Influence of metallic porous microlayer on pressure drop and heat transfer of stainless steel plate heat exchanger

This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.The experimental analysis of passive heat transfer intensification in the case of plate heat exchanger has been carried out. On the heat transfer surface of heat exchanger the metallic porous layer was created. The experiment was accomplished in two stages. In the first stage the commercial stainless steel gasketed plate heat exchanger was investigated, while in the second one – the identical heat exchanger but with the modified heat transfer surface. The direct comparison of thermal and flow characteristics between both devices was possible due to the assurance of equivalent conditions during the experiment. Equivalent conditions mean the same volumetric flow rates and the same media temperatures at the inlet of heat exchangers in the corresponding measurement series. Experimental data were collected for the single-phase convective heat transfer in the water-ethanol configuration. The heat transfer coefficients were determined using the Wilson method

Dynamic Behaviour of a Continuous Heat Exchanger/Reactor after Flow Failure

The intensified technologies offer new prospects for the development of hazardous chemical syntheses in safer conditions: the idea is to reduce the reaction volume by increasing the thermal performances and preferring the continuous mode to the batch one. In particular, the Open Plate Reactor (OPR) type “reactor/ exchanger” also including a modular block structure, matches these characteristics perfectly. The aim of this paper is to study the OPR behaviour during a normal operation, that is to say, after a stoppage of the circulation of the cooling fluid. So, an experiment was carried out, taking the oxidation of sodium thiosulfate with hydrogen peroxide as an example. The results obtained, in particular with regard to the evolution of the temperature profiles of the reaction medium as a function of time along the apparatus, are compared with those predicted by a dynamic simulator of the OPR. So, the average heat transfer coefficient regarding the “utility” fluid is evaluated in conductive and natural convection modes, and then integrated in the simulator. The conclusion of this study is that, during a cooling failure, a heat transfer by natural convection would be added to the conduction, which contributes to the intrinsically safer character of the apparatus

The mean condensate heat resistance of dropwise condensation with flowing inert gases

The quantification of the condensate heat resistance is\ud studied for dropwise condensation from flowing air-steam\ud mixtures. Flows are essentially laminar and stable with gas\ud Reynolds numbers around 900 and 2000. The condensate shaping\ud up as hemispheres on a plastic plane wall and the presence\ud of inert gases make it possible that thermocapillary convection\ud occurs making the resistance less than the mean condensate\ud thickness (ca. 0.185 mm) divided by the heat conduction coefficient.\ud The analysis of experiments shows that the effective\ud mean condensate resistance might indeed be less, by a factor of\ud 0.8+0.2. The analysis takes account of the sensible heat transfer\ud which may be as large as 35% of the total heat transfer if inlet\ud vapor concentration, cin, is low (ca. 0.07). A method is presented\ud to determine the gas-condensate interface temperature,\ud ti, that is needed in the analysis of the heat resistance. The\ud highest temperature differences (t i- tw), t w being the mean\ud temperature of the condenser plate at the gas side, have been\ud found to occur for relatively high values of Cin (ca. 0.3)

Experimental assessment of a helical coil heat exchanger operating at subcritical and supercritical conditions in a small-scale solar organic rankine cycle

In this study, the performance of a helical coil heat exchanger operating at subcritical and supercritical conditions is analysed. The counter-current heat exchanger was specially designed to operate at a maximal pressure and temperature of 42 bar and 200 °C, respectively. The small-scale solar organic Rankine cycle (ORC) installation has a net power output of 3 kWe. The first tests were done in a laboratory where an electrical heater was used instead of the concentrated photovoltaic/thermal (CPV/T) collectors. The inlet heating fluid temperature of the water was 95 °C. The effects of different parameters on the heat transfer rate in the heat exchanger were investigated. Particularly, the performance analysis was elaborated considering the changes of the mass flow rate of the working fluid (R-404A) in the range of 0.20–0.33 kg/s and the inlet pressure varying from 18 bar up to 41 bar. Hence, the variation of the heat flux was in the range of 5–9 kW/m2. The results show that the working fluid’s mass flow rate has significant influence on the heat transfer rate rather than the operational pressure. Furthermore, from the comparison between the experimental results with the heat transfer correlations from the literature, the experimental results fall within the uncertainty range for the supercritical analysis but there is a deviation of the investigated subcritical correlations

Evaluation of an intensified continuous heat-exchanger reactor for inherently safer characteristics

The present paper deals with the establishment of a new methodology in order to evaluate the inherently safer characteristics of a continuous intensified reactor in the case of an exothermic reaction. The transposition of the propionic anhydride esterification by 2-butanol into a new prototype of ‘‘heatexchanger/ reactor’’, called open plate reactor (OPR), designed by Alfa Laval Vicarb has been chosen as a case study. Previous studies have shown that this exothermic reaction is relatively simple to carry out in a homogeneous liquid phase, and a kinetic model is available. A dedicated software model is then used not only to assess the feasibility of the reaction in the ‘‘heat-exchanger/reactor’’ but also to estimate the temperature and concentration profiles during synthesis and to determine optimal operating conditions for safe control. Afterwards the reaction was performed in the reactor. Good agreement between experimental results and the simulation validates the model to describe the behavior of the process during standard runs. A hazard and operability study (HAZOP) was then applied to the intensified process in order to identify the potential hazards and to provide a number of runaway scenarios. Three of them are highlighted as the most dangerous: no utility flow, no reactant flows, both stop at the same time. The behavior of the process is simulated following the stoppage of both the process and utility fluid. The consequence on the evolution of temperature profiles is then estimated for a different hypothesis taking into account the thermal inertia of the OPR. This approach reveals an intrinsically safer behavior of the OPR

Study of zero-gravity, vapor/liquid separators

Heat exchange, mechanical separation, surface tension, and dielectrophoretic methods of separating vapor from liquid at zero gravity for vapor ventin

Cryogenic zero-gravity prototype vent system

Design, fabrication, and tests of prototype cryogenic zero-gravity heat exchanger vent syste

In-Space technology experiments program. A high efficiency thermal interface (using condensation heat transfer) between a 2-phase fluid loop and heatpipe radiator: Experiment definition phase

Space Station elements and advanced military spacecraft will require rejection of tens of kilowatts of waste heat. Large space radiators and two-phase heat transport loops will be required. To minimize radiator size and weight, it is critical to minimize the temperature drop between the heat source and sink. Under an Air Force contract, a unique, high-performance heat exchanger is developed for coupling the radiator to the transport loop. Since fluid flow through the heat exchanger is driven by capillary forces which are easily dominated by gravity forces in ground testing, it is necessary to perform microgravity thermal testing to verify the design. This contract consists of an experiment definition phase leading to a preliminary design and cost estimate for a shuttle-based flight experiment of this heat exchanger design. This program will utilize modified hardware from a ground test program for the heat exchanger