Elsevier

Food Control

Volume 40, June 2014, Pages 278-285
Food Control

The optimization and effect of back panel structure on the performance of refrigerated display cabinet

https://doi.org/10.1016/j.foodcont.2013.12.009Get rights and content

Highlights

  • The porosity of BP should be controlled within 3%.

  • The air flow ratio between the DAG and the BP should be maintained at the 70%–30%.

  • Suitable porosities in the BP are propitious to improve the uniformity of temperature.

Abstract

In this paper, the effect of the back panel structure on the performance of fluid flow and heat transfer of vertical open refrigerated display cabinets (VORDC) is presented by experiments and numerical simulation. Experimental tests are performed to validate the accuracy of numerical predictions. The characteristics of heat transfer and fluid flow of VORDC are investigated at the different locations of the perforations of back panel at the same porosity and the different flow ratios between back panel and air curtain at different porosities. By comparing numerical results with experimental results, the predictive abilities of the computational model have been revealed. Further computational results have also shown that less than 3% porosities can provide a better performance in the VORDC; the location of perforations has a minor influence on the temperature distribution of products. Furthermore, the suitable porosities in the back panel among the shelves are more likely to improve the uniformity of products temperature in the VORDC. As a result, the overall uniformity of product temperature inside the refrigerated display cabinet and the maximum deviation values of product temperature have been improve to 41% and 49%, respectively. The present study can provide the theoretical guide for the design of the narrow VORDC.

Introduction

Keeping product temperature within an appropriate range is a challenging task for refrigerated display cabinets, so the cabinets must be properly designed (Morelli, Noel, Rosset, & Poumeyrol, 2012). For vertical open refrigerated display cabinets (VORDC), the infiltration of air curtain costs about 70% of the cooling load (Chen and Yuan, 2005, Cortella et al., 2001). Simultaneously, the results also show that the infiltration has had a significant effect on the temperature distribution of products which are located at the front of air curtain, and the problems of the uneven temperature distribution of products have existed widely in the open refrigerated display cabinets (Foster, Madge, & Evans, 2005). The results given by Evans et al. (Evans, Scarcelli, & Swain, 2007) also indicated that the highest temperature of products was situated in the front of VORDC. Therefore, a large number of researches had been focused on the heat transfer characteristics and the various factors on the influence of air curtain performance of VORDC. Gasper et al. (Gaspar et al., 2011, Gaspar et al., 2008) analyzed the influence of ambient air temperature, humidity and convection on the thermal entrainment factor of air curtains in the VORDC. Chen (Chen, 2009) evaluated the thermal barrier performance of air curtain by adjusting its height/width radio and discharge angle. Ge et al. (Ge, Tassou, & Hadawey, 2010) studied the influence of ambient air temperature and humidity, and air flow velocity of air curtain on the temperature distribution in the VORDC. Laguerre et al. (Laguerre and Flick, 2010, Laguerre et al., 2012, Laguerre et al., 2012) focused on the heat transfer and air flow characteristics and proposed a heat transfer model of refrigerated display cabinet, they also investigated the influence of operating conditions on the system performance of refrigerated display cabinet. Hammond et al. (Hammond, Quarini, & Foster, 2011) studied the thermal barrier performance by analyzing the air flow velocity of air curtain; while Gasper et al. (Gaspar et al., 2012, Gaspar et al., 2012) investigated the performance of VORDC affected by some parameters, such as air flow rate through evaporator heat exchangers, air curtain behavior, hole dimensions and distribution on the back panel, discharge and return grilles angles and flow deflector locations inside the internal duct.

Although air curtain plays an important role in the resistance of infiltration, the effect of cold air from the back panel should not be ignored. The study by Axell et al. (Axell, 2002) showed that the unreasonable proportion of cold air from the back panel would increase the temperature difference and decrease the performance of the air curtain. Chen et al. (Chen et al., 2004) proved that the porosity of the back panel should normally be controlled at 1%–2%. The study by Navaz et al. (Navaz, Henderson, Faramarzi, Pourmovahed, & Taugwalder, 2005) indicated that about 70%–80% of air flow across the back panel would enter the return air grill. D'Agaro et al. (D'Agaro, Cortella, & Croce, 2006) observed that the unreasonable flow ratio between air curtain and back panel would increase the entrainment of the ambient air. Gray et al. (Gray et al., 2008) observed that the 70%–30% air flow ratio between discharge air grill and back panel obtained a favorable stability of air curtain and maintain the internal temperature of the cabinet; therefore, the air flow from back panel has a certain effect on the internal temperature of cabinet and the temperature of the return air grille (RAG).

From above literature reviews, it can be seen that a few researchers focused on the effect of back panel on the performance of refrigerated display cabinets, whereas some paid more attention on the wide vertical open refrigerated display cabinet which had two air curtains. Recently, owing to the limitations of supermarket area, some supermarketeers put forward that the display area of VORDC should be as large as possible, but the volume of VORDC should be as narrow as possible instead. Accordingly, this paper will focus on the effects of porosities and the locations of the perforations of back panel in a narrow vertical open refrigerated display cabinet with a single air curtain and a 400 mm-width shelf. The aim of the paper is to obtain a lower and uniform temperature of products in the refrigerated display cabinet.

Section snippets

Mathematical model

In the present investigation, the cabinet model is simplified as a two-dimensional model, for the refrigerated display cabinet is larger in length than in width. The mathematical model of the refrigerated display cabinet is assumed to be steady, incompressible fluid flows, and neglect the viscous dissipation. The influence of external relative humidity is incorporated by the species transport model. The mathematical model is as follows:div(ρVφ)=div(Γφgradφ)+Sφwhere: φ is the common variable; Γ

Experimental setup

The methodology of experimental investigation is based on the Chinese Standard GB/T21001.2-2007 and European Standard EN 441-1 for the test of open refrigerated display cabinet. The dimensions of narrow refrigerated display cabinet are 2500 × 680 × 2050 mm (L × W × H), which have six-shelves and only single air curtain with the width of 400 mm. The refrigeration system uses air-cooled condensing unit. The experimental test facility works in an environmental chamber with an air conditioning

The effects of porosity and location of perforations

In this section, we mainly focus on the analysis of the effects of the porosity and the location of the perforations on the back panel on temperature distribution of products in the VORDC. Products are renumbered and shown in Fig. 4.

The optimum of the back panel structure

To optimize the temperature distribution and keep the lower temperature in the refrigerated display cabinet, the porosities of back panel are rearranged as shown in Table 6. In Table 6, the parameter of original model is provided by the manufacturer and the parameters of other models are all based on the experimental model.

Fig. 13 shows the temperature of products with the above model described in Table 6. Except the 13th and 24th products, the temperature distribution of the products of

Conclusions

This paper focuses on the analysis of the effects of porosities and the location of the perforations of back panel on the temperature distribution of the products in the vertical open refrigerated display cabinet. Experimental tests based on GB/T21001.2-2007 (In China) and European Standard EN 441-1 are performed to validate the predictions of numerical model.

By analyzing the influence of porosities and the locations of the perforations on back panel, the computational results show that the

Acknowledgments

The present work is supported by the Project of National Natural Science Foundation of China (No. 21076200), Innovation Scientists and Technicians Troop Construction Projects of Zhengzhou City (10CXTD151) and Foundation of Henan Educational Committee (2011A470013).

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