Search

Thermal design and analysis of heat exchangers are predominantly conducted considering constant heat transfer coefficients. However, these vary along the length and affect the calculations of heat transfer rates and area allocations. The current paper investigates the variations in the heat transfer coefficients in plate heat exchangers (PHX), using different numerical approaches. The heat transfer coefficient is calculated at the inlet, outlet, and systematically selected intermediate points for each method. The analysis is conducted for two different systems, i.e., a laboratory-scale and an industrial scale PHX at different chevron angles. It is concluded that the effect of the variable heat transfer coefficient is more significant for the large-scale heat exchanger due to high flow rates, geometrical specifications, Reynolds number, and thermophysical properties. The deviation of the local heat transfer coefficient along the heat exchanger length is approximately 9–14% and 3–6% for industrial and laboratory scale PHX, while an area deviation of around 15% is observed.

The concept of non-uniform heat flux distributions has emerged because of its potential to make the design of thermal systems more flexible. Therefore, the current study highlights the impact of non-uniform heat flux distributions on the thermal characteristics of a high Prandtl number fluid for forced convective laminar flow regime in a horizontal pipe. The steady-state 2-D simulations have been employed using ANSYS Fluent. The variations in heat flux distributions as a wall boundary condition are systematically analyzed while keeping the total heat transfer constant. The results obtained for various distributions are compared in terms of a dimensionless maximum wall temperature (hot spot), local and average Nusselt numbers, and entropy generation rate. The analysis showed that the heat flux distributions significantly affected the heat transfer pattern. It was found that the hot spot temperature was lower for the descending heat flux boundary conditions compared to the ascending type of distributions. However, a higher entropy generation rate was observed for descending distributions as compared to ascending ones. It was also found that the ascending heat flux distributions provided higher average Nusselt number values than the descending cases of heat flux.

Heat exchangers are used to transfer energy from one medium to another and increase contact area for higher efficiency. In case of fluids, higher flow area would lead to high/low flow zones that severely affect the fluid dynamics and thermal performance. Channels are used to distribute the flow uniformly to fully utilize the whole heat exchanger area. The flow uniformity in a flow distribution manifold is dependent on several factors such as flow rate, inlet and exit locations, and the manifold and channel geometrical configuration. In the current work, flow distribution measurements were performed using a particle image velocimetry (PIV) technique in two types of rectangular manifolds. The experimental results are further verified against the results obtained from numerical modeling with similar trends. The flow distribution in U- and Z-type arrangements are evaluated and compared with ten channels incorporated in the design. It was found that the flow is more in the channels near the inlet for U-type design, while more near the outlet for the Z-type. An increase in the inlet flow rate enhances the flow distribution for the U-type while results in more maldistribution for the Z-type. For the U-type, the normalized velocity varies from 1.34 to 0.52 in a wide manifold, and between 2.82 and 0.18 for a narrow manifold. A U-type wider manifold is recommended for all conditions examined in this work since at lower flow rates, both have similar mirrored distribution, while at higher flow rates, U-type manifold has better flow distribution.

Performance is analyzed for kinetic energy variation in high velocity stream heat exchangers that are subjected to external heat transfer. Analytical solutions are obtained using the method of inverse operators. They are verified against the reported expressions in the appropriate limits for constant kinetic energy system as well as for perfectly insulated conditions. Kinetic energy decay in hot stream enhances performance that exceeds the conventional heat exchanger effectiveness. For kinetic-to-thermal energy ratio and dimensionless characteristic length constant each equaling unity on the hot side, the terminal effectiveness under balanced operation is 136% for counter-flow arrangement and 82% for parallel-flow in the absence of external heat load. On the contrary, decay on the cold side lowers performance. For unbalanced flow, kinetic energy change in the higher heat capacity rate fluid has a lesser impact on the effectiveness. Thermal interaction with the ambient generally has a deleterious effect on the hot stream effectiveness of the cryogenic system. However, the performance improves under certain conditions such that the rise in fluid temperature caused by kinetic energy deterioration promotes heat loss to the surroundings.

For non-axisymmetric conditions, the traditional fluid mean (bulk) temperature at a tube cross section, subjected to constant heat flux, can be higher than the temperature of a point on the wall. T...

Shell-and-tube heat exchangers are frequently used in several industrial applications. A model was developed using engineering equations solver software to predict the performance of variou...

This paper introduces a novel humidification-dehumidification (HDH) system coupled with adsorption desalination (AD) system to produce freshwater as well as to obtain chilled water for an air-conditioning purpose. Two hybrid HDH-AD schemes are proposed in which the condenser of the AD system replaces the HDH heater. The difference is that the HDH inlet seawater is precooled in the AD evaporator before feeding the HDH system in Scheme # 1, while in Scheme # 2 the seawater is used to cool the adsorption process. Seawater mass flowrate and temperature, heating source mass flowrate and temperature, cycling time, and HDH mass flowrate ratio are the key parameters investigated to influence the hybrid system performance. The results exhibit that the gained output ratio (GOR) and cost values are higher in Scheme #1 (about 7.8 and 0.64 ¢/Liter, respectively). Scheme # 2 achieves an excellent GOR and cost values (about 7.6 and 0.65 ¢/Liter) with a cooling effect as a by-product (coefficient of performance (COP) is >0.45 under the same conditions of optimal GOR value). For the hybrid HDH-AD system, the HDH contribution in the total performance is vital while AD system can be used to control the HDH operating conditions.

The performance of photovoltaic modules is adversely affected by an increase in photovoltaic cell temperature. Cooling of panels may lead to temperature non-uniformity in the photovoltaic panel, thus limiting the maximum efficiency of the cooled photovoltaic panel. In the current work, the design of a novel heat exchanger that can be used for uniform cooling of photovoltaic modules is presented. For this purpose, a computational fluid dynamics model has been set up. Using the model, the effects of various heat exchanger design parameters (like channel numbers, manifold width, the location of inlet/exit ports, and tapered channels) on its performance are sequentially analyzed resulting in fourteen designs. The performance is quantified by three parameters: top surface average temperature, temperature non-uniformity for photovoltaic module cooling quality, and the heat transfer per unit pumping power. The resulting optimized design is found to be a novel V-shaped heat exchanger design for the photovoltaic module cooling. It has a lower average temperature and temperature non-uniformity, smaller hotspots, and lower pumping power. The optimal design is further examined using experimental particle image velocimetry measurements.

This paper evaluates an optimal airside thermal-hydraulic performance of compact heat exchangers. Seventy-five airside surfaces have been chosen, i.e. standard reference of Kays and London, to represent louver-fin, strip-fin, wavy-fin, plain-fin, pin-fin, finned circular tubes and finned flat tubes. A robust evaluation method is implemented by an estimation of the heat transfer rate per unit pumping power with and without considering the heat exchanger compactness. Experimental data of Colburn j-factor and Fanning friction factor (f) are used to estimate both the heat transfer rates and the friction power, respectively. The results demonstrate that strip-fin surface 1/10-27.03 shows an optimal heat transfer values per unit friction power when the compactness is taken into consideration. Nonetheless, pin-fin surface PF-4(F) shows an optimal heat transfer rate per pumping power when neglecting the importance of the compactness. The geometries having an optimal thermal-hydraulic performance for each airside type (with or without considering the compactness) are recommended as benchmarks to assess the performance of similar airside surfaces.

This work focuses on proposing generalized air-side thermal-hydraulic correlations for wavy-fin compact heat exchangers. The new correlations are modeled from experimental and numerical f- and j-factor data reported in the literature and presented in this paper. We have simulated twenty-one new geometries, using experimentally validated three-dimensional model implemented in ANSYS Fluent program, to obtain heat-transfer and fluid-flow characteristics of unreported geometries. Data of 50 geometries are used to propose new f and j correlations with an rms error of 9.23% and 9.90%, respectively. Testing and comparing the present correlations with those reported in the literature demonstrate that the present air-side f- and j-factor correlations are more accurate and generalized for regular wavy-fin compact heat exchangers.

In this work, the fabrication and characterization of a dual-purpose membrane is reported: (i) oil-water separation with high efficiency, and (ii) effective and rapid photocatalytic degradation of hazardous environmental pollutants. Nanoparticles of a rare-earth oxide, cerium (IV) oxide, synthesized by a simple co-precipitation technique, were spray-coated onto stainless steel membranes to obtain a uniform coating with superwetting characteristics. The as-synthesized cerium (IV) oxide nanoparticles and its spray-coated stainless steel membrane were characterized by advanced analytical techniques. X-ray diffraction, selected area electron diffraction, and electron microscopy results of the cerium oxide particles showed a high degree of crystallinity and uniform particle size of ∼50 nm. Elemental surface analysis using X-ray photoelectron spectroscopy showed the characteristic peaks for Ce4+, thereby confirming the presence of cerium oxide nanoparticles. Contact angle measurements showed the coated membranes to be superhydrophobic (∼150°) and superoleophilic (∼0°). When used in a simple laboratory setup, the membranes were able to separate oil and water with a high efficiency (∼99%). Furthermore, the coated membrane showed enhanced photocatalytic activity under UV light irradiation resulting in the rapid degradation of organic persistent pollutants like MB dye in water. To summarize, this work presents an innovative approach in the application of multifunctional membranes for effective water treatment.

An optimal assessment of heat transfer and friction power performance is investigated to address a robust method for facilitating performance evaluation of different wavy-fin arrangements. Two benchmark geometries are presented to compare the performance of all the reported wavy-fin arrangements with and without considering heat exchanger compactness. New 21 wavy-fin geometries are numerically studied to represent the unreported arrangements in the literature. The performance results of 105 geometries showed that the reference standard geometries of Kays and London could be used as benchmarks to evaluate the airside arrangements, with and without considering the compactness effect, respectively. Heat transfers versus friction power plots are found to be a useful approach for performance evaluation purpose. The surface GK2 is found to have the optimal thermal-hydraulic performance when comparing the heat exchanger compactness, whereas GI1 and GK1 might represent the geometries having optimal performances when neglecting the compactness importance.

In this work, we report the preparation of superhydrophobic and superoleophilic surfaces on stainless steel meshes by spray-coating of Cerium(IV) oxide (CeO2) nanoparticles obtained by a co-precipitation method. The synthesized particles and the coated meshes were characterized using advanced techniques. Scanning electron microscopy images showed the particles to be present in distinct lumps; merged with each other on calcination to give a homogeneous structure. Transmission electron microscopy analyses showed the agglomeration of individual particles to form the clusters. Contact angle measurements revealed the superhydrophobic and superoleophilic nature of the modified mesh surface in air. Fourier transform infra-red analyses of the synthesized particles showed the characteristics peaks of CeO2 found in commercial samples. X-ray photoelectron spectroscopy of the glass coated with ceria confirmed the predominant presence of Ce4+ that also explained the wetting behavior. Oil-water separation studies using a simple gravity-driven setup showed high separation efficiency of an oil water mixture. An analytical model is discussed in detail to account for the wetting behavior and efficacy of the prepared surfaces in separating the two fluids. To summarize, this work presents a very simple and effective route for oil-water separation with high efficiency.

This paper focuses on thermodynamic balancing of the regeneration process in a hybrid liquid desiccant cooling/desalination system. The thermal balancing technique is investigated by adding a single extraction between the system regenerator and condenser. This technique is considered as a potential method to reduce energy consumption and increase the hybrid system performance, dramatically. The mathematical procedure to model the proposed system using enthalpy pinch is outlined to study the effect of extraction on the hybrid system performance. The hybrid system, with a single extraction and without extraction (zero extraction), is analyzed in terms of the normalized entropy generation, local enthalpy losses, the coefficient of performance, and proper extraction location. The results show that at enthalpy pinch of 20 kJ per kg of dry air, single extraction system performance is 85.7% better than zero extraction. In addition, the single extraction produces 103.2 kg of fresh water per hour as a by-product compared to 94.2 kg per hour for the zero extraction system.

Sulfate reducing bacteria (SRB) wreaks havoc in the oil industry by being an agent for oil souring and building corrosion in pipelines and thereby degrade the quality of crude oil. Palladium nanoparticles decorated silicon carbide nanomaterial (Pd-SiC) was synthesized by a facile single step synthesis process and this nanomaterial as a photo-catalyst, as compared to pure silicon carbide (SiC) nanoparticles showed a significant enhancement in the photo-catalytic efficiency in the process of the photo-catalytic deactivation of hazardous SRB. The morphological characterization studies such as Field emission scanning electron microscopy, Transmission electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy unambiguously revealed that SiC surface was successfully decorated with palladium (Pd) nanoparticles. Also the Pd nanoparticles decorated on the SiC surface was further substantiated by EDX and elemental mapping analysis, which clearly revealed the presence of Pd along with Si and O. The band gap energy estimated using Diffuse reflectance spectra (DRS) showed the reduction of band gap energy from 2.82 eV to 2.72 eV. The observed enhancement in the efficiency of photo-catalytic deactivation of SRB with Pd-SiC can be attributed to the significant reduction in the recombination of photo-generated charge carriers, characteristically resulting from the metal (Pd) semiconductor (SiC) junction established by this synthesis process.

The analysis for fin thermal performance under dehumidifying conditions is conducted using a numerical approach. Finite-Element method is used to account for the non-linear effects due to temperature dependent parameters and humidity-temperature relationship. The temperature profiles, as well as the overall fin efficiency, are studied. The fin efficiency is found to be highly dependent on the operating conditions and the degree to which the heat transfer coefficient is a function of temperature. It is found that the effect of temperature-dependent thermal conductivity on fin performance is less as compared to heat transfer coefficient over the considered range of operating conditions.

The current study provides a detailed analysis of multi-effect mechanical vapor compression desalination systems. Three different feed flow arrangements including forward-feed (FF), parallel-feed (PF) and parallel-crossfeed (PCF) are analyzed and compared in terms of energy consumption, exergy destruction, heat transfer area and product cost. For this purpose, energy, exergy, and economic models are simultaneously solved numerically. In this regard, a component-based exergo-economic model is used to calculate the fresh water cost. It is observed that FF has the highest energy consumption followed by PF and PCF. While, the heat transfer area is calculated to be the highest for PCF followed by PF and FF, respectively. Finally, the product cost is estimated to be 0.867 for FF, 0.865 for PCF, and 0.842 $/m3 for PF MVC systems operating with 4 evaporators.

The paper presents an exergo-economic analysis of humidification-dehumidification (HDH) desalination system operating under a conventional open-water open-air (OWOA) and a modified closed-water open-air (CWOA) configuration. Besides, the possibility of coupling a reverse osmosis (RO) system with HDH unit is also analyzed. The hybrid HDH-RO system is studied under three different retrofits including a simple HDH-RO, HDH-RO with a Pelton turbine and HDH-RO with a pressure exchanger. The analysis reveals that the modified cycle has a higher exergetic efficiency and lower product cost than the basic cycle. The product cost for the basic cycle with an electrical heater is calculated to be $6.56/m3 and with the solar heater $5.98/m3. Moreover, it is observed that the hybrid HDH-RO system with a pressure exchanger has the highest gained output ratio and second-law efficiency followed by HDH-RO with a Pelton turbine and simple HDH-RO, respectively. The product cost for hybrid HDH-RO with a pressure exchanger is calculated to be $0.13/m3 and $0.12/m3 with an electrical and solar heater, respectively.

For oil-water separation, micron-sized stainless steel membranes were fabricated by spray-coating using dispersions of ytterbium oxide (Yb2O3). The operational parameters such as particles concentration and annealing temperature were optimized to achieve the best separation efficiency. Scanning electron microscopy (SEM) images of (Yb2O3) particles revealed that annealing at 200 °C results in sharp-edged grains that are uniformly distributed on the surface. These findings were further corroborated by X-ray diffraction (XRD) and selected area electron diffraction (SAED) analyses that confirmed the highest degree of crystallinity for the particles annealed at 200 °C. The analyses with Fourier Transform Infra-Red (FTIR) spectroscopy showed that annealing does not alter the bonding chemistry of the particles. SEM of the surface-modified membrane showed that the particles completely cover the target surface and are distributed uniformly. Wettability studies with water and oil clearly demonstrated that the membranes coated with Yb2O3 particles acted to be simultaneously superhydrophobic (contact angle of ~ 150°) and superoleophilic (near-zero contact angle). By measuring water contact angle of coated membranes annealed at different temperatures, a relationship between crystallinity and hydrophobicity was also established. These findings were reflected in oil-water separation studies performed under gravity where the modified membrane allowed all of the oil to pass through but completely blocked the water having a separation efficiency close to 100%. This efficiency was maintained after repeated cycles of oil-water passage confirming the stability of the coating.

The number of baffles has an impact on the thermal-hydraulic performance of a shell-and-tube heat exchanger (STHX), thus a model was developed using Engineering Equations Solver software to solve t...

The flow distribution from a manifold to tubes occurs in the tube side of a shell and tube heat exchanger. The tubes increase the contact surface area thus improving the thermal performance, with an accompanied pressure loss due to the split and smaller hydraulic diameter after the split. The surface conditions of uniform temperature and heat flux are examined. Additionally, the manifold is subjected to the same thermal conditions to examine the impact on thermal-hydraulic performance. Three layouts are being considered, including a single tube, 4 tube, and 37 tube system. It is found that for a combined manifold and tube heating, a non-axisymmetric flow exists in the smaller tubes. To accommodate such flow behavior, it is recommended to define the thermal axis at the minimum temperature for each cross-section, to calculate the peripheral Nusselt number distribution. This procedure is applied to different channel geometries subjected to non-axisymmetric inflow from the heated manifold. All the computed results presented in this paper are also validated against the results available in the literature.

This paper presents the experimental performance of a cross-flow packed-bed humidifier. In this humidifier, hot water is sprayed over packing material where air flows though it in a cross flow arrangement. The air is heated and humidified while flowing through the humidifier duct. The humidification capacity, saturation efficiency, and specific energy consumption are calculated using the experimental data of the inlet and outlet conditions for both air and water streams. The variation of these performance indicators with the mass flow rate ratio of water-to-air, the water inlet temperature, and the packing volume; is investigated. It was found that the specific energy consumption is almost constant with variation of the mass flow rate ratio, packing thickness, and water inlet temperature within the investigated range of these parameters. An effectiveness model originally developed for cross-flow packed-bed cooling tower is adopted to estimate the effectiveness of the humidifier. In addition, the effectiveness and the number of transfer units of the humidifier are determined using the experimental data. The model was found to be in a good agreement with the experimental measurement at high capacity ratio with a deviation of 6%. However, the model underestimates the effectiveness at lower capacity ratio with a maximum deviation of 30%.

In this article, we report effect of surface coatings on organic fouling in reverse osmosis (RO) desalination membranes at the two operating pressure extremes of 20.7 and 55.2 bar. The surface of commercial RO membranes was modified by depositing surface-enriched zwitterionic films in order to achieve enhanced organic fouling resistance. Antifouling performance of both the surface-modified and bare (uncoated) RO membranes was evaluated under cross-flow filtration conditions in the presence of sodium alginate (SA). Filtration studies of the model organic foulant solution showed that both reversible and irreversible flux declines were significantly lower and, as a result, considerably higher flux recovery was achieved after simple hydraulic flushing in the surface-modified membranes when compared to virgin RO membranes. The FE-SEM analysis revealed that foulant deposition on the surface of the modified membranes was patchy/irregular and porous in structure at both lower and higher pressures as opposed to dense and continuous foulant deposition with full coverage of bare membranes with SA at both low and high operating pressures. FTIR scans also qualitatively confirmed a higher amount of SA deposition and revealed that the foulant deposition is further enhanced at higher operating pressure of 55.2 bar on the surface of bare membranes.

Thermal performance characteristics of orthotropic material annular fins subjected to dehumidifying operating conditions are studied using two-dimensional finite element method. The method accounts for non-linear temperature–humidity ratio psychrometric relationship under both partially and fully wet operating conditions. Limits of one-dimensional solutions for orthotropic material fins subject to dehumidifying conditions are investigated in somewhat more detail by introducing dimensionless parameters. The dry fin parameter that fully governs fin efficiency under a set of operating conditions is also defined. The optimum fin dimensions are also estimated for a set of operating conditions and fixed fin volume.

A counter-flow heat exchanger with longitudinal conduction in separating wall is analyzed along with external heat flux. The inhomogeneous system of model equations is solved with the method of variation of parameters. Closed-form expressions are obtained for balanced flow with three types of wall end-conditions and the zero heat in-leak limit verified against reported expressions. In addition, analytical solution is derived for the general unbalanced flow model with non-adiabatic wall ends that is validated against the limiting case of no axial conduction. It enables examining property variations and arbitrary external load by dividing the system into smaller segments and applying the derived expressions to each element. Heat in-leak has higher impact on deterioration in the low NTU region studied when directed toward the hot fluid. As the external parasitic enhances with NTU, a critical NTU is noted in the range 2.8–5.1 for the various cases analyzed. At this optimum condition, the net energy reaching colder stages is between 27% and 55%.

A novel hybrid system consists of an efficient humidification-dehumidification (HDH) desalination unit driven by an absorption (AB) heat pump. A thermodynamically-balanced HDH unit with multiple air extractions is used, while single- and double-effect absorption (SEAB and DEAB, respectively) heat pumps are considered. The proposed systems are examined for simultaneous production of desalinated water and cooling effect under a fixed cooling load of 5 kW. As observed, the SEAB-HDH unit can produce up to 152.4 kg/h of desalinated water at a GOR value of around 10, for 0.002–0.0058 $/l. While the DEAB-HDH system delivers water of up to 135.4 kg/h for 0.0026–0.0098 $/l, at a GOR value approaching 15. Besides, COP values of about 0.50 and 0.81 are recorded for the SEAB- and the DEAB-HDH systems, respectively. It is noted that the DEAB-HDH system always supersedes the SEAB-HDH system in both GOR and COP values. An enhancement of over 100% in the GOR value is observed when air extraction is applied. Also, it is noted that single and double extractions improve water production by about 110 and 90%, respectively. A jump of nearly 500% is recorded in the water production when the cooling capacity increases from 2 to 15 kW. This jump is accompanied by a rise of 60 and 80% in the GOR and COP values, respectively. Finally, the theoretical GOR limit of the proposed systems is estimated.

In this study, a novel hybrid desalination/cooling system is investigated. The system combines a triple-effect absorption (TEAB) heat pump (whose working fluid is LiBr/water solution) and a water-heated humidification dehumidification (HDH) desalination unit. The system is investigated for simultaneous production of freshwater and cooling effect. A low-grade energy source (natural gas) is utilized to operate the system, while solar PV panels are used to power the auxiliary components of the system, such as pumps and blowers. A detailed mathematical model is established to explore the influence of different parameters on the thermodynamic and economic performance of the system. From the HDH unit’s side, it is observed that the effectiveness of the HDH components (dehumidifier and humidifier), the mass flow rate ratio, and the inlet conditions of the saline water have a considerable impact on the system performance. On the other hand, from the TEAB system’s side, the performance of the hybrid system is found to be significantly affected by the effectiveness of both the solution heat exchangers and the absorber. The results reveal that the system can produce, at its optimal operating conditions, 10 kg of fresh water per hour for 0.85 ȼ/l with a gained-output-ratio (GOR) value approaching 5.0. Additionally, the system can produce a cooling capacity of about 2.0 kW at a coefficient of performance (COP) value close to 1.5. Furthermore, the proposed TEAB-HDH system shows comparable performance to other heat-pump-powered HDH systems available in the literature.

The humidification-dehumidification (HDH) desalination is a favorable option for small scale and off-grid applications. Its main disadvantage is the low thermal efficiency compared with other thermal desalination techniques. This study demonstrates the importance of using the thermodynamic balancing concept in enhancing the thermal efficiency of HDH systems. An experimental HDH setup has been built to produce 276 kg of pure water per day (peak capacity) costing 0.033 $/L. The physical understanding of the balancing concept is clarified by representing the experimental results on the temperature enthalpy diagram. The enthalpy pinch model can be solved numerically, analytically, or pseudo-analytically to estimate the performance at the balanced conditions (upper limit of performance). Moreover, a novel parameter, dimensionless enthalpy pinch ( Ψ ¯ ) is proposed to be a measure of the thermal efficiency and a size index. The theoretical model has been validated against the experimental results with a maximum error of 6%. It can be concluded that adjusting the operating conditions to balance the system thermodynamically can improve economic performance by about 40%. Moreover, theoretically, the parametric study shows that the dehumidifier Ψ ¯ is more dominating on the gain output ratio (GOR) than the humidifier Ψ ¯ . Also, at a fixed Ψ ¯ , the maximum ( T max ) and minimum ( T min ) temperature influences the GOR significantly only at a low enthalpy pinch value ( Ψ ¯ ) where decreasing T max or increasing T min has a positive effect on the GOR.

In this paper, the result of an experimental study on thermal performance of different metal foam heat sinks is presented and compared with conventional solid heat sink. Experiments were performed on aluminum metal foams having 93% porosity with pore density of 4 and 8 PPI (i.e. pores per inch). The forced convection results show that heat sink with thermal spray coating outperforms a thermally glued sample with up to 9.8% more temperature drop under same operating test conditions. Air flow speed variations reveal that heat transfer rate changes significantly with the variation of air speed. Further studies with multiple fin samples show that 45° is the best orientation between the heat sink and the flow for maximum heat dissipation. For a single fin, the best orientation is 90°. Results show that power dissipation at a fixed fin base temperature is an appropriate metrics for comparing thermal performance of metal foam heatsinks.

The thermal performance of hyperbolic profile annular fins subjected to dehumidifying operating conditions is studied. An analytical solution for completely wet fin is derived using an approximate linear temperature–humidity relationship. A numerical solution using actual psychrometric relationship for completely and partially wet operating conditions is then obtained to account for the actual temperature–humidity ratio psychrometric relationship under both partially and fully wet operating conditions. An excellent agreement is observed between analytical and numerical solutions for completely wet fin. The fin optimization is presented based on the analytical solution of completely wet fin. Finally, a finite element formulation is used for studying the two-dimensional effects of orthotropic thermal conductivity on the thermal performance of fin under partially and fully wet operating conditions.

Energy consumption by cooling and desalination systems is huge and increasing with growing demand. The integration of two or more energy systems to form a hybrid system and work on a single energy source is one of the strategies for better energy utilization. This paper introduces a novel hybrid cooling-desalination system. The cooling unit is based on the ejector refrigeration cycle (ERC) and combined with water-heated humidification dehumidification (HDH) desalination cycle to make the hybrid system. A validated model of the hybrid system is developed and evaluated using the Engineering Equation Solver (EES) software. The basic ERC is analyzed with R134a as the refrigerant at different operating temperatures. The results show that the increase in the generator temperature improved the entrainment ratio (w) and the coefficient of performance (COP). The COP and entrainment ratio also increases with the increase in evaporator temperature. The increase in the condenser temperature resulted in a decrease in COP and entrainment ratio. The gain output ratio (GOR) of the HDH system is improved by 20%. This is due to the increase in the minimum temperature of the HDH system by 15 °C as a result of the hybrid configuration. This led to a 17% enhancement on the overall energy utilization factor.

Humidification-dehumidification desalination systems are best suited for small-scale and off-grid applications. The primary drawback of humidification-dehumidification systems is their low thermal performance. Thermodynamic balancing of the heat and mass exchange processes between the humidifier and dehumidifier can substantially improve their performance. The optimal thermal design is still needed; thus, the present study mostly focuses on the design of a thermodynamically-balanced system both with and without extractions. This study starts with the implementation of the temperature-enthalpy diagram model to investigate the effect of system enthalpy pinch and minimum and maximum saltwater temperatures on the performance of zero-, single-, and double-extraction systems. After that, design details are investigated to determine the size of the humidifier and dehumidifier under various conditions and power requirements. It is found that the system performance increases as a function of the heat and mass transfer areas (energy effectiveness) of the humidifier and dehumidifier. The systems’ performance is represented by the gained output ratio, recovery ratio, energy effectiveness, and enthalpy pinch. The gained output ratio of the single- and double-extraction systems is better than that of the zero-extraction system by a factor of 91% and 112%, respectively. The areas of the single- and double-extraction systems are larger than that of the zero extraction system by a factor of about 51% and 80%, respectively.

Entropy generation analysis is an important tool to evaluate the irreversible losses of the electrodialysis desalination system. Conventional entropy generation analysis of electrodialysis cell pair comprises of various sources of entropy generation. The primary sources were reported to be salt transport through ion exchange membranes, viscous losses, and pressure drop. In the present study, an exergy-based approach is implemented to calculate the maximum possible entropy generation rates (which was not addressed in the literature), in addition to current efficiency, voltage efficiency, and exergy efficiency. Unlike prior research, the present study calculated higher entropy generation rates (~20%) due to the accommodation of entropy generation from all the contributed sources. The exergy-based model is used to quantify entropy generation in various zones of the electrodialysis cell pair. The possible locations of entropy generation in a cell pair are found to be ion-exchange membranes, solutions, boundary layers, and so on. The membranes' contribution reaches 80% of the total entropy generation value, while the diluate and concentrate channels could contribute to 16%. The rest (~4%) is attributed to the boundary layers at the membrane-solution interfaces, while other sources are minimal. It is found that the optimal performance can be obtained at a channel width of 0.5–0.65 mm.

This paper evaluates the thermal-hydraulic performance of flat-plate solar air heaters having roughened ducts using different turbulence generators. About 220 roughened ducts have been selected from the literature based on the availability of experimental f-factor and Nusselt number data. In particular, roughness elements are rectangular/square ribs, arc/wavy ribs, V-shaped ribs, wedge-shaped ribs, protrusions, and metal mesh. To assess the performance of different solar air heaters, collector efficiency (as a function of useful energy and pumping power) and entropy generation are estimated. The optimal duct is chosen based on the maximum collector efficiency and the minimum entropy generation and hence, is suggested to be a benchmark. The results show that the Reynolds number range of 10000 –16000 is recommended to be used for operating solar air heaters to get the optimal performance. The solar duct GKS3 is found to have the optimal performance when Re 16000, the solar collector GB5 is found to have optimal performance.

In this paper, thermoeconomic considerations are given to heat exchanger inventory allocation in irreversible refrigeration cycles and heat pumps with finite thermal capacitances. Investigation is made with respect to specified rate of cooling and heating for the refrigeration cycle and heat pump, respectively. Exact expressions are obtained without the use of an internal irreversibility parameter. The optimum hot-to cold-end unit cost ratio resulted in unequal division of heat exchanger conductances for the heat pump in contrast to the endoreversible case where they were the same. At a constant evaporator to condenser fluid temperature ratio, the COP of both refrigeration and heat pump systems was found to vary in an almost asymptotic manner in contrast to the endoreversible case where it was constant. In conclusion, it is best to measure the effect of internal dissipation by deriving exact mathematical expressions as the effect on some performance parameters could be lost due to the averaging effect of the internal irreversibility parameter.

A detailed assessment of irreversibility, predominantly heat in-leak and axial wall conduction, is essential in accurately predicting the performance of high effectiveness heat exchangers employed in cryogenic applications. Integration into a refrigeration system as well requires consideration of parasitic heat loss by conduction from exchanger cold end to the adjacent components. Governing equations incorporating these effects in a counterflow exchanger are solved numerically and the model predictions evaluated for heat exchanger ineffectiveness and heat loss by conduction. The optimum performance mandates minimization of both. Although ineffectiveness decreases at higher longitudinal conduction, cold end loss increases with deterioration of the overall performance. Utilizing lower heat capacity rate hot fluid, nevertheless, reduces the cold end loss. Heat in-leak is relatively high with concurrent consideration of axial wall conduction and has adverse consequence on heat exchanger effectiveness. Analysis of the net heat transferred to lower stages of refrigeration reveals a critical NTU.

Cost optimization of heat exchanger inventory in power cycles with one open feedwater heater is undertaken. In this regard, thermoeconomic analysis for an endoreversible power cycle with an open feedwater heater is shown. The scenarios of constant heat rejection and addition rates, power as well as rate of heat transfer in the open feedwater heater are studied. All cost functions displayed minima with respect to the high-side absolute temperature ratio (θ1). In this case, the effect of the Carnot temperature ratio (Φ1), absolute temperature ratio (ξ) and the phase-change absolute temperature ratio for the feedwater heater (Φ2) are qualitatively the same. Furthermore, the constant heat addition scenario resulted in the lowest value of the cost function. For variation of all cost functions, the smaller the value of the phase-change absolute temperature ratio for the feedwater heater (Φ2), lower the cost at the minima. As feedwater heater to hot end unit cost ratio decreases, the minimum total conductance required increases.

In this paper, a model is presented to predict properties and performance parameters of refrigeration systems under fouled conditions. This was based on the fact that the majority of the heat transfer in these systems occurs in the phase-change region. By applying the Buckingham Pi theorem, it was established through the use of the reversed Curzon–Ahlborn cycle that the effect of fouling on thermodynamic properties and performance parameters can be predicted but that this is possible through combining data under specific conditions. The fact that real refrigeration systems are based upon these cycles pointed to the conclusion that this can be used on actual industrial and residential systems. Therefore, this was demonstrated through application upon the simulated model of a simple vapor compression cycle. The advantage provided by the fouling prediction model is the saving of time and money as it will reduce the amount of simulations and/or experimental work needed.

In this paper, an experimental study on the nature of the effects of condenser fouling on some performance characteristics and properties of a simple vapor compression system is presented. This is performed by gradually blocking the condenser air passage and measuring the change in condenser pressure, superheat temperature at the compressor exit, compressor power consumption and COP. The room temperature is kept at approximately 21 °C while the ambient temperature is at 31.6 °C with R22 as the cycle refrigerant. The variation in the above-mentioned quantities is found to be logarithmic in nature and this is connected to heat exchanger theory for phase change processes. Comparison with other works is also done and a consistent behavior is concluded for both properties as well as performance parameters.

For electric and hybrid electric vehicles, a battery thermal management system (BTMS) is an essential component to maintain a proper operating temperature for the battery pack. In this paper, a modern BTMS involving an evaporator (for cooling passenger cabinet) and a chiller (for cooling battery pack) is investigated under different cooling temperatures. Three systems are studied in which (a) the refrigerant lines coming from the chiller and evaporator have the same temperature (for the basic system), or they have different temperatures to be connected by (b) the mixing chamber, or (c) an ejector for a suggested novel system. For a mixing-chamber based system, the results show that the refrigerant charge decreases by 12% compared to the basic system leading to improving the coefficient of performance (COP) by 4.7%. Alternatively, the ejector can efficiently be used instead of the mixing chamber. One of the advantages for the use of ejector is to increase the inlet pressure of the compressor, resulting in minimizing the required power input. Therefore, COP improvement is found to be in a range of 7.17%–77.9%, compared to the basic system under the investigated conditions. The refrigerant charge and the rejected heat by the condenser decrease by 12% and 14.4%, respectively.

The effectiveness–number of transfer units (NTU) relations are useful data for designing and performance evaluation of heat exchangers with fluids having considerable variation in velocities in the presence of heat leak. In this article, the closed-form (benchmark) solutions for counterflow heat exchangers, when the heat leak is either on the hot or cold side of the heat exchanger in the presence of kinetic energy variation, are presented. It was found that the effectiveness depends on NTU and fluid capacity ratio along with six other dimensionless variables that reflect the magnitude and axial distribution of the kinetic energy and heat leak on the hot and cold sides of the heat exchanger. The results are also presented in a graphical form exhibiting the variation of effectiveness of the heat exchanger with the already-mentioned parameters. It was demonstrated that when the dimensionless heat leak and kinetic energy terms approach zero, the solution reduces to the classical effectiveness–NTU relations fo...

The effectiveness-NTU relations are valuable information for heat exchangers with fluids having significant variation in velocities in the presence of heat leak. In this paper, the closed-form relations for parallel-flow heat exchangers, when the heat leak is either on the cold or hot side of the heat exchanger in the presence of kinetic energy variation, are presented. The effectiveness was found to depend on NTU and fluid capacity ratio along with six other quantities that reflect the magnitude and axial distribution of the kinetic energy and heat leak on the hot and cold sides of the heat exchanger. The results are presented in a graphical form demonstrating the variation of effectiveness of the heat exchanger with the relevant parameters. It was demonstrated that in the limiting case, the solution reduces to the classical effectiveness-NTU relations for parallel-flow heat exchangers.

In this paper, thermoeconomic considerations are given to heat exchanger inventory allocation in vapor compression cycles with mechanical subcooling. Investigation is made with respect to constant work rate, heat rejection and cooling rates as well as heat transfer in the subcooler. It was found that no minima exist for any of the cost functions with respect to the absolute temperature ratio ( ξ ) and the average subcooling absolute temperature ratio ( θ 3 ). The derivatives for the integrated subcooling cycle can be generated from the derivatives of the dedicated subcooling cycle. It was concluded that the cost optimization of the integrated mechanical subcooling system is qualitatively the same as the dedicated subcooling system.

Thermal management of electronic products relies mainly on the effective dissipation of heat. Heat sinks (containing multiple extended surfaces or fin array) are commonly used for heat dissipation network. The performance of an individual fin depends on its geometry, material properties and operating environment (i.e. free or forced convection). In the first part of this paper, the four most commonly used fin profiles are studied for pin, longitudinal and annular fins using non-dimensional finite element formulation. In the second part, the performance of different thermal interfaces is studied for polymer and metallic fins. Polymer composite materials result in significant increase in the performance of a fin; however manufacturing can be a constraint to construct an effective heat sink due to interface conditions at the fin and base plate junction. It is found that the joint at fin base plate has considerable stress effect in the heat sink system. The press fit joint must have high contact pressure to maintain an appropriate thermal contact conductance (TCC) in order to have thermal performance comparable to an adhesive joint, but the two joints have different state of thermal and contact stresses.

The use of dimensional analysis and dimensionless parameters is very common in the field of heat transfer; nevertheless, the concept of dimensionless finite element formulation has been applied to a limited type of thermofluid problems. This article uses a nondimensional finite element formulation for studying longitudinal composite fins with interface resistance. Two nondimensional governing parameters have been identified, one each for coating and interface, that completely govern the coating and interface resistance effects. The presented results, for the considered range of geometric, material, and operating conditions, permit identification of the limiting values of the two nondimensional parameters for which the coating and interface effects become negligible. It is found that the coating and interface effects are similar for considered constant- and variable-thickness profile longitudinal composite fins over the studied range of nondimensional material, geometry, and operating condition parameters.

Light weight composite fins are considered to deal with thermal management problems for many microelectronic components. These composite fins are inherently anisotropic, therefore cannot be handled by a traditional one-dimensional approach; however, these materials can be designed to provide high thermal conductivity values in the desired direction to handle application-specific demands. In this article, we present analytical solutions for temperature distribution and heat transfer rate for orthotropic two-dimensional pin fins subject to convective-tip boundary condition and the contact resistance at the fin base. The generalized results are presented in terms of fin aspect ratio (fin length-to-radius ratio) and three dimensionless fin parameters that relate the internal conductive resistance to three convective resistances discussed in terms of dimensionless variables such as contact, tip, and axial Biot numbers, in addition to the axial-to-radial conductivity ratio. Several special cases including the i...

The optimal dimensions of annular fins of constant and variable cross sectional area when subjected to both heat and mass transfer were investigated by a numerical scheme. A non-linear model representing both heat and mass transfer mechanisms was solved using finite difference over-relaxation scheme. Numerical solutions are obtained for the dimensionless heat transfer rate for completely wet conditions as a function of important dimensionless parameters ( u , v , w ) for annular fins. The results are presented in a graphical form as well as regression equations for rectangular, triangular, convex and concave parabolic annular fins. It is shown that these dimensionless parameters represent modified version of fin parameter ( m o L ) , non-dimensional fin material volume and fin base ratio (outer radius of tube to thickness of fin at its conjunction with tube). Keeping the two dimensionless parameters constant ( u , v ) and considering w as the only independent variable, the maximum heat dissipated from the fin is obtained.

A numerical analysis is carried out to study efficiency and temperature distribution of annular fins of different fin profiles (constant and variable cross-sectional area) when subjected to simultaneous heat and mass transfer mechanisms. The temperature and humidity ratio differences are driving forces for heat and mass transfer, respectively. Actual psychrometric relations are used in the present work instead of a linear model between humidity ratio and temperature that has been used in the literature. A non-linear model representing heat and mass transfer mechanisms was solved using a finite difference successive over-relaxation method. Solutions are obtained for temperature distribution over the fin surface in addition to fin efficiency for both fully wet and partially wet fin surfaces. The numerical results are compared with those of previous studies. It was found that one of the linear models for the relation between the humidity ratio and temperature is a reasonable approximation.

The non-dimensional finite element method is used to study performance characteristics of annular fins when subjected to both interface resistance as well as coating layer over the fin surface. Governing dimensionless parameters are identified for coating and interface resistance effects. It is found that the coating (interface) effects are governed by a single dimensionless parameter that groups all important material and geometric parameters of the fin substrate and coating (interface) layer. The analysis is first conducted for a rectangular profile or constant thickness fin, over the range of fin lateral Biot number 0.001 ⩽ Biz f ⩽ 1, which showed an upper bound of the governing dimensionless parameters for which the coating and interface effects become negligible. The investigation is then extended to variable thickness profile annular fins, which showed the behavior of coating and interface resistances very similar to that of rectangular profile.