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Title: An improved technique for computing the top heat loss factor of a flat-plate collector with a single glazing

Abstract

A different approach to evaluate the top heat loss factor of a flat plate solar collector with a single glass cover is proposed. The equation for the heat loss factor in the analytical form is employed instead of the semi-empirical form hitherto employed for solar collectors. The glass cover temperature is, however, estimated by an empirical relation. (This relation replaces the empirical relation for the factor f of the earlier work). Values of the top heat loss factor calculated by this simple technique are within 3 percent (maximum error) of those obtained by iterative solution of the heat balance equations. There is an improvement in accuracy by a factor greater than five over the current semi-empirical equations. The range of variables covered is 50/sup 0/C to 150/sup 0/C in absorber plate temperature, 0.1 to 0.95 in absorber coating emittance, and 5 W/m/sup 2/C to 45 W/m/sup 2/C in wind heat-transfer coefficient. The effect of variation in air properties with temperature has been taken into account.

Authors:
;
Publication Date:
Research Org.:
Centre for Energy Studies, Indian Institute of Technology, Delhi, New Delhi 110 016 (IN)
OSTI Identifier:
6429940
Resource Type:
Journal Article
Resource Relation:
Journal Name: J. Sol. Energy Eng.; (United States); Journal Volume: 110:4
Country of Publication:
United States
Language:
English
Subject:
14 SOLAR ENERGY; 42 ENGINEERING; FLAT PLATE COLLECTORS; HEAT LOSSES; AIR; ANALYTICAL SOLUTION; CALCULATION METHODS; DESIGN; EQUATIONS; GLAZING; ITERATIVE METHODS; VARIATIONS; COVERINGS; ENERGY LOSSES; EQUIPMENT; FLUIDS; GASES; LOSSES; SOLAR COLLECTORS; SOLAR EQUIPMENT; 141000* - Solar Collectors & Concentrators; 420400 - Engineering- Heat Transfer & Fluid Flow

Citation Formats

Mullick, S.C., and Samdarshi, S.K. An improved technique for computing the top heat loss factor of a flat-plate collector with a single glazing. United States: N. p., 1988. Web. doi:10.1115/1.3268266.
Mullick, S.C., & Samdarshi, S.K. An improved technique for computing the top heat loss factor of a flat-plate collector with a single glazing. United States. doi:10.1115/1.3268266.
Mullick, S.C., and Samdarshi, S.K. Tue . "An improved technique for computing the top heat loss factor of a flat-plate collector with a single glazing". United States. doi:10.1115/1.3268266.
@article{osti_6429940,
title = {An improved technique for computing the top heat loss factor of a flat-plate collector with a single glazing},
author = {Mullick, S.C. and Samdarshi, S.K.},
abstractNote = {A different approach to evaluate the top heat loss factor of a flat plate solar collector with a single glass cover is proposed. The equation for the heat loss factor in the analytical form is employed instead of the semi-empirical form hitherto employed for solar collectors. The glass cover temperature is, however, estimated by an empirical relation. (This relation replaces the empirical relation for the factor f of the earlier work). Values of the top heat loss factor calculated by this simple technique are within 3 percent (maximum error) of those obtained by iterative solution of the heat balance equations. There is an improvement in accuracy by a factor greater than five over the current semi-empirical equations. The range of variables covered is 50/sup 0/C to 150/sup 0/C in absorber plate temperature, 0.1 to 0.95 in absorber coating emittance, and 5 W/m/sup 2/C to 45 W/m/sup 2/C in wind heat-transfer coefficient. The effect of variation in air properties with temperature has been taken into account.},
doi = {10.1115/1.3268266},
journal = {J. Sol. Energy Eng.; (United States)},
number = ,
volume = 110:4,
place = {United States},
year = {Tue Nov 01 00:00:00 EST 1988},
month = {Tue Nov 01 00:00:00 EST 1988}
}
  • This paper reports on an analytical equation for the top heat loss factor of a flat-plate collector with double glazing that has been developed. The maximum computational errors resulting from the use of this equation are plus or minus three percent compared to numerical solution of the heat balance equations. The equation is considerably more accurate than the currently used semi-empirical equations over the entire range of variables covered. It is found that the computational errors resulting from simplification of the proposed equation by approximation of the individual heat-transfer coefficients are much lower than the errors resulting from the usemore » of semi-empirical equations.« less
  • A generalized analytical equation for the top heat loss factor of a flat-plate collector with one or more glass covers has been developed. The maximum computational errors resulting from the use of the analytical equation with several simplifications are [+-] 5 percent compared to numerical solution of the set of heat balance equations. The analytical equation is considerably more accurate than the available semi-empirical equations over the entire range of variables covered. An additional advantage of the proposed technique over the semi-empirical equations is that results can be obtained for different values of sky temperature, using any given correlation formore » convective heat transfer in the air gap spacings, and for any given values of fluid (air in the present case) properties.« less
  • A different approach to evaluate the heat loss factor of a tubular absorber with a concentric glass cover, often employed as the target of a linear solar concentrator, is proposed. The equation for the heat loss factor in analytical form is employed instead of the semiempirical form hitherto employed for solar collectors. The glass cover temperature is, however, estimated by an empirical relation, replacing the empirical relation for the factor f of earlier work. This simple method predicts the overall heat loss factor, U{sub L}, within {plus minus}1% of the value obtained by iterative solution of the simultaneous equations inmore » the range of variables-absorber temperature 60 to 240{degree}C, absorber coating emittance 0.1 to 0.95, wind velocity 1.5 to 10 m/s, and absorber diameter 12.5 to 75 mm. The method can also predict this factor for absorber temperatures up to 350{degree}C with maximum computational error {plus minus}2% compared to iterative solution. There is an improvement in computational accuracy by a factor greater than five over the current practice using a semiempirical equation. The effect of variation of air properties with temperature has been taken into account.« less
  • The performance of a flat-plate solar collector is investigated. The collector is of the sheet-and tube design and the tube is bonded to the absorbing plate in a serpentine fashion. Equations describing the variation of the fluid temperature in the different segments of the serpentine are derived. These equations are then used to determine the heat removal factor F/sub R/ for the collector. It is shown that for the general case of an N-bend serpentine, the heat removal factor depends on three non-dimensional groups containing the different operational and design variables of the collector. A generalized chart for estimating F/submore » R/ for collectors with serpentines of arbitrary geometry and number of bends is presented.« less
  • Within the work on new collector designs for the Central European climate, investigations on two different collector systems using Transparent Insulation Materials (TIMs) are presented in this paper. The thermal and optical properties of a polycarbonate honeycomb material are discussed with respect to the design of improved flat-plate collectors and integrated storage collectors with TIMs. Measurements on a collector with this material proved the good collector performance in the temperature range of 80 to 140C. But the collector is not stagnation proof, as the honeycombs start melting at 120C. The paper also describes a collector with newly developed, temperature resistantmore » glass capillaries, with which a stagnation temperature of 261C was measured. Finally, new measurements of an integrated collector storage with polycarbonate honeycomb are reported which confirm the good performance of this simplified solar domestic hot water system.« less