To stud study y the the rela relati tions onshi hip p betwe between en the the satu satura rati tion on pres pressu sure re and and temp temper erat atur uree water/steam in the range 0 – 14 bar (gauge) and to study the change in temperature o a body when being heated or cooled.
Safety The appar The apparat atus us is a press pressur uree vesse vessel. l. (gauge)!
Thee press Th pressur uree must must not not excee exceed d 14 Ba
Background
1) In order to to carry out a heat heat transfer transfer experiment experiment simulta simultaneousl neously y with measurem measurement ent o vapour pressure, it is required that the rates of heating and cooling of the pressur vessel, the rate of energy addition by the heater and the ambient temperature a recorded.
2) Study Study the follow following ing deriva derivati tion on of a simplifi simplified ed 1st Law (energy) equation relating th temperature of the boiler to time as it is heated and cooled.
Assumptions i.
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The The tempe tempera ratu ture re is unif unifor orm m thro throug ugho hout ut the the boile boiler. r. Thus Thus the the outsi outside de surf surf temperature of the boiler is the same as the steam temperature, T .
The 1st law balance for the boiler at time t (secs) is dQ dt
=
dQ t dt
+ Rate of change of internal energy of the boiler and contents.
Therefore, dQ dt
=
dQ t dt
+
MC
dT dt
Where MC (kJ/ K) is the heat capacity of the boiler which in this simplified developmen is assumed constant. So, when being heated, dQ dt
A s (T −T )
= α
α
+
MC
dT dt
(1)
heating
and when cooling,
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0
A s (T −T )
= α
α
+
dT MUnlock C access with a free trial. dt full cooling
(2)
Freecurve Trial and at a value T2 on the coolin At a value of T1 on the lot of theDownload measuredWith heating curve, the respective slopes,
dT dt
cooling
and
dT dt
heating
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may be calculated are determined by construction. The value of dQ/dt from tabulate measurements of electrical energy consumption (kWh) versus time (hrs), or from a direc ding of e, the values of the produc A and MC can b Useful
During the lab and subsequent analysis A. Sketch the apparatus B. Carry out the experiment and calculate the results. C. Plot p versus T for both heating and cooling on a graph. Also plot p versus using published values (ref 1) comment on this graph.
D. Plot graphs of measured T versus time and calculate the products α As and MC Hence calculate Tmax, and the time t for the boiler to cool from the maximum temperature achieved in the test to 10 oC above ambient temperature and comme on the values obtained. E. Derive, from (1) and (2),
a. An expression for the maximum temperature T max, the boiler would reac if heating were to continue at the rate dQ/dt (kW).
b. The time, t it would for the boiler to cool 100oC, to 10oC abov You'retake Reading a Preview ambient temperature. (This requires solution of the differential equatio Unlock full access with a free trial. (2)). Reference Download With Free Trial Thermodynamic and Transport Properties of Fluids, Rogers G.F.C and Mayhew Y.R., 5th edition, “Steam Tables”
