Гибридные режимы работы термоэлектрических модулей

It is suggested that thermoelectric coolers designing should not be limited to the extreme modes of their operation. In some cases, it is convenient to use the so called hybrid modes - a combination of the extreme mode of maximum coefficient of performance for large temperature differences and a general cooling mode for small ones. The proposed hybrid mode makes it possible to control the cooling capacity of the module and not to confine this value to that under the extreme operating conditions, the maximum coefficient of performance in particular.

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Performance Evaluation of a Gravity-Assisted Heat Pipe-Based Indirect Evaporative Cooler

Energies ◽

10.3390/en13010200 ◽

2020 ◽

Vol 13 (1) ◽

pp. 200 ◽

Cited By ~ 3

Author(s):

Krzysztof Rajski ◽

Jan Danielewicz ◽

Ewa Brychcy

Keyword(s):

Mathematical Model ◽

Heat Pipe ◽

Cooling Capacity ◽

Operating Conditions ◽

Coefficient Of Performance ◽

Mass Transfer Processes ◽

Air Cooler ◽

Evaporative Cooler ◽

The Mathematical Model ◽

Further Development

In the present work, the effects of different operating parameters on the performance of a gravity-assisted heat pipe-based indirect evaporative cooler (GAHP-based IEC) were investigated. The aim of the theoretical study is to evaluate accurately the cooling performance indicators, such as the coefficient of performance (COP), wet bulb effectiveness, and cooling capacity. To predict the effectiveness of the air cooler under a variety of conditions, the comprehensive calculation method was adopted. A mathematical model was developed to simulate numerically the heat and mass transfer processes. The mathematical model was validated adequately using experimental data from the literature. Based on the conducted numerical simulations, the most favorable ranges of operating conditions for the GAHP-based IEC were established. Moreover, the conducted studies could contribute to the further development of novel evaporative cooling systems employing gravity-assisted heat pipes as efficient equipment for transferring heat.

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Performance Investigation of Single Adsorption Refrigeration System Driven by Solar Heat Storage

International Journal of Air-Conditioning and Refrigeration ◽

10.1142/s2010132518500256 ◽

2018 ◽

Vol 26 (03) ◽

pp. 1850025

Author(s):

Hicham Boushaba ◽

Abdelaziz Mimet

Keyword(s):

System Performance ◽

Heat Storage ◽

Cooling Capacity ◽

Operating Conditions ◽

Coefficient Of Performance ◽

Solar Irradiation ◽

Cooling Power ◽

Condensation Temperature ◽

Adsorption Refrigeration ◽

Solar Heat

The aim of this paper is to provide a global study of an adsorption refrigeration machine driven by solar heat storage and collected by parabolic trough collector. The system operates with ammonia (as refrigerant) and activated carbon (as adsorbent). A mathematical model interpreting the progression of the heat and the mass transfer at each element of the prototype has been developed. The solar irradiation and the real ambient temperature variations corresponding to a usual summer day in Tetouan (Morocco) are considered. The system performance is evaluated trough specific cooling power (SCP) as well as solar coefficient of performance (SCOP), which was estimated by a dynamic simulation cycle. The pressure, temperature and adsorbed mass profiles in the Adsorber have been calculated. The effects of significant design and operating parameters on the system performance have been investigated. The results show the capability of our system to realize an encouraging performance and to overcome the intermittence of the adsorption refrigeration machines. For a daily solar irradiation of 18[Formula: see text]MJ[Formula: see text]m[Formula: see text] and operating conditions of evaporation temperature [Formula: see text]C, condensation temperature [Formula: see text]C and generation temperature [Formula: see text]C, the results show that the process could achieve an SCP of 115[Formula: see text]W[Formula: see text]kg[Formula: see text] and it could produce a daily specific cooling capacity of 3310[Formula: see text]kJ[Formula: see text]kg[Formula: see text], whereas its SCOP could attain 0.141.

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Effects of Evaporator and Condenser Temperatures on the Performance of a Chiller System With a Variable Speed Compressor

Engineering and Technology Journal ◽

10.30684/etj.v39i1a.1647 ◽

2021 ◽

Vol 39 (1A) ◽

pp. 45-55

Author(s):

Ahmed H. Al-Hassani ◽

Alaa R. Al-Badri

Keyword(s):

Power Consumption ◽

Water Temperature ◽

Experimental System ◽

Cooling Capacity ◽

Pi Controller ◽

Operating Conditions ◽

Coefficient Of Performance ◽

Rotary Compressor ◽

Variable Speed ◽

Control Loops

The operation and performance of heat-pump systems are affected by indoor and outdoor operating conditions. Power consumption and system efficiency are related to evaporator and condenser working pressures. Intelligent controllers such as a proportional integral (PI) controller improve the performance of variable speed refrigeration systems (VSRs) with electronic expansion valve (EEV). Evaporator and condenser pressures affect the system power consumption and efficiency. In this study, the influence of evaporator and condenser temperatures on the performance of a variable speed refrigeration system with an EEV was experimentally investigated at constant cooling load. The experimental system comprises of a rotary compressor, shell-and-coil condenser, EEV, and shell-and-coil evaporator for one-ton cooling capacity with refrigerant R410. Compressor speed and EEV opening are controlled by a PI controller with two control loops and the refrigerant superheat (DS) is maintained at 7°C. The results show that at constant cooling capacity, the refrigerant flow rate rises with the increase in the compressor speed. The coefficient of performance (COP) is improved with low compressor speed. The System COP is increased by 3.3% with increasing evaporator inlet water temperature for 2°C due to the reduction in the compressor speed and compression ratio. High condenser inlet water temperature promotes the refrigerant subcooling.

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Evaporator Frosting in Refrigerating Appliances: Fundamentals and Applications

Energies ◽

10.3390/en14185991 ◽

2021 ◽

Vol 14 (18) ◽

pp. 5991

Author(s):

Christian J. L. Hermes ◽

Joel Boeng ◽

Diogo L. da Silva ◽

Fernando T. Knabben ◽

Andrew D. Sommers

Keyword(s):

First Principles ◽

Simulation Models ◽

Cooling Capacity ◽

Operating Conditions ◽

Coefficient Of Performance ◽

Trial And Error ◽

Refrigeration System ◽

Duty Cycles ◽

Transfer Principles ◽

Frost Layer

Modern refrigerators are equipped with fan-supplied evaporators often tailor-made to mitigate the impacts of frost accretion, not only in terms of frost blocking, which depletes the cooling capacity and therefore the refrigerator coefficient of performance (COP), but also to allow optimal defrosting, thereby avoiding the undesired consequences of condensate retention and additional thermal loads. Evaporator design for frosting conditions can be done either empirically through trial-and-error approaches or using simulation models suitable to predict the distribution of the frost mass along the finned coil. Albeit the former is mandatory for robustness verification prior to product approval, it has been advocated that the latter speeds up the design process and reduces the costs of the engineering undertaking. Therefore, this article is aimed at summarizing the required foundations for the design of efficient evaporators and defrosting systems with minimized performance impacts due to frosting. The thermodynamics, and the heat and mass transfer principles involved in the frost nucleation, growth, and densification phenomena are presented. The thermophysical properties of frost, such as density and thermal conductivity, are discussed, and their relationship with refrigeration operating conditions are established. A first-principles model is presented to predict the growth of the frost layer on the evaporator surface as a function of geometric and operating conditions. The relation between the microscopic properties of frost and their macroscopic effects on the evaporator thermo-hydraulic performance is established and confirmed with experimental evidence. Furthermore, different defrost strategies are compared, and the concept of optimal defrost is formulated. Finally, the results are used to analyze the efficiency of the defrost operation based on the net cooling capacity of the refrigeration system for different duty cycles and evaporator geometries.

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An IoT-Based Thermoelectric Air Management Framework for Smart Building Applications: A Case Study for Tropical Climate

Sustainability ◽

10.3390/su12041564 ◽

2020 ◽

Vol 12 (4) ◽

pp. 1564

Author(s):

Kashif Irshad ◽

Abdulmohsen Almalawi ◽

Asif Irshad Khan ◽

Md Mottahir Alam ◽

Md. Hasan Zahir ◽

...

Keyword(s):

Cooling Capacity ◽

Input Power ◽

Climatic Conditions ◽

Coefficient Of Performance ◽

Air Cooling ◽

Thermoelectric Coolers ◽

Air Conditioners ◽

Management Framework ◽

Smart Building ◽

Thermal Management System

This study investigates the performance of the thermoelectric air conditioning (TE-AC) system smartly controlled by the Internet of Things (IoT)-based configuration for real tropical climatic application. Air cooling management was done through thermoelectric coolers, and an Arduino microcontroller with various sensors such as a temperature sensor, simple RF modules, and actuators was used to control the indoor climatic conditions based on outdoor conditions. The result shows that when the input power supply to the IoT-based TE-AC system is increased, the cooling capacity of the framework is also enhanced. Significant power and carbon emission reduction was observed for the IoT-based TE-AC system as compared to the TE-AC system without IoT. The IoT-incorporated system also ensures better microclimatic temperature control. Additionally, the system cooling capacity improves by 14.0%, and the coefficient of performance is increased by 46.3%. Thus, this study provides a smart solution to the two major energy harvesting issues of traditional air conditioners—an increase in energy efficiency by employing a TE-AC system and a further improvement in efficiency by using an IoT-based thermal management system.

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Simulation of the performance of alternative refrigerants in liquid chillers

Proceedings of the Institution of Mechanical Engineers Part A Journal of Power and Energy ◽

10.1243/0957650011538695 ◽

2001 ◽

Vol 215 (4) ◽

pp. 429-441 ◽

Cited By ~ 2

Author(s):

I. N. Grace ◽

S. A. Tassou

Keyword(s):

Dynamic Models ◽

Control Strategies ◽

Cooling Capacity ◽

Operating Conditions ◽

Coefficient Of Performance ◽

System Component ◽

Alternative Refrigerants ◽

Expansion Valve ◽

Shell And Tube Evaporator ◽

The Impact

The impact of refrigeration systems on the environment can be reduced by (a) the use of alternative refrigerants which are less harmful to the environment and (b) the optimization of systems and control strategies to deliver increased levels of energy efficiency. Mathematical modelling offers the opportunity to test the performance of systems under different operating conditions and with alternative refrigerants. Dynamic models allow comparison of both transient and steady state behaviour and this is of particular importance for liquid chillers since these systems can operate under transient conditions for long periods. This paper covers the development of a general dynamic model for the simulation of liquid chillers. Brief descriptions of the system component models are given, including a semihermetic reciprocating compressor and thermostatic expansion valve as well as a shell-and-tube evaporator and condenser. The paper demonstrates the application of the model to simulate the performance of a liquid chiller retrofitted with a range of alternative refrigerants. The performance of the system is determined in terms of cooling capacity, power consumption and coefficient of performance for a range of different operating conditions. The relative performance of each refrigerant is discussed and the preferred alternative identified for typical applications.

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Performance Results of a Solar Adsorption Cooling and Heating Unit

Energies ◽

10.3390/en13071630 ◽

2020 ◽

Vol 13 (7) ◽

pp. 1630 ◽

Cited By ~ 2

Author(s):

Tryfon C. Roumpedakis ◽

Salvatore Vasta ◽

Alessio Sapienza ◽

George Kallis ◽

Sotirios Karellas ◽

...

Keyword(s):

Coefficient Of Performance ◽

Vapor Compression ◽

Solar Thermal Energy ◽

Cooling Mode ◽

Heating Unit ◽

Adsorption Chiller ◽

Maximum Coefficient ◽

Solar Powered ◽

Evacuated Tube Collectors ◽

Performance Results

The high environmental impact of conventional methods of cooling and heating increased the need for renewable energy deployment for covering thermal loads. Toward that direction, the proposed system aims at offering an efficient solar powered alternative, coupling a zeolite–water adsorption chiller with a conventional vapor compression cycle. The system is designed to operate under intermittent heat supply of low-temperature solar thermal energy (<90 °C) provided by evacuated tube collectors. A prototype was developed and tested in cooling mode operation. The results from the testing of separate components showed that the adsorption chiller was operating efficiently, achieving a maximum coefficient of performance (COP) of 0.65. With respect to the combined performance of the system, evaluated on a typical week of summer in Athens, the maximum reported COP was approximately 0.575, mainly due to the lower driving temperatures with a range of 75 °C. The corresponding mean energy efficiency ratio (EER) obtained was 5.8.

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Effect of Hydrofluorocarbons and Hydrofluoroolefins in a Household Refrigerator as a Substitute for R134a

Materials Science Forum ◽

10.4028/www.scientific.net/msf.969.199 ◽

2019 ◽

Vol 969 ◽

pp. 199-204

Author(s):

Shaik Mohammad Hasheer ◽

Kolla Srinivas

Keyword(s):

Cooling Capacity ◽

Operating Conditions ◽

Coefficient Of Performance ◽

Condensation Temperature ◽

Outlet Temperature ◽

Refrigeration System ◽

Volumetric Cooling ◽

Work Done ◽

Theoretical Results ◽

Hfc 152A

Now a days R134a can be used in domestic refrigerators and in air conditioning of automobiles. As per Kyoto protocol the usage of R134a is restricted due to their higher GWP value. The GWP value of this refrigerant is around 1430. So in this article, thermodynamic analysis of HFC-152a, HFO refrigerants-1234ze(E) and 1234yf was done in a household refrigeration system as direct substitute to HFC-134a.The performance of the household refrigerator was compared in terms of outlet temperature of the compressor, volumetric cooling capacity (VCC), refrigeration effect, work done by the compressor and coefficient of performance (COP). The entire analysis is carried out at various operating conditions of condenser and evaporator temperatures i.e. condensation temperature of 25°C,35°C & 45°C and evaporating temperatures ranging between −20°C to 10°C.From the theoretical results, it can be concluded that R1234yf can be used as a direct substitute to R134a.

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Experimental Thermodynamic Investigation on the Refrigerant Charge in a Transcritical CO2 Electric Bus Air Conditioning System

Applied Sciences ◽

10.3390/app11125614 ◽

2021 ◽

Vol 11 (12) ◽

pp. 5614

Author(s):

Haidan Wang ◽

Shengbo Li ◽

Yulong Song ◽

Xiang Yin ◽

Feng Cao ◽

...

Keyword(s):

System Performance ◽

Air Conditioning ◽

Cooling Capacity ◽

Exergy Efficiency ◽

Coefficient Of Performance ◽

Air Conditioning System ◽

Electric Bus ◽

Maximum Coefficient ◽

Considerable Impact ◽

Air Conditioning Systems

Due to its considerable impact on climate, bus air conditioning systems are being pushed to take a new and sustainable path. Electric buses relying on transcritical CO2 air conditioning units are perceived to be eco-friendly and future-proof solutions to achieving such a target. However, in order to have highly efficient air conditioning systems, the CO2 charge needs to be optimized. In this paper the energy and exergy-based analyses were performed to investigate the effect of normalized refrigerant charge on the system performance by using a test rig of a transcritical CO2 air conditioning unit for an 8 m electric bus. Results showed that the normalized refrigerant charge range of 0.248~0.336 was recommended in order to ensure the maximum coefficient of performance (COP). In addition, in sufficient charge conditions, the optimal COP, cooling capacity and exergy efficiency were 1.716, 18.97 kW and 29.79%, respectively, under the standard refrigeration condition of 35 °C/27 °C. As the ambient temperature rose from 35 °C to 40 °C, the COP, cooling capacity and exergy efficiency decreased by 16.03%, 10.90% and 12.22%, respectively. Furthermore, the exergy efficiency was found not to be sensitive to slightly insufficient charge, whereas overcharge was observed to be even beneficial to exergy efficiency under the condition of ensuring the maximum COP. In addition, insufficient refrigerant charging seriously affected the irreversible losses in the indoor and outdoor heat exchangers, whereas slight overcharge had little effect on the component exergy efficiency. Finally, the need to improve the CO2 compressor efficiency to enhance the system performance was revealed.

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Method for increasing the dynamic characteristics of thermoelectric coolers

Herald of Advanced Information Technology ◽

10.15276/hait.04.2021.6 ◽

2021 ◽

Vol 4 (4) ◽

pp. 354-367

Author(s):

Yurii I. Zhuravlov

Keyword(s):

Dynamic Characteristics ◽

Thermoelectric Materials ◽

Operating Mode ◽

Cooling Capacity ◽

Coefficient Of Performance ◽

Limiting Factors ◽

Maximum Temperature ◽

Thermoelectric Cooler ◽

Modes Of Operation ◽

Thermoelectric Coolers

The influence of the efficiency of the initial thermoelectric materials on the dynamics of the functioning of the thermoelectric cooling device for various characteristic current modes of operation in the range of operating temperature drops and heat load at a given geometry of thermoelement legs is considered. The parameters of thermoelectric materials of thermoelements are conventionally divided into three groups: used for batch production, laboratory research and maximum values. The criterion for choosing the operating mode of the thermoelectric cooler takes into account the mutual influence and weight of each of the limiting factors. Since the design conditions can be very diverse, simultaneously varying several limiting factors (constructive, energy and reliability), you can choose the most rational mode of operation. The analysis was carried out for typical current modes of operation of thermoelectric coolers: maximum cooling capacity, maximum cooling capacity at a given current, maximum coefficient of performance, minimum failure rate. It is shown that with an increase in the efficiency of the initial thermoelectric materials, the time for reaching the stationary operating mode of the thermoelectric cooler, the required number of thermoelements, and the maximum temperature difference increase. A method is proposed for reducing the time constant of thermoelectric coolers due to the revealed relationship between the efficiency of thermoelectric materials and the dynamic characteristics of thermoelements. It is shown that an increase in the dynamic characteristics of thermoelectric coolers is achieved without changing the design documentation, manufacturing technology and additional climatic and mechanical testing of products.

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