Fresh Food Compartment Research Articles

Experimental analysis of hybrid household refrigerators including thermoelectric and vapour compression cooling systems

Two different hybrid refrigerators which include vapour compression and thermoelectric (TE) cooling technologies were built and tested. Serial refrigerators, which use vapour compression only were first tested to collect reference data for comparisons. Then, the hybrid prototypes were constructed by attaching thermoelectric coolers (TECs) to different compartments of these serial units. Among the chill, fresh food and freezer compartments of the refrigerators, the TECs were only used at chill and fresh food compartments, which have different cooling power requirements. Energy consumption, cooling and freezing capacity, and noise tests were conducted in compliance with three different standards.All hybrid refrigerators operated successfully in various ambient temperatures and loading conditions. The test results showed that the hybrid refrigerators had at least three times higher energy consumption levels over those of serial ones, because of the lower operating efficiencies of the TECs and higher transmission losses. Moreover, their noise levels are extremely high, at least 25 dB(A) higher than those of serial ones. However, the TECs provided a more sensitive temperature control in the compartment in which they were used. Additionally, the hybrid refrigerators’ performance in terms of cooling capacity was very promising. They were able to cool 17.5 kg of loads from an ambient temperature of 25 °C to the desired temperatures faster than the original serial refrigerators. Since the freezer compartments of both the serial and hybrid units are cooled by compressor-based cooling systems, the freezing capacity results were identical.

Experimental study of R1234yf as a drop-in replacement for R134a in a domestic refrigerator

This paper presents an experimental study for three identical domestic refrigerators using R1234yf as a drop-in replacement for R134a. An alternative methodology was proposed to estimate the optimal mass charge for R1234yf; with the use of such methodology, new evidences were sought on the thermal behavior of the refrigerator compartments as well as at the heat exchangers. Additionally, energy performance for both refrigerants was measured, and, finally, a TEWI analysis was conducted. For the type of refrigerator evaluated, results showed that R1234yf presented an average (for the 3 refrigerators) of 0.4 °C for the fresh food compartment, and 1.2 °C for the freezer, among different charges with respect to R134a. The optimal charge for R1234yf was 92.2 g, which is about 7.8% lower than the one for R134a, which represents a small increase of 4% in energy consumption in comparison to R134a. Finally, the TEWI analysis for the R1234yf was 1.07% higher than the R134a.

Thermal Simulation of the Fresh Food Compartment in a Domestic Refrigerator

In the field of domestic refrigeration, it is important to look for methods that can be used to simulate, and, thus, improve the thermal behavior of the fresh food compartment. In this sense, this study proposes some methods to model the thermal behavior of this compartment when the shelves’ positions are changed. Temperature measurements at specific locations in this compartment were obtained. Several shelf position combinations were performed to use three 2D interpolation methods in order to simulate the temperature mean and the temperature variance. The methods used were: Lagrange’s interpolation, cubic spline interpolation and bilinear interpolation. Two validation points were chosen to verify the proposed methods. By comparing the experimental results with the computer simulations, it was possible to conclude that the method of Lagrange’s interpolation provided values that were not close to the real measured values. On the other hand, it was observed that the method of bilinear interpolation offered the best results, estimating values which were very close to the actual experimental measurements. These interpolation methods were used to build color thermal graphs that can be used to find some of the most appropriate shelf position combinations in this type of refrigerator. By inspection of these thermal graphs, it can be seen that the lowest average temperature was obtained when one shelf was located at 24.5 cm while the second shelf was located at 29.5 cm measured from the top of the compartment. In the same way, it can be seen that the minimum temperature variance was obtained when only one shelf was inside the compartment and this shelf was located at 29.5 cm.

Mathematical application to analyze the thermal behavior of a domestic refrigerator: Influence of the location of the shelves

This paper presents a mathematical application in the thermal analysis of a domestic refrigerator. The main idea of this work is to observe and analyze the thermal effect in the fresh food compartment when the glass shelves are changed of location. Thus, the use of the moving variance is proposed to analyze the thermal distribution of the refrigerator compartments and the use of finite differences to examine the temperature change rate by computing the temperature derivative with respect to time. Additionally, the use of 2D interpolation methods is proposed to build thermal maps in order to analyze the mean and variance of the temperature when the locations of the shelves change. These maps are a very important tool to find a good combination of the shelves locations to attain a proper temperature for the best conservation of perishable food.

Copolymer-bound phase change materials for household refrigerating appliances: experimental investigation of power consumption, temperature distribution and demand side management potential

This study presents the results of an experimental investigation of the influence of latent thermal heat storage elements on the power consumption as well as the temperature distribution of commercial household refrigerators. Two evaporator types and a standard wire-and-tube condenser are equipped with copolymer-bound phase change materials (PCM) and the performance is determined under standard conditions. The results show that refrigerating appliances equipped with PCM can be optimized through modifications of the control strategy to achieve different targets: (a) Power consumption can be significantly reduced by increasing the evaporator and decreasing the condenser temperature. (b) Temperature fluctuations in the refrigerator's fresh-food compartment during the cooling cycle can be reduced from 4 °C to 0.5 °C. (c) The cooling cycle duration can be tripled without compromising the fresh-food compartment conditions. The latter may help to meet the growing demand for balancing power consumption to stabilize the power grid, e.g. if the share of highly fluctuating, sustainable energy supply is large.

Conjugate heat transfer analysis using a simplified household refrigerator model

Air circulation and heat transfer in a simplified household refrigerator model was numerically studied. Three refrigerator configurations were analyzed and compared to highlight the influence of inner structures. The results show that radiation enhances heat transfer between evaporator and inner walls, resulting in a higher temperature gradient across the insulation foams and a higher heat loss rate. Radiation also weakens the natural convection but increases the air circulation between shelves. A vertical temperature stratification is observed in the fresh food compartment for all configurations. The shelves and food strengthen air circulations between the shelves and inner walls, which increases vertical temperature gradient and decreases the temperature homogeneity in the compartment.

Analysis of the temperature stratification of a no-frost domestic refrigerator with bottom mount configuration

The following paper presents the analysis of the temperatures stratification in the fresh food and freezer compartments from a forced-convection domestic refrigerator set in a bottom mount configuration. Initially the analysis is done through experimental tests measuring parameters like: temperature, cold air velocity and energy consumption. Thereafter, CFD is employed to model and simulate the refrigerator. The original model results reveal an inadequate thermal operational profile, which compared with a new design proposal shows a better distribution of air flow in the latter and therefore a more uniform temperature in the fresh food compartment. Experimentally, the new design proposal represents less ON stages for the compressor compared with those of the original refrigerator under the same operational conditions.

Performance optimization of dual-loop cycles using R-600a and hydrocarbon mixtures designed for a domestic refrigerator-freezer

A dual-loop cycle for a domestic refrigerator-freezer (RF) has a large energy saving potential because it has a lower compression ratio due to a higher evaporating temperature in the fresh food compartment (R)-operation compared to a conventional refrigeration cycle, as well as individual optimization flexibility for each loop. In this study, optimizations of dual-loop cycles using R-600a and hydrocarbon (HC) mixtures were individually carried out. Each optimization process included both a theoretical analysis and an experimental investigation. The theoretical analysis was conducted to optimize the specifications of cycle components and the HC mixture compositions for each loop. Based on the experimental results, the energy consumptions of the optimized dual-loop cycles using R-600a and HC mixtures were decreased by 14.2% and 18.6%, respectively, compared with that of a bypass two-circuit cycle using R-600a in the same RF platform.

Performance optimization of a Lorenz–Meutzner cycle charged with hydrocarbon mixtures for a domestic refrigerator-freezer

A Lorenz–Meutzner cycle (called the “LM cycle”) for a domestic refrigerator-freezer (RF) has energy saving potential because of lower entropy generation in the fresh food compartment (R)-evaporator and lower compression ratio due to higher mean evaporating temperature, compared to a conventional cycle using pure refrigerant. In this study, a thermodynamic analysis for the optimum compositions of hydrocarbon (HC) mixtures and cycle specifications was performed. In addition, the effects of the refrigerant charge, capillary tube, compressor capacity, and mixture composition on the performance of the LM cycle using R-290/R-600 were investigated experimentally. Based on the experimental data, the energy consumption of the optimized LM cycle using R-290/R-600 (40:60%) was 11.2% lower than that of a bypass two-circuit cycle using R-600a in the same RF platform.

Performance optimization of a two-circuit cycle with parallel evaporators for a domestic refrigerator–freezer

A two-circuit cycle with parallel evaporators (called a “parallel cycle”) for a domestic refrigerator–freezer (RF) shows energy saving potential compared with a conventional cycle with a single loop or serial evaporators because of a low compression ratio in the fresh food compartment (R)-operation. The objective of this study is to investigate the effects of the refrigerant charge, R-capillary tube, and refrigerant recovery operation on the performance of a parallel cycle. In addition, design guidelines for the heat transfer area and air flow rate of an R-evaporator are proposed. When the parallel cycle was optimized in terms of the refrigerant charge and R-capillary tube diameter, the energy consumption was reduced by 7.8% over a bypass two-circuit cycle with the same RF platform. In addition, an additional energy saving of 1.8% was obtained by the optimization of the operating sequence and refrigerant recovery operation.

Prediction of the energy consumption of household refrigerators and freezers via steady-state simulation

A simplified model to assess the energy performance of vapor compression ‘on–off’ controlled refrigerators is presented herein. The model consists of first-principles algebraic equations adjusted with experimental information obtained from the refrigeration system under study. The experimental work consisted of controlling and measuring the system and component operating conditions in order to gather key information for the development and validation of the model. The methodology showed similar accuracy to that using more sophisticated dynamic simulation codes, but with lower computational costs. When compared to experimental data, the model predicted AHAM energy consumption tests within a ±5% deviation band. A sensitivity analysis considering the number of tube rows in the condenser coil, the number of fins in the evaporator coil and the compressor stroke is also reported. The refrigeration system under study was a top-mount ‘Combi’ 600-l refrigerator, ‘on–off’ controlled by the temperature of the fresh-food compartment.

A first-principles simulation model for the start-up and cycling transients of household refrigerators

A first-principles model for simulating the transient behavior of household refrigerators is presented in this study. The model was employed to simulate a typical frost-free 440-l top-mount refrigerator, in which the compressor is on–off controlled by the freezer temperature, while a thermo-mechanical damper is used to set the fresh-food compartment temperature. Innovative modeling approaches were introduced for each of the refrigerator components: heat exchangers (condenser and evaporator), non-adiabatic capillary tube, reciprocating compressor, and refrigerated compartments. Numerical predictions were compared to experimental data showing a reasonable level of agreement for the whole range of operating conditions, including the start-up and cycling regimes. The system energy consumption was found to be within ±10% agreement with the experimental data, while the air temperatures of the compartments were predicted with a maximum deviation of ±1 °C.

Temperature and time-sharing running combination control strategy of two-circuit cycle refrigerator–freezer with parallel evaporators

A two-circuit cycle refrigerator/freezer (RF) with parallel evaporators is more efficient than a single-loop RF and a bypass two-circuit cycle RF, and its cost is less than that of a dual-loop RF with two compressors. The existed control strategies for this kind of RFs are only based on the temperature control with freezer compartment (FZC) prior to fresh food compartment (FFC) or FFC prior to FZC. When a lot of foods are put into FFC or FZC at a time, the compartment temperatures will go up very high and the food will be damaged. In order to solve this problem, the combination control strategy based on both the temperature control and the time-sharing running control is put forward in this paper. The rules to determine the maximum set on-time of FFC loop and that of FZC loop are presented based on theoretically analyses. The new control strategy is validated in a two-circuit cycle RF with parallel evaporators, and the compartment temperature fluctuations can be controlled within rational ranges under the conditions that a lot of food are put into FFC or FZC at a time, or the ambient temperature is very high. The daily energy consumption of the tested RF with the new control strategy is about 0.99% larger than that with the existed control strategies, which may be caused by the frequent shifts between FZC loop and FFC loop.

03/02357 VAR pricing computation in multi-areas by nonlinear convex network flow programming: Zhu, J. Z. Electric Power Systems Research, 2603, 65, (2), 129–134

A dual-loop cycle for a domestic refrigerator-freezer (RF) has a large energy saving potential because it has a lower compression ratio due to a higher evaporating temperature in the fresh food compartment (R)-operation compared to a conventional refrigeration cycle, as well as individual optimization flexibility for each loop. In this study, optimizations of dual-loop cycles using R-600a and hydrocarbon (HC) mixtures were individually carried out. Each optimization process included both a theoretical analysis and an experimental investigation. The theoretical analysis was conducted to optimize the specifications of cycle components and the HC mixture compositions for each loop. Based on the experimental results, the energy consumptions of the optimized dual-loop cycles using R-600a and HC mixtures were decreased by 14.2% and 18.6%, respectively, compared with that of a bypass two-circuit cycle using R-600a in the same RF platform.

SIMULATION AND EXPERIMENTAL STUDY ON THE AIR FLOW AND HEAT LOADS OF DIFFERENT REFRIGERATOR CABINET DESIGNS

As the economy has been growing in the past decade, consumers in Taiwan start to consider how to raise living quality. As people tend to adopt the westerners' living style of purchasing food once every week or two weeks. Large grocery stores, hence, have been built both in urban and suburban areas. This change results in a growing need of better-designed refrigerator-freezers (RFs). Consequently, consumers need RF models with better or more cooling functions, larger volumetric capacity, and efficient energy use A 1997 top-mount refrigerator with a volume of about 460 liters was selected as the baseline model. This study used computer aided finite element methods (FEM) to analyse and establish designs for RFs. These designs included different insulation properties and various cool air flow rates and outlets in the freezer and fresh food compartments. The following outcomes were investigated in the simulating work: •The thermal responses of the insulation material on RF cabinets •The effect of a modified cool air outlet on the air flow distribution and heat loads The simulation results were then compared with experimental data. Agreement was found between simulation and experimental results. This suggested that computer-aided simulation could serve as a reliable tool for other designs similar to cases practiced in this RF study.

An adaptive demand defrost and two-zone control and monitor system for refrigeration products

A defrost system that adapts to usage patterns and ambient conditions is described. The following parameters determine the interval between defrost operations: the amount and duration of door openings, the length of previous defrost operations, and the current freezer temperature. A two-temperature control system which allows the user to independently select freezer and fresh-food compartment temperatures is also discussed. The compressor run time and the air flow to the fresh-food compartment are controlled to achieve the desired results. These controls have been incorporated in a total control and monitor system which was recently introduced. The other features of this control are also briefly described.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>