Experimental investigation of a radiative heat pipe for waste heat recovery in a ceramics kiln

Following the energy crisis in the 1980s, energy-saving technologies have been investigated and implemented in order to decrease the energy consumption and greenhouse gas emissions of major industrial sectors such as metals, ceramics and concrete. The ceramics industry is still, in Europe, one of the major energy consuming manufacturing processes. Hence energy saving solutions have been investigated in order to decrease the energy consumption of the manufacturing process. The main energy-consuming process is the firing stage with more than 50% of all of the energy required for the process. The energy used during the firing stage is then released during the cooling stage. To improve the heat recovered during the cooling stage, a radiative heat pipe ceiling has been investigated. The heat recovered during the cooling stage is then sent to the drying stage. The proposed system is composed of a radiative heat pipe, a kiln and a ceramics heater. The radiative heat pipe is made of ten parallel pipes of 28 mm diameter and a wall thickness of 2 mm the tubes are connected at the bottom by a 28 mm pipe and a condenser section of 50 mm the condenser is a shell and tube system with 9 pipes of 10 mm. The system was cooled by water. The radiative heat pipe has been tested at different flow rate and ceramics heater temperature. The experimental results shown that the radiative heat pipe was able to recover heat using radiation and natural convection in an enclosed kiln. The system was able to recover up to 4 kW. This paper describes this innovative solution for recovering heat from the cooling stage of an earth roller kiln for tile ceramics manufacturing, transformed into hot clean air for the drying stage of the ceramics manufacturing process

Investigation on a full-scale Heat Pipe Heat Exchanger in the ceramics industry for waste heat recovery

European Union's Horizon 2020 framework ; Innovation and Networks Executive Agenc

Waste heat recovery solution based on a heat pipe heat exchanger for the aluminium die casting industry

Data availability: Data will be made available on request.Copyright © 2022 The Authors. An analysis of the end use of energy in the EU reveals that industry is one of the three dominant categories, which accounts for 26.1% of the final end use of energy. In the case of the aluminium industry, approximately 70% of energy consumption is due to heat and thermal processes, highlighting a vast potential for waste heat recovery technologies. Within the aluminium die casting industry, liquid aluminium is cast, formed, cooled, and further processed within a thermal heat process, which includes three sub-processes: solubilising, quenching, and ageing. In the case presented, a thermal heat process is the second most energy intensive process within the factory, and the ageing heat treatment furnace accounts for 15% of the thermal heat process. The thermal heat treatment generates a significant amount of waste heat. The recovery of that waste heat, with minimal risk of cross contamination between streams and reduced chance of equipment failure, has been achieved via the use of a heat pipe heat exchanger (HPHE). The HPHE has been designed, manufactured, and installed in the solution furnace exhaust stack. The HPHE was designed to recover up to 88.6 kW in steady state operating conditions at 400 °C. The return on investment has been evaluated at 35 months with an expected CO2 emissions reduction of 86 tCO2/year when best engineering practices are applied. Furthermore, a theoretical modelling tool to predict the thermal performance of the HPHE was developed and validated within a ±20% deviation from the experimental results. This paper further presents the development of the theoretical model to allow a characterisation of HPHE technology and will act as a guideline for the design of HPHEs within the aluminium industry.European Commission and the partners of the European H2020 project “Heat pipe technology for thermal energy recovery in industrial applications” (https://www.etekina.eu/, H2020-EE-2017-PPP- 768772). Additional information is available in the project Web page www.etekina.eu or www.etekina.com

Experimental investigation of a confined heated sodium jet in a co-flow

Low-Prandtl-number convection is investigated in vertical axisymmetric turbulent buoyant sodium jets discharging into a slowly moving ambient. Measurements of mean velocity, mean temperature and temperature fluctuations are performed simultaneously using a miniature permanent-magnet flowmeter probe. By varying the ratio of momentum to buoyancy flux, or the densimetric Froude number, different intensities of buoyancy are obtained giving a range of conditions encompassing forced-convection jets, buoyant jets and plumes. In line with the classical properties of jets the radial velocity and temperature profiles can be described by the Gaussian function, independent of the flow regime, at all axial measuring positions. The axial decay of the centreline mean velocity for sodium is the same as for fluids of higher Prandtl number, governed by power laws with indices of −1 for forced convection, −2/3 for the transitional buoyant region and −1/3 for plume flow. In contrast, the centreline mean temperatures for sodium plumes decrease with a power of −1 compared with the −5/3 decay for fluids of higher Prandtl number. The different behaviour in sodium is due to the dominance of molecular diffusion in heat transport, while momentum transport is dictated by turbulent diffusion, which gives a similarity solution for forced-convection jets but not for buoyant jets or plumes. The radial profiles of the temperature r.m.s. values can be described by an axisymmetric curve with two maxima, independent of the flow regime, at all axial measuring positions and the two maxima are more pronounced than in conventional fluids. The temperature fluctuations are analysed to give statistical parameters such as minimum and maximum values, skewness, flatness, probability density functions and spectral distribution. The spectral distributions display both a convective subrange and the conductive subrange predicted for fluids of low Prandtl number. Integral length scales of the temperature fluctuations are evaluated and found to be significantly smaller than turbulent velocity scales.</jats:p