Analytical and experimental investigation to determine the variation of H-W-B constants for a scaled forced circulation flat plate solar water heater

Arunachala Chandavar, Siddhartha Bhatt, Sreepathi Krishnamurthy

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

Fixed tilt flat plate solar thermal collectors, popularly known as solar water heaters still remain as one of the most interesting technologies for utilization of solar energy. The system performance deteriorates due to scaling because of continuous use of hard water as feed water. The present study deals with the experimental and analytical approach to determine the variation of H-W-B (Hottel - Whillier - Bliss) constants (which compactly represent the efficiency characteristics of a solar water heater) due to variation in solar power input and degree of scaling in case of forced circulation system without considering the variation of input power to the circulating pump. Indoor tests are performed with a copper tube to investigate the flow characteristics. This forms a part of conventional forced circulation system, in place of the usual nine-fin tube array in a full fledged collector. In indoor tests, electrical heating is favored to simulate solar radiation level. Various energy parameters are determined and compared by incorporating the developed numerical code FLATSCALE. Variation between experimental and analytical mass flow rate, overall heat loss coefficient, H-W-B constants with simulated solar radiation level are plotted. In scaled condition, the drop in instantaneous efficiency is due to both scale thickness and reduced water flow rate. Scale thickness acts as an additional thermal conductive resistance between absorber plate and flowing water. Overall heat loss coefficient increases as absorber plate temperature is high during reduced flow rate. The maximum deviation observed is 21.68 % in mass flow rate, 14.64 % in absorber plate mean temperature, 7.86 % in overall heat loss coefficient and 12.04 % in instantaneous efficiency. Compared to a clean tube, a highly scaled tube of 3.7 mm scale thickness indicates a drop of 4.76 % in instantaneous efficiency and 40.28 % in mass flow rate. It is concluded that the growth of scale in forced circulation system does not affect the instantaneous efficiency significantly because of the margin in heat carrying capacity of water inspite of high drop in the flow rate.

Original languageEnglish
Title of host publicationEnergy
PublisherAmerican Society of Mechanical Engineers(ASME)
Volume6 B
ISBN (Print)9780791856291
DOIs
Publication statusPublished - 01-01-2013
EventASME 2013 International Mechanical Engineering Congress and Exposition, IMECE 2013 - San Diego, CA, United States
Duration: 15-11-201321-11-2013

Conference

ConferenceASME 2013 International Mechanical Engineering Congress and Exposition, IMECE 2013
CountryUnited States
CitySan Diego, CA
Period15-11-1321-11-13

Fingerprint

Solar water heaters
Flow rate
Heat losses
Water
Solar radiation
Solar energy
Pumps
Copper
Heating
Temperature
Hot Temperature

All Science Journal Classification (ASJC) codes

  • Mechanical Engineering

Cite this

Chandavar, Arunachala ; Bhatt, Siddhartha ; Krishnamurthy, Sreepathi. / Analytical and experimental investigation to determine the variation of H-W-B constants for a scaled forced circulation flat plate solar water heater. Energy. Vol. 6 B American Society of Mechanical Engineers(ASME), 2013.
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abstract = "Fixed tilt flat plate solar thermal collectors, popularly known as solar water heaters still remain as one of the most interesting technologies for utilization of solar energy. The system performance deteriorates due to scaling because of continuous use of hard water as feed water. The present study deals with the experimental and analytical approach to determine the variation of H-W-B (Hottel - Whillier - Bliss) constants (which compactly represent the efficiency characteristics of a solar water heater) due to variation in solar power input and degree of scaling in case of forced circulation system without considering the variation of input power to the circulating pump. Indoor tests are performed with a copper tube to investigate the flow characteristics. This forms a part of conventional forced circulation system, in place of the usual nine-fin tube array in a full fledged collector. In indoor tests, electrical heating is favored to simulate solar radiation level. Various energy parameters are determined and compared by incorporating the developed numerical code FLATSCALE. Variation between experimental and analytical mass flow rate, overall heat loss coefficient, H-W-B constants with simulated solar radiation level are plotted. In scaled condition, the drop in instantaneous efficiency is due to both scale thickness and reduced water flow rate. Scale thickness acts as an additional thermal conductive resistance between absorber plate and flowing water. Overall heat loss coefficient increases as absorber plate temperature is high during reduced flow rate. The maximum deviation observed is 21.68 {\%} in mass flow rate, 14.64 {\%} in absorber plate mean temperature, 7.86 {\%} in overall heat loss coefficient and 12.04 {\%} in instantaneous efficiency. Compared to a clean tube, a highly scaled tube of 3.7 mm scale thickness indicates a drop of 4.76 {\%} in instantaneous efficiency and 40.28 {\%} in mass flow rate. It is concluded that the growth of scale in forced circulation system does not affect the instantaneous efficiency significantly because of the margin in heat carrying capacity of water inspite of high drop in the flow rate.",
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Chandavar, A, Bhatt, S & Krishnamurthy, S 2013, Analytical and experimental investigation to determine the variation of H-W-B constants for a scaled forced circulation flat plate solar water heater. in Energy. vol. 6 B, American Society of Mechanical Engineers(ASME), ASME 2013 International Mechanical Engineering Congress and Exposition, IMECE 2013, San Diego, CA, United States, 15-11-13. https://doi.org/10.1115/IMECE2013-63453

Analytical and experimental investigation to determine the variation of H-W-B constants for a scaled forced circulation flat plate solar water heater. / Chandavar, Arunachala; Bhatt, Siddhartha; Krishnamurthy, Sreepathi.

Energy. Vol. 6 B American Society of Mechanical Engineers(ASME), 2013.

Research output: Chapter in Book/Report/Conference proceedingConference contribution

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