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Remarks on “cascade solar still for distilled water production”
Solar Energy, Vol. 17, p. 8I. Pergamon Press 1975. Printed in Great llritain
CORRESPONDENCE REMARKS ON "CASCADE SOLAR STILL FOR DISTILLED WATER PRODUCTION" (Received 19 February 1974) In a recent paper [1] it is claimed that the efficiencies obtained for the stills described therein were of the order of 60--75 per cent. Table 5 of the paper gives some typical results in which it is shown that a still efficiency of as high as 77.5 per cent had been achieved. These orders of magnitude are obviously of a nature which require very close scrutiny. Having access to the meterological data sheets from which the author had been abstracting his insolution data, I have been able to examine the figures very carefully and have found that these data are in fact in error, giving rise to the rather high values for the elSciencies. The solar radiation measuring equipment consisted of [2] a Kipp solarimeter feeding a Honeywell-Brown potentiometric pen recorder which is fitted with a ball-and-disc integrator. In effect,
Jan 1971
June 1917
Nov. 1971"
12 13 20 29 4 10 12 26 2 16 17 24
474 452 459 398 505 407 322 330 284 416 286 211
485 438 469 402 585 497 433 533 -444 344 267
----53 59 63 77.5 58 49 57 51
therefore, there are available two records of the insolation: one in chart form from the strip chart recorder, and the other the daily totals as read off the integrator and logged in the meterorological data sheet. On examining the records, it is apparent that the integrator readings are erratic and fail to match the insolation charts for the period end April 1971-November 1971 at which time the integrator failed completely. The integrator readings for this period are, therefore, unreliable. Unfortunately, it appears that the author had obtained his data from the meteorological data sheets in which the integrator readings were logged and the results presented in the paper are for the period of integrator malfunction indicated above. The correct values of daily insolution may however be obtained by measuring the areas under the insolation curves. I have performed the necessary measurements and calculations with the insolation charts for the days specified in Table 5 of the paper under discussion and for a few days in January 1971, at which time the integrator appeared to have been functioning normally. The results of this exercise are summarised in the Table. Also given in the Table are the values of the efficiencies of Table 5 of the paper under discussion and those obtained using the correct values of the insolation. It is now clear that the correct efficiencies are of the order to be expected in solar stills [3] and, in fact, are slightly less than may be expected of properly designed and oriented cascade type stills [4].
----46 48 47 46 -46 48 40
S. SATCUNANATHAN
Department of Mechanical Engineering University o.f the West Indies St. Augustine, Trinidad REFERENCES 1. O. St. C. Headley, Cascade solar still for distilled water production. Solar Energy 15, 245-258 (1973). 2. G. W. Smith, Solar radiation measurements at St. Augustine, Trinidad, an interim report. University of the West Indies (1967). 3. P. I. Copper, The maximum efficiency of single-effect solar stills. Solar Energy 15, 205-217 (1973). 4. S. G. Talbert, J. A. Eibling and G. O. G. Lof, Manual on solar distillation of saline water. Research & Progress Report No. 546, Off, of Saline Water, U.S. Dept. of the Interior (1970).
*The chart for this day indicates that the recording had been interrupted. The length of the record shows that this interruption was for a period of 4 hr out of a total of 12 hr. These readings are therefore meaningless.
81
CORRESPONDENCE REMARKS ON "CASCADE SOLAR STILL FOR DISTILLED WATER PRODUCTION" (Received 19 February 1974) In a recent paper [1] it is claimed that the efficiencies obtained for the stills described therein were of the order of 60--75 per cent. Table 5 of the paper gives some typical results in which it is shown that a still efficiency of as high as 77.5 per cent had been achieved. These orders of magnitude are obviously of a nature which require very close scrutiny. Having access to the meterological data sheets from which the author had been abstracting his insolution data, I have been able to examine the figures very carefully and have found that these data are in fact in error, giving rise to the rather high values for the elSciencies. The solar radiation measuring equipment consisted of [2] a Kipp solarimeter feeding a Honeywell-Brown potentiometric pen recorder which is fitted with a ball-and-disc integrator. In effect,
Jan 1971
June 1917
Nov. 1971"
12 13 20 29 4 10 12 26 2 16 17 24
474 452 459 398 505 407 322 330 284 416 286 211
485 438 469 402 585 497 433 533 -444 344 267
----53 59 63 77.5 58 49 57 51
therefore, there are available two records of the insolation: one in chart form from the strip chart recorder, and the other the daily totals as read off the integrator and logged in the meterorological data sheet. On examining the records, it is apparent that the integrator readings are erratic and fail to match the insolation charts for the period end April 1971-November 1971 at which time the integrator failed completely. The integrator readings for this period are, therefore, unreliable. Unfortunately, it appears that the author had obtained his data from the meteorological data sheets in which the integrator readings were logged and the results presented in the paper are for the period of integrator malfunction indicated above. The correct values of daily insolution may however be obtained by measuring the areas under the insolation curves. I have performed the necessary measurements and calculations with the insolation charts for the days specified in Table 5 of the paper under discussion and for a few days in January 1971, at which time the integrator appeared to have been functioning normally. The results of this exercise are summarised in the Table. Also given in the Table are the values of the efficiencies of Table 5 of the paper under discussion and those obtained using the correct values of the insolation. It is now clear that the correct efficiencies are of the order to be expected in solar stills [3] and, in fact, are slightly less than may be expected of properly designed and oriented cascade type stills [4].
----46 48 47 46 -46 48 40
S. SATCUNANATHAN
Department of Mechanical Engineering University o.f the West Indies St. Augustine, Trinidad REFERENCES 1. O. St. C. Headley, Cascade solar still for distilled water production. Solar Energy 15, 245-258 (1973). 2. G. W. Smith, Solar radiation measurements at St. Augustine, Trinidad, an interim report. University of the West Indies (1967). 3. P. I. Copper, The maximum efficiency of single-effect solar stills. Solar Energy 15, 205-217 (1973). 4. S. G. Talbert, J. A. Eibling and G. O. G. Lof, Manual on solar distillation of saline water. Research & Progress Report No. 546, Off, of Saline Water, U.S. Dept. of the Interior (1970).
*The chart for this day indicates that the recording had been interrupted. The length of the record shows that this interruption was for a period of 4 hr out of a total of 12 hr. These readings are therefore meaningless.
81