Recovery Heat Exchanger Research Articles

Investigation of Thermal Performance of Heat Pipe Heat Exchanger for Waste Heat Recovery

Investigation of Thermal Performance of Heat Pipe Heat Exchanger for Waste Heat Recovery

Influence of superheat and expansion ratio on performance of organic Rankine cycle-based combined heat and power (CHP) system

The purpose of this study is to investigate the performance characteristics of subcritical organic Rankine cycle (ORC) based combined heat and power (CHP) system according to a variation of major operating parameters and to confirm the possibility of system performance improvement. The CHP system is designed to provide output using a 200 °C heat source, including at least 2 kW of electric power and 25 kW of thermal power with 60 °C of hot water supply. Besides examining a basic ORC-based CHP system, variations of system configurations combined with heat exchangers for additional heat recovery have been considered. The effects of changes in superheat and expander volumetric expansion ratio on system performance were evaluated based on thermodynamic analysis and optimization results for each system and working fluids.Eight candidate working fluids selected for superior thermophysical properties and environmental impacts were classified into three groups according to the magnitude of latent heat, and four types of CHP system configuration with additional heat exchangers were considered. Group A working fluids with the largest latent heat include cyclopentane, isopentane, n-pentane, and diethyl ether, while medium latent heat group B working fluids include R-1233zd and R-245fa. The smallest latent heat group C working fluids include HFE-7000 and HFE-7100. The operating conditions and performance of the CHP systems were calculated considering the fixed heat source temperature (200 °C), the superheat amount, the volumetric expansion ratio and the isentropic efficiency of the expander for parametric analyses.Studies have shown that the group A working fluid systems are superior in performance to other fluid systems. According to the parametric analyses, the increase in superheat has a positive effect regardless of the configuration in the system using the group B working fluids. Other working fluid systems can also be expected to enhance the performance by increasing the degree of superheat in system configurations where an internal heat exchanger (IHE) and a post-heater (PH) are employed together. Increasing the volumetric expansion ratio and the isentropic efficiency of the expander improves the performance of all working fluid systems. Especially, it has been concluded that the addition of the post-heater is essential if the CHP performance is to be improved by increasing the volumetric expansion ratio and the isentropic efficiency of the expander.

Thermodynamic analysis of a novel combined cooling and power system driven by low-grade heat sources

A novel combined cooling and power system which combines a conventional ammonia-water power/cooling cycle named Goswami cycle and an ejector refrigeration cycle is proposed and investigated. This new combined system can improve the refrigerating capacity of the conventional power/cooling system, and it can also adjust the cooling capacity to power ratio by changing the proportion of the ammonia-water flow into the turbine and the ejector. A mathematical model is developed to study the system performance. It is shown that under the given conditions the combined thermal efficiency and the combined exergy efficiency are 17.49% and 26.15%, respectively. The exergy analysis shows that the exergy destruction mainly occurs in the recovery heat exchanger, followed by boiler and rectifier, respectively. Parametric study shows that the absorber temperature, the cycle highest pressure and low pressure, the boiler temperature and the split ratio have significant effects on the net work output, the cooling capacity, the combined thermal efficiency and the combined exergy efficiency.

Experiments on novel heat recovery systems on rotary kilns

In this paper, we have proposed a novel heat recovery system installed on the rotary kiln. The experimental measurements are carried out to investigate the heat transfer characteristic and fluid flow performance of the nine heat recovery exchangers in the heat recovery system. The experimental platform is set up to study the operational characteristic of the system. The measurement results show that the outlet temperatures of the heat recovery exchangers mostly varies as the inlet temperatures increases while the experiments have certain hysteresis. Besides, the outlet pressure of the heat recovery exchanger varies as the inlet pressure changes. The measurement parameters of the inlet and outlet pressure have the same variation trend and quick responses with no hysteresis. When the inlet mass flow rate varies from 0 to 6 kg/s, the heat recovery exchangers with coiled pipes could effectively improve the heat recovery performance compared with the radiant type. Then the heat recovery performance of three different types of heat recovery exchangers in the system are investigated to obtain the heat transfer surfaces with better thermal efficiency on rotary kilns. The experimental measurements indicate that the heat recovery performance of the heat recovery exchanger with two layer of coiled pipes is better than the others. Furthermore, the heat transfer rate of the heat recovery exchanger with two layer of coiled pipes is increased by 15.3% compared with the existing heat recovery exchanger in literatures.

Comparative study of vertical and horizontal indirect evaporative cooling heat recovery exchangers

This paper presents a comparative study of a counter-cross flow plate heat recovery exchanger, which operates as an indirect evaporative air cooler in cooling conditions. In the study, thermal performance of this exchanger with different placement modes (vertical and horizontal) was investigated by numerical simulation based on original mathematical model. To validate the numerical model, vertically and horizontally positioned prototypes with the same exchangers were made and tested on the test rig. According to the test results, the numerical model has a satisfactory accuracy. For these two types of prototypes, influence of supply and exhaust air inlet parameters (temperature and relative humidity) on the thermal performance of the two prototypes in both constant inlet airflow rate and variable inlet air flow rate was researched. The results show that, under conditions of constant airflow rate with variable supply air parameters, the outlet supply air temperature of the exchanger set vertically is 1.41–2.40 °C lower than that of exchanger set horizontally, meanwhile, 24–44% more cooling capacity is obtained by the vertical exchanger. It indicates that placement mode has important effects on thermal performance of the exchangers and the exchanger set vertically always shows a better performance. The main reason is considered to be the existence of larger dry areas in exhaust air channels of the horizontal exchanger that reduce the heat transfer between supply air and exhaust air. Therefore, characteristics of the heat transfer in horizontal exchangers was especially studied in this paper.

Thermodynamic analysis and multi-objective optimization of a novel power/cooling cogeneration system for low-grade heat sources

A novel power/cooling cogeneration system based on an ammonia-water power cycle is proposed and investigated. The cooling capacity of the conventional combined system is much improved since an absorption-ejector refrigeration cycle is introduced. Besides the novel combined system could get more high-grade work at the same time obtain amounts of refrigeration due to the unique coupling mode. A mathematical model of the novel system is developed for system simulations under steady-state conditions. The results show that the thermal efficiency and the exergy efficiency are 21.34% and 38.95%, respectively. Exergy analysis shows that the exergy destruction mainly occurs in the recovery heat exchanger, followed by boiler and rectifier, respectively. Parametric study shows that the absorber temperature, the cycle high pressure, the temperature at boiler outlet and the extracting ratio have significant effects on the system performance. In addition, a multi-objective optimization using NSGA-II method is carried out to obtain the final optimums of the proposed system. The optimization results show that the exergy efficiency and the overall capital cost rate are 37.24% and 0.69408 $/h, respectively, and the thermal efficiency versus the overall capital cost rate are found to be 20.99% and 0.73351 $/h.

Experimental study on the thermal performance of nano enhanced pentaerythritol in IC engine exhaust heat recovery application

The performance of IC engine can be enhanced by exhaust gas heat recovery using solid state phase change materials, such as pentaerythritol (C5H12O4). Further enhancement was achieved by adding Al2O3 nanoparticle to improve heat transfer performance of C5H12O4, that has rather poor thermal conductivity. In this study the effect of adding Al2O3 nanoparticle on heat transfer performance of pentaerythritol (PE) was studied using a heat recovery heat exchanger integrated with the exhaust pipe of an internal combustion engine. The experimental results showed when 0.1% and 0.5% Al2O3 were added to PE, instead ofusing purePE, the charging efficiency increased by 5.48% and 14.77% and energy savings by 11.46% and 18.3%, respectively. The characterization methods such as TGA-DTA, DSC, FTIR and LFA were used. Thermal degradation kinetics of pentaerythritol added with Al2O3 nanoparticles was studied by Coats-Redfern method. The dispersion stability, thermal/chemical degradation and thermal energy storage performance of PE with Al2O3 nanoparticles are reported in this paper.

The improvement on efficiency and drying performance of a domestic venting tumble clothes dryer by using a heat pipe heat recovery heat exchanger

The domestic venting tumble clothes dryer consumes a lot of energy during the drying process, which has drawn more and more attention. This article reports a method to reduce its energy consumption by using heat recovery. A self-made heat pipe heat exchanger was used for a domestic venting tumble clothes dryer as a heat recovery unit. The performance of the clothes dryer in the case of heat recovery and no heat recovery was tested under the same conditions, including weighing before drying, drying and weighing after drying. Compared with the case of without heat recovery, it can be found that the exergy efficiency of the venting tumble clothes dryer with heat recovery is increased from 10.122% to 12.292%, and the energy efficiency is increased from 47.211% to 57.335%. The increase of the temperature of the moist air entering the drum increases the temperature difference between the hot dry air and the moisture in the clothes. This enhances the evaporation of moisture. So it takes less energy to evaporate the same amount of moisture. The electricity consumption can reduce 17.606%. The effect of heat pipe heat recovery on the dryer can be a guide to the optimization of clothes dryers.

Engine oil warm-up through heat recovery on exhaust gases – Emissions reduction assessment during homologation cycles

Fuel saving is currently the most important technology driver in the development of low-emissions internal combustion engines. As known, friction is responsible for losses during engine operation, leading to an increased fuel consumption and ultimately increased emissions. Among all options for friction reduction, the oil thermal management has not yet received the attention it deserves, despite the fact that its potential compares to the one of other more consolidated techniques. Such a lack of interest appears even worse, when the impact of an accelerated oil warm up on the emissions reduction during reference homologation cycles is considered: in standard NEDC cycles, the oil viscosity reaches its design value only during the final part of the cycle, i.e. once the most part of harmful emissions has already occurred. This is due to a delayed thermal stabilization of the lubricant oil and poor friction reduction performances during the NEDC early phases.In this paper, the Authors investigate the effectiveness of the waste heat recovery on the exhaust gases, to speed up the lubricant oil warm up, effective immediate after engine ignition and thus, with little or no delay on the start of NEDC homologation cycle. The experimental activity, performed on a turbocharged engine (F1C 3L IVECO), starts with the setting up of a proper oil circuit and exhaust line layout, to allow the exhaust tailpipe to include a shell and tube heat exchanger for heat recovery. The unsteady heat availability on the exhaust gases, along with the variability the mass flowrate experiences during the NEDC cycle represents a major variable to account for in the heat exchanger selection and design. All interactions between the modified oil circuit, engine, coolant circuit and the exhaust line needed to be evaluated as well. Significant reduction of fuel consumption and pollutant emissions have been experimentally demonstrated.

Functional exergy efficiency of an air heat recovery exchanger under varying environmental temperature

The ventilation heat recovery exchanger (HRE) for low energy buildings is becoming one of the important heat transformers in the HVAC systems. The purpose of this paper is to develop the possibilities of exergy analysis for the HRE, when the reference temperature (RT) is variable. The method was prepared through consideration of the exergy flow direction changes, when variable RT was placed below, above and across the operating temperature of working fluids. By using the coenthalpy diagrams, there were obtained three functional exergy efficiencies which had greater sensitivity than universal exergy efficiency. The prepared solution allows the reliable using of the ubiquitous thermodynamic (exergy) analysis for energy chain in the HVAC systems. This methodology may be developed for other heat exchangers with different mass flows, operated at near-environmental temperatures. The results could have a practical application for designing the HVAC systems and implementing their exergy optimum operation controls.

Energy efficient heat pipe heat exchanger for waste heat recovery in buildings

This study presents a Computational Fluid Dynamics (CFD) Heat Transfer Analysis for an originally designed Energy Efficient Heat Pipe Heat Exchanger for Waste Heat Recovery in Buildings. The research is focused on developing a heat pipe heat exchanger for domestic hot water and thermal agent preparation, preheating / heating the air from ventilation systems in buildings, using as a primary agent the return of the existing heating system. The proposed device has a lot of advantages as high efficiency for heat recovery, low cost of manufacturing, exploitation and maintenance and it is very easy to install and use.

Functional exergy efficiency of an air heat recovery exchanger under varying environmental temperature

The ventilation heat recovery exchanger (HRE) for low energy buildings is becoming one of the important heat transformers in the HVAC systems. The purpose of this paper is to develop the possibilities of exergy analysis for the HRE, when the reference temperature (RT) is variable. The method was prepared through consideration of the exergy flow direction changes, when variable RT was placed below, above and across the operating temperature of working fluids. By using the coenthalpy diagrams, there were obtained three functional exergy efficiencies which had greater sensitivity than universal exergy efficiency. The prepared solution allows the reliable using of the ubiquitous thermodynamic (exergy) analysis for energy chain in the HVAC systems. This methodology may be developed for other heat exchangers with different mass flows, operated at near-environmental temperatures. The results could have a practical application for designing the HVAC systems and implementing their exergy optimum operation controls.

An analysis of the innovative exhaust air energy recovery heat exchanger

Heating, ventilation and air conditioning systems are responsible for a nearly 50% of total energy consumption in operated buildings. One of the most important parts of the ventilation system is an air handling unit with a heat exchanger for energy recovery which is responsible for effective and efficient energy recovery from exhaust air. Typically heat exchangers are characterised by the producers by heat and humidity recovery efficiency up to 90% and 75% respectively. But these very high values are usually evaluated under laboratory conditions without taking into account a dynamic change of outdoor and indoor air conditions significantly affecting the recovery efficiency. In this paper, results of thermal, humidity and enthalpy recover efficiency of innovative energy recovery exchanger have been presented. The analysed system allows adjustment of the humidity recovery especially useful in the winter period and forefends energy use for an anti-froze system of energy exchanger. Presented result show that analysed innovative system can achieve the value of thermal efficiency recovery higher than 90% and efficiency of humidity recovery about 80%. This is possible because the analysed system is able to work without the use of any primary source energy or other anti-freeze systems. Presented in this research unique solution is able to work without external anti-freeze systems even in extremely adverse outdoor air conditions such as minus 20°C and humidity 100% RH.

Experimental investigation of a heat pipe heat exchanger for heat recovery

An air-to-air heat pipe heat exchanger has been designed, constructed and tested. Gravity-assisted wickless heat pipes (thermosiphons) were used to transfer heat from one air stream to another air stream, with a low temperature difference. A thermosiphon heat exchanger has its evaporation zone below the condensation zone. Heat pipes allow keeping a more uniform temperature in the heat transfer area. The heat exchanger consists of 20 copper tubes with circular copper fins on their outer surface. The tubes were arranged in a row and the air passed across the pipes. R245fa was used as a working fluid in the thermosiphons. Each heat pipe had a 40 cm evaporation section, a 20 cm adiabatic section and a 40 cm condensation section. The thermosiphon heat exchanger has been tested in different conditions of air stream parameters (flows, temperatures and humidity). The air face velocity ranged from 1,0 m/s to 4,0 m/s. The maximum thermal efficiency of the thermosiphon heat exchanger was between 26÷40%, depending on the air velocity. The freezing of moisture from indoor air was observed when the cold air temperature was below - 13°C.

A Numerical Study on Using Air Cooler Heat Exchanger for Low Grade Energy Recovery from Exhaust Flue Gas in Natural Gas Pressure Reduction Stations

Heat EXchangers (HEX) that are used in City Gate Station (CGS) systems are modeled numerically to recover the exhaust waste heat. It was tried to find the best viscous model to obtain results in accordance with experimental results and to change the heat exchanger design. This HEX is used for recovering heat from exhaust flue gas with a mixture of 40% water and 60% ethylene glycol as the cooling fluid. Then, the effects of sizes and numbers of fins and tube rows on recovered heat rate were investigated under various pump speeds. As the first step in solving the problem, SST k–ω and RNG k–e suitable viscous models were chosen for these kinds of problems. Secondly, a new HEX is designed at a fixed coolant speed, pipe and fin thickness, and shell dimension because of operational constraints. Finally, the best HEX with the minimum pressure drop (minimum fin number) is numerically analyzed, and the new HEX specifications were extracted.

Design of Heat Exchanger for Waste Heat Recovery from Exhaust Gas of Diesel Engine

The Diesel Generating set (DG Set) which uses diesel engine is gaining popularity in rural areas as it produces electricity for irrigation and agricultural purposes. But there are various losses associated with diesel engine which tend to reduce its efficiency and performance. Among these exhaust heat loss is major loss which contribute almost 33-36% and leads to the waste of heat which could be recovered and a considerable amount of primary fuel could be saved. The literature survey reviews that exhaust gases from diesel engine having heat potential that can be recovered. In the present paper attempt have been made recovering of waste heat energy of exhaust gas of diesel engine by placing specially designed heat exchanger just near the inlet and outlet duct of the engine so that energy from the exhaust can be used for preheating the air passed to the engine. A simple counter flow shell and tube type heat exchanger was designed and fabricated based on the output obtained from initial design. The experiments were conducted with and without out heat exchanger on vertical, single cylinder, 5 HP, cold start, water cooled, four stroke diesel engine working on high speed diesel oil. The diesel engine with incorporation of heat exchanger shows improved performance of engine and also shown reduction in smoke level.

Experimental and theoretical investigation of a flat heat pipe heat exchanger for waste heat recovery in the steel industry

Abstract 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.

Optimization design of waste heat power generation systems for cement plants based on the thermal resistances analyses

Heat loss from the cement production accounts for a large amount of the energy consumption in energy-intensive industry. In order to recover the heat loss, a waste heat power generation system is proposed in this work. The system contains a suspension preheater boiler, an air quenching cooler boiler, a condenser, a turbine and a heat recovery system with nine heat recovery exchangers. Then, integration of the thermodynamic and thermal resistance analyses yields physical model relations between the system requirements and the design parameters, i.e. the thermal conductance and the mass flow rates, which form the constraint equation group of a global optimization model. With the aid of the conditional extremum principles, the equation group is solved to obtain the optimal structural and operational parameters for the heat power generation system. Besides, experimental measurements are investigated to determine the heat transfer characteristics of the heat recovery exchangers. Finally, an optimization case of a practical system is studied and some factors that affect the optimal results are discussed. The results illustrate that the global optimization method can obtain the optimal design parameters for each component in the waste heat power generation system. The required thermal conductance of the heat recovery system could reduce by 22% compared with the values before optimization. The vaporization temperature will decrease as the total mass flow rate and the work output of the turbine increase. Besides, the total thermal conductance will increase as the inlet temperature of the cooling water in the condenser and the work output in the turbine increase.

Optimum waste heat recovery from diesel engines: Thermo-economic assessment of nanofluid-based systems using a robust evolutionary approach

Nearly 30% of the input energy to a diesel engine is wasted through the exhaust gas; thus, considerable attention has been directed toward developing efficient heat recovery systems for these engines. Given the demonstrated ability of nanofluids to boost the heat transfer rate of heat exchangers, these heat transfer fluids merit consideration for use in diesel exhaust heat recovery systems. In this study, the effects of employing nanofluids on the optimum design of these systems are investigated. An existing heat diesel engine exhaust heat recovery system is modeled to work with Al2O3/water and a modified imperialist competitive algorithm is employed for the optimization. Seven variables consisting of five heat exchanger geometric characteristics together with nanoparticle volume fraction and coolant mass flow rate are considered as design variables. The heat exchanger cost and charging rate of the storage tank are optimization objectives, while the greenhouse gas savings of the heat recovery system are assessed for measuring the environmental impact of the energy recovery. The results indicate that the proposed approach can overcome the challenge of finding the near-optimal design of this complex system and using nanofluids enhances the performance of the heat recovery heat exchanger.

Recent trends in the development of heat exchangers for geothermal systems

The potential use of geothermal resources has been a remarkable driver for market players and companies operating in the field of geothermal energy conversion. For this reason, medium to low temperature geothermal resources have been the object of recent rise in consideration, with strong reference to the perspectives of development of Organic Rankine Cycle (ORC) technology.The main components of geothermal plants based on ORC cycle are surely the heat exchangers. A lot of different heat exchangers are required for the operation of ORC plants. Among those it is surely of major importance the Recovery Heat Exchanger (RHE, typically an evaporator), in which the operating fluid is evaporated. Also the Recuperator, in regenerative Organic Rankine Cycle, is of major interest in technology. Another important application of the heat exchangers is connected to the condensation, according to the possibility of liquid or air cooling media availability. The paper analyzes the importance of heat exchangers sizing and the connection with the operation of ORC power plants putting in evidence the real element of innovation: the consideration of the heat exchangers as central element for the optimum design of ORC systems.