Secondary Heat Exchanger Research Articles

Validated model of a thermoelectric heat pump clothes dryer using secondary pumped loops

The energy associated with clothes drying makes up 4% of the total residential electrical energy consumption in the US. The cost is high since most clothes dryers use electric resistance heating which is inexpensive but also energy inefficient. State-of-the-art vapor-compression heat pump clothes dryers offer significant energy savings but have limited market penetration in the US. In this work, a new configuration of clothes dryer was studied that utilizes a solid-state thermoelectric heat pump with pumped secondary water loops and conventional fin-and-tube water-to-air heat exchangers. Experimental results are presented for the thermoelectric dryer prototype with a combined energy factor of 6.89 lbBDW/kWh (specific moisture extraction rate of 1.71 kgw/kWh) and a dry time of 84 min for a standard load size of 8.45 lb (3.83 kg) with 57.5% starting moisture content. This is a 85% energy efficiency improvement over baseline electric resistance dryers. The efficiency and drying time results achieved are similar to vapor compression heat pump dryers. Compared to previous air-based thermoelectric clothes dryers, the energy efficiency has been increased by 6%, but drying time has been reduced by as much as 47% using secondary pumped loops and separate heat exchangers, which represents a significant advancement in the technology. In addition to the experimental prototype, a model was also developed to study the performance. The model was validated against experimental prototype data and used to identify the range of performance (dry time and efficiency) that could be expected of the design.

Introducing a Novel Air Handling Unit Based on Focusing on Turbulent Exhaust Air Energy-Exergy Recovery Potential

Abstract A novel air handling unit (AHU) aimed at reducing energy consumption was introduced in this study. In the proposed novel AHU, the heating coil is completely removed, and therefore, no heating coil energy demand is needed. The novel AHU used primary energy recovery as well as secondary one to utilize the return air energy and exergy. Through the first energy recovery unit, the return air exergy was recovered, while in the secondary heat exchanger, return air energy was recycled. Results showed that using the novel AHU leads to a reduction in energy consumption as well as the exergy losses. Three climate zones of A, B, and C were selected to assess the novel AHU performance. From the first law viewpoint, at zone B, using novel AHU has priority over other zones, while in the second law analysis, utilizing the novel AHU at zones B and C is more beneficial. Based on the first law analysis, owing to using novel AHU, energy consumption reduced up to 55.2% at Penang climate zone. Second law analysis revealed that utilizing the novel AHU decreased the irreversibility up to 51.4% in the Vancouver climate region.

Heat recovery and metal oxide particles trapping in a power generation system using a swirl-stabilized metal-air burner

In order to tackle future challenges concerning zero greenhouse gases emissions, an innovative power generation system was designed and analyzed. It included a swirled-stabilized metal-air burner confined in a water-cooled combustion chamber, a secondary heat exchanger and a particle filtration system leading to a unique system of this kind. Magnesium particles in the range 50–70 µm were used as metal fuel. The effect of the swirl intensity was evaluated first on the flame position within the combustion chamber. As expected, the flame was stabilized closer to the burner head with the high swirl number than with the low one. To reach optimal heat to-mechanical conversion efficiency, an analysis of the heat recovery in the power generation system was performed. Experiments were conducted with a total chemical power ranging from 6 kW to 11 kW. Eighty percent of the power released by combustion were recovered in the power generation system and 50% in the combustion chamber. Ninety-eight percent of the magnesium oxide produced by combustion were trapped inside the system. Laser granulometry showed a number distribution for the metal oxide particles around 500 nm. Untrapped particles were measured by a Pegasor Particle Sensor (PPS), which was previously calibrated by comparison with measurements of the total suspended particles (TSP). Complementary TEM analysis confirmed that the metal oxide particles were aggregates of elementary submicron MgO cubic particles (10–1000 nm).

Comparative study on the annual performance between loop thermosyphon solar water heating system and conventional solar water heating system

Loop thermosyphon (LT) is usually introduced to overcome the freezing and corrosion problems associated with the conventional solar water heating (SWH) system. Compared with the conventional SWH system, the LT-SWH system possesses a lower nighttime heat loss because of the thermal diode property of loop thermpsyphon but bigger daytime heat loss because of the secondary heat exchange. However, the effect of above interaction to the system performance is rarely reported based on long-term running. In this study, based on the typical meteorological year data of Fuzhou city, annual performances of above two systems, including the effective number of supplying days, effective heat gain and nighttime heat loss, are comparatively analyzed under two different operational modes. Variations of above mentioned variables with the increment in the set temperature are discussed. The results indicate that, under the discontinuous heating mode, the effective numbers of supplying days of SWH system and LT-SWH system are 139 and 153, respectively. While the numbers of days are respectively 168 and 173 under the continuous heating mode. The SWH system possesses an expected bigger nighttime heat loss ratio with an average annual value of 15.07% corresponding to 6.15% for the LT-SWH system. Particularly, for the LT-SWH system, the different relative magnitudes of heat loss coefficients functioning at different times leads to a smaller temperature drop at night and also a smaller temperature rise at the subsequent day. It generates an unanticipated results that corresponds to the same month from November to April, the two systems have the approximate effective heat gain. The set temperature significantly influences the relative magnitudes of annual effective number of supplying days and annual effective heat gain, the superiority of LT-SWH system gradually diminishes and even reverses with the increment in the set temperature. The bigger daytime heat loss dominating the dominance is responsible for that transition. Combining with a longer static payback period, it is conditional to substitute the conventional SWH system with the LT-SWH system, especially when the water temperature on demand is high.

Simulation of an aircraft environmental control system

The environmental control system of a civil aircraft is a major driver of maintenance. Legacy systems, such as those on the Boeing 737, are particularly at risk, as they are not instrumented for health management. These systems degrade in operation and allow compensation within their operation for degrading components, until severe degradation or failure results. The required maintenance is then both costly and disruptive. The goal of this research is to produce a simulation environment that can model the aircraft environmental control system, in order that analysis for sensor placement and algorithms can be performed without extensive, and expensive, testing. A simulation framework called SESAC – Simscape Environmental Control System Simulation under All Conditions – has been proposed and implemented. It offers a library of components that can be assembled into specific aircraft environmental control system simulation configurations. It is capable of simulating the health state indicating parameters at sub-system and component levels under a wide-range of aircraft operating scenarios. The developed framework has been successfully implemented to simulate a Boeing 737-800 passenger air conditioner. Its verification and validation has been carried out against the actual data corresponding to a Boeing 737-800 passenger air conditioner operating at two different cruise operating points. An extensive comparison of the simulation is presented against the data for all the passenger air conditioner components. The overall acquired results suggest that changes in the aircraft ambient conditions can have a noticeable impact on the demanded passenger air conditioner outlet temperature, and a substantial impact on the heat transfer in the primary and secondary heat exchangers. The reported simulation capability serves as a first step towards formulating an environmental control system fault simulation and diagnostic solution.

Численное моделирование для анализа параметров эффективности нового типа плоского солнечного коллектора

This article discusses a new design concept for a flat solar collector using flexible tubes. A flat-plate solar collector is designed to run cold water into solar heating systems instead of using expensive antifreeze fluids and to remove secondary media. The development of this type of solar thermal collectors will reduce the installation costs of traditional solar thermal systems without the need for secondary heat exchangers. We determined the main parameters of the heat capacity of a flat solar collector and computed the temperature profile of the absorber plate of a flat-plate solar collector with an inlet temperature of 30 °C. In contrast to a tube coil type temperature loop, it was found that the maximum temperature of the collector plate under the same inlet temperature conditions is much lower than that of the former. Using the CFD (Computational Fluid Dynamics) ANSYS FLUENT 19.0 commercial software package, a phase design was developed based on predictions of the reservoir thermal characteristics and the equivalent heat transfer coefficient of the absorber plates. Experimental test variables for a flat-plate solar collector were also calculated; these were higher with incident solar radiation than with ambient temperature.

Reducing AHU energy consumption by a new layout of using heat recovery units

In this study, a new design for energy recovery from the return air has been introduced to improve the air handling unit (AHU) performance through the energetic analysis. The main objective is defined as the reduction in cooling and heating coils energy demand. In the novel AHU, the coldness from the exhaust air is transferred to the fresh air through the primary heat exchanger to reduce the cooling coil energy usage, while in the secondary heat exchanger, the warmness from the return air is recovered to the outlet cold air of the cooling coil to reduce the heating coil energy usage. Results showed that using air-to-air heat exchanger in hot and dry climate regions, the total energy consumption decreased up to 26.38%, which in turn increased the first law efficiency up to 35.84%, while in hot and humid climate these figures are 13.11% and 10.57%, respectively. It is concluded that the effect of using the air-to-air heat exchangers in hot and dry climate has priority over the hot and humid one.

Pretest in forced circulation molten salt heat transfer loop: Studies with thermia‐B

AbstractMolten salts have potential application as an efficient heat transfer medium in a primary and secondary heat exchanger in high temperature next‐generation nuclear power plant. Thermal hydraulic studies are vital for reliable and cost‐effective design of the nuclear power plant. Therefore heat transfer study of molten salts will play a vital role in this area. In this work, an experimental system was designed to study thermal hydraulics of the molten salt system up to 700°C. This work describes the pretest results of the experimental facility for extremely corrosive molten fluoride salts with a simulant thermia‐B as the working fluid. In the present work, the details of the system are discussed and thermal‐hydraulic data for heat transfer fluid thermia‐B has been presented. Experiments were carried out at Reynolds number in the range of 4500 to 40 500 and Prandtl number in the range of 34 to 144. Effect of Reynolds number, melting tank temperature, and heat input to test section on forced convective heat transfer was studied under turbulent conditions. Comparison of the experimental data with different empirical correlations has been presented.

Passive decay heat removal system design for the integral inherent safety light water reactor (I2S-LWR)

The Integral, Inherently Safe Light Water Reactor (I2S-LWR) is an innovative Pressurized Water Reactor (PWR) concept being developed by a multi-institutional team led by Georgia Tech and in collaboration with Westinghouse, under the Department of Energy’s Nuclear Energy University Programs Integrated Research Projects (DOE NEUP IRP). The University of Michigan leads the design of the thermal-hydraulic and passive safety systems, in collaboration with Westinghouse and Bringham Young University. The I2S-LWR features an integral primary system configuration and is more conducive to the implementation of inherent safety features by eliminating potential accidents. In this paper, a novel passive Decay Heat Removal System (DHRS), is presented, consisting of a primary loop, an intermediate loop and a cooling tower loop. This passive system is designed to remove the I2S-LWR decay heat in the case of emergency heat removal transients, without the need for external power or operator action. The proposed DHR uses atmosphere as ultimate heat sink, to achieve indefinite decay heat removal. In this paper, firstly, the design of primary and secondary DHRS heat exchangers is optimized. Then the DHR heat removal characteristics are studied using the best-estimate thermal hydraulic code RELAP5. In addition, CFD simulations have been performed in order to investigate the DRHS helical coil primary heat exchanger performance with different coil pipe arrangements, and optimize its design. The performance of the proposed DHRS concept is investigated in case of a Station Black-Out (SBO) scenario. Operation of two, three and four DHRS trains is studied respectively. The results show that three out of four DHRS trains are sufficient to indefinitely remove the core decay heat successfully during a SBO, and keep the reactor in a safe state without the need of any other auxiliary active system.

Thermal performance analysis of a new refrigerant-heated radiator coupled with air-source heat pump heating system

Air-source heat pump (ASHP) is considered to be one of the most energy conservation heating system in the areas without district heating. To improve the performance of the ASHP heating system, a new type of refrigerant-heated radiator (RHR) is proposed. As a new direct-condensation terminal, it avoids the secondary heat exchange and is conducive to reduce the condensing temperature and heat loss. Experiments are conducted to investigate the temperature and operating characteristics of the heating system with the new radiator, as well as the thermal performance and system efficiency during the heating period. The results indicate that the radiator has favorable thermal performance with the heat flux varies from 89.2 W/m2 to 211.4 W/m2 during the testing period. Heat storage material is employed in the radiator to maintain the stability of indoor thermal environment during the defrosting process, and it can provide the heat of 750.9–1699.6 kJ. The convective heat transfer coefficient of the RHR was regressed and the coefficient of performance (COP) of the new system could be as high as 3.5 during the tests. Meanwhile, the ASHP heating system with RHR is superior in the indoor thermal comfort with the reasonable indoor PMV and lower vertical temperature gradient. It is demonstrated that the refrigerant-heated radiator matches well with the heat pump heating system, and can effectively improve the thermal performance and indoor thermal environment, as well as it has significant effects on the application of ASHP in the severe cold areas.

Techno-economic and environmental analyses of a biomass based system employing solid oxide fuel cell, externally fired gas turbine and organic Rankine cycle

This paper presents a techno-economic and environmental assessment of a biomass gasification based power plant integrating a solid oxide fuel cell module, an externally fired gas turbine and an organic Rankine cycle. The proposed biomass based system is nonparallel with the conventional biomass based power generation system because of biomass gasification, solid oxide fuel cell, externally fired gas turbine, organic Rankine cycle have been combined in a single system. The thermodynamic and economic performances of the plant have been investigated under the varying operating and design parameters. The maximum energetic and exergetic efficiencies of the system are computed to be 49.47% and 44.2%, respectively. Exergy analysis predicts that the biomass gasifier unit contributes highest amount of exergy destruction (38.91%) in terms of total exergy destruction of the system, followed by solid oxide fuel cell (21.24%) and secondary heat exchanger (13.11%). Economic analysis forecasts that the minimum levelized unit cost of electricity would be 0.086 $/kWh. A performance comparison with other conventional biomass based power generation systems shows that the proposed system exhibits better efficiency and cost of electricity than others. Environmental analysis predicts that the maximum CO2 emission reduction potential is computed to be 3564 t CO2/year compared to the fossil fuel based power plant.

System design of aircraft air conditioning system (2<sup>nd</sup> Report: Study on the simulation modelling of the cross flow heat exchanger)

The purpose of this study is to develop an analytical model of cross-flow heat exchangers with offset strip fins which are usually equipped in the aircraft air conditioning system (so called the environmental control system, ECS). The ECS mainly consists of four cross-flow heat exchanges, i.e., a primary heat exchanger, a secondary heat exchanger, a reheater and a condenser. Because of the special requirements of the design for the aircraft, the primary and secondary heat exchangers are set adjoiningly; the reheater and the condenser are also set adjoingly. Therefore, in both the pairs, the effect of the temperature profile of the upstream component (the secondary heat exchanger or the reheater) on those of the downstream component (the primary heat exchanger or the condenser) should be taken into account for precise prediction of the system. To this end, a core element model was newly proposed in this study. In addition to the effect of temperature profile, phase changes (condensation and evaporation) of water included in the humid air simultaneously occur except for the primary heat exchanger. Regarding these phenomena, the method of sensible heat fraction (SHF) to convert the latent heat into the equivalent sensible heat was introduced, and the global and local SHF models were examined by comparison with the experiments. The prediction by these models were found to agree well with the actual performance of the ECS operations.

Design and manufacturing of travelling wave thermo-acoustic engine with varying regenerator length

ABSTRACT Thermo-acoustic engines are devices suitable to convert heat energy into acoustic energy and vice versa. In this paper, travelling wave thermo-acoustic engine was designed and fabricated for the operating conditions of 30 bar mean pressure of working fluid (Air, Helium, Hydrogen, Nitrogen) and 500°C hot side temperature. The regenerator was made up of the can(s) of stainless steel SA-347and can be adjusted to achieve the required length. The access to change wire mesh size and its length enables to reduce the test set-up time and to enhance flexibility during experimentation. The modified secondary cold heat exchanger was developed for effective heat extraction from the working fluid and the effect of modified regenerator on the intensity of the thermo-acoustic power was also addressed. The present study shares the suitable alternatives for material selection, design considerations and preliminary estimation of heat exchangers at the operating temperature and pressure. It provides initial dimensions and enables to make a prototype.

Passive Control and Enhancement of Low Reynolds Number Slot Jets Through the Use of Tabs and Chevrons

Liquid microjets are emerging as candidate primary or secondary heat exchangers for the thermal management of next generation photonic integrated circuits (PICs). However, the thermal and hydrodynamic behavior of confined, low Reynolds number liquid slot jets is not yet comprehensively understood. This investigation experimentally examined jet outlet modifications—in the form of tabs and chevrons—as techniques for passive control and enhancement of single-phase convective heat transfer. The investigation was carried out for slot jets in the laminar flow regime, with a Reynolds number range, based on the slot jet hydraulic diameter, of 100–500. A slot jet with an aspect ratio of 4 and a fixed confinement height to hydraulic diameter ratio (H/Dh) of 1 was considered. The local surface heat transfer and velocity field characteristics were measured using infrared (IR) thermography and particle image velocimetry (PIV) techniques. It was found that increases in area-averaged Nusselt number of up to 29% compared to the baseline case could be achieved without incurring additional hydrodynamic losses. It was also determined that the location and magnitude of Nusselt number and velocity peaks within the slot jet stagnation region could be passively controlled and enhanced through the application of outlet tabs of varying geometries and locations.

Dynamic modeling of AP1000 steam generator for control system design and simulation

A lumped parameter dynamic model for AP1000 U-tube steam generator (UTSG) is developed based upon the fundamental conservation of fluid mass, energy, and momentum. The steam generator model consists of 15 lumps with the effective secondary heat exchange region divided into a subcooled heat transfer region and a boiling heat transfer region with a dynamic boundary. Moreover, a linear Takagi-Sugeno (TS) model for the steam generator is also proposed using multiple model approach, composed of several locally accurate linear models. The linear TS model can describe the global nonlinear steam generator system with some degree accuracy. In MATLAB/Simulink environment, six types of typical operational transients are simulated by both the linear and nonlinear models using the results obtained from the CENTS as the inputs to the proposed models. Under the same model inputs, the comparison of simulation results obtained by proposed models and CENTS shows a good agreement in terms of the changing trends. In addition, the results also demonstrate that the TS model not only has a satisfactory precision but also at least a five times faster running speed than the nonlinear model, which makes it easy to be applied to the design and optimization of feedwater control system.

Characteristics of spent coffee ground as a fuel and combustion test in a small boiler (6.5 kW)

Spent Coffee Ground is a residue of coffee drink mainly used at a coffee shop. Spent coffee ground is used as an odor removal, manure in flowerpot and so on. However most of spent coffee ground is discarded as garbage. In this study, we investigated characteristics of spent coffee ground as a fuel and combustion characteristics in a small boiler system (6.5 kW based on input lower heating value), such as CO, NOx, O2 and heating characteristic of heating boiler. Drying of spent coffee ground in the open air condition takes less than 6 days in case of height of 11 mm. More than 96% of spend coffee ground is between 100 and 500 μm in particle size. Lower heating value of spent coffee ground used as fuel is about 18.8 MJ/kg (4500 kcal/kg at water content 10%). Combustion chamber of the boiler is a crucible type with primary and secondary air supply and heat exchanger is one through type. Spent coffee ground consumption as a fuel of the boiler is about 1.17 kg/hr. O2 concentration of the flue gas of the boiler is about 17.8% which is higher than a commercial domestic gas boiler or a domestic wood pellet boiler. CO and NOx concentration are 643 and 163 ppm respectively.

Thermal Performances of Two Stage Molten Salt Steam Generator

Abstract Thermal performances of two stage molten salt steam generator were experimentally investigated in this article. The two stage system consisted of primary U shape heat exchanger and secondary shell and tube heat exchanger, and its overall heat transfer coefficient, steam generation rate and thermal efficiency were further analyzed under different molten salt flow rates and water flow rates. According to the experimental results, the overall heat transfer coefficients of the primary and secondary heat exchanger both increase as the molten salt flow rising. As the water flow rate increases, the overall heat transfer coefficient of the primary heat exchanger first increases and then decreases, while that of the secondary heat exchanger gradually increases. As the molten salt flow rate and water flow rate increase, the steam generation rate and the thermal efficiency of the secondary heat exchanger both increase, while the thermal efficiencies of the primary heat exchanger and the whole system first increase, approaching their maximums with optimal molten salt flow rate and water flow rate respectively, and then begin to drop.

Study of Coil Heat Exchanger of Mechatronic Sample Conditioning System

The heat exchanger is the main part of mechatronic sample conditioning system. Static and dynamic characteristics of heat exchanger influence on the accuracy of sample temperature maintaining. Adjustable parameter of the heat exchanger is the final sample temperature; the control factor is cooling water flow rate. The inlet sample temperature, the inlet cooling water temperature and the sample flow rate can be attributed to disturbing factors. To ensure the efficient operation of sampling system is necessary to know of heat exchanger characteristics when the control and disturbing factor are present. In present work, secondary countercurrent coil heat exchanger with core tube is studied. On the basis of 30 experiments semi-empirical correlation for prediction of overall heat transfer coefficient is proposed. Temperature transient response is investigated theoretically and experimentally when inlet sample temperature is subjected to sudden change. The dynamic behavior is approximated by aperiodic link with time delay link. The obtained for heat exchanger dynamic dependences can be used in the design of mehatronic sample conditioning system, operating at steady and transient state, in the choice of the law of the controlling sample temperature and the algorithm of diagnosing deposits on the surface of the coil.

Control of Advanced Reactor-Coupled Heat Exchanger System: Incorporation of Reactor Dynamics in System Response to Load Disturbances

Abstract Alternative control schemes for an Advanced High Temperature Reactor system consisting of a reactor, an intermediate heat exchanger, and a secondary heat exchanger (SHX) are presented in this paper. One scheme is designed to control the cold outlet temperature of the SHX (Tco) and the hot outlet temperature of the intermediate heat exchanger (Tho2) by manipulating the hot-side flow rates of the heat exchangers (Fh/Fh2) responding to the flow rate and temperature disturbances. The flow rate disturbances typically require a larger manipulation of the flow rates than temperature disturbances. An alternate strategy examines the control of the cold outlet temperature of the SHX (Tco) only, since this temperature provides the driving force for energy production in the power conversion unit or the process application. The control can be achieved by three options: (1) flow rate manipulation; (2) reactor power manipulation; or (3) a combination of the two. The first option has a quicker response but requires a large flow rate change. The second option is the slowest but does not involve any change in the flow rates of streams. The third option appears preferable as it has an intermediate response time and requires only a minimal flow rate change.

Design study and cost assessment of straight, zigzag, S-shape, and OSF PCHEs for a FLiNaK–SCO2 Secondary Heat Exchanger in FHRs

This study focused on designing a cost-effective heat exchanger for a 20-MW FLiNaK–SCO2 Secondary Heat Exchanger in Fluoride salt-cooled High-temperature Reactors. Specific Printed Circuit Heat Exchanger geometries were investigated for those cases where Fanning factor and Nusselt number correlations were available. Straight, S-shape, Offset Strip Fin, and zigzag 52° channels were considered for the SCO2 side while straight, zigzag 15°, rectangle OSF 7.565mm, and rectangle OSF 2.40mm channels were considered for the FLiNaK side. Thermal-hydraulics, mechanical aspects, and corrosion rate were taken into account. A cost analysis was performed to combine the effects of heat transfer performance and pressure drop in heat exchangers. Single banking and double banking were also considered. Finally, the best PCHE channel configurations on SCO2 and FLiNaK sides were proposed.