Modified efficiency-NTU method (m-ε-NTU) for calculating air coolers in dehumidifying or frost conditions. Part I

Abstract

In this part of the article, a literary review of various methods of stationary calculations of air coolers operating under dehumidifying or frost conditions is performed. The approaches used at the moment are reviewed, namely, the dehumidification coefficient method, logarithmic enthalpy difference method, equivalent dry-bulb temperature method, and the efficiency–number of heat transfer units (ε–NTU) method, for calculating counterflow, chilled water coils. Their main differences are demonstrated, and the key expressions used in them are provided. A comparison of the advantages and disadvantages of the methods showed the rationality of using the ε–NTU approach owing to the possibility of its application for both design and verification calculations of heat exchangers. The classical ε–NTU method is not directly applicable under dehumidifying or frost conditions. Hence, we must adapt it to calculations of air coolers of all types (both counterflow and parallel-flow air coolers with and without phase transition of cooling fluid, respectively) to correctly describe the effect of the abovementioned processes on heat exchange.

Keywords

heat transfer / mass transfer / air coolers / fin-and-tube heat exchangers / cooling of humid air / dehumidifying conditions / frost conditions / efficiency-NTU method

References

[1] Grigoriev VA, Krokhin YuI. Heat and mass transfer apparatus of cryogenic technology: tutorial for universities. Moscow: Energoizdat; 1982. (in Russ).

[2] Григорьев В.А., Крохин Ю.И. Тепло- и массообменные аппараты криогенной техники: Учебн. пособие для вузов. М.: Энергоиздат, 1982.

[3] Danilova GN, Bogdanov SN, Ivanov OP, et al. Heat exchangers for refrigeration installations. Ed. Danilova GN, 2nd ed. Leningrad: Mashinostroenie; 1986. (in Russ).

[4] Данилова Г.Н., Богданов С.Н., Иванов О.П. и др. Теплообменные аппараты холодильных установок. Под ред. Г.Н. Даниловой, 2-е изд. Л.: Машиностроение, 1986.

[5] Goodman W. Performance of coils for dehumidifying air. Heating, Piping and Air Conditioning. 1938;11(10):697–707.

[6] Goodman W. Performance of coils for dehumidifying air // Heating, Piping and Air Conditioning. 1938. Vol. 11, N 10. P. 697–707.

[7] Threlkeld JL. Thermal environmental engineering. Hoboken: Prentice Hall, 1970.

[8] Threlkeld J.L. Thermal environmental engineering. Hoboken: Prentice Hall, 1970.

[9] Elmahdy AH, Mitalas GP. A simple model for cooling and dehumidifying coils for use in calculating the energy requirements of buildings. ASHRAE Transactions. 1977;83(2):103.

[10] Elmahdy A.H., Mitalas G.P. A simple model for cooling and dehumidifying coils for use in calculating the energy requirements of buildings // ASHRAE Transactions. 1977. Vol. 83, N 2. P. 103.

[11] HVAC Systems and Equipment Handbook (SI Edition). Peachtree Corners: ASHRAE; 2016.

[12] HVAC Systems and Equipment Handbook (SI Edition). Peachtree Corners: ASHRAE, 2016.

[13] AHRI Standard 410-2001. Standard for Forced-Circulation Air-Cooling and Air-Heating Coils. Arlington: AHRI; 2011.

[14] AHRI Standard 410-2001. Standard for Forced-Circulation Air-Cooling and Air-Heating Coils. Arlington: AHRI, 2011.

[15] Pirompugd W, Wongwises S, Wang CC. A tube-by-tube reduction method for simultaneous heat and mass transfer characteristics for plain fin-and-tube heat exchangers in dehumidifying conditions. Heat and Mass Transfer. 2005;41(8):756–765. doi: 10.1007/s00231-004-0581-x

[16] Pirompugd W., Wongwises S., Wang C.C. A tube-by-tube reduction method for simultaneous heat and mass transfer characteristics for plain fin-and-tube heat exchangers in dehumidifying conditions // Heat and Mass Transfer. 2005. Vol. 41, N 8. P. 756–765. doi: 10.1007/s00231-004-0581-x

[17] Pirompugd W, Wongwises S, Wang CC. Simultaneous heat and mass transfer characteristics for wavy fin-and-tube heat exchangers under dehumidifying conditions. Int. J. Heat and Mass Transfer. 2006. № 1–2 (49). P. 132–143. doi: 10.1016/j.ijheatmasstransfer.2005.05.043

[18] Pirompugd W., Wongwises S., Wang C.C. Simultaneous heat and mass transfer characteristics for wavy fin-and-tube heat exchangers under dehumidifying conditions // Int. J. Heat and Mass Transfer. 2006. Vol. 49, N 1–2. P. 132–143. doi: 10.1016/j.ijheatmasstransfer.2005.05.043

[19] Xia L, Chan MY, Deng SM, et al. A modified logarithmic mean enthalpy difference (LMED) method for evaluating the total heat transfer rate of a wet cooling coil under both unit and non-unit Lewis Factors. Int. J. Therm. Sci. 2009;48(11):2159–2164. doi: 10.1016/j.ijthermalsci.2009.04.002

[20] Xia L., Chan M.Y., Deng S.M., et al. A modified logarithmic mean enthalpy difference (LMED) method for evaluating the total heat transfer rate of a wet cooling coil under both unit and non-unit Lewis Factors // Int. J. Therm. Sci. 2009. Vol. 48, N 11. P. 2159–2164. doi: 10.1016/j.ijthermalsci.2009.04.002

[21] Wang J, Hihara E. Prediction of air coil performance under partially wet and totally wet cooling conditions using equivalent dry-bulb temperature method. Int. J. Refrigeration. 2003;26(3):293–301. doi: 10.1016/S0140-7007(02)00132-9

[22] Wang J., Hihara E. Prediction of air coil performance under partially wet and totally wet cooling conditions using equivalent dry-bulb temperature method // Int. J. Refrigeration. 2003. Vol. 26, N 3. P. 293–301. doi: 10.1016/S0140-7007(02)00132-9

[23] Braun JE. Methodologies for the Design and Control of Chilled Water Systems. Wisconsin: University of Wisconsin; 1988.

[24] Braun J.E. Methodologies for the Design and Control of Chilled Water Systems. Wisconsin: University of Wisconsin, 1988.

[25] Braun JE, Klein SA, Mitchell JW. Effectiveness Models for Cooling Towers and Cooling Coils. ASHRAE Transactions. 1989;95(2):164–174.

[26] Braun J.E., Klein S.A., Mitchell J.W. Effectiveness Models for Cooling Towers and Cooling Coils // ASHRAE Transactions. 1989. Vol. 95, N 2. P. 164–174.

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