ANALYSIS OF THE MAISOTSENKO CYCLE BASED COOLING SYSTEM FOR ACCUMULATOR BATTERIES

Transcription

1 International Journal of Energy for a Clean Environment, 12(2 4), (2011) ANALYSIS OF THE MAISOTSENKO CYCLE BASED COOLING SYSTEM FOR ACCUMULATOR BATTERIES Manap Khazhmuradov, Dmitrij Fedorchenko, Yegor Rudychev, Sergej Martynov, Alexander Zakharchenko, Svetlana Prokhorets, Anna Skrypnyk, Mikhail Krugol, Anatoliy Yurkin, Alexei Lukhanin, Alexander Lukhanin, Andrej Belyaev, Evgenij Sporov, & Viktor Popov NSC Kharkov Institute of Physics and Technology, 1, Akademicheskaya St, Kharkov, 61108, Ukraine Address all correspondence to Dmitrij Fedorchenko fdima@kiptkharkovua A Maisotsenko cycle (M cycle) application for accumulator battery cooling is considered M cycle thermodynamics for cooling systems are analyzed and required working parameters of the inlet air cooling module are calculated The advantages and drawbacks of M cycle based heat exchangers for electric vehicle accumulator battery cooling systems are discussed KEY WORDS: Maisotsenko cycle, evaporation, heat exchanger, cooling system, accumulator battery 1 INTRODUCTION At the present time considerable attention has been paid to the development of environmentally friendly vehicles: electric vehicles and hybrid cars Almost all the leading automobile companies have in their lineup this type of vehicle One of the important issues in the development of electric vehicles is the operation mode temperature of the battery The problem arises because the operation temperature range of the Li-ion batteries used in modern electric driven vehicles is 10 o C 30 o C, while the inlet air temperature under real operating conditions may vary in the range from 30 o C to +50 o C This puts forward the actual task of developing an efficient and reliable battery cooling system for electric vehicles and hybrid cars One of the promising methods for removing heat from the battery is the socalled Maisotsenko cycle (M-cycle) (see Chandracant et al, 2012; Gillan, 2008; /11/$ by Begell House, Inc 95

2 96 Khazhmuradov et al NOMENCLATURE c P,air the air specific heat at constant T out outlet air absolute temperature pressure V air volumetric flow rate c water water specific heat V air volumetric air flow through the f 1, f 2 absolute humidity heat exchanger m water water mass flow rate W e exchanger heat power T in inlet air absolute ρ air air density temperature λ water water evaporation latent heat Maisotsenko and Reizin, 2005; Wicker, 2003) This thermodynamic cycle is based on the psychrometric temperature difference and provides cooling of product gas or fluid to near the dew point temperature of the inlet working air stream The M- cycle is patented in the US and other countries and is used in industrial design of heat exchangers and power facilities Heat-exchange units based on the M-cycle use the indirect evaporation method The system of interconnected channels for both dry and moist air provides an effective saturation of the working air stream with water vapor, respectively, increasing the heat transfer from the cooled gas or liquid The evaporation takes place at constant pressure, so the cooling system based on the M-cycle needs no air pump to compress air This improves the size and weight characteristics of the system, as well as its reliability, which is an important factor for mobile vehicle applications 2 M-CYCLE-BASED BATTERY COOLING SYSTEM M-cycle-based battery cooling systems could be implemented in several ways: An inlet air flow precooling module Small-sized cooling modules for the individual battery cells A module for cooling the heat-removing elements: heat pipes, radiators, etc Below we shall consider in more detail only the first option as it is the most suitable for technical application The M-cycle-based heat exchanger cooling the inlet air actually operates as an air conditioner, providing the required temperature regime for the accumulator battery In order to estimate the required input parameters of the heat exchanger, we have calculated the temperature fields for the battery with a heat generation rate of 15 kw consisting of 100 elements The calculated dependence of the required cooling air flow rate on the inlet air temperature at an average battery element temperature of 30 o C is shown in Fig 1 From calculations it follows that for the desired battery operation temperature regime for cooling air flow speeds of up to International Journal of Energy for a Clean Environment

3 Analysis of the Maisotsenko Cycle Based Cooling System for Accumulator Batteries 97 FIG 1: Dependence of the required air flow rate on the temperature of inlet air 3 m/s, inlet air temperature must not exceed 20 o C At the same time, lowering the temperature reduces the cooling air flow rate, thus reducing the power cooling fan s consumption and acoustic noise Thus a compact M-cycle-based heat exchanger in the inlet channel of the cooling system will provide the desired temperature regime for the battery operating in an ambient temperature above 20 o C and improve cooling-system working parameters However, it should be noted that the actual performance of the heat exchanger depends on the humidity of the inlet air To assess the possibility of using the M-cycle at temperatures of 20 o C 50 o C, we assume a boundary value of the inlet air dew point of 20 o C Figure 2 shows the air relative humidity temperature dependence at atmospheric pressure for a 20 o C dew point The area below the curve theoretically limits the possible operating range of the heat exchanger For humidity values above the curve additional dehumidification is necessary FIG 2: Relative humidity at 20 o C dew point Volume 12, Numbers 2 4, 2011

4 98 Khazhmuradov et al 3 HEAT EXCHANGER PARAMETERS CALCULATION In order to calculate the parameters of the M-cycle-based heat exchanger we consider the thermodynamics of the inlet air cooling As input parameters we consider the most severe thermal conditions: air temperature at the inlet of the heat exchanger T in = 50 o C, relative humidity 30%, which corresponds to a dew point of 19 o C The heat exchanger should provide the outlet air temperature T out, and the temperature difference is ΔT = T in T out = 30 o C According to our calculations, for a battery with heat generation rate of 15 kw consisting of 100 elements for a cooling air flow rate of 3 m/s, total inlet air flow is V = 018 m 3 /s Then the required exchanger heat power W e is given by the relation W e = c P,air ρ air V ΔT, (1) where c P,air is the air specific heat at constant pressure and ρ air the air density Calculation by formula (1) gives the value of the heat exchanger capacity W e = 6900 W This heat output is provided by water evaporation, and thus the corresponding water flow is given by W e m water = (λ water + c water ΔT), (2) where λ water is the water evaporation latent heat and c water the water specific heat Usually, we can neglect the second term in the denominator, which describes the heating of water vapor, compared to the first, corresponding to evaporation Substituting the values in relation (2), we get the water mass flow rate under these conditions, m water = 0003 kg/s The corresponding volume flow rate will then be 108 l/h FIG 3: Psychrometric chart of heat exchanger working cycle International Journal of Energy for a Clean Environment

5 Analysis of the Maisotsenko Cycle Based Cooling System for Accumulator Batteries 99 The working cycle of the heat exchanger is shown in Fig 3 The line describes the ideal M-cycle In this cycle, air absolute humidity increases from an initial value f 1 = 166 g/m 3 to a value of f 2 = 83 g/m 3 Then the volumetric air flow through the heat exchanger is V air = m water (3) f 2 f 1 Substitution of numerical values gives V air = 045 m 3 /s 4 RESULTS AND DISCUSSION The analysis shows that it is possible to create a compact M-cycle-based heat exchanger for accumulator battery cooling It should be noted that calculated parameters correspond to the most severe regime of the heat exchanger The most critical parameter is a rather high consumption of water, while the air flow through the heat exchanger is only 25% of the air flow that cools the battery Under lower inlet air temperature, less heat power is necessary for cooling and consequently, the water flow will decrease For example, at temperature difference ΔT = 10 o C the required heat power and water consumption decrease by three times Real world applications of heat exchangers of this type must also consider the limitations on acceptable humidity values Cooling system operation in a humid climate requires a dehumidification device for inlet air flow However, it is sufficient to provide dehumidification only for the air passing through the heat exchanger This allows the system design to be used on hygroscopic materials or compact moisture evaporators Note that the characteristics of the heat exchanger were obtained for the ideal M-cycle Further experimental studies are necessary to verify this theoretical consideration REFERENCES Chandracant, W et al, A review on potential of Maisotsenko cycle in energy saving applications using evaporative cooling, Int J Adv Res Sci, vol 1, no 1, pp 15 20, 2012 Gillan, L, Maisotsenko cycle for cooling processes, Int J Energy Clean Environ, vol 9, no 1 3, pp 47 64, 2008 Maisotsenko, V and Reizin, I, The Maisotsenko cycle for electronic cooling, ASME InterPack 2005, Proc of IPACK2005, pp 1 10, 2005 Wicker, K, Life below the wet bulb: Maisotsenko cycle, Power Mag, vol 147, no 10, pp 29 32, 2003 Volume 12, Numbers 2 4, 2011

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