Heat Exchanger Design Methods Research Articles

연소시스템 화석연료 사용량 저감을 위한 잠열에너지저장 기술동향 연구: Part II 상변화물질의 열전달 특성과 열교환기 설계유형, 실증사례

Following the publication of Part 1, Part 2 focuses on the development trends of key element technologies associated with heat transfer characteristics. Previous research focused on methods to overcome low thermal conductivity, and various heat exchanger design methods have been proposed to improve this using solid media such as fins or additives such as carbon particles. In addition, the operation method for optimal performance, when the latent heat energy storage system is connected to the main combustion system, is discussed. Finally, demonstration research cases, which are being conducted in Germany and Korea, are introduced to discuss the current status and future direction of this technological development in combined heat and power, and steam generation. In Korea, R&D for a latent heat energy storage system, through waste heat recovery, is an ongoing national project and is scheduled to be demonstrated in 2025. Projects involved in high-temperature latent heat energy storage technology to reduce carbon emissions, by reducing the direct use of fossil fuels, are currently ongoing.

In tube condensation heat transfer and pressure drop for R454B and R32—Potential replacements for R410A

The heating, ventilation and air conditioning (HVAC) industry in the United States seeks near-term alternative refrigerants to replace R-410A in unitary equipment. Two potential replacement refrigerants are R-454B and R-32. It is of interest to investigate the capability and accuracy of existing heat exchanger design methods when applied to these replacement refrigerants. To that end, this work presents empirical condensation quasi-local heat transfer coefficient and pressure drop data for R-454B and R-32. These data were obtained in a 38 in. (9.52 mm) outside diameter (OD) smooth copper tube with a wall thickness of 0.032 in. (0.81 mm). The experimental variables and their ranges included refrigerant absolute pressure (1960≤Pabs≤3196 kPa), condensation temperature (35≤Tcond≤50oC), mass flux (100≤G≤200 kg m-2 s-1), vapor quality (0≤x≤1), and heat flux (32.9≤q″≤62.97 kW m-2). It was found that the heat transfer correlation developed by Cavallini et al. Cavallini et al. (2006) predicted the experimental condensation heat transfer data, for both R-454B and R-32, with the greatest accuracy. Using the Cavallini et al. correlation, it was found that the mean absolute percentage error (MAPE) was 10.5% and 15.1% for R-454B and R-32, respectively. Additionally, the pressure drop correlation developed by Friedel Friedel (1979) predicted the experimentally determined pressure gradient with a MAPE of 7.7% and 5.5% for R-454B and R-32, respectively. These results will assist the practicing thermal engineer to choose the most appropriate design correlation for these near-term replacement refrigerants.

Performance enhancement of cabinet cooling system by utilizing cross-flow plate heat exchanger

Gas-gas plate heat exchanger is an important component to remove heat generated from electronic devices in the cabinet cooling system. The counter-flow plate heat exchanger is usually used due to its higher heat transfer performance than the cross-flow plate heat exchanger. However, in the cabinet cooling system, the overall dimensions for the heat exchanger is limited. Therefore, it is necessary to consider the overall dimensions of the system during heat exchanger design, but the traditional thermal design method of heat exchanger doesn’t consider the effect of system parameters. In this paper, a cross-flow plate heat exchanger is proposed to improve the cooling performance of cabinet cooling system, and is compared with the counter-flow plate heat exchanger. The ε-NTU method and effectiveness-thermal resistance method are applied to evaluate the performance. It is found that for large width of cabinet cooling system, the system with cross-flow plate heat exchanger has higher cooling performance and lower thermal resistance than the system with counter-flow plate heat exchanger. When the width is 700 mm, the cooling capacity of the two systems are 176.13 W/K and 138.95 W/K, respectively. The dimensionless thermal resistance can characterize the irreversibility of the heat transfer at constant mass flow rate.

Experimental analysis of heat transfer coefficients in phosphoric acid concentration process

In typical heat exchanger design methods it is generally assumed that the overall heat transfer coefficient is constant and uniform; however, the heat transfer coefficients on the hot and cold sides of the heat exchanger may vary with times. In this work, a large number of operating parameters were collected for three types of heat exchangers, namely stainless-steel tubular and two graphite blocks from different suppliers (A and B), in an industrial phosphoric acid concentration unit over a period of two years. An experimental study performed to determine both the overall heat transfer coefficients in the clean state and the overall heat transfer coefficients at time t. A statistical approach was proposed to determine the overall heat transfer coefficients in the clean state as well as the retain cycles. The overall heat transfer coefficients were evaluated at different times. Our results show that the overall heat transfer coefficients decreased exponentially with the time and reach a minimum value ranging between 1419 to 2406 W m−2 K−1 according to the type of heat exchanger.

A novel heat exchanger design method using a delayed rejection adaptive metropolis hasting algorithm

In this study, a shell-and-tube heat exchanger (STHX) design based on seven continuous independent design variables is proposed. Delayed Rejection Adaptive Metropolis hasting (DRAM) was utilized as a powerful tool in the Markov chain Monte Carlo (MCMC) sampling method. This Reverse Sampling (RS) method was used to find the probability distribution of design variables of the shell and tube heat exchanger. Thanks to this probability distribution, an uncertainty analysis was also performed to find the quality of these variables. In addition, a decision-making strategy based on confidence intervals of design variables and on the Total Annual Cost (TAC) provides the final selection of design variables. Results indicated high accuracies for the estimation of design variables which leads to marginally improved performance compared to commonly used optimization methods. In order to verify the capability of the proposed method, a case of study is also presented, it shows that a significant cost reduction is feasible with respect to multi-objective and single-objective optimization methods. Furthermore, the selected variables have good quality (in terms of probability distribution) and a lower TAC was also achieved. Results show that the costs of the proposed design are lower than those obtained from optimization method reported in previous studies. The algorithm was also used to determine the impact of using probability values for the design variables rather than single values to obtain the best heat transfer area and pumping power. In particular, a reduction of the TAC up to 3.5% was achieved in the case considered.

An optimal design method for a heat exchanger for a dual-stage circulating high-temperature heat pump system

This paper presents an optimal design method for heat exchangers in a dual-stage circulating high-temperature heat pump (HTHP) system. The paper first presents a series of steady-state models of components and a simulation platform of whole system; the output of the simulated system is verified by the operational data of a real heat pump plant. The method is investigated and implemented by the simulation platform based on these models, and it consists of four steps: 1) the selection of an optimal condenser and evaporator (the C-E plant), 2) the optimization of the total heat transfer area of the C-E plant, 3) the optimization of the condenser-to-evaporator heat transfer area ratio (AR) and 4) a matching scheme for the AR and heat transfer area of the regenerator. The method adopts the coefficient of performance (COP) as the optimization target and employs the heating capacity, water velocities and water-side pressure drops and the compressor discharge temperature as constraints. The case studies demonstrate that the presented method is effective at solving the problem of mismatches among single components. The optimal design scheme provides the same heating capacity with a 13% decrease in the total area of the exchangers.

경계층 이론을 이용한 고효율 열교환기 설계를 위한 이론적 접근법

Abstract The objective of this study is theoretically to suggest the effective heat exchanger design method using boundary layer analysis. The boundary layer formation and interruption on rectangular plate and round plate fins are explained and the heat transfer coefficients showed with the variation of the velocity and temperature boundary layer. In addition, the flow pattern on one plate fin surface considered as external flow and flow pattern between fins considered as internal flow. As a result, theoretical method for the boundary layer interruption avoidance is suggested and the heat transfer coefficient of the round plate fin was higher than that of the rectangular plate fin because of the less thermal and velocity boundary layer thickness except the centerline. Key Words : Boundary layer, Heat exchanger, Heat transfer coefficient, Interruption, Plate fin 본 논문은 이 논문(작품)은 동아대학교 교내연구비 지원에 의하여 연구되었음. * Corresponding Author : Moo-Yeon Lee (Dong-A University)Tel: +82-10-5440-8421 email: mylee@dau.ac.krReceived September 18, 2012 Revised (1st September 27, 2012, 2nd October 12, 2012) Accepted December 12, 2012

Theoretical analysis of a method for segmented heat exchanger design

In the process of the design of heat exchangers, it is difficult to establish the factors governing the optimal points of the design objective functions due to the contradictions and uncertainties of the design objectives. The variation of fluid properties is one of the main factors causing this type of uncertainty. Conventional design methods have not completely solved these problems. In the present work, based on the logarithmic mean temperature difference, a new heat exchanger design method (called the segmented design method) is proposed which takes into account the variation of fluid properties with respect to the temperature. In this method, the whole heat exchanger is first divided into several segments. Then by applying the principle of the conservation of energy and taking into account the initial conditions as well as the connecting conditions of the adjacent segments, the inlet and outlet temperatures of each segment are determined. Finally, the application of the logarithmic mean temperature difference method on each segment defines the heat transfer area.

Heat Exchangers Design Under Variable Overall Heat Transfer Coefficient: Improved Analytical and Numerical Approaches

In typical heat exchanger design methods it is generally assumed that the overall heat transfer coefficient is constant and uniform; however, the heat transfer coefficients on the hot and cold sides of the heat exchanger may vary with flow Reynolds number, surface geometries, fluid thermophysical properties, and other factors. In this article we present simple analytical and numerical methods for calculating heat transfer area for data sets introduced earlier in the literature. For the analytical methods presented in the article, the variation in the overall heat transfer coefficient with the local hot and cold fluid temperature difference is expressed as a power-law model and as a general polynomial model. The procedure for calculating the heat transfer area with the power-law model is explained with respect to a simple closed-form solution, while the polynomial model can also provide an analytical solution that seems to be quite accurate for the data sets examined. It is also shown that a Chebyshev numerical integration scheme that requires four points compared to the Simpson method of three points is quite accurate (within 1% of the exact value).

Conventional heat exchanger design methods and their applicability to thermoacoustics

Heat exchangers (HEX) play an important role in many engineering applications, and well established methods for their modeling and optimization are available. Conventional heat exchangers take advantage of forced convection or phase change to transport thermal energy from the hot to the cold fluid, as opposed to thermoacoustic applications where the mean velocity of the oscillatory flow is zero. Conventional HEX are typically classified according to flow arrangement and type of construction. The most commonly implemented methods for HEX analysis are the logarithmic mean temperature difference (LMTD) method and the number of transport units (NTU) approach. Both methods require a set of input parameters and the analysis yields, for example, the appropriate heat exchanger size, i.e., the heat transfer surface area, and type that achieve the desired fluid outlet temperature. The applicability of conventional heat exchanger design methods to thermoacoustic HEX is explored. HEX design solutions developed for thermoacoustics are analyzed in light of the LMTD and NTU approaches. Key differences and issues requiring further research are addressed in the study. [Work supported by the Office of Naval Research.]

Irreversibility and Thermoeconomics Based Design Optimization of a Ceramic Heat Exchanger

This paper illustrates the optimization procedure for heat exchangers residing in complex power plants. A specific case of optimizing a new technology ceramic heat exchanger, which is a part of the complex power plant, is shown. The heat exchanger design methods presented are based on two different objective functions, namely, a modified irreversibility rate based objective function proposed by the authors in earlier work and an objective function based on thermoeconomics. This paper also extends existing work by illustrating a method to obtain the cost coefficients for thermoeconomic optimization, based on the use of an overall plant simulation model. A discussion on possible methods of improving the design guideposts obtained from irreversibility minimization analysis is also presented.

Heat Exchanger Theory Applied to the Design of Water- and Air-Heating Flat-Plate Solar Collectors

A general method for the design of flat-plate solar collectors based on solar collector theory has been developed. It can be applied to both liquid- and air-heating solar collectors. The solar collector efficiency is determined by the product of the effectiveness (ε) and the insolation use factor (IUF). The effectiveness describes the heat transfer characteristics of the collector and is shown to be a function of a solar number of transfer units (SNTU) and a parameter ψ. For an air-heating collector, the ψ parameter equals the collector efficiency factor, while for a liquid-heating collector it must account for the difference between the plate and tube heat transfer areas. The effectiveness and SNTU parameters are similar to the effectiveness and NTU parameters used in heat exchanger design methods. The IUF is a measure of the operating conditions of the collector. It represents the difference between the transmittance-absorptance product and the ratio of the minimum heat loss to the insolation on the exterior cover. The relationship between the effectiveness and the SNTU parameter is general for all nonconcentrating collectors. One advantage of this method over the traditional Hottel-Whillier method is that it separates the heat transfer characteristics of the solar collector from its optical properties and the operating conditions.

The Concept of Irreversibility in Heat Exchanger Design: Counterflow Heat Exchangers for Gas-to-Gas Applications

The thermal design of counterflow heat exchangers for gas-to-gas applications is based on the thermodynamic irreversibility rate or useful power no longer available as a result of heat exchanger frictional pressure drops and stream-to-stream temperature differences. The irreversibility (entropy production) concept establishes a direct relationship between the heat exchanger design parameters and the useful power wasted due to heat exchanger nonideality. The paper presents a heat exchanger design method for fixed or for minimum irreversibility (number of entropy generation units NS). In contrast with traditional design procedures, the amount of heat transferred between streams and the pumping power for each side become outputs of the NS design approach. To illustrate the use of this method, the paper develops the design of regenerative heat exchangers with minimum heat transfer surface and with fixed irreversibility NS.