Comparison of Heat Transfer from Flue Gas Waste Heat in a Charcoal Kiln Using Heat Transfer Oil in a Helical Tube Heat Exchanger

This paper presents an approach that utilizes waste heat from the exhaust of Biomass Cookstoves (BCS), which is dominantly used for food grilling in tropical Asian countries, Thailand's fish grilling stoves were used as a case study. The study involves designing and comparing computationally the exergy quantities from four types of spiral heat exchangers— (H01, H02, H03, and H04) - using Computational Fluid Dynamics (CFD) within a flow rate range of 0.5-2.5 l/min with heat transfer oil as the working fluid. Subsequently, the economic feasibility was analyzed using the Net Present Value (NPV) and Internal Rate of Return (IRR) methods, and the carbon dioxide emissions to the atmosphere were evaluated across four helical coil configurations, C01, C02, C03, and C04. The results from the CFD analysis under specified conditions demonstrate that the helical heat exchanger can reclaim up to 2900W of exergy from BCS exhaust, which is transferred to water used by coffee machines for commercial use. This system can reduce electricity consumption for water heating by 38.48%, equating to a cost savings of 22,311.81 THB (621.50 USD) per year, with a maximum NPV of 20,195.49 THB (562.55 USD). The investment in upgrading BCS can be recouped within 4.6 years. On the environmental conservation front, using waste heat from BCS exhaust can also reduce carbon dioxide emissions to the atmosphere by up to 3,606.04 kg CO2e per year per stove. The findings from this analysis can help restaurant operators make informed decisions on investing in BCS improvements and aligning business operations with environmental conservation efforts.

Numerical investigation and performance enhancement of 210 MW boiler by utilization of waste heat in flue gas

Heat transfer plays a critical role in thermoelectric (TE) power generation because the higher the heattransfer rate from the hot to the cold side of the TE material, the higher is the generation of electric power. However, high heat-transfer rate is difficult to achieve compactly when the hot and/or the cold sources are maintained by a flow of gas such as waste heat from the gas exhaust of an engine or a power plant. Also, when the temperature of the hot and the cold sources differs considerably, thermal stress can create damage and thereby affect reliability and service life. In this study, computational fluid dynamics (CFD) analyses were performed to evaluate two compact gasphase heat-exchanger (HX) designs on their ability to enable high heat-transfer rates from the hot to the cold sides of the TE material with minimal thermal stress. One HX utilizes the leading portion of developing momentum and thermal boundary layers, and the other HX involves jet impingement. The CFD analyses take into account the convection heat transfer of the hot gas in the HX flow passages and the conduction heat transfer in the HX walls, the TE materials, the electrical conducting plates, and the insulation material that fills the space between the TE material, the conducting plates, and the HX walls. Both laminar and turbulent flows in the HX flow passages were investigated. When the flow is turbulent, the analysis of the gas phase is based on the ensemble-averaged continuity, Navier-Stokes, and energy equations, closed by the realizable k-e turbulence model that are integrated to the wall (i.e., wall functions were not used). The analysis of the solid phase is based on the Fourier law. Results obtained showed that the new design is useful in increasing heat-transfer rate through the TE material with minimal thermal stresses. For the HX that utilizes the leading part of the boundary-layer flow, a heat-transfer rate of 1 W/cm 2 can be achieved with reasonable pressure loss. For the HX with jet impingement, a heat-transfer rate of about 3 W/cm 2 can be achieved but the pressure loss is considerably higher.

From a practical perspective, it is essential to incorporate thermal interaction with surrounding components, as it significantly influences solid oxide fuel cell (SOFC) stack behavior. Computational fluid dynamics (CFD) analysis is widely used in the design and analysis of SOFC stacks. However, CFD simulations for the entire stack require extensive computational resources, and few studies have considered peripheral components. One approach to reducing the computational load is developing a surrogate model of an SOFC stack using proper orthogonal decomposition (POD). POD is a technique for extracting dominant eigenmodes from multidimensional data, enabling efficient simulations by reconstructing a reduced-order model using only the most significant modes. Sato et al. [1] applied POD to an unsteady electrochemical potential analysis of an SOFC and developed a surrogate model. In our previous study [2], a detailed three-dimensional CFD analysis of an SOFC stack was conducted, and a surrogate model was developed utilizing POD [3] based on the results. This surrogate model provides computational results equivalent to full CFD analysis while significantly reducing computation time. In this study, a method for simulating the thermal interactions between the stack and peripheral components such as heat exchangers and reformers is developed using this approach within a CFD framework.The analysis object is a system in which an anode-supported planar SOFC stack is adjacent to a planar heat exchanger, with both components exhibiting thermal interactions, as shown in Figure 1. The heat exchanger operates in a counter-flow configuration, where air is supplied from the top, heated, and then directed into the air inlet manifold of the stack. In contrast, the hot post-reactor air from the stack enters from the bottom of the heat exchanger and is discharged from the top. The surface highlighted in red in Figure 1(b) is in direct contact with the stack. The stack consists of 21 cells, each comprising a Ni-YSZ anode layer, a YSZ electrolyte layer, and an LSCF cathode layer, as illustrated in Figure 1(d). Each cell has a square shape with an active area of 10 × 10 cm2.A CFD simulation was performed under different air supply temperatures for the heat exchanger and varying SOFC stack voltages, and based on the obtained data such as temperature distribution (see Figure 2(a)), a surrogate model of the SOFC stack was developed using POD [3]. The region enclosed by the dotted line in Figure 2(a) corresponds to the area modeled by the surrogate model. Figure 2(b) shows the schematic view of the coupled analysis, in which the heat exchanger is solved using CFD, while the SOFC stack is computed with a surrogate model. Coupled analysis provided the temperature distribution in the heat exchanger (see Figure 2(c)), temperature distribution at the electrode surface of the SOFC stack (see Figure 2(d)), and current density distribution (see Figure 2(e)). While a full CFD simulation of the entire SOFC stack and heat exchanger required approximately 10 hours to complete, the proposed surrogate model approach achieves convergence in under one minute, demonstrating a substantial reduction in computational time.Overall, a method for efficiently analyzing thermal interactions between an SOFC stack and surrounding components by coupling a surrogate model with CFD analysis. While this study focused on a heat exchanger as the surrounding component, the proposed method is applicable to multiple peripheral elements, including reformers. Acknowledgement This research was conducted as part of a collaborative project funded by the Daigas Group. We extend our gratitude to Professor Kenjiro Terada (Tohoku University), Associate Professor Mayu Muramatsu (Keio University), and Dr. Masami Sato (Mechanical Design Co., Ltd.) for their guidance and advice on surrogate modeling.

An economic analysis of waste heat recovery and utilization in data centers considering environmental benefits

This study is part of a broader study on a novel method for harvesting algae by evaporation, and it investigated the feasibility of heating algal biomass using low-grade waste heat in a heat exchanger. Computational fluid dynamic (CFD) analysis was performed with ansysfluent, and the results were verified with experiments. The results of CFD analysis showed the overall heat transfer coefficient increased by 4, 13, and 100% as inlet gas temperature increased from 150 to 245 °C, liquid mass flow rate increased from 1.82 to 9.1 g/s, and gas mass flow increased from 2.2 to 13.2 g/s, respectively. It was also observed the overall heat transfer coefficient was not significantly affected with variations of properties of the liquid (thermal conductivity, density, and viscosity), thermal conductivity of the tube wall, and thickness of the tube banks, but it was sensitive to thermal conductivity of the gas. The experimental data were analyzed with logarithmic mean temperature difference (LMTD), number of transfer units (NTU), and Nusselt number correlation methods. There was an excellent agreement between the overall heat transfer coefficient calculated with the LMTD and NTU methods. The coefficients calculated with the LMTD method and Nusselt number correlation exhibited slight variations. This is likely because the LMTD is a theoretical method covering all experimental conditions and material properties, but Nusselt number correlation is an empirical approach based on correlations. The overall heat transfer coefficient calculated by CFD was slightly overestimated because the CFD analysis assumed complete insulation.

Theoretical and experimental study on total heat recovery of condensing gas boiler flue gas by gas engine-driven compression heat pump

Advanced exergy analysis for Organic Rankine Cycle-based layout to recover waste heat of flue gas

This paper presents the preliminary experimental results of a liquid desiccant cooling system driven by the flue gas waste heat of a biomass boiler. The desiccant cooling system is mainly composed of a regenerator, a dehumidifier and an evaporative cooler. The flue gas waste heat is applied to the regenerator to regenerate the desiccant solution. The environmentally friendly liquid desiccant potassium formate (HCOOK) solution is used in the dehumidifier for air dehumidification due to its less corrosion, lower cost, lower density and lower viscosity. A cross-flow heat and mass exchanger for indirect evaporative cooling is adopted in the evaporative cooler to ensure that product air meets the indoor air quality and thermal comfort standard. The desiccant cooling system operated in Autumn days in Nottingham was found to be able to decrease the air temperature by 4°C and reach a cooling capacity of up to 2381 W. Moreover, the dehumidifier is able to reduce the relative humidity of the humid air by 13%. The biomass boiler's flue gas waste heat extracted and supplied to the regenerator was found to be 554 W, which is insufficient to regenerate the dilute liquid desiccant solution under current experimental conditions. To obtain sufficient heat to regenerate the liquid desiccant, the existing first-of-its-kind concentric helical coil heat exchanger extracting the waste heat of the boiler needs to be redesigned, and, in particular, the concentric helical coils of the heat exchanger need to be placed inside the chimney to enhance the waste heat extraction.

Summary Computing the internal rate of return(IRR) of an investmentefficiently and under a wide range of conditions is a problem ofteninsufficiently addressed in finance literature. This paper reviewsarticles and books that deal with the IRR. The term is defined, andexamples are given. Problems that arise in computing and using the IRR arediscussed. Finally, a program is presented that computes and analyzes theIRR efficiently for a wide range of cash flows. Introduction The IRR is a widely used criterion for measuringinherent project acceptability and for comparing and rankingdifferent projects. The literature points out a number ofdefects, some of which remain controversial. This paperreviews some of the literature on the subject, particularly papers that deal with the IRR on a quantitative basis, and presents a computer program that calculates ordescribes the IRR under a wide range of conditions. Definitions of the IRR The simplest definition of the IRR. as stated by Jean, is the interest rate that makes the net present value (NPV)of a project equal to zero. If a curve of NPV vs. discountrate (DR) is drawn, the IRR ideally is the intersection ofthis curve with the x axis, which may never occur or may occur one or more times. Several other definitions of the IRR exist. Cissell andCissell state that the IRR is the rate that makes theinflows and outflows equal at a certain point in time. Thisis essentially the same as the first definition because a zeroNPV implies zero value at all times. Renwick has two definitions that help to clarify theway the IRR works. The IRR is the equivalent of therequired rate of interest on a savings account, with positivecash flows viewed as withdrawals and negative cash flowsviewed as deposits, so that the balance is zero at the endof the project. Alternatively, the IRR can be viewed asdenoting total profits expressed as a percent of totalinvestment outlay, as opposed to the NPV, which measurestotal dollars of net profit directly. Bernhard defines the IRR with an equation. First, to define the initial investment (PO, which is usuallynegative) and succeeding cash flows (PI to P, for Years1 through n), the IRR is the interest state such that ..........................................(1) He refers to this as the simple IRR. where a moregeneral IRR is the set of IRR's that solve the following equation: ..........................................(2) This allows interest rates to vary from year to year as inreal life but produces a measure that is very difficult tocompute or to use. The simple IRR is a special case ofthe general one, where all the IRR's are equal. Someinteresting consequences of this approach are discussedlater. Bernhard also points out that the literature usesmany alternative terms for the IRR, including yield, marginal efficiency of capital, profitability index, interest rateof return, and the project rate of return by the discounted-cash-flow, investor's, or scientific method. Computation of the IRR Literature on the actual means of computing the IRR isquite varied. A good portion of the literature states thatthe IRR is usually found by trial and error. Vichaspresents a technique based on interpolation of financial-table values that is valid but of limited accuracy. In fact, much better techniques are available. Eq. 1 can be rewritten as a polynomial in x by makingthe substitution x = 1 / (1 + IRR) as follows: ..........................................(3) Finding IRR = (1/x) - I corresponds to finding acceptablereal roots to Eq. Some authors have restricted therange of acceptable IRR's to positive real numbers, making the range of x 0 is lesser than x less than 1. Other authorsallow consideration of negative IRR's down to 1 and work on the range 0 less than x less than oo. It is clear that projects with negative IRR's are not normally acceptable. but externalconsiderations and ranking requirements could mean suchprojects need to be considered. P. 577^

In this paper, an improved system to efficiently utilize the low-temperature waste heat from the flue gas of coal-fired power plants is proposed based on heat cascade theory. The essence of the proposed system is that the waste heat of exhausted flue gas is not only used to preheat air for assisting coal combustion as usual but also to heat up feedwater and for low-pressure steam extraction. Air preheating is performed by both the exhaust flue gas in the boiler island and the low-pressure steam extraction in the turbine island; thereby part of the flue gas heat originally exchanged in the air preheater can be saved and introduced to heat the feedwater and the high-temperature condensed water. Consequently, part of the high-pressure steam is saved for further expansion in the steam turbine, which results in additional net power output. Based on the design data of a typical 1000 MW ultra-supercritical coal-fired power plant in China, an in-depth analysis of the energy-saving characteristics of the improved waste heat utilization system (WHUS) and the conventional WHUS is conducted. When the improved WHUS is adopted in a typical 1000 MW unit, net power output increases by 19.51 MW, exergy efficiency improves to 45.46%, and net annual revenue reaches USD 4.741 million while for the conventional WHUS, these performance parameters are 5.83 MW, 44.80% and USD 1.244 million, respectively. The research described in this paper provides a feasible energy-saving option for coal-fired power plants.

The objective of the present work is to study the behavior of a helical tube and shell heat exchanger, for the cooling of the wort in the process of making craft beer with cold water, through the methodology of computational fluid dynamics (CFD) by finite volume models for heat exchanger modeling. This by using the ANSYS Fluent software, which allows to understand the behavior of the fluid through equations that describe their movement and behavior, using numerical methods and computational techniques. In the mesh convergence, two methods were used, orthogonality and obliquity, with which it was confirmed that the meshing is ideal in the simulations that were carried out. For the simulation, the k-epsilon turbulence model and the energy model were used. Through various simulations, it was obtained that by varying the mass flow, better results are reducing the outlet temperature, with a variation of 15.16 °C, while varying the inlet temperature of the water, there is just a variation from 2.71 °C to 0.01 °C. Therefore, a significant improvement in the performance of the heat exchanger was found. In the same way, it was confirmed that the number of spikes in the heat exchanger is adequate, since the outlet temperature would not be reached with less spikes.

To improve the economy and safety of the power plant, the waste heat and water co-recovery system with two-stage flue gas coolers (FGC) was put forward. Two-stage FGCs were equipped between the induced draft fan (IDF) and the wet limestone flue gas desulfurization (WFGD), the WFGD and the wet stack. To ensure safety, Each stage flue gas cooler consisted of two independent heat exchangers (hot end heat exchanger named FGC-H, cold end heat exchanger named FGC-C) with a coupling fluid which is circulated by a pump, and this method named fluid coupled indirect heat exchange (FCHE) technology. Due to the temperature of flue gas through two FGC-Hs being below the acid and/or water vapor dew points, two FGC-Hs adopted the plastic heat exchanger to prevent the sulfur attack. Then, the impact of the waste heat and water co-recovery system on the dynamic behavior and the economic performance of the studied power plant have been verified by simulation tests on the full-scale simulator of the studied 330 MW coal-fired power plant. The results show that the waste heat and water co-recovery system could effectively improve the economy and environmental performance of the studied power plant. It is an effective way to realize further flue gas waste heat utilization.

Purpose – It is well known that internal rate of return (IRR) and net present value (NPV) rankings of mutually exclusive investments are sometimes inconsistent. This inconsistency, when it occurs, requires decision makers to choose between the two ranking methods. The purpose of this paper is to deduce sufficient conditions for consistent IRR and NPV investment rankings of mutually exclusive investments. Design/methodology/approach – Deductive reasoning is used to obtain the sufficient conditions required for consistent rankings of mutually exclusive investments. Findings – There are different sufficient conditions (methods) that can be used to resolve inconsistent IRR and NPV rankings. However, the different methods do not necessarily produce the same consistent rankings. In particular, different size adjustment methods and reinvestment rate assumptions can produce different IRR and NPV consistent rankings. This paper suggests the appropriate criteria for selecting a particular method for ranking mutually exclusive investments. Research limitations/implications – Like all deduced models, the results apply only to the set of assumptions and preconditions adopted in the model. Furthermore, the application is to ranking mutually exclusive investments. Practical implications – There is probably no other issue in the capital budgeting literature that has generated more attention and debate than the consistency (or lack thereof) between IRR and NPV rankings. This paper summarizes conditions that can be followed to resolve the conflict which should have near universal interest to those working in the capital budging area. This paper offers alternative methods for obtaining consistent IRR and NPV rankings which can be used to improve investment ranking decisions. The particular method used should depend on the decision environment. Guides for choosing the appropriate ranking method are described in the paper. Social implications – Significant decisions, projects, and investments are evaluated using either IRR or NPV methods. This paper shows that existing evaluation methods can lead to sub-optimal investment choices and provides an improved framework that facilitates better investment choices. Lacking an understanding of the sufficient conditions for IRR and NPV consistency – means that resource allocations have been made to investments and projects that are not optimal. Originality/value – To the best of the authors’ knowledge, the results are this paper have not been published nor are they available elsewhere. That said, this paper builds on important earlier work which is carefully cited and credited.

A computer based iterative solution for accurate estimation of heat transfer coefficients in a helical tube heat exchanger