May 2016

IndiKart India 4:05 PM ,
Objective of the lecture :

  • Heat Engine
  • Refrigerator
  • Heat Pump


 Heat Engine :

A heat engine is a device that does a certain amount of net positive work by the extraction of heat from a high temperature body and releasing it to low temperature body. In this, the required output is the net positive work done by the heat extracted from the hot body. Example of heat engine includes : Steam power plant etc.

Refrigerator : 

Refrigerator is a device which is used to reduce and maintain the temperature of the cold chamber below the atmospheric temperature by extracting the heat from the cold chamber and releasing it continuously in the environment by consuming certain amount of external work. In this, the required output is the heat extracted from the cold chamber. Examples includes : Domestic Refrigerators etc.

Heat Pump : 

Heat Pump is a device which used to transfer the heat of the cold body by extracting the heat from the cold body and releasing it continuously in the hot chamber by consuming certain amount of external work. A heat pump is much similar to refrigerator, however, here the required output is the heat rejected to the high temperature body.


LECTURE RELATED QUESTIONS :

1. What is a Heat Engine?

2. Define "Refrigerator".
 
3. What is Heat Pump?

4. Write down the difference in between Heat Engine, Refrigerator and Heat Pump and explain them.
Read more »

IndiKart India 8:16 PM ,
Objective of the lecture :
  • Standard Rating Of Refrigerating Machine
  • Tonne of refrigeration


Standard Rating Of Refrigerating Machine :

The "standard rating of refrigeration" is obtained by refrigerating effect or amount of heat extracted in a given time from a refrigerating body. The practical unit of refrigeration is generally represented in terms of “tonne of refrigeration” (briefly expressed as TR). 

One Tonne Of Refrigeration :

A “tonne of refrigeration” is a common term used to indicate the capacity of the refrigerating unit. A “tonne of refrigeration” is defined as the amount of refrigeration effect produced by uniform melting of one tonne of ice from and, at OoC in 24 hours.

Since, Latent Heat of Ice = 335 kJ/kg.

Therefore, tonne of refrigeration in 24 hour = 335 x 1000 kJ in 24 hr.

So, tonne of refrigeration per hr. = [ { (335 kJ/kg) x (1000 kg) } / ( 24 hr. ) ]
                                                              = 13958.33 kJ/hr.

So, tonne of refrigeration per min. = [ { (335 kJ/kg) x (1000 kg) } / ( 24 hr. x 60 min. ) ]
                                                              = 232.6 kJ/min.

And, tonne of refrigeration per sec. = [ { (335 kJ/kg) x (1000 kg) } / ( 24 hr. x 60 min.  x 60 sec.) ]
                                                                  = 3.5 kJ/sec.

When one tonne of ice requiring 335 kJ/kg got melted in 24 hour period, it is termed as "heat transfer rate" of 1 tonne of refrigeration.


Also, tonne of refrigeration is also expressed in Btu/hr.

Then, Latent Heat of Ice = 144 Btu/lb.

Therefore, tonne of refrigeration in 24 hour = 144 x 2000 kJ in 24 hr.

So, tonne of refrigeration per hr. = { (144kJ/kg) x (2000lb) } / ( 24hr. ) ]

                                                = 12000 Btu/hr.


LECTURE RELATED QUESTIONS : 

1. What do you know about "Standard Rating Of Refrigerating Machine"?

2. What do you understand by "tonne of refrigeration"? 

3. What do you mean by "Heat transfer rate" in relation to tonne of refrigeration?

4. Write down the unit values of "tonne of refrigeration" expressed in Btu/hr. , Btu/min. and kJ/sec. respectively.
Read more »

IndiKart India 7:51 AM ,
Objective of the lecture :
  • Human Comfort

HUMAN COMFORT 

Thermal comfort, also termed as neutral comfort, may be defined as “that condition of mind which expresses satisfaction with the thermal environment”.

As we all know that, the chemical energy of our food get converted into heat and work which is then utilised for the proper functioning of our body organs including heart, brain, lungs, liver and other parts of body organ and then ultimately, the energy is rejected into the environment in the form of the waste and urea.

Such process of conversion of conversion of chemical energy present in the food to heat and work is termed as “metabolism”. The rate at which the process of conversion of the chemical energy presented in the food into heat and work happens is termed as “metabolic rate”.  The knowledge of metabolic rate and other factors including humidity, air temperature and air velocity etc. are very necessary so as to know the  cooling load of the air conditioned building. To define thermal efficiency of a human being, one can termed it as “the ratio of the useful work output to the energy input”. The thermal efficiency of a human being can vary from 0% to as high as 15-20% for a short duration of time.
For the efficient working condition of human body, the internal organs require the temperature close to 35o C and this is achieve by rejecting appropriate amount of heat in the surroundings.

Core temperature = 36.8o C
Skin Temperature = 33.7o C

If the temperature of the human body rises above this temperature, then human body tries to achieve this temperature range which is achieved by perspiration process of the body. Human beings do not feel comfortable if the body require some extra effort to reject this energy to the environment, which results in major loss in efficiency.  


LECTURE RELATED QUESTIONS : 

1. Define the term "Human Comfort".

2. Define "Metabolism".

3. Define "Metabolic Rate".

4. Write down the factors affecting the human comfort.

5. Define "thermal efficiency" of a human being.

6. What is the core and skin temperature of a human body?
Read more »

IndiKart India 12:20 PM ,

Objective of the lecture:
  • Meaning of Refrigeration
  • Applications of Refrigeration

 Meaning Of Refrigeration:

Refrigeration may be defined as the process of extraction of the heat from the cold bodies and releasing it to the higher temperature bodies so as to achieve and maintain the temperature below that the surrounding. 

Applications of Refrigeration:

The application of refrigeration are too wide in domestic as well as in industries. Some of them are mentioned below:

1. Manufacturing of ice
2. Medical applications
3. Preservation of perishable food product
4. Storage and Distribution of Beverages
5. Ice skating rinks
6. Meat and poultry products
7. Preservation of Dairy Products
8. Application in Chemical Industries
9. Application in Printing Industries
10. Desalination of water
11. Cold treatment of metals
12. Removal of heat of extraction
13. Dehumidification of air
14. Condensation of gases

LECTURE RELATED QUESTIONS:

1. Explain the term 'Refrigeration'.

2.Write down the domestic and industrial applications of Refrigeration.
Read more »
Subscribe to: Posts (Atom)

Contact Form

Name

Email *

Message *

Powered by Blogger.