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This article, written as a result of theoretical and practical research, describes a survey of condensate nucleation in heat exchangers utilizing low-potential heat of humid air. The authors conducted a series of studies aimed at developing energy-independent technical solutions to protect heat exchangers from the freezing of the moisture condensing on their exchange surfaces in the course of humid air heat recovery. There was a negative dependence of the thickness of the layer of condensate formed on the heat exchange surface, the condensation rate, and the moisture content of warm air. The article presents the outcomes of the numerical study aimed at building a model of the condensation processes that occur due to a flow of moist air when the air is cooled and heat is utilized. The study provided experimental validation for the consistency of the processes related to water vapor condensation in the flow of cooled moist air. The outcomes presented in the article can apply to both the exchange systems using the low potential heat of the atmospheric air, e.g., for room heating or snow melting, and to the exhaust air energy recovery systems of the building ventilation plant.

Micro heat exchangers provide improved heat transfer capacities, but also increased pressure losses due to the small characteristic dimensions. Additional pressure losses are generated by modified micro structure geometries used for heat transfer enhancement of these micro devices. Therefore, an overall heat exchanger assessment needs to be considered to generate energy efficient micro heat exchangers. A characterization of gas-to-gas micro heat exchangers has been performed in terms of pressure loss behavior and heat transfer performance. The gas-to-gas micro heat exchangers differ by partition foil material and partition foil thickness, respectively. The pressure loss behavior is influenced by the density which depends on the temperature and pressure. The heat transfer performance shows overlapping trends due to axial conduction. Comparison between different partition foil materials and partition foil thicknesses showed no significant criteria of the influence of thermal conductivity on the temperature jump effectiveness. An assessment due to overall heat exchanger effectiveness has been performed to compare gas-to-gas micro heat exchangers. For this purpose, the overall exergy loss has been calculated by combination of heat transfer performance and pressure loss behavior. A strong impact of the fluidic exergy loss due to pressure loss has been detected which mainly influences the overall exergy loss of the gas-to-gas micro heat exchangers.

Phase change materials (PCMs), due to their extraordinary latent heat storage characteristic, have been widely investigated in the thermal management of electronic devices. However, the current PCM-based heat sinks generally suffer a long heat dissipation time after heat absorption. To address this issue, the modularized thermal storage unit (MTSU) was proposed in this paper. The online charging and offline discharging working modes of the MTSU allow it to cool the intermittent electronic devices with a high duty cycle. In this paper, the MTSU samples were fabricated with paraffin wax as latent heat storage core unit and polymer encapsulation shell. The specific latent heat storage and morphology of the MTSU samples were studied. Afterward, the thermal storage performance of each individual MTSU sample was specially characterized with the sample subjected to the constant heat flux. The MTSU samples showed desirable performance on encapsulating the PCMs and stabilizing the heat source temperature. The safe operation time of the heat source was prolonged by 181% with 16 g of PCM in the vacuum environment. Furthermore, the performance of the MTSU samples on cooling of the electronic devices with a relatively high duty cycle was investigated. The results show that owing to the modularization and replaceability of the samples, the ON/OFF working time ratio of the heat source was greatly enlarged. When cooled by the MTSU sample with 11.42 g of paraffin, the heat source could work with an ON/OFF time ratio up to 6.7 at 4 W and 14.9 at 3 W.

Today widespread application of energy-saving equipment based on heat pipes makes a significant contribution to the task of resources saving. Using the heat pipes as heat transfer and heat exchange design elements allows creating new effective equipment generation for solar energy systems. Heat pipes are widely used both to improve the outdated equipment, increase its efficiency, reliability and lifetime and in the creation of new high-quality and economic technology samples. Up to the present day there are the following systems and solar energy equipment where heat pipes are widely used: photovoltaic-thermal solar collectors, solar thermal collectors, concentrating photovoltaic and concentrating solar plant. The article presents an analysis of the current state and prospects of heat pipes using in solar energy systems.

Particle-based concentrating solar power (CSP) plants have been proposed to increase operating temperature for integration with higher efficiency power cycles using supercritical carbon dioxide (sCO2). The majority of research to date has focused on the development of high-efficiency and high-temperature particle solar thermal receivers. However, system realization will require the design of a particle/sCO2 heat exchanger as well for delivering thermal energy to the power-cycle working fluid. Recent work has identified moving packed-bed heat exchangers as low-cost alternatives to fluidized-bed heat exchangers, which require additional pumps to fluidize the particles and recuperators to capture the lost heat. However, the reduced heat transfer between the particles and the walls of moving packed-bed heat exchangers, compared to fluidized beds, causes concern with adequately sizing components to meet the thermal duty. Models of moving packed-bed heat exchangers are not currently capable of exploring the design trade-offs in particle size, operating temperature, and residence time. The present work provides a predictive numerical model based on literature correlations capable of designing moving packed-bed heat exchangers as well as investigating the effects of particle size, operating temperature, and particle velocity (residence time). Furthermore, the development of a reliable design tool for moving packed-bed heat exchangers must be validated by predicting experimental results in the operating regime of interest. An experimental system is designed to provide the data necessary for model validation and/or to identify where deficiencies or new constitutive relations are needed.

In the present study, the heat transfer performance of dimpled double-pipe heat exchangers for fuel cells that are utilized as cooling systems of fuel cells was studied. In addition, to comparatively analyze the heat transfer performance of dimpled double-pipe heat exchanger for fuel cells, plain double-pipe heat exchangers were also studied. Experimental results were derived on changes in the Reynolds numbers of the cooling water flowing in dimpled and plain double-pipe heat exchangers and changes in the heat flux of the air. Thereafter, to verify the reliability of the experimental results, the theoretical overall heat transfer coefficients and the experimental overall heat transfer coefficients were comparatively analyzed and the following results were derived. The heat transfer rate lost by the hot air and that of the heat transfer rate obtained by the cooling water were well balanced. The experiments of plain double-pipe heat exchangers and dimpled double-pipe heat exchangers were conducted under normal conditions and the theoretical overall heat transfer coefficient and the experimental overall heat transfer coefficient coincided well with each other. In both plain double-pipe heat exchangers and dimpled double-pipe heat exchangers, heat transfer rates increased as the cooling water flow velocity increased. Under the same experimental conditions, the heat transfer performance of dimpled double-pipe heat exchangers was shown to be higher by 1.2 times than that of plain double-pipe heat exchangers.Key words : Dimpled double pipe heat exchanger, Heat transfer, Fuel cell, Performance, Overall heat transfer coefficientCorresponding author: 031-539-1973, chodh@daejin.ac.kr

To predict the hydrogen storage performance, this study presents a mathematical model for simulating the thermal-fluid behaviours in the metal hydride beds embedding heat pipes. Computational fluid dynamics (CFD) simulations were conducted using a commercial code (ANSYS Fluent) using LaNi5 as the storage media. The model was validated by comparison with previous experimental data in literature that proves the effectiveness of heat pipes to increase the heat transfer rate between the metal hydride bed and outside the storage tank. The results showed that heat pipes profoundly changed the distribution of temperature, hydrogen content and equilibrium pressures over the metal bed. The dry-out limits of the heat pipe exerted considerable effects on the tank performance. By contrast, changing the thermal conductivity of the heat pipe made little difference because the effective thermal conductivity of the metal beds was typically much smaller than that of the heat pipe. The model was then applied to compare tank designs, with and without heat pipes and internal fins, to demonstrate the effects of using heat pipes to improve the heat and mass transfer in a hydrogen storage tank.

Driven by the low density, corrosion resistance, manufacturability, and low raw material and manufacturing costs of polymer composite materials, significant attention is being devoted to the innovation, characterization, and implementation of such materials. In this study the thermal and mechanical properties of a broad range of commercially available, injection moldable, thermally enhanced polymer composite materials are reviewed to help identify candidate materials that could replace conventional metal alloys in microelectronics cooling heat sink and heat exchanger applications. The material property characterization data reviewed consists of vendor data generated in accordance with applicable characterization standards. From twenty seven commercially-available polymeric composite materials, two promising groups of materials, namely polyphenylene sulfide (PPS) and polyimide 66 (PA66), are identified.A preliminary investigation of exchanger heat transfer rate is undertaken using computational fluid dynamics (CFD) to identify the envelope of thermally enhanced composite material thermal conductivities required for effective heat transfer in gas-liquid heat exchanger applications. The thermal performance of a thermally enhanced PPS, parallel plate cross-flow air-water heat exchanger prototype is shown numerically and experimentally to be comparable to that of a conventional aluminum exchanger having the same geometry, demonstrating the potential feasibility of replacing conventional metallic heat exchangers with thermally enhanced polymeric composite heat exchangers in microelectronic air-liquid cooling applications. Review of thermal and mechanical properties of polymer composite materials.Promising materials identified for heat exchangers in microelectronics cooling.Numerical assessment of polymer composite heat exchanger thermal performance.Heat transfer feasibility of replacing metallic exchangers with polymer composites.

The cold battery is a heat exchanger between two fluids, air (secondary fluid) and iced water (primary fluid). The cold battery is composed of two heat exchangers in series, one of which is made up of flat-plate in galvanized steel serving as a reservoir for the iced water and the other one a copper shell and-tube exchanger with aluminum cooling blades. The two heat exchangers a connected pipe of the same diameter. These pipes will permit the transit of the iced water coming from the flat-plate exchanger by gravitation towards the tubes of the second exchanger. These two heat exchangers are incorporated in a galvanized container coupled with a centrifugal fan for the improvement of the thermal comfort. The water, after passing through the two heat exchangers is stored in an adiabatic reservoir and will serve as a water fountain [1]. The modeling will be done in a humid mode that is the temperature of the surface of the battery is very low compared with the dew temperature of air. The cooling allows the condensation of water vapor [2]. The characterization of that cold battery will be done in a dry regime where there is only one heat exchanger and the quantity of vapor contained in the air does not vary and also the surface temperature of the battery is greater than the dew temperature of air [2; 3].

The cold battery is a heat exchanger between two fluids, air (secondary fluid) and iced water (primary fluid).The cold battery is composed of two heat exchangers in series, one of which is made up of flat-plate in galvanized steel serving as a reservoir for the iced water and the other one a copper shell- and-tube exchanger with aluminum cooling blades. The two heat exchangers are connected to a pipe of the same diameter. These pipes will permit the transit of the icy water coming from the flat-plate heat exchanger by gravitation towards the tubes of the second exchanger (1). The good operation of this cold battery depends on the knowledge of its operating point. We are proposing a technique of determination of the operating point by using one of the two fluids (water or air) and the efficiencies (2, 3).The Knowledge of that operating point will enable us, through experimental means, determine the mean surface temperatureand then determine the mean surface enthalpy from the specific heat capacity at saturation obtained from the linearization of the entrance and exit air temperatures on the saturation curves.

A novel combined thermoelectric power generation and water desalination system is described with a system schematic. The proposed system utilises low grade thermal energy to heat thermoelectric generators for power generation and water desalination. A theoretical analysis presents the governing equations to estimate the systems performance characteristics combined with experimental validation. Experimental set-up consists of an electric heat source, thermoelectric modules, heat pipes, a heat sink and an evaporator vessel. Four heat pipes are embedded in a heat spreader block to passively cool the bottom side of the thermoelectric cells. The condenser of these four heat pipes is immersed in a pool of saline water stored in an evaporation vessel which is maintained at sub-atmospheric pressure. The liquid to vapour phase change cooling method achieve low saturation temperature and offers a high heat transfer coefficient for the cooling of the thermoelectric generators. At the same time this method utilises the low temperature heat extracted from the cold side of the thermoelectric generator for water desalination. It was observed that at low saturation temperatures greater heat flux could be supplied to the thermoelectric generators with less heat losses to the atmosphere.

There is an increasing interest in post-combustion CO2 capture related to climate change and further use of the captured CO2 in enhanced oil and gas recovery, as well as a feed to produce products such as methanol or dimethylether, the use in hot dry rock technologies, etc. The currently used post-combustion capture method based on MEA (monoethanolamine) absorption without stream split has significant steam consumption to regenerate the amine solution. In this work, the HEN ADU (Heat Exchanger Network of an Absorption Desorption Unit) is analysed using the Process Integration methodology. It is supplemented with the search of economically viable options of desorption column parameters by computer modelling and the use of compact PHEs (plate heat exchangers) with intensified heat transfer. Based on the presented case study, the variation of temperature approach inside the rich/lean heat exchanger is considered. Its influence on the heat consumption, the energy efficiency and the investment cost of the HEN ADU unit are discussed. The use of PHEs in HEN ADU allows with the same or even smaller purchased cost of heat exchangers to save up to 13% more energy as compare to HEN with conventional shell and tube heat exchangers.

Wastewater heat recovery applications are becoming widespread in energy saving applications. A sustainable and low emissions operation in air conditioning and heating processes is achieved by harvesting the otherwise wasted energy in wastewater through specially designed heat exchangers, lying at the core of heat pumps. This combined system is called wastewater source heat pump. In this study, a review of wastewater heat exchangers in wastewater source heat pump applications is presented, and wastewater heat exchangers are classified in detail based on multiple features, including utilization and construction methodology. Also, the potential of wastewater, types of wastewater source heat pumps, and their applications are briefly discussed. (C) 2015 Elsevier B.V. All rights reserved.

The concept of borehole heat exchanger (BHE) field exploitation is described, along with problems regarding the sustainability of heat resources in rock masses. A BHE field sometimes has problems with the stability of the heat carrier temperature during long-term exploitation. The main reason for this is an insufficient heat stream with which to transfer heat by conduction in rock. Possibilities for the regeneration of heat in rock masses, based on experiences at the Geoenergetics Laboratory (Drilling, Oil and Gas Faculty, AGH University of Science and Technology), are described.

With the rapid development of the national economy, the use of low-temperature heat in thermal power plant boiler can not be ignored.Although low temperature economizer is widely used in low-temperature waste heat recovery of thermal power plant boiler, the problems of corrosion and fouling are very significant.New type PTFE heat exchanger filled with high thermal conductivity properties can replace the existing metal heat exchanger, fundamentally solve the problems of corrosion and fouling, meet the future development of the thermal power plant, and realize the energy recycling to maximize the benefit of energy.

Thermal energy represents a large part of the global energy usage and about 43% of this energy is used for industrial applications. Large amounts are lost via exhaust gases, liquid streams and cooling water while the share of low temperature waste heat is the largest. Heat pumps upgrading waste heat to process heat and cooling and power cycles converting waste heat to electricity can make a strong impact in the related industries. The potential of several alternative technologies, either for the upgrading of low temperature waste heat such as compression-resorption, vapor compression and trans-critical heat pumps, or for the conversion of this waste heat by using organic Rankine, Kalina and trilateral cycle engines, are investigated with regards to energetic and economic performance by making use of thermodynamic models. This study focuses on temperature levels of 45–60 °C as at this temperature range large amounts of heat are rejected to the environment but also investigates the temperature levels for which power cycles become competitive. The heat pumps deliver 2.5–11 times more energy value than the power cycles in this low temperature range at equal waste heat input. Heat engines become competitive with heat pumps at waste heat temperatures at 100 °C and above.

Integral pressurized water reactors are innovative reactors in which all of the components typically associated with the nuclear steam supply system of a nuclear power station are located within th...

This study was conducted to develop a heat pump system to utilize waste heat within the greenhouse during the daytime in winter season. The system runs at 8 am to 6 pm for the heat storage operation, and from 6 pm to 8 am of the next day for the heat radiant work. In the case of the heat storage operation, the average solar radiation was with outside temperature. The of the system shows 4.59 in this operation mode. When the temperature goes up to , the system reached at 5.10. On the other hand, the of the system in heat radiation mode shows 2.63. In this case, the inside of the greenhouse temperature was reaches at when the outside temperature was .

In this paper heat pipes have been constructed and tested using solutions of ethanol and water as the working fluid at different tilt angles and concentrations. Tests were carried out to investigate the effects of ethanol concentration as well as the pipe evacuation and the use of a wick inside the pipe to ensure a continuous performance of the system. The tests indicate that ethanol in the solution enhances the heat pipe performance at low heat flux, and that concentrations of 50% and 75% show the best performance characteristics in transferring the heat. An efficiency of about 52% was obtained for the heat pipe operated solar collector in this case. It was concluded that the evacuation of a heat pipe or using a wick do not add much effect to the enhancement of a heat pipe performance, and that the collector had its highest heat transfer coefficient at a tilt angle of 35°. Using the results from testing the heat pipes, a thermo-syphon type solar water heater was developed, using the high efficiency heat pipe with evacuated glass cover tubes. The results of these experiments revealed that the collector water flow rate and evacuation of the glass cover tubes had little effect on the enhancement of the solar collector thermal performance.

This paper presents an experimental investigation of thermal performance for four types of heat sinks. The investigated heat sinks were: extruded uncoated longitudinal fin heat sink, extruded coated longitudinal fin heat sink by aluminum nanoparticles, rectangular block of commercially available aluminum metallic foam, and the innovative heat sink using water as a working fluid with the velocity of 1.17 m/s, aluminum nanocoated metallic foams, and uncoated metallic foams. Each heat sink was cooled by a confined stream of ambient air. The experiments were done in a wind tunnel where the free stream velocity ranged from 1 m/s to 3 m/s. Temperatures were measured at the base of heat sinks to represent the Application Specific Integrated Circuits (ASIC) chip temperature. The effects of air flow velocity on the thermal resistance of the heat sinks were also investigated. The thermal resistances of the four heat sinks were compared as well. The results showed that the innovative heat sink with aluminum nanoparticles had the best performance in comparison to the above mentioned heat sinks used for the study. Although the metallic foam heat sink had better performance than uncoated heat sinks, it cannot be an economic replacement for industrial applications due to its high price and dirt absorbing property.

The improvement of effectiveness of work furnaces depends on increasing the efficiency as well as the decrease the elementary consumption of energy. The character of the analyzed electric chamber furnace to thermal processing in work was introduced. over the discussed results concern the efficiencies, consumption of electric energy as well as the coefficient of elementary consumption of energy. The improvement of coefficients of furnace solutions were proposed.

A thermoelectric generator prototype has been built; it produces 21.56 W of net power, the produced thermoelectric power minus the consumption of the auxiliary equipment, using an area of 0.25 m2 (approximately 100 W/m2). The prototype is located at the exhaust of a combustion chamber and it is provided with 48 thermoelectric modules and two different kinds of heat exchangers, finned heat sinks and heat pipes. Globally, the 40 % of the primary energy used is thrown to the ambient as waste heat; one of the many different applications in which thermoelectricity can be applied is to harvest waste heat to produce electrical power. Besides, the influence on the thermoelectric and on the net power generation of key parameters such as the temperature and mass flow of the exhaust gases, the heat dissipation systems in charge of dispatching the heat into the ambient and the consumption of the auxiliary equipment has been studied. In terms of heat dissipation, the heat pipes outperform the finned dissipators, a 43 % more net power is obtained. The authors would like to thank the Spanish Ministry of Economy and Competitiveness, and European Regional Development Fund for providing funding for this work included in the DPI2011-24287 research project.

The scope of this research is to obtain a film coating on stainless-steel surfaces in order to reduce the interaction between the metal surface and the precipitates, so as to mitigate fouling in heat exchangers. Perfuoropolyethers were used to obtain nano-range fluorinated layers in order to make hydrophobic the stainless-steel surfaces. A pilot plant with two identical heat exchangers was built to investigate the ability of the hydrophobic coating of preventing fouling. The heat exchangers, installed in parallel, operated at the same temperature and pressure conditions, namely, laminar flow regime and inlet flow temperatures of 291–293 K for cold streams and 313–333 K for hot streams. We compared the heat transfer performance of the two heat exchangers. After a 5-month operation, the decrease in the heat transferred was 56% for the coated heat exchanger and 62% for the uncoated heat exchanger. Moreover, the increase of heat transfer resistance due to scale on the uncoated heat exchanger, with respect to ...

This paper contains an analysis of the process carried out in a heating system for the treatment of aqueous kaolin suspension in order to identify the causes of cyclical, relatively frequent loss of system functionality. The analysis showed that the main cause of the short usability time of the installation is the inappropriateness of the heat exchangers' construction for the implemented technology, while the physical and chemical parameters and the rheological properties of kaolin suspensions are of secondary importance. It is proposed to replace the plate heat exchangers used in the installation with heat pipe exchangers of special construction. The results of laboratory and experimental tests of a heat pipe exchanger designed specifically for the described application are presented. An empirical comparison of the effectiveness of the proposed heat exchanger with a double pipe exchanger was performed by conducting tests in the process conditions of genuine installations and using the method of ϵ–NTU for...

The effect of using nanofluid in thermosyphon-type heat pipe heat exchangers on energy conservation of an air-conditioning system was sought in this study. Innovatively, two heat exchangers in-series were deployed using TiO2/methanol nanofluids with 0–4 wt% concentrations as working fluids. The impacts of temperature and relative humidity on the effectiveness of 2 and 4-row heat exchangers were analyzed experimentally and more that 40 % energy saving was obtained.

We present the results of an experimental study of cooling systems on the basis of the finned heat pipes by applying a system of spherical recesses/projections at the ribs. The possibility of reducing the total thermal resistance of the cooling systems by 20–40% is presented in the entire range of studied thermal loads. Recommendations for rational application of heat transfer intensifier are given.

Contribution is aimed on lost heat of plate heat exchangers to surrounding environment. Heat losses to vicinity are insignificant relative to transferred heat flow in the plate heat exchangers. This small part of the lost heat is demonstrated in parametric case study of plate heat exchanger, where is the lost part of heat energy lower than 0.50 % in ordinary cases.

Recently, as the demand for sustainable energy sources is increasing, ground-source heat pump (GSHP) systems are receiving growing attention. However, the initial cost of GSHP system is higher than it of the conventional systems, especially, in small-size buildings. Therefore, for the application to the small-size building, it is necessary to develop small-size ground heat exchanger with small-size buildings. In this study, analysis of unit-type heat exchanger due to grouting materials. As a result, 1492.14 W of heat exchange rate was acquired in the condition of cement-silica sand-graphite materials.

In this paper, a method of designing horizontal ground heat exchanger for high energy demand applications is presented as the role of ground heat exchangers on the performance of the ground source heat pumps (GSHP) is very critical. A numerical model was developed and validated to predict the thermal performance of various types of ground heat exchangers. A parametric study was performed to identify the important factors affecting the thermal performance of the ground heat exchanger. It was found that thermal conductivity of soil plays a vital role in the heat transfer process. The heat transfer fluid velocity, thereby mass flow rate was an important parameter affecting the amount of heat exchanged with soil. The depth of installation was found to have negligible effect on the thermal performance of ground heat exchangers. A novel design concept was introduced for designing ground heat exchanger for high energy applications for given foot print area and the mean thermal energy dissipation with low cost of installation. The new configuration can be considered as the combination of horizontal and vertical ground heat exchanger.

Ground source heat pump systems represent an interesting example of renewable energy technology for heating and cooling of buildings. The connection with the ground is usually done by means of a closed loop where a heat-carrier fluid (pure water or a solution of antifreeze and water) flows and, in heating mode, moves heat from ground to refrigerant fluid of heat pump. A new solution is the direct expansion heat pump. In this case, the heat-carrier fluid inside the ground loop is the same refrigerant fluid of heat pump. This paper focuses on the energy performance of direct expansion ground source heat pump with borehole heat exchangers in heating mode, looking at residential building installations. For this purpose, the evaporating process of the refrigerant fluid inside vertical tubes is investigated in order to analyze the influence of the convective heat transfer coefficient on the global heat transfer with the surrounding ground. Then, an analytical model reported in literature for the design of common borehole heat exchangers has been modified for direct expansion systems. Finally, the direct expansion and common ground source heat pumps have been compared in terms of both total borehole length and thermal performance. Results indicate that the direct expansion system has higher energy performance and requires lower total borehole length compared to the common system. However, when the two systems are compared with the same mean fluid evaporating temperature, the overall length of the ground heat exchanger of the direct expansion heat pump is greater than that of the common system.

Huge amount of energy wasted through the flue gas in thermal power station causes great concern in recent years. Discharging hot flue gas in the environment is not only a wastage of energy but also increases the rate of global warming. Efforts are given world -wide to harness the energy for useful purposes. In this work, the waste heat of flue gas in a 350 MW thermal power plant is utilized in vapor absorption air conditioning plant. Gas to liquid multi-pass cross flow heat exchanger that have been placed in the existing space between boiler and chimney. The dimensions of the finally selected heat exchanger are 0.106m × 2.4m × 3.4m. The number of pipes required for the heat exchanger is found to be 12 using iteration method and temperature of water at the outlet of last pipe is 101.1℃. The extracted energy from the flue gas is used to heat water to be utilized in the generator of a vapor absorption refrigeration system that has produced a refrigerating capacity of 70 TR. approximately. Due to the corrosive nature of flue gas, heat recovery is confined up to the acid dew point temperature of the flue gas. Suitable software is used to find out the detailed design parameters of Gas to liquid multi-pass cross flow heat exchangers. Out of many feasible designs of heat exchangers, the most economic design is selected as the final design.

This work discusses a waste heat recovery system (WHRS) applied to chimneys for heating water in residential buildings. A prototype illustrating the suggested system is implemented and tested. Different waste heat scenarios by varying the quantity of burned firewood (heat input) are experimented. The temperature at different parts of the WHRS and the gas flow rates of the exhaust pipes are measured. Measurements showed that the temperature of 95 L tank of water can be increased by 68 °C within one hour. Obtained results show that the convection and radiation exchanges at the bottom surface of the tank have a considerable impact on the total heat transfer rate of the water (as high as 70%).

Latent heat storage using a phase change material (PCM) is a promising method for utilizing the exhaust heat from steelworks. The purpose of this study was to improve the heat release performance of a direct-contact heat exchanger using a PCM and heat transfer oil (HTO). Erythritol (with a melting point of 391 K), which is a kind of sugar alcohol, was selected as a PCM. A vertical stainless steel cylinder with an inner diameter of 200 mm and height of 1400 mm was used as the heat storage unit (HSU). A ring-shaped injector with 18 holes positioned vertically downward was placed at the bottom of the HSU. Each hole in this injector had a diameter of 2.5 mm. We investigated the effects of the height of the PCM in the HSU, the HTO flow rate, and an increase in the number of injection-nozzle holes on the temperature effectiveness and heat exchange rate as indices of the heat release performances. As results, we found that an increase in the number of nozzle holes accelerated the uniform distribution of the HTO in the liquid PCM, prevented the HTO drift flow and adverse solidification of the PCM, and improved the heat release performance under the condition of a high HTO flow rate.

A study of energy retrofit by combined heat pipe heat exchanger with cold condensate was carried out and results are presented in this paper. The parameters of study including inlet water temperature, water flow rate, primary air velocity, and exhaust air velocity on systems performance are experimentally investigated. Experiment results indicate that for a small condensate flow rate, both the latent heat of exhaust air and sensible heat of condensate can simultaneously be utilized for cooling and dehumidifying primary air, which is expected to be efficient for energy retrofit in central air conditioning systems. Practical application: Cold condensate from Heating, Ventilating, and Air-Conditioning (HVAC) plants are usually discharged or drained off. Reuse of cold condensate not only reduces wastage of water, it also fully utilizes energy and improves overall efficiency of HVAC plants. The installation and capital cost for heat pipe heat exchanger are reasonable. The physical space required is also affordable. Its practical value is useful.