High-temperature Sink Research Articles

Demand reduction and energy saving potential of thermal energy storage integrated heat pumps

A heat pump (HP) moves heat from a low-temperature source to a high-temperature sink with an input of energy. Often, one temperature body fluctuates with time (e.g., diurnal ambient temperature), causing the HP efficiency to vary. Integrating thermal energy storage (TES) into a HP system adds a third temperature body, enabling the HP to be advantageously coupled to any two: the application, the ambient, or the TES at strategic times. Although TES integration with HPs is an important emerging technology to lower energy consumption and decrease energy demand during critical times, the favorable circumstances for TES integration are poorly understood. This paper establishes the energy reduction and demand reduction potential of TES-integrated HPs with both analytical and numerical HP models. All possible temperature arrangements are considered for HP-TES systems with two fixed temperature bodies (application and TES) and one variable temperature (ambient). Results show that overall energy savings are most attainable when the TES temperature is near the application temperature, whereas a large temperature difference between the TES and the application leads to the most peak demand reduction. The potential for overall energy savings increases as the magnitude of ambient temperature fluctuations increases.

Magnesium isotopic composition of submarine vent fluids from arc and back-arc hydrothermal systems in the western Pacific

Seafloor hydrothermal systems are important sinks for Mg as their concentration in high-temperature hydrothermal vent fluids decreases to near zero through the formation of secondary minerals. However, the problem of mass balance still persists regarding the global sink for Mg via sub-seafloor high-temperature hydrothermal reactions. In this study, we measured isotopic compositions of Mg in high-temperature hydrothermal vent fluids from 5 arc and back-arc systems in the western Pacific. This was done to better understand Mg behavior during hydrothermal circulation and to quantify the oceanic Mg cycle. The samples with significantly low Mg concentrations showed 26Mg depletion due to Mg fractionation and Mg fixation during hydrothermal circulation. Addition of Mg to the permeable sub-seafloor during venting is the probable reason for the isotopic variation of Mg. The vent fluids (return flux) with lighter Mg isotopic compositions contain much smaller amounts of Mg than seawater. This confirms that the high-temperature hydrothermal sinks have a less significant effect on the oceanic Mg isotopic composition. Based on the simple steady state equations and low-temperature hydrothermal sinks of 26Mg (−0.25‰ to 0.00‰ of δ26Mg), 7–26% of the riverine Mg input is presumed to be removed through the high-temperature sink. This estimate is lower than that proposed by Mottl and Wheat (1994), which was 10–40%. Thus, other Mg sinks such as the low-temperature hydrothermal sink and/or the dolomite sink need to be considered.

A Clean Energy Generation System of In-Tandem Combinations Each of Heat Pump, Compressor and Turbine in Wind Tunnel

This is a series of in-tandem combinations each of heat pump, air compressor, and air turbine disposed in a wind tunnel, working together to generate clean/renewable electricity. The air compressor, located at downstream of the preceding air turbine, extracts air from this turbine thus reduces its backpressure and causes pressure drop at the turbine exit. Turbine output work Wtb is proportional to temperature difference (T3-T4) of turbine inlet/outlet air, which varies exponentially with turbine outlet/inlet air pressure ratio P4/P3 in adiabatic process as below: Wtb = MCp (T3-T4) = MCpT3{1-P4/P3(1-1/k)} as T4=T3(P4/P3)(1-1/k) where, M=mass flow rate of air; Cp&Cv=constant pressure/volume specific heat capacities of air; k= Cp/Cv=1.4. An ASME paper [1] verifies that a suction blower put at turbine exit reducing back pressure of 200 mbar can increase turbine inlet/outlet air pressure ratio P3/P4by 25%. Therefore, Wtb becomes more than those turbines without such blowers as (T3-T4) becomes larger, thus this unique Clean Energy Generation System of Heat Pumps, Compressors, and Turbines (HPCT system) achieves producing net useful electric power. In HPCT system, each air compressor works efficiently to reduce air pressure at preceding turbine outlet, as it extracts more air from the turbine than the blower mentioned in the ASME paper, because compressors have higher compression ratio than blowers. Thus, such feature gives higher turbine pressure ratio to each combination of HPCT system than those turbines without blowers (or compressors) to reduce back pressure at turbine exit. Therefore, HPCT system of higher turbine air pressure ratio P3/P4 achieves producing more turbine output work, as air temperature at turbine exit simultaneously drops more when P3/P4 becomes larger. Heat pump is an efficient device to move heat from low-temperature source to high-temperature sink, and geothermal heat source is preferable as it provides steady and warmer heat energy. This “moved” heat is used to heat up the air in wind tunnel to offset the energy extracted by turbine from HPCT system. Also, HPCT system is fully thermally insulated, thus theoretically being of zero heat loss, as it works adiabatically. P-V&T-S curves and performance of each combination of HPCT system working cycle are studied to compare it with actual gas turbine cycle and ideal Brayton cycle. Working examples of HPCT system are presented to simulate practical applications of HPCT system, and find out virtual net useful output work and energy efficiency. HPCT system is a “COLD” Engine of Zero Carbon Emission, works under moderate energy efficiency and with higher energy density than most existing renewable energy generation systems. More importantly, it is a simply designed system using only conventional knowledge, and can be made by the existing technology under the least investment risk.

Renormalization group analysis of theM-p-spin glass model withp=3andM=3

We study an M-p-spin spin glass model with p=3 and M=3 in three dimensions using the Migdal-Kadanoff renormalization group approximation (MKA). In this version of the p-spin model, there are three (M=3) Ising spins on each site. At mean-field level, this model is known to have two transitions; a dynamical transition and a thermodynamic one at a lower temperature. The dynamical transition is similar to the mode-coupling transition in glasses, while the thermodynamic transition possibly describes what happens at the Kauzmann temperature. We find that all the coupling constants in the model flow under the MKA to the high-temperature sink implying that the mean-field features disappear in three dimensions and that there is no transition in this model. The behavior of the coupling constant flow is qualitatively similar to that of the model with p=3 and M=2, for which only a single transition is predicted at the mean-field level. We conclude that for p-spin models in three dimensions, fluctuation effects completely remove all traces of their mean-field behavior.

Optimal configuration of a class of two-heat-reservoir refrigeration cycles

The optimal coefficient of performance (COP) of a class of two-heat-reservoir refrigeration cycles can be determined by a given cycle time and absorbed heat (cooling load) with consideration of heat leak, finite heat capacity low-temperature source and infinite heat capacity high-temperature heat sink. The refrigeration cycles considered in this paper include (1) infinite low- and high-temperature reservoirs without heat leak, (2) infinite low- and high-temperature reservoirs with heat leak, (3) finite low-temperature source and infinite high-temperature sink without heat leak, and (4) finite low-temperature source and infinite high-temperature sink with heat leak. It is assumed that the heat transfer between the working fluid and the reservoirs obeys Newton’s law. It is shown that the existence of the heat leak does not affect the optimal configuration of a cycle with an infinite low-temperature source. The finite heat capacity of a low temperature source without heat leak makes the cycle a generalized Carnot refrigeration cycle. There exists a great difference of the cycle configurations for the finite low temperature source with heat leak and the former three cases. Moreover, the relations between the optimal cooling load and the COP of the former three configurations are derived, and they show that the heat leak affects the cooling load versus COP characteristics of the refrigeration cycles.

Thermoacoustic engines

Thermoacoustic engines, or acoustic heat engines, are energy-conversion devices that achieve simplicity and concomitant reliability by use of acoustic technology. Their efficiency can be a substantial fraction of Carnot’s efficiency. In thermoacoustic prime movers, heat flow from a high-temperature source to a low-temperature sink generates acoustic power (which may be converted to electric power using a transducer). In thermoacoustic heat pumps and refrigerators, acoustic power is used to pump heat from a low-temperature source to a high-temperature sink. This review teaches the fundamentals of thermoacoustic engines, by analysis, intuition, and example.

Two-Stage Radiant-Energy Sink

A method is described for absorbing radiant energy by means of a pair of radiant energy sinks maintained at different temperatures. A dispersive element separates the incident energy into two wavelength bands. Each band is absorbed by a heat sink that is black for that band, and has low emissivity in the wavelength range of the other band so that it does not radiate. The major portion of the heat load is removed by the high-temperature sink, while the apparent temperature of the system is nearly equivalent to the low-temperature sink. The conventional system, by contrast, removes all the radiant energy by means of a single heat sink at a temperature sufficiently low to cool the lowest energy source.