design bench test heat exchangers

[Calender]

Good morning to all,

we are setting up a test bench for heat exchangers (which cool a product brought at high temperature). the goal is to show the performance of a new exchanger compared to the previous model. It's the first time I've been interfacing with testing equipment and in general hydraulics and heat exchange are not my strong, so I ask advice to the most experienced.

the idea is to use a pump "1" to feed with water the exchangers "6" and "7" (posed at a height of about 2 meters from the ground, for various reasons that I am not discussing while the pump and the tank are on the ground), the valve "2" regulates the flow rate (measured with a flowmeter "3"). before the exchangers a measurement of the temperature and pressure of the water is carried out, measurement that is carried out immediately after (to evaluate heat exchanged and load losses). then the fluid returns to the tank.

there is a replenishment of water in the tank with a system that exploits a float (not present in figure)

Now:
1)valve 4 is for the vent of air, I do not know whether to predict or not other systems to "degas" water, especially when filling. what are the shortcomings you need to keep (there are commercial devices of cost and bulk content you can use in the tank)? I would like to avoid the pump manifesting cavitation phenomena. . .
2) they almost imposed me to use two valves marked in red ("8" and "9") downstream of the heat exchangers, to be closed in the start-up phase to facilitate the pump in the caption. in the past they told me about various types of starters for the pumps, but sincerely I never found detailed indications about it. in my case the pump never works dry. Does anyone pass me some notes or reference where I can study the start of the pumps well? because I have the impression that the fact of putting two valves after the heat exchangers has been proposed without solid theoretical bases (in fact the answer of those who proposed it was always so..).. the methods that I know preview all to act or not on the control valve (according to the type of pump), but of these additional hypothetical valves I have never heard of it. . .
3) to maintain the constant t1, is there any other method besides predicting a possible cooling in the tank itself (with possible chiller)? Would a larger reservoir make it "thermal flow"?

thanks to everyone for the answers

 

[paulpaul]

Bye!

some observations on the flight:

1. I would test a heat exchanger at a time: with two, it is much more difficult to control the flow on one branch without affecting the other;

2. considering that you have two branches, with "naturally" squilibrate courses (at least without hypothesize of flow regulators), valve 2 would say that it serves little (regulating the overall flow rate, not the individual flows of the branches);

3. on 2, the global flow meter also loses meaning: two must be installed, one per branch. same speech for incoming pressure to the exchangers, which is not said to be the same (a pressure gauge per branch was installed, just before the exchanger, since the load losses are different). the temperature, however, varies little between the two incoming branches, unless the exchangers are very distant from the tee. for uniformity, I would install two thermometers anyway;

4. The valves 8 and 9, to adjust the flow rate on each branch and to keep the circuit upstream of these pressures: However, it becomes very complicated to regulate the two courses independently;

5. lacks a cooler for water, which inevitably warms up: it must be equipped with thermoregulation (e.g. cooler water/air with variable speed fan with control of the temperature of the outgoing water), otherwise you lose control of the incoming temperature to the exchangers;

6. as it is designed, there is a non-return valve in pump outlet: at a fixed installation, being the tank at a lower level than the rest of the circuit, the second would empty, complicating the successive loading operations (the branch of the exchangers would still be empty);

7. reconnecting me to 6, why put that vascone free and not make a circuit closed in pressure? at this point close the circuit and put an expansion vase at the highest point of the same (or a pressurized vase at any point), connected with a tee in derivation to the suction of the pump to always have a positive swing: such a vase (if atmospheric) would also be the filling and degassing point of the circuit, while if pressurized you will have to put in the highest points of the circuit, and in the eventual siphons, manual valves of exhaust air to keep open during the filling (there are also automatic, from boiler). These valves are always appropriate to provide them at the highest points.

remains the problem of the difficulty of adjusting independently the flow in the two branches without changing the input pressure.

 

[Calender]

Hello paulpaul, thank you for the surgery.

1. I would test a heat exchanger at a time: with two, it is much more difficult to control the flow on one branch without affecting the other;

2. considering that you have two branches, with "naturally" squilibrate courses (at least without hypothesize of flow regulators), valve 2 would say that it serves little (regulating the overall flow rate, not the individual flows of the branches);

3. on 2, the global flow meter also loses meaning: two must be installed, one per branch. same speech for incoming pressure to the exchangers, which is not said to be the same (a pressure gauge per branch was installed, just before the exchanger, since the load losses are different). the temperature, however, varies little between the two incoming branches, unless the exchangers are very distant from the tee. for uniformity, I would install two thermometers anyway;

6. as it is designed, there is a non-return valve in pump outlet: at a fixed installation, being the tank at a lower level than the rest of the circuit, the second would empty, complicating the successive loading operations (the branch of the exchangers would still be empty);

summarizing, since they do not want to make two separate circuits (which would certainly be better for adjustments as you have rightly pointed out), they would be:

- installed two flow/pressure meters and two thermometers immediately before the heat exchangers. two flow regulators must also be installed before such meters (one in each branch).
- the two should be replaced with a non-return valve (I had not represented it but had thought about it ; )

4. The valves 8 and 9, to adjust the flow rate on each branch and to keep the circuit upstream of these pressures: However, it becomes very complicated to regulate the two courses independently;

7. reconnecting me to 6, why put that vascone free and not make a circuit closed in pressure? at this point close the circuit and put an expansion vase at the highest point of the same (or a pressurized vase at any point), connected with a tee in derivation to the suction of the pump to always have a positive swing: such a vase (if atmospheric) would also be the filling and degassing point of the circuit, while if pressurized you will have to put in the highest points of the circuit, and in the eventual siphons, manual valves of exhaust air to keep open during the filling (there are also automatic, from boiler). these valves are always appropriate to predict them in the highest points

from what I had communicated in the company those two valves were not regulation but interception (on/off). That was the weird thing I couldn't explain. However, once I put flow regulators before the heat exchangers and I preview a pressurized closed circuit or an open expansion vase in the highest position (positive enough), I could also remove them well? What do they mean?

5. lacks a cooler for water, which inevitably warms up: it must be equipped with thermoregulation (e.g. cooler water/air with variable speed fan with control of the temperature of the outgoing water), otherwise you lose control of the incoming temperature to the exchangers;

where would it be better to place the cooler? before the exchangers? do you know any manufacturer who offers cheap commercial solutions?

remains the problem of the difficulty of adjusting independently the flow in the two branches without changing the input pressure.

Could you explain this to me better? can only be overcome by two separate circuits?

thanks in advance :d

 

[paulpaul]

Bye!

what I mean is that if you install "something" (manual or automatic) that regulates the flow on one branch, you will have repercussions on the other: imagine to significantly rub branch 1 through valve 8 or with a flow regulator: the incoming flow from the pump will flow more on branch 2, so also the conditions on that branch would change
They probably used valves 8 and 9 to avoid emptying the circuit at a fixed plant.. .other uses (other than the function of adjusting the flow) do not come to mind!
ok replace the two with a vnr, but put it near the pump
for coolers there are many builders: in the oleodynamic field there are those who sell them with a built-in control, but in the hydraulic field more often you have to create control with a small plc, buying all the separate pieces (cooler, thermal resistance, control book): for the cooler there are many builders, ser look in net "drycooler" you should find many (thermokey, alfa laval, luve, etc.). Usually the cooler puts itself after the heat exchangers and before the pump, so this works on colder fluid (and therefore less at risk of cavitation).
good work