Dual Heat Research Articles

Optimization and Evaluation of a Low Temperature Waste Heat Recovery System for a Heavy Duty Engine over a Transient Cycle

<div class="section abstract"><div class="htmlview paragraph">Powertrain efficiency is a critical factor in lowering fuel consumption and reducing the emission of greenhouse gases for an internal combustion engine. One method to increase the powertrain efficiency is to recover some of the wasted heat from the engine using a waste heat recovery system e.g. an organic Rankine cycle. Most waste heat recovery systems in use today for combustion engines use the waste heat from the exhaust gases due to the high temperatures and hence, high energy quality. However, the coolant represents a major source of waste heat in the engine that is mostly overlooked due to its lower temperature. This paper studies the potential of using elevated coolant temperatures in internal combustion engines to improve the viability of low temperature waste heat recovery. The paper first uses engine experiments and multi-linear regression analysis to model the indicated efficiency and recoverable power for a Scania D13 heavy duty engine across a range of engine loads, speeds and coolant temperatures. The recoverable power is obtained from simulations of a dual loop waste heat recovery system using ten working fluids as potential candidates for recovering heat from the exhaust gases and the coolant. The paper then investigates the maximum potential fuel consumption benefit by using elevated coolant temperatures for the Scania engine running on the World Harmonized Transient Cycle. From the simulation results, it was seen that cyclopentane and methanol were the best performing working fluids for the coolant and exhaust gas heat sources respectively. From the analysis on the World Harmonized Transient cycle, when using the best performing working fluids and elevated coolant temperatures, a potential net reduction in fuel consumption of 9% could be obtained.</div></div>

Numerical modelling of a PV-T collector working as evaporator in a solar assisted heat pump

A numerical study of a PV-T collector working as an evaporator for a solar assisted heat pump is presented. The work has been realized in the framework of the SolairHP project for the study of a reversible dual source heat pump. The main objective is to increase the seasonal coefficient of performance of the heat pump compared to an air source heat pump and reduce the overall electrical consumption by including a solar collector-evaporator. A mathematical steady state model of the solar evaporator device has been realized in Matlab environment: it considers the energy and mass fluxes in three dimensions by working a discretization of the main surfaces of the PV sandwich and of the absorber plate (roll-bond plate). The input of the model are the ambient conditions (irradiance components and air temperature), the thermodynamic conditions of the refrigerant at the inlet (enthalpy and mass flowrate) and the circuitation. The main results of the model are the electric and thermal efficiency, the conditions of the refrigerant all along the channels and the temperature distribution on the PV-T surfaces. The numerical model has been used in the design procedure of the solar evaporators to be coupled to a 8 kW heat pump working with R32. A preliminary seasonal analysis on the PV-T evaporator has been realized in order to evaluate the advantage of the dual source system.

Experimental study on a dual compensation chamber loop heat pipe with dual bayonet tubes

Dual compensation chamber loop heat pipe (DCCLHP) holds great application potential in the future aircraft thermal management. In this work, a DCCLHP with dual bayonet tubes was first proposed and fabricated, aiming to improve its startup performance especially at small heat loads in the terrestrial surroundings. Extensive experimental validation was conducted at three typical attitudes of the evaporator/CCs, i.e., the vertical attitude, 45° tilt angle and the horizontal attitude, mainly focusing on its startup characteristics and heat transport capability. According to the experimental results, the DCCLHP with dual bayonet tubes can successfully realize the startup at small heat loads in whatever attitudes of the evaporator/CCs in the ground condition, and reach a heat transport limit greater than 400 W over a distance of 2.0 m. No obvious operating instability was observed in the DCCLHP operation. In addition, a new flow mechanism was observed in the experiment, i.e., a local natural circulation of the working fluid driven by gravity occurred in the loop composed of the evaporator, the CCs, the bayonet tubes, and the branches of the liquid line. This local circulation of working fluid was identified to appear only when the evaporator/CCs were at a certain tilt angle and the heat loads were relatively small.

Solar Assisted Dehydrator for Decentralized Controlled and Homogeneous Multi-Product Drying

Abstract Batch type food dryers are common for drying agricultural produce due to simple in design, but they are prone to nonuniform drying and significant heat cost exclusively if they fall in the medium to large size range. The current study illustrates a solar hybrid food dryer using a gas burner and solar collector (evacuated tube collector, ETC) as heating source along with an inline perforation inside the drying chamber to obtain spatial drying homogeneity. Air distribution was assessed through three-dimensional simulation using computational fluid dynamics (CFD) analysis. Performance trials were conducted under three heating options (ETC, gas, and dual) using green chilies at 60 °C. Throughout drying chamber, under all heating modes, the average difference in drying rates ranged from 0.61 to 1.30 kg water/kg dry matter, demonstrating homogeneous drying. Simulated and experimental results of air distribution were found to be in agreement with each other. Using three options for thermal heating (ETC, gas, and dual) and an overall 58% efficiency for evacuated tube collector, the specific energy for moisture evaporation was found to be 4.5–5.7 MJ/kg and specific product energy 19.2–24.9 MJ/kg. In case of dual heating option, the energy supplied by solar and gas sources for a 20 hours period was 50.64% (160.22 MJ) and 49.35% (156.13 MJ), respectively. Compared with dual heating option, energy cost can be reduced by 68% if only solar energy is used as a heating option but with a protracted drying time.

A sustainable exergy model for energy–water nexus in the hot regions: integrated combined heat, power and water desalination systems

Water scarcity is a worldwide concern for Earth citizens. Finding new methods for water concentration is essential for the extension of life. The water issue is more intense in the regions with a warm to the tropical environment. Considering the cooling demand of these regions, which consequently requires excess energy to satisfy the cooling load, having a thermal system to support three concerns of the water, cooling, and power would be the key for the warm/hot weather areas. In the present study, a novel model by integration of gas turbine power cycle with a solar parabolic collector, a steam turbine, heat recovery, steam generator, multi-effect desalination, and absorption chiller is proposed. The suggested model is optimized through developing a comprehensive multi-objective function to maximize the exergy efficiency and minimize the cost. Using the genetic algorithm method, the model is optimized based on six design parameters such as condenser pressure, number of solar parabolic through collector rows, gas turbine and steam turbine inlet temperature, high and low pressure, high- and low-pressure pinch points. The final optimal design point of this cycle enables the overall exergy efficiency of $$36.16\%$$ and $$188.43\;\$ \;{\text{h}}^{ - 1}$$ of the total cost rate value; also, this integrated energy system provides the net electrical generation of $$5.18\;{\text{MW}}$$ and the cooling load rate of $$406.18\;{\text{KW}}$$ and generates $$2.57\;{\text{kg}}\;{\text{s}}^{ - 1}$$ of desalinated water. In this novel cycle solar energy is used for preheating the inflow of the combustion chamber. A dual pressure heat recovery exploits thermal energy of flue gas, which runs both desalination and multi-effect absorption system and circulates in simultaneous water and cooling load generation. Finally, by utilizing the genetic 1 algorithm, the optimal system is developed.

Signal processing for in situ detection of effective heat pulse probe spacing radius as the basis of a self-calibrating heat pulse probe

Abstract. A sensor comprised of an electronic circuit and a hybrid single and dual heat pulse probe was constructed and tested along with a novel signal processing procedure to determine changes in the effective dual-probe spacing radius over the time of measurement. The circuit utilized a proportional–integral–derivative (PID) controller to control heat inputs into the soil medium in lieu of a variable resistor. The system was designed for onboard signal processing and implemented USB, RS-232, and SDI-12 interfaces for machine-to-machine (M2M) exchange of data, thereby enabling heat inputs to be adjusted to soil conditions and data availability shortly after the time of experiment. Signal processing was introduced to provide a simplified single-probe model to determine thermal conductivity instead of reliance on late-time logarithmic curve fitting. Homomorphic and derivative filters were used with a dual-probe model to detect changes in the effective probe spacing radius over the time of experiment to compensate for physical changes in radius as well as model and experimental error. Theoretical constraints were developed for an efficient inverse of the exponential integral on an embedded system. Application of the signal processing to experiments on sand and peat improved the estimates of soil water content and bulk density compared to methods of curve fitting nominally used for heat pulse probe experiments. Applications of the technology may be especially useful for soil and environmental conditions under which effective changes in probe spacing radius need to be detected and compensated for over the time of experiment.

Integro-differential form of the first-order dual phase lag heat transfer equation and its numerical solution using the Control Volume Method

The start point of the dual phase lag equation (DPLE) formulation is the generalized Fourier law in which two positive constants (the relaxation and thermalization times) appear. This type of equation can be used (among others) to describe the heat conduction processes proceeding in micro-scale. Depending on the number of components in the development of the generalized Fourier law into a power series, one can obtain both the first-order DPLE and the second-order one. In this paper the first-order dual phase lag equation is considered. The primary objective of this research is the transformation of DPLE differential form to the integro-differential one supplemented by the appropriate boundary-initial conditions. The obtained form of the differential equation is much simpler and more convenient at the stage of numerical computations – the numerical algorithm based on the three-time-level scheme reduces to the two-time-level one. To find the numerical solution, the Control Volume Method is used (the heating of thin metal film subjected to a laser beam is considered). The choice of the numerical method was not accidental. The method has a simple physical interpretation ensuring the preservation of the local and global energy balances. To our knowledge, it has not been used so far in this type of tasks. In the final part of the paper the examples of numerical simulations are presented and the conclusions are formulated.

Thermo-economic analysis and multi-objective optimization of S-CO2 Brayton cycle waste heat recovery system for an ocean-going 9000 TEU container ship

Supercritical CO2 recompression Brayton cycle (S-CO2 RBC) can be used as waste heat recovery system in a ship because of the advantages of high efficiency, compact size and lower cost. This paper proposes a modified S-CO2 RBC system, namely the dual turbine-alternator-compressor (TAC) S-CO2 RBC system, which to be used to recover the waste heat from the main engine exhaust gas of an ocean-going 9000 TEU container ship. Mathematical and simulation models for the modified system are established to investigate the improvement in the performance. Parametric study is conducted to analyze the effects of key thermodynamic parameters on the system performance. The Imperialist Competitive Algorithm - based multi-objective optimization is carried out to get the modified system’s optimal operating parameters, aiming to maximize the system net power output, energetic efficiency and exergetic efficiency as well as to minimize the heat exchanger area per unit power and the levelized cost of energy. The results show that the performance of the modified system is strengthened significantly, whose highest net power output, energetic efficiency and exergy efficiency are 452.2 kW, 24.53% and 41.47%, approximately 26.58%, 16.67% and 16.90% higher than that of the S-CO2 RBC system. Compared with the S-CO2 RBC system, the modified system is more compact because its heat exchanger area per unit power decreased by 44.08%. The modified system can contribute to decreasing the ship auxiliary engine fuel consumption and the Energy Efficiency Design Index by about 1.01% and 1.02%, and improving the thermal efficiency of the ship main engine system by 3.23%. The results of this study can provide theoretical support for the application of the dual TAC S-CO2 RBC waste heat recover system on ships.

Energy Analysis of a Dual-Source Heat Pump Coupled with Phase Change Materials

Installation costs of ground heat exchangers (GHEs) make the technology based on ground-coupled heat pumps (GCHPs) less competitive than air source heat pumps for space heating and cooling in mild climates. A smart solution is the dual source heat pump (DSHP) which switches between the air and ground to reduce frosting issues and save the system against extreme temperatures affecting air-mode. This work analyses the coupling of DSHP with a flat-panel (FP) horizontal GHE (HGHE) and a mixture of sand and phase change materials (PCMs). From numerical simulations and considering the energy demand of a real building in Northern Italy, different combinations of heat pumps (HPs) and trench backfill material were compared. The results show that PCMs always improve the performance of the systems, allowing a further reduction of the size of the geothermal facility. Annual average heat flux at FP is four times higher when coupled with the DSHP system, due to the lower exploitation. Furthermore, the enhanced dual systems are able to perform well during extreme weather conditions for which a sole air source heat pump (ASHP) system would be unable either to work or perform efficiently. Thus, the DSHP and HGHE with PCMs are robust and resilient alternatives for air conditioning.

Mechanical Property Association of Dual Phase and Austempered AISI 4140 Normalized Steel

The present investigation intended to analyse the mechanical properties of medium carbon low alloy steel (AISI 4140) under dual phase heat treatment condition. Formation of dual phase, ferrite and martensite (F+M) from normalized condition followed by heating in the intercritical temperature range to form different volume fractions of ferrite and martensite alters tensile, hardness and impact strength of medium carbon steel. Effect of alloying elements in dual phase treatment will change the mechanical properties. Tensile strength and hardness of austempered steel shows higher value followed by dual phase condition. Ductility of normalized shows better as compared to as bought and dual phase, but austempered shows almost similar to normalized result. Impact strength of the austempered is excellent followed by dual phase condition. Heat treated specimen microstructures reveal the different phase’s present.

Thermo-Economic Performance of an Organic Rankine Cycle System Recovering Waste Heat Onboard an Offshore Service Vessel

Recent regulatory developments in the global maritime industry have signalled an increased emphasis on the improvement of energy efficiency onboard ships. Among the various efficiency enhancement options, recovering waste heat using the organic Rankine cycle (ORC) has been studied and identified as a promising one in many earlier studies. In this paper, a marine application of ORC for waste heat recovery will be discussed by performing the first law thermodynamic analysis based on the operating profile and machinery design data of an offshore service vessel (OSV) and defining four standard cycle configurations that include simple, recuperated, dual heat source, and with intermediate heating. The use of five hydrocarbon working fluids that are suitable for shipboard usage comprising cyclopentane, n-heptane, n-octane, methanol and ethanol are examined. The economic analysis found that annual fuel saving between 5% and 9% is possible and estimated a specific installation cost of $5000–8000 USD/kW. Among the various options, the methanol ORC in a simple cycle configuration is found to have the shortest payback time relatively balancing between annual fuel saving and total module cost. Finally, the simple cycle ORC running on methanol is further examined using the second law entropy generation analysis and it is found that the heat exchangers in the system accounted for nearly 95% of the overall entropy generation rate and further work is recommended to reduce this in the future.

Design and performance analysis of a novel Transcritical Regenerative Series Two stage Organic Rankine Cycle for dual source waste heat recovery

A Transcritical Regenerative Series Two stage Organic Rankine Cycle (TR-STORC) is proposed to improve the efficiency of existing Series Two stage ORC (STORC) architecture by combining supercritical heating in the high pressure (HP) stage and partial evaporation with regeneration in the low pressure (LP) stage. Exhaust gas and jacket water from a stationary IC engine is used as the primary and secondary heat source respectively. Using cyclopentane as working fluid, system exergy performance is analysed for a range of heat source temperatures and for different ratios of heat available between the heat sources. At lower HP evaporator pressures, lower values of vapour outlet temperatures lead to maximum power output. For a wide range of heat ratios and temperatures, TR-STORC delivers improved exergetic performance over STORC and pre-heated ORC. It is the recommended choice for all scenarios of dual source heat recovery. For the engine design point, TR-STORC delivers increased power output by up to16% and 23% than STORC and pre-heated ORC respectively. TR-STORC maintains exergetic superiority for all the working fluids investigated with maximum net power outputs exceeding STORC by15–34% and preheated ORC by 15–52%.

Experimental study on operating characteristics of a dual compensation chamber loop heat pipe in periodic acceleration fields

Systematic experiments were firstly designed and conducted to investigate the operating characteristics of a dual compensation chamber loop heat pipe (DCCLHP) under periodic acceleration conditions. A new acceleration test rig was built to generate acceleration magnitude up to 11 g. The heat load ranged from 150 W to 300 W. Three different periodic acceleration patterns, two loading modes and two acceleration directions were used to study their influence on the operating characteristics of the DCCLHP. The results demonstrated that the loop temperature could periodically oscillate with the periodic change of the acceleration. A large acceleration could lead to a high operating temperature. Configuration B could cause the lower operating temperature than configuration A for a fixed case. There were stable operating temperature difference and thermal resistance variation before and after the periodic acceleration acting for the loading mode 1. Temperature overshooting after unloading the periodic acceleration was also confirmed for the loading mode 2. Such phenomena could be explained by the change of the vapour-liquid distribution in the loop and the heat leak from the evaporator to the compensation chambers (CCs). The loop temperature oscillation with different frequency and amplitude might also occur during each periodic acceleration. For the cases of 150 W and configuration A, the acceleration effect could trigger the operating temperature exceeding 60 °C. Our work proves significant phenomena existing in the DCCLHP and presents detailed analysis, which would be of great importance for the development of new generation of loop heat pipe used in aircraft thermal management system.

이중관식 열교환기가 설치된 역방향 공기 주입 방식 무화염 연소로 내 열유동 특성에 대한 연구

이중관식 열교환기가 설치된 역방향 공기 주입 방식 무화염 연소로 내 열유동 특성에 대한 연구

Experimental and analytical study of dual compensation chamber loop heat pipe under acceleration force assisted condition

In this article, a combined experimental and theoretical study has been conducted to investigate the operating characteristics of a dual compensation chamber loop heat pipe (DCCLHP) with ammonia as the working fluid under acceleration force conditions. The DCCLHP with nickel wick consists of a cylindrical evaporator and dual compensation chambers at both ends of evaporator. In the current study, a new DCCLHP test rig is set up which can provide the acceleration up to 11 g. Two types of loading mode are utilized for applying heat load prior to acceleration. The heat load ranges from 25 W to 300 W. Comparisons of operating performance of the DCCLHP are carried out under both gravity and acceleration conditions. A novel acceleration force assisted concept is proposed to address the observed operating behavior. Experimental results show that: (i) the acceleration effect with the proposed orientation can improve the operating performance of the DCCLHP which may operate at the centrifugal force driven mode and capillary-centrifugal force co-driven mode. The operating temperature profile at different heat loads shows “/-shape” oblique line with the increase of the acceleration; (ii) the transition heat load from centrifugal force driven mode to capillary-centrifugal force co-driven mode changes with the variation of acceleration magnitude at both loading modes; (iii) the acceleration effect on the operating temperature is remarkably significant as the heat load is less than 100 W. The operating temperature under acceleration conditions is apparently lower than that under terrestrial gravity; (iv) the coupling change of the loop pressure, vapor-liquid distribution, two-phase flow and heat transfer caused by acceleration effect leads to the unique operating performance of the DCCLHP.

On the effects of increased coolant temperatures of light duty engines on waste heat recovery

In this paper, an investigation is done into the potential of increasing the coolant temperature of an engine to maximize the powertrain efficiency. The study takes a holistic approach by trying to optimise the combined engine and waste heat recovery system. The work was done experimentally on a Volvo 4-cylinder light duty diesel engine in combination with Rankine cycle simulations. For the study, the coolant temperature was swept from 80 °C to 160 °C at different operating points. It was seen that with increased coolant temperatures, the brake efficiency of the engine increased by up to 1 percentage point due to reduced heat losses. An optimum coolant temperature was observed, dependent on the operating point, for maximizing coolant recoverable power. An expansive study was done simulating 48 working fluids for a dual loop waste heat recovery system. From the working fluids simulated, cyclopentane was seen as the best for coolant waste heat recovery, whereas methanol and acetone were better for the exhaust gases. The gain in efficiency seen, was up to 5.2 percentage points, with up to 1.7 percentage points as the effect due to recovered power from the coolant.

Measurement of the Seebeck coefficient under high pressure by dual heating.

This study presents a new method for measuring the Seebeck coefficient under high pressure in a multi-anvil apparatus. The application of a dual-heating system enables precise control of the temperature difference between both ends of the sample in a high-pressure environment. Two pairs of W-Re thermocouples were employed at both ends of the sample to monitor and control the temperature difference, and independent probes were arranged to monitor the electromotive force (emf) produced by temperature oscillation at a given target temperature. The temperature difference was controlled within 1 K during the resistivity measurements to eliminate the influence of the emf owing to a sample temperature gradient. The Seebeck measurement was successfully measured from room temperature to 1400 K and was obtained by averaging the two measured values with opposite thermal gradient directions (∼20 K). Thermoelectric properties were measured on disk-shaped p-type Si wafers with two different carrier concentrations as a reference for high Seebeck coefficients. This method is effective to determine the thermoelectric power of materials under pressure.

Measurement and prediction of thermal properties of pantoa during deep-fat frying

Thermal properties of pantoa were determined during deep-fat frying in sunflower oil at 125-145°C. Thermal conductivity (k: 0.357 to 0.199 Wm -1 K -1 ), thermal diffusivity (α: 0.105x10 -6 to 0.140x10 -6 m 2 s -1 ) and volumetric specific heat (C p : 3.275 to 1.401 MJm -3 K -1 ) were measured simultaneously using dual probe heat pulse technique. Thermal conductivity and volumetric specific heat of pantoa decreased as the moisture content decreased, while thermal diffusivity increased with the decrease in moisture content. Empirical models were also developed as a function of moisture content, fat content and temperature of frying of pantoa . It was found that moisture content was inversely related to fat content during the progress of frying. The thermal properties and the developed models would be useful in the mathematical modeling of heat transfer in pantoa during DFF.

Acoustic field alteration in a 100 Hz dual acoustic driver straight tube travelling wave thermoacoustic heat pump for thermoacoustic heat transport control

A dual acoustic driver thermoacoustic heat pump was constructed to investigate the effect of acoustic field control on travelling wave thermoacoustic heat transport at a frequency of 100 Hz. The acoustic field was controlled by varying the phase difference and magnitude between the two drivers. Variation of phase difference demonstrated the change of both acoustic power flow direction and standing-travelling wave characteristics. Maximum temperature differences obtained between the ends of the regenerator were 23 °C and 19 °C when the acoustic power was flowing in the negative and positive directions, respectively. It has been shown that matching impedances on the cold and hot side of the regenerator influence the thermoacoustic heat pumping characteristics. Where monodirectional acoustic flow was observed on both sides of the regenerator, the impedance angles also coincided well. Variation of magnitude displayed a trend in which activation of an opposing acoustic driver at weaker power enhanced acoustic power flow and heat transport. A maximum temperature difference between the hot and cold sections of 23 °C is obtained when the input electric power of the opposing acoustic driver was 17% of the power of the initial acoustic driver where the impedances and impedance angles on both ends of the regenerator are matched but the acoustic field travelling wave characteristics are still sufficient for travelling wave device operation.

Performance investigation of two stage Organic Rankine Cycle (ORC) architectures using induction turbine layouts in dual source waste heat recovery

Abstract Improvement in performance of Organic Rankine Cycle (ORC) systems, particularly in the context of dual heat sources such as IC engines, leads to better return on investments. However, the choice of architecture to achieve the best performance is not evident from available literature. When two separate heat sources are present concurrently at different temperature levels with heat contents such as in IC engines, single stage pre-heated ORC and dual loop ORC are the two commonly deployed ORC architectures. In this study, two stage architectures: Series two stage ORC (STORC) and Parallel two stage ORC (PTORC) are analysed and their performance is compared against a single stage pre-heated ORC at sub-critical conditions in the utilization of high temperature (primary) exhaust gases (573–773 K) and low temperature (secondary) jacket water (353–393 K) representing IC engine waste heat conditions. Results show that STORC and PTORC are able to achieve the maximum net power output for an intermediate utilization of secondary heat source. The power output gains from two stage layouts improves significantly with a reduction in heat source temperature difference and for lower ratios of the heat available between the primary to secondary heat source. For a 2.9 MW natural gas IC engine operating at its design point, STORC delivers 8.5% more power output whereas PTORC delivers 0.3% less power output than pre-heated ORC. Compared to a dual–loop ORC, STORC presents a less complex and improved cycle architecture with a 13.1% increased power output and a 27.9% reduced heat exchanger requirements.