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.
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