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Title: Porous absorber for solar air heaters

Abstract

A general discussion of the factors affecting solar collector performance is presented. Bench scale tests done to try to determine the heat transfer characteristics of various screen materials are explained. The design, performance, and evaluation of a crude collector with a simple screen stack absorber is treated. The more sophisticated absorber concept, and its first experimental approximation is examined. A short summary of future plans for the collector concept is included. (MHR)

Authors:
Publication Date:
Research Org.:
Finch (John A.), Madison, WI (USA)
OSTI Identifier:
5029156
Report Number(s):
DOE/R5/10154-1
DOE Contract Number:
FG02-79R510154
Resource Type:
Technical Report
Resource Relation:
Other Information: Portions of this document are illegible
Country of Publication:
United States
Language:
English
Subject:
14 SOLAR ENERGY; SOLAR ABSORBERS; MATERIALS; SOLAR AIR HEATERS; DESIGN; BENCH-SCALE EXPERIMENTS; HEAT TRANSFER; PERFORMANCE; PLASTICS; POROUS MATERIALS; SCREENS; AIR HEATERS; ENERGY TRANSFER; EQUIPMENT; HEATERS; PETROCHEMICALS; PETROLEUM PRODUCTS; SOLAR COLLECTORS; SOLAR EQUIPMENT; 141000* - Solar Collectors & Concentrators

Citation Formats

Finch, J.A. Porous absorber for solar air heaters. United States: N. p., 1980. Web. doi:10.2172/5029156.
Finch, J.A. Porous absorber for solar air heaters. United States. doi:10.2172/5029156.
Finch, J.A. 1980. "Porous absorber for solar air heaters". United States. doi:10.2172/5029156. https://www.osti.gov/servlets/purl/5029156.
@article{osti_5029156,
title = {Porous absorber for solar air heaters},
author = {Finch, J.A.},
abstractNote = {A general discussion of the factors affecting solar collector performance is presented. Bench scale tests done to try to determine the heat transfer characteristics of various screen materials are explained. The design, performance, and evaluation of a crude collector with a simple screen stack absorber is treated. The more sophisticated absorber concept, and its first experimental approximation is examined. A short summary of future plans for the collector concept is included. (MHR)},
doi = {10.2172/5029156},
journal = {},
number = ,
volume = ,
place = {United States},
year = 1980,
month = 9
}

Technical Report:

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  • Tests were conducted to determine the thermal performance of a number of transpired porous-bed solar air heaters. Improvements were made to a reference double-glazed transpired solar air heater and the performance experimentally determined. An air heater incorporating two parallel glass-plate honeycombs for air heater incorporating two parallel glass-plate honeycombs for heat-loss control was also tested. The performance of the double-honeycomb collector proved to be superior to the reference solar air heater's due to the increased transmittance of the coverglass assembly. Both collectors exhibited performance greater than any current state-of-the-art collectors. Two steady-state performance models of the reference double-glazed solar airmore » heater were formulated. One (reference model) incorporated the theoretical work of Edwards and Leung to predict the air temperature rise through the porous bed while the other assumed an isothermal bed with a heat-exchanger effectiveness of one. An energy balance was performed at each collector element, and the resultant system of nonlinear equations was solved iteratively to predict the collector's performance. Air recirculation above the porous bed was modeled using the reference formulation. Collector performance was predicted closely using the isothermal bed model. The reference model yielded close prediction using a recirculation rate of 20%.« less
  • An experimental air heater having a selective black thin-channel absorber and one glass and two Teflon glazings was designed, fabricated, and tested. The performance of the heater proved to be superior to many current state-of-the-art air heaters. A steady-state performance model was formulated. An energy balance was performed on each element and the resultant set of nonlinear equations was solved iteratively to predict the collector's performance. The maximum discrepancy between the predicted and experimental performance characteristics was less than 2 percentage points. Sensitivity studies were done to study the effect of various design parameters on the collector's performance, and themore » results of those studies are presented.« less
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  • Numerical solutions are obtained for hydrodynamically and thermally developing steady-state laminar flow in a long rectangular cavity with uniform suction and one wall and uniform temperature or heat flux independently prescribed at each wall. Fully developed velocity profiles obtained for Re/sub w/ = 4.0 and 10.0 show excellent agreement with the similarity solutions of previous investigators. For the temperature field, building-block solutions and linear superposition allow the construction of the solution for any case of uniform boundary conditions. Application of the results to the analysis and design of transpired solar air heaters is discussed. Collection efficiencies for several solar airmore » heaters are predicted by performing a system analysis. Result of the system analysis obtained through computer simulation are in good agreement with experimental data; the maximum deviations are a 2% overprediction and a 3% underprediction in instantaneous efficiency. Five selective-black-metal-plate experimental solar air heaters with and without transpiration were designed, fabricated, and tested to compare their technical merits and to prove how well the theoretical results and system analysis predict performance of actual solar collectors. Based on the test results, the configuration with slotted absorber plate (the working fluid transpires through the slots) is the best solar air heater in terms of collector efficiency and pressure drop among the five configurations. Based on the knowledge obtained from the theoretical results, system analysis, and experimental results, discussion of the design of a full-scale selective-black-metal-plate solar air heater with transpiration through slots is presented. Discussed are: (1) the number of teflon films for cover glazing assembly; (2) the spacing between glazing elements; (3) the spacing between the absorber plate and the inner glazing; and (4) the design of inlet and outlet manifolds.« less
  • This is Volume 3 in a series of documents on energy efficiency of consumer products. This volume discusses energy efficiency of water heaters. Water heaters are defined by NAECA as products that utilize oil, gas, or electricity to heat potable water for use outside the heater upon demand. These are major appliances, which use a large portion (18% on average) of total energy consumed per household (1). They differ from most other appliances in that they are usually installed in obscure locations as part of the plumbing and are ignored until they fail. Residential water heaters are capable of heatingmore » water up to 180{degrees}F, although the setpoints are usually set lower.« less