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Recent advancement in the micro-scale and nano-scale electronics systems, the demand of an innovative solution for the thermal management to dissipate the high amount of heat flux generated have become more rigorous to ensure good reliability of the devices. Micro-channel heat sink has been introduced to dissipate the heat flux with capacity of 10 MW m−2, which providing an ideal solution in the thermal management technology. Researches have been done experimentally or numerically to investigate effect of different geometric designs of micro-channel heat sinks to promote better heat transfer between micro-channel walls and cooling fluid. Other than micro-channel geometric design, type of cooling fluids and two-phase flow boiling are important issues in the micro-channel based thermal management system. In addition, applications of nano-fluids in the micro-channel heat sink are also highlighted which helps in improving the thermal conductivity of the coolant and leads to better heat dissipation rate. In addition, applications of micro-channel in the engineering sector such as solar cell, fuel cell and medical devices are reviewed. For the literature, implementation of micro-channel in the electronic devices as a thermal management solution is highly recommended due to its ability to protect and prolong the lifespan of electronic devices.

International audience; Due to climate change, worldwide power consumption for air conditioning is forecasted to increase by 33 times its current level by 2100. To face this trend, the efficiency of air conditioning and refrigeration systems must increase. Water spraying on the condenser of a refrigeration unit is one solution to reach this aim. Indeed, spraying water on a heat exchanger improves heat transfer by adiabatic cooling or direct impact on the heat-exchanger surface. In the present paper, water spraying is designed for an embedded air conditioning application. A pilot designed for air conditioning conditions was built and equipped with a set of atomizer. The results obtained with this pilot show that heat transfer enhancement is higher at low heat exchanger surface temperature. Moreover, a thermal image analysis has highlighted that the surface impacted by the spray excluding the clogged parts is appropriate to express the local efficiency of the spray. Indeed, this surface reaches a steady-state approximately after the same time than heat transfer enhancement. This surface depends on heat-exchanger surface temperature, and not on the air flow. Finally, the efficiency of water spraying on a heat exchanger is correlated with the impacted surface.

This study explores the feasibility of using heat pipes as heat exchangers inside an absorption heat pump type II (Absorption Heat Transformer) of a thermal capacity of 0.7 kW. The heat pipe is a passive device to transfer heat because of low thermal resistance. A heat exchanger with heat pipes can be integrated between the condensation and evaporation processes of an Absorption Heat Transformer. This study has demonstrated that seven commercial heat pipes are required to condense 0.714 kW and to reuse 0.177 kW at 60 °C in the evaporator, representing almost a third part of total heat supplied without heat pipes, provided that the generator temperature is over 55 °C. Therefore, the efficiency of the Absorption Heat Transformer can be improved based on the concept of the Coefficient of Performance up to 20%.

Air-cooled heat exchangers for power plant cooling are receiving much attention lately, as they require little or no water for cooling when compared to water-cooled systems. This paper focuses on the design, fabrication, and experimental characterization of a novel additively manufactured air–water heat exchanger for dry cooling of power plants. The heat exchanger consists of manifold-microchannels on the air side and rectangular channels on the water side in a cross-flow configuration. By using additive manufacturing, the manifold-microchannel heat exchanger can be fabricated as a single component, which eliminates the assembly process. Three prototype heat exchangers were fabricated using direct metal laser sintering (DMLS) out of stainless-steel (SS17-4), titanium alloy (Ti64), and aluminum alloy (AlSi10Mg). Air-side heat transfer coefficients in the range of 100–450 W/m2 K at pressure drops of 50–2000 Pa were recorded for the titanium alloy heat exchanger for air flow rate ranging from 1.89 L/s to 18.9 L/s. Based on our analysis and compared to conventional heat exchangers, the performance of this manifold-microchannel heat exchanger was superior. Compared to wavy fin and plain plate fin heat exchangers, up to 30% and 40% improvement, respectively, in gravimetric heat transfer density was recorded for the entire range of experimental data. Compared to state-of-the-art dry cooling, nearly 27% improvement in gravimetric heat transfer density was noted at air-side coefficient of performance ( COP air ) of 172.

Grout plays an important role in the heat-transfer performance of borehole heat exchangers. The current study developed a numerical model to investigate the effect of grout thermal conductivity and heat capacity on the heat-transfer performance of borehole heat exchangers. The “relative thermal conductivity” was defined to obtain the best matching relationship of thermal conductivity between grout and soil. The numerical model was validated through sandbox experiments. The results showed that, when the grout thermal conductivity and heat capacity were both varied by 47.00%, the effect of the grout thermal conductivity on the pipe wall temperature was 26.44% stronger than that of the grout heat capacity; whereas the effect of the grout heat capacity on the heat-transfer radius was 5.21% stronger than that of the thermal conductivity. As the same variation of the grout thermal conductivity, when the soil thermal conductivity change from 1.30 to 1.90 W/(m·K) (1.60 kcal/[m2 · h · °C]), the effect of the chang...

Most of the energy demand in the steel industry is used for heating purposes. The recovery of residual heat contributes to significant reductions in both production costs and greenhouse gas emissions. In this paper, the design, manufacture and testing of an innovative heat recovery system based on a Flat Heat Pipe heat exchanger (FHP) is described. The FHP system consists of stainless steel heat pipes linked by a bottom header and a shell and tube top header. The thermal performance of the FHP was investigated both in the laboratory and on an industrial plant and the energy recovered and the working temperatures of the FHP are reported. A theoretical modelling tool has been built to predict the performance of the device in the laboratory. Reasonable agreement has been obtained between experimental and theoretical results. It is concluded from the results that the FHP is an innovative high efficiency technology for waste heat recovery from such industrial applications.

A novel system for long-distance heat transportation that uses two types of absorption heat exchanger (AHE) is introduced in this paper. Using this system, industrial waste heat at 65–70 °C can be recovered and transported through long-distance pipelines. The Transportation Temperature Difference (TTD) can be doubled compared with ordinary system that is based on conventional heat exchangers. Considering the reduction of the pipe network cost balance with the added AHEs cost, the Minimal Economic Distance (MED) is presented. When the transportation distance is longer than the MED, the AHEs system can save both initial cost and operation cost. The ratio between the MED and the pipe diameter is in direct proportion to inside water velocity of the long-distance pipeline. Moreover, the MED would be shorter with lower relative cost of AHEs, or better performance of AHE, or the poor performance of the normal heat exchanger. In this paper, the development of the AHEs is briefly introduced. Applications in some projects show a great potential in district heating that uses low-grade heat from industries as the heat source.

The absorption heat exchanger (AHE) combined by an absorption heat pump (AHP) and a plate heat exchanger (PHE) is invented for replacing conventional plate heat exchangers at the heating substation in the district heating system, which could decease the return water temperature of primary pipe (PP) significantly when compared with the conventional PHE. The return water temperature of PP is much lower than that of secondary pipe (SP) in the AHE without consuming extra energy. The heating capacity of an original heating pipe is increased obviously, and it is much more convenient to recover different kinds of low grade industrial waste heat by the low temperature return water of PP. Meanwhile, inlet and outlet temperatures of PP and SP vary obviously during a whole heating period, therefore, the effect on heat exchange process caused by the LiBr (lithium bromide) solution circulating rate and the ratio of flow rates of PP and SP in the PHE is studied, which could ensure optimal performance of AHE under different working conditions. Operation regulation curves are given for regulation of the AHE during the whole heating period.

A potential cascaded vapor compression heat pump is proposed to address the high temperature heat demand in the copper chlorine (Cu-Cl) thermochemical cycle for hydrogen production. The configuration studied is a cuprous chloride CuCl vapor compression heat pump cascaded with a biphenyl (C 6 H 5 ) 2 heat pump. Such cascaded heat pumps is meant to upgrade heat from nuclear power plants with a heat input temperature of approximately 300 °C or industrial waste heat to meet the Cu 2 OCl 2 decomposition reactor heat demand. Energy and exergy analyses are performed to understand the performance of the heat pump. It is determined that the CuCl-biphenyl heat pump exhibits a high coefficient of performance for certain operating conditions relating to the compressor isentropic efficiency and the excess CuCl feed temperature. The base energetic and exergetic coefficient of performances of the CuCl-biphenyl heat pump are 1.76 and 1.15 respectively.

Heat generation in an electric motor will increase its temperature. The excessive working temperature will reduce the motor performance and shorten its lifetime, therefore, a thermal management system is needed to reduce the working temperature. The objective of this study is to determine the performance of the electric motor thermal management system using L-shaped flat heat pipes experimentally. Evaporator sections of heat pipes are typically placed inside the motor housing or buried in the motor shaft while the condenser sections are placed outside the motor housing and cooled with circulated liquid or air stream. However, in this study, the heat pipes were placed on the surface of the motor housing thus simplifying installation and maintenance. A prototype was made of a 0.5 HP conventional electric motor where the rotor and the coil were replaced by a cartridge heater to simulate the heat generation and to simplify the heat generation adjustment. Eight pieces of L-shaped flat heat pipes were mounted on this prototype. Each evaporator section was mounted on a heat pipe holder that was inserted between the motor fins. Each condenser section was placed in front of the motor fan. Heat sinks were mounted on each condenser section to increase the rate of heat transfer to the ambient air. The heat pipes were made of flattened copper tubes with sintered copper capillary wick and water as working fluid with a filling ratio of 50%. Experiments were conducted with varied heating power while the fan speed was kept constant. The thermal resistance of the motor fins - heat pipe - heat sink did not change much with the heat load. It reached a minimum value of 0.28 °C/W at the heat load of 150 W. The motor surface temperature was reduced from 102.2 °C to 68.4 °C or a reduction by 33.8 °C.

Current district heating systems based on natural gas-fired boilers have lower primary energy efficiency due to its higher-temperature exhaust flue gas, and it cannot meet high-density heat load demand by the existing primary heating network. A new district heating system based on natural gas-fired boilers with absorption heat exchangers is presented to increase its primary energy efficiency and meet high-density heat load demand. In this new district heating system, absorption heat exchangers installed in heating substations could greatly decrease return water temperature of the primary heating network. The lower temperature return water could be used to cool exhaust flue gas and increase heat transmission capacity of the existing primary heating network. This new district heating system was analyzed by thermodynamics and economics. Results show that its primary energy efficiency and heat transmission capacity of the primary heating network are increased by about 11% and 47% respectively. When the heat transmission distance of the primary heating network is over 2.6 km, the new district heating system has better thermodynamic performance, economic benefit and environmental benefit, therefore, it would be a better choice for district heating systems based on natural gas-fired boilers with longer heat transmission distance of the primary heating network.

Finding a solution to store industrial wasted heat for later use in order to reduce energy usage has been on the rise in recent years. This paper investigates the capability of latent heat Thermal Energy Storage (TES) system using Phase Change Material (PCM) to store/release a large amount of energy in a small volume compared to sensible heat TES system. In this work, the issue of the low conductivity of PCMs has been addressed by using an embedded finned water-charged heat pipes into the PCM bulk. Both heat pipes and the PCM tank used in this investigation were made of 316L stainless steel. The PCM used in this work was PLUSICE S89, which has a melting temperature of 89°C and crystallization point of 77°C. The evaporator section of the heat pipe was heated by condensing a steam flow. The heat that was absorbed in the evaporator section was then discharged to the PCMs by the heat pipe multi-legged finned condenser. Tests were conducted for both charging (melting) and discharging (crystallization) of PLUSICE S89. It was observed that the thermal resistance posed by PCM during the discharging stage was higher compared to that during the charging process. Spirax Sarco Engineering PLC

We demonstrate the embedding of heat pipes as a solution for heat management in high density applications where heat spreading and heat guiding can be extremely important. Measurements results describe the advantages of the presented technology in comparison with thick copper inlays in the PCB. Further, this paper will also discuss the transient aspects of the heat transport in PCBs with embedded heat pipes.

In the present work, two different types of heat exchangers are experimentally compared, namely a fin-and-tubes custom made HEX and a commercial asymmetric plate heat exchanger, for the application with phase change materials. In particular, the two devices were tested in a specifically designed testing rig located at CNR-ITAE and suitable for the characterization of thermal energy storages. The testing bench allows simulating a heat source up to 100°C (e.g. solar thermal collectors, low-grade waste heat) and to set the desired discharge temperature in the range 20°C-80°C. The phase change material with which the exchangers were filled, is a commercial paraffin (Plus ICE A82), having a nominal melting temperature of 82°C. The experimental results on charge and discharge tests, realized with the same protocol, were used for a comparison of the systems, through the identification of suitable performance figures and Key Performance Indicators, such as material-to-metal ratio, heat storage density, maximum and average power achievable and effectiveness of the system. The results show that, for the tested material, characterised by a very low thermal conductivity (i.e. about 0.2 W/mK), the selected plate heat exchanger allows a better exploitation of the heat stored inside the material, letting at the same time to reach a power output in the range 1-10 kW.

Around the world the implementation of heat recovery systems play an increasingly important role in the engineering industry. Recovered energy is utilised in production plants (especially in the food industry) and saves companies millions in expenses per year. Waste heat recovery associated with hydrocarbon combustion in the transport industry is identified as a significantly under-utilised energy resource. The aim of this project was to investigate the recovery of waste heat in a small scale system for the purpose of electrical conversion in order to serve as a secondary energy source. A theoretical analysis concerning the design and construction of the system, utilising researched theory and a control-volume-based simulation program of the recovery system, is presented. It was found that heat exchangers for the required duty are not readily available in South Africa. A high pressure, cross flow, stainless steel finned tube heat exchanger with a water side pressure rating of 2 MPa was therefore designed and constructed. By using the exhaust gases of a continuous combustion unit as an energy source and water as the working fluid, efficiencies of up to 74% in direct steam generation testing were obtained.

Most commercial and industrial facilities require very low temperatures for refrigeration and high temperatures for space heating and hot water purposes. Single stage heat pumps have not been able to meet these temperature demands and have been characterized by low capacities and coefficient of performance (COP). Cascade heat pump has been developed to overcome the weaknesses of single stage heat pumps. This study reviews recent works done by researchers on cascade heat pumps for refrigeration, heating and hot water generation. Selection of suitable refrigerants to meet the pressure and temperature demands of each stage of the cascade heat pump has been discussed. Optimization of design parameters such as intermediate temperature (low stage condensing and high stage evaporating temperatures), and temperature difference in the cascade heat exchanger for optimum performance of the cascade heat pump has been reviewed. It was found that optimising each design parameter of the cascade heat pump is necessary for maximum system performance and this may improve the exergetic efficiency, especially of cascade refrigeration systems, by about 30.88%. Cascade heat pumps have wider range of application especially for artificial snow production, in the supermarkets, for natural gas liquefaction, in drying clothes and food and as heat recovery system. The performance of cascade heat pumps can be improved by 19% when coupled with other renewable energy sources for various real time applications. Also, there is the need for much research on refrigerant charge amount of cascade heat pumps, refrigerant-refrigerant heat exchangers to be used as cascade heat exchanger, cascade heat pumps for simultaneous cooling, heating and hot water generation and on the use of variable speed compressors and their control strategies in matching system capacity especially at part load conditions.

Compact-sized organic Rankine cycle (ORC) power generators call for higher performance and down-sized heat exchangers. Heat exchangers in ORC systems, especially evaporators contribute to a big portion of the system size as well as the capital cost, and their price is also directly related to their size. Since the heat transfer area plays a direct role in the performance of heat exchangers, high-porosity metal foams are proposed for insertion into heat exchanger channels to enhance the heat transfer mechanism in evaporators. Their high surface area to volume ratio makes them a good candidate for manufacturing high-performance heat exchangers. The metalfoams are being considered to improve performance while keeping the size of heat exchangers small. In this experimental study, the performance of a 100 kW class heat exchanger with the channels brazed with nickel based metal foam and stainless steel sheets was investigated. A hot water loop was designed for heat input. The cold side of the heat exchanger works with R245fa as the working fluid. The phase-change heat transfer experiments were performed with different mass flow rates ranging from 0.32 to 0.51 kg/s while the operating pressure was at 10 to 13 bar with hot water inlet temperature was 133℃. Furthermore, the heat transfer performance is compared with a commercial plate heat exchanger (produced by Alfalaval, AC120EQ) which was custom-made as a 100kW class evaporator. In the comparison test, refrigerant side has 0.5kg/s of mass flow rate at 44℃ and heat source side has 1.23 kg/s mass flow rate at 132℃. Although the pressure drop in the metal foam plate heat exchanger is increased compared to that of the conventional plate heat exchanger, increase of the recovered waste heat from the heat source is much higher due to higher overall heat transfer coefficient. As a result, the energy density of the new heat exchanger is about 2.5 times higher than that of the conventional plate heat exchanger.

This article discusses low temperature energy recovery systems that are being installed on three Federal buildings in the Washington, DC, area. The three projects discussed use simple systems that deliver low cost heat to buildings in innovative ways. Each uses a source of low temperature heating available from within the building to reduce fossil fuel use. One system recovers heat from the ventilation return air to heat water for the hydronic reheat loop serving variable air volume boxes in the building. The second system recovers heat from an attic space below a plywood roof deck covered with asphalt shingles to heat a domestic hot water loop for a barracks. The third system recovers heat from the solar re-roofing of a building to supply heated air for swimming pool heating and for a heating, ventilating, and air conditioning system. The purpose of this article is to demonstrate the versatility of these low temperature heat recovery systems.

Micro heat exchangers are the integral part of advanced technologies such as space technologies. However, the cooling of these micro heat exchangers encounters various challenges due to large aspect ratios. Further, the conventional coolants could not dissipate the heat due to limited thermal conductivity and specific heat. Hence, suspension of nanoparticles in such coolants would increase the efficiency of micro heat exchanges. Nanofluids are widely used in biomedical applications, as coolants in transportation, industrial cooling, nuclear reactor cooling and defense applications due to their higher stability, higher heat transfer capabilities and reduced particle clogging. In the present work, the thermophysical properties of Al2O3, SiO2, SiC, CuO and TiO2 nanoparticles in Liquid Nitrogen (LN2) are studied with the volume concentration of 3%. It is observed that thermal conductivity of nanofluid is enhancing with the increase in volume concentration of nanoparticles which result in enhancing the heat transfer rate in micro heat exchangers. In order to confirm this fact, a computational investigation on pressure drop and heat transfer is performed with Liquid Nitrogen as a base fluid and CuO, SiO2, SiC, Al2O3 and TiO2 as nanoparticles. A computational geometry is developed in ANSYS® and the pressure drop and heat transfer analysis is done using FLUENT®. Relevant boundary conditions are applied to reflect the practical operating conditions of micro heat exchangers. It is observed from the results that the decrease in pressures drop with the suspension of CuO nanoparticle is low. Further, the heat transfer is observed to be increasing with the addition of Al2O3 and SiO2 nanoparticles with the concentration of 3% by volume. Finally, it can be concluded that the dispersion of the nanoparticles in Liquid Nitrogen (LN2) is beneficial to be used in micro heat exchangers.

The majority of the energy demand in industrial application is primarily used for heating purposes. Recovering waste heat could contribute to significant reduction of production cost and greenhouse gas emission. In this paper, an innovative heat recovery system was designed, manufactured and tested. The Flat Heat Pipe (FHP) is designed to recover the heat by radiation from hot steel rods during the manufacturing cooling process. The FHP system is composed of stainless steel heat pipes linked by a collector at the bottom and a shell and tube top header. The thermal performance of the FHP was investigated by testing the system at two positions from the barrier of the wires conveyor. The amount of the energy recovered and the working temperature of the FHP is also reported. The experimental results show that the heat transfer capability of the FHP is strongly influenced by the hot source temperature. It was observed from the results that the FHP is an innovative technology for waste heat recovery from industrial applications with high efficiency.

Many commercial solar thermal power plants rely on indirect thermal storage systems in order to provide a stable and reliable power supply, where the working fluid is commonly thermal oil and the storage fluid is molten salt. The thermal oil - molten salt heat exchanger control strategies, to charge and discharge the thermal storage system, strongly affect the performance of the whole plant. Shell-and-tube heat exchangers are the most common type of heat exchangers used in these facilities. With the aim of developing advanced control strategies accurate and fast dynamic models of shell-and-tube heat exchangers are essential. For this reason, several shell-and-tube heat exchanger models with different degrees of complexity have been studied, analyzed and validated against experimental data from the CIEMAT-PSA molten salt test loop for thermal energy systems facility. Simulation results are compared in steady-state as well as transient predictions in order to determine the required complexity of the model to yield accurate results.

In many industrial drying processes, water is evaporated in the drying section by a large volume of fresh air supply, which contains a large amount of sensible and latent heat. Recovering heat and water from the dryer exhaust is a potential way to realize energy and water conservation in drying systems. In this paper, the experimental and theoretical investigations of the waste heat and water recovery characteristics of heat exchangers for dryer exhaust are presented. A hot air and water vapor mixture was used to simulate dryer exhaust. Convection–condensation heat transfer and water recovery characteristics were first obtained under various water vapor mass fractions, flow velocities, and humid air inlet temperatures through experiments, which revealed that the convection–condensation heat transfer coefficient increased with the increase in water vapor mass fraction and humid air velocity, and decreased with the increase in inlet temperature. The condensed water rate increased with the increase i...

Economic issues associated with designing deep flue gas heat recovery units for natural gas-fired boilers are examined. The governing parameter affecting the performance and cost of surface-type condensing heat recovery heat exchangers is the heat transfer surface area. When firing natural gas, the heat recovery depth depends on the flue gas temperature at the condenser outlet and determines the amount of condensed water vapor. The effect of the outlet flue gas temperature in a heat recovery heat exchanger on the additionally recovered heat power is studied. A correlation has been derived enabling one to determine the best heat recovery depth (or the final cooling temperature) maximizing the anticipated reduced annual profit of a power enterprise from implementation of energy-saving measures. Results of optimization are presented for a surface-type condensing gas–air plate heat recovery heat exchanger for the climatic conditions and the economic situation in Tomsk. The predictions demonstrate that it is economically feasible to design similar heat recovery heat exchangers for a flue gas outlet temperature of 10°С. In this case, the payback period for the investment in the heat recovery heat exchanger will be 1.5 years. The effect of various factors on the optimal outlet flue gas temperature was analyzed. Most climatic, economical, or technological factors have a minor effect on the best outlet temperature, which remains between 5 and 20°С when varying the affecting factors. The derived correlation enables us to preliminary estimate the outlet (final) flue gas temperature that should be used in designing the heat transfer surface of a heat recovery heat exchanger for a gas-fired boiler as applied to the specific climatic conditions.

Aside from the low adsorption capacity of silica gel, often used in commercially available low-temperature adsorption chillers today, the cooling performance of such chillers is limited due to the high heat capacity of the mostly metal-based heat exchangers. As a completely new approach, thermally conductive polymers have been studied and examined as heat exchanger materials for low temperature adsorption chillers in order to decrease the energy consumption during the adsorption cycle. The modification of polyamide 6, which was chosen as a model polymer in this study, with expanded graphite leads to enhanced thermal part properties for adsorption heat exchangers. Compared to aluminum as the commonly used heat exchanger material, the heat capacity of a chiller can be reduced by 30%, if such a thermally conductive polymer is applied. Moreover, the increased thermal conductivity of the polymer based part leads to no significant limitation in the adsorption kinetic of water used as a refrigerant in adsorption chillers.

The paper shows that heat pipes with metal-fibrous capillary structures and evaporation-condensation cooling system based on heat pipes are highly efficient means of providing optimal thermal conditions for different electronic instruments and devices. Such cooling system combining the functions of effective heating conduit (equivalent heat conductivity is much higher than the heat conductivity of the best heat-conducting materials) and effective radiator with the possibility of passive heat dissipation is characterized by a high heat transport ability, low thermal resistance, relatively small size and weight, reliable performance at different orientation in space under exposure to mass forces action. The paper presents examples of developed designs and investigations of heat pipes and evaporation-condensation systems with metal-fibrous capillary structures aimed at cooling the different heat generating items of electronic equipment. In this case, special types and designs of systems are discussed. These systems operate under different conditions of heat removal to absorbing medium and feature both a high heat transport ability and specific dielectric properties. In addition, the thermotechnical characteristics of proposed cooling systems are also presented.

This paper presents the development and experimental study of an ammonia water absorption refrigeration prototype for waste heat utilization of diesel engine exhaust. Side cooling rectification and side heating generation are designed to achieve desirable heat matching for better internal heat recovery thus improving the system performance. An active open heat pipe method is applied for taking the exhaust heat to make the heat input stable. The condensation and absorption processes are combined in one unit and cooled by circulated precooled solution. Small diameter tube bundle heat exchangers with large specific surface area are employed for all components. Both the features make the system bulk small. The experimental results show that the operation of the system is reliable with a sharp variation of the exhaust condition. The prototype produces cooling capacity of 33.8 kW and the system thermal COP reaches 0.53 under the test conditions that the temperatures of the cooling water, secondary refrigerant and exhaust inlet are 26.1 °C, −15.2 °C and 567 °C, respectively. The novel design of the prototype is proved to be valid and its concept can be extended to other applications.

The results of experimental studies of thermal conductivity of the dominant types of external contaminants of air coolers are given. Reed down, peat litter, leaves, sand, pine needles, and ash were investigated, as well as mixtures: sand with ash, sand with reed down, peat litter with leaves. The results are presented as the dependence of thermal conductivity on the density of contaminants. A linear approximation generalizing the found dependences is recommended. It is shown that thermal conductivity is significantly dependent on the pollutant porosity.

This study focuses on the application of heat pipes in thermal management for high-power semiconductor lasers. The heat pipe cooling systems are used for heat dissipation in high-power semiconductor lasers. These systems are used instead of water cooling machines to realize a compact and lightweight laser module. The n-shaped heat pipe cooling system, which consists of eight 6 mm copper heat pipes with sintered powder wicks, can easily handle a heat load of up to 73 W from a single-laser unit. The fabricated U-shaped heat pipe cooling system, which consists of ten 12 mm copper heat pipes with sintered powder wicks, can easily handle a heat load of up to 300 W from five laser units. The optical power of the multi-laser module cooled by the U-shaped heat pipe cooling system reaches 210 W. These results indicate that high-power semiconductor lasers can be cooled using heat pipe cooling systems instead of water cooling machines.

An experimental investigation on the thermal performance of Nano Embedded Phase Change Material (NEPCM) heat sink with heat pipe has been conducted for electronic cooling in Personal computers. The NEPCM and heat pipe configuration in the heat sink effectively eliminates the use of electronic fan. A flat plate heater was used to simulate the computer's microprocessor. The heat sink configurations were placed above the flat plate heater and tested for multiple head load conditions. The addition of NEPCM increases the heat storage capacity, causes a delay effect on the sensible temperature rise and maintained the core temperature of the heat sink at room temperature for prolonged time. Heat pipe charged with R134a refrigerant placed inside the heat sink cavity for regeneration of NEPCM in heat sink. The results showed that use of heat pipe aided NEPCM heat sink caused a 3 °C decrease in the heater's surface plate temperature during six hours of the operating period without the help of electronic fan or any other forced convection.

The accelerated growth of heat load in high-density data centers presents challenges to the design of effective cooling solutions. Both energy efficiency and the information technology (IT) equipment reliability are key requirements. Localized hybrid air-water cooling systems such as Rear Door Heat eXchangers (RDHXs) are an effective means to achieve these requirements. In this paper, the transient aerodynamic and thermal performance of a commercial RDHX was investigated experimentally. The RDHX was attached to an isolated server cabinet with a controllable heat load. A localized containment system was used to direct the airflow to the equipment in the cabinet that emanates from a single perforated tile within the enclosure. The water flow rate and supply water temperature to the RDHX was controlled, and a grid of 36 air velocity/temperature sensors was employed to monitor the airside of the cooling system. The cooling performance of the RDHX in an air blower failure scenario was investigated. The failure scenario was designed to diminish different parts of the overall system. The impact on the IT equipment and the cabinet outlet temperatures was assessed. Also, there was a significant reduction in the airflow to the IT equipment. The impact of the reduced airflow on different parts of the cabinet as well as the cooling performance of the heat exchanger was characterized during both failure and recovery.

By reviewing development of waste heat utilization in sintering process and sinter cooling process, two major difficulties are more and more apparent. A system of low temperature waste heat utilization based on organic fluids is proposed, which is composed of flue gas waste heat utilization heat exchanger, thermal storage subsystem and organic Rankine cycle (ORC) subsystem. The sintering flue gas and the sinter cooling air are adopted as the heat source. And on this basis, we establish the simulation analysis platform for the whole thermodynamic system. From a comprehensive perspective, the low temperature waste heat utilization could run well when the sintering heat source fluctuates within a certain range. It means that, the ORC-based system could overcome difficulties in utilizing waste heat in sintering process.

A set of stainless steel tabular heat pipes are successfully fabricated, for the purpose of the low-grade heat recovery applications in a corrosion exhaust environment. The fabrication, the thermal performance testing systems, and modeling are presented in the paper. Experimental results show that the water filling ratio plays a significant role in the thermal performance of heat pipes. A numerical model is developed and the model prediction is trustworthy in comparison with experimental data. The model reveals that a better heat pipe thermal performance could be achieved by selecting a material with higher thermal conductivity coefficient. However, it should be compromised in terms of the thermal performance and the application concerns like corrosion.

The development and preliminary tests of a 5 kg Mg2FeH6 heat storage system which is useable for short and long-term storage applications at temperatures around 500 °C are described. The heat transfer for the heat storage process (dehydrogenation of the hydride Mg2FeH6) and heat release (hydrogenation of the hydride precursor 2Mg-Fe) is done by the flow of molten salt in appropriate heat exchangers serving as heat source or heat sink. The construction of the tube bundle reactor as a heat storage tank is presented. 1.6 kWh of heat could be released and 1.5 kWh of heat could be stored during the first experimental tests. Difficulties, which occured during the preliminary tests, are described.

The developments and the enhancements in all the heat transfer equipments are mainly purposed for energy savings and savings in projects capital investment, through reducing the costs (energy or material). The better heat exchanger is one that transfer's high heat rate at low pumping power with a minimum cost. The spent of money for the research and development in corrugated plate heat exchangers, in last decades, from some companies, offered different and versatile types and models of that heat exchanger. In the current study I made a focus on researcher's efforts in research and developments for corrugated plate heat exchanger. This type of heat exchangers is widely used for different engineering fields and applications. Research reactors represent one of the important engineering fields that extensively use corrugated plate heat exchangers due to their simplicity in assembly/disassembly and their easy maintainability. The corrugated plate heat exchanger has a great flexibility than the other types of heat exchangers; both its heat transfer area and its cooling flow could be increased or decreased easily, so; it is commonly used for enlargement and upgrading works. The current revision incorporated different topics like; the plate heat exchanger structure, thermal performance, heat transfer enhancement mechanisms as well as plate heat exchanger advantages and limitations. The corrugated plate heat exchanger works efficiently in both single phase and two phase flow, while the two phase flow region still needs a lot of research work. Also; the corrugated plate heat exchanger thermal performance and pressure drop behaviours when using nano-fluids were discussed in the current revision.

The purpose of this research is to evaluate the primary energy savings of a desiccant-enhanced evaporative (DEVap) cooling system with a district heat source. The DEVap system consists of an internally cooled liquid desiccant dehumidifier and dew point evaporative cooler connected in series. The liquid desiccant unit requires a heat source for regenerating the weak desiccant solution, which means that the DEVap cooler is a thermally driven cooling system. It can provide energy benefits when the supplied heat comes from waste heat or renewable heat sources. In this research, district heat obtained from a combined heat and power (CHP) system was used as the heat source for the DEVap system. The primary energy consumption and CO 2 emission rate of the proposed system with a district heat source were estimated using a detailed energy simulation and compared with those powered by a conventional gas boiler. The results showed that the DEVap system with district heat source consumed 46.2% less primary energy and produced 40.5% less CO 2 compared with the system using the conventional gas boiler.

Heat transfer characteristics and thermal performance enhancements of heat exchangers for thermal systems under frosting, defrosting, and dry/wet operating conditions have been investigated extensively over the years. The complex physical phenomena of heat exchangers under different operating conditions and effects on thermal performance have been analyzed and evaluated by theoretical, numerical and experimental methods. Although this article takes into consideration both earlier and recent research, the focus was on research carried out in the last decade. In this article, the first section deals with the reviews of heat transfer of heat exchangers operating under frosting conditions, while subsequent sections survey the heat transfer of heat exchangers operating under defrosting and wet/dry conditions. Finally, heat transfer enhancement of heat exchangers were summarized.

A plate heat exchanger is a type of heat exchangers that provides more surface area for heat transfer between two fluids. Plate heat exchangers are widely used for heat transfer applications in the industry. In addition, they are now widely used in many applications such as food processing, chemical reaction processes, heating and cooling applications in sectors such as petroleum. However, the design of plate heat exchangers is complicated by the large number of variables and geometries that affect its performance. A better heat exchanger design is to achieve a high heat transfer rate at low pumping power with low cost. In this study, the focus is on the research and development efforts of different plate materials, various fluid types, their flow regimes and the plate grooving angles on plate heat exchanger performance. For this purpose, the Computational Fluid Dynamics (CFD) is used. The results show that the heat efficiency is the best performing heat exchanger that can be designed as parallel- and counter-flow, geothermal fluid, titanium plate and 60° groove angle from the point of view.

Geothermal heat exchangers system composed of two conic baskets serially connected is designed and realized. Both heat exchangers are made in polyethylene high-density material and have a length of 3 m each one. They will be used for greenhouse cooling and heating through a geothermal heat pump. Its conical geometry is selected to reduce the operation cost and the exploited area, compared to vertical and horizontal geothermal heat exchangers often used. It also assures the maximum of heat exchange with the soil. The aim of this study is to determine the thermal performance of one Conic Basket Geothermal Heat Exchanger (CBGHE), buried at 3 m deep, in the exploitation of the soil thermal potential, in summer. A rate of heat exchange with the soil is determined and the global heat exchange of the CBGHE is assessed. Its energy and exergy efficiencies are also evaluated using both first and second law of thermodynamic. Results show that the specific heat exchange ranges between 20 W m−1 and 50 W m−1. Maximal energetic and exergetic efficiencies of the CBGHE, equal to 62% and 37% respectively, are reached for a mass flow rate of 0.1 kg s−1. For this value of mass flow rate, the overall heat exchange coefficient is of 52 W m−2 K−1.

For heat storage applications designed to recover and recycle waste heat energy, it is usually advantageous to store heat in a phase-change material. One-dimensional numerical analysis and evaluation of a heat storage system that uses a phase-change material to store latent heat in addition to sensible heat was carried out, and it was found that up to 30% of the total heat energy generated by the fuel and subsequently lost to cooling can be recovered. A heat storage system was installed to reduce warm-up time by releasing heat directly into the engine coolant during cold start, and the corresponding reduction in fuel consumption was measured. With the addition of a heat storage device, the warm-up time to 95 °C was reduced by between 18.1% and 27.1%. A numerical simulation of the New European Driving Cycle was carried out for a vehicle equipped with a 1.6-L diesel engine and a heat storage system. Analytical results showed that the warm-up time was reduced by 40.5% and the fuel consumption was reduced by 2.71% compared to a vehicle without a heat storage system installed.

Efficient energy recovery from used air with the goal of reducing energy use is important for realizing low energy houses. Rotary heat exchangers are very energy efficient, but have the drawback of transferring odours from exhaust air to fresh supply air. To avoid this, flat plate heat exchangers are commonly used where odour transfer might cause problems. Nevertheless, these may not properly handle water condensation and frost formation at low outdoor temperatures. The so-called membrane-based energy exchangers are an alternative to the flat plate heat exchanger. In a membrane-based exchanger, moisture is transferred from the humid exhaust air to the dry supply air, avoiding condensation at the exhaust airside. In this work, a membrane energy exchanger was compared to a thin non-vapour permeable plastic foil heat exchanger. The study focused on verifying condensation and freezing problems and evaluating the performance of the membrane energy exchanger. The experiments showed that non-permeable heat exchangers have problems with condensation and freezing under test conditions. Under the same conditions, the membrane-based exchanger did not experience the same problems. However, additional problems with swelling of the membrane in high humidity conditions showed that the tested membrane type had drawbacks and needs further development to become commercially applicable.

In order to improve the uniformity of underground temperature, three optimal layouts including 36 buried pipes are proposed with cooling/heating load ratio of 2.5:1.The results show that the less the number of tubes are located in the central area, the more uniform the temperature field will be. The surrounding temperature is slightly higher than that of traditional layout. The results proved that the proposed layouts can effectively reduce the peak value of temperature field, and the results also provide reference for ground source heat pump system designers.

Latent heat recovery is a significant issue in heat recovery of nature gas, and it can improve thermal efficiency of boilers greatly. A scheme involving AHPs (absorption heat pumps) to generate cold water to recover latent heat in flue gas is proposed and applied to northern China. COP of AHPs is greatly affected by solution HXs (heat exchangers), so performance of the HX cannot be too low. In the article, a new system is put forward, investment of solution heat exchanges can be decreased greatly. Afterwards, key parameters and investment saving ratio are discussed. Optimal flue gas temperature drop in flue gas-solution HXs is calculated and maximum of investment saving ratio is put forward.

Due to the limitation of fossil fuels, shortage of energy, optimization of energy consumption in various industrial processes becomes very important and challenging issue all over the world. A reduction in energy consumption is possible by enhancing the performance of heat exchanger and it is one of the most important devices related to energy and heat transfer. Heat transfer is one of the most important processes in industrial and consumer products. For decades, efforts have been done to enhance heat transfer, reduce the heat transfer time. Minimize of heat exchangers and finally increase energy and fuel efficiency. Nanofluid is a new engineering fluid which could improve the performance of heat exchanger. Nanofluids have greater potential for heat transfer enhancement and highly suited to application in practical heat transfer processes. Heat exchanger has potential applications such as heat recovery from engine cooling circuit, oil cooling; desuper heating in refrigeration and air conditioning, dairy and chemical industry, pharmaceutical industry and refinery. In many industrial applications the conventional heat transfer fluids are refrigerants, water, engine oil, acetone and ethylene glycol etc. An important in energy efficiency is possible from the perspective of the heat transfer fluids. Enhancement in heat transfer is always in demand and it depends on the cooling rates, so the need for more efficient heat transfer systems increases, researchers have introduced various heat transfer enhancement techniques.