Cooling Mode Research Articles

Interannual and Decadal Variations of Planetary Wave Activity, Stratospheric Cooling, and Northern Hemisphere Annular Mode

Abstract Using NCEP–NCAR 51-yr reanalysis data, the interannual and decadal variations of planetary wave activity and its relationship to stratospheric cooling, and the Northern Hemisphere Annular mode (NAM), are studied. It is found that winter stratospheric polar temperature is highly correlated on a year-to-year basis with the Eliassen–Palm (E–P) wave flux from the troposphere, implying a dynamical control of the former by the latter, as often suggested. Greater (lower) wave activity from the troposphere implies larger (smaller) poleward heat flux into the polar region, which leads to warmer (colder) polar temperature. A similar highly correlated antiphase relationship holds for E–P flux divergence and the strength of the polar vortex in the stratosphere. It is tempting to extrapolate these relationships found for interannual timescales to explain the recent stratospheric polar cooling trend in the past few decades as caused by decreased wave activity in the polar region. This speculation is not suppor...

Emergency Core Cooling Mode of the European Pressurized Water Reactor: The Evolution from Combined Injection to Cold-Leg Injection

The European Pressurized Water Reactor’s (EPR’s) safety injection system (SIS) comprises four trains, each of them consisting of a medium head safety injection, an accumulator, and a low head safety injection (LHSI). Injection mode is into the cold legs of the main coolant line for the short term. This emergency core cooling (ECC) mode is quite different from the typical German concept with combined injection, i.e., safety injection into both the cold and the hot legs of the main coolant line at least for accumulator and LHSI. Therefore, the German Safety Authority requested justification for giving up the ECC-mode used in German pressurized water reactors, the so-called “combined injection.” Furthermore, the Reaktor-sicherheitskommission requested a comparison between cold-leg injection and combined injection in terms of ECC efficiency over all relevant accident sequences.The evolution from combined injection to cold-leg injection is described and results of comparative analysis are summarized. It is demonstrated that EPR’s SIS is a well-balanced system, which ensures high ECC efficiency and limits loads to containment over the whole accident spectrum. For the entire loss-of-coolant accident (LOCA) spectrum, ECC efficiency of EPR’s SIS is practically equivalent to ECC efficiency of a SIS of the KONVOI type with combined injection. The smaller the break, the more insignificant are differences. The ECC mode has a negligible impact on containment pressure and temperature evolution during a LOCA. Neither with combined injection nor with cold-leg injection is a containment spray system needed.

Large and Mono-Sized Product Crystals from Natural Cooling Mode Batch Crystallizer.

The performance of a 12.2L batch crystallizer operated under natural cooling mode was remarkably improved with seeding. The product crystal size distribution (CSD) was bi-modal at low seed concentrations, reflecting the contribution of crystals newly generated by a secondary nucleation mechanism. With increasing seed concentration, the fraction of the newly generated particles decreased. At high seed concentrations, a large and mono-dispersed product was obtained. A comprehensive seed chart for potassium alum crystallization incorporating the effects of seed concentration, seed size and seed quality on the product weight mean size was developed. With the aid of this chart, an appropriate seed size and seed concentration can be chosen either to maximize growth or to minimize nucleation in a given batch crystallizer configuration. In addition to the natural cooling mode, the other two cooling policies, either of which requires a respective temperature control, were examined. The bi-modal crystal size distribution characteristics remained the same at low seed concentrations. At high seed concentrations, no effect of cooling mode on the CSD was observed. Hence, natural cooling, a simple and easily operable mode with no temperature control, can be beneficially applied to obtain large and mono-dispersed product crystals with adequate seed concentration.

Energy Exchanges and Related Temperatures of an Earth-tube Heat Exchanger in the Cooling Mode

Since soil temperatures below the surface of the earth are normally out of phase with the ambient air temperatures, this study was to investigate the potential of using deep soil as a heat source or sink. An instrumented earth-tube heat exchanger was designed, installed, and operated as a single-pass heat exchanger. The system consisted of 64 m (210 ft) of 15-cm (6-in.) diameter corrugated metal pipe buried 1.8-m (6-ft) deep in red clay soil with risers provided at the inlet and outlet ends and at 15-m (50-ft) intervals. The system was equipped with a high pressure direct-drive industrial-type blower with radial blade wheels. Air temperatures and peripheral soil temperatures were obtained at both the inlet and outlet ends of the tube, and the outlet air was exhausted to the atmosphere. Energy exchange magnitudes were determined and related to concurrent temperatures of operation. Parameters investigated were energy exchanges and related temperatures, composite days for both temperature and energy exchange, longitudinal and lateral earth-tube gradients, polynomial equations for longitudinal gradients, psychrometric conditions, cumulative monthly and seasonal energy exchange values, coefficients of performance (COP), and efficiency ratings. The results of the study indicate a promising potential for earth-tube performance in the cooling mode.

Transient Dehumidification Characteristics of a Heat Pump in Cooling Mode

Much of the seasonal cooling operation of the heat pump occurs at part-load conditions when the unit cycles on and off to meet the cooling load. The seasonal efficiency under part-load conditions of the heat pump is typically estimated from a laboratory measurement of the degradation coefficient (CD). Manufacturers are only required to estimate CD at a single test condition where the indoor coil performs sensible cooling only. The effects of transient dehumidification losses are not accounted in estimating the seasonal efficiency. In hot and humid climates, dehumidification performance of a heat pump is as important as the sensible cooling performance. Therefore, a series of tests were designed to quantify the part-load dehumidification characteristics of a three ton residential air-to-air heat pump. The tests include: cycling rates from 0.8 to 10 cycles per hour (cph), percent on-times of 20, 50, and 80 percent, indoor dry-bulb temperature between 22.2°C and 26.7°C, and indoor relative humidity between 20 to 67 percent. The outdoor conditions and the indoor air flow rate were constant for all test runs. All experiments were performed in psychometric chambers under controlled conditions. The dehumidification process started between 60 to 150 seconds after start-up depending on the test conditions. During start-up, the losses in the latent capacity were greater than the losses in the sensible capacity. The dehumidification response increased with indoor dry-bulb temperature at constant relative humidity and decreased with indoor temperature at constant dew-point temperature.