intermittent ammonia-water system

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Intermittent Ammonia-Water Refrigeration System

Training in Alternative Technologies4th SessionAugust 31 - December 10, 1981

byJacob Sandikie, Liberia Girish Kumnar Sharma, IndiaMalcolm Whitfield, Sierra Leone VirYilio Fernandez, Philippines


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onto actually get hands The objective of this group project has been ammoniathe intermittent on the construction and operation of experience

in the conthe basic activitiesthus, givesThis report,water system. in such a wayNH3/H20 system, simplifiedoperation of the struction and

laboratory working guidelines.that it could be used as in the TAET are discussed and possibleon the existing unitProblems

commercially viable modifications are also suggested.

I


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Valve 2 Valve 3.P 2 T2Valve 1 7 Valve

NH 3

* 4:'B- NHH 0 vNH w3 2

0 V2Heat

Figure 1The Intermittent Ammonia-Water Refrigeration Unit

Components2 propane tanks (20 Ib) (V1 & V2 )Stainless steel piping2 pressure gauges (P1 & P2)4 regular middle valves2 type-k thermal couple probes


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T1 PI ValVe 2 Valve 3P2TP21 . Valve4

Valve 1

VV 2

Figure 2

OperationI Pressure Testing

a) Open valves 1, 2 and 3 and leave Valve 4 closed.b) PUmD enough water into the system to completely fill the 2 tanks

and the piping arrangements.c) The system is now kept under a pressure of approximately 125 to

150 pounds per square inch for several hours (24 hr).d) All leaks discovered during this testing process are tightly

closed or sealed by either welding or tightening the screws.


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T 39 psi P2 39 psi T

Vi v2

Figure 3

e) Drain the system of all the water.f) Pull a vacuum on the system by hooking a regular vacuum pump at

Valve 1 and leaving all valves open except 4. Run the vacuum pumpuntil a lowest possible pressure is obtained as indicated by thepressure gauges, PI and P2. In ideal laboratory conditions avacuum pressure of as low as 30 psi can be obtained. However inthis case a pressure of 39 psi was reported.

g) Before removing the vacuum pump all valves are closed and then thepump is removed. The unit is now ready for charging.


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T Pi Valve 2 Valve 3 P2 T24:-..~V .Valve .. -

Figure 4

2 Charging the Systema) A weighed quantity of distilled water is taken in a bucket and

connected to the system through opening q. Valves 1 and 2 areopened.

b) Next ammonia is introduced in a similar manner as water in anamount that will give 60% by weight of ammonia. With still somevacuum left in Vl, after adding water the ammonia willspontaneously flow into V1 . Valves 1 and 2 are now closed andthe hose is removed. At this stage the system is in a generatingmood, or ready for operation.

5


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;eneration of the NHI as Part of Operation of the System

Valve 2 ave 3 vT4

: - T" s *.. .

", -- , . --- v

denser;1100"1 Generator' er Bath)

Figure 5

a) To operate the system, heat is added to V1 now referred to asthe generator. In doing this, Valves 1, 3 and 4 are kept closed.This will permit initial pressure to build up in tile generator.b) Next, Valves 2 and 3 are allowed to open and NH3 to flow intothe condenser. At this stage heat at V1 is removed. During theammonia generation process V2 was being cooled to increase thecondensation process of ammonia. All valves are now closed.

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T P Valve 2 Valve 3 P2 T2_Valve__"_ _ __ 2__Valve 1

4 Environmental~- 3'3 2

Generator/Absorber Condenser/Evaporator

Figure 6

c) At this stage, V2 is cool. After an approximate equilibrium isachieved between ambient' temperature and TI, V2 is placed intoa conformed area to be cooled and V1 is further cooled toincrease ammonia absorption. Here, V1 is acting as an absorberof ammonia and V2 is the evaporator. As the evaporation ofammonia is an endothermic reaction, it absorbs heat from theenvironment, resulting in the cooling of that environment. Inthis case, an insulated box is used as the environment to becooled.

7


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2T p1J Valve 2 Valve 3 2T

'q 3

Figure 7

ResultsGeneration time 2 hoursTemperature of NH3/H20 mixture, T1 160OFTemperature T2 during heating 850FTemperature T2 during the cooling mode 360FAmbient air temperature 77OFTemperature of Box b 590FCooling time 1 hourQuantity of water in the system 4 lbQuantity of ammonia in the system 8 lb

8


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--

__ __ __

--

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1 4 ii i.1 i14i f-iI

Id It +I~~ I 17~

t'


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Observations1. In order to accelerate the absorption process of ammonia in VI during

the cooling process, the propane tank V1 containing the NH3/H20mixture has to be manually shaken. Agitation of the NH3/H20mixture accelerates the absorption of NH3 from V2 and hence, themore shaking done, the more cooling achieved.

In effect: shaking increases the surface area between N113 andH20 for a more rapid absorption.

NH3 + H20 --, NH3/H20Ice can be obtained if mixing is sufficiently rapid and efficient.

2. From theoretical results, it is known that for every pound of ammoniaabsorbed, there are 500 lb Btu of cooling.

At this rating, this unit is a 40,000 Btu unit at a 100% ammoniageneration and reabsorption, or it is a 3 ton unit. However, itsperformance was found to be far less than this.

Disadvantages of the System1. The system has to be charged and shaken manually often requiring

extensive time and physical strength for the mixing.2. The time frame between charging and the Lime when cooling of the box

begins is so large that it is difficult to aaintain continuously lowtemperature of the box being cooled.


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Advantages of the Systejm1. The components of the system are simple, and fairly simple techniques

are needed to understand, construct and operate it.2. The temperatures needed to operate the unit are fairly low, so that

there are several alternatives for obtaining the necessary solar heatedwater.

This suggested model (Figure 10) consists of two generators/absorbers(a) that permit the total system to work continuously. While the leftgenerator is being heated by the heat source the right generator is beingair cooled by a fan. This fan can work on the same energy from the heatsource. After ammonia is discharged from the right the fan arm is rotatedso that the left is now being ,heated while the right is being cooled.

(b) serves as condenser of the NH3 generated and flowing through theouter pipe. Cooling water can be run from the regular pipeline if tilesystem is on a very large scale.

(c) serves as the cooling chamber for condensing and collecting NH3.The box area, which can be larger, is then cooled and the evaporatedammonia is toeturned generator (a ) through the by-passing pipe that runsthrough the center of the larger outer pipe.


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Suggested Modifications

Cooling H 0. 24 -.-..-..

f(b)~P

(a)

'",[ 11

- GeneratorAboreBOX A~'Pvi.

.------

I 1'

Il

" (a

(a) ~~~Generator!ArN/I03 2

/l FanGenerator/

(a

Absorber

Ileat

intermittent ammonia-water system

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