| Author | Supachart Chungpaibulpatana |
| Call Number | AIT Diss. no.ET-89-01 |
| Subject(s) | Solar collectors--Testing
|
| Note | A dissertation submitted in partial fulfillment of the
requirements for the degree of Doctor of Engineering |
| Publisher | Asian Institute of Technology |
| Abstract | A transient test method has been developed Lo determine solar
collector thermal performance parameters from experimental tests conducted
outdoor under variety of environmental conditions ranging from highly
variable to almost steady. A simple one-node heat capacitance model is
used to characterize the collector thermal performance. Four significant
collector parameters, namely: the effective heat capacity He, the optical
efficiency η0, the first order heat loss coefficient U1 and the second
order heat loss coefficient U2, are to be determined from experimental
tests. In the test, the collector inlet and outlet are connected in a
closed circuit by a tube equipped with a circulating pump and the fluid
inside the whole system is circulated at a very high flow rate. An
experimental setup has been designed and constructed for the tests. A
number of experimental procedures were developed before obtaining the
finalized transient test procedure that can determine the collector
performance parameters accurately.
In the first test procedure, all collector parameters are
simultaneously determined. Because of the simultaneous determination, the
discrepancies in the results obtained are difficult to investigate. A
second procedure is therefore developed in such a way that each collector
parameter is separately determined by its individual sub-procedure.
However, significant differences were found in the results obtained from
the tests of a collector using the two test procedures. The major cause is
the fact that the effective one-node heat capacity combines the effects
from various heat capacity nodes and the responses of these nodes to the
external driving forces are different; hence the effective heat capacity
depends on the opera ting conditions.
Simulation studies were made to investigate how far the single node
assumption is valid for determining the collector parameters using
transient test procedures. Various hypothetical solar collectors were used
in the investigation and their performance data were simulated by a two-node
model in which the absorber plate and fluid is represented by one node
and the transparent cover by the other. In some procedures the Variation
of the collector effective heat capacity with the operating conditions
produces large errors in the collector parameters obtained.
A new test procedure is proposed to overcome these difficulties. Only
three collector parameters: η0, U1, and U2 are obtained from the transient
experiments. There is no intention to give any fixed value for the
effective heat capacity of the collector since it varies with the operating
conditions and is considered to be unimportant in predicting the energy
output from the collector if hourly meteorological data are used. One-node
heat capacity determinations are made in the proposed procedure only for
the purpose of accurately determining the three collector parameters. The
test procedure was examined using the performance data of the various
hypothetical collectors simulated by the two-node model and sati satisfactory
results were achieved.
Further simulation studies were made to investigate two important
effects on the determination of the collector parameters using the
proposed test procedure with various hypothetical collectors. One is the
non- uniform temperature distribution around the fluid loop of the system,
which occurs because the whole fluid in the system is not heated
simultaneously during the test. The other is the heat resistance between
the absorber plate and the fluid. In the investigation of the first effect
the system is assumed to be divided into sections along the flow direction.
For the second effect, the performance data are generated by a three-node
collector model which assumes the absorber plate, the fluid and the
transparent cover to be represented by different heat capacity nodes. Both
effects were found to be important in affecting the determination of the
collector parameters when there is an abrupt change in power input to the
collector. To overcome these difficulties, the integration of data over
specific time periods and the use of techniques for selecting good data are
introduced ln the parameter determinations. Satisfactory results were
obtained from the stimulated test s on these hypothetical collectors.
The effects of the solar incidence angle, the amount of diffuse solar
radiation and the wind speed on the collector parameters were included in
the test procedure in order to determine their functional relationships. A
method for analysing the uncertainties contained in the experimental test
results was also developed to investigate the significance of measurement
errors and errors resulting from environmental variations.
Three commercial fIat-plate solar collectors were tested under actual
environmental conditions using the transient test method developed. At. the
95% confidence level, the maximum uncertainties in the collector parameters
obtained are between ±3 and ±8% depending on the collector and
environmental conditions prevailing in the tests. The collector
performance parameters obtained for the three collectors were compared with
those obtained in accordance with the well-known steady state ASHRAE 93-77
test method and satisfactory agreement was achieved.
In addition, satisfactory results were also obtained with the
transient test method for determining the performance parameters of solar
collectors with very large fluid heat capacities.
The great advantage of this transient test method is that it enables
solar collector testing to be carried out almost all the year round,
especially during periods when steady-state testing is not possible. |
| Year | 1989 |
| Type | Dissertation |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Department of Energy and Climate Change (Former title: Department of Energy, Environment, and Climate Change (DEECC)) |
| Academic Program/FoS | Energy Technology (ET) |
| Examination Committee(s) | Exell, R.H.B.;Prida Wibulswas;Mora, Jean-Claude;Huynh, Ngoc Phien;Wood, B. D. |
| Scholarship Donor(s) | Asian Institute of Technology;French Agency for Energy Management (AFME); |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 1989 |