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