Thermal Performance Of Exchanger Research Articles

Experimental study of the thermal-frictional behavior of a horizontal straight tube equipped with a vibrating string turbulators: A novel active method

The active methods are recently considered to increase the heat transfer rate. Compared to the passive methods, the active ones experience less pressure drop. Some inherent disadvantages, such as inefficiency in terms of energy consumption or the necessity of specific properties for the working fluid can limit using active methods. In this study, a novel idea is experimentally studied to explore the changes in the rate of heat carried by the fluid passing through a heated tube. To this end, a stretched string is implemented coaxially inside the tube and excited to vibrate at its natural frequency in the presence of an adjustable frequency AC magnetic field. This new approach to vibrating a starched oscillator remotely is called electro-magnetic vibration method (EMV). The vibration of a string inside the tube is predicted to cause severe turbulence and strong radial flow. The impacts of the changing diameter of the vibrating string turbulator (VST) and the position of the exciter on the heat transfer rate are studied at different mass flow rates. The thermal enhancement factor (TEF) is calculated to choose the best diameter and excitation location. The results showed that in the best scenario, TEF could reach up to 1.47, which indicates that the EMV method is an effective way to generate harsh radial flow to increase heat exchanger's thermal performance.

Performance Assessment of Heat Exchangers for Process Heat Integration

Pinch Analysis is an attractive solution for reduction of thermal energy costs in thermo-chemical industries. In this approach, maximum internally recoverable heat is determined and a heat exchange network is designed to meet the recovery targets. The thermal performance of a heat exchanger over its lifetime is however a concern to industries. Thermal performance of a heat exchanger is affected by many factors which include the physical properties of the shell and tube materials, and the chemical properties of the heat transfer fluid. In this study, thermal performance of shell and tube heat exchangers designed to meet heat recovery targets in a Pinch Analysis study is simulated. The aim of this paper is to present predictions of thermal performances of shell and tube heat exchangers with different heat transfer fluids and geometries as they undergo fouling degradation. Engineering approaches based on thermodynamic analysis, heat balance and Kern Design equations, as well as what-if simulation modeling are used in this work. Shell and tube heat exchangers were designed to meet internal heat recovery targets for three process plants, A, B and C. These targets were published in a separate paper. The effects of degradation of the tubes-due to incremental growth of fouling resistance - on thermal performance of the exchanger were simulated using Visual Basic Analysis (VBA). Overall, it was found that growth in fouling reduces thermal efficiency of shell and tube heat exchangers with an exponential relationship. An increase of 100% of fouling resistance leads to an average reduction of 0.37% heat transfer. Higher values of logarithmic mean temperature difference (LMTD) and higher ratios of external diameter to internal diameter of the exchanger tubes amplify the effect of fouling growth on thermal performance of the exchangers. The results of this work can be applied in pinch analysis, during design of heat exchangers to meet the internal heat recovery targets, especially in predicting how fouling growth can affect these targets. This can also be useful in helping operators of shell and tube heat exchangers to determine cleaning intervals of the exchangers to avoid heat transfer loss.

Thermal Performance of Borehole Heat Exchanger under Groundwater

Thermal Performance of Borehole Heat Exchanger under Groundwater

Numerical study of a PCM-air heat exchanger's thermal performance

In this paper, the use of PCMs in HVAC applications is investigated by studying numerically the thermal performance of a PCM-air heat exchanger. The PCM used in this study is dodecanoic acid. A symmetric 3D model, incorporating conductive and convective heat transfer (air only) as well as laminar flow, was created in COMSOL Multiphysics 5.0. Simulations examined the dependence of the heat transfer rate on the temperature and velocity of the incoming air as well as the size of the channels in the heat exchanger. Results indicated that small channels size lead to a higher heat transfer rates. A similar trend was also obtained for high incoming air temperature, whereas the heat transfer rate was less sensitive to the incoming air velocity.

Experimental investigation of distributor configuration on flow maldistribution in plate-fin heat exchangers

Plate-fin heat exchangers are a class of compact heat exchangers that are extensively applied in industry. The distributor configuration used to distribute fluid flow among the channels of a plate-fin heat exchanger can significantly influence the thermal performance of such heat exchangers. In this work, various distributor configurations were used with a plate-fin heat exchanger under different operating conditions to assess the resultant change in its flow distribution and thermal performance. It was found that certain design features of the distributor caused severe flow maldistribution and that the flow Reynolds number based on the average flow velocity in the heat exchanger channels and the channel hydraulic diameter substantially affected the flow distribution, which in turn significantly influenced the heat exchanger's thermal performance. An improved distributor design, with a complementary fluid cavity was built and tested in this work. The experimental results show that improved distributors are very effective in improving the flow distribution in heat exchangers, and consequently, their thermal performance. The most uniform flow distribution and heat transfer were obtained, when the improved distributor configuration parameter, which represents the ratio of the height of the complementary cavity (h) to the total distributor height (H), is 0.2. By incorporating this distributor at the inlet of the plate-fin heat exchanger, the flow and temperature non-uniformity in the same were reduced to 57.4% and 13.7% of the baseline design respectively, at the main test condition. Correlations between the flow distribution uniformity and Reynolds number for the various distributor configurations have also been provided.

Heat Transfer Enhancement in Shell-and-Tube Heat Exchangers Using Porous Media

A numerical simulation has been carried out to investigate the heat transfer enhancement in a shell-and-tube heat exchanger using a porous medium inside its shell and tubes, separately. A three-dimensional geometry with k-ϵ turbulent model is used to predict the heat transfer and pressure drop characteristics of the flow. The effects of porosity and dimensions of these media on the heat exchanger's thermal performance and pressure drop are analyzed. Inside the shell, the entire tube bundle is wrapped by the porous medium, whereas inside the tubes the porous media are located in two different ways: (1) at the center of the tubes, and (2) attached to the inner wall of the tubes. The results showed that this method can improve the heat transfer at the expense of higher pressure drop. Evaluating the method showed that using porous media inside the shell, with particular dimension and porosity can increase the heat transfer rate better than pressure drop. Using this method inside the tubes leads to two diverse results: In the first configuration, pressure loss prevails over the heat transfer augmentation and it causes energy loss, whereas in the second configuration a great performance enhancement is observed.

A Multi-Domain Coupled Numerical Method for a Flat Tube Bank Fin Heat Exchanger with Delta-Winglet Vortex Generators

Along with the improvement of numerical methods and the development of computer power, using a numerical method to design a tube bank fin heat exchanger becomes increasingly possible. In real working conditions, the conjugate heat transfer process arises in this type of exchanger. To provide a feasible numerical model and its relevant method to properly assess the thermal performance of exchanger, in this article, a multi-domain coupled numerical method is presented, in which the conduction in solid regions and the convection in flow regions are calculated together with a fully coupled manner. The reliability of a numerical method was tested through comparing average numerical results with experimental results of a real heat exchanger. The results reveal that the multi-domain coupled numerical method can achieve more accurate positions of the interfaces, arrange the orthogonal grids close to the interfaces, and use more reasonable criteria of convergence. Thus, we have achieved reasonable results that agree with the experimental data of the real heat exchanger under the working condition within 10% deviation in the Reynolds number region studied, and got overall heat transfer coefficient of a flat tube bank fin heat exchanger.

Thermal Performance of Intermediate Heat Exchanger during High-Temperature Continuous Operation in HTTR

Thermal Performance of Intermediate Heat Exchanger during High-Temperature Continuous Operation in HTTR

Heat-transfer characteristics of wet heat exchangers in parallel-flow and counter-flow arrangements

Wet heat exchangers have many applications in the fields of air conditioning, refrigeration and power plants. They can achieve higher heat-transfer rates than dry heat exchangers. Heat transfer takes place from a hot fluid flowing inside the tubes to air, through the film which is formed by spraying water onto the heat- transfer surface. Both sensible and latent heats are transferred from the spray water to air; the latter makes the major contribution and causes a small amount of spray water to evaporate into the air stream. These heat exchangers are classified according to the flow arrangement of spray water and air, and the geometry of the tubes. Many researchers have studied the thermal characteristics of wet heat exchangers using different mathematical models. The effect of the wetted surface as the main factor of heat-transfer enhancement on the thermal performance of heat exchanger has been investigated extensively. In the present study, a mathematical model was applied to analyse the performance of the wet heat exchangers. Temperature distribution of three fluids flowing through the exchanger and the humidity distribution of the air for parallel and counter-current exchangers were obtained using the mathematical model. The effects of various operating conditions, such as mass flow rates of three fluids on the thermal performance of the exchanger were investigated. The results of the model were compared against reference experimental data.

Thermal and flow analysis for the optimization of a parallel flow heat exchanger

The present paper examines the thermal and flow characteristics of a parallel flow heat exchanger and investigates the effects of the parameters on thermal performance by defining the flow nonuniformity. Thermal performance of a parallel flow heat exchanger is maximized by the optimization using Newton's searching method. The flow nonuniformity is chosen as an object function. The parameters such as the locations of separator, inlet, and outlet are expected to have a large influence on thermal performance of a parallel flow heat exchanger. The effect of these parameters are quantified by flow nonuniformity. The results show that the optimal locations of inlet and outlet are 19.73 mm and 10.9 mm, respectively. It is also shown that the heat transfer increases by 7.6% and the pressure drop decreases by 4.7%, compared to the reference model.

97/04122 Thermal and hydraulic performance of a graphite block heat exchanger

97/04122 Thermal and hydraulic performance of a graphite block heat exchanger

95/05117 Life cycle coating

Plate-fin heat exchangers are a class of compact heat exchangers that are extensively applied in industry. The distributor configuration used to distribute fluid flow among the channels of a plate-fin heat exchanger can significantly influence the thermal performance of such heat exchangers. In this work, various distributor configurations were used with a plate-fin heat exchanger under different operating conditions to assess the resultant change in its flow distribution and thermal performance. It was found that certain design features of the distributor caused severe flow maldistribution and that the flow Reynolds number based on the average flow velocity in the heat exchanger channels and the channel hydraulic diameter substantially affected the flow distribution, which in turn significantly influenced the heat exchanger's thermal performance. An improved distributor design, with a complementary fluid cavity was built and tested in this work. The experimental results show that improved distributors are very effective in improving the flow distribution in heat exchangers, and consequently, their thermal performance. The most uniform flow distribution and heat transfer were obtained, when the improved distributor configuration parameter, which represents the ratio of the height of the complementary cavity (h) to the total distributor height (H), is 0.2. By incorporating this distributor at the inlet of the plate-fin heat exchanger, the flow and temperature non-uniformity in the same were reduced to 57.4% and 13.7% of the baseline design respectively, at the main test condition. Correlations between the flow distribution uniformity and Reynolds number for the various distributor configurations have also been provided.

Mittlere Temperaturdifferenz und Wirkungsgrad in mehrgängigen Rohrbündel‐Wärmeübertragern mit und ohne Umlenksegmente

AbstractMean Temperature Difference and Efficiency of Multipass Shell‐and‐Tube Heat Exchangers with and without Segmental Baffles. Branched flow in a multi‐passes shell‐and‐tube heat exchanger with segmental baffles causes a reduction in the mean temperature difference and the thermal efficiency of the apparatus compared with a pure counter‐flow. The influence of the shell‐side flow induced by the segmental baffles on the thermal performance of the heat exchanger is mostly ignored. Making certain assumptions (e.g. constant overall heat transfer coefficient) theoretical relations of the thermal performance of the exchanger can be derived from the energy balance and the kinetic equation. If these assumptions are not valid, a numerical integration of the differential equations is necessary. Ignoring the influence of the shell‐side flow induced by the baffles is only possible under certain conditions. If these conditions are not fulfilled, the cell‐method can be used.

Effects of Some Types of Maldistribution on the Performance of Heat Exchangers

The effects of several types and patterns of maldistribution in heat exchangers on the exchanger thermal performance are investigated. For turbulent flow most exchangers show only a small reduction in performance; however, for laminar flow the reduction can be large. It is shown that substantial errors in the apparent heat transfer coefficient occur for nonuniform flows.