Abstract: Plate heat exchangers were first developed about 100 years ago but have won increasing interest during the last two decades, primarily due to the development of methods of manufacturing brazed plate heat exchangers. This type of heat exchanger offers very good heat transfer performance in single-phase flow as well as in evaporation and condensation. Part of the reason is the small hydraulic diameters, typically being less than 5 mm. Other advantages of plate heat exchangers are the extremely compact design and the efficient use of the construction material. In spite of their long use, the calculation methods for predicting heat transfer and pressure drop are not widely known. It is the purpose of this article to present such calculation methods for single-phase flow and for flow boiling and to discuss some of the specifics of this type of heat exchangers.

Abstract: Despite the low energy consumption and lower maintenance benefits of ground-source heat pump (GSHP) systems, little work has been undertaken in detailed analysis and simulation of such systems. Lon...

Abstract: Convective heat transfer coefficient is a critical parameter in analyzing heating systems. When air impingement technology is applied to the thawing of frozen foods, the resulting effective heat transfer coefficient becomes quite complicated. The airflow from impingement jets result in heat transfer coefficient that varies with position. In addition, transient thawing results in effective heat transfer coefficient that varies with time and surface temperature. Effective heat transfer coefficients as a function of position and surface temperature were determined using an inverse method for thawing from a single impingement jet. Regularization parameters used in this inverse method were determined using simulated data. Effective heat transfer coefficients tended to increase with time as thawing progressed. Heat transfer coefficients decreased radially, but exhibited secondary maxima at radial distances approximately equal to the nozzle diameter. This inverse method enables estimation of heat transfer coefficient as a function of both time and position.

Abstract: Purpose – To study the thermal performance of both co‐current and counter‐current parallel flow heat exchangers. The hot stream is assumed to flow in the middle of two cold streams and exchange heat with them.Design/methodology/approach – The dimensionless governing equations are derived based on the conservation of energy principle and solved using FEM based on subdomain collocation method and Galerkin's method. The results show that the subdomain collocation method is more accurate than the Galerkin's method, as observed when the results obtained are compared with the analytical results for the classical two‐fluid heat exchangers.Findings – The results are presented in terms of effectiveness and number of transfer units (Ntu) for different values of the governing parameters. The governing parameters are the Ntu, the heat capacity ratios, the overall heat transfer coefficient ratio, and the inlet temperatures parameter. The results show that the effectiveness of the three‐fluid heat exchanger is always h...

Abstract: In this study, a mathematical model and simulation code has been developed to investigate the performance of a transcritical CO2 heat pump dryer. The model takes into account detailed heat and mass transfer and pressure drop phenomena occurring in each component of the system. To take care of the variable heat transfer properties, the heat exchanger components were divided into several infinitesimal segments to examine the state, heat and mass balance and pressure drop for both refrigerant and air, and hence accurate results are expected. In Part 2 of the article, the model developed has been validated with experimental data and then the model was used to investigate effects of important operating parameters on the performance.

Abstract: An ecological performance analysis for an irreversible Brayton heat engine with variabletemperature thermal reservoirs based on the ecological criterion called Ecological Coefficient of Performance (ECOP) is presented. The model considered includes irreversibilities due to finiterate heat transfer and internal dissipations. The effects of design parameters such as isentropic temperature ratio, heat exchanger effectiveness, thermal reservoir inlet temperature ratio and the ratio of hot-to-cold thermal capacity rates of thermal reservoirs, on the general and optimal ecological performances have been investigated in detail. Comparisons of the results with those of an alternative ecological objective function defined in the literature, the maximum power output conditions, and thermal efficiency are also provided.

Abstract: Pasteurization or sterilization of food and bioproducts is mostly performed using heat exchangers in countercurrent flow. The lack of appropriate analytic solutions for temperature profiles in the heating and cooling sections of such processes is most likely the main reason for the traditional cautious approach of disregarding the contribution of these stages in the total thermal history calculation. This approach leads to excessive thermal abuse of the product. The current manuscript describes the derivation and validation of an analytic solution for the temperature profiles within a double-pipe heat exchanger with countercurrent turbulent flow of Newtonian fluids, at any possible flow rate and not necessarily assuming an isothermal heating medium or coolant. The presented solution is based on application of the “heat exchanger effectiveness” concept in a partial heat exchanger, and can be easily solved and plotted using a spreadsheet. An interactive ExcelTM workbook was developed for fast prediction of temperature profiles and used in a simulated case study to demonstrate the influence of operating conditions on the temperature profile and thermal history of a pasteurized liquid product.

Abstract: PROBLEM TO BE SOLVED: To provide a heat exchanger improved in its heat exchanger effectiveness by reducing frost formation on a fin caused by condensed water or the like, and reducing a dead water region formed at a downstream region of a heat transfer tube, and to provide an air conditioner including the heat exchanger SOLUTION: This heat exchanger 21 includes the heat transfer tube 11 as a refrigerant flow channel, and the fin 212 supporting the heat transfer tube 211 The fin 212 has a main guide 214 for guiding the air flow to a downstream region of the heat transfer tube 211, and the main guide 214 has a frost formation inhibiting shape composed of a projecting portion gently raised from a surface of the fin 212 COPYRIGHT: (C)2006,JPO&NCIPI

Abstract: A new program for simulation and optimization of the shell-and-tube heat exchangers is prepared to obtain useful results by employment of the computing technology fast and accurately. As an application of this program, the effects of transverse and longitudinal tube pitch in the in-line and staggered tube arrangements on the Nusselt numbers, heat transfer coefficients and thermal performance of the heat exchangers were investigated. The obtained values of the tube pitch were compared with literature values.

Abstract: Because of the dramatic variation of physical properties with a modest change of temperature, no existing engineering correlation or models can accurately predict heat transfer of supercritical fluids. This paper seeks to classify the conditions where the existing models are applicable and to better understand these local heat transfer mechanisms. The first objective is the focus of this paper. FLUENT was employed to compute the wall temperatures for various heat flux and mass flux conditions and to be compared with experimental data. Because the model was developed for a wide range of flow conditions, it was necessary to make certain assumptions. The simulations showed a good agreement with high mass flux conditions, where buoyancy effects could be neglected. The FLUENT model, however, had difficulty predicting the localized low heat transfer rates seen in the combined condition of high heat flux and low mass flux. A new generalized parameter, dependent on the heat and mass flux, was developed to classify under which conditions this FLUENT standard model was applicable. This global Froude number can be used as the parameter to predict under which conditions the buoyancy effect will be dominant and lower heat transfer rates will occur.

Abstract: Cyclones can be used for heating solid particles where the direct contact with the gas is permitted. Since cyclones have potential applications as heat exchangers in fertilizer, polymer powder, pharmaceutical and other industries, study of cyclone as heat exchanger is deemed important. Experiments on air-solid heat transfer were carried out in a cyclone heat exchanger of 100 mm inside diameter, using sand. The effects of solid feed rate (0.5-7.5 g/s), cyclone inlet air velocity (9-22 m/s), and four average particle sizes (163-460 μm) on the heat transfer rate, exit solid temperature, and heat transfer coefficient have been studied. An empirical correlation has been proposed for the prediction of heat transfer coefficients based on the present experimental data. The proposed correlation predicts the heat transfer coefficients with an error of +10% to -15% for the present data and within an error of +25% to -15% for the data of other investigators.

Abstract: A formula is derived for the dependence of heat exchanger effectiveness on the number of transfer units for a spiral-plate heat exchanger with equal capacitance rates. The difference-differential equations that describe the temperature distributions of the two counter-flowing fluids, neglecting the effects of thermal radiation, are solved symbolically to close approximation. Provision is made for the offset inlet and exit of the hot and cold fluids at the outer periphery and for large heat transfer coefficients in the entrance regions. The peak effectiveness and the number of transfer units at which it occurs are linear functions of the maximum angle of the Archimedean spiral that describes the ducts; entrance region effects reduce both.

Abstract: Two-dimensional compressible momentum and energy equations are solved to obtain the heat transfer characteristics of gaseous flows in micro-channels with constant heat flux for which the value is negative for no-slip flow. The numerical methodology is based on the Arbitrary-Lagrangian-Eulerian method. The computations are performed for channels with constant heat flux ranging from −104 to −102 W/m2. The channel height ranges from 10 to 100 μ m and the aspect ratio of the channel height and length is 200. The stagnation pressure is chosen such that the exit Mach number ranges from 0.1 to 0.7. The outlet pressure is fixed at the atmosphere. The wall and bulk temperatures in micro-channels with negative heat flux are compared with those of positive heat flux cases obtained in our previous work and also those of the incompressible flow in a conventional sized channel. In the case of fast flow, temperatures normalized by heat flux have different trends whether heat flux value is positive or negative. A correla...

Abstract: A simplified model of heat transfer was developed to investigate the thermal behavior of heat exchangers and stack plates of thermoacoustic devices. The model took advantage of previous results describing the thermal behavior of the thermoacoustic core and heat transfer in oscillating flow to study the performance of heat exchangers attached to the core. The configuration considered is a flat tube (with a working fluid flowing in the tube) of the thickness of the stack plate attached to both ends of the stack plate. Geometrical and operational parameters as well as thermophysical properties of the heat exchangers, transport fluids in the heat exchangers, stack plate and the thermoacoustic working fluid were organized into dimensionless groups that allowed accounting for their impact on the performance of the heat exchangers. Two types of thermal boundary conditions were considered: constant temperature and constant heat flux along the heat exchanger tubes. Numerical simulations were carried out with the model introduced in the paper. The temperature distributions and heat fluxes near the edge of the stack plate were found to be nonlinear. The influence of system parameters on the thermal performance of the heat exchangers was analyzed.

Abstract: The performance of a waste water heat recovery devices in a typical residential water heating installation was analyzed2 and Energy factor (EF) enhancement coefficients determined as a function of fuel (electricity or gas), GAMA Directory/DOE EF3, volume of hot water use, water main inlet temperature, proportion of hot water use that is "batch" vs. "continuous"4, heat exchanger effectiveness of the device, and waste water stream.

Abstract: Thermal efficiency is optimized for an irreversible closed intercooled regenerated gas-turbine cycle coupled to variable-temperature heat reservoirs in the viewpoint of the theory of thermodynamic optimization (or finite-time thermodynamics). It is first performed by searching the optimum intercooling pressure ratio and the optimum heat conductance distributions among the four heat exchangers (the hot- and cold-side heat exchangers, the intercooler, and the regenerator) for fixed total heat exchanger inventory. Secondly, the optimization is performed further with respect to the total pressure ratio of the cycle, the maximum efficiency is maximized twice and the double-maximum efficiency is obtained. Thirdly, the optimization is performed additionally with respect to the thermal capacitance rate matching between the working fluid and the heat reservoir, the double-maximum efficiency is maximized again and a thrice-maximum efficiency is obtained. In the optimization, the following effects are taken ...