Optimization of Flow Passage Geometry for Air-Heating, Plate-Type Solar Collectors

1981 ◽  
Vol 103 (4) ◽  
pp. 323-330 ◽  
Author(s):  
K. G. T. Hollands ◽  
E. C. Shewen
Keyword(s):  
Air Flow ◽  
Solar Collectors ◽  
Absorber Plate ◽  
Flow Passage ◽  
Air Heating ◽  
Path Design ◽  
Air Stream ◽  
Back Plate ◽  
Collector Efficiency ◽  
Plate Type

The effect of the choice of shape and dimensions of the air flow passages in plate-type, air-heating solar collectors is assessed. Particularly examined is their effect on the overall heat transfer coefficient Upf between the air stream and the plate, which has an important effect on collector efficiency. It is emphasized in this study that in comparing various designs of flow passage, they should be compared for the same pressure drop Δp suffered by the air in passing through the collector, and for the same mass flow rate m per unit of collector area. On the basis of this type of comparison, two main conclusions are drawn. First, when the length of the air flow passage L is made less than about 1 m, Upf increases dramatically with decreasing values of L. Second, outside the transition regime, the value of Upf for a V-corrugated absorber plate is from 47 to 300 percent higher than that for a flat absorber plate, depending on whether the flow is laminar or turbulent, and on whether the V-corrugated plate is thermally bonded to the back plate. The first conclusion has led to a proposal for a novel air-heating solar collector design, called the “short-path” design.

Experimental Study of Solar Air Heating System Based on Unglazed Transpired Collector

2011 ◽  
Author(s):  
Lixin Gao ◽  
Hua Bai ◽  
Xiumu Fang
Keyword(s):  
Surface Temperature ◽  
Air Temperature ◽  
Flow Rate ◽  
Temperature Rise ◽  
Air Flow ◽  
Heating System ◽  
Airflow Rate ◽  
Air Flow Rate ◽  
Air Heating ◽  
Collector Efficiency

An experimental rig was set up to test the thermal performance of a solar air heating system based on an unglazed transpired collector of 2.5 m2. The experiment was carried out at Harbin Institute of Technology in the city of Harbin, which is located in northeastern China, at latitude 45°41′ N and longitude 126°37′ E. The tests were spread over a number of days, in which the 4-day experimental data within the period were selected as the sample for analysis. Experimental results show that solar collector’s surface temperature and exit air temperature increase with increasing solar irradiation. The influence of ambient temperature on surface temperature and exit temperature is negligible. Temperature rise decreases with increasing air flow rate, while collector efficiency increases with increasing air flow rate. For an air flow rate of 100 m3/h in Test 1, the average air temperature rise and collector efficiency were 28.86°C and 72% respectively; for an air flow rate of 235 m3/h in Test 2, the average air temperature rise and collector efficiency were 11.52°C and 78% respectively. Higher airflow rate tends to operate the collector at lower surface temperature, which results in lower overall heat losses from the collector to the surroundings, therefore increasing airflow rate reduces air temperature rise and enhances the collector efficiency. The average efficiency of the experimental solar air heating system in the 4-day experiment period was 72%, 78%, 61%, and 72% respectively, which are higher than most conventional glazed flat-plate solar air collectors. With better coordination with architectural design at early stage in a project, this building-integrated solar air heating system can be both aesthetically and technically viable.

Pressure Drop as a Function of Air Flow Rate for Roll-Punched Transpired Solar Collectors With Different Porosities

2011 ◽  
Author(s):  
Greg Barker ◽  
Kosol Kiatreungwattana
Keyword(s):  
Pressure Drop ◽  
Flow Rate ◽  
Air Flow ◽  
Cost Effective ◽  
Solar Collectors ◽  
Air Flow Rate ◽  
Heated Air ◽  
Absorber Material ◽  
Collector Efficiency ◽  
Metal Absorber

Transpired solar collectors are simple and cost-effective devices suited for preheating ventilation air for buildings. They work by drawing outside air through a south-facing perforated metal absorber. The absorber is heated by solar radiation, heat is transferred to the air as it is drawn through the perforations in the absorber, and the pre-heated air is delivered to the building. Often overlooked in the design of transpired collector systems is the effect on collector efficiency of pressure drop across the absorber. The pressure drop is a function of the air flow rate through the perforations, the overall porosity of the absorber, and the properties of the air. The National Renewable Energy Laboratory (NREL) conducted a series of laboratory tests to characterize the pressure drop as a function of the relevant parameters for six commercially-available absorber configurations; three porosities in aluminum and three in steel. Each absorber material is roll-punched to one of three depths to create absorbers with three different porosities. Pressure drop, air flow rate, air temperature, and air relative humidity data were collected during the tests. The data were fit to a model that can be used to predict pressure drop across the absorber as a function of air properties and flow rate. Use of these correlations is expected to aid designers in ensuring that transpired collector systems are designed for optimal thermal efficiency and cost effectiveness.

Parametric Study of a Flat Plate Wick Assisted Heat Pipe Solar Collector

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
Brahim Taoufik ◽  
Mhiri Foued ◽  
Jemni Abdelmajid
Keyword(s):  
Flat Plate ◽  
Heat Pipe ◽  
Solar Collector ◽  
Solar Collectors ◽  
Absorber Plate ◽  
Steady State Condition ◽  
Collector Efficiency ◽  
Evacuated Tube Collectors ◽  
Gap Spacing ◽  
Evacuated Tube

The use of heat pipes in solar collectors offers several advantages regarding flexibility in operation and application, as they are very efficient in transporting heat even under a small temperature difference. Compared with other systems powered by evacuated tube collectors or flat plate solar collectors using a wickless heat pipe, little attention has been paid to a flat plate solar collectors wick assisted heat pipe. In this paper an analytical model based on energy balance equations assuming a steady state condition was developed to evaluate the thermal efficiency of a flat plate wick assisted heat pipe solar collector. Parameters which affect the collector efficiency are identified, such as tube spacing distance, gap spacing between the absorber plate and the glazing cover, and the emissivity of the absorber plate. The results reflect the contribution and significance of each of these parameters to the collector overall heat loss coefficients. Three heat pipe working fluids are examined and results show that acetone performs better than methanol and ethanol.

Heat Exchanger Theory Applied to the Design of Water- and Air-Heating Flat-Plate Solar Collectors

1988 ◽  
Vol 110 (2) ◽  
pp. 132-138 ◽  
Author(s):  
Gregory J. Kowalski ◽  
Arthur R. Foster
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Flat Plate ◽  
Solar Collector ◽  
Operating Conditions ◽  
Solar Collectors ◽  
Heat Transfer Characteristics ◽  
Air Heating ◽  
Collector Efficiency ◽  
The Difference

A general method for the design of flat-plate solar collectors based on solar collector theory has been developed. It can be applied to both liquid- and air-heating solar collectors. The solar collector efficiency is determined by the product of the effectiveness (ε) and the insolation use factor (IUF). The effectiveness describes the heat transfer characteristics of the collector and is shown to be a function of a solar number of transfer units (SNTU) and a parameter ψ. For an air-heating collector, the ψ parameter equals the collector efficiency factor, while for a liquid-heating collector it must account for the difference between the plate and tube heat transfer areas. The effectiveness and SNTU parameters are similar to the effectiveness and NTU parameters used in heat exchanger design methods. The IUF is a measure of the operating conditions of the collector. It represents the difference between the transmittance-absorptance product and the ratio of the minimum heat loss to the insolation on the exterior cover. The relationship between the effectiveness and the SNTU parameter is general for all nonconcentrating collectors. One advantage of this method over the traditional Hottel-Whillier method is that it separates the heat transfer characteristics of the solar collector from its optical properties and the operating conditions.

scholarly journals Numerical modeling of a flat air solar collector fitted with obstacles

2021 ◽  
Vol 321 ◽  
pp. 04016
Author(s):  
Mohammed Amine Amraoui ◽  
Fayssal Benosman
Keyword(s):  
Heat Transfer ◽  
Numerical Modeling ◽  
Fluid Flow ◽  
Heat Exchange ◽  
Solar Collector ◽  
Air Flow ◽  
Flow Path ◽  
Solar Collectors ◽  
Air Stream ◽  
Ansys Cfx

The weakness of the solution of flat-air solar collectors in the absence of a turbulence promoter has led researchers to seek other means to improve the performance of the collector. to improve the heat exchange in the air stream from the flat solar collector to the air is the creation of baffles or obstacles to give the longest possible flow path and create a large possible turbulence network. In this article, we studied an air flow around an obstacle field in a flat air solar collector, using the Ansys CFX calculator software, we make a digital 3 D similarity and we give results on the heat exchange in the flat air solar collector and the aim of this study is to show the effect of the obstacles for the fluid flow and the heat transfer in the fluid flow of the flat air solar collector.

Performance analysis of domestic solar air heating system using V-shaped baffles – An experimental study

2021 ◽  
pp. 095440892110162
Author(s):  
Vijayakumar Rajendran ◽  
Harichandran Ramasubbu ◽  
Karthick Alagar ◽  
Vignesh Kumar Ramalingam
Keyword(s):  
Experimental Study ◽  
Performance Improvement ◽  
Mass Flow ◽  
Thermal Efficiency ◽  
Heating System ◽  
Solar Air Heater ◽  
Absorber Plate ◽  
Air Heating ◽  
Mass Flow Rates ◽  
Carbon Dioxide Mitigation

An experimental study has been carried out to enhance a solar air heater’s performance by integrating artificial roughness through baffles on the absorber plate. In this paper, the thermal and energy matrices analysis of a Solar Air Heater (SAH) roughened with V up perforated baffles have been investigated. The effect of various mass flow rates on the SAH was analyzed with and without baffles. Experimental outputs like outlet air temperature, useful energy (heat) gain and thermal efficiency were evaluated to confirm the performance improvement. The baffled absorber plate SAH was found to give the maximum thermal efficiency and useful energy gain of 89.3% and 1321.37 W at a mass flow rate of 0.0346 kg/s, 13% and 12% higher than SAH without baffle. This result showed that the V up-shaped ribs in flow arrangement provide better thermal performance than smooth plate SAH for the parameter investigated. Energy matrices analysis and carbon dioxide mitigation of the SAH system were also analyzed.

Method to Determine an Optimal Air-Flow Rate in Solar Collectors

1979 ◽  
Vol 3 (6) ◽  
pp. 357-362
Author(s):  
H. C. Hewitt ◽  
E. I. Griggs
Keyword(s):  
Flow Rate ◽  
Air Flow ◽  
Solar Collectors ◽  
Air Flow Rate
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