There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Advances in heat pump systems: A review

The continuously increasing share of Renewable Energy Sources (RES) and EU targets for CO2 reduction and energy efficiency necessitate significant changes both on technical and regulatory level. Environmental challenges of CO2 emissions are assessed in a review of CO2 capture and utilisation technologies, offering new opportunities in CO2 economy. Commercial applications in the thermal power and industrial sector for pre and post combustion capture as well as the potential of direct air CO2 capture are reviewed. The potential of Carbon Capture and Utilisation (CCU) is assessed focusing on the use of CO2 for fuel as well as for combined heat and power production. Combining CCU with energy storage as an evolutionary measure for balancing RES with thermal power under the power to fuel concept presents high market potentials for fuel and chemical production. Moreover, the recent progress in supercritical CO2 cycles for combined heat and power production is reported.

The CO2 economy: Review of CO2 capture and reuse technologies

https://docs.lib.purdue.edu/cgi/viewcontent.cgi?article=1116&context=coolingpubs

A composite heat transfer correlation for saturated flow boiling in small channels

Hydrogen technologies can play an important role in decarbonising our energy system in a variety of ways across the energy value chain. It is therefore critical to identify the strategic roles as well as the conditions under which hydrogen energy systems become attractive for the energy transition. In this paper, the authors present a techno-economic review of hydrogen energy systems including power-to-power, power-to-gas, hydrogen refuelling and stationary fuel cells. We focus on their optimal operation as flexible assets and we identify three actions that can foster their uptake beyond technological progress. First, we recommend optimal electricity supply with dedicated control strategies considering that electricity dominates the levelised cost of hydrogen production via electrolysis. Secondly, hydrogen can enable the further integration of traditionally independent sectors, namely electricity, heat and transport while contributing to decarbonise all. This position can also be advantageous for investors who sell heat and fuels as energy efficient products. Lastly, we examine a whole range of revenues from different products and applications which can be combined (i.e. benefit stacking) to match capital and operational expenditures. We discuss these roles in depth and we conclude that policy makers together with technology developers should elaborate smart strategies to reduce cost by scaling production, stimulate standardisation (e.g., similar to the PV industry) as well as develop new market structures and regulatory frameworks which allow hydrogen technologies to deliver multiple low carbon applications and products.

A review on the role, cost and value of hydrogen energy systems for deep decarbonisation

https://docs.lib.purdue.edu/cgi/viewcontent.cgi?article=2875&context=iracc

High temperature heat pumps: Market overview, state of the art, research status, refrigerants, and application potentials

Air-source heat pumps for residential heating are more widely used than geothermal heat pumps mainly due to their lower installation costs. Major disadvantages of air-source heat pumps are the decrease of heat output and coefficient of performance (COP), and increase in discharge temperature, towards low outdoor temperatures. In this paper an air-source two-stage heat pump using R410A as the refrigerant was simulated, designed, constructed, and tested at ambient temperatures as low as −30 °C and supply temperatures of up to 50 °C in air and water heating mode. In addition, the system is able to provide sufficient air conditioning in cooling mode (approximately 50–60% of the design heat transfer rate in heating mode). A short summary of an extended literature review is shown as well as a theoretical screening study of the three most promising cycles. Furthermore, the design and test results of a breadboard system and a comparison with commercially available heat pumps are presented. Second law efficiencies of up to 45% could be achieved, resulting in a coefficient of performance (COP) of 2.1 at −30 °C ambient temperature.

Two-stage air-source heat pump for residential heating and cooling applications in northern U.S. climates

Abstract This study reviews the current state of the art and the current research activities of high temperature heat pumps (HTHPs) with heat sink temperatures in the range of 90 to 160 °C. The focus is on the analysis of the heat pump cycles and the suitable refrigerants. More than 20 HTHPs from 13 manufacturers have been identified on the market that are able to provide heat sink temperatures of at least 90 °C. Large application potentials have been recognized particularly in the food, paper, metal and chemical industries. The heating capacities range from about 20 kW to 20 MW. Most cycles are single-stage and differ primarily in the refrigerant (e.g. R245fa, R717, R744, R134a or R1234ze(E)) and compressor type used. The COPs range from 2.4 to 5.8 at a temperature lift of 95 to 40 K. Several research projects push the limits of the achievable COPs and heat sink temperatures to higher levels. COPs of about 5.7 to 6.5 (at 30 K lift) and 2.2 and 2.8 (70 K) are achieved at a sink temperature of 120 °C. The refrigerants investigated are mainly R1336mzz(Z), R718, R245fa, R1234ze(Z), R600, and R601. R1336mzz(Z) enables to achieve exceptionally high heat sink temperatures of up to 160 °C.

High Temperature Heat Pumps: Market Overview, Stateof the Art, Research Status, Refrigerants, and Application Potentials

https://docs.lib.purdue.edu/cgi/viewcontent.cgi?article=1118&context=coolingpubs

Stefan S. Bertsch

Papers

A composite heat transfer correlation for saturated flow boiling in small channels

High temperature heat pumps: Market overview, state of the art, research status, refrigerants, and application potentials

Two-stage air-source heat pump for residential heating and cooling applications in northern U.S. climates

High Temperature Heat Pumps: Market Overview, Stateof the Art, Research Status, Refrigerants, and Application Potentials

Effects of heat flux, mass flux, vapor quality, and saturation temperature on flow boiling heat transfer in microchannels