Kim Choon Ng

Experimental investigation of the silica gel–water adsorption isotherm characteristics

Abstract In designing adsorption chillers that employs silica gel–water as adsorbent-adsorbate pair, the overriding objective is to exploit low temperature waste-heat sources from industry. This paper describes an experimental approach for the determination of thermodynamic characteristics of silica gel–water working pair that is essential for the sizing of adsorption chillers. The experiments incorporated the moisture balance technique, a control-volume-variable-pressure (CVVP) apparatus and three types of silica gel have been investigated, namely the Fuji Davison Type A, Type 3A and Type RD. As evidenced by the experimental results, the Henry-type equation is found to be suitable for describing the isotherm characteristics of silica gel–water working pair at the conditions of adsorption chiller. The regeneration of adsorbent depends on the correct allocation of temperature as well as the amount of regeneration time. From the experiments, the isotherm characteristics of silica gel–water in the low- to high-pressure regimes and hence, its isosteric heat of adsorption will be determined. Key parameters for optimizing the amount of heat recovery such as the cycle and switching time of chiller can also be implied from the measured results.

Improved thermodynamic property fields of LiBr-H2O solution

This article presents a thermodynamically consistent set of specific enthalpy, entropy, and heat capacity fields for LiBr-

Thermodynamic modeling of reciprocating chillers

H_2O

Multi-bed regenerative adsorption chiller - improving the utilization of waste heat and reducing the chilled water outlet temperature fluctuation

solution. The temperatures span from 0 to

Predictive and diagnostic aspects of a universal thermodynamic model for chillers

190^oC

Centrifugal chillers: Thermodynamic modelling and a diagnostic case study

, while the concentrations span from 0 to 75 wt%. The work is based on the empirical inputs of Duhrings gradient and intercept, specific heat capacity data at a reference concentration of 50 wt% and density data. These properties have been evaluated using most of the experimental data available in the literature. The present approach circumvents the issue of negative dew point at low temperatures and high concentrations. The information provided in this article could be useful for designers of absorption chillers.

On the thermodynamic modeling of the isosteric heat of adsorption and comparison with experiments

A simple model for predicting the performance of reciprocating chillers is developed. The basic irreversibilities that mitigate against fast and slow cooling rates are accounted for. The model proposed here is consistent with real performance data for 30 chillers that span a range of cooling rates from 30 to 1300 kW and, with adjustable parameters that characterize a particular chiller, is shown to be capable of reproducing actual performance data to within better than experimental uncertainty.

Theoretical insight of physical adsorption for a single-component adsorbent+adsorbate system: I. Thermodynamic property surfaces.

A multi-bed regenerative adsorption chiller design is proposed. The concept aims to extract the most enthalpy from the low-grade waste heat before it is purged into the drain. It is also able to minimise the chilled water temperature fluctuation so that downstream temperature smoothing device may be downsized or even eliminated in applications where tighter temperature control may be required. The design also avoids a master-and-slave configuration so that materials invested are not under-utilised. Because of the nature of low-grade waste heat utilization, the performance of adsorption chillers is measured in terms of the recovery efficiency, η instead of the conventional COP. For the same waste heat source flowrate and inlet temperature, a four-bed chiller generates 70% more cooling capacity than a typical two-bed chiller. A six-bed chiller in turn generates 40% more than that of a four-bed chiller. Since the beds can be triggered into operation sequentially during start-up, the risk of ice formation in the evaporator during start-up is greatly reduced compared with that of a two-bed chiller.

A general model for studying effects of interface layers on thermoelectric devices performance

Abstract There are fundamental aspects of chiller behavior—characterized by the chiller coefficient of performance as a function of cooling rate and coolant temperatures—that pertain to all refrigeration devices. We review, further develop, and validate against extensive experimental measurements a simple thermodynamic model that captures the universal aspects of chiller behavior. The model provides a procedure for predicting chiller performance over a broad range of operating conditions from a small number of selected measurements, as well as a diagnostic tool. The accuracy of the model is illustrated for reciprocating, centrifugal and absorption chillers. Universal aspects of chiller behavior are further illustrated with less conventional small-scale cooling devices such as thermoacoustic and thermoelectric chillers.

A general thermodynamic model for absorption chillers: Theory and experiment

Abstract The diagnostic capability of a simple thermodynamic model for chiller performance is illustrated by a case study for a commercial, installed centrifugal chiller. Performance data were measured both prior to, and subsequent to, chiller maintenance that improved chiller efficiency. Using these experimental measurements, we show that the simple thermodynamic model, originally developed for reciprocating and absorption chillers, (1) succeeds in predicting the fundamental relation between coefficient of performance and cooling rate for the centrifugal chiller, and (2) permits a clear diagnostic analysis of heat exchanger fouling on chiller performance.