An instantaneous condensing gas-fired water heater: Modelling and performance

Miscellaneous · Wed Jan 01 00:00:00 EST 1986

OSTI ID:6117087

Idem, S A

The water heater employed a ceramic fiber matrix burner, which emitted significant infrared radiation when heated by combustion. A copper finned tube multi-pass heat exchanger was located within the refractory-lined combustion chamber. The coil was designed to condense the water vapor present in the flue gases, thereby extracting the latent heat. Due to the high heat exchanger surface area to thermal input ratio, the water heater performed with a high efficiency (typically 90% or higher). Convective transfer to the coil was described by means of experimentally determined coefficients obtained in a wind tunnel. Coils of several geometries were examined, and the influence of flow circuiting and external baffles was also studied. Correlations of Colburn j-factors for heat and mass transfer versus Reynolds number are presented. The model employed the experimental j-factors to describe the convective transfer occurring at the outer coil surface. The rectangular combustion chamber was modeled as a six surface enclosure bounding a uniform mixture of combustion product gases. All possible thermal radiation inter-reflections were accounted for by means of energy balances performed at each surface. Gas radiation was calculated by the exponential wide band model. The combustion gas temperature was obtained by performing an overall energy balance on the system. Flue losses were obtained by means of an empirical flue loss equation which accounts for vapor condensation. Two separate heat exchangers were installed in a prototype of the water heater, and baseline performance data were obtained. A model sensitivity analysis indicated that improved predictions of heater performance could be obtained provided more accurate surface emissivity data were employed.

• Research Organization: Purdue Univ., Lafayette, IN (USA)
• OSTI ID: 6117087
• Resource Relation: Other Information: Thesis (Ph.D)
• Country of Publication: United States
• Language: English

Related Subjects

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATION
03 NATURAL GAS
GAS APPLIANCES
MATHEMATICAL MODELS
WATER HEATERS
BURNERS
COMBUSTION CHAMBERS
COMBUSTION PRODUCTS
CONVECTION
EFFICIENCY
EMISSION
ENERGY BALANCE
FLUE GAS
HEAT EXCHANGERS
HEAT LOSSES
HEAT RECOVERY
HEAT TRANSFER
INFRARED RADIATION
MASS TRANSFER
PERFORMANCE
REYNOLDS NUMBER
SENSITIVITY ANALYSIS
SURFACE AREA
VAPOR CONDENSATION
WATER VAPOR
APPLIANCES
ELECTROMAGNETIC RADIATION
ENERGY LOSSES
ENERGY RECOVERY
ENERGY TRANSFER
FLUIDS
GASEOUS WASTES
GASES
HEATERS
LOSSES
RADIATIONS
RECOVERY
SURFACE PROPERTIES
VAPORS
WASTES
320106* - Energy Conservation
Consumption
& Utilization- Building Equipment- (1987-)
034000 - Natural Gas- Combustion