Modelling, Design, and Optimization of Membrane based Heat Exchangers for Low-grade Heat and Water Recovery

Transport Membrane Condenser (TMC) is an innovative technology based on the property of a nano-scale porous material which can extract both waste heat and water from exhaust gases. This technology tremendously improves the efficiency of boilers and gas/coal combustors by lowering waste heat and increasing water recovery. Contaminants in the flue gases, such as CO2, O2, NOx, and SO2 are inhibited from passing through the membrane by the membrane’s high selectivity. The condensed water through these tubes is highly pure and can be used as the makeup water for many industrial applications. The goal of this research is to investigate the heat transfer, condensation rate, pressure drop and overall performance of crossflow heat exchangers. In this research, a numerical model has been developed to predict condensation of water vapor over and inside of nano-porous layers. Both capillary condensation inside the nanoscale porous structure of the TMC and the surface condensation were considered in the proposed method using a semi-empirical model. The transport of the water vapor and the latent heat of condensation were applied in the numerical model using the pertinent mass, momentum, turbulence and energy equations. By using the proposed model and simulation procedure, the effect of various inlet parameters such as inlet mass flow rate, inlet temperature, and water vapor content of the inlet flow on the performance of the cross-flow TMC heat exchanger was studied to obtain the optimum performance of the heat exchangers at different working conditions. The performance of the TMC heat exchangers for inlet flue gas rate 40 to 120 kg/h, inlet water rate 60 to 140 kg/h, inlet flue gas relative humidity 20 to 90%, and tube pitch ratio 0.25 to 2.25 has been studied. The obtained results show that the water condensation flux continuously increases with the increase of the inlet flue-gas flow rate, water flow rate, and the flue-gas humidity. The total heat flux also follows the same trend due to the pronounced effect of the latent heat transfer from the condensation process. The water condensation flux and the overall heat transfer increase at the beginning for small values of the tube pitches and then decreases as the tube pitch increases furthermore. In addition to the cross-flow TMC heat exchangers, the performance of a shell and tube TMC heat exchanger for high pressure and temperature oxy-combustion applications has been investigated. The performance analysis for a 6-heat exchanger TMC unit shows that heat transfer of the 2-stage TMC unit is higher than the 2-stage with the same number of the heat exchanger in each unit

Reciprocating Mechanism–Driven Heat Loop (RMDHL) Cooling Technology for Power Electronic Systems

The most significant hindrances to the technological advances in high power electronics (HPE) and digital computational devices (DCD) has always been the issue of effective thermal management. Energy losses during operation cause heat to build up in these components, resulting in temperature rise. Finding effective thermal solutions will become a major constraint for the reduction of cost and time-to-market, two governing factors between success and failure in commercial evolution of technology. Even when high temperatures are not reached, high thermal stresses because of temperature variations are major causes of failure in electronic components mounted on circuit boards. An effective electronic cooling technique, which is based on reciprocating heat pipe, is the so-called reciprocating mechanism–driven heat loop (RMDHL) that has a heat transfer mechanism different from those of traditional heat pipes. Experimental results show that the heat loop worked very effectively and a heat flux as high as 300 W/cm2 in the evaporator section could be handled. In addition to eliminating the cavitation problem associated with traditional two-phase heat loops, the RMDHL also provides superior cooling advantage with respect to temperature uniformity. Considering the other advantages of coolant leakage free and the absence of cavitation problems for aerospace-related applications, the single phase RMDHL could be an alternative of a conventional liquid cooling system (LCS) for electronic cooling applications. This chapter will provide insight into experimental, numerical and analytical study undertaken for RMDHL in connection with high heat and high heat flux thermal management applications and electronic cooling. In addition to clarifying the fundamental physics behind the working mechanism of RMDHLs, a working criterion has also been derived, which could provide a guidance for the design of a reciprocating mechanism–driven heat loop

Flow characteristics and heat transfer performance in a Y-Fractal mini/microchannel heat sink

This article presents a combined experimental and computational study to investigate the flow and heat transfer in a Y-fractal microchannel. Experimental apparatus was newly built to investigate the effect of three different control factors, i.e., fluid flow rate, inlet temperature and heat flux, on the heat transfer characteristics of the microchannel. A standard k-Ɛ turbulence computational fluid dynamics (CFD) model was developed, validated and further employed to simulate the flow and heat transfer microchannel. A comparison between simulated results and the obtained experimental data was presented and discussed. Results showed that good agreement was achieved between the current simulated results and experimental data. Furthermore, an improved new design was suggested to further increase the heat transfer performance and create uniformity of temperature distribution.Peer reviewe

Experimental and Analytical Studies of Reciprocating Flow Heat Transfer in a Reciprocating Loop Device for Electronics Cooling

The thermal management of electronics is essential, since their lifetime and reliability are highly dependent on their operating temperature and temperature uniformity. Regarding that, Reciprocating-Mechanism Driven Heat Loop (RMDHL) technology has been invented and shows potentiality to become an effective high heat flux cooling system. In this paper, the performance of a reciprocating cooling loop, in terms of heat transfer and temperature distribution, is studied experimentally and analytically. The experimental results showed that, as the reciprocating flow amplitude increases, the loop surface temperature decreases, and the temperature uniformity along the loop improves. However, in contrast to the amplitude effect, a higher frequency may not necessarily improve the temperature uniformity, although the condenser section temperature may be lower. Further, adiabatic section temperature appears to be insensitive to the reciprocating frequency. The experimental results were then summarized in a semi-empirical correlation that demonstrates a useful design tool for the thermal engineer community. Additionally, the analytical results provide critical design requirements that should be considered during Reciprocating-Mechanism Driven Heat Loop (RMDHL) system design

Experimental and Analytical Studies of Reciprocating Flow Heat Transfer in a Reciprocating Loop Device for Electronics Cooling

The thermal management of electronics is essential, since their lifetime and reliability are highly dependent on their operating temperature and temperature uniformity. Regarding that, Reciprocating-Mechanism Driven Heat Loop (RMDHL) technology has been invented and shows potentiality to become an effective high heat flux cooling system. In this paper, the performance of a reciprocating cooling loop, in terms of heat transfer and temperature distribution, is studied experimentally and analytically. The experimental results showed that, as the reciprocating flow amplitude increases, the loop surface temperature decreases, and the temperature uniformity along the loop improves. However, in contrast to the amplitude effect, a higher frequency may not necessarily improve the temperature uniformity, although the condenser section temperature may be lower. Further, adiabatic section temperature appears to be insensitive to the reciprocating frequency. The experimental results were then summarized in a semi-empirical correlation that demonstrates a useful design tool for the thermal engineer community. Additionally, the analytical results provide critical design requirements that should be considered during Reciprocating-Mechanism Driven Heat Loop (RMDHL) system design