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Title: Analysis of boiling flat-plate collectors

Abstract

A detailed model for use with TRNSYS, capable of modelling a wide range of boiling collector types, was used to analyze boiling flat-plate collector systems. This model can account for a subcooled liquid entering the collector, heat losses in the vapor and the liquid return line, pressure drops due to friction in the collector and piping, and pressure drops due to the hydrostatic head of the fluid. The model has been used to determine the yearly performance of boiling flat-plate solar collector systems. A simplified approach was also developed which can be used with the f-Chart method to predict yearly performance of boiling flat-plate collector systems.

Authors:
; ;
Publication Date:
Research Org.:
Solar Energy Lab., Univ. of Wisconsin-Madison, Madison, WI 53706
OSTI Identifier:
5472076
Resource Type:
Journal Article
Resource Relation:
Journal Name: J. Sol. Energy Eng.; (United States); Journal Volume: 108:2
Country of Publication:
United States
Language:
English
Subject:
14 SOLAR ENERGY; FLAT PLATE COLLECTORS; COMPUTERIZED SIMULATION; HEAT TRANSFER FLUIDS; MATHEMATICAL MODELS; BOILING; ANNUAL VARIATIONS; F-CHART; FRICTION; HEAT LOSSES; HYDROSTATICS; PERFORMANCE; PIPES; PRESSURE DROP; SUBCOOLING; T CODES; VAPORS; COMPUTER CODES; COOLING; ENERGY LOSSES; EQUIPMENT; FLUIDS; GASES; LOSSES; PHASE TRANSFORMATIONS; SIMULATION; SOLAR COLLECTORS; SOLAR EQUIPMENT; VARIATIONS; 141000* - Solar Collectors & Concentrators

Citation Formats

Price, H.W., Klein, S.A., and Beckman, W.A. Analysis of boiling flat-plate collectors. United States: N. p., 1986. Web. doi:10.1115/1.3268083.
Price, H.W., Klein, S.A., & Beckman, W.A. Analysis of boiling flat-plate collectors. United States. doi:10.1115/1.3268083.
Price, H.W., Klein, S.A., and Beckman, W.A. 1986. "Analysis of boiling flat-plate collectors". United States. doi:10.1115/1.3268083.
@article{osti_5472076,
title = {Analysis of boiling flat-plate collectors},
author = {Price, H.W. and Klein, S.A. and Beckman, W.A.},
abstractNote = {A detailed model for use with TRNSYS, capable of modelling a wide range of boiling collector types, was used to analyze boiling flat-plate collector systems. This model can account for a subcooled liquid entering the collector, heat losses in the vapor and the liquid return line, pressure drops due to friction in the collector and piping, and pressure drops due to the hydrostatic head of the fluid. The model has been used to determine the yearly performance of boiling flat-plate solar collector systems. A simplified approach was also developed which can be used with the f-Chart method to predict yearly performance of boiling flat-plate collector systems.},
doi = {10.1115/1.3268083},
journal = {J. Sol. Energy Eng.; (United States)},
number = ,
volume = 108:2,
place = {United States},
year = 1986,
month = 5
}
  • In stationary heat-loss experiments, the thermal losses by gas conduction of an evacuated flat-plate solar collector (EFPC) were experimentally determined for different values of interior gas pressure. The experiments were carried out with air and argon in the pressure range from 10{sup {minus}3} to 10{sup 4} Pa. For air, loss reduction sets in at 100 Pa, whereas at 0.1 Pa heat conduction is almost completely suppressed. Using argon as filling gas, gas conduction is reduced by 30% (compared to air) at moderate interior pressures of 1,000 Pa. With decreasing pressure this reduction is even greater (50% reduction at 10 Pa).more » A theory was developed to calculate thermal losses by gas conduction in an EFPC: Fourier`s stationary heat conduction equation was solved numerically (method of finite differences) for the special geometry of the collector. From kinetic gas theory a formula for the pressure dependency of the thermal conductivity was derived covering the entire pressure range. The theory has been validated experimentally for the gases air and argon. Calculations for krypton and xenon show a possible gas conduction loss reduction of 60--70% and 75--85% (with respect to air, depending on gas pressure), corresponding to a reduction of the overall collector losses of up to 40%.« less
  • Existing test procedures for measuring and rating thermal performance require the determination of the angular response of collectors in order to account for nonnormal incident beam irradiance. Angular response measurements for four different types of collectors, each type tested by three different laboratories, are presented and analyzed. Substantial differences, both within and between laboratories, are reported for the same type collectors. An analysis of the measurement procedure shows that experimentally determined angular response parameters are subject to relatively large uncertainties. The problem results to a large extent from measuring collector efficiencies at non-normal incident angles where measurement uncertainty is ofmore » the same order of magnitude as the efficiency reduction attributable to these off-normal angles. Other factors which can affect angular response measurements and the method of correlating results are also discussed. A theoretical analysis shows that shading of the absorber by the collector air space side- and end-walls for non-normal incident angles can be of the same order of importance as the decrease in the transmittance of the cover assembly. While this situation complicates an analytical approach, it is concluded that calculations are adequate to depict the angular response of conventional flat-plate tube-in-sheet collector designs. A simplified analytical procedure and nomographs are presented for rapid calculation of incident angle modifiers. The predicted seasonal performance of solar energy systems and clear-day ratings of typical flatplate collectors are shown to be relatively insensitive to large uncertainties in incident angle modifiers. Typically, the values of these calculated quantities could be affected by approximately five percent as a result of uncertainty in the test-derived angular response parameter.« less
  • New comparative tests on two different types of solar collectors are presented in this paper. A standard glazed flat plate collector and an evacuated tube collector are installed in parallel and tested at the same working conditions; the evacuated collector is a direct flow through type with external compound parabolic concentrator (CPC) reflectors. Efficiency in steady-state and quasi-dynamic conditions is measured following the standard and it is compared with the input/output curves measured for the whole day. The first purpose of the present work is the comparison of results in steady-state and quasi-dynamic test methods both for flat plate andmore » evacuated tube collectors. Besides this, the objective is to characterize and to compare the daily energy performance of these two types of collectors. An effective mean for describing and analyzing the daily performance is the so called input/output diagram, in which the collected solar energy is plotted against the daily incident solar radiation. Test runs have been performed in several conditions to reproduce different conventional uses (hot water, space heating, solar cooling). Results are also presented in terms of daily efficiency versus daily average reduced temperature difference: this allows to represent the comparative characteristics of the two collectors when operating under variable conditions, especially with wide range of incidence angles. (author)« less
  • The extended mathematical model of a flat-plate solar collector-evaporator permits prediction of the effects of boiling of the working fluid in the collector tubes on the efficiency of the collector. The efficiency increases sharply and approaches the ideal on transition from single phase flow to the subcooled and saturated boiling regimes, regardless of the nature of the working fluid. 9 references.
  • The extended mathematical model of a flat-plate solar collector-evaporator permits prediction of the effects of boiling of the working fluid in the collector tubes on the efficiency of the collector. The efficiency increases sharply and approaches the ideal on transition from single phase flow to the subcooled and saturated boiling regimes, regardless of the nature of the working fluid.