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Compact heat exchangers which were initially developed for the aerospace industries in the 1940s have been considerably improved in the past few years. The main reasons for the good performance of compact heat exchangers are their special design which includes turbulent which in turn use high heat transfer coefficient and resists fouling, and maximum temperature driving force between the hot and cold fluids. Numerous types use special enhancement techniques to achieve the required heat transfer in smaller plot areas and, in many cases, less initial investment. One such type of compact heat exchanger is the Plate-fin heat exchanger. The complexity of compact heat exchanger design equations results from the exchangers unique ability to transfer heat between multiple process streams and a wide array of possible flow configurations. This paper presents the performance evaluation of cross flow plate fin heat exchanger with several different Gas-Liquid systems. Experimental results such as exchanger effectiveness, overall heat transfer coefficients were calculated for the flow systems of Cross flow Heat Exchangers. A steady state model for the outlet temperature of both the cold and hot fluid and overall heat transfer coefficient of a plate-fin cross flow heat exchanger was developed and simulated using MATLAB, which was verified with the experiments conducted. Key words: Overall heat transfer coefficient, surface effectiveness, exchanger effectiveness, fin effectiveness, INTRODUCTION Heat Exchanger is process equipment designed for effective transfer of heat energy between two fluids (a hot fluid and a cold fluid). Many types of heat exchangers are used [...]

In France, where a division by 4 of the greenhouse gases emissions is aimed from 1990 to 2050, technical solutions are studied in order to reduce energy consumption while providing a satisfactory thermal comfort level in buildings. A two-dwelling passive building has been carried out in Formerie (North-West of France), complying the 'Passivhaus' standard. This building, not yet monitored, has been modeled using the dynamic simulation software COMFIE, which is dedicated to building eco-design. In order to account for the implemented ventilation system, including a heat recovery unit and an earth-to-air heat exchanger, a specific model has been developed and integrated to COMFIE as a new module. In this article, this model is described first. In order to quantify the benefits brought by a passive design, the simulation results are presented for the passive house and a reference house complying with the French thermal regulation for buildings. The heating load and thermal comfort level of both houses are compared, showing for the passive design a tenfold reduction of the heating load and a clear reduction of summer discomfort. Finally, the environmental assessment carried out with the life cycle assessment tool EQUER--shows the reduction in primary energy consumption, global warming potential and other impacts brought by the passive house design. Passive house appears to be an adequate solution to improve the environmental performances of buildings in the French context. Keywords: Thermal simulation; Passive house; Earth-to-air heat exchanger; Life cycle assessment

An experimental investigation on comparative heat transfer study on a solvent and solution were made using 1-1 Shell and Tube Heat Exchanger. Steam is the hot fluid, whereas Water and Acetic acid-Water miscible solution serves as cold fluid. A series of runs were made between steam and water, steam and Acetic acid solution. In addition to, the volume fraction of Acetic acid was varied and the experiment was held. The flow rate of the cold fluid is maintained from 120 to 720 lph and the volume fraction of Acetic acid is varied from 10-50%. Experimental results such as exchanger effectiveness, overall heat transfer coefficients were calculated. A mathematical model was developed for the outlet temperatures of both the Shell and Tube side fluids and was simulated using MATLAB program. The model was compared with the experimental findings and found to be valid. Key words: Heat exchanger design, simulated annealing, overall heat transfer coefficient, INTRODUCTION A heat exchanger is a device in which energy is transferred from one fluid to another across a solid surface. Exchanger analysis and design therefore involve both convection and [...]

Two-phase cross flow exists in many shell-and-tube heat exchangers. Flow-induced vibration excitation forces can cause tube motion that will result in long-term fretting-wear or fatigue. Detailed vibration excitation force measurements in tube bundles subjected to two-phase cross flow are required to understand the underlying vibration excitation mechanisms. An experimental program was undertaken with a rotated-triangular array of cylinders subjected to air/water flow to simulate two-phase mixtures over a broad range of void fraction and mass fluxes. Both the dynamic lift and drag forces were measured with strain gage instrumented cylinders. The experiments revealed somewhat unexpected but significant quasi-periodic forces in both the drag and lift directions. The periodic forces appeared well correlated along the cylinder with the drag force somewhat better correlated than the lift forces. The periodic forces are also dependent on the position of the cylinder within the bundle. [DOI: 10.1115/1.2388996]

The design of one secondary loop of a complex network often neglects the effect that its operation has on the others. The present is a study of hydrodynamic and thermal interaction between secondaries in a thermal-hydraulic network as the system goes from one steady state to another. Experimental results are related to those derived from a mathematical model. The network consists of a primary and three secondary loops. There is a water-to-water heat exchanger on each secondary, with the cooling coming from the primary and the heating from a separate loop. A step change is introduced by manually actuating a valve in one of the secondaries, resulting in changes in the other loops also. The response time of the temperature is found to be an order of magnitude higher than that of the flow rate, which is again an order of magnitude higher than the pressure difference. The steady-state results show that there is significant interaction, and that it is dependent on the initial operating condition. The hydrodynamic and thermal responses are found to be very different. [DOI: 10.1115/1.2363411]

The Oak Ridge National Laboratory. (ORNL) has been involved in research and development related to improved performance of recuperators for industrial gas turbines since about 1996, and in improving recuperators for advanced microturbines since 2000. Recuperators are compact, high efficiency heat-exchangers that improve the efficiency of smaller gas turbines and microturbines. Recuperators were traditionally made from 347 stainless steel and operated below or close to 650[degrees]C, but today are being designed for reliable operation above 700[degrees]C. The Department of Energy (DOE) sponsored programs at ORNL have helped defined the failure mechanisms in stainless steel foils, including creep due to fine grain size, accelerated oxidation due to moisture in the hot exhaust gas, and loss of ductility due to aging. ORNL has also been involved in selecting and characterizing commercial heat-resistant stainless alloys, like HR120 or the new AL20-25+Nb, that should offer dramatically improved recuperator capability and performance at a reasonable cost. This paper summarizes research on sheets and foils of such alloys over the last few years, and suggests the next likely stages for manufacturing recuperators with upgraded performance for the next generation of larger 200-250 kW advanced microturbines.

The major alternatives for producing work from fuel energy include combustion systems and fuel cells. Combustion systems are subject to several performance-limiting constraints. Key amongst these is the fact that combustion is an uncontrolled chemical reaction and is typically highly irreversible. The requirement to operate below the metallurgical limit adds to the irreversibility of practical combustion systems. Furthermore, the use of heat exchangers, which must have finite temperature differences between fluid streams, compounds the exergy consumption. The fuel cell conversion system is a major alternative to combustion systems. It operates as a direct conversion device and is often cited as having a potential for 100% second-law efficiency. Realistically, however, the chemical reactions involved are not reversible. More importantly, the available fuel resources must be reformed to make the chemical energy of the fuel convertible to work. The significant exergy input required must be factored into the determination of the overall exergy conversion efficiency attainable. This paper gives a simplified first- and second-law analysis for the limits of efficiency of these alternate systems for the conversion of fuel exergy to mechanical work, thus providing a more realistic comparison of the potential of both systems. [DOI: 10.1115/1.2213278]

A prime concern with the design of ultra-compact heat exchangers is the impact on performance of flow channel variations due to flow channel hydraulic diameter variations caused by manufacturing tolerances. This paper uses analytical methods to show that as the standard deviation in flow channel sizes, caused by manufacturing tolerances in a rotary regenerative exchanger, is increased compared to the average flow channel diameter the effective number of transfer units decreases. Depending on the operating conditions, the entropy generation number either increases or decreases with increasing flow channel size variations. These findings extend previous findings that showed that flow channel variations cause lower pressure drops and effectiveness. [DOI: 10.1115/1.2132380]

A quantification of the impact of the shape on the drag coefficient and forced convection Nusselt numbers of streamlined tubes for cross flow in the subcritical flow regime is presented. Interest in developing a method to improve the performance of heat exchangers made of polymer tubes is the reason to study this impact.

The fin efficiency of a high-thermal-conductivity substrate coated with a low-thermal-conductivity layer is considered, and an analytical solution is presented and compared to alternative approaches for calculating fin efficiency, by a model, which is appropriate for frost formation on a round-tube-and-fin metallic heat exchanger. However, the analytical solution seems to give rise to an eigenvalue problem with an unusual orthogonality condition.

The quality of experimental steady-state heat transfer data is demonstrated with an accurate energy balance between the gas and particle streams are presented. The result showed that the combination of experimental data and a one-dimensional analytic model results gives useful insight for developing falling-bed heat exchangers and provides a useful test case for future modeling efforts.

The stability behavior of natural circulation loops (NCL) with end heat exchangers is described in which the one-dimensional transient conservation equations of the loop fluid and the two fluid streams of cold end and hot end heat exchangers are solved simultaneously using the finite element program. The stability behavior is scanned over a wide range of C(sub h)(super *) and Gr(sub L) values and the stability envelope is also constructed.

Preliminary design and performance calculations for a silicon-based micro Rankine machine are discussed. The designs considered draw heat from a high temperature air stream with inlet temperatures between 770 and 1000 K and reject heat to an ambient air stream at 300 K. Most of the designs have a typical footprint of 6 [cm.sup.2]. Water and benzene are considered as working fluids. Effects of the limits of heat exchanger and turbomachinery performance are analyzed and discussed. The designs of two types of heat exchangers (hole type and fin type) are described in detail. Their respective performances are compared. The calculations indicate that a machine with a 6 [cm.sup.2] footprint area is capable of delivering in excess of 40 W of shaft power.

A new concept of porous reciprocal flow burner (RFB) for heat generation was developed and tested by arranging the reaction zone to travel back and forth along the length of the burner. The heat exchangers embedded into the ends of the bed make it an appealing alternative for high efficiency, low-emission heat generation.

The results of an experimental study of forced convection heat transfer in a narrow rectangular duct fitted with a circular tube and/or a delta-winglet pair are presented. The duct was designed to simulate a single passage in a fin-tube heat exchanger.

An experimental study of the growth of scale on copper, nylon 6,6, semiaromatic high temperature nylon, polypropylene, polybutylene, and Teflon tubes exposed to hard water is presented. Results provide qualitative information on the scaling of polymer tubes in nonisothermal, flowing conditions expected in heat exchangers and solar absorbers. The 89-cm-long tubes were placed in tube-in-shell heat exchangers. The tubes were exposed to flowing water for 1660 h, a 1120-h pretreatment phase using tap water adjusted to supersaturation of about 2 and pH of 8, followed by a 540-h acceleration phase using tap water with an adjusted total calcium concentration of 4 X [10.sup.-3] M, and a pH of 9. Flow rate was 4 cm/s. A 50% propylene glycol solution at 60[degrees]C was maintained on the shell side of the heat exchanger. Sections of the tubes were removed periodically to determine the extent of scaling. Results include scanning electron microscope images of the tube surfaces before and after exposure to the flowing water, x-ray diffraction to determine the crystalline phase content of the observed deposits, and chemical analysis to estimate the mass of calcium carbonate per unit surface area. A model of the scaling process is presented to help interpret the data. The data show conclusively that polymer tubes are prone to scaling. With the exception of nylon 6,6, the scaling rate on the polymers is about the same as that on copper. The nylon 6,6 substrate appears to enhance scaling. The enhancement is attributed to hydrolysis of the substrate. [DOI: 10.1115/1.1823492]

In year 2000 a 336 [m.sup.2] solar domestic hot water system was built in Sundparken, Elsinore, Denmark. The solar heating system is a low flow system with a 10000 l hot-water rank. Due to the orientation of the buildings half of the solar collectors are facing east, half of the solar collectors are facing west. The collector tilt is 15[degrees] from horizontal for all collectors. Both the east-facing and the west-facing collectors have their own solar collector loop, circulation pump, external heat exchanger and control system. The external heat exchangers are used to transfer the heat from the solar collector fluid to the domestic water. The domestic water is pumped from the bottom of the hot-water tank to the heat exchanger and back to the hot-water tank through stratification inlet pipes. The return flow from the DHW circulation pipe also enters the tank through stratification inlet pipes. The tank design ensures an excellent thermal stratification in the tank. The solar heating system was installed in May 2000. The thermal performance of the solar heating system has been measured in the first two years of operation. Compared to other large Danish solar domestic hot water systems the system is performing well in spite of the fact that the solar collectors are far from being orientated optimally. The utilization of the solar radiation on the collectors is higher, 46% in the second year of operation, than for any other system earlier investigated in Denmark, 16%-34%. The reason for the good thermal performance and for the excellent utilization of the solar radiation is the high hot-water consumption and the good system design making use of external heat exchangers and stratification inlet pipes. [DOI: 10.1115/1.1767190]

Natural convection is measured in an enclosure that represents an integral collector storage system (ICS) with an immersed tube-bundle heat exchanger. Heat transfer coefficients for bundles of 240 tubes contained in a thin enclosure of aspect ratio of 9.3:1 and inclined at 30 deg to the horizontal are obtained for a range of transient operating modes and pitch-to-diameter ratios of 1.5, 2.4, and 3.3. Results for isothermal and stratified enclosures yield a correlation for the overall Nusselt number [Nu.sub.D] = (2.45 [+ or -] 0.03) [Ra.sup.0.188.sub.D], 230 [less than or equal to] [Ra.sub.D] [less than or equal to] 9800. The characteristic temperature difference in the Rayleigh number is that between the average water temperature within the bundle and the tube wall temperature. Nusselt numbers are three times larger than those for a similarly configured single-tube and an eight-tube bundle. This increase is attributed to stronger fluid motion within the bundle and higher overall large scale circulation rates in the enclosure. [DOI: 10.1115/1.1824106]

The flow structure inside the inner tank and inside the mantle of a vertical mantle heat exchanger was investigated using a full-scale tank designed to facilitate flow visualisation. The flow structure and velocities in the inner tank and in the mantle were measured using a Particle Image Velocimetry (PIV) system. A Computational Fluid Dynamics (CFD) model of the vertical mantle heat exchanger was also developed for a detailed evaluation of the heat flux at the mantle wall and at the tank wall. The flow structure was evaluated for both high and low temperature incoming flows and for both initially mixed and initially stratified inner tank and mantle. The analysis of the heat transfer showed that the flow in the mantle near the inlet is mixed convection flow and that the heat transfer is dependent on the mantle inlet temperature relative to the core tank temperature at the mantle level.

Heat exchanger performance behavior is discussed in the text for 18 exchanger flow arrangements based on the First and Second Law analyses. An emphasis was made on investigating the existence of entropy generation extrema and a relationship between the extrema and the heat exchanger effectiveness.

The Navier-Stokes equations for an unsteady and compressible flow are solved numerically to investigate the flow near the stack of a thermoacoustic refrigerator. The computational domain is a resonator 'slice' including the resonator end but not the source. An incoming wave is introduced into the domain using the method of characteristics. Also included in the domain is a stack plate and two heat exchangers. The effects of the acoustic Mach number and geometrical parameters on refrigerator performance is investigated. Of special interest are some nonlinear temperature oscillations, which are not predicted by linear models and are due to acoustic propagation, and coupling between the stack plate and the heat exchangers. It is shown that the maximum heat pumping occurs for a stack/heat exchanger separation that is of the order of one particle displacement amplitude.

A new ground resistance was developed for use in existing vertical bore heat exchanger ([VBHE.sub.x]) design algorithms. The new ground resistance accounts for the added heat transfer mode of convection due to groundwater flow by using as its foundation the solution for a moving line heat source. The combined ground resistance is presented in terms of the dimensionless Fourier and Peclet parameters. Results show that significant convection heat transfer may occur within a variety of hydrogeological regimes, particularly when the Peclet number is larger than 0.01. Since the new model captures the influence of groundwater flow, the resulting ground resistance differs markedly from the conduction-only ground resistance currently used in many vertical borehole heat exchanger design algorithms. [DOI: 10.1115/1.1591203]

A performance evaluation for a residential window air conditioning system with microchannel condensers has been performed. First, a series of wind-tunnel calorimeter tests were conducted for two different prototype microchannel heat exchangers. The measured heat transfer and pressure drop characteristics for the heat exchangers were then compared to calculated value for four conventional finned round-tube designs, which were obtained using a validated simulation model for identical air and refrigerant inlet conditions. Finally, two prototype microchannel condensers are installed in the system and system performance tests were conducted. System characteristics such as capacity, energy efficiency ratio, and suction and discharge pressures and temperatures are presented, and compared with those for the conventional system. Refrigerant charge requirements for a window air conditioner with a microchannel condenser can be decreased by 35 percent compared to the conventional baseline system. The condenser core volume and weight can be reduced by 55 and 35 percent, respectively.

Two-phase forced convective flow in microchannels is promising for the cooling of integrated circuits. There has been limited research on boiling flow in channels with dimensions below 100 [micro]m, in which bubble formation and flow regimes can differ from those in larger channels. This work develops single and multichannel experimental structures using plasma-etched silicon with pyrex glass cover, which allow uniform heating and spatially-resolved thermometry and provide optical access for visualization of boiling regimes. Boiling was observed with less than 5 [degrees] C of superheating in rectangular channels with hydraulic diameters between 25 and 60 [micro]m. The channel wall widths are below 350 [micro]m, which minimizes solid conduction and reduces variations in the heat flux boundary condition. Pressure drop and wall temperature distribution data are consistent with predictions accounting for solid conduction and homogeneous two-phase convection. [651] Index Terms--Heat exchanger, microchannel, two-phase cooling.

Fluidelastic instability of tube arrays in crossflow is interesting academically and important in steam generators and heat exchangers. The key elements necessary to accurately predict fluidelastic instability of tube arrays in crossflow are motion-dependent fluid force coefficients. This paper presents several series of experiments that measure motion-dependent fluid forces for various tube arrays. Fluid damping and stiffness coefficients based on the unsteady flow theory were obtained as a function of reduced flow velocity, excitation amplitude, and Reynolds number, and the characteristics of motion-dependent fluid force coefficients were applied to provide some additional insights into fluidelastic instability. [DOI: 10.1115/1.1401022]

Research is presented describing measurement of He II heat transfer through a short section of the triplet quadrupole heat exchanger of the Large Hadron Collider (LHC) being developed at the European Organization for Nuclear Research (CERN). There are also tests for a series of surface treatments and bath temperatures.

Nusselt numbers in rectangular ducts with laminar viscous dissipation have been analytically determined for a Newtonian incompressible fluid for any combination of heated and adiabatic duct sides. That the temperature field in a fully developed T boundary condition can be obtained as a particular case of the H1 problem and that the corresponding Nusself numbers do not depend on the Brinkman number has been proved.

Dehumidifying heat exchangers with and without wetting coatings have been evaluated. All tests were done for fully wet surfaces. Tests were done on uncoated and coated heat exchangers. For all fin geometries, of which there were three, the wet-to-dry pressure drop ratio was 1.2 at 2.5 m/s frontal air velocity. Coatings had no influence on the wet or dry heat transfer coefficient. The wet surface heat-transfer coefficient was 10-30% less than the dry heat transfer coefficient depending on the fin geometry. If the oil has a surfactant, good temporary wetting can be had on an uncoated surface. The effect degrades quickly as the oil is washed away in wet operation.

Viscous liquid flows and their enhanced heat transfer characteristics in a chevron plate heat exchanger are discussed. Vegetable oil was used as the test fluid with three plate arrangements. A rather complex influence of plate surface corrugations was found on the enhanced thermal-hydraulic behavior.

A new method for estimating heat transfer between solid material and fluid gas in porous media has been developed. The method gives the longitudinal characteristics of the heat transfer in a porous medium. Local Nusselt numbers on the heated wall of a flow passage are obtained numerically in advance in the first stage. Experimental Nusselt numbers on the wall are obtained by measurement of wall temperatures and heat flux in the next stage.

Heat exchangers with plain fins on a staggered array of circular tubes are discussed. Topics include air-side heat transfer and friction correlations for these exchangers. The correlations are intended to predict the air-side heat transfer coefficient and friction factor as a function of Reynolds number and geometric variables of the heat exchanger. Multiple regression technique was used for correlation. Correlations can be applied to heat exchangers with small-diameter tubes.

Numerical prediction of transitional features of turbulent forced-gas flows with strong heating in circular tubes is discussed. A study has been carried out with the object of extending the Abe, Kondoh and Nagano (AKN) model to treat the strongly heated gas flows and of looking at the validity of the extension by comparing to careful measurements for the same situations.

In this paper a second level mathematical model for the computational simulation of the working process of a 1-kW Stirling engine has been used and the results obtained are presented. The internal circuit of the engine in the calculation scheme was divided into five chambers, namely, the expansion space, heater, regenerator, cooler and the compression space, and the governing system of ordinary differential equations for the energy and mass conservation were solved in each chamber by Euler's method. In additional, mechanical losses in the construction of the engine have been determined and the computational results show that the mechanical losses for this particular design of the Stirling engine may be up to 50% of the indicated power of the engine.

Nusselt numbers are measured in three counterflow tube-in-shell heat exchangers with flow rates and temperatures representative of thermosyphon operation in solar water heating systems. Mixed convection heat transfer correlations for these tube-in-shell heat exchangers were previously developed in Dahl and Davidson (1998) from data obtained in carefully controlled experiments with uniform heat flux at the tube walls. The data presented in this paper confirm that the uniform heat flux correlations apply under more realistic conditions. Water flows in the shell and 50 percent ethylene glycol circulates in the tubes. Actual Nusselt numbers are within 15 percent of the values predicted for a constant heat flux boundary condition. The data reconfirm the importance of mixed convection in determining heat transfer rates. Under most operating conditions, natural convection heat transfer accounts for more than half of the total heat transfer rate.

A study on periodic flow and heat transfer was conducted to develop a method for calculating radiative heat transfer in either translational- or rotational-type, periodically repeating domains. The technique developed is based on the unstructured finite volume scheme formulated by two researchers in a previous study. The scheme was applied to a number of periodic problems and found to match ray tracing results and published numerical solutions.

A diagonal cartesian method for thermal analysis developed in a previous study was applied to the evaluation of flow and conjugate heat transfer in three compact, complex fin heat heat exchangers, two of whose regular fins were modified. Results of the study indicate that one heat exchanger (C1) increases the heat transfer compared to the regular fin heat exchanger and incurs about the same temperature drop. The other heat exchanger, C2, had comparable heat transfer characteristics but the pressure drop was considerably lower than that in the regular fin exchanger or in C1.

The improvement in performance of a double pipe heat exchanger fitted with twisted tape as a turbulence promoter with twist ratios of 15.649, 8.54, 5.882, 4.95, and 4.149 was experimentally studied. A maximum percentage gain of 44.7% in energy transfer rate was obtained for the twisted tape of twist ratio 4.149. For all twist ratios, the gain decreases with the Reynolds number and becomes constant for Reynolds numbers greater than 3,000. The smaller the twist ratio is, the larger the gain in energy for a specific Reynolds number.

Research is conducted to examine symmetrically heated parallel-plate channels with a series of transverse V-grooves formed in both walls. Channel Reynolds number is used to characterize the flow rate in two open-circuit flow channels under consideration. Experimental results reveal that air flows in symmetrically V-grooved channels become fully developed and the fully developed property of the flow is maintained to the last groove-pair in the series.

The effects of chevron angle beta on the thermal-hydraulic performance of a plate heat exchanger are studied. Three different chevron plate arrangements are taken into account with two symmetric and one mixed chevron plate arrangements. Results reveal substantial effects of both the surface area enlargement factor and the chevron angle. The heat transfer enhancement in the plate arrangements are also examined.

The aim of this paper is the analysis of heat transfer in a radial fin assembly during the process of dehumidification. An individual tinned tube geometry is a reasonable representation of heat exchangers used in air conditioning. The condensation process involves both heat and mass transfer and the cooling takes place by the removal of sensible as well as latent heat. The ratio of sensible to total heat is an important quantity that defines the heat transfer process during a dehumidifier operation. A one-dimensional model for heat transfer in the fin and the heat exchanger block is developed to study the effects of condensation on the fin surface. The combined heat and mass transfer process is modeled by incorporating the ratio of sensible to total heat in the formulation. The augmentation of heat transfer due to fin was established by comparing the heat transfer rate with and without fins under the same operating conditions. Calculations were carried out to study the effects of relative humidity and dry bulb temperature of the incoming air, and cold fluid temperature inside the coil on the performance of the heat exchanger. An analysis of the overall efficiency for the assembly was also done. Results were compared to those under dry conditions, wherever appropriate. Comparison between present results and those published for rectangular as well as radial fins under fully wet conditions were made. These comparisons established the validity of the present model. It was found that the heat transfer rate increased with increment in both dry bulb temperature and relative humidity of the air. The augmentation factor, however, decreased with increment in relative humidity and the dry bulb temperature. The fin efficiency decreased with relative humidity.

A study was conducted to analyze the performance of a novel swirl flow duct utilized for compact heat exchangers. The ducts analyzed were made in copper and supported a hydraulic diameter of 8.89 mm. Pressure drop measurements were carried out at isothermal conditions. In addition, a heat transfer rig was used that was characterized by a fan and a flow rate control system similar to the pressure drop test system. Experimental results indicated that rib-roughened tubes generated the largest heat transfer increase per unit pressure drop increase.

Research was conducted to examine work at maximum power for a general family of internally reversible Stirling-like cycles through a cycle time minimization procedure. The approach was shown to simultaneously minimize internal entropy generation while maximizing specific work for the cycle between the optimized operating temperatures at the hot and cold ends. Results are in line with observations that the simultaneous use of entropy and energy balances as the prerequisite for meaningful analyses of thermal processes.

A new numerical process to solve equations governing matrix heat exchanger thermal performance has recently been published. The scheme was found not to include full effects of longitudinal heat transfer in such heat exchangers. The effect has been demonstrated by correcting the parameter linked to longitudinal heat transfer in the approximate analytical solution, deviating from the numerically calculated results.