''HEAT TRANSFER STUDIES"

Transcription

1 QUARTERLY REPORT TO US DOE YMSCO FROM HEAT TRANSFER LABORATORY MECHANCAL ENGNEERNG DEPARTMENT UNVERSTY OF NEVADA, LAS VEGAS HEAT TRANSFER STUDES" R BOEHM, P YT, CHEN, COP L, MA APRL 2, 995

2 Abstract Nitrogen gas has been repaced by room air in the extension of mutiphase modes to subresidua saturation experiments on drying The TOUGH2 code has been used to simuate the same probem with the identica boundary conditions A constant heat fux boundary condition on the heater has been performed in the repository drift experiment The desired constant heat fux can produce a steadystate heater temperature (= 238OC) cose to the constant heater surface temperature used before What occurs in the air annuus and in the porous medium with the different therma boundary conditions and water quantities is reported Tabe of Contents Abstract A Study on the Extension of MutiPhase Modes to SubResidua Saturation A Study of Unsaturated Fows with Heat Transfer in the Repository Drift DSCLAMER This report was prepared as an account of work sponsored by an agency of the United States Government Neither the United States Government nor any agency thereof nor any of their empoyees, makes any warranty, express or impied, or assumes any ega iabiity or responsibiity for the accuracy, competeness, or usefuness of any information, apparatus, product, or process discosed, or represents that its use woud not infringe privatey owned rights Rcfcrence herein to any specific commercia product, process or service by trade name, trademark, manufacturer, or otherwise does not necessariy constitute or impy its endorsement, recommendation, or favoring by the United States Government or any agency thereof The views and opinions of authors expressed herein do not necessariy state or refect those of the United States Government or any agency thereof 2 6

3 DSCLAMER Portions of this document may be iegibe in eectronic image products mages are produced from the best avaiabe origina document

4 A Study of the Extension of MutiPhase Modes to SubResidua Saturation This study is focusing on the imitations of appying mutiphase fow modes to the hydrotherma processes occurring when the iquid saturation fas beow residua eves Mutiphase transport in geoogica media at subresidua saturations is of considerabe importance in various appications incuding performance studies of the higheve radioactive waste repository, decontamination of hazardous waste sites, wood drying processes, and severa other drying appications The majority of the work performed in hydrogeoogic modeing has been confined to isotherma studies and/or at iquid saturations we above residua eves Recenty, the probem of contaminant transport in the subresidua regime has attracted considerabe attention, particuary when deaing with the disposa of higheve radioactive waste in an underground repository As a consequence, it is of importance to understand the drying effects of residua water in porous media The capiary pressure within the porous medium is a function of therma gradients present An experimenta program in our aboratory continues to study the drying effects of residue water in porous media A fow of air through a porous medium is used to determine from experimenta measurements the physica reationship between the iquid saturation, capiary pressure, and temperature n one set of experiments a ow fow rate of air with an isotherma boundary condition has been used, and in another set, a high fow rate of the same air with an adiabatic boundary condition wi be appied These resuts may give usefu information for numerica modeers To furnish data to support numerica modeers in evauating their resuts is the main task of this experiment As a step in this direction, the TOUGH2 code is being used to simuate the same probem with the identica boundary conditions Resuts wi be compared from the cacuations and the experiment The new experimenta setup is shown in Figure The detais of the redesigned test section is shown in Figure 2 As currenty conceived, the test section has been reconstructed of a 6" ong auminum cyinder that has an inside diameter of 5" and two windows (275" x 5625") The reason why auminum was chosen for this appications is because it is rust resistant and it has a high therma conductivity A constant heat fux or temperature boundary condition can be appied on the outside of the auminum wa Room air is used as the dispacing fuid and water is the dispaced fuid in the gass beads Severa different mass fow rates of air with heating effect wi be added

5 to the experimenta study The mass fow rate of air is controed by a vacuum and a buffer tank system The very ow mass fow rate of air is cacuated using a soap bubbe voumetric instrument and Utube manometer Tests begin at the residua saturation condition and continue unti steadystate conditions are reached, which may or may not find a competey dried porous medium Air TC Differentia Pressure Transmitter n signa Conditioning ind Data Acquisition evices Signa Conditioning and Data Acquisition Devices Water Drain Beaker UTube Manometer u Vacuum Pump Buffer Tank bto Computer T C Thermocoupe 9:Reative Humidity Sensor Figure Diagram of piping and instrumentation used in the drying experiment

6 Two new commercia reative humidity sensors, the product of the Phys Chem Scientific Corp, are used to measure the inet and outet water moisture content of the air These sensors have about f % accuracy, based on the fu range measurement The operating reative humidity range is from to % The operating temperature range is 4 to OC These sensors have a sec response for a step change from % RH to 93% The average temperature coefficient is about 3% RH/OC The sensor size is 3" x 5"~ 25", and it has SP connections with " mounting centers Caibration of the humidity sensors as a function of water content and temperature is done foowing the appropriate ASTM method During the tests, the output of the humidity sensors are recorded as a function of time Most of the instrumentation used has been described in earier reports n the current tests, a smarange differentia pressure transmitter repaces a argerrange one for measuring the pressure drop across the porous medium The output votages from the transmitter are aso recorded as function of time A Setra Mode 264 differentia pressure transmitter (25" water maximum range) has been purchased t demonstrates an accuracy better than k % of fu scae 37" diameter (average) gass beads are used as the fi materia in the test section The gass beads are ceaned using a % hydrochoride soution and distied water Weight readings of the entire test section with respect to time are aso recorded during the test, and these are accompished with a digita baance with an eectrica signa output A digita baance of 4 kiogram capacity, a gram readabiity, and +% accuracy is used to measure the weight of test section Comparisons can be made between the change of water content in the test section inferred from the mass fow of water out (estimated from the air mass fow and humidity measurements) with readings taken from the digita baance Nine 3 gauge Ktype thermocoupes are used in the test section to measure the temperatures with a maximum of 75% error These are paced at severa ocations within the test section as we as in the inet and outet humidity sensor boxes Room temperature and atmospheric pressure are measured A computer with a LabVEW data acquisition system is used to coect a data from the experiment

7 Heater and nsua tor 6" Auminum Cyinder (Not to Scae) Figure 2 Schematic diagram of the test section used in the drying experiments Two windows on one side aow visua observations during the test runs The test section can be operated with or without heating

8 A Study of Unsaturated Fows with Heat Transfer in the Repository Drift The experimenta design described in the previous report has been used to investigate the water fow through a rigid porous medium with heat transfer around a nonbackfied hoe Figure 3 shows a rigid porous redium approximatey 5" x 2" x 2" (high) that was prepared with a 5" hoe through the thin dimension of the medium A " diameter, 5" ong 5 W eectrica cartridge heater was instaed horizontay through the medium, forming an air annuus in the hoe A ceramic insert was used to sea both sides of the air annuus and to support the heater in the air annuus Water Reservoir RTV Siicone Moisture Barrier (on 4 sides) Therma nsuator Drain Reservoir Drain Hose Figure 3 A frontview schematic of the experimenta setup to simuate some aspects of fows around an underground repository The dimension into the page is 5 in Thermocoupes are inserted into the medium from the arge surface side Nine and twentythree 3 gauge Ktype thermocoupes are used to measure the temperatures in the air annuus and the porous medium structure, respectivey Two capacitance humidity sensors are used to measure the humidities in the porous medium and in the air annuus The configuration of thermocoupes in the porous medium is shown in Figure 4 The sides of the porous medium are seaed so that

9 moisture cannot escape through those surfaces The permeabiity of the porous media structure is about 554 x o f? O f particuar concern is the determination of the temperatures near and in the annuus, and the humidity in the annuus Data are ogged every seconds on a persona computer using LabVEW software and hardware 32 Thermocoupes [ Reative Humidihr Figure 4 Schematic ocation of the thermocoupes and humidity sensors in the repository fow experiments An experimenta run begins with a dry porous materia and the constant heat fux (ie 22 V and 64 A) on the heater dissipating the necessary power to achieve a specific temperature n this report, studies of a constant heat fux condition is reported that yieds a high heater temperature (= 238OC) at the dry condition Tap water at ambient temperature is introduced from the top of the porous medium when a steady state dry condition in the porous medium and air annuus is reached With constant heat fux conditions, the heater temperature does not remain constant when water and/or vapor penetrates into the air annuus The particuar focus of the work reported here is the comparison of two different therma boundaries on the heater The constant surface temperature of

10 heater and the constant heat fux from the heater have been studied Experiments was performed using 2 m water being poured onto the top of the 2" x 5" surface The effect of water quantity on the response of the constant heat fux system wi be investigated ater W n 9 W Y $ ti" L 8 /""" 6 4 "" Constant Heat n u x Power Density :43 W/sq G ~, admitted at 2488sec Figure 5 Variations of temperature and reative humidity in the air annuus with a constant heat fux and 2 m of water fowing through the system Figure 5 shows the variations of temperature and reative humidity in the air annuus with a constant heat fux from the heater with a sma (2 m) quantity of water The temperatures in the air annuus and on the wa of annuus have different responses when moisture reaches those points Heater temperature decreases from 237OC to 45 C whie moisture stays in the air annuus t increases graduay back to the steadystate condition when the drying process starts Thermocoupes and 2 indicate that the temperatures are higher than the water boiing point when moisture reaches there Thermocoupes 3 and 4 show a sma fuctuation when moisture reaches there and indicate temperatures decrease to a saturated steam temperature vaue Thermocoupes 5 and 6 show a big fuctuation and thermocoupe 6 indicates an overcooing phenomena at the bottom wa of the air annuus This may indicate that steam condensation occurs on the bottom wa The reative humidity in the air annuus shows two peaks that indicate a 25%

11 increase a t the first peak and a 43% increase at the second peak when steam penetrates the air annuus The reason why the reative humidity has two peaks may be that subcooed condensation occurs in the air annuus The therma resistance to the moisture is no onger strong enough to keep moisture away from the air annuus The system needs about an hour to return to steady state at approximatey the same temperature as existed before water admission The water boiing point is about 98oC, and this is cacuated from the atmospheric pressure during the test Detais of the responses of thermocoupes 5 and 6 are shown in Figure u n W L ~ U \ ;, tf t # f ""r% m;t s ~at admitted 2mwater Constant Heat nux Power Density: 43 W /sq cm # ~, Figure 6 Variations of temperature at thermocoupes 5 and 6 in the air annuus with a constant heat fux and 2 m of water fowed through Figure 7 shows variations of temperature at a 5 in height within the porous medium, which is 25 in above the rim of air annuus, when a constant heat fux and 2 m water is present The temperatures dropped from above the water boiing point, which was 98OC during these tests, to a mixture of water vapor and iquid temperatures when moisture reached these points The ocations of thermocoupes 7 and 2 showed a water vapor and iquid retention for about one and haf hour before those ocations dried out Thermocoupes 9 and 2 show a

12 97OC and 95OC decrease when water fowed through, respectivey A phase change apparenty occurred at the ocations of thermocoupes 7,8,9,2, and 2 A mixed heat transfer mechanism of convection and conduction coud be substantiated Constant Heat Fm Power Density : 43 W/sq admitted at 2488 sec i t J C Figure 7 Variations of temperature at a 5" height in the porous medium with a constant heat fux and 2 m quantity of water Figures 8 shows variations of temperature at a 55 in height in the porous medium with a constant heat fux and 2 m of water Thermocoupe 5 shows a 56OC decrease when coo water is admitted from the top t remained at 88OC for about 45 minutes, which apparenty shows that hot water is present during this time This temperature then increases sowy back above the water boiing point Thermocoupes 4 and 6 show saturated steam and water were apparenty there for a few minutes when water vapor reaches those points Both thermocoupes showed an increase in temperature foowed by a cooing phenomenon This atter effect, where the thermocoupes showed a drop of about 4 C and 32OC, respectivey, probaby indicates that some evaporation occurred A significant refuxing phenomena occurs in these regions Thermocoupes 4, 5, and 6 decrease when the coo water fowed through those points and increase when the water vapor is present t is an important to note that this observation agrees with the effects of the high heater temperature with the 2 m water experiment

13 5 Constant Heat Fux admitted at : 2488sec Figure 8 Variations of temperature at a 55" height in the porous medium with a constant heat fux and 2 m quantity of water Figure 9 shows variations of temperature at the eft hand side of the air annuus with a constant heat fux and 2 m water Thermocoupe 24 is ocated in the porous medium 25 in to the eft of the rim of the air annuus ts temperature remains at a constant vaue which is above the water boiing point before water admission from the top of porous medium When water fows through this point, the region around thermocoupe 24 contains saturated steam and water This region then dries out and temperatures return back to their steady state vaues Thermocoupe 23 shows a contrasting behavior to this Readings from thermocoupe 23 remained at a constant vaue which is beow the water boiing point before the water vapor reached this point The reason why the temperature did not drop first when the water fowed through this point coud aso be expained by a heating effect from the top of the porous medium to that point A detaied check of recorded temperature data showed that steam above the boiing point was present for about 55 minutes around this thermocoupe This was apparenty foowed by some iquid being evaporated, and this caused the temperature to decrease The net resut yieded a temperature about 4 C beow the steady state temperature t can be inferred from the two major peaks present that significant

14 refuxing phenomena occurred within the next 7 hours A compicated heat transfer mechanism of conduction and convection probaby took pace, but the convection heat transfer dominates in the refuxing region Thermocoupe 22 has a simiar response to that shown for thermocoupk 23 but without an significant indication of refuxing being present Continuous phase change phenomena may be taking pace here The right and eft hand sides of the air annuus show symmetrica temperature responses 2 5 u n 5 W E a z ) C Figure 9 Variations of temperature at the eft hand side of air annuus with a constant heat fux and 2 m quantity of water Figure shows variations of temperature at a 3 in height in the porous medium with a constant heat fux with 2 m water Thermocoupe 29 shows that this ocation in the porous medium remains at the boiing point (saturated steam is probaby present) for a very short time and then a cooing effect occurs at this point when the ow temperature moisture reaches there t is of interest to note the response of thermocoupe 29 t starts to increase drasticay after an hour retention Thermocoupes 28 and 3 aso indicate that the boiing point is reached The fuid is apparenty heated up when it traves through and around the air annuus Thus, it causes a sma heating effectin the regions of thermocoupes 28 and 3

15 ; : 29: 5 # : : 95 : T Constant Heat Fux Power Density : 43 W/sq cm,, / iq S / / / 8 : : 9 r 85 : i (:! 8 :,o,,, : 2m water 75 r admitted at : 2488sec 7 Figure Variations of temperature at a 3" height in the porous medium with a constant heat fux and 2 m quantity of water Thermocoupes,, and 2 a demonstrate the same kinds of responses due to fuid cooing effects on these regions Figure shows variations of temperature at a 8 in height in the porous medium for the constant heat fux with 2 m water Figure 2 shows the variations of temperature at a vertica top in the porous medium with a constant heat fux and 2 m water Figure 3 shows the variations of temperature at a vertica bottom in the porous medium with a constant heat fux and 2 m water Figure 3 shows variations of temperature in a vertica ine directy beow the center of the annuus Thermocoupe 3 in Figure 3 indicates that ocation reaches the boiing point for a short period of time The temperature then sowy decreases as the medium dries A simiar response, but ower in temperature overa, is shown for thermocoupe 32 Figure 4 shows the reative humidity at air annuus and thermocoupe 5 with a constant heat fux and 2 m water vs time Between 329 and 338 seconds there are few disturbances shown on the reative humidity curve and this is foowed by a 4% increase and then drops back to the steady state vaue

16 Constant Heat Fux Power Density : 43 W/sq cm : 75 r % : 2 m water 45 :admitted at : 2488sec C Figure Variations of temperature at a 8" height in the porous medium with a constant heat fux and 2 m quantity of water 4 Constant Heat F w Power Densitv : 43 W/sa cm A 2 7 i 2488 sec i C Figure 2 Variations of temperature at a vertica top the porous medium with a constant heat fux and 2 m quantity of water

17 W n W 2 m water admitted at 2488 ssec C Figure 3 Variations of temperature at a vertica bottom the porous medium with a constant heat fux and 2 m quantity of water 9 ;! Porous Media at TC5 2 m water admitted at Figure 4 Reative humidity at air annuus and thermocoupe 5 with a constant heat fu and 2 m quantity of water

18 Figures 5, 6, 7, 8, 9, and 2 show the comparison of temperature in the air annuus with the different therma boundaries on the heater and water quantities from the top of porous medium The resuts are apparenty consistent t is not difficut to find the constant heat fux boundary condition on the heater wi proong the time for returning the temperatures back to steadystate This is because the heater temperature has a simiar profie after water penetrated into the air annuus Figure 5 shows the air temperatures in the annuus above the heater t can be noted that the temperature decrease is ess for the constant heater surface temperature (238OC) case than the constant heat fux case after moisture reaches that point, with the same water quantity Figure 6 shows the top wa temperatures in the air annuus They have a very simiar temperature drop for both the constant surface heater temperature (238OC) and the constant heat fux with the same water quantity Figure 7 shows the air temperatures in the annuus on the side of the heater Less temperature decrease is seen for the constant heater surface temperature (238 C) case than,for the constant heat fux situation Figures 8 and 9 show the side wa and bottom air temperatures in the air annuus, respectivey Figure 2 shows the bottom wa temperatures in the air annuus At the constant heat fux boundary condition, retention time is onger than the cnnstant heater surface temperature Figures 2, 22, 23, 24, 25, 26, 27, 28, and 29 show the comparison of temperature in the porous medium for the different therma conditions and water quantities Figure 2 shows the temperatures from thermocoupe 9 The constant heater surface temperature boundary condition and the constant heat fux boundary condition have a simiar temperature response The ony difference is the constant heat fux boundary condition needs a onger time to return back to steadystate Figures 22 and 23 show the temperatures from the thermocoupes 7 and 8, respectivey Figure 22 shows a simiar temperature drop for the two therma boundary conditions and a onger drying time for the constant heat fux boundary condition Figure 24 shows the temperatures from thermocoupe 22 Figure 25 shows the temperatures from thermocoupe 23 The refuxing phenomena can be found for both therma boundary conditions Figures 26, 27, 28, and 29 show the temperatures from thermocoupes 24, 28, 29, and 3, respectivey The temperature responses are very consistent for the different therma boundary conditions

19 t C Figure 5 Comparisons of temperature in the air annuus with different therma boundaries and water quantities OOm, 238 C 2m, 238 C 2m,43 W/sq cm 2m, C C Figure 6 Comparisons of temperature in the air annuus with different therma boundaries and water quantities

20 v E P) i$ ; Figure 7 Comparisons of temperature in the air annuus with different therma boundaries and water quantities f " _ """ """ 3m, 238 C 2Om, 238OC " _ " W (d w P) i$ F C Figure 8 Comparisons of temperature in the air annuus with different therma boundaries and water quantities

21 C Figure 9 Comparisons of temperature in the air annuus with different therma boundaries and water quantities 8 " 3m,238"C 2m, 43 W/sq cm 4 2m, C C Figure 2 Comparisons of temperature in the air annuus with different therma boundaries and water quantities

22 4 3 W n W C Figure 2 Comparisons of temperature in the porous medium with different therma boundaries and water quantities zf a 7; 6 : 5 r Figure 22 Comparisons of temperature in the porous medium with different therma boundaries and water quantities

23 3, 5 t 4 23 Thermocoupe 8 3m,238"C " " C Figure 23 Comparisons of temperature in the porous medium with different therma boundaries and water quantities : r s Thermocoupe 22 : 2m,43 W/sq 9 T 8 : "r ZOOm, 238 C 7 ; 6 c 5 4 : 3m,238"C 2m, C /, 3oom, C Figure 24 Comparisons of temperature in the porous medium with different therma boundaries and water quantities

24 W h v EE Q? F Figure 25 Comparisons of temperature in the porous medium with different therma boundaries and water quantities 4 3 " " " " ~ " Thermocoupe 24 3m,238"C W n 22 v 2m, 43 W/sq cm Q? 3oom, C F C Figure 26 Comparisons of temperature in the porous medium with different therma boundaries and water quantities

25 Figure 27 Comparisons of temperature in the porous medium with different therma boundaries and water quantities Figure 28 Comparisons of temperature in the porous medium with different therma boundaries and water quantities

26 Thermocoupe 3 = 7 r 6 : 5 : OOm, 238 C 2OOm, 43 W/sq cm 2m,O C 3m, O C C Figure 29 Comparisons of temperature in the porous medium with different therma boundaries and water quantities