the DEMO lecture that will be most probably asked to deliver. 
    6. SAY "NO" IF YOU ARE NOT VERY SURE ABOUT QUESTION'S ANSWER. IF YOU GIVE the WRONG ANSWER THEY WILL TRAP YOU AND ULTIMATELY TIME AND YOUR REPUTATION WILL BE WASTED. Just say 'No' and pass the question. The new question might be familiar to you. This will have the impact of honesty on the interviewer. 
    7. DO NOT ARGUE. DO not hurt them by saying I AM right even though they are wrong. They just make sure about your character. 

    Tuesday, April 22, 2014

    Tips to avoid common errors or mistakes in technical papers or writing

    In current technological era, everything get done by machine and related technology. Each needs research and development. So, to convey the information or findings one need to write technical report, paper or writings. Most of the times, technical reports are full of quality but they contain common errors which might change the meaning or may cause rejection of technical papers also.  So, read the following tips to know what are the common errors and its solutions.

    Numeric numbers:
    Technical writings are full of numbers and data. Normally integers or numbers less than ten are written in words. Say to convey '2 components, one should write 'two components'. Numbers greater than ten and fractional numbers can be written in digits like 11, 12.4 etc.

    Take care of 'a, an, the':
    Always remember than 'a' & 'an' can be used when we talk about indefinite things while 'the' can be used while talking about 'definite' things.