•The simulated rotary heat exchanger provided moisture concerns in several rooms.•The rotary heat exchanger was only suitable for ventilation of so-called dry rooms.•Varying heat recovery or ...temperature can limit indoor relative humidity in dry rooms.•Single-room ventilation allows selection of heat recovery to match the needs of rooms.
The investigation constructed and simulated moisture balance equations for single-room ventilation with a non-hygroscopic rotary heat exchanger. Based on literature, the study assumed that all condensed moisture in the exhaust subsequently evaporated into the supply. Simulations evaluated the potential for moisture issues and compared results with recuperative heat recovery and whole-dwelling ventilation systems. To assess the sensitivity of results, the simulations used three moisture production schedules to represent possible conditions based on literature. The study also analyzed the sensitivity to influential parameters, such as infiltration rate, heat recovery, and indoor temperature. With a typical moisture production schedule, the rotary heat exchanger recovered excessive moisture from kitchens and bathrooms, which provided a mold risk. The rotary heat exchanger was only suitable for single-room ventilation of dry rooms, such as living rooms and bedrooms. The sensitivity analysis concluded that varying heat recovery or indoor temperature could limit indoor relative humidity in dry rooms when a moderate risk was present. The rotary heat exchanger also elevated the minimum relative humidity in each room, which could help to avoid negative health impacts. A discussion emphasized the potential benefits of selecting heat recovery to match the individual needs of each room.
•A plate rotary heat exchanger applied in CMC was presented.•The effects of operating parameters on MRT were investigated.•Empirical correlations for MRT prediction were regressed.
The plate rotary ...heat exchanger (PRHE) was developed as a new type of heat transfer equipment applied in coal moisture control (CMC) industrial process. Being an important factor during the producing process, the mean residence time (MRT) of particles inside PRHE was investigated. Visual experiments on MRT were carried out under identical filling degree (f=10%), while the particle flow rate, rotating speed and inclination of PRHE were varied. A Perspex rotary drum was used with an inner diameter of 300mm and a length of 1000mm. Eight rectangular plates were designed as the “heating plates”. Two different types of particles were utilized as experimental materials. The results indicated that MRT decreased with the increments of particle flow rates, rotating speed and inclination of PRHE. Compared with particle flow rate, the variable of MRT was sensitive to the increasing of rotating speed and PRHE slope, especially when the rotating speed was low. And the distribution of MRT was similar ideally normal. Then, based on the experimental results two empirical correlations were regressed by least square method, both of the two correlations were valid under most of the conditions and the mean deviations in MRT prediction were 8.1% and 8.0% respectively.
In the last 50 years, the technology of rotary heat exchangers has not changed considerably. A reliable simulation can help improve the design of this technology. In this work, a simulation for ...rotary heat exchangers was developed and validated with multiple experimental data. This simulation takes an innovative approach based on locally calculated heat transfer coefficients and considers the entry region effect. This approach proved to be accurate since the average difference between the experimental results and the proposed model with a constant heat boundary condition is 0.1% and the maximum absolute deviation 1%. Experimental, as well as simulation results, indicate that lower empty tube gas velocity (1 m/s) and higher rotational speed (12 rpm) improve thermal efficiency compared to commonly used operating conditions. Additionally, a new model for predicting the local internal Nusselt number for sine ducts in the rotor channels is proposed, which considers the entry region effect.
It is possible to greatly mitigate the increase of water usage associated with the addition of carbon capture to fossil fuel power generation. This article presents a first-of-a-kind feasibility ...study of a series of technology options with rotary regenerative gas/gas heat exchangers for the management of the water balance around post-combustion carbon capture process integrated with CCGT (Combined Cycle Gas Turbine) plants with and without EGR (exhaust gas recirculation). Hybrid cooling configurations with a gas/gas heat exchanger upstream of the direct contact cooler reduce cooling and process water demand by 67% and 35% respectively compared to a wet system where the flue gas is primarily cooled prior to the absorber in larger direct contact coolers. The CO2-depleted gas stream is then reheated above 70 °C with enough buoyancy to rise through the stack. Dry air-cooled configurations, relying on ambient air as the cooling medium, eliminate the use of process and cooling water prior to the absorber and the temperature of the flue gas entering the absorber is unchanged. Rotary regenerative heat exchangers do not introduce significant additional pressure drop and gas leakage from a high CO2 concentration stream to a stream with lower concentration can be minimized to acceptable levels with available strategies using a purge and a scavenging slipstream from the higher pressure flow.
•Dry air-cooled systems reduce water usage associated with post-combustion capture.•Dry cooling can be achieved with Regenerative rotary gas/gas heat exchangers.•CO2-depleted gas is reheated and gains enough buoyancy to rise through a dry stack.•Ambient air and flue gas temperature at absorber inlet are critical design factors.
Reducing energy usage to save the environment is one of the main goals for the future. The energy losses in ventilation have a huge impact on energy consumption in buildings. In this work, the energy ...performance of a heat recovery wheel system equipped in an air handling unit was tested year-round, and the results compared with the simulation output for the system using TRNSYS software. The selected conditioned space was the staff offices of an H&M fashion shop, located in Eger, Hungary. Temperature, relative humidity, and air velocity sensors were placed at the wheel inlet and outlet sections to record data and determine the annual energy saving. The results revealed a good agreement between the measured and simulated results.
The paper presents a new method to determine the sensible effectiveness and pressure loss of rotary regenerative heat exchangers using computational fluid dynamics (CFD). It is based on CFD ...simulations of a single thermal wheel microchannel with a small cross-sectional area and thin walls, with cyclic inlet and outlet boundary conditions. Two unique measurement set-ups were designed and built for the experimental measurement of the heat exchanger characteristics. Five different types of thermal wheels were manufactured, measured, and simulated in ANSYS Fluent. All wheels achieve an effectiveness greater than 73% under certain (air flow) conditions, which is the minimum effectiveness required by Ecodesign (in the EU). For the examined exchangers, the effectiveness ranges from 66.5% to 83.3%, depending on the boundary conditions and geometric parameters of the rotors. The highest sensible effectiveness is achieved by heat exchangers with the largest heat exchange surface
A
c
; on the other hand, these wheels have the largest pressure loss. The paper discusses the use of a simplified
ε
-NTU correlation model for the HVAC systems (typically
C
* = 1). The correlation model and CFD results were compared and found to be different from each other. The results of the CFD simulation were compared with measurements to prove that the proposed simulation method can predict the behaviour of the real heat exchanger as a whole. It was demonstrated that the sensible effectiveness and pressure loss of the rotary heat exchanger predicted by the CFD simulations correspond well to the measured values within the measurement uncertainty ±1.3%. The proposed method can be used for the comparison of different rotary regenerative heat exchangers before their manufacturing and for verification that they meet the EU Ecodesign requirements set by the current legislation. It reduces the cost of the initial optimisation and testing of new designs.
Rotary heat exchangers have been widely used in paint shops, combustion power plants, and in heating, ventilation, and air conditioning systems in buildings. For these processes, many types of heat ...exchangers are available in the market: Tube-shell heat exchangers, plate heat exchangers, and rotary heat exchangers, among others. For the rotary heat exchangers, the problem is that there is no net present value method and lifecycle assessment method-based optimization found in the literature. In this work, we address this issue: An optimization is carried out with help of an empirically validated simulation model, a life-cycle assessment model, an economical assessment, and an optimization algorithm. The objective function of the optimization simultaneously considers economic and environmental aspects by using different CO2 pricing. Different CO2 pricing scenarios lead to different optimization results. The ambient air empty tube velocity va, 2.1 optimum was found at 1.2 m/s, which corresponds to a specific mass flow msp of 5.4 kg/(m2·h). For the wave angle β, the optimum was found in the range between 58° and 60°. For the wave height h* the optimum values were found to be between 2.64 mm and 2.77 mm. Finally, for the rotary heat exchanger length l, the optimum was found to be between 220 mm and 236 mm. The optimization results show that there is still potential for technical improvements in the design and operation of rotary heat exchangers. In general terms, we recommend that the optimized rotary heat exchanger should cause less pressure drop while resulting in similar heat recovery efficiency. This is because the life cycle assessment shows that the use phase for rotary heat exchangers has the biggest impact on greenhouse gases, specifically by saving on Scope 2 emissions.
•We study the movement of the particles in the velocity layer on the rotating surfaces.•The coefficient of the near-surface resistance CD* was found experimentally.•The trajectories of the particles ...are well approximated by logarithmic spirals.•The average distance between the particles and the surface is calculated.
Experiments on rotating in the air cones with vertex angle β=120∘ and the flat disc (i.e. a cone with β=180∘) show that for frequencies Ω ≥ 150 rpm projections of the particles' trajectory on a horizontal plane are close to a logarithmic spiral. The analysis of this approximating function and the results of the physical modeling, which helped to determine the coefficient dependence of the particles’ near-surface resistance CD* when moving in the viscous fluid (air), demonstrated that the particles do neither slide nor roll on the surface of the rotary heat exchangers. The average distance between a single particle and the surface is less than but comparable to the thickness of the stationary near-surface velocity layer of the viscous fluid, the thickness of which is at least 10 times greater than the size of the particles. When subjected to the gravity field and the centrifugal force, particles are “jumping” on the surface, the height of these “jumps” being approximately equal to the displacement thickness of the velocity layer. The movement of the particles alongside the normal to the surface as well as their unidirectional rotation under the influence of the velocity gradient in the velocity layer lead to the mass exchange between the layers of the viscous fluid; consequently they intensify the heat abstraction from the hot surface and its transfer to the air and the particles. These factors lead to the reduction of the heating time of the particles and the increase the quality of the flash-products.
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•Theoretical model for the contact heat transfer in rotary heat exchanger was analyzed.•The contact heat transfer was experimentally investigated in a pilot plate rotary heat exchanger.•Periodic ...unsteady heat transfer characteristics of the heating plate was presented.•The effects of the operating parameters on thermal behaviors were analyzed.
In the present work, the contact heat transfer between the granular materials and heating plates inside plate rotary heat exchanger (PRHE) was investigated. The heat transfer coefficient is dominated by the contact heat transfer coefficient at hot wall surface of the heating plates and the heat penetration inside the solid bed. A plot scale PRHE with a diameter of Do = 273 mm and a length of L = 1000 mm has been established. Quartz sand with dp = 2 mm was employed as the experimental material. The operational parameters were in the range of ω = 1 – 8 rpm, and F = 15, 20, 25, 30%, and the effect of these parameters on the time-average contact heat transfer coefficient was analyzed. The time-average contact heat transfer coefficient increases with the increase of rotary speed, but decreases with the increase of the filling degree. The measured data of time-average heat transfer coefficients were compared with theoretical calculations from Schlünder’s model, a good agreement between the measurements and the model could be achieved, especially at a lower rotary speed and filling degree level. The maximum deviation between the calculated data and the experimental data is approximate 10%.
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