proudly sponsored by
|
archiving of SOWACS proudly sponsored by |
|
Hans, We installed close to 50 heat dissipation sensors at a large field site in Arizona and used them to monitor changes in water tension (not water content) during a field infiltration experiment. We also placed tensiometers immediately adjacent to them as a way of comparing the response time and accuracy. I have the following basic conclusions regarding HDS performance: 1. The response time of the sensors to water arrival was excellent. Often, tension would change from ~500 cm water to ~100 cm water in four hours. 2. The units were virtually free of maintenance; only one unit failed during the experiments which spanned about 12 months. 3. We found that the units were less sensitive to drying cycles than tensiometers, even though both units were backfilled in the same manner. We used sieved native soil material as a backfill slurry. 4. With respect to accuracy, our calibration curves were linear to R^2 = 0.981, for del temperature and ln tension as dependent and independent parameters. >From a practical side, our HDS units were calibrated for tension, not water content. We felt that, because moisture moves into and out of the ceramic cup due to matric potential gradients (not water content gradients), this would provide more direct information on soil water conditions. You can always convert data from water tension to water content using a retention curve, but, that can be very tricky. Good luck with your project. It's always good to see soil science crossing over into other disciplines. Regards, Michael , At 06:41 PM 11/17/98 GMT, you wrote: >NOTE: To get off this list, send email to majordomo@aqua.ccwr.ac.za >with the body of the message containing the line: >unsubscribe sowacs > >Dear all, > > >My Ph.D. project concerns the heat transfer between buildings and the ground, >more particularly, >the influence of the coupling between heat and moisture transfer in this >process. > >One aspect of this project is the performance of scale model measurements, in >which I would like >to observe the thermal and hygric behaviour of the ground domain around a >foundation structure. >For the in situ measurement of the thermal properties - and their variation >- I am planning to use >heat dissipation probes. The results of such measurements allow the >determination of the moisture >content of the soil as well. > >I was wondering though, if this particular measurement technique - the heat >dissipation method - >is competitive with other soil moisture measuring techniques. How accurate >is such a heat probe >measurement ? If anyone has any practical experience with such measuring >devices, and may be >able to inform me about this topic, please do. > > >Thank you, > > >hans > ================================================================= >Hans Janssen IWT Research Fellow >Laboratory for Building Physics >Celestijnenlaan 131, 3001 Heverlee, Belgium >Tel: +16 321767 Fax: +16 321980 >http://www.bwk.kuleuven.ac.be/bwf >E-mail: Hans.Janssen@bwk.kuleuven.ac.be >================================================================= > > _______________________________________________________ Michael H. Young, Ph.D. Senior Research Scientist School of Civil and Env. Engineering 200 Bobby Dodd Way Georgia Institute of Technology Atlanta, GA 30332-0512 tel: 404-894-5009 fax: 404-894-8266 _______________________________________________________