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Title: Measurement of frost characteristics on heat exchanger fins. Part 1: Test facility and instrumentation

Abstract

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 on 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.

Authors:
; ;
Publication Date:
Research Org.:
Univ. of Saskatchewan, Saskatoon, Saskatchewan (CA)
Sponsoring Org.:
American Society of Heating, Refrig. and Air Conditioning Engineers; Natural Sciences and Engineering Research Council of Canada (NSERC)
OSTI Identifier:
20085625
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; TEST FACILITIES; HEAT EXCHANGERS; FROST; DEPOSITION; FINS; FREEZERS; MEASURING METHODS; FLOW BLOCKAGE; AIR FLOW

Citation Formats

Thomas, L., Chen, H., and Besant, R.W. Measurement of frost characteristics on heat exchanger fins. Part 1: Test facility and instrumentation. United States: N. p., 1999. Web.
Thomas, L., Chen, H., & Besant, R.W. Measurement of frost characteristics on heat exchanger fins. Part 1: Test facility and instrumentation. United States.
Thomas, L., Chen, H., and Besant, R.W. Thu . "Measurement of frost characteristics on heat exchanger fins. Part 1: Test facility and instrumentation". United States. doi:.
@article{osti_20085625,
title = {Measurement of frost characteristics on heat exchanger fins. Part 1: Test facility and instrumentation},
author = {Thomas, L. and Chen, H. and Besant, R.W.},
abstractNote = {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 on 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.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Thu Jul 01 00:00:00 EDT 1999},
month = {Thu Jul 01 00:00:00 EDT 1999}
}

Conference:
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  • 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.
  • 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
  • A compact heat exchanger which consists of air-cooled aluminum fins and copper tubes circulating refrigerant has been used in a cooling system for a long time. There are two key parameters to be seriously considered for a design of the heat exchanger and its performance improvement. These are the heat transfer rate and pressure drop coefficient which varies with the change of the tube size, its arrangement and the fin configuration. In here, a numerical study was carried to understand the effect of the fin configuration on the heat transfer and pressure drop of the heat exchanger. The diameter andmore » the arrangement of tubes were fixed but three different types of the fin configuration were used to see its effect on the heat transfer capacity and the static pressure drop. The calculation results were compared with that of a flat plate fin. From the comparison, it was found that the slitted fins have higher pressure drop; however, they have higher heat transfer rate. It means that the simpler of the fin configuration, the lower pressure drop and heat transfer coefficients are obtained. It is mainly due to the discretisation of the thermal boundary layer on the fin surface to maximize the heat transfer to air. The slitted sides of fins act like obstacles in the airflow path. From the experimental result, it was found that the same trend in the variation of the heat transfer rate and the pressure drop with the change of the fin configuration was obtained.« less
  • 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.
  • An approximate analytical model is described that may be used to calculate the rates of heat transfer and evaporation from the surface of a wet finned heat exchanger. The model is analogous to the conventional expression for convective heat transfer. However, the driving potential is an enthalpy difference instead of a temperature difference. The overall heat transfer coefficient can be computed in the usual manner using a simple transformation of variables. The value of the model is that wet heat exchanger performance can be estimated accurately using dry performance data.