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Title: Frost characteristics and heat transfer on a flat plate under freezer operating conditions: Part 2, Numerical modeling and comparison with data

Abstract

An existing numerical model for frost growth as a porous media is modified to include boundary conditions for a relatively high-density frost layer adjacent to a cold plate and turbulent airflow over a rough frost-air interface. Low-density frost grows on top of this high-density surface layer. Simulation results compare well with the data for selected test conditions where experimental uncertainty is small. When the experimental uncertainty is small, a validated physical/numerical model may be the best means of interpreting the physical nature of frost growth and extrapolating a limited database for frost growth.

Authors:
; ;
Publication Date:
Research Org.:
Univ. of Saskatchewan, Saskatoon, SK (CA)
Sponsoring Org.:
American Society of Heating, Refrig. and Air Conditioning Engineers; Natural Sciences and Engineering Research Council of Canada (NSERC)
OSTI Identifier:
20085620
Resource Type:
Conference
Resource Relation:
Conference: ASHRAE Annual Meeting, Seattle, WA (US), 06/18/1999--06/23/1999; Other Information: PBD: 1999; Related Information: In: ASHRAE Transactions: Technical and symposium papers presented at the 1999 annual meeting in Seattle, Washington of the American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc.; Volume 105, Part 2, by Geshwiler, M.; Harrell, D.; Roberson, T. [eds.], 1360 pages.
Country of Publication:
United States
Language:
English
Subject:
32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATION; FREEZERS; FROST; DEPOSITION; MATHEMATICAL MODELS; BOUNDARY CONDITIONS; EQUATIONS

Citation Formats

Chen, H., Besant, R.W., and Tao, Y.X. Frost characteristics and heat transfer on a flat plate under freezer operating conditions: Part 2, Numerical modeling and comparison with data. United States: N. p., 1999. Web.
Chen, H., Besant, R.W., & Tao, Y.X. Frost characteristics and heat transfer on a flat plate under freezer operating conditions: Part 2, Numerical modeling and comparison with data. United States.
Chen, H., Besant, R.W., and Tao, Y.X. 1999. "Frost characteristics and heat transfer on a flat plate under freezer operating conditions: Part 2, Numerical modeling and comparison with data". United States. doi:.
@article{osti_20085620,
title = {Frost characteristics and heat transfer on a flat plate under freezer operating conditions: Part 2, Numerical modeling and comparison with data},
author = {Chen, H. and Besant, R.W. and Tao, Y.X.},
abstractNote = {An existing numerical model for frost growth as a porous media is modified to include boundary conditions for a relatively high-density frost layer adjacent to a cold plate and turbulent airflow over a rough frost-air interface. Low-density frost grows on top of this high-density surface layer. Simulation results compare well with the data for selected test conditions where experimental uncertainty is small. When the experimental uncertainty is small, a validated physical/numerical model may be the best means of interpreting the physical nature of frost growth and extrapolating a limited database for frost growth.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = 1999,
month = 7
}

Conference:
Other availability
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  • An experimental investigation of frost growth on a flat, cold surface supplied by subfreezing, turbulent, humid, parallel flow of air is presented. The operating conditions are typical of many commercial freezers. A test loop was constructed to perform the tests, and the frost height, frost mass concentration, and cold surface heat flux were measured using specially designed and calibrated instrumentation. Twenty tests were done for steady operating conditions, each starting with no initial frost accumulation, and were run for two to six hours giving 480 data samples. Measured results show that the frost characteristics differ significantly with frost growth datamore » taken previously for room temperature airflow. Depending on the temperature of the cold plate and the relative humidity of the subfreezing supply air, the frost could appear to be either smooth or rough. Smooth frost, which occurred at warmer plate temperatures and lower supply air relative humidities, gave rise to frost growth that was much thinner and denser than that for the rough, thick, low-density frost. Frost growth characteristics are correlated as a function of five independent variables (time, distance from the leading edge, cold plate temperature ratio, humidity ratio, and Reynolds number). These correlations are presented separately for the full data set, the rough frost data, and the smooth frost data.« less
  • Part 1 of this paper described the frost growth test facility and instrumentation. In Part 2, results are presented for typical operating conditions with frost growth on heat exchanger fins. Typical data are presented for frost height distributions on fins, increase in pressure loss for airflow through a finned test section, frost mass accumulation on fins, and heat rate. Special attention is given to the uncertainty in each of these measurements and calculations.
  • In order to provide higher cooling performance for transformer windings which use nonflammable coolants, conductors wound with thread spacers were applied to the windings to enlarge the cooling surface area. Since a coolant would flow in the narrow spaces around the conductors, it was necessary to clarify the flow and cooling characteristics in the thread-spacer windings. Using a tow-dimensional winding model, the pressure drop in the windings and the temperature rise in the conductors were measured for different heat fluxes and flow rates. The winding model consisted of model conductors in which thermocouples and thin heater pins were soldered andmore » wrapped in insulating papers. The conductors were wound with thread spacers of 0.75 mm diameter. The temperature increases in these thread-spacer windings were found to be significantly lower than those in conventional baffle-plate windings. The maximum difference in the temperature increases in the windings was also small and overheating of conductors did not occur at the low flow rates in the present test. The pressure drops for the thread-spacer windings were predicted as being almost equal to those in baffle-plate windings for commercial transformers.« less
  • A numerical approach based on adjoint formulations of convection heat transfer is proposed to predict the heat transfer characteristics under arbitrary thermal boundary conditions. The main features of the present method can be summarized as follows: (1) By numerically solving the adjoint problem of forced convection heat transfer, the total heat transfer rate or the temperature at a specific location can be obtained under arbitrary thermal boundary conditions. The computation time for the adjoint problem is equal to that required in a numerical simulation of forced convection heat transfer under a specific thermal boundary condition. (2) For natural or mixedmore » convection heat transfer problem, by introducing the perturbations from the base thermal boundary conditions, the adjoint system can be derived for the perturbations. Thus, by numerically solving the base and the adjoint systems, the change of total heat transfer rate or the change of the temperature at a specific location can be predicted for arbitrary thermal boundary perturbations.« less
  • A special test facility was developed to characterize frost growing on heat exchanger fins where the cold surfaces and the air supply conditions were similar to those experienced in freezers, i.e., cold surface temperatures ranging from {minus}35 C to {minus}40 C, air supply temperatures from {minus}10 C to {minus}20 C, and 80% to 100% relative humidity (RH). This test facility included a test section with removable fins to measure the frost height and mass concentration. Frost height on heat exchanger fins was measured using a new automated laser scanning system to measure the height of frost and its distribution onmore » selected fins. The increase in air pressure loss resulting from frost growth on the fins was measured directly in the test loop. The frost mass accumulation distribution was measured for each test using special pre-etched fins that could be easily subdivided and weighed. The total heat rate was measured using a heat flux meter. These frost-measuring instruments were calibrated and the uncertainty of each is stated.« less