High-temperature heat pumps are a promising pathway for electrifying industrial process heat, but their application to large-temperature-glide duties remains technically challenging. Milk powder spray drying is one such application, requiring air heating to approximately 200 °C while offering only low-to-medium-temperature waste heat sources. Transcritical CO2 heat pumps are attractive for this duty because the sensible cooling profile of supercritical CO2 can be matched to the large temperature glide of air heating. However, the high operating pressures required in transcritical CO2 cycles lead to substantial expansion losses, creating a potential opportunity for expansion work recovery. This study evaluates ejector- and expander-based expansion work recovery in high-temperature transcritical–transcritical CO2 heat pump cycles for spray dryer air heating. Baseline and modified cycle configurations were modelled using steady-state thermodynamic analysis and compared using heating coefficient of performance, maximum achievable sink temperature, component-level exergy destruction, and discharge-pressure sensitivity. Under the investigated conditions and assumed component efficiencies, expanders improved the COP of all evaluated cycles. TTX-2 achieved a COP of 2.35, 5.4% above its corresponding TT-2 baseline. TT-2 and the external benchmark TT-4 each achieved a COP of 2.23 at 150 bar for the investigated duty. The comparison with TT-4 is a benchmark comparison, not an evaluation of a TT-4 recovery variant. The improvement was modest, and an upper-bound break-even expander cost of approximately 150 EUR/kW of delivered heat was estimated for the most favourable expander case. Ejector cycles reduced expansion losses in some cases but did not provide a clear cycle-level COP improvement because they altered compressor pressure ratios, gas-cooler outlet conditions, and cascade heat transfer performance. These findings apply to the investigated spray dryer duty and demonstrate that reducing expansion exergy destruction alone is insufficient to guarantee improved whole-cycle performance under the stated operating and component-efficiency assumptions.

Heat flow in heterogeneous materials is of interest to engineers and scientists in a range of applications. In this paper a simplified conduction shape factor which may be used for a range of particle geometries is proposed. The shape factor may be employed using a modification of Maxwell’s effective conductivity model. Numerical simulations were performed for ellipses and ellipsoids that demonstrated that the shape factor is effective for both individual and multiple ellipses or ellipsoids up to volume fractions of 0.32, with differences between the simulated and predicted effective thermal conductivities being of the order of 1

Industrial process heat users face great uncertainty due to the cost and complexity of transitioning to renewable energy sources. High-temperature heat pumps offer a promising solution due to the high Coefficients of Performance that can be achieved compared to electric heating. However, it can be difficult to identify which heat pump systems are most suitable for which applications. This is particularly true for transcritical heat pumps where the temperature glide in the gas cooler (equivalent to a condenser) is very high. This paper aims to quantify the potential decarbonisation impact that could be realised from the development of new high-temperature heat pump cycles with large temperature glides (>100 C-degrees), using carbon dioxide as the refrigerant. To this end, this study identifies potential process applications, including suitable sink and source streams to supply the heat pump system, and discusses the opportunities and barriers for high-temperature heat pump implementation. Thermodynamic models of three heat pump cycles were used to estimate the Coefficients of Performance and the carbon abatement potential for the identified applications. Drying applications such as for producing milk powder, starch and instant coffee, were identified as suitable applications and the Coefficients of Performance estimated based on the required process temperatures and available waste heat.

High temperature heat pumping (HTHP) is a key technology for decarbonizing industrial process heat. This paper describes an investigation into the thermodynamic and economic performance of a cascade HTHP configured with internal heat exchangers (IHXs), using low global warming potential (GWP) refrigerants in both the top cycle and the bottom cycle. The proposed system was applied to a spray dryer case study with supply air temperature over 200 degrees C. A differential evolution (DE) method was used to optimize operating parameters to obtain the maximum COP. The simulation results indicated that of the cycles and refrigerants considered, the maximum COP can be obtained when using acetone or ethanol in the top cycle (TC) and butane or neopentane in the bottom cycle (BC). The use of acetone/neopentane and ethanol/neopentane achieved a highest COP of 2.42; however, better economic performance was achieved when using butane as the BC refrigerant rather than neopentane, while the economic and thermodynamic performance of the heat pumps were similar when acetone and ethanol were used as TC refrigerants. The performance of the most promising refrigerants was analyzed under off-design conditions, with minimum and maximum COP being 2.19 and 2.82, respectively obtained with the sink inlet/outlet temperature of 50 degrees C/230 degrees C and 15 degrees C/200 degrees C.

Industrial heat pumps are becoming increasingly popular as a low-emissions technology due to the ability to leverage renewable electricity at high efficiencies. While heat pumps are already well-established for process temperatures below 100 degrees C, high-temperature heat pumps that can produce greater temperatures are limited by high pressure and temperature requirements that surpass the performance of conventional heat pump compressor technologies. Alongside this, new heat pump cycles which are being developed need to be compatible with low GWP and low ODP refrigerants. This paper presents a numerical evaluation on the thermodynamic performance of high-temperature heat pumps for supplying 200 degrees C sink temperatures with large temperature glides. Four new transcritical-transcritical cascade CO2 heat pump systems are modelled in this study which aim to limit the pressure requirements required to achieve high sink temperatures. An air heating case study for milk powder spray drying is presented. To achieve a COP of 3, all cycles had a similar maximum air outlet temperature between 110 degrees C and 113 degrees C. The transcritical-transcritical cascade cycle with internal heat exchangers on both the top and the bottom cycles achieved the lowest compressor discharge pressure (13.47 MPa maximum) for this case. The same cycle also achieved the highest COP of 2.22 when air outlet temperature was fixed at 200 degrees C (i.e., complete replacement of external heating). For such a heat pump to be economically feasible for heating air to 200 degrees C, an electricity-to-reference price ratio equal to or below 2.06 is required.

Digital Twins (DTs) are high-fidelity virtual models that behave-like, look-like and connect-to a physical system. In this work, the physical systems are operations and processes from energy-intensive industrial plants and their local communities. The creation of DTs demands expertise not just in engineering, but also in computer science, data science, and artificial intelligence. Here, we introduce the Adaptive Digital Twins (ADT) concept, anchored in five attributes inspired by the self-adaptive systems field from software engineering. These attributes are self-learning, self-optimizing, self-evolving, self-monitoring, and self-protection. This new approach merges cutting-edge computing with pragmatic engineering needs. ADTs can enhance decision-making in both the design phase and real-time operation of industrial facilities and allow for versatile 'what-if' scenario simulations. Seven applications within the energy-intensive industries are described where ADTs could be transformative.

Approximately, 10% of food consumed in developed countries has been frozen at some stage between production and consumption, and air blast freezing is the most commonly applied freezing method. Blast freezer designs range from blast cells that are essentially refrigerated rooms with fans to promote air movement operating in batch mode, to more sophisticated designs that are capable of handling products with multiple retention (residence) times as part of a continuous production line. In any blast freezer, it is important that the air movement around the product is sufficient to achieve cooling within the specified residence time and to minimize nonuniformity of cooling rates. Modeling tools, particularly those that make use of numerical methods (such as computational fluid dynamics), are able to aid the process of designing blast freezers. Although it depends to a certain extent on the food in question, the quality of frozen product is generally improved by employing faster freezing rates. However, increasing the freezing rate comes at the cost of additional energy consumption in what is an inherently energy intensive operation, so the design process should identify the optimum scenario.

Two methods of heat transfer enhancement that have received considerable interest in recent years are nanofluids and heat transfer inserts. Comparatively few studies have evaluated the performance of systems with heat transfer inserts and nanofluids used in combination. In this study, heat transfer enhancement effects of alumina/water (Al2O3/H2O), copper oxide/cetyltrimethyl ammonium bromide/water (CuO/H2O/CTAB), and activated carbon/arabinogalactan/water (C/H2O/ARB) nanofluids both with and without hiTRAN (R) inserts were investigated using double-pipe heat exchangers in a customized experimental rig. The increase in heat transfer rates due to the nanoparticles (1% by mass of the nanofluids) was comparable in magnitude to the increase observed for the inserts without nanoparticles (i.e. water only), however, the friction factors of the inserts in water were considerably higher than for the nanofluids. The effects of the two heat transfer enhancement methods appeared to be additive when inserts were used in conjunction with nanoparticles. Of the three nanofluids the C/H2O/CTAB nanofluid had the best thermal enhancement assessed using the most commonly applied enhancement index, both with and without inserts. Due to agglomeration of nanoparticles, particularly for the Al2O3/H2O nanofluid that did not have a surfactant, the nanofluids were much less practical to deal with than the inserts.

The present article responds to the food engineering community’s growing interest in an emerging and lauded approach to food preservation, popularised by its developers as ‘isochoric freezing’. A strong campaign in the scientific literature and mass media has recently promoted this technique as a universal replacement for traditional food freezing and the frozen supply chain by highlighting a number of alleged advantages of ‘isochoric freezing’. Some of these claims therefore require a more neutral and critical assessment against the background of the today’s state of the art in food freezing technologies. Hence, this article spotlights several concerns regarding the plausibility, energy expenditure, resource efficiency, process rate, throughput and safety of ‘isochoric freezing’, as well as the correct use of food refrigeration terminology. The aspects considered are intended to make food scientists, technologists and engineers more aware of the real capabilities and the application perspectives of this still immature mode of refrigerated food processing.

Optimisation of the refrigerating system for food processing requires accurate prediction of the processing time, product temperature distributions, and heat flow. The accuracy of model predictions depends strongly on the accuracy of the thermal property data used, regardless of the modelling methodology. This paper explores the influences of thermal property models on chilling and freezing time prediction accuracy of a simple, numerical heat transfer model based on a one-dimensional solution approach for three-dimensional objects. It is concluded that the additive effective specific heat model and Dul'nev and Novikov thermal conductivity model provide the greatest prediction accuracy when incorporated into the heat transfer model. Predicted results showed good agreement with experimentally measured temperature profiles when applied to a single block of cheese during chilling and a single plastic-wrapped whole chicken during freezing.

Significant exergy destruction occurs during expansion and compression in high-temperature transcritical heat pumps due to the large temperature and pressure difference between heat absorption and heat rejection. Minimising the exergy destruction can be achieved by subcooling the refrigerant prior to expansion and superheating the refrigerant prior to compression. Limited research exists on the use of transcritical CO2 ejectors for high-temperature heat pumps. This paper investigates the influence of ejectors on the thermodynamic performance of new and existing single-stage and cascade cycles. The cycles are compared for a spray dryer air heating case, where the sink is water being heated up to 220 degrees C using exhaust heat recovery as the source. It was found that the COP increased with the addition of ejectors in single-stage cycles and cascade cycles with ejectors in both the top and bottom cycles but decreased for cascade cycles with ejectors in only one cycle.

Design of experiments is a branch of applied statistics that deals with the preparation, undertaking, and analysis of experiments used to investigate the effect of parameters or factors on response variables. Under the appropriate assumptions, design of experiments can enable information to be obtained more efficiently than conventional "one factor at a time" approaches. This study shows how design of experiments can be used for product development in agricultural applications, as demonstrated by the optimisation of a grass cutting blade. Particular attention is given to the collection of valid, reliable, and reproducible quantitative and qualitative results, which can be challenging in the field of agricultural engineering due to the influence of variation from the experimental environment. Significant improvement in performance is obtained when compared to a pre-existing product.

Many countries across the globe are facing the challenge of replacing coal and natural gas-derived process heat with low-emission alternatives. In countries such as New Zealand, which have access to renewably generated electricity, industrial heat pumps offer great potential to reduce sitewide industrial carbon emissions. In this paper, a new Pinch-based Total Site Heat Integration (TSHI) method is proposed and used to explore and identify multi-level heat pump integration options at a meat processing site in New Zealand. This novel method improves upon standard methods that are currently used in industry and successfully identifies heat pump opportunities that might otherwise be missed by said standard methods. The results of the novel method application suggest that a Mechanical Vapour Recompression (MVR) system in the Rendering plant and a centralized air-source heat pump around the hot water ring main could reduce site emissions by over 50%. Future research will develop these preliminary results into a dynamic emissions reduction plan for the site, the novel methods for which will be transferrable to similar industrial sites.

When modelling a thermal process such as freezing, it is convenient to make use of thermal property models based on the food's composition; however, there does not appear to be any suitable models specifically for thermal diffusivity. In the absence of such models, thermal diffusivity may be determined from models for effective thermal conductivity, specific heat capacity and density as functions of composition, as well as an appropriate ice fraction model. However, the accuracy of the predictions is strongly dependent on the choice of effective thermal property models. In particular, the effective specific heat capacity model must incorporate the effect of latent heat release as a function of temperature. For meat during freezing, it is recommended that the Dul'Nev Novikov effective thermal conductivity model, Pham's ice fraction model and Chen's effective heat capacity model are used.

Educators in chemical engineering have a long and rich history of employing digital tools to solve fundamental engineering problems. Today, with the megatrend of digitalisation, there is a growing set of tools that can be used for chemical engineering education. However, identifying which tool is ideally suited to support teaching a given chemical engineering concept can be challenging. To answer this question a survey was distributed to Heads of Departments at IChemE institutions and members of the IChemE committees focused on digitalisation. The survey respondents rated Microsoft Excel (VBA), commercial simulators, and scripting tools as ideal for teaching core subjects such as mass and energy balances, mass transfer and reaction engineering while respondents found 3D Models, and Virtual/Augmented Reality models as being most suited for teaching subjects such as process design, safety and sustainability. Mathematical/programming simplicity, ease of maintenance, and low initial investment costs were identified as key non-technical aspects that will hinder the adoption of a given digital tool. Weighing the benefits of education and non-technical hurdles, the respondents preferred the use of simpler digitalisation platforms such as Excel and scripting languages over the more advanced platforms such as Virtual/Augmented Reality where possible. It was identified that the widespread adoption of more advanced digitalisation tools will require removal of the above mentioned non-technical barriers as well as other barriers such as tool shareability.

Electricity in New Zealand is approximately 80% renewably generated, giving electrification via Industrial heat pump integration great potential to recover waste heat and reduce sitewide industrial carbon emissions. This paper looks at a non-continuous meat processing site in New Zealand. The wide range of processes and products leads to dynamic utility usage, and complex heat recovery potential. A multi steady state analysis was used to investigate non-continuous operation within Total Site Heat Integration (TSHI) methods. This research helps understand the accuracy of these TSHI methods in the placement and sizing of heat recovery equipment such as heat pumps on dynamic, non-continuous industrial sites. Ultimately it was found that mechanical vapour recompression (MVR), and a heat pump in the hot water utility system are promising installations for reducing the site's emissions.

Nanofluids have been proposed for use as working fluids in order to increase energy efficiency. While a large number of studies have been performed, there is comparatively high variation in reported physical property and heat transfer enhancement data. In addition, comparatively few thermal enhancement studies consider the effects of surfactants that may be required to ensure sufficient stability of the nanofluid over time. In this study, nanofluids were prepared by combining different nanoparticles, base fluids and surfactants and were subsequently evaluated for stability using the sedimentation method. Based on the sedimentation trials and viscosity measurements, three nanofluids (aluminium oxide/water; activated carbon/CTAB/water; copper oxide/ARB/water) were selected for thermal performance enhancement experiments. Thermal enhancement performance was tested in a closed loop with two double pipe heat exchangers and all physical properties required in the calculations were measured directly as part of this study. The carbon/CTAB/water nanofluid had the highest heat transfer enhancement index (a comparison of increased heat transfer rate against increased pressure drop) of the three nanofluids considered. Sedimentation of nanoparticle agglomerates was most noticeable with the aluminium oxide/water nanofluid that did not contain a surfactant.