Review of applications and developments of ultra-thin micro heat pipes for electronic cooling

Two phase heat transfer devices based on the miniature version of loop heat pipe (LHP) can provide very promising cooling solutions for the compact electronic devices due to their high heat flux management capability and long distance heat transfer with minimal temperature losses. This paper discusses the effect of the wick properties on the heat transfer characteristics of the miniature LHP. The miniature model of the LHP with disk-shaped evaporator, 10 mm thick and 30 mm disk diameter, was designed using copper containment vessel and water as the working fluid, which is the most acceptable combination in electronic cooling applications. In the investigation, wick structures with different physical properties including thermal conductivity, pore radius, porosity, and permeability and with different structural topology including monoporous or biporous evaporating face were used. It was experimentally observed that copper wicks are able to provide superior thermal performance than nickel wicks, particularly for low to moderate heat loads due to their low heat conducting resistance. With monoporous copper wick, maximum evaporator heat transfer coefficient (hev) of 26,270 W/m2 K and evaporator thermal resistance (Rev) of 0.06–0.10°C/W were achieved. For monoporous nickel wick, the corresponding values were 20,700 W/m2 K for hev and 0.08–0.21°C/W for Rev. Capillary structure with smaller pore size, high porosity, and high permeability showed better heat transfer characteristics due to sufficient capillary pumping capability, low heat leaks from evaporator to compensation chamber and larger surface area to volume ratio for heat exchange. In addition to this, biporous copper wick structure showed much higher heat transfer coefficient of 83,787 W/m2 K than monoporous copper wick due to improved evaporative heat transfer at wick wall interface and separated liquid and vapor flow pores. The present work was able to classify the importance of the wick properties in the improvement of the thermal characteristics for miniature loop heat pipes.

Effect of Wick Characteristics on the Thermal Performance of the Miniature Loop Heat Pipe

The refrigerator is an essential domestic appliance product and is available worldwide. Additionally, the technologies on which the majority of refrigerators are based involve high energy consumption, and environmental deterioration due to the type of energy input and the use of certain work fluids. Therefore, how refrigerators work is of great interest, and in recent years the development of diverse research in this field has intensified. As a consequence, in this article we present an exhaustive review of the research with the greatest impact on domestic refrigeration, based on vapor compression such as modeled, thermal stratification, control, environmentally innocuous refrigerants, thermal isolation, and hybrid systems, among others. Based on the above, we present the principal trends in this area, of interest to both industry and researchers.

Enhancements in domestic refrigeration, approaching a sustainable refrigerator – A review

Evaluation of capillary performance of sintered porous wicks for loop heat pipe

Experimental investigation of a thermosyphon based heat exchanger used in energy efficient air handling units

Development of an experimental loop heat pipe for application in future space missions

The paper presents a critical review of different approaches for reciprocating compressors thermal analysis. It is well established that a major part of the inefficiency in small reciprocating compressors used for household refrigeration is associated with thermal effects, mainly reflected in terms of superheating. Therefore, the capability to optimize the compressor thermal behavior is crucial to increase its efficiency. In fact, there is a perception that new compressor developments will be strongly dependent on how effectively the thermal issue is handled. The aim of this paper is to present an overview of different numerical and experimental methodologies currently applied in the industry for compressor thermal design. A brief description of each methodology is given, with possible applications for the compressor analysis, along its main advantages and drawbacks. Finally, some insights about new developments in this area are also presented.

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Thermal Analysis of Reciprocating Compressors - A Critical Review

The design of a high-efficiency reciprocating compressor requires an understanding of the interactions between different phenomena occurring inside the compressor. This paper describes a comprehensive simulation approach for hermetic reciprocating compressors including modeling of the electrical motor. The simulation of the compression cycle follows an integral control volume formulation for mass and energy conservation. A thermal model is adopted with steady-state thermal energy balances applied to the compressor components via global thermal conductances. The equivalent circuit method is employed to form a steady-state model of a single-phase induction motor. The coupling between the three models provides the motor slip and mean compressor speed, which are seen to affect the compressor efficiency. The simulation model is validated through comparisons between predictions and measurements of the parameters associated with the compressor efficiency, temperature distribution and motor performance. A parametric analysis is carried out to investigate the dependence of the motor temperature on the input voltage and the results are discussed.

A simulation approach for hermetic reciprocating compressors including electrical motor modeling

This paper presents the validation of a first-order winding thermal model in machine operative conditions. The proposed model can be used in motor control strategies for the winding temperature prediction during transient overload, or vice versa , for the prediction of the maximum time duration of the overload maintaining the winding temperature within the limit imposed by the class of insulation. The thermal model has been validated using two different electrical machines. The first one is a 10-kW automotive starter-generator prototype for mini-hybrid powertrain equipped with distributed bar windings, while the second one is a 2.2 kW total enclosed fan cooled industrial induction motor equipped with conventional stranded wire windings. Depending on the application for both machines, a short-duty transient operation in overload conditions could be required. In particular, the automotive starter-generator must accomplish engine cranking and torque assistance during the vehicle acceleration and braking, while the industrial induction machine could operate in intermittent service in overload conditions when used in machine tool applications. As a consequence, an accurate stator winding temperature prediction is mandatory to fully exploit the machine performance. For both motors, the thermal model parameters have been evaluated by fast experimental approach, and, subsequently, the model has been validated during operative overload conditions.

Winding Thermal Model for Short-Time Transient: Experimental Validation in Operative Conditions

The use of fractional-slot concentrated windings (FSCW) in electrical machines allows more compact, efficient, and reliable design with respect to machines equipped with distributed windings. However, an electromagnetic design linked to a thermal analysis of the electrical machine is mandatory to achieve the desired performance, and to fulfill the requirements of efficiency and reliability. One of the most critical issues in thermal design of electrical machines is to assign fair values for the input parameters of the thermal simulation models, particularly those related to the stator winding insulation system. This paper deals with the assessment of the equivalent thermal conductivity of the insulation system of FSCW machines. For this purpose, three FSCW electrical machines for different applications were evaluated via an experimental method based on a dc thermal transient test. Whereas the investigated machines present different characteristics among themselves, different approaches were required to properly estimate the thermal conductivity.

Thiago Dutra

Papers

Development of an experimental loop heat pipe for application in future space missions

Thermal Analysis of Reciprocating Compressors - A Critical Review

A simulation approach for hermetic reciprocating compressors including electrical motor modeling

Winding Thermal Model for Short-Time Transient: Experimental Validation in Operative Conditions

Thermal Conductivity Evaluation of Fractional-Slot Concentrated-Winding Machines