Results 1 to 13 of 13
Thread: 2079 Question Reference 04.01
-
08-05-2009, 03:37 PM #1
2079 Question Reference 04.01
Hi people I am currently being used to assess both the Practical and online parts of 2079, I have come across a question that although the correct answer has been found I do not understand why?
Which of the following is most likely to increase refrigerant leakage potential from an Air to water heat pump system? Excessive
a) Expansion valve superheat
b) liquid line subcooling
c) discharge vapour superheat
d) expansion line subcooling.
I really would apreciate an explanation on the problem if anyone is interested.
Sparrow.
Always easy on the eye.
-
08-05-2009, 04:07 PM #2
Re: 2079 Question Reference 04.01
I think the answer is Expansion valve superheat!
Am i correct?
-
08-05-2009, 04:17 PM #3
Re: 2079 Question Reference 04.01
answer c)
Why? - I think the keyword is excessive. A significant increase in discharge superheat would increase the surface temp of the discharge pipe to, possibley, beyond reasonable parameters. As the question refers to specifically air to water heat pump I can only conclude that
A) the water could overheat.
B) the thermal expansion may become a problem.
C) any steam would be considered aggressive to the heat exchanger.
That is all I can think of. I hope someone else has a more concise answer.Quidvis Recte Factum Quamvis Humile Praeclarum.
Latine dictum, sit altum videtur.
Si hoc comprehendere potes, gratias age magistro Latinae.
-
08-05-2009, 05:37 PM #4
-
08-05-2009, 08:06 PM #5
-
08-05-2009, 08:34 PM #6
Re: 2079 Question Reference 04.01
Sorry, can "superheat" - by definition - refer to discharge vapour leaaving the compressor? What may be hotter than the vapour itself so as to add additional heat to it?
-
08-05-2009, 08:39 PM #7
Re: 2079 Question Reference 04.01
Of course, the gas inside the comp is hotter.
-
09-05-2009, 04:05 PM #8
Re: 2079 Question Reference 04.01
I am an electrician - not a "ref" mechanic - working in a HVAC firm these last few years, and untill now thought "superheat" was a specific term reflecting, representing the qwantity of refrigerant in an evaporator, describing its state, etc., during a refrigeration cycle (for one of hundreds other possible definitions). From the silence which followed my last post I infer the term's application field is wider.
-
09-05-2009, 05:18 PM #9
- Join Date
- Sep 2007
- Location
- Split Croatia
- Age
- 57
- Posts
- 6,151
- Blog Entries
- 6
- Rep Power
- 36
Re: 2079 Question Reference 04.01
Refrigerant gases has their saturation point where they change state from gases to liquids and vice-versa.
For every pressure there is corresponding saturation temperature.
Compressor and expansion device serves to raise and lower pressure, and in that way change saturation temperatures to level which is suitable for our usage in particular equipment.
Also, in system gases could be superheated when all available liquid refrigerant in that part of circuit has changed state from liquid to gas and further heated.
That is what we call superheat and amount of that superheat could tell us how many, or if any, refrigerant is evaporated in that part of circuit.
Subcooling is simmilar. When all gas refrigerant has changed state and started to cool below its saturation temperature for corresponding pressure we call it subcooled. Amount of that subcooling tell us how many of liquid refrigerant is in that part of circuit.
These two values tells us where in circuit is refrigerant and ind what state, since we don't have mean to see his state by our eyes.
Interpreting these two values (along with others) serves to evaluate system operation and therefore all the time their usage in different subjects and relations.
-
09-05-2009, 05:21 PM #10
- Join Date
- Sep 2007
- Location
- Split Croatia
- Age
- 57
- Posts
- 6,151
- Blog Entries
- 6
- Rep Power
- 36
Re: 2079 Question Reference 04.01
Last edited by nike123; 09-05-2009 at 05:27 PM.
-
10-05-2009, 09:24 AM #11
Re: 2079 Question Reference 04.01
Hello Nike 123! Your last but one post is redundant, sorry for your effort, the last one is key one, elucidating me. Thus, I knew, liquids are subcooled, so water at 20 C and atmospheric pressure, thermodinamically speaking, is subcooled 80 C. I just missed, somehow, the point that it also refers (now as 'superheat') to gases - in ALL their states. Thank you.
-
10-05-2009, 09:48 AM #12
Re: 2079 Question Reference 04.01
Self-precision: water at 20 C is subcooled 80 K.
-
10-05-2009, 10:11 AM #13
- Join Date
- Sep 2007
- Location
- Split Croatia
- Age
- 57
- Posts
- 6,151
- Blog Entries
- 6
- Rep Power
- 36
Similar Threads
-
Heat Transfer Exam Question
By alexdouglas1969 in forum FundamentalsReplies: 10Last Post: 13-12-2008, 04:19 PM -
Refriferation cycle question
By ozmecheng in forum FundamentalsReplies: 32Last Post: 26-03-2008, 10:38 PM -
question reference vrf installations
By frosty74 in forum Air ConditioningReplies: 0Last Post: 02-08-2007, 03:35 AM -
quizy type question thingy
By rbartlett in forum Chit Chat & Service StoriesReplies: 25Last Post: 06-02-2006, 09:22 PM -
Urgent, Kirchoff question
By Peter_1 in forum FundamentalsReplies: 4Last Post: 20-01-2004, 03:12 PM