The simplest solution is to use a *Steam Water mixing* *valve*,in which the
heated mixture coming out from the demo is mixed with a constant flow of
cold water, you can know the enthalpy performance in any moment.
Peter

On Tue, Sep 27, 2011 at 7:41 PM, Horace Heffner <hheff...@mtaonline.net>wrote:

> A simple inexpensive continuously operating steam/water calorimeter can be
> obtained using a combined barrel and flow calorimetry.
>
> A water container, a barrel, or perhaps a trash can which is silicone
> sealed for leaks, can be used to condense steam via a submerged copper coil,
> preferably mostly located near the top of the barrel to avoid imposing a
> steam pressure head on the tested device.  This water container can be
> insulated cheaply using construction foam board and fiberglass.  A stirrer
> can be driven via a shaft through the foam board.
>
> A secondary coil can be used for pumped coolant.  A fixed flow rate pump
> can be used to deliver the coolant flow.  The coolant flow circuit can be
> open or closed. A closed secondary coolant temperature can be maintained via
> either water or air heat exchange or ice heat exchange.  The source of the
> coolant energy is not important if the Tin and Tout are measured close to
> the water container, and any tubing between the temperature measuring
> stations and the water container is insulated.  Ideally the secondary flow
> rate would be measured by a digital flow meter, and driven by a variable
> speed pump.  The coolant flow rate can then be adjusted to suit the coolant
> delta T and the thermal power of the device under test. Alternatively, an
> accurate fixed flow rate pump can be chosen with a flow rate approximately
> matching the expected thermal power of the device under test given the
> expected coolant delta T.  A reasonable goal for the water container
> temperature is the range 50°C to 70°C.
>
> Use of a large water container provides some degree of momentary heat pulse
> energy integration and confidence in the device thermal power measurements.
> It applies a significant time constant to the thermal data that reduces the
> frequency temperature data must be taken.  It even permits manual
> temperature reading if a modestly stable condition is established.  This is
> at the cost of being able to see instant response thermal and energy output
> curves. There is no need to see such fast response curves if the primary
> goal is to measure total energy in vs total energy out for a long run.
>
> The primary circuit water flow can be pumped directly from the water
> container. Ideally the primary water flow should be measured by digital flow
> meter. If a low pressure head is presented to the primary circuit flow pump,
> then a precision fixed flow rate pump can be used.  If precision digital
> flow meters are not used, and reliance is placed on precision flow rate
> pumps, then at minimum simple (flow integrating) water meters should be
> monitored periodically to verify assumed pump mean flow rates. Calibration
> runs on dummy devices should be used to verify the calorimeter over the
> thermal range expected.  A calibration control run should be used with the
> device under test to determine the water capacity of the device so the
> volume of water in the barrel is known in order to provide improved
> intermediate time thermal power  measurements.  At the conclusion of a run,
> the circuits should continue to be driven until thermal equilibrium is
> obtained and essentially all thermal energy is drained form the device under
> test. A water depth gage for the barrel may be of use, calibrated to depth
> vs volume, in order to keep track of the amount of water in the device under
> test.
>
> The secondary circuit input and output temperature should be recorded
> frequently.  Alternatively, a direct delta T can be measured frequently
> using an appropriate dual thermocouple arrangement, thus providing improved
> data quality and reducing data acquisition required. Flow stirrers should be
> used, if feasible, in the secondary circuit prior to the thermometer wells.
> Barrel water temperature should be monitored. Ideally primary circuit water
> input temperature and room temperature should be monitored as well.
>
> A thermal decline curve should be measured for the water container when
> there is no primary circuit flow, and the water is stirred.   The
> calorimeter constant C(dT) as a function of the difference between room
> temperature and water contained temperature (dT) should be determined. The
> curve C(dT) can be fit to a polynomial using regression analysis for
> convenient use in data analysis. Experience shows this method is not very
> accurate if the water container is not well insulated.  This is due to room
> drafts, variations in humidity and temperature during the day, etc.  Ideally
> active insulation could be used, whereby an extra envelope surrounds the
> water container insulation and the temperature there is maintained at the
> temperature of the water, thereby producing a dT = 0, and no heat loss.
>  This is excessive for this approach, however, the goals of which are
> "cheap", "simple",  and "good enough".
>
> In summary, a minimum configuration then would consist of an insulated
> barrel with copper condensing coil, and secondary heat exchanger coil, a
> stirrer, and two precision volume pumps, one primary, the other secondary.
>  Temperatures would be monitored frequently for the secondary in and out
> flows, perhaps less frequently for room temperature, barrel temperature, and
> test device input temperature.  As a second level, ordinary integrating
> water meters could be added, for flow confirmation, on both the primary and
> secondary circuits.  Ideally, precision digital flow meters should be used
> for both the primary and secondary circuit input flows.
>
> Best regards,
>
> Horace Heffner
> http://www.mtaonline.net/~**hheffner/<http://www.mtaonline.net/~hheffner/>
>
>
>
>
>


-- 
Dr. Peter Gluck
Cluj, Romania
http://egooutpeters.blogspot.com

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