Abstract
JOURNAL OF ASIAN ARCHITECTURE AND BUILDING ENGINEERING https://doi.org/10.1080/13467581.2023.2183774 ENVIRONMENTAL ENGINEERING Optimization of the performance of M-Cycle indirect evaporative cooling via thermodynamic approach a,b,c c c b Chenxia Jia , Daxi Sun , Xingfu Hu and Chengjun Jing a b School of Intelligent Construction and Environmental Engineering, Chengdu Textile College, Chengdu, China; Department of Electromechanical and Information Engineering, Sichuan College of Architectural Technology, Deyang, China; College of architecture and Environment, Sichuan University, Chengdu, China ABSTRACT ARTICLE HISTORY Received 20 May 2022 For the further energy conservation, the study on the optimizing the M-Cycle indirect eva- Accepted 4 November 2022 porative cooling (MIEC) performance is meaningful. With the aim of the optimization, a model of a general MIEC system was established, the thermodynamic entropy production optimiza- KEYWORDS tion method was used to fully reflect the energy quality and irreversibility. The inlet parameters, M-Cycle indirect evaporative supply air ratio, dew point temperature efficiency, unit-cooling capacity and Entropy cooling; entropy production Production Number were used to analyze and improve the cooling and thermodynamic number; cooling and performance of the general MIEC. A total of 6750 air treatment processes have been studied thermodynamic performance with the self-programmed FORTRA. It is concluded that when the inlet temperature is high, with the increase in inlet relative humidity, the unit-cooling capacity of the system greatly improves while the Entropy Production Number increases relatively small. When the ambient humidity variation range is large, the irreversible loss of the system can be reduced by coordinating the supply air ratio and dew point temperature efficiency of the MIEC system. Ultimately, the results of this study will provide theoretical reference for the design and operation of the practical engineering of the MIEC. investigated two efficient humidified gas turbine 1. Introduction cycles, a hybrid cooler of indirect evaporative and Improving energy efficiency and reducing energy con- Maisotsenko cycle and a conventional indirect eva- sumption is an important way to deal with the world porative cooler, by simulation in his study. Results energy crisis. Technological revolutions on indirect show that the application of Maisotsenko cycle-based evaporative cooling have recently hit the industrial air saturator could further improve the gas turbine world. The theory of M-Cycle indirect evaporative cool- cycle efficiency. Shahzad et al. (2021) took the thermo- ing was proposed by Dr Valerij Maisotsenko et al. in dynamic analysis of the improved evaporative cooling 2003 (Maisotsenko et al. 2003). The M-Cycle indirect systems (DEC, IEC, MEC) from the viewpoint of heat evaporative cooling (MIEC) is famous for its outstand- stress in poultry houses in Multan, Pakistan. ing cooling performance, low energy consumption Research on the M-Cycle indirect evaporative cool- and no environmental pollution. Theoretically, the pro- ing systems has attracted many scholars. Additionally, duct air can be cooled to as low as the dew point one of the most interesting research topics is the temperature of the inlet air (Maisotsenko et al. 2003). performance optimization of M-Cycle indirect evapora- During the past decade, the M-Cycle indirect evapora- tive cooling (Tariq et al. 2018; Shahzad et al. 2018; Li tive cooling system has application in various fields, et al. 2021; Fan et al. 2021; Sohani, Sayyaadi, and such as air conditioning, refrigeration, etc. Much work Hoseinpoori 2016; Zhan et al. 2011; Rogdakis et al. has been reported recently (Pan De Lidis et al. 2018; 2014; Pandelidis and Anisimov 2015; Pandelidis et al. Pandelidis 2020; Zhu et al. 2019; Shahzad et al. 2021). 2017). The published information that is relevant to Pan De Lidis et al. (2018) analyzed the application of this topic is mainly about evaluating the performance three arrangements of the cross-flow M-Cycle air of the MIEC by investigating different types of config - cooler, where it is used as a heat recovery device in urations, arrangement, and size (Fan et al. 2021; the air conditioning system, and each arrangement is Sohani, Sayyaadi, and Hoseinpoori 2016; Zhan et al. justified depending on the moderate climate. 2011; Rogdakis et al. 2014; Pandelidis and Anisimov Pandelidis (2020) studied the Maisotsenko cycle cool- 2015; Pandelidis et al. 2017). Fan et al. (2021) con- ing tower through numerical modeling. The study con- structed a novel dew point evaporative cooling tower firmed high practical potential of using M-Cycle in based on M-cycle and its cooling performance such as water cooling applications. Zhu et al. (2019) outlet water temperature, precooled air temperature CONTACT Chenxia Jia chenxiajia@163.com School of Intelligent Construction and Environmental Engineering, Chengdu Textile College, Chengdu 611731, China © 2023 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group on behalf of the Architectural Institute of Japan, Architectural Institute of Korea and Architectural Society of China. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. 2 C. JIA ET AL. and wet bulb effectiveness were experimentally inves- of the MIEC at a loose end to a certain extent. Attempts tigated. The results confirmed high practical potential to resolve these dilemmas have resulted in the devel- of using M-Cycle in water cooling applications. Sohani, opment of the thermodynamic entropy production Sayyaadi, and Hoseinpoori (2016) implemented the optimization method. developed GMDH model for multi-objective optimiza- The thermodynamic entropy production optimiza- tion of a prototype m-cycle cross-flow indirect eva- tion method uses the entropy production parameter to porative cooler. The average annual values of reveal the energy quality and irreversibility in the ther- coefficient of performance and cooling capacity were modynamic process and optimize the heat exchanger maximized, simultaneously, while working to air ratio furthermore. However, studies do not give much atten- and inlet air velocity were decision variables of optimi- tion to the unique features of the MIEC. Previous zation. Results of their studies implied that the opti- research has shown that this method has a certain mized inlet air velocity for all climates varied between application and analysis in the study of heat exchanger −1 −1 1.796 m.s and 1.957 m.s , while the optimum WAR optimization (Wang et al. 2018; Farzaneh-Gord, Ameri, was 0.318 for “A” class cities. Moreover, the mean and Arabkoohsar 2016; Nima et al. 2019; Sepehr et al. values of the COP and CC were improved 8.1% and 2018; Guzmán et al. 2018). Wang et al. (2018) studied 6.9%, respectively. Zhan et al. (2011) studied the cool- the transient processes of heat exchangers by entropy ing performance of the counter-flow and cross-flow generation analyses and the results can guide their heat exchangers through the development of designs and operations. Farzaneh-Gord, Ameri, and a dedicated computer model and case-by-case experi- Arabkoohsar (2016) studied the optimal geometry mental testing and validation. The results showed that and operational conditions of helically coiled heat the counter-flow exchanger offered greater (around exchangers for both laminar and turbulent flows 20% higher) cooling capacity, as well as greater (15%- based on the second law of thermodynamics. Nima 23% higher) dew-point and wet-bulb effectiveness et al. (2019) studied the second law features of an when equal in physical size and under the same oper- innovative nanofluid having hybrid nanoparticles of ating conditions. The cross-flow system, however, had graphene nanoplatelets-Pt through a ribbed triple- a greater (10% higher) energy efficiency (COP). In the tube heat exchanger. Sepehr et al. (2018) numerically study of Rogdakis et al. (2014), an alternative geometry investigated heat transfer, pressure drop and entropy of an M-cycle is developed and evaluated. Using generation in shell and helically coiled tube heat a smart network of air channels, a wet-bulb efficiency exchangers in their study. JEV Guzmán et al. (2018) of about 120% was achieved. The efficiency of the studied the entropy transportation process inside proposed system has been estimated to be about a plate and tube heat exchanger by numerical simula- 105%, while the product air temperatures satisfy the tions. They analyzed and compared the entropy levels cooling demands of buildings at regions of low relative around tubes with circular and elliptical cross sections. humidity. Pandelidis and Anisimov (2015) investigated The purpose of the comparison is to determine how the carefully selected geometrical and operational the entropy flux contributes to increase, or decrease, aspects of the cross-flow Maisotsenko cycle heat and the value of the entropy in certain regions of the flow mass exchanger used for indirect evaporative air cool- field. ing by mathematical simulation. Pandelidis et al. (2017) Recently, a few studies have been conducted on the numerically investigated the performance of three entropy production optimization on the MIEC (Wang highly efficient, advanced indirect evaporative air cool- et al. 2019; Lin et al. 2020). Wang et al. (2019) studied ers: the “classical” cross-flow M-Cycle heat and mass the especial dew point air cooler under various opera- exchangers and two novel combined M-Cycle air cool- tional and structural conditions via the entropy pro- ers proposed by them. As can be seen from the above duction number parameter. Additionally, the entropy research results, for the research object is limited to production number is found to be a promising indica- a specific structure, the results of these studies are not tor for optimized design. Lin et al. (2020) proposed generalisable and optimization research on the MIEC a robust optimization framework of the dew point mostly starts from the change of structure, and opti- evaporative cooler toward favorable dew point effec - mization research methods based on thermodynamic tiveness, cooling capacity and coefficient of perfor- methods are relatively rare. In addition, all MIECs were mance. Two optimization algorithms, multi-to-single- compared in terms of cooling efficiency, COP, energy objective and multi-objective optimizations, were saving rate, exergy efficiency, exergy efficiency ratio, developed using genetic algorithm. In their study, it and exergy destruction. The energy quality and irrever- was found that the multi-to-single-objective optimiza- sibility in the thermodynamic process cannot fully tion is able to obtain appropriate objective functions reflect. Furthermore, the existing research results according to predefined. Previous work (Wang et al. show that multiple evaluation indexes always have 2019; Lin et al. 2020) deals only with the working contradictory conclusions (Anisimov and Pandelidis situations of an MIEC with a particular structure. To 2015), which makes the optimal design and operation the author’s knowledge, there is little application of JOURNAL OF ASIAN ARCHITECTURE AND BUILDING ENGINEERING 3 the thermodynamic entropy production optimization method to a general MIEC. More research is still required before the final goal of obtaining the optimi- zation method by evaluating the energy quality and irreversibility used in a general MIEC. In this paper, the thermodynamic entropy production optimization method is used in the optimization of the performance of a general MIEC. The entropy production of a general M-Cycle evaporative cooling system was studied, and the research results were used to analyze and improve the operational capability and cooling process of a general MIEC. Ultimately, the results of this study will provide theoretical reference for the design and operation of the practical engineering of the MIEC. Figure 3. Psychrometric process. 2. Physical and mathematical models Before analyzing the heat and mass transfer in the M-Cycle indirect evaporative cooling system is famous wet and dry channels, to simplify the mathematical for its outstanding cooling performance. Theoretically, model, first make the following assumptions: the product air can be cooled as low as the dew point temperature of the working air at inlet. Figure 1 is (1) The unit counter-flow dew-point indirect eva- a schematic of the MIEC. The MIEC is composed of porative cooler is adiabatic; no heat is trans- a certain number of working units, and each working ferred to the outside; unit is made up of a set of dry and wet channels. The (2) Moisture is evenly distributed on the wet working unit of the MIEC is shown in Figure 2. The inlet surface; air (the state 1 in Figure 3) flows into the dry channel, (3) The properties of the air streams are uniform; and the temperature of the inlet air decreases for its (4) The heat and mass transfer coefficient of moist constantly exchanging sensible heat with the surface air conforms to the Lewis relation; of the plate between the dry and wet channels during (5) The air and moisture in the wet channel can fully its flow. The air is divided into two parts at the exit of contact. the dry channel, one part is supplied to the user as product air (State 2), the other part enters the wet The mathematical description of the MIEC is written channel. The air in the wet channel is continuously as follows: humidified and transfers heat to the water film, further Mass conservation equation: reducing the surface temperature of the plate between m þ m ¼ m þ m (1) 1 3 2 4 the dry and wet channel. The air exhausted from the wet channel is at state 4. The psychrometric processes Thermal balance equation: in the MIEC are shown in Figure 3. m ðh h Þ ¼ m ðh h Þ (2) 1 1 2 4 4 2 In wet channel: α ðT T ÞLþ C m ðT T Þ ¼ m r (3) w w s pd 1 1 2 3 φ ¼ φ (4) 2 4 In dry channel: m d ðm m Þd ¼ ρ h ðd d ÞL ¼ m (5) 4 4 1 2 w w s 3 Figure 1. Schematic diagram of the MIEC. d1 ¼ d2 (6) Subscripts “1”, “2” and “4” represent the air states of the inlet air, the product air, and the exhausted air, respectively. The subscript “3” represents the increased water vapour of air flowing through the wet channel. The subscript “d” or “w” indicates whether the para- meter is in the dry or wet channel, respectively. m is the mass flow rate. ρ is the air density, r is latent heat of Figure 2. Working unit of the MIEC. evaporation. h is the mass transfer coefficient, L is the w 4 C. JIA ET AL. channel length, (d -d ) is the moisture content differ - P d v4 4 w s ¼ (12) ence between the water film surface and the air in the B 0:622þ d wet channel. α is coefficient of heat transfer at the For M-Cycle evaporative cooling system, the pres- surface of the sheet between the dry and wet channels, sure drop of the cooler is much lower than that of the α =Nu λ /δ , λ is the heat conductivity coefficient of w s s s s resistance consumption of the entire cooling system. water, δ is the thickness of the water film. The mass Thus, the pressure drop ratio, (P -P )/P , (P -P )/P , (P - 2 4 2 1 2 1 s transfer coefficient and the coefficient of heat transfer P )/P , in Equation 8 can be ignored. The reference 2 2 at plate surface in the wet channels obey the Lewis temperature T is taken to be 273.15 K and the refer- relation. ence pressure P is considered to be 101.325 kPa. On 2=3 this basis, equation 9, equation 10 and equation 11 are α =h ¼ ρ C Le (7) w w pw substituted into equation 8 to acquire the unit entropy Where Le is the Lewis number and it is taken as 1 for production in the system. the wet channel. � � � � T T 2 4 S ¼ C ln þð1 γÞ C ln gen pd pw T T 1 2 � � �� d d T d 4 4 4 þð1 γÞ 9:160þC ln R ln pv v 3. Calculation method of thermodynamic 1 d T 0:622þd 4 0 4 irreversibility (13) In accordance with the entropy balance for the MIEC Unit entropy production reflects the total irreversi- shown in Figure 1, total entropy production (S) can be bility of thermodynamic process involving heat and written as: mass transfers, but the heat transfer rate is not taken into account. The Entropy Production Number (Ns) S ¼ m s þ m s m s (8) 2 2 4 4 1 1 (Bejan 1977) was introduced for thermodynamic irre- where s and m are, respectively, entropy flow and 2 2 versibility analysis of the MIEC. The Entropy Production mass flow rate of product air in the system. Number is a parameter describing the thermodynamic Homoplastically, s and m are for the outlet air while 4 4 perfection degree of M-Cycle indirect evaporative s and m are for the inlet air system in the system. 1 1 cooling system and it at the same time takes into Unit entropy production (S ) is defined as the ratio gen consideration the influence of entropy production of the total entropy production in the MIEC to the mass and heat transfer rate, which has practical significance. flow of inlet air in the cooler, i.e., S =S/m . For moist gen 1 It is defined as the following: air is assumed to be an ideal gas, unit entropy produc- T S 0 gen tion of the system can be expressed as: Ns ¼ (14) � � �� T P P 2 1 2 S ¼ C ln R ln 1 where, T is reference temperature. Q is unit-cooling gen pd d 0 T P 1 1 � � �� capacity, which is defined as the ratio of total system T P P 4 2 4 þð1 γÞ C ln R ln 1 pw w cooling capacity to inlet air mass flow. Unit-cooling T P 2 2 � � capacity can be written as: d d T P 4 4 v4 þð1 γÞ 9:160þC ln R ln pv v � 1 d T B 4 0 Q ¼ γðt t Þ C þ C d (15) 1 2 pg pq 1 (9) where C and C are mean specific heat capacity of pd pw moist air in dry and wet channels, respectively. Mean 4. Research approach and validation specific heat capacity of moist air can be calculated by the following equation. 4.1. Research approach dC þ C pq pg The M-Cycle evaporative cooling system is environ- C ¼ (10) 1þ d mentally friendly and energy efficient for no CFCs and no traditional compressor in used. The tempera- where C is the specific heat capacity of dry air; C is pg pq ture of the product air can be cooled as low as the dew the specific heat capacity of water vapor. point temperature of the inlet air by isohygrometric The supply air ratio (γ) definition of M-Cycle indirect treatment. Different temperatures of the product air evaporative cooling system is given. can be obtained via the MIEC with different structures, size, or working conditions. Conventional optimization γ ¼ (11) of the MIEC is to improve the evaporative cooling P is partial evaporation pressure of saturated performance by optimizing the structure, size or work- v4 water of outlet air, and d is moisture content of outlet ing conditions. For instance, the length or width of air in the M-Cycle indirect evaporative cooler. The channel, air supply rate, flow speed, thickness and relationship between them can be expressed as: temperature of the water film, etc. The excellent JOURNAL OF ASIAN ARCHITECTURE AND BUILDING ENGINEERING 5 Figure 4. Energy balance error with inlet air temperature and dew point effectiveness. cooling performance of the MIEC means high dew air treatment processes were studied. Various data point efficiency, high cooling efficiency, large cooling needed in the study were obtained from the self-pro- capacity, high COP, high energy saving rate, etc. grammed FORTRA. Obviously, the relationship between efficient and energy-saving cooling performance with the inlet parameters, structure, is useful to optimize the 4.2. Validation M-Cycle evaporative cooling system. The validation on the energy balance is carried out by Theoretically, for the M-Cycle evaporative cooling the energy balance error of different psychrometric system, the product air can be cooled as low as the processes in the MIEC. The energy balance error is dew point temperature of the working air at the inlet. calculated as: According to the basic theory, research on optimiza- tion of the performance of M-Cycle indirect evapora- E ¼ jE E j=E (16) r out in in tive cooling can be carried out by using a calculation program compiled by Fortran language, as follows. where the inlet and outlet of the energy, E , E , is the in out First, parameters of the inlet air are given and para- sum of the enthalpy leaving and entering the MIEC. meters of product air and the supply air ratio of the Dew point temperature efficiency of evaporative cool- system are pre-setted, then parameters of the ers is evaluated in accordance with the following exhausted air and the mass flow ratio of product air equations. and exhausted air can be obtained according to Equation 1. In addition, evaporative cooling perfor- t t 1 2 η ¼ (17) mance of the system, such as dew point efficiency t t 1 d and unit-cooling capacity, and thermodynamic perfor- mance, such as entropy production and the Entropy Figure 4 shows the relationship between the energy Production Number, can be obtained according to balance error, inlet temperature t and dew point effi - equations 7–15, 17-18. The characteristic parameter ciency η. It is clearly seen that the maximum disequili- range of high efficiency and energy saving MICE can brium rate of the energy equation is 0.00052%. be obtained by analyzing the relationship between the Accordingly, the present model is solved with a high inlet parameter, supply air ratio, cooling performance degree of precision. and thermodynamic performance. Obviously, this parameter range is of great significance for the opti- mization of the MICE. 5. Result and analysis With the aim of performance optimization of the For the MICE model shown in Figure 1, its cooling M-Cycle indirect evaporative cooling, 75 kinds of inlet performance and thermodynamic performance para- air states with a temperature range of 28℃-42℃ and meters are obtained through numerical calculation. relative humidity range of 50%–90% were involved. In The applicable ranges of temperature and relative addition, the expected dew point efficiency is taken the humidity of the inlet air are 28℃–42℃, 50%–90% range of 10%–100%, and supply air ratio is taken the respectively. The supply air ratio is set to 0.1–0.9, and range of 0.1–0.9. Ninety air treatment processes occurred the expected dew point efficiency is set to 10%–100% for different supply air ratios and dew point efficiency of when the cooling system is working. the system in the condition of a certain inlet air. So, 6750 6 C. JIA ET AL. Figure 5. Influence of inlet air temperature on unit-cooling capacity (γ=0.6). 5.1. Influence of inlet parameters on unit-cooling when the inlet relative humidity is constant and capacity the system works on the same supply air ratio and the same dew point efficiency. The influence of inlet Figure 5 depicts the impact of the inlet air temperature relative humidity on the unit-cooling capacity is on unit-cooling capacity of the M-Cycle evaporative analyzed under the same supply air ratio and the cooling system. The unit-cooling capacity refers to same dew point efficiency, the results are shown in the ratio of the sum of the cooling capacity produced Figure 6. As shown in Figure 6, the unit-cooling by the M-Cycle cooler to the inlet mass. capacity increases with the decreases of inlet rela- tive humidity when the inlet temperature remains Q ¼ Q =m (18) s 1 constant. In other words, the unit-cooling capacity increases with the increase in the inlet temperature As seen in Figure 5, the unit-cooling capacity and the decrease of inlet relative humidity. increase as the increase in the inlet temperature Figure 6. Influence of inlet air relative humidity on unit-cooling capacity(η=0.9). JOURNAL OF ASIAN ARCHITECTURE AND BUILDING ENGINEERING 7 Figure 8. Unit-cooling capacity under different supply air ratios and dew point temperature efficiency (inlet parameters: 30℃, 60%). Figure 7. Influence of dew point temperature efficiency on unit-cooling capacity(γ=0.6). 5.3. Influence of supply air ratio on unit-cooling 5.2. Influence of dew point temperature efficiency capacity on unit-cooling capacity The supply air ratio of MICE is the ratio of the mass flow Figure 7 depicts the relationship between the dew rate of product air and inlet air, which is less than 1. The point temperature efficiency and unit-cooling capa- smaller supply air ratio will reduce product air and city on the condition that the inlet parameters are enhance secondary air in the system, which will result respectively (28℃, 60%), (28℃, 70%), (38℃, 60%), in low temperature of the product air and high dew when the supply air ratio is set as 0.6. As shown in point temperature efficiency. Figure 8 shows the rela- Figure 7, the unit-cooling capacity increased with the tionship between unit-cooling capacity and supply air increase in the inlet air temperature by comparing the ratio, the dew point temperature efficiency when an curves of inlet parameters as (28℃, 60%) and (38℃, inlet air with a temperature of 30℃ and relative 60%). The comparison of curves of the two inlet para- humidity of 60%. Figure 8 shows that the same unit- meters, (28℃, 60%) and (28℃, 70%), shows that the cooling capacity can be obtained in different supply air greater the humidity, the smaller the unit-cooling ratios and dew point temperature efficiency of the capacity. The unit-cooling capacity of the M-Cycle cooling system. Table 1 shows unit-cooling capacity evaporative cooling system increases as the dew when the inlet air parameters are 30℃ and 60%. As point temperature efficiency increases when the can be seen from Table 1, a unit-cooling capacity of 5.0 inlet parameters are constant. When the system ± 0.5 kJ/kg was obtained through the following supply works at the same dew point temperature efficiency, air ratios and dew point temperature efficiency: γ = 0.6, the unit-cooling capacity of the system will increase η = 90% or 100%; γ = 0.7, η = 80%; γ = 0.8, η = 70%; γ = with the increase in the inlet air temperature and 0.9, η = 60%. decrease with the increase in the inlet relative humid- Figure 9 depicts the impact of the supply air ratio ity. It indicates that the unit-cooling capacity of the on unit-cooling capacity of M-Cycle evaporative cool- M-Cycle evaporative cooling system with lower inlet ing system with different inlet parameters. As shown air relative humidity and higher inlet temperature in Figure 9, the unit-cooling capacity increases with increases more than that with the higher inlet air the increase in the supply air ratio in the condition relative humidity and lower inlet temperature. that the dew point temperature efficiency is constant. Table 1. Unit-cooling capacity (kJ/kg) when the inlet air parameters are 30℃ and 60%. 1 γ (%) 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10 0.0892 0.1784 0.2677 0.3569 0.4461 0.5353 0.6361 0.7138 0.8030 20 0.1784 0.3569 0.5353 0.7138 0.8922 1.0706 1.2723 1.4275 1.6059 30 0.2677 0.5353 0.8030 1.0706 1.3383 1.6059 1.9084 2.1413 2.4089 40 0.3569 0.7138 1.0706 1.4275 1.7844 2.1413 2.5446 2.8550 3.2119 50 0.4461 0.8922 1.3383 1.7844 2.2305 2.6766 3.1807 3.5688 4.0149 60 0.5353 1.0706 1.6059 2.1413 2.6766 3.2119 3.8168 4.2825 4.8178 70 0.6245 1.2491 1.8736 2.4981 3.1227 3.7472 4.4530 4.9963 5.6208 80 0.7138 1.4275 2.1413 2.8550 3.5688 4.2825 5.0891 5.7100 6.4238 90 0.8030 1.6059 2.4089 3.2119 4.0149 4.8178 5.7252 6.4238 7.2267 100 0.8922 1.7844 2.6766 3.5688 4.4610 5.3531 6.3614 7.1375 8.0297 1 2 Note: Dew point temperature efficiency. Supply air ratio. 8 C. JIA ET AL. Figure 9. Influence of supply air ratio on unit-cooling capacity. 5.4. Influence of inlet parameters on the entropy Number that occurs in the cooling system increases production number with the increase in inlet air relative humidity. The irreversible loss of the system decreases largely with Figure 10 depicts the impact of the inlet parameters on the increase in inlet air temperature when the inlet air the Entropy Production Number of M-Cycle evapora- relative humidity is extremely high. tive cooling system working with a constant supply air In Figure 10(a), the Entropy Production Number ratio and dew point temperature efficiency. As can be decreases rapidly as the inlet air temperature rises seen from Figure 10, the Entropy Production Number when the inlet air relative humidity is 80% or 90% first increases and then decreases with the increase in and η = 80%, γ = 0.5. The maximum Entropy the inlet air temperature and the maximum and mini- Production Number occurs when the inlet temperature mum Entropy Production Number occurs in the pro- is taken as 28℃ and its values are 4.621 and 4.577, cess. Furthermore, the Entropy Production Number respectively. The Entropy Production Number changes more dramatically with the inlet temperature increases first and then decreases with the increase in in a larger inlet air relative humidity. The inlet air the inlet air temperature when the inlet air relative humidity is 50%, 60% or 70%. For inlet air relative temperature at the maximum Entropy Production Figure 10. Influence of inlet parameters on the entropy production number. JOURNAL OF ASIAN ARCHITECTURE AND BUILDING ENGINEERING 9 Table 2. The limiting value for entropy production number and its corresponding inlet parameters. 1 1 2 2 γ η (%) RH (%) t (℃) t (℃) Ns Ns |Ns -Ns | 1 1.max 1.min max min max min 0.5 0.8 50 35 28 4.745 4.682 0.063 0.5 0.8 60 32 42 4.790 4.688 0.101 0.5 0.8 70 30 42 4.828 4.659 0.169 0.5 0.8 80 28 42 4.862 4.621 0.241 0.5 0.8 90 28 42 4.883 4.577 0.306 0.5 0.9 50 35 28 4.736 4.678 0.058 0.5 0.9 60 32 42 4.782 4.680 0.103 0.5 0.9 70 29 42 4.823 4.653 0.170 0.5 0.9 80 28 42 4.858 4.617 0.241 0.5 0.9 90 28 42 4.881 4.575 0.305 0.6 0.8 50 35 28 3.920 3.872 0.047 0.6 0.8 60 32 42 3.965 3.882 0.083 0.6 0.8 70 29 42 4.004 3.866 0.138 0.6 0.8 80 28 42 4.039 3.840 0.199 0.6 0.8 90 28 42 4.063 3.809 0.253 0.6 0.9 50 35 28 3.908 3.865 0.043 0.6 0.9 60 32 42 3.955 3.872 0.084 0.6 0.9 70 29 42 3.997 3.858 0.139 0.6 0.9 80 28 42 4.034 3.836 0.199 0.6 0.9 90 28 42 4.060 3.807 0.253 t and t are the inlet temperature at maximum and minimum Entropy Production Number. 1.max 1.min Ns and Ns are the value of maximum and minimum Entropy Production Number. max min humidity is 50%, the maximum Entropy Production Production Number of the system is less than 0.06 Number occurs at 35℃ and its value is 4.745; the when the cooling system works in a supply air ratio minimum value occurs at 28℃ is 4.682. For inlet air of 0.5 with inlet air temperature varying from 34℃ to relative humidity is 60%, the maximum value occurs at 38℃ or in supply air ratio of 0.6 with an inlet air 32℃ is 4.790 and the minimum value occurs at 42℃ is temperature varying from 35℃ to 41℃. Therefore, 4.688. For inlet air relative humidity of 70%, the max- for the inlet air within a certain temperature range, imum value occurs at 30℃ is 4.828 and the minimum the energy consumption of the M-Cycle evaporative value occurs at 42℃ is 4.659. However, the inlet air cooling system can be reduced by coordinating the relative humidity has a substantial effect on the supply air ratio and dew point temperature efficiency Entropy Production Number of the system. In addition, of the MIEC when the humidity variation range is large. minimum range of Entropy Production Number with an inlet air relative humidity from 50% to 90% is 5.5. Influence of dew point temperature efficiency acquired at 36℃, inlet air temperature. As shown in on entropy production number Figure 10(b)-(d) that the variation curves of Entropy Production Number with inlet parameters when the The relationship between the dew point temperature system works, respectively, under conditions η = 90%, efficiency and Entropy Production Number is shown in γ = 0.5; η = 80%, γ = 0.6 and η = 90%, γ = 0.6, and the Figure 12. Obviously, the Entropy Production Number variation trends are consistent with those in increases with the increase in the dew point tempera- Figure 10(a). The limiting values for the Entropy ture efficiency. However, the curve slope of Entropy Production Number of the cooling system with differ - Production Number varies with the dew point tem- ent operating parameters are listed in Table 2. The data perature efficiency with different inlet parameters. in Table 2 were obtained under conditions of the MIEC The maximum Entropy Production Number varies works with inlet air temperatures from 28℃ to 42℃ with the dew point temperature efficiency. As shown and relative humidity from 50% to 90%, with a supply in Figure 12(a) and 12, when the inlet air relative air ratio of 0.5 or 0.6 and the dew point temperature humidity is 50%, the maximum Entropy Production efficiency of 80% or 90%. Number is obtained at inlet temperature of 36–37℃. The influence of the inlet air temperature on the When the inlet temperature is less than 36℃, the rangeability of Entropy Production Number is investi- Entropy Production Number decreases relatively gated in Figure 11. The rangeability of Entropy slowly with an increase in the dew point temperature Production Number is the difference between the efficiency. However, when the inlet temperature is maximum and minimum values of the cooling system greater than 37℃, the Entropy Production Number with a constant inlet air temperature and inlet air decreases sharply with the increase in the dew point relative humidity varying within a certain range. In temperature efficiency. In the condition of the cooling here, the humidity variation range is 50%–90%. As system works in the same dew point temperature shown in Figure 11, the variation range of Entropy efficiency, Entropy Production Number increases with 10 C. JIA ET AL. Number is slower when the supply air ratio is greater than 0.3. Figure 13(b), (d) and (f) respec- tively depict the inlet air relative humidity varying from 50% to 90% and the benchmark for compar- ison is inlet air relative humidity of 50% for the same inlet air temperature. As shown in Figure 13(b), the deviation of the Entropy Production Number from the reference base increases with the increasing supply air ratio and inlet air relative humidity. In Figure 13(d), when the inlet air temperature is 33℃and supply air ratio is greater than 0.5, the deviation of the Figure 11. Influence of the inlet air temperature and the Entropy Production Number from the reference rangeability of the entropy production number. base increases much more with the increase in the supply air ratio at a higher inlet air relative humidity. In Figure 13(f), when inlet air tempera- the increase in inlet temperature from 28℃ to 36℃ ture is 38℃and supply air ratio is less than 0.4, the and decreases with the increase in inlet temperature deviation of the Entropy Production Number from from 37℃ to 42℃. As shown in Figure 12(c) and (d), the reference base decreases much more with the when the inlet air relative humidity is 60%, the max- increase in the supply air ratio at a higher inlet air imum Entropy Production Number is obtained at inlet relative humidity. It can be further concluded from air temperatures of 33℃-34℃. When the inlet tem- Figure 13(b), (d) and (f) that when the supply air perature is less than 33℃, the Entropy Production ratio of the MIEC is set within the range of 0.4–0.7, Number decreases slowly with the increase in the the inlet parameters have little influence on the dew point temperature efficiency, but when the inlet Entropy Production Number. temperature is greater than 34℃, the Entropy Figure 14 depicts the impact of the supply air Production Number decreases sharply. Under the con- ratio on the Entropy Production Number of M-Cycle ditions in the cooling system works at the same dew with a constant inlet air relative humidity. The point temperature efficiency, the Entropy Production benchmark for comparison is inlet air temperature Number increases with an increase in the inlet tem- of 28℃ and the same inlet air relative humidity. perature from 28℃ to 33℃ and decreases with the Figure 14(a) shows the supply air ratio has increase in the inlet air temperature from 34℃ to 42℃. a greater impact on the Entropy Production As shown in Figure 12(e), (f) and (g), when the inlet air Number with the inlet temperature of 33℃ and relative humidity is 70%, 80% or 90%, the maximum 38℃ than with 28℃ for the same inlet air relative Entropy Production Number is obtained at an inlet air humidity of 50%. Moreover, the Entropy Production temperature of 28℃ and the Entropy Production Numbers at different inlet temperatures of 28℃, Number decreases sharply with the increase in the 33℃, 38℃ tend to approach as the supply air dew point temperature efficiency. Under the condition ratio increases. Figure 14(b) shows that the supply in the cooling system works at the same dew point air ratio has a greater impact on the Entropy temperature efficiency, the Entropy Production Production Number with the inlet temperature of Number decreases with the increase in the inlet tem- 33℃ than with 28℃ but has a smaller impact with perature from 28℃ to 42℃. 38℃ than with 28℃ for the same inlet air relative humidity of 60%. As shown in Figure 14(c), (d), (e), for the inlet air relative humidity is, respectively, 5.6. Influence of supply air ratio on entropy 70%, 80%, 90%, the supply air ratio has a smaller production number impact on the Entropy Production Number with the Figure 13 depicts the impact of the supply air ratio inlet temperatures of 33℃ and 38℃ than with on the Entropy Production Number of M-Cycle 28℃. It is concluded from Figure 14 that the rela- evaporative cooling system with the same inlet tionship between the supply air ratio and the air temperature. Figure 13(a), (c) and (e) respec- Entropy Production Number is significantly affected tively depict the inlet air temperatures of 28℃, by inlet air relative humidity. The Entropy 33℃, 38℃ and the inlet air relative humidity of Production Number decreases with the increase in 50%. It is found that the Entropy Production the supply air ratio in the condition of the cooler Number decreases sharply with the increasing of works with a constant inlet air temperature and the supply air ratio when the supply air ratio is less inlet air relative humidity greater than 70%, the than 0.3 and the decrease of Entropy Production supply air ratio less than about 0.6. JOURNAL OF ASIAN ARCHITECTURE AND BUILDING ENGINEERING 11 Figure 12. Influence of the dew point temperature efficiency on the entropy production number (with different inlet parameters). 12 C. JIA ET AL. Figure 13. Influence of the supply air ratios on the entropy production number (with same inlet air temperature). 6. Conclusion (1) The unit-cooling capacity of the M-Cycle eva- porative cooling system increases with the With the world’s energy dilemma, using energy effi - increase in the inlet air temperature, dew point ciently is highly respected. The M-Cycle evaporative temperature efficiency and supply air ratio but cooling system is environmentally friendly and decreases with an increase in inlet air relative energy efficient for no CFCs and no traditional com- humidity. pressors. The primary goal of this research was to (2) The Entropy Production Number of the M-Cycle optimize the performance of M-Cycle indirect eva- evaporative cooling system increases with the porative cooling system. The method used in this increase in the dew point temperature efficiency research is known as the thermodynamic entropy and supply air ratio. production optimization. The inlet parameters, sup- (3) The Entropy Production Number of M-Cycle eva- ply air ratio, dew point temperature efficiency, unit- cooling capacity and Entropy Production Number porative cooling system first increases and then and so on are used to analyze the cooling perfor- decreases with the increasing of the inlet air mance and thermodynamic performance of a general temperature. The curve of the Entropy M-Cycle evaporative cooling system. The main con- Production Number varies with the inlet air tem- clusions are given as follows: perature and is smoother in a lower inlet air JOURNAL OF ASIAN ARCHITECTURE AND BUILDING ENGINEERING 13 Figure 14. Influence of the supply air ratios on the entropy production number (with same inlet relative humidity). relative humidity, while the curve is more decreases with an increase of the inlet tempera- intense in a higher inlet air relative humidity. ture for various inlet relative humidity which is The Entropy Production Number increases with greater than 70%, the supply air ratio is less than the increase in air relative humidity at a low inlet about 0.6. temperature. However, the difference in the Entropy Production Number between different The research conducted suggests that the cooling and thermodynamic performance of a general M-Cycle inlet air relative humidity decreases when the evaporative cooling system is influenced by the inlet inlet temperature is high. parameters, the supply air ratio, the dew point tem- (4) Inlet relative humidity has little effect on perature efficiency, etc. It is concluded that the unit- Entropy Production Number under a certain cooling capacity improves and the Entropy Production range of supply air ratio, dew point temperature Number reduces with a higher inlet temperature and efficiency and inlet parameters. For example, the a lower inlet relative humidity. When the inlet tem- rangeability of the Entropy Production Number perature is high, with the increase in inlet relative is less than 0.06 when the cooler works in supply humidity, the unit-cooling capacity of the system air ratio of 0.5 with inlet temperature varying greatly improves while the Entropy Production from 34℃ to 38℃ or in supply air ratio of 0.6 Number increases relatively small. As for the inlet tem- with inlet temperature varying from 35℃ to perature within a certain range, when the humidity 41℃. variation range is large, the irreversible loss of the (5) The impact of supply air ratio on the Entropy system can be reduced by coordinating the supply air Production Number is related to inlet relative ratio and dew point temperature efficiency of the humidity. The Entropy Production Number M-Cycle evaporative cooling system. 14 C. JIA ET AL. Nomenclature Fan, X., X. Lu, H. Nie, H. Zhu, and J. 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Journal
Journal of Asian Architecture and Building Engineering
– Taylor & Francis
Published: Mar 15, 2023
Keywords: M-Cycle indirect evaporative cooling; entropy production number; cooling and thermodynamic performance
