ON THE MECHANISM BY WHICH WATER MOVES THROUGH A POROUS MATERIAL SUBJECTED TO A TEMPERATURE GRADIENT

THE MOVEMENT OF MOISTURE FROM THE HOT TO THE COLD SIDE OF A POROUS MATERIAL HAS BEEN OBSERVED BY MANY WORKERS, HOWEVER, THE MECHANISM BY WHICH THE MOVEMENT TAKES PLACE HAS NOT BEEN DEFINITELY ESTABLISHED. THERE HAS BEEN NO DIRECT EXPERIMENTAL EVIDENCE TO SHOW THAT THE DISCREPANCY BETWEEN THE EXPERIMENTAL AND CALCULATED RATES OF MOISTURE FLOW IS DUE TO FLOW IN THE LIQUID PHASE. ATTEMPTS TO PRESENT SUCH EVIDENCE OF FLOW IN THE LIQUID PHASE FROM THE HOT TO THE COLD SIDE ARE DESCRIBED. THE VAPOR GAP EXPERIMENT WAS CONDUCTED USING AN APPARATUS THAT WAS A MODIFICATION DEVELOPED BY SWENSON AND SEREDA TO MAINTAIN A FIXED MOISTURE CONTENT IN A SAMPLE AT THE SAME TIME THAT THE MOVEMENT OF MOISTURE DUE TO TEMPERATURE GRADIENT IS TAKING PLACE. IN THIS SYSTEM OF TWO POROUS PLATES IN THE GAP BETWEEN THEM, THERE WAS NO FLOW DUE TO THE TEMPERATURE GRADIENT AS LONG AS THE GAP REMAINED SATURATED. FLOW BEGAN WHEN THE GAP BEGAN TO UNSATURATE. THE FLOW OBTAINED ITS MAXIMUM WHEN THE GAP WAS COMPLETELY UNSATURATUATED. THESE RESULTS ARE IN AGREEMENT WITH THE THEORY THAT MOISTURE MOVEMENT DUE TO A TEMPERATURE GRADIENT ACROSS A POROUS MATERIAL TAKES PLACE IN THE VAPOR PHASE. A SALT TRACER EXPERIMENT WAS CONDUCTED TO DETECT FLOW IN THE LIQUID PHASE USING A SALT TRACER. RESULTS SHOW THAT EXPERIMENTAL RATE OF TRANSFER OF SALT IS MUCH SMALLER THAN THAN THE CALCULATED RATE. THE CALCULATED RATE IS THE RATE AT WHICH THE SALT SHOULD HAVE PASSED THROUGH THE BED OF SAND IF THE OBSERVED FLOW OF WATER HAD OCCURRED ENTIRELY IN THE LIQUID PHASE. THE EXPERIMENTAL RATE OF TRANSFER OF SALT AT CONSTANT TEMPERATURE IS THE SAME AS IN THE EXPERIMENT WITH THE TEMPERATURE GRADIENT. DURING DIFFUSION, NO FLOW OF WATER FROM THE FORMERLY HOT TO COLD SIDE WAS OBSERVED IN THE MEASURING SYSTEM. THE DIFFUSION DESCRIBED OCCURS EVEN WHEN THE TEMPERATURE GRADIENT IS APPLIED. THEREFORE, THE FLOW DUE TO DIFFUSION MUST BE SUBTRACTED FROM THE FLOW OBSERVED IN THE TEMPERATURE GRADIENT EXPERIMENT. A STREAMING POTENTIAL EXPERIMENT WAS CONDUCTED TO DETECT FLAW IN THE LIQUID PHASE. FLOW IN THE LIQUID PHASE WAS NOT DETECTED. EXPERIMENTAL WHEN WATER MOVES, DUE TO A TEMPERATURE GRADIENT FROM THE THE HOT TO THE COLD SIDE OF A PARTIALLY UNSATURATED POROUS MATERIAL. THEREFORE, IT APPEARS THAT THE FLOW OCCURS IN THE VAPOR PHASE. HOWEVER, WHEN WATER MOVES DUE TO A SUCTION GRADIENT, THE FLOW OCCURS ENTIRELY IN THE LIQUID PHASE.

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  • Accession Number: 00235713
  • Record Type: Publication
  • Files: TRIS, TRB
  • Created Date: Aug 17 1970 12:00AM